2009 Vol. 26, No. 01
2009, 26(01): 1-6.
Abstract:
Taking vacuum pack techniques for patches of boron fiber/epoxy (Bf/epoxy) composites，this study tested thermal properties and quasi-static mechanics properties of the single-sided repaired aluminum alloy plate of different thickness with a cent ral crack in it . It analyzed the residual thermal strain and stress intensity factor (SIF) of the repair specimen by using a 3D finite element model，The results show that the bending deflection of the repair specimen decreases with the increase of the plate thickness. The residual thermal strain at the crack tip of the lower plate surface increases with the increase of the plate thickness，and the residual thermal strain of the upper patch surface increases with the decrease of plate thickness , which conformed well to the finite element analysis results.SIF of the aluminum alloy plate with central crack decreases with the increase of plate thickness，while the SIF of the single-sided repair specimen increases with the increase of plate thickness. Af ter the patches of unidirectional Bf/epoxy composites of the same length and width was repaired , the retention rate of bearing capacity for the repair specimen of 1. 76mm thick plate is 93. 85 % while for the plate of 10. 20 mm it is only 84. 01 %. The stiffness of the repair specimen is reactivated and the equivalent stiffness is larger than that of the no-flaw specimen.
Taking vacuum pack techniques for patches of boron fiber/epoxy (Bf/epoxy) composites，this study tested thermal properties and quasi-static mechanics properties of the single-sided repaired aluminum alloy plate of different thickness with a cent ral crack in it . It analyzed the residual thermal strain and stress intensity factor (SIF) of the repair specimen by using a 3D finite element model，The results show that the bending deflection of the repair specimen decreases with the increase of the plate thickness. The residual thermal strain at the crack tip of the lower plate surface increases with the increase of the plate thickness，and the residual thermal strain of the upper patch surface increases with the decrease of plate thickness , which conformed well to the finite element analysis results.SIF of the aluminum alloy plate with central crack decreases with the increase of plate thickness，while the SIF of the single-sided repair specimen increases with the increase of plate thickness. Af ter the patches of unidirectional Bf/epoxy composites of the same length and width was repaired , the retention rate of bearing capacity for the repair specimen of 1. 76mm thick plate is 93. 85 % while for the plate of 10. 20 mm it is only 84. 01 %. The stiffness of the repair specimen is reactivated and the equivalent stiffness is larger than that of the no-flaw specimen.
2009, 26(01): 7-12.
Abstract:
A high temperature adhesive was prepared using phenol -formaldehyde resin ( PF) as the matrix and boron carbide (B4C) particles as the modifier，with which silicon carbide ( SiC) ceramics were bonded. The mechanical property of the adhesive was tested at room temperature af ter being heat-treated in the temperature range from 300℃ to 800℃respectively. The result s indicate that an out standing shearing st rength over 20 MPa could be achieved for SiC ceramics after treatment at 700～800℃. The micro-morphologies at bonding interfaces were investigated by SEM and EDAX，and the main volatiles originating f rom pyrolysis were investigated by pyrolysis gas chromatography-mass spectroscopy. A compact and stable st ructure can be achieved through the modifying reaction between B4C and volatiles such as CO. The reaction product B2O3 being melt at high temperature possesses satisfactory wet tability and adhesive capacity，which can close and mend the shrinkage lacunas. B2O3 also combines with active groups in the resin matrix，which can be responsible for the improvement of the bonding cement stability and adhesive st rength at high temperature.
A high temperature adhesive was prepared using phenol -formaldehyde resin ( PF) as the matrix and boron carbide (B4C) particles as the modifier，with which silicon carbide ( SiC) ceramics were bonded. The mechanical property of the adhesive was tested at room temperature af ter being heat-treated in the temperature range from 300℃ to 800℃respectively. The result s indicate that an out standing shearing st rength over 20 MPa could be achieved for SiC ceramics after treatment at 700～800℃. The micro-morphologies at bonding interfaces were investigated by SEM and EDAX，and the main volatiles originating f rom pyrolysis were investigated by pyrolysis gas chromatography-mass spectroscopy. A compact and stable st ructure can be achieved through the modifying reaction between B4C and volatiles such as CO. The reaction product B2O3 being melt at high temperature possesses satisfactory wet tability and adhesive capacity，which can close and mend the shrinkage lacunas. B2O3 also combines with active groups in the resin matrix，which can be responsible for the improvement of the bonding cement stability and adhesive st rength at high temperature.
2009, 26(01): 13-18.
Abstract:
Allyl-functional novolac (AN) with allylation degree of 173% was synthesized，followed by copolymerizing with 4 , 4-bismaleimide biphenyl methane (BMI) at a mass ratio of 1∶1 to obtain BMI-modified allyl-functional novolac (BMAN173) resin. The processing property，cure schedule，and thermal stability of BMAN173 resin were studied. The results showed that BMAN173 resin possessed excellent processing properties，which are suitable for several kinds of molding processes，such as resin transfer molding (RTM) and compression molding. The initial decrease temperature of storage modulus and thermal decomposition temperature of cured BMAN173 resin were about 390℃ and 430℃，indicating that BMAN173 resin had good thermal properties. The mechanical and thermal properties of BMAN173 resin/ silica weave laminate composites were determined. BMAN173 resin/ silica weave composites exhibited excellent mechanical properties at high temperature，whose flexural strength and interlaminar shear strength retention at 350℃were about 57% and 62%，respectively. The result s of DMA showed that BMAN173 resin/silica weave possessed excellent heat-resistant property. Initial decrease temperature of storage modulus of the composites was about 410℃ and its glass transition was above 450℃. Therefore，BMAN173 resins would be a potentially ideal candidate for the matrix of high temperature-resistant composites.
Allyl-functional novolac (AN) with allylation degree of 173% was synthesized，followed by copolymerizing with 4 , 4-bismaleimide biphenyl methane (BMI) at a mass ratio of 1∶1 to obtain BMI-modified allyl-functional novolac (BMAN173) resin. The processing property，cure schedule，and thermal stability of BMAN173 resin were studied. The results showed that BMAN173 resin possessed excellent processing properties，which are suitable for several kinds of molding processes，such as resin transfer molding (RTM) and compression molding. The initial decrease temperature of storage modulus and thermal decomposition temperature of cured BMAN173 resin were about 390℃ and 430℃，indicating that BMAN173 resin had good thermal properties. The mechanical and thermal properties of BMAN173 resin/ silica weave laminate composites were determined. BMAN173 resin/ silica weave composites exhibited excellent mechanical properties at high temperature，whose flexural strength and interlaminar shear strength retention at 350℃were about 57% and 62%，respectively. The result s of DMA showed that BMAN173 resin/silica weave possessed excellent heat-resistant property. Initial decrease temperature of storage modulus of the composites was about 410℃ and its glass transition was above 450℃. Therefore，BMAN173 resins would be a potentially ideal candidate for the matrix of high temperature-resistant composites.
2009, 26(01): 19-23.
Abstract:
Adding CaO，MgO and ZnO in the biodegradable poly( L-lactic acid) (PLLA) respectively，the effect of these metallic oxides was investigated in the soil supernatant of Shannxi local soil . The chemical structure before and after degradation of PLLA was characterized by FT-IR spect rum，The results show that the pure PLLA film and the PLLA films adding with metallic oxides can be degraded in the soil supernatant，and the adding of CaO and MgO can fasten the degradation rest of PLLA. The microscope observation shows that more remarkable defect and microbiology erosion trace occurred on the surface of PLLA films adding with CaO,MgO after degradation.
Adding CaO，MgO and ZnO in the biodegradable poly( L-lactic acid) (PLLA) respectively，the effect of these metallic oxides was investigated in the soil supernatant of Shannxi local soil . The chemical structure before and after degradation of PLLA was characterized by FT-IR spect rum，The results show that the pure PLLA film and the PLLA films adding with metallic oxides can be degraded in the soil supernatant，and the adding of CaO and MgO can fasten the degradation rest of PLLA. The microscope observation shows that more remarkable defect and microbiology erosion trace occurred on the surface of PLLA films adding with CaO,MgO after degradation.
2009, 26(01): 24-30.
Abstract:
To improve the mechanical property and the bioactivity of composites，the hydroxyapatite/polycaprolacton-chitosan (HA/PCL-CS) composites were prepared in a Hakke twin screw extruder . The composite (ω(HA) = 30%) was immersed in the simulated body solution and physiological saline to examine it s bioactivity and degradation respectively. The structure and component were characterized by scanning elect ron microscope (SEM)，X-ray diff raction (XRD) and Fourier transform infrared spect roscope (FTIR) . The results show that the tensile strength and fracture strain decrease with increasing of HA content，while the Young‘s modulus increases. The surfaces of HA/ PCL-CS composites are covered by a coating of carbonated hydroxyapatite (CHA) with low crystallinity，indicating the excellent bioactivity of the composites. After immersion in the physiological saline for 28d，the molecular mass decreases while pH and mass loss increase to 9. 54 and 5.86%，respectively，indicating a good biodegradation property of the composites.
To improve the mechanical property and the bioactivity of composites，the hydroxyapatite/polycaprolacton-chitosan (HA/PCL-CS) composites were prepared in a Hakke twin screw extruder . The composite (ω(HA) = 30%) was immersed in the simulated body solution and physiological saline to examine it s bioactivity and degradation respectively. The structure and component were characterized by scanning elect ron microscope (SEM)，X-ray diff raction (XRD) and Fourier transform infrared spect roscope (FTIR) . The results show that the tensile strength and fracture strain decrease with increasing of HA content，while the Young‘s modulus increases. The surfaces of HA/ PCL-CS composites are covered by a coating of carbonated hydroxyapatite (CHA) with low crystallinity，indicating the excellent bioactivity of the composites. After immersion in the physiological saline for 28d，the molecular mass decreases while pH and mass loss increase to 9. 54 and 5.86%，respectively，indicating a good biodegradation property of the composites.
2009, 26(01): 31-35.
Abstract:
Using polypropylene (PP) and poly ( ethylene terephthalate) (PET) with the multifunction interlayer active agent riveting-embedded (PET-MFIAA)，the PET-MFIAA/PP in situ fiberized composites were prepared by blending-extrusion-drawing. By means of scanning electronic microscope (SEM)，polarized microscope (PLM) and mechanical properties measuring，the PET microfibril morphology，fracture surface morphology of samples and the mechanical properties of the PET-MFIAA/PP were studied and contrasted with two other kinds of in situ fiberized composites of PET/PP and MFIAA/PET/PP. The results show that there is strong interfacial adhesion in the PET-MFIAA/PP in situ fiberized composites，which has structure characteristics of powerful interaction between PET microfibril and PP matrix，PET microfibril presenting profiled morphology of diameter variation and concave and convex surface，flexible interlayer，etc. Both rigidity and toughness of PET-MFIAA/PP are apparently higher than those of the pure PP. The tensile yield strength，flexural modulus and notched izod impact strength of the PET-MFIAA/PP composite containing 7. 00 % MFIAA are raised to 1.04 times，1.23 times and 1.79 times as the pure PP respectively.
Using polypropylene (PP) and poly ( ethylene terephthalate) (PET) with the multifunction interlayer active agent riveting-embedded (PET-MFIAA)，the PET-MFIAA/PP in situ fiberized composites were prepared by blending-extrusion-drawing. By means of scanning electronic microscope (SEM)，polarized microscope (PLM) and mechanical properties measuring，the PET microfibril morphology，fracture surface morphology of samples and the mechanical properties of the PET-MFIAA/PP were studied and contrasted with two other kinds of in situ fiberized composites of PET/PP and MFIAA/PET/PP. The results show that there is strong interfacial adhesion in the PET-MFIAA/PP in situ fiberized composites，which has structure characteristics of powerful interaction between PET microfibril and PP matrix，PET microfibril presenting profiled morphology of diameter variation and concave and convex surface，flexible interlayer，etc. Both rigidity and toughness of PET-MFIAA/PP are apparently higher than those of the pure PP. The tensile yield strength，flexural modulus and notched izod impact strength of the PET-MFIAA/PP composite containing 7. 00 % MFIAA are raised to 1.04 times，1.23 times and 1.79 times as the pure PP respectively.
2009, 26(01): 36-42.
Abstract:
A representative volume element (RVE) model was developed to investigate the relation between thermal property and microstructure of the particle filled composite. The model was based on two novel algorithms ，and was constructed with the same particle spatial distribution structure of the real heterogeneous composite by the introduction of two parameters，i . e. the ratio and the radius of particle-poor region，which both were estimated from SEM micrographs. The model was verified by comparing the predicted and the practical thermal conductivity.It has been found that the simulation results are accurate in the large scale of filler content . The system with non-uniform particle spatial distribution shows higher thermal conductivity than that with random or uniform particle spatial distribution，especially at the high filler volume fraction when conductive pathways or networks form. And at the same filler volume fraction，the thermal conductivity of the composites can be significantly different due to the different particle spatial distributions.
A representative volume element (RVE) model was developed to investigate the relation between thermal property and microstructure of the particle filled composite. The model was based on two novel algorithms ，and was constructed with the same particle spatial distribution structure of the real heterogeneous composite by the introduction of two parameters，i . e. the ratio and the radius of particle-poor region，which both were estimated from SEM micrographs. The model was verified by comparing the predicted and the practical thermal conductivity.It has been found that the simulation results are accurate in the large scale of filler content . The system with non-uniform particle spatial distribution shows higher thermal conductivity than that with random or uniform particle spatial distribution，especially at the high filler volume fraction when conductive pathways or networks form. And at the same filler volume fraction，the thermal conductivity of the composites can be significantly different due to the different particle spatial distributions.
2009, 26(01): 43-47.
Abstract:
Flax noil fibers reinforced polylactide composites were prepared by means of the non-woven method and hot pressing technology. The effects of volume fraction on tensile strength of the composites were discussed. Based on Kelly-Tyson tensile strength model and some related theories，a new model for predicting discontinuous natural fibers reinforced biodegradable composite (D-NFRBC) was proposed，which contains not only the effect of probability distributing features of the fibers strength，length，fibers tropism angle and diameter on the predicted strength，but also the effect of the rest ricted connection among the shear strength of the composite，the critical length of the fibers and the terminal tensile strength of the fibers in the composite on the strength. The results reveal that the tensile strengths reach a peak at the fiber volume fraction of 39.6%，and the predicted values calculated by the new model agree well with the experimental values.
Flax noil fibers reinforced polylactide composites were prepared by means of the non-woven method and hot pressing technology. The effects of volume fraction on tensile strength of the composites were discussed. Based on Kelly-Tyson tensile strength model and some related theories，a new model for predicting discontinuous natural fibers reinforced biodegradable composite (D-NFRBC) was proposed，which contains not only the effect of probability distributing features of the fibers strength，length，fibers tropism angle and diameter on the predicted strength，but also the effect of the rest ricted connection among the shear strength of the composite，the critical length of the fibers and the terminal tensile strength of the fibers in the composite on the strength. The results reveal that the tensile strengths reach a peak at the fiber volume fraction of 39.6%，and the predicted values calculated by the new model agree well with the experimental values.
2009, 26(01): 48-53.
Abstract:
The two-stage process has been developed to generate the nanometer silica modified by acrylate monomer
(SiO2-HPA) through surface-modification of silica with vinyl groups. The silica surfaces were treated with excess，4-toluene diisocynate (TDI)，and the residual isocyanate groups were converted into vinyl groups by reaction with hydroxypropylacrylate (HPA). The SiO2-HPA/PVC nanocomposites were prepared via the melt blending method. The effects of silica content and interfacial property on the mechanical properties were investigated. It is found that the SiO2-HPA/PVC nanocomposites have higher tensile and impact strength than the nanocomposites filled with unmodified silica or pure PVC，and the strength will achieve their maximum with silica mass fraction of 3%～4%. The interfacial interaction and compatibility between the silica and PVC have been greatly improved resulting in the reinforcing and toughening effects of the surface-modified silica on PVC. In addition，the reinforcing and toughening mechanisms of SiO2-HPA based nanocomposites were studied in detail .
The two-stage process has been developed to generate the nanometer silica modified by acrylate monomer
(SiO2-HPA) through surface-modification of silica with vinyl groups. The silica surfaces were treated with excess，4-toluene diisocynate (TDI)，and the residual isocyanate groups were converted into vinyl groups by reaction with hydroxypropylacrylate (HPA). The SiO2-HPA/PVC nanocomposites were prepared via the melt blending method. The effects of silica content and interfacial property on the mechanical properties were investigated. It is found that the SiO2-HPA/PVC nanocomposites have higher tensile and impact strength than the nanocomposites filled with unmodified silica or pure PVC，and the strength will achieve their maximum with silica mass fraction of 3%～4%. The interfacial interaction and compatibility between the silica and PVC have been greatly improved resulting in the reinforcing and toughening effects of the surface-modified silica on PVC. In addition，the reinforcing and toughening mechanisms of SiO2-HPA based nanocomposites were studied in detail .
2009, 26(01): 54-58.
Abstract:
3D UHMWPE fiber and carbon fiber (CF) reinforced epoxy resin (ER) hybrid composites were prepared using resin transfer molding (RTM) process. The friction and wear properties were analyzed，and the friction coefficient was predicted by a hybrid positive pressure model . The results show that with the increase of the carbon fiber volume fraction of the hybrid composites with a fixed total fiber fraction of 36 %，the friction coefficient of the hybrid composites increases，and their specific wear rate decreases. The wear mechanisms of the UH3D/ER and C3D/ER composites are mainly adhesive wear and abrasive wear，respectively. The wear mechanism of the hybrid composites is mainly determined by the relative volume ratio of CF to UHMWPE fiber . The hybrid positive pressure model can be used to predict the friction coefficient of UH3D/ER composites.
3D UHMWPE fiber and carbon fiber (CF) reinforced epoxy resin (ER) hybrid composites were prepared using resin transfer molding (RTM) process. The friction and wear properties were analyzed，and the friction coefficient was predicted by a hybrid positive pressure model . The results show that with the increase of the carbon fiber volume fraction of the hybrid composites with a fixed total fiber fraction of 36 %，the friction coefficient of the hybrid composites increases，and their specific wear rate decreases. The wear mechanisms of the UH3D/ER and C3D/ER composites are mainly adhesive wear and abrasive wear，respectively. The wear mechanism of the hybrid composites is mainly determined by the relative volume ratio of CF to UHMWPE fiber . The hybrid positive pressure model can be used to predict the friction coefficient of UH3D/ER composites.
2009, 26(01): 59-64.
Abstract:
The Al2O3/SiO2/PAN composite membrane was prepared as the separator for Li-ion batteries in order
to replace the traditional microporous polyolefin membrane. The composite membrane has high porosity，and can be well wetted by the liquid electrolyte. The ion conductivity of the membrane is easily achieved by absorbing the liquid electrolyte due to the high capillary effect. The amphoteric character of Al2O3/SiO2 can scavenge acidic hydrogen fluoride，which is inevitably present in the LiPF6-based elect rolytes used currently in the Li-ion batteries. With the composite membrane as a separator，the graphite/ cathode cell exhibited a good capacity retention. It is also found that the Li-ion cell fabricated in this manner not only has stable capacity retention and high temperature safety，but also shows good high-rate performance and overcharge proof performance.
The Al2O3/SiO2/PAN composite membrane was prepared as the separator for Li-ion batteries in order
to replace the traditional microporous polyolefin membrane. The composite membrane has high porosity，and can be well wetted by the liquid electrolyte. The ion conductivity of the membrane is easily achieved by absorbing the liquid electrolyte due to the high capillary effect. The amphoteric character of Al2O3/SiO2 can scavenge acidic hydrogen fluoride，which is inevitably present in the LiPF6-based elect rolytes used currently in the Li-ion batteries. With the composite membrane as a separator，the graphite/ cathode cell exhibited a good capacity retention. It is also found that the Li-ion cell fabricated in this manner not only has stable capacity retention and high temperature safety，but also shows good high-rate performance and overcharge proof performance.
2009, 26(01): 65-73.
Abstract:
Low cost technology for composites is the key issue in the present development of composite materials. However the processing time estimation is the central objective in the manufacturing cost estimation. This paper provides a processing time estimation model based on the process of manufacturing composite waved beams by autoclave molding. This paper clearly identifies the method of defining the parameters and variables estimated，which is applied to the time estimation model. The experimental data is fitted by the least squares algorithm. It shows that the model is preferable to estimate manufacturing composite waved beams. Moreover，modifying the time constant for single short wave-length beam and the velocity constant for single long wave-length beam could get a result with little difference from the practical data. So，it is verified that this manufacturing time estimation model could realize accurate time estimating for different configuration designs.
Low cost technology for composites is the key issue in the present development of composite materials. However the processing time estimation is the central objective in the manufacturing cost estimation. This paper provides a processing time estimation model based on the process of manufacturing composite waved beams by autoclave molding. This paper clearly identifies the method of defining the parameters and variables estimated，which is applied to the time estimation model. The experimental data is fitted by the least squares algorithm. It shows that the model is preferable to estimate manufacturing composite waved beams. Moreover，modifying the time constant for single short wave-length beam and the velocity constant for single long wave-length beam could get a result with little difference from the practical data. So，it is verified that this manufacturing time estimation model could realize accurate time estimating for different configuration designs.
2009, 26(01): 74-79.
Abstract:
Ferrotitanium powder，nickel powder and sucrose (carbonaceous precursor) were used as raw materials. A kind of Ti-Fe-Ni-C composite powder for reactive thermal spraying was fabricated by heating a mixture of ferrotitanium，nickel and sucrose to carbonize the sucrose. TiC/Fe-Ni composite coatings were prepared by plasma spraying of the Ti-Fe-Ni-C composite powder . It shows that the composite coatings are mainly composed of layers in which the TiC particles are uniformly dist ributed within (Fe，Ni) solid solution alloy matrix，and the TiC particles in these layers are spherical or near-spherical of submicron-scale or nano-scale sizes. Although erosion wear characters of brittle materials are represented in the erosion wear performance test of the TiC/Fe-Ni composite coatings，the ratio of mass loss of erosion wear is slightly affected by the jet angles，which demonst rates that the composite coatings have good cooperation of plasticity and hardness. The erosion wear performance of the TiC/Fe-Ni composite coating is higher than that of Cr2C3/Ni-Cr composite coating，and is more than two times that of 20G steel .
Ferrotitanium powder，nickel powder and sucrose (carbonaceous precursor) were used as raw materials. A kind of Ti-Fe-Ni-C composite powder for reactive thermal spraying was fabricated by heating a mixture of ferrotitanium，nickel and sucrose to carbonize the sucrose. TiC/Fe-Ni composite coatings were prepared by plasma spraying of the Ti-Fe-Ni-C composite powder . It shows that the composite coatings are mainly composed of layers in which the TiC particles are uniformly dist ributed within (Fe，Ni) solid solution alloy matrix，and the TiC particles in these layers are spherical or near-spherical of submicron-scale or nano-scale sizes. Although erosion wear characters of brittle materials are represented in the erosion wear performance test of the TiC/Fe-Ni composite coatings，the ratio of mass loss of erosion wear is slightly affected by the jet angles，which demonst rates that the composite coatings have good cooperation of plasticity and hardness. The erosion wear performance of the TiC/Fe-Ni composite coating is higher than that of Cr2C3/Ni-Cr composite coating，and is more than two times that of 20G steel .
2009, 26(01): 80-85.
Abstract:
(TiB2)PNi/(TiB2)PNi3Al/Ni3Al/Ni gradient materials were prepared by mechanical alloying (MA) and field-activated pressure-assisted synthesis (FAPAS) . The effects of the electric field to synthesis and diffusion of layers have been investigated. The microst ructure and the phase composition of the interfaces and the microhardness of the gradient materials were characterized. The results show that it is feasible for the four-layered gradient materials samples of (TiB2)PNi/(TiB2)PNi3Al/Ni3Al/Ni to be produced by FAPAS process，and that this method is fast，simple and the product is of uniformity. Concent ration profiles of elements across the interfaces of the layers show significant inter-diffusion and good metallurgical bonding. The measured microhardness values of the sample increase smoothly from the side of the nickel subst rate to the surface layer .
(TiB2)PNi/(TiB2)PNi3Al/Ni3Al/Ni gradient materials were prepared by mechanical alloying (MA) and field-activated pressure-assisted synthesis (FAPAS) . The effects of the electric field to synthesis and diffusion of layers have been investigated. The microst ructure and the phase composition of the interfaces and the microhardness of the gradient materials were characterized. The results show that it is feasible for the four-layered gradient materials samples of (TiB2)PNi/(TiB2)PNi3Al/Ni3Al/Ni to be produced by FAPAS process，and that this method is fast，simple and the product is of uniformity. Concent ration profiles of elements across the interfaces of the layers show significant inter-diffusion and good metallurgical bonding. The measured microhardness values of the sample increase smoothly from the side of the nickel subst rate to the surface layer .
2009, 26(01): 86-90.
Abstract:
Zinc-based composite powder containing cerium compounds was successfully prepared in 10g·L-1Ce (NO3)3 solution by means of ultrasonic immersion. The formation mechanism of the cerium compounds on the zinc powder substrate was preliminarily discussed，and the effect s of the cerium compounds on the cycle and discharge properties of the zinc electrodes were also investigated. The zinc-based composite powder was characterized and analyzed using scanning electron microscopy (SEM)，energy dispersion spectrometry (EDS)，X-ray photoelect ron spectroscopy (XPS) , and discharge-charge cycle measurements. The results show that the cerium compounds consist of Ce(OH)3/Ce(OH)4 and Ce2O3/CeO2，exist in the form of particles and are excellently distributed on the zinc powder substrate. The capacity-loss of the zinc electrodes is evidently suppressed while the discharge capacity and cycle life can be markedly improved due to the application of the zinc-based composite powder as negative materials of the silver-zinc battery. Especially，discharge capacity of 231.4mAhg-1 is still achieved at the 50th cycle for the zinc electrode using the composite powder. It is demonst rated that the cerium compounds on the zinc powder substrate enhance the electrochemical performance of the zinc electrodes.
Zinc-based composite powder containing cerium compounds was successfully prepared in 10g·L-1Ce (NO3)3 solution by means of ultrasonic immersion. The formation mechanism of the cerium compounds on the zinc powder substrate was preliminarily discussed，and the effect s of the cerium compounds on the cycle and discharge properties of the zinc electrodes were also investigated. The zinc-based composite powder was characterized and analyzed using scanning electron microscopy (SEM)，energy dispersion spectrometry (EDS)，X-ray photoelect ron spectroscopy (XPS) , and discharge-charge cycle measurements. The results show that the cerium compounds consist of Ce(OH)3/Ce(OH)4 and Ce2O3/CeO2，exist in the form of particles and are excellently distributed on the zinc powder substrate. The capacity-loss of the zinc electrodes is evidently suppressed while the discharge capacity and cycle life can be markedly improved due to the application of the zinc-based composite powder as negative materials of the silver-zinc battery. Especially，discharge capacity of 231.4mAhg-1 is still achieved at the 50th cycle for the zinc electrode using the composite powder. It is demonst rated that the cerium compounds on the zinc powder substrate enhance the electrochemical performance of the zinc electrodes.
2009, 26(01): 91-95.
Abstract:
Because of the low fracture toughness，Ti(C，N) based cermets are limited for wider utilization in the field of cutting tools，carbon nano-tubes (CNTs) were deposited with Ni by electroless plating and the ultra-fine Ti(C，N) based cermets with various CNTs mass fractions were made by vacuum sintering in order to study the effect of CNTs on the fracture toughness of ultra-fine Ti(C，N) based cermets. The effect of different CNTs contents both Ni deposited and undeposited on the microstructure and fracture toughness of the cermets was studied. The micrographs observed by SEM show that coreless grains and micro pores exist in the cermets with CNTs. The results of fracture toughness conducted by indentation show that the addition of CNTs toughens ultra-fine Ti(C，N) based cermets by 29. 4 %～62. 7 %. Crack deflection，crack bridging，coreless grains and micro pores are responsible for the toughening mechanisms. In addition，the relative density and hardness of ultra-fine cermets decrease slightly with the increasing of CNTs mass fraction. CNTs both Ni deposited and undeposited can play an active role in improving the fracture toughness of Ti(C，N)cermets.
Because of the low fracture toughness，Ti(C，N) based cermets are limited for wider utilization in the field of cutting tools，carbon nano-tubes (CNTs) were deposited with Ni by electroless plating and the ultra-fine Ti(C，N) based cermets with various CNTs mass fractions were made by vacuum sintering in order to study the effect of CNTs on the fracture toughness of ultra-fine Ti(C，N) based cermets. The effect of different CNTs contents both Ni deposited and undeposited on the microstructure and fracture toughness of the cermets was studied. The micrographs observed by SEM show that coreless grains and micro pores exist in the cermets with CNTs. The results of fracture toughness conducted by indentation show that the addition of CNTs toughens ultra-fine Ti(C，N) based cermets by 29. 4 %～62. 7 %. Crack deflection，crack bridging，coreless grains and micro pores are responsible for the toughening mechanisms. In addition，the relative density and hardness of ultra-fine cermets decrease slightly with the increasing of CNTs mass fraction. CNTs both Ni deposited and undeposited can play an active role in improving the fracture toughness of Ti(C，N)cermets.
2009, 26(01): 96-102.
Abstract:
The agglomerated powders consisting of nano ceramic particles ZrO2-8wt%Y2O3，YSZ and doped respectively with 25wt% and 50wt% nanoscale CeO2 in the nano-YSZ were used as insulation top materials，and NiCrAlY(Ni-25Cr-5Al-0.5Y，wt %) alloy was used as the bonding coating. Thermal barrier coatings of the three kinds of materials were prepared on the GH30 high temperature alloy surface by an atmospheric plasma spray (APS) process. The morphology and microstructures of the coating doped with 25wt%CeO2 in the nano-YSZ powders were characterized using scanning electron microscopy ( SEM) and X-ray diffraction ( XRD) . The thermal conductivity of the three kinds of coatings were measured at room-temperature and 300，500 and 700℃. Thermal insulation property of the as-received coatings was also examined under the same edge conditions. The results show that a relatively stable t-phase (t-ZrO2、t-Zr0.82Y0.18O1.91、t-Zr0.82Ce0.18O2) and c-phase (c-CeO2) form and the closed pores and microcracks are also observed in the coating. Moreover , the thermal barrier coatings doped with nano-CeO2 reduce the thermal conductivity and accordingly，the thermal insulation property can be developed with the amount of CeO2 increased. For CeO2/ZrO2 -Y2O3 coating ( CYZ，doped with 25wt%CeO2) with 400μm thickness，the temperature drop of the matrix alloys increases by 10.7% compared to nano-YSZ coating. As the mass fraction of CeO2 increased from 25wt% to 50wt%，the thermal insulation property increases by 7.1%.
The agglomerated powders consisting of nano ceramic particles ZrO2-8wt%Y2O3，YSZ and doped respectively with 25wt% and 50wt% nanoscale CeO2 in the nano-YSZ were used as insulation top materials，and NiCrAlY(Ni-25Cr-5Al-0.5Y，wt %) alloy was used as the bonding coating. Thermal barrier coatings of the three kinds of materials were prepared on the GH30 high temperature alloy surface by an atmospheric plasma spray (APS) process. The morphology and microstructures of the coating doped with 25wt%CeO2 in the nano-YSZ powders were characterized using scanning electron microscopy ( SEM) and X-ray diffraction ( XRD) . The thermal conductivity of the three kinds of coatings were measured at room-temperature and 300，500 and 700℃. Thermal insulation property of the as-received coatings was also examined under the same edge conditions. The results show that a relatively stable t-phase (t-ZrO2、t-Zr0.82Y0.18O1.91、t-Zr0.82Ce0.18O2) and c-phase (c-CeO2) form and the closed pores and microcracks are also observed in the coating. Moreover , the thermal barrier coatings doped with nano-CeO2 reduce the thermal conductivity and accordingly，the thermal insulation property can be developed with the amount of CeO2 increased. For CeO2/ZrO2 -Y2O3 coating ( CYZ，doped with 25wt%CeO2) with 400μm thickness，the temperature drop of the matrix alloys increases by 10.7% compared to nano-YSZ coating. As the mass fraction of CeO2 increased from 25wt% to 50wt%，the thermal insulation property increases by 7.1%.
2009, 26(01): 103-107.
Abstract:
The oxidation kinetics of ZrO2-C2ZrB2 composites with 10% ZrB2 were investigated in the temperature range from 800 to 1100℃ in air by differential thermal analysis (DTA) and thermogravimetry (TG) techniques. A mathematical model was proposed based on the reaction principle between gas and solid. The apparent activation energy and experimental expression of oxidation rate vs temperature were obtained. The results show that the oxidation process of the composites at 800℃can be controlled by two stages：chemical reaction-controlled process and then the mixture processes both chemical reaction-controlled and gas diffusion. However，the oxidation rate within 900～1100℃ is controlled by the chemical reaction at the initial stage；then both chemical reaction and diffusion at an intermediate stage and finally controlled only by diffusion. The apparent activation energy for the three stages was calculated and equal to 111.7，71.5 and 166.0kJ·mol-1 respectively. The rules of the unit area mass change as a function of isothermal processes for specimens indicate that the protective oxidation was performed during 900℃ to 1100℃.
The oxidation kinetics of ZrO2-C2ZrB2 composites with 10% ZrB2 were investigated in the temperature range from 800 to 1100℃ in air by differential thermal analysis (DTA) and thermogravimetry (TG) techniques. A mathematical model was proposed based on the reaction principle between gas and solid. The apparent activation energy and experimental expression of oxidation rate vs temperature were obtained. The results show that the oxidation process of the composites at 800℃can be controlled by two stages：chemical reaction-controlled process and then the mixture processes both chemical reaction-controlled and gas diffusion. However，the oxidation rate within 900～1100℃ is controlled by the chemical reaction at the initial stage；then both chemical reaction and diffusion at an intermediate stage and finally controlled only by diffusion. The apparent activation energy for the three stages was calculated and equal to 111.7，71.5 and 166.0kJ·mol-1 respectively. The rules of the unit area mass change as a function of isothermal processes for specimens indicate that the protective oxidation was performed during 900℃ to 1100℃.
2009, 26(01): 108-112.
Abstract:
According to the working requirements of hypersonic spacecrafts，reusable space vehicles and next generation rocket engines operating under the ultra-high temperature condition，a proposal to improve the anti-ablative property of 2D C/SiC composites by introduction of ZrB2 was presented. 2D C/SiC-ZrB2 composites with different ZrB2 contents were prepared via precursor infiltration and pyrolysis (PIP) process，and the mechanical properties and anti-ablative properties and the microstructures were investigated. The result s show that the mechanical properties (flexural strength and flexural modulus) of the composites decrease with ZrB2 content increase，but the anti-ablative properties are greatly improved. The sample with 19.4vol% ZrB2 has the flexural strength of 242.6MPa and flexural modulus of 37.1GPa. After ablation for 90s in an oxygen-acetylene torch environment , the surface temperature of the sample is as high as 2329℃，and the mass loss rate and the linear recession rate are as low as 0.005g/s and 0.015mm/s，respectively.
According to the working requirements of hypersonic spacecrafts，reusable space vehicles and next generation rocket engines operating under the ultra-high temperature condition，a proposal to improve the anti-ablative property of 2D C/SiC composites by introduction of ZrB2 was presented. 2D C/SiC-ZrB2 composites with different ZrB2 contents were prepared via precursor infiltration and pyrolysis (PIP) process，and the mechanical properties and anti-ablative properties and the microstructures were investigated. The result s show that the mechanical properties (flexural strength and flexural modulus) of the composites decrease with ZrB2 content increase，but the anti-ablative properties are greatly improved. The sample with 19.4vol% ZrB2 has the flexural strength of 242.6MPa and flexural modulus of 37.1GPa. After ablation for 90s in an oxygen-acetylene torch environment , the surface temperature of the sample is as high as 2329℃，and the mass loss rate and the linear recession rate are as low as 0.005g/s and 0.015mm/s，respectively.
2009, 26(01): 113-117.
Abstract:
The temperature fields of C/C composites braking discs (B757) were studied by the finite element method and experiment，as they were difficult to measure and reveal during the braking process. The loads，boundary conditions and loading processes in the finite element analysis of temperatures were discussed according to the heat t ransfer theory and braking principle of the braking discs. The postprocessing of simulation describes the temperature fields of braking discs during braking clearly and visually. The results show that the temperature of the midial stator rises to the maximum 659℃ at 46s；the temperature of the pressure bearing disk and pressurizing disk rises to the maximum at 48. 5s and the temperature of each test point increases firstly and then decreases in the whole braking process，while the midial stator endures the biggest thermal load，followed by the pressure bearing disk and the pressurizing disk endures the least thermal load. The simulation results are consistent with the experiment data，which verifies the validity of the temperature field results.
The temperature fields of C/C composites braking discs (B757) were studied by the finite element method and experiment，as they were difficult to measure and reveal during the braking process. The loads，boundary conditions and loading processes in the finite element analysis of temperatures were discussed according to the heat t ransfer theory and braking principle of the braking discs. The postprocessing of simulation describes the temperature fields of braking discs during braking clearly and visually. The results show that the temperature of the midial stator rises to the maximum 659℃ at 46s；the temperature of the pressure bearing disk and pressurizing disk rises to the maximum at 48. 5s and the temperature of each test point increases firstly and then decreases in the whole braking process，while the midial stator endures the biggest thermal load，followed by the pressure bearing disk and the pressurizing disk endures the least thermal load. The simulation results are consistent with the experiment data，which verifies the validity of the temperature field results.
2009, 26(01): 118-122.
Abstract:
The material mass ablative law of the carbon fiber epoxy composite irradiated by continuous wave Nd∶ YAG laser was researched by experiment. The results indicate that the composite ablative mass is directly proportional to the laser radiation energy when the laser radiation intensity is greater than 10 kW/cm2；with the same laser energy radiation , the mass ablative rate at high intensity of 0.65 mm laser spot radius is nearly twice that at low intensity of 5.5mm laser radius；combustion phenomena cause the mass ablative rate to fluctuate when the irradiation laser power is near the composite burning threshold.
The material mass ablative law of the carbon fiber epoxy composite irradiated by continuous wave Nd∶ YAG laser was researched by experiment. The results indicate that the composite ablative mass is directly proportional to the laser radiation energy when the laser radiation intensity is greater than 10 kW/cm2；with the same laser energy radiation , the mass ablative rate at high intensity of 0.65 mm laser spot radius is nearly twice that at low intensity of 5.5mm laser radius；combustion phenomena cause the mass ablative rate to fluctuate when the irradiation laser power is near the composite burning threshold.
2009, 26(01): 123-133.
Abstract:
A spatial and temporal multiple scale method used to simulate the phenomenon of non-Fourier heat conduction in multi-dimensional periodic heterogeneous materials was systematically studied. The model was derived from the high-order homogenization theory with multiple spatial and temporal scales. Amplified spatial and reduced temporal scales were respectively int roduced to account for fluctuations of non-Fourier heat conduction due to material heterogeneity and nonlocal effect of the homogenized solution. By combining various orders of homogenized non-Fourier heat conduction equations，the reduced time dependence was eliminated，the homogenized coefficients were solved by the numerical method，and then multi-dimensional high-order nonlocal equations of non-Fourier heat conduction were derived. The two-dimensional numerical examples were computed to analyze the non-Fourier heat conduction in the different microstructures of multiphase materials. Numerical result s demonst rated the validity and effectiveness of the multi-dimensional high-order nonlocal model obtained by the high-order mathematical homogenization theory.
A spatial and temporal multiple scale method used to simulate the phenomenon of non-Fourier heat conduction in multi-dimensional periodic heterogeneous materials was systematically studied. The model was derived from the high-order homogenization theory with multiple spatial and temporal scales. Amplified spatial and reduced temporal scales were respectively int roduced to account for fluctuations of non-Fourier heat conduction due to material heterogeneity and nonlocal effect of the homogenized solution. By combining various orders of homogenized non-Fourier heat conduction equations，the reduced time dependence was eliminated，the homogenized coefficients were solved by the numerical method，and then multi-dimensional high-order nonlocal equations of non-Fourier heat conduction were derived. The two-dimensional numerical examples were computed to analyze the non-Fourier heat conduction in the different microstructures of multiphase materials. Numerical result s demonst rated the validity and effectiveness of the multi-dimensional high-order nonlocal model obtained by the high-order mathematical homogenization theory.
2009, 26(01): 134-139.
Abstract:
A three-dimensional thermal-chemical-stress coupling numerical model was developed for the hot-pressing process of composites. Thermo-chemical strain，viscoelastic behavior，anisotropy，glass transition temperature related to the cure were fully considered during the autoclave cycle. The model was numerically solved by FEM，fully coupled for thermal-chemical model and one way coupled for the stress model. The results of AS4/3501-6 composite laminate show good agreement in simulated curvature with experimental results.The numerical results reveal that reducing the thickness or increasing the length of the laminate causes the curvature deformation to grow up. The autoclave pressure has little influence on the curvature deformation. The smaller the difference of the coefficient of thermal expansion(CTE) between tool and laminate，the smaller the curvature deformation.
A three-dimensional thermal-chemical-stress coupling numerical model was developed for the hot-pressing process of composites. Thermo-chemical strain，viscoelastic behavior，anisotropy，glass transition temperature related to the cure were fully considered during the autoclave cycle. The model was numerically solved by FEM，fully coupled for thermal-chemical model and one way coupled for the stress model. The results of AS4/3501-6 composite laminate show good agreement in simulated curvature with experimental results.The numerical results reveal that reducing the thickness or increasing the length of the laminate causes the curvature deformation to grow up. The autoclave pressure has little influence on the curvature deformation. The smaller the difference of the coefficient of thermal expansion(CTE) between tool and laminate，the smaller the curvature deformation.
2009, 26(01): 140-145.
Abstract:
An elasticity solution was developed for the rotating infinite double-layered cylinder composed of an isotropic elastic core and a piezoelectric layer. The electric displacement expression including an undetermined constant of the piezoelectric layer was first obtained by virtue of the charge equation of electrostatics. Then the general solutions for the isotropic elastic core and the piezoelectric layer were derived respectively. All the unknown constants were determined by means of the boundary conditions and the continuity conditions and the analytical solution was finally obtained. The numerical results denote that if both the interior and exterior surfaces of the piezoelectric layer are electrically shorted，the amplitude of the radial stress in the piezoelectric layer grows gradually with the increase of Young modulus of the elastic core and that of the tangential stress is just the contrary. Poisson ratio of the elastic core and the amplitude of electric potential applied to the piezoelectric layer have important effects on the stress responses.
An elasticity solution was developed for the rotating infinite double-layered cylinder composed of an isotropic elastic core and a piezoelectric layer. The electric displacement expression including an undetermined constant of the piezoelectric layer was first obtained by virtue of the charge equation of electrostatics. Then the general solutions for the isotropic elastic core and the piezoelectric layer were derived respectively. All the unknown constants were determined by means of the boundary conditions and the continuity conditions and the analytical solution was finally obtained. The numerical results denote that if both the interior and exterior surfaces of the piezoelectric layer are electrically shorted，the amplitude of the radial stress in the piezoelectric layer grows gradually with the increase of Young modulus of the elastic core and that of the tangential stress is just the contrary. Poisson ratio of the elastic core and the amplitude of electric potential applied to the piezoelectric layer have important effects on the stress responses.
2009, 26(01): 146-149.
Abstract:
The loading capacity of filament-wound composite materials pressure vessels with pseudo-elastic inner alloy lining depends on the pseudo-elasticity of the inner lining. The optimum loading capacity of vessels can be obtained by designing the pseudo-elasticity range of the alloy reasonably. Based on the phase transformation theory of the pseudo-elasticity alloy and mechanics of the composite materials with combination of the strength theory，the analytical method of strength and the enhancement conditions of the load-bearing capability of the composite materials pressure vessels with pseudo-elastic inner alloy lining were suggested. The research results show that the pseudo-elastic inner alloy lining can improve the stress state，change the inner lining master into the shell master，and make full use of the functions of the composite materials. Meanwhile，it can ensure that the inner lining works in the linear elastic range，and the pressed buckling phenomenon cannot happen when unloading. So the composite materials pressure vessels with pseudo-elastic inner alloy lining can increase the limit loading capacity and lengthen the work life of the inner lining.
The loading capacity of filament-wound composite materials pressure vessels with pseudo-elastic inner alloy lining depends on the pseudo-elasticity of the inner lining. The optimum loading capacity of vessels can be obtained by designing the pseudo-elasticity range of the alloy reasonably. Based on the phase transformation theory of the pseudo-elasticity alloy and mechanics of the composite materials with combination of the strength theory，the analytical method of strength and the enhancement conditions of the load-bearing capability of the composite materials pressure vessels with pseudo-elastic inner alloy lining were suggested. The research results show that the pseudo-elastic inner alloy lining can improve the stress state，change the inner lining master into the shell master，and make full use of the functions of the composite materials. Meanwhile，it can ensure that the inner lining works in the linear elastic range，and the pressed buckling phenomenon cannot happen when unloading. So the composite materials pressure vessels with pseudo-elastic inner alloy lining can increase the limit loading capacity and lengthen the work life of the inner lining.
2009, 26(01): 150-155.
Abstract:
A series of cross-section images of three-dimensional (3D) five-directional braided composites were investigated by the charge-coupled device (CCD) microscope，and then the yarn‘s arrangements and their section patterns were discussed. A 3D solid unit cell model was established. The model reasonably reflected the fiber architecture and the cross-section of the yarns. On the basis of the model，the relations between the braiding parameters were determined. The predictions about the dimensions and the fiber volume fractions of preforms show good agreement with experimental results，which provided a basis for finite element analysis (FEA) .
A series of cross-section images of three-dimensional (3D) five-directional braided composites were investigated by the charge-coupled device (CCD) microscope，and then the yarn‘s arrangements and their section patterns were discussed. A 3D solid unit cell model was established. The model reasonably reflected the fiber architecture and the cross-section of the yarns. On the basis of the model，the relations between the braiding parameters were determined. The predictions about the dimensions and the fiber volume fractions of preforms show good agreement with experimental results，which provided a basis for finite element analysis (FEA) .
2009, 26(01): 156-161.
Abstract:
According to the curing process of composite T-shaped integrated st ructures，the mechanism of the
warpage deformation was analyzed and an theoretical model was established. Some important cure properties of the T-shaped structure were calculated using the finite element method，such as the internal temperature and the degree of cure , the warpage deformation due to internal exothermic chemical reaction and volume shrinkage. The evolution of material parameters was also considered while the degree of cure was varied，and the relationship between the geometry size and the warpage deformation was studied. The results show that a suitable geometry size of the T-shaped composite structure can reduce the warpage deformation during the curing process.
According to the curing process of composite T-shaped integrated st ructures，the mechanism of the
warpage deformation was analyzed and an theoretical model was established. Some important cure properties of the T-shaped structure were calculated using the finite element method，such as the internal temperature and the degree of cure , the warpage deformation due to internal exothermic chemical reaction and volume shrinkage. The evolution of material parameters was also considered while the degree of cure was varied，and the relationship between the geometry size and the warpage deformation was studied. The results show that a suitable geometry size of the T-shaped composite structure can reduce the warpage deformation during the curing process.
2009, 26(01): 162-167.
Abstract:
A rigid-plastic analytical model is developed for the dynamic response of a sandwich beam with lattice truss cores. The beam is simply supported at the ends without axial rest raints，and the impulsive loads are uniformly distributed over the span. The maximum deflection and structural response time of the sandwich beam predicted by the rigid-plastic theory and three-dimensional FEM are compared. It is found that the theoretical predictions of the maximum deflection and structural response time are in good agreement with those of FEM，and sandwich beams with lattice truss cores can offer superior shock resistance to impulsive loadings in comparison with monolithic beams of the same mass and material. Through an optimal design for the pyramidal cores，it is revealed that the dynamic response of the simply supported sandwich beam without axial rest raints is sensitive to the relative density and thickness of the lattices truss core，and the angle of inclination between truss and face sheet. As the applied impulse per unit area is enhanced，the maximum deflection of the sandwich beam increases. Refined finite element modeling of the pyramidal truss core sandwich beam made from strain-rate sensitive 304 stainless steel is employed. The finite element calculations reveal that the maximum deflection of the sandwich beam is decreased as the strain-rate effect is considered.
A rigid-plastic analytical model is developed for the dynamic response of a sandwich beam with lattice truss cores. The beam is simply supported at the ends without axial rest raints，and the impulsive loads are uniformly distributed over the span. The maximum deflection and structural response time of the sandwich beam predicted by the rigid-plastic theory and three-dimensional FEM are compared. It is found that the theoretical predictions of the maximum deflection and structural response time are in good agreement with those of FEM，and sandwich beams with lattice truss cores can offer superior shock resistance to impulsive loadings in comparison with monolithic beams of the same mass and material. Through an optimal design for the pyramidal cores，it is revealed that the dynamic response of the simply supported sandwich beam without axial rest raints is sensitive to the relative density and thickness of the lattices truss core，and the angle of inclination between truss and face sheet. As the applied impulse per unit area is enhanced，the maximum deflection of the sandwich beam increases. Refined finite element modeling of the pyramidal truss core sandwich beam made from strain-rate sensitive 304 stainless steel is employed. The finite element calculations reveal that the maximum deflection of the sandwich beam is decreased as the strain-rate effect is considered.
2009, 26(01): 168-173.
Abstract:
A theoretical calculation method for stress concentrations in anisot ropic plates with a circular opening was suggested to composite laminates with a circular opening. Based on the classical laminated plate theory，the finite composite laminate with a circular opening was treated as an anisot ropic plate. The anisot ropic plate was equivalently transformed into a single-oriented fibers plate subjected to off-axial loading. The stress concentration factors of composite laminates with a circular opening can be obtained by means of a similar calculation formulas in the single-oriented fibers plate subjected to off-axial loading. Using the derived expressions，the effects of diameter (opening) to width (plate) ratio d/w on the stress concentration were compared and analyzed. The predicted stress concentration factors are verified with finite element simulation and the experimental results.
A theoretical calculation method for stress concentrations in anisot ropic plates with a circular opening was suggested to composite laminates with a circular opening. Based on the classical laminated plate theory，the finite composite laminate with a circular opening was treated as an anisot ropic plate. The anisot ropic plate was equivalently transformed into a single-oriented fibers plate subjected to off-axial loading. The stress concentration factors of composite laminates with a circular opening can be obtained by means of a similar calculation formulas in the single-oriented fibers plate subjected to off-axial loading. Using the derived expressions，the effects of diameter (opening) to width (plate) ratio d/w on the stress concentration were compared and analyzed. The predicted stress concentration factors are verified with finite element simulation and the experimental results.
2009, 26(01): 174-178.
Abstract:
On the basis of analyzing the interrelationship of the complex physical and chemical phenomena in the composite cure process，a three-dimensional (3D) finite element analysis ( FEA) model was developed for simulating the process and predicting the process-induced deformation. By an integrated sub-model approach，the cure process was divided into three relatively independent modules：thermo-chemical，flow-compaction and stress-deformation. The thermo-chemical module was based on the Fourier’s heat conduction and cure kinetics equation with the consideration of the coupling relation between temperature and cure degree. In the flow-compaction module，Darcy law and effective stress principle were employed to describe the interaction between resin viscous flow and fiber bed consolidation. In the stress-deformation module，multi-layer complex composite laminates subjected to thermal load and resin cure shrinkage were analyzed by the 3D finite element method. Which module and its subroutines should be called was determined by resin gelation and vitrification. The interaction of these three modules is realized through exchanging the data between them. The representative structure simulation comparison with experiment verified the 3D FEA model in this paper.
On the basis of analyzing the interrelationship of the complex physical and chemical phenomena in the composite cure process，a three-dimensional (3D) finite element analysis ( FEA) model was developed for simulating the process and predicting the process-induced deformation. By an integrated sub-model approach，the cure process was divided into three relatively independent modules：thermo-chemical，flow-compaction and stress-deformation. The thermo-chemical module was based on the Fourier’s heat conduction and cure kinetics equation with the consideration of the coupling relation between temperature and cure degree. In the flow-compaction module，Darcy law and effective stress principle were employed to describe the interaction between resin viscous flow and fiber bed consolidation. In the stress-deformation module，multi-layer complex composite laminates subjected to thermal load and resin cure shrinkage were analyzed by the 3D finite element method. Which module and its subroutines should be called was determined by resin gelation and vitrification. The interaction of these three modules is realized through exchanging the data between them. The representative structure simulation comparison with experiment verified the 3D FEA model in this paper.
2009, 26(01): 179-184.
Abstract:
By integrated sub-model approach，a three-dimensional finite element analysis (FEA) model was developed to simulate the cure process and predict the process-induced deformation for thermoset composites. L shape structure cure process was simulated to analyze the effect of these cure process parameters on the process-induced deformation. The simulation results show：The heating-rate and convection coefficient influence the deformation by changing peak temperature；cure pressure affects the deformation by changing resin distribution and fiber volume fraction；the ply direction induced mechanical property difference is the main reason of the spring-in angle diversity；the influence of thickness should consider its effect on peak temperature and structure stiffness；the radius has a little influence on deformation；the mold style changes resin distribution gradient direction and mold force position；selection of mold materials and style has crucial influence on the process-induced deformation control.
By integrated sub-model approach，a three-dimensional finite element analysis (FEA) model was developed to simulate the cure process and predict the process-induced deformation for thermoset composites. L shape structure cure process was simulated to analyze the effect of these cure process parameters on the process-induced deformation. The simulation results show：The heating-rate and convection coefficient influence the deformation by changing peak temperature；cure pressure affects the deformation by changing resin distribution and fiber volume fraction；the ply direction induced mechanical property difference is the main reason of the spring-in angle diversity；the influence of thickness should consider its effect on peak temperature and structure stiffness；the radius has a little influence on deformation；the mold style changes resin distribution gradient direction and mold force position；selection of mold materials and style has crucial influence on the process-induced deformation control.
2009, 26(01): 185-189.
Abstract:
The stability behavior of advanced grid stiffened structures (AGS) with delamination considering progressive failure and hygrothermal effects was investigated by numerical method. Based on the first order shear theory and the Von Karman non-linear assumption，the corresponding finite element formula was developed，and an appropriate progressive failure criterion was adopted. By some typical numerical examples，the effects of delamination，hygrothermal and the progressive failure on the stability behaviors of the AGS plate and shell are discussed. The numerical results indicate that the effects of delamination，hygrothermal and progressive failure on the stability of composite AGS structures can not be neglected when the above factors result in a jump of the buckling mode.
The stability behavior of advanced grid stiffened structures (AGS) with delamination considering progressive failure and hygrothermal effects was investigated by numerical method. Based on the first order shear theory and the Von Karman non-linear assumption，the corresponding finite element formula was developed，and an appropriate progressive failure criterion was adopted. By some typical numerical examples，the effects of delamination，hygrothermal and the progressive failure on the stability behaviors of the AGS plate and shell are discussed. The numerical results indicate that the effects of delamination，hygrothermal and progressive failure on the stability of composite AGS structures can not be neglected when the above factors result in a jump of the buckling mode.
2009, 26(01): 190-195.
Abstract:
Coupling of flexure and shear exists in three-point bend beams. The coupling coefficients of flexure and shear were introduced，and the coupling equations of flexure and shear were deduced based on Tsaicriteria. The coupling effect of flexure and shear was analyzed quantificationally，and the modification method of the experimental results was presented. It was shown that the experimental results of three-point bend were influenced obviously by the coupling of flexure and shear. The flexural strength error from the coupling effect increased with the flexural-shear strength ratio， whereas the shear strength error decreased with it. For the given coupling coefficients of flexure and shear，the test errors were determined by the division of span-height ratio into the flexural-shear strength ratio. The experimental results were modified by the modification methods，and the correctional results of three-point bend on different span-height ratios became more comparable. The inherent properties were reflected by the correctional results.
Coupling of flexure and shear exists in three-point bend beams. The coupling coefficients of flexure and shear were introduced，and the coupling equations of flexure and shear were deduced based on Tsaicriteria. The coupling effect of flexure and shear was analyzed quantificationally，and the modification method of the experimental results was presented. It was shown that the experimental results of three-point bend were influenced obviously by the coupling of flexure and shear. The flexural strength error from the coupling effect increased with the flexural-shear strength ratio， whereas the shear strength error decreased with it. For the given coupling coefficients of flexure and shear，the test errors were determined by the division of span-height ratio into the flexural-shear strength ratio. The experimental results were modified by the modification methods，and the correctional results of three-point bend on different span-height ratios became more comparable. The inherent properties were reflected by the correctional results.
2009, 26(01): 196-199.
Abstract:
The polyimide films were placed into composites before solidifying in order to simulate the composite laminations damage. The inherent frequency of the composites with and without damage was tested by using the free vibration method. The damage positions of the composite laminations were identified by using the frequency dactylogram. The detection results show that the frequency dactylogram can be constructed using the frequency data of structures，which is only related with the positions of damage and not the degree of structural damage. The orientation of structural damage can be carried through making use of such frequency dactylogram. The method is proved easy and efficient in solving composites damage problems.
The polyimide films were placed into composites before solidifying in order to simulate the composite laminations damage. The inherent frequency of the composites with and without damage was tested by using the free vibration method. The damage positions of the composite laminations were identified by using the frequency dactylogram. The detection results show that the frequency dactylogram can be constructed using the frequency data of structures，which is only related with the positions of damage and not the degree of structural damage. The orientation of structural damage can be carried through making use of such frequency dactylogram. The method is proved easy and efficient in solving composites damage problems.
2009, 26(01): 200-204.
Abstract:
The humidity-sensing property of carbon black (CB)/hydroxyethyl cellulose (HEC) humidity sensors and its dependence on the chemical composition of the sample were investigated. Sorbitol was incorporated into the samples as a sensitizing agent and its effect on the nonlinearity of the devices‘ performance was studied. The measurement results of conductivity，sensitivity to humidity and complex impedance spectrum (CIS) suggest that the amounts of CB and sorbitol affect the sensing performance greatly. A nonlinear increase in resistance was observed at 80% humidity on the sample with 2% CB，and the sensitivity response shifts to lower humidity values when an appropriate amount of sorbitol is added. The sensor equivalent circuits derived from the CIS results can be modeled by a Warburg impedance in series with a number of resistance-capacitance circuits that correspond to bulk resistance，CB-grain-boundary resistance and contact resistance，respectively. The number of semicircles in the CIS increases with humidity level，which indicates different polarization mechanisms due to the adsorbed water.
The humidity-sensing property of carbon black (CB)/hydroxyethyl cellulose (HEC) humidity sensors and its dependence on the chemical composition of the sample were investigated. Sorbitol was incorporated into the samples as a sensitizing agent and its effect on the nonlinearity of the devices‘ performance was studied. The measurement results of conductivity，sensitivity to humidity and complex impedance spectrum (CIS) suggest that the amounts of CB and sorbitol affect the sensing performance greatly. A nonlinear increase in resistance was observed at 80% humidity on the sample with 2% CB，and the sensitivity response shifts to lower humidity values when an appropriate amount of sorbitol is added. The sensor equivalent circuits derived from the CIS results can be modeled by a Warburg impedance in series with a number of resistance-capacitance circuits that correspond to bulk resistance，CB-grain-boundary resistance and contact resistance，respectively. The number of semicircles in the CIS increases with humidity level，which indicates different polarization mechanisms due to the adsorbed water.
