2012 Vol. 29, No. 4
2012, (4): 1-9.
Abstract:
Based on ex-situ toughening concept, the polyamide nonwoven fabric(PNF) with high porosity was chosen as structural toughening layer, and the U3160 carbon fiber reinforced epoxy 3266 composites toughened by interlaminar PNF(U3160-PNF/3266) was fabricated via RTM process. The properties of U3160-PNF/3266 composite were investigated as well as toughening mechanism. The results indicate that the PNF still keep original structure in composites interlaminar, and formed a unreactional co-continuous structure with based resin which show remarkable toughening effect. Mode Ⅰ fracture toughness (GⅠ C) and mode Ⅱ fracture toughness (GⅡ C) of the U3160-PNF/3266 composites are 1.1 times and 1.4 times higher respectively than that of the control system, and the compression after impact (CAI) increase from 212 MPa to 281 MPa.
Based on ex-situ toughening concept, the polyamide nonwoven fabric(PNF) with high porosity was chosen as structural toughening layer, and the U3160 carbon fiber reinforced epoxy 3266 composites toughened by interlaminar PNF(U3160-PNF/3266) was fabricated via RTM process. The properties of U3160-PNF/3266 composite were investigated as well as toughening mechanism. The results indicate that the PNF still keep original structure in composites interlaminar, and formed a unreactional co-continuous structure with based resin which show remarkable toughening effect. Mode Ⅰ fracture toughness (GⅠ C) and mode Ⅱ fracture toughness (GⅡ C) of the U3160-PNF/3266 composites are 1.1 times and 1.4 times higher respectively than that of the control system, and the compression after impact (CAI) increase from 212 MPa to 281 MPa.
2012, (4): 10-16.
Abstract:
Multi-walled carbon nanotubes(MWCNTs) were modified through grafting C16 alkyl chains. MWCNTs/polypropylene(PP) composites were prepared through solution blending. The crystallization behaviors of MWCNTs/PP composites were studied. The experimental results show that 3% (mass fraction) grafted MWCNTs with C16 alkyl chains could be dispersed very well in PP matrix.The grafted MWCNTs could be dispersed on nano-scale. The presence of the grafted MWCNTs does not change the α-crystal form of PP. The introduction of the grafted MWCNTS induces the heterogeneous nucleation of PP in the grafted MWCNTs/PP composites, which will affect the mechanism of nucleation and the crystal growth of PP. After the addition of 3% (mass fraction) grafted MWCNTs in the PP matrix, the crystallizing temperature is increased by 8℃, the crystallizing rate is improved one time, and the crystallinity of PP matrix is increased by 3%. Moreover, the spherulity size decreases.
Multi-walled carbon nanotubes(MWCNTs) were modified through grafting C16 alkyl chains. MWCNTs/polypropylene(PP) composites were prepared through solution blending. The crystallization behaviors of MWCNTs/PP composites were studied. The experimental results show that 3% (mass fraction) grafted MWCNTs with C16 alkyl chains could be dispersed very well in PP matrix.The grafted MWCNTs could be dispersed on nano-scale. The presence of the grafted MWCNTs does not change the α-crystal form of PP. The introduction of the grafted MWCNTS induces the heterogeneous nucleation of PP in the grafted MWCNTs/PP composites, which will affect the mechanism of nucleation and the crystal growth of PP. After the addition of 3% (mass fraction) grafted MWCNTs in the PP matrix, the crystallizing temperature is increased by 8℃, the crystallizing rate is improved one time, and the crystallinity of PP matrix is increased by 3%. Moreover, the spherulity size decreases.
2012, (4): 17-22.
Abstract:
The wetting agent containing carbon nanotubes (CNTs) and deionized water was prepared, in which carbon fibers were infiltrated, and then dried. The effects of CNTs content and infiltrating process on CNTs distribution on the surfaces of carbon fibers were studied by means of SEM and AFM. The influence of CNTs wetting agent on the interface bonding property of carbon fiber/epoxy resin and the mechanism were investigated using single fiber fragmentation test. The results show that T700 and T300 carbon fibers can be coated with CNTs after infiltrated in the wetting agent and the content of CNTs on the surfaces is higher using the wetting agent with higher content of CNTs. For the wetting agent with low content of CNTs, the method of increasing infiltrating times is an effective way to increase the CNTs content and roughness of carbon fiber surfaces. The interface bonding strength of carbon fiber/epoxy resin is obviously improved by 35.8% at maximum after carbon fiber being infiltrated in the CNTs wetting agent, resulting from the enhancement of mechanical interlocking at the interphase regions.
The wetting agent containing carbon nanotubes (CNTs) and deionized water was prepared, in which carbon fibers were infiltrated, and then dried. The effects of CNTs content and infiltrating process on CNTs distribution on the surfaces of carbon fibers were studied by means of SEM and AFM. The influence of CNTs wetting agent on the interface bonding property of carbon fiber/epoxy resin and the mechanism were investigated using single fiber fragmentation test. The results show that T700 and T300 carbon fibers can be coated with CNTs after infiltrated in the wetting agent and the content of CNTs on the surfaces is higher using the wetting agent with higher content of CNTs. For the wetting agent with low content of CNTs, the method of increasing infiltrating times is an effective way to increase the CNTs content and roughness of carbon fiber surfaces. The interface bonding strength of carbon fiber/epoxy resin is obviously improved by 35.8% at maximum after carbon fiber being infiltrated in the CNTs wetting agent, resulting from the enhancement of mechanical interlocking at the interphase regions.
2012, (4): 23-28.
Abstract:
The thermal conductivities of carbon fiber/epoxy prepreg, in the directions of perpendicular and parallel to the fiber direction, were determined during its curing process by modulated differential scanning calorimetry (MDSC). During the carbon fiber/epoxy prepreg curing process the binary quadratic function models of thermal conductivity in different directions were set up based on the experimental results, which was used to determine the value of thermal conductivity with the temperature and the cure degree during the curing process. The results show that the thermal conductivity of the T800/epoxy prepreg is 0.85~1.25 W/(m稫) and 1.15~1.40 W/(m稫) in the directions of perpendicular and parallel to the fiber direction. The thermal conductivity of the prepreg decreases with the degree of cure at the same temperature, and increases with increasing temperature in the same degree of cure. The verification results show that the binary quadratic function model of the thermal conductivity will improve the accuracy of the parameters in numerical simulation.
The thermal conductivities of carbon fiber/epoxy prepreg, in the directions of perpendicular and parallel to the fiber direction, were determined during its curing process by modulated differential scanning calorimetry (MDSC). During the carbon fiber/epoxy prepreg curing process the binary quadratic function models of thermal conductivity in different directions were set up based on the experimental results, which was used to determine the value of thermal conductivity with the temperature and the cure degree during the curing process. The results show that the thermal conductivity of the T800/epoxy prepreg is 0.85~1.25 W/(m稫) and 1.15~1.40 W/(m稫) in the directions of perpendicular and parallel to the fiber direction. The thermal conductivity of the prepreg decreases with the degree of cure at the same temperature, and increases with increasing temperature in the same degree of cure. The verification results show that the binary quadratic function model of the thermal conductivity will improve the accuracy of the parameters in numerical simulation.
2012, (4): 29-35.
Abstract:
Continuous glass fiber (GF) reinforced poly(cyclic butylene terephthalate) (PCBT) composites were prepared via in-situ polymerization of cyclic butylene terephthalate (CBT). The effects of the catalyst contents on the crystallinity and the mechanical properties of GF/PCBT composites were studied. When the catalyst mass fraction reaches 0.5%, the crystallinity is 53% and the GF/PCBT composites show the highest values of mechanical properties, tensile strength 522 MPa, tensile modulus 27 GPa, flexural strength 481 MPa, flexural modulus 24.8 GPa and interlaminar shear strength (ILSS) 43 MPa. The SEM results show good bonding quality between the fiber and the matrix at 0.5% of catalyst. The effects of quenching and annealing treatments on the mechanical properties of GF/PCBT composites were further investigated. The results show that the improved mechanical properties after annealing treatment, tensile strength is 545 MPa and flexural strength is 495 MPa.
Continuous glass fiber (GF) reinforced poly(cyclic butylene terephthalate) (PCBT) composites were prepared via in-situ polymerization of cyclic butylene terephthalate (CBT). The effects of the catalyst contents on the crystallinity and the mechanical properties of GF/PCBT composites were studied. When the catalyst mass fraction reaches 0.5%, the crystallinity is 53% and the GF/PCBT composites show the highest values of mechanical properties, tensile strength 522 MPa, tensile modulus 27 GPa, flexural strength 481 MPa, flexural modulus 24.8 GPa and interlaminar shear strength (ILSS) 43 MPa. The SEM results show good bonding quality between the fiber and the matrix at 0.5% of catalyst. The effects of quenching and annealing treatments on the mechanical properties of GF/PCBT composites were further investigated. The results show that the improved mechanical properties after annealing treatment, tensile strength is 545 MPa and flexural strength is 495 MPa.
2012, (4): 36-41.
Abstract:
For the sake of comparing the different electricity conductivities of composite materials when the UHMWPE filled singleness and mixed, graphene nanosheets (GNS)-multi-walled carbon nanotubes(MWCNTs)/ultrahigh molecular weight polyethylene (UHMWPE) composites with a segregated network structure were prepared by alcohol-assisted dispersion, ultrasound and hydrazine. SEM and TEM results show that MWCNTs or GNS homogeneously disperse around UHMWPE particle, and from a segregated conductive network during the hot-pressing. It is found that the percolation threshold of GNS/UHMWPE composites (0.059%, volume fraction) is much lower than that of MWCNTs/UHMWPE composites (0.148%, volume fraction). At the same filler content, the electrical conductivity of GNS/UHMWPE composites is much lower than that of the MWCNTs/UHMWPE composites (2.0?10-2 S/m, 1.0%, mass fraction). The percolation threshold of GNS-MWCNTs/UHMWPE hybrid composites (0.039%, volume fraction) is lower than that of composites filled with GNS and MWCNTs alone, while the conductivity of GNS-MWCNTs/UHMWPE hybrid composites (1.0?10-2 S/m, 1.0%, mass fraction) is similar to the MWCNTs/UHMWPE composites. The mechanical properties of composites increase and then decrease with the increasing content of fillers.
For the sake of comparing the different electricity conductivities of composite materials when the UHMWPE filled singleness and mixed, graphene nanosheets (GNS)-multi-walled carbon nanotubes(MWCNTs)/ultrahigh molecular weight polyethylene (UHMWPE) composites with a segregated network structure were prepared by alcohol-assisted dispersion, ultrasound and hydrazine. SEM and TEM results show that MWCNTs or GNS homogeneously disperse around UHMWPE particle, and from a segregated conductive network during the hot-pressing. It is found that the percolation threshold of GNS/UHMWPE composites (0.059%, volume fraction) is much lower than that of MWCNTs/UHMWPE composites (0.148%, volume fraction). At the same filler content, the electrical conductivity of GNS/UHMWPE composites is much lower than that of the MWCNTs/UHMWPE composites (2.0?10-2 S/m, 1.0%, mass fraction). The percolation threshold of GNS-MWCNTs/UHMWPE hybrid composites (0.039%, volume fraction) is lower than that of composites filled with GNS and MWCNTs alone, while the conductivity of GNS-MWCNTs/UHMWPE hybrid composites (1.0?10-2 S/m, 1.0%, mass fraction) is similar to the MWCNTs/UHMWPE composites. The mechanical properties of composites increase and then decrease with the increasing content of fillers.
2012, (4): 42-46.
Abstract:
The rheological behavior in extensional flow of the melt of mica/polypropylene (PP) blend was researched by twin-bore capillary rheometer and Haul-off equipment. The results show that rheological property of all the Mica/PP samples appear extensional thinning behavior, with the increase of the mica content, the apparent extensional viscosity increases. The extensional stress and the apparent extensional viscosity decline with the rise of temperature. The extensional stress increases, the apparent extensional viscosity and the activation energy of extensional flow viscosity decrease with increasing the extensional strain rate. The added mica particles make the tensile modulus of PP melt increase remarkably, but with the increase of drawing speed, the tensile modulus of the blend melt decreases significantly. In order to improve the spinning stability of Mica/PP blend, it was important to control the drawing speed and processing temperature.
The rheological behavior in extensional flow of the melt of mica/polypropylene (PP) blend was researched by twin-bore capillary rheometer and Haul-off equipment. The results show that rheological property of all the Mica/PP samples appear extensional thinning behavior, with the increase of the mica content, the apparent extensional viscosity increases. The extensional stress and the apparent extensional viscosity decline with the rise of temperature. The extensional stress increases, the apparent extensional viscosity and the activation energy of extensional flow viscosity decrease with increasing the extensional strain rate. The added mica particles make the tensile modulus of PP melt increase remarkably, but with the increase of drawing speed, the tensile modulus of the blend melt decreases significantly. In order to improve the spinning stability of Mica/PP blend, it was important to control the drawing speed and processing temperature.
2012, (4): 47-55.
Abstract:
A kind of multi-walled carbon nanotubes (MWCNTs)/perfluorosulfonate resin (Nafion) ionic exchange membrane(IEM) was prepared with Nafion solution and MWCNTs by mass ratios of 100:1, 100:3 and 100:5 using solvent evaporation method and ultrasonic dispersion method. Based on the IEMs, Ionic exchange polymer metal composites with Pt as electrodes (Pt-IPMC) were manufactured by chemical deposit method. The influence of MWCNTs contents on IEM and Pt-IPMC performance was investigated. The effect of Pt deposit was measured with SEM and EDAX, mechanical properties of IEM and Pt-IPMC samples were studied by tension testing, and Pt-IPMC dynamic deformation was observed under different excitation signals. The experimental results reveal that, owing to the MWCNTs, thicknesses of inter-locked electrodes and surface electrodes are respectively increased by 200%~250% and 180%~200%, elastic moduli of IEM and Pt-IPMC are respectively increased by 57.92%~140.85% and 9.06%~52.85%, inter-locked electrodes of Pt-IPMC are effectively modified. The samples’ dynamic displacement, response and deforming velocity are enhanced.
A kind of multi-walled carbon nanotubes (MWCNTs)/perfluorosulfonate resin (Nafion) ionic exchange membrane(IEM) was prepared with Nafion solution and MWCNTs by mass ratios of 100:1, 100:3 and 100:5 using solvent evaporation method and ultrasonic dispersion method. Based on the IEMs, Ionic exchange polymer metal composites with Pt as electrodes (Pt-IPMC) were manufactured by chemical deposit method. The influence of MWCNTs contents on IEM and Pt-IPMC performance was investigated. The effect of Pt deposit was measured with SEM and EDAX, mechanical properties of IEM and Pt-IPMC samples were studied by tension testing, and Pt-IPMC dynamic deformation was observed under different excitation signals. The experimental results reveal that, owing to the MWCNTs, thicknesses of inter-locked electrodes and surface electrodes are respectively increased by 200%~250% and 180%~200%, elastic moduli of IEM and Pt-IPMC are respectively increased by 57.92%~140.85% and 9.06%~52.85%, inter-locked electrodes of Pt-IPMC are effectively modified. The samples’ dynamic displacement, response and deforming velocity are enhanced.
2012, (4): 56-62.
Abstract:
The modified multi-walled carbon nanotubes (MWCNTs) with different functional groups on the surface were prepared by the methods of mixed acid oxidation and surface graft reaction. The impact strength at cryogenic temperature and the coefficient of thermal expansion (CTE) values for the pure epoxy and different MWCNTs modified epoxy were studied. The results show that—NCO group terminated PEO oligomer can be introduced to the surface of MWCNTs through surface grafting reaction, which can improve the dispersion state of nanotubes and strengthen the interfacial bonding between nanotubes and epoxy matrix. In comparison to pure epoxy, impact strength at cryogenic temperature of MWCNTs, O-MWCNTs and S-MWCNTs modified epoxy composites with 0.5% mass fraction are increased 10.27%, 26.13% and 32.95%, respectively, and CTE values under Tg range are decreased 14.79%, 29.59% and 40.29%, respectively. It indicates that S-MWCNTs can improve the impact strength at cryogenic temperature and decrease the CTE values under Tg range of epoxy resins.
The modified multi-walled carbon nanotubes (MWCNTs) with different functional groups on the surface were prepared by the methods of mixed acid oxidation and surface graft reaction. The impact strength at cryogenic temperature and the coefficient of thermal expansion (CTE) values for the pure epoxy and different MWCNTs modified epoxy were studied. The results show that—NCO group terminated PEO oligomer can be introduced to the surface of MWCNTs through surface grafting reaction, which can improve the dispersion state of nanotubes and strengthen the interfacial bonding between nanotubes and epoxy matrix. In comparison to pure epoxy, impact strength at cryogenic temperature of MWCNTs, O-MWCNTs and S-MWCNTs modified epoxy composites with 0.5% mass fraction are increased 10.27%, 26.13% and 32.95%, respectively, and CTE values under Tg range are decreased 14.79%, 29.59% and 40.29%, respectively. It indicates that S-MWCNTs can improve the impact strength at cryogenic temperature and decrease the CTE values under Tg range of epoxy resins.
2012, (4): 63-68.
Abstract:
Based on the process of liquid composite molding(LCM), it existed unsaturated regional experiment phenomenon, can be understood flow in dual-scale porous media gradually. Some scholars proposed to use sink model to study of unsaturated flow in dual-scale porous media. The features of dual-scale porous media in the LCM by volume averaging method were described, and dual-scale LCM mass conservation equation which contained sink term was obtained, and the finite element method was used to solve differential equation numerically. Through a specific example, under the condition of constant pressure, the pressure distribution in the different periods in dual-scale porous media is calculated. The change process of unsaturated regional near resin flow front is got. The different injection pressures are used to simulate and compare. Compared with single-scale porous media, dual-scale porous media can reflect unsaturated regional phenomenon in practical filling process better.
Based on the process of liquid composite molding(LCM), it existed unsaturated regional experiment phenomenon, can be understood flow in dual-scale porous media gradually. Some scholars proposed to use sink model to study of unsaturated flow in dual-scale porous media. The features of dual-scale porous media in the LCM by volume averaging method were described, and dual-scale LCM mass conservation equation which contained sink term was obtained, and the finite element method was used to solve differential equation numerically. Through a specific example, under the condition of constant pressure, the pressure distribution in the different periods in dual-scale porous media is calculated. The change process of unsaturated regional near resin flow front is got. The different injection pressures are used to simulate and compare. Compared with single-scale porous media, dual-scale porous media can reflect unsaturated regional phenomenon in practical filling process better.
2012, (4): 69-74.
Abstract:
The dynamic contact angle analytical method of sisal fiber based on Wihelmy plate principle was developed on the basis of the quantification of the cross-section area by using Weibull statistical distribution function and the measurment of liquid wicking quality caused by the hollow structure of sisal fiber. On this basis, the influences of different surface treatment methods on the surface microstructure, the surface chemical composition, the surface energy as well as its dispersion, polar component were analyzed. Also the wettability between sisal fiber and E51 epoxy resin was measured. The results show that the surface polar functional groups and polar component of surface energy of sisal fiber are significantly increased after being treated by NaOH and flame retardants. Although the surface polar functional groups are increased by silane treatment, the polar component decreased with the total surface energy slightly reduced. The wettability between sisal fiber and E51 resin is closely related to the matching characteristics of polar ratio of surface energies.
The dynamic contact angle analytical method of sisal fiber based on Wihelmy plate principle was developed on the basis of the quantification of the cross-section area by using Weibull statistical distribution function and the measurment of liquid wicking quality caused by the hollow structure of sisal fiber. On this basis, the influences of different surface treatment methods on the surface microstructure, the surface chemical composition, the surface energy as well as its dispersion, polar component were analyzed. Also the wettability between sisal fiber and E51 epoxy resin was measured. The results show that the surface polar functional groups and polar component of surface energy of sisal fiber are significantly increased after being treated by NaOH and flame retardants. Although the surface polar functional groups are increased by silane treatment, the polar component decreased with the total surface energy slightly reduced. The wettability between sisal fiber and E51 resin is closely related to the matching characteristics of polar ratio of surface energies.
2012, (4): 75-82.
Abstract:
MCA-PPO/PS composites were prepared by melt-compounding PPO/PS and melamine cyanurate (MCA) as a halogen-free flame retardant. The structure of the composites was characterized by XRD and SEM, and their combustion behavior and flowability were investigated. It is discovered that the microstructure of MCA in the composites is the same as that of pure MCA after the sample preparation and processing procedure. Thus the flame retardant effect of MCA remains unchanged. MCA is dispersed evenly in the composites, with no obvious agglomeration. In comparison with that of pure PS, the oxygen index (OI) of PPO/PS with mass ratio of 100:100 increases by 5.4%, the peak heat release rate (PHRR) decreases by 33.1% and the total smoke release (TSR) increases by almost 1.5 times. With rise of MCA loading, the flame retardancy of the MCA-PPO/PS composite gradually improves, while the total smoke release (TSR) decreases remarkably. Meanwhile, the melt viscosity of the composites decreases and the flowability increases with MCA loading. The addition of 5%, 25% and 45% mass fraction of MCA to the MCA-PPO/PS composite can decrease the TSR by 43.7%, 82.6%, and 91.6%, respectively. The flame retardant mechanism of PPO/PS is condensed phase charring mechanism. The flame-retarding mechanism of the MCA-PPO/PS composite changes from condensed phase charring mechanism to gas phase diluting and cooling effect of polymer matrix with MCA loading. The addition of MCA can enhance flame retardancy, suppress smoke release and improve melt flowability of the MCA-PPO/PS composite simultaneously.
MCA-PPO/PS composites were prepared by melt-compounding PPO/PS and melamine cyanurate (MCA) as a halogen-free flame retardant. The structure of the composites was characterized by XRD and SEM, and their combustion behavior and flowability were investigated. It is discovered that the microstructure of MCA in the composites is the same as that of pure MCA after the sample preparation and processing procedure. Thus the flame retardant effect of MCA remains unchanged. MCA is dispersed evenly in the composites, with no obvious agglomeration. In comparison with that of pure PS, the oxygen index (OI) of PPO/PS with mass ratio of 100:100 increases by 5.4%, the peak heat release rate (PHRR) decreases by 33.1% and the total smoke release (TSR) increases by almost 1.5 times. With rise of MCA loading, the flame retardancy of the MCA-PPO/PS composite gradually improves, while the total smoke release (TSR) decreases remarkably. Meanwhile, the melt viscosity of the composites decreases and the flowability increases with MCA loading. The addition of 5%, 25% and 45% mass fraction of MCA to the MCA-PPO/PS composite can decrease the TSR by 43.7%, 82.6%, and 91.6%, respectively. The flame retardant mechanism of PPO/PS is condensed phase charring mechanism. The flame-retarding mechanism of the MCA-PPO/PS composite changes from condensed phase charring mechanism to gas phase diluting and cooling effect of polymer matrix with MCA loading. The addition of MCA can enhance flame retardancy, suppress smoke release and improve melt flowability of the MCA-PPO/PS composite simultaneously.
2012, (4): 83-87.
Abstract:
The aluminum salt of methylethylphosphinate (Al(MEP)) was used as a flame retardant filler for EP, Al(MEP)/EP composites with different composition were prepared. The flame retardancy was investigated with limited oxygen index (LOI) and UL 94 vertical burning test. The structure, thermal stability, glass transition temoerature (Tg) and morphology of the samples were characterized by Fourier transform infrared analysis (FTIR), TG analysis, DSC and SEM, respectively. The flexural and impact properties of the composites were also investigated. Results show that Al(MEP)/EP composite with only 15% mass fraction of Al (MEP) can achieve the optimal flame retardancy with LOI value of 32.5% and UL 94 V-0 rating. The evaluation indicats that Al(MEP)/EP composites have good thermal and mechanical properties.
The aluminum salt of methylethylphosphinate (Al(MEP)) was used as a flame retardant filler for EP, Al(MEP)/EP composites with different composition were prepared. The flame retardancy was investigated with limited oxygen index (LOI) and UL 94 vertical burning test. The structure, thermal stability, glass transition temoerature (Tg) and morphology of the samples were characterized by Fourier transform infrared analysis (FTIR), TG analysis, DSC and SEM, respectively. The flexural and impact properties of the composites were also investigated. Results show that Al(MEP)/EP composite with only 15% mass fraction of Al (MEP) can achieve the optimal flame retardancy with LOI value of 32.5% and UL 94 V-0 rating. The evaluation indicats that Al(MEP)/EP composites have good thermal and mechanical properties.
2012, (4): 88-93.
Abstract:
The modified nano-TiO2 by aminopropyl triethoxy silane(KH550) was used to prepare nano-TiO2/PVA composites through a solution casting method (PVA types: 17-88 and 17-99). The different contents of PVA 17-88 in nano-TiO2/PVA composites were characterized by TG analysis, and the structures of the composites were analyzed by SEM. The mechanical and water resistance and transparency of the composites were also characterized. The results show that when the mass fraction of PVA 17-88 is 30% and the thickness of membrane is controlled in 25~30 μm, the tensile strength is up to 28.72 MPa, the mass loss rate is the lowest.
The modified nano-TiO2 by aminopropyl triethoxy silane(KH550) was used to prepare nano-TiO2/PVA composites through a solution casting method (PVA types: 17-88 and 17-99). The different contents of PVA 17-88 in nano-TiO2/PVA composites were characterized by TG analysis, and the structures of the composites were analyzed by SEM. The mechanical and water resistance and transparency of the composites were also characterized. The results show that when the mass fraction of PVA 17-88 is 30% and the thickness of membrane is controlled in 25~30 μm, the tensile strength is up to 28.72 MPa, the mass loss rate is the lowest.
2012, (4): 94-98.
Abstract:
The interface of the bamboo fibers/polylactic acid was controlled by alkali(NaOH) treatment, isocyanate (MDI) treatment and NaOH+MDI treatment, respectively. The results show that the NaOH treatment could further refine bamboo fibers and increase specific surface area, realizing the physical control of bamboo fibers/polylactic acid composites interface; MDI treatment could realize the chemical control of bamboo fibers/polylactic acid composites interface. All of the three kinds of the interface control methods could improve the mechanical properties of bamboo fibers/polylactic acid composites, among which NaOH+MDI treatment has the best positive effects on the interface properties of the composites, the tensile strength and impact strength of the bamboofibers/polylactic acid composites with interface control are increased 36.9% and 36.5%, respectively.
The interface of the bamboo fibers/polylactic acid was controlled by alkali(NaOH) treatment, isocyanate (MDI) treatment and NaOH+MDI treatment, respectively. The results show that the NaOH treatment could further refine bamboo fibers and increase specific surface area, realizing the physical control of bamboo fibers/polylactic acid composites interface; MDI treatment could realize the chemical control of bamboo fibers/polylactic acid composites interface. All of the three kinds of the interface control methods could improve the mechanical properties of bamboo fibers/polylactic acid composites, among which NaOH+MDI treatment has the best positive effects on the interface properties of the composites, the tensile strength and impact strength of the bamboofibers/polylactic acid composites with interface control are increased 36.9% and 36.5%, respectively.
2012, (4): 99-104.
Abstract:
The non-crimp fabrics (NCF) were used as reinforcement to improve the drape efficiency and accuracy. According to the structural characteristics of the T-joint, an I-beam composed of four T-joints was manufactured via resin transfer moulding (RTM) process. The tensile and compressive properties of T-joint were tested. The results show that the tensile failure of T-joint can be reckoned to the fiber broken of skin around the holes and the delamination of web. While the compressive failure is resulted from the buckling of flange and fiber snap of skin at the middle of T-joint. The failure load of T-joint tension is greater than those of compression.
The non-crimp fabrics (NCF) were used as reinforcement to improve the drape efficiency and accuracy. According to the structural characteristics of the T-joint, an I-beam composed of four T-joints was manufactured via resin transfer moulding (RTM) process. The tensile and compressive properties of T-joint were tested. The results show that the tensile failure of T-joint can be reckoned to the fiber broken of skin around the holes and the delamination of web. While the compressive failure is resulted from the buckling of flange and fiber snap of skin at the middle of T-joint. The failure load of T-joint tension is greater than those of compression.
2012, (4): 105-112.
Abstract:
The optimized configuration of thick-wall drag brace was designed according to the permissibility of composites and the characteristics of resin transfer molding (RTM) process. The permeability of the preforms was measured and the RTM process was investigated by the numerical simulation. The RTM mold was manufactured based on the results of the flow simulation. A specimen of thick-wall drag brace was successfully manufactured via RTM process and the specimen was evaluated by mechanical test. The mechanical results show that the drag brace designed based on the numerical simulation well meet the manufacturing and loading requirements.
The optimized configuration of thick-wall drag brace was designed according to the permissibility of composites and the characteristics of resin transfer molding (RTM) process. The permeability of the preforms was measured and the RTM process was investigated by the numerical simulation. The RTM mold was manufactured based on the results of the flow simulation. A specimen of thick-wall drag brace was successfully manufactured via RTM process and the specimen was evaluated by mechanical test. The mechanical results show that the drag brace designed based on the numerical simulation well meet the manufacturing and loading requirements.
2012, (4): 113-118.
Abstract:
The grinding experiments were conducted on 2D-C/SiC composites by using resin bond diamond wheel in this work. The ground surface/subsurface damages were observed. The theory expression of grinding force for the friction layer (surface) of 2D-C/SiC was proposed, and the effect of grinding machining process amount on grinding force and force ratio was also discussed. The result indicates that the removal mechanisms involved in the grinding process for 2D-C/SiC composites are dominated by their brittleness fractures and related to their microstructures, which are different from those of ordinary plastic and brittle materials.
The grinding experiments were conducted on 2D-C/SiC composites by using resin bond diamond wheel in this work. The ground surface/subsurface damages were observed. The theory expression of grinding force for the friction layer (surface) of 2D-C/SiC was proposed, and the effect of grinding machining process amount on grinding force and force ratio was also discussed. The result indicates that the removal mechanisms involved in the grinding process for 2D-C/SiC composites are dominated by their brittleness fractures and related to their microstructures, which are different from those of ordinary plastic and brittle materials.
2012, (4): 119-125.
Abstract:
As a new kind of method to prepare composites, pressureless Ti-activated reactive melt infiltration was investigated. The Ti-WC porous ceramics skeleton preform was prepared by gelcasting using sugar as pore former. Under vacuum condition, the Ti-WC porous ceramics skeleton preform was infiltrated by Fe-Cr-C alloy melt with in-situ reaction to prepare the (W,Ti)C/Fe composites. The microstructures, element composition and phase analysis were investigated by using SEM-EDS and XRD. And the wear resistance was studied using a rotating disc rig with SiC mortar as the abrasive material. The results show that the infiltration process is accelerated by the dissolution and precipitation of titanium and the in-situ reaction between titanium and carbon. At 1370℃ for 1 h, the porous ceramics skeleton is permeated by the melt, and the space structure has not been changed in the infiltration process. The reinforced phase (W,Ti)C which has a concentration gradient of Ti and W from core to the periphery is produced by in-situ reaction of Ti-C-WC. As the result of the wear testing shown, (W,Ti)C/Fe composites have excellent abrasive wear resisitance, which is better than that of the wear resistant cast iron commonly used in industry.
As a new kind of method to prepare composites, pressureless Ti-activated reactive melt infiltration was investigated. The Ti-WC porous ceramics skeleton preform was prepared by gelcasting using sugar as pore former. Under vacuum condition, the Ti-WC porous ceramics skeleton preform was infiltrated by Fe-Cr-C alloy melt with in-situ reaction to prepare the (W,Ti)C/Fe composites. The microstructures, element composition and phase analysis were investigated by using SEM-EDS and XRD. And the wear resistance was studied using a rotating disc rig with SiC mortar as the abrasive material. The results show that the infiltration process is accelerated by the dissolution and precipitation of titanium and the in-situ reaction between titanium and carbon. At 1370℃ for 1 h, the porous ceramics skeleton is permeated by the melt, and the space structure has not been changed in the infiltration process. The reinforced phase (W,Ti)C which has a concentration gradient of Ti and W from core to the periphery is produced by in-situ reaction of Ti-C-WC. As the result of the wear testing shown, (W,Ti)C/Fe composites have excellent abrasive wear resisitance, which is better than that of the wear resistant cast iron commonly used in industry.
2012, (4): 126-131.
Abstract:
Roll-bonding was used to prepare of Cu-Fe-Cu laminated composite for electromagnetic shielding, oxygen-free copper sheet and electrical iron sheet were chosen as its components. Mechanical property experiments on the laminated composite were executed by using of material testing machine, the microstructure and mechanism of bonding were investigated by means of metalloscope, SEM and EDS. The results show that Cu and Fe can be bonded by hot rolling when reduction rate achieves 50%, thickness deviation and parallelism of each laminates are fine. After the annealing process, it is hard to find the diffusion of Cu and Fe, and the shear strength of interface comes to 167 MPa. The mechanism of bonding by hot rolling is mechanically engage.
Roll-bonding was used to prepare of Cu-Fe-Cu laminated composite for electromagnetic shielding, oxygen-free copper sheet and electrical iron sheet were chosen as its components. Mechanical property experiments on the laminated composite were executed by using of material testing machine, the microstructure and mechanism of bonding were investigated by means of metalloscope, SEM and EDS. The results show that Cu and Fe can be bonded by hot rolling when reduction rate achieves 50%, thickness deviation and parallelism of each laminates are fine. After the annealing process, it is hard to find the diffusion of Cu and Fe, and the shear strength of interface comes to 167 MPa. The mechanism of bonding by hot rolling is mechanically engage.
2012, (4): 132-137.
Abstract:
In-situ Al3Ti reinforced Mg-Al matrix composites were prepared by vacuum hot-pressing. The mechanism of in-situ synthesized Al3Ti was discussed and a model of micro structural reaction between Ti and Al was brought forward. Effects of sintering schedules on microstructures of composites were researched by methods, such as XRD and SEM. Results indicate that Mg-Al matrix composites are dense in structure, while uniformly distributed in-situ Al3Ti particulates with the size of 0.5~2.0 μm are combined closely with Mg-Al matrix. Small quantities of remnant Ti and intermediate phases Al-Ti also exist.
In-situ Al3Ti reinforced Mg-Al matrix composites were prepared by vacuum hot-pressing. The mechanism of in-situ synthesized Al3Ti was discussed and a model of micro structural reaction between Ti and Al was brought forward. Effects of sintering schedules on microstructures of composites were researched by methods, such as XRD and SEM. Results indicate that Mg-Al matrix composites are dense in structure, while uniformly distributed in-situ Al3Ti particulates with the size of 0.5~2.0 μm are combined closely with Mg-Al matrix. Small quantities of remnant Ti and intermediate phases Al-Ti also exist.
2012, (4): 138-142.
Abstract:
Fe-Al alloy blended with different levels of tungsten concentrate powder was prepared by laser ignition induced self-propagating high-temperature synthesis (SHS). By means of the XRD, SEM, hardness test and abrasion test, the effect of the content of tungsten concentrate powder on the sintered alloy microstructure and macroscopic properties was studied. The experimental results show that through the sintering process, the self-propagating combustion synthesis of the blank was achieved. The structures of the sintered alloy are acicular, which grow up with the increase of the content of tungsten concentrate powder. The product phase of the sintering alloy are AlFe, AlFe3, WO3 and Fe7W6. When the mass fraction of the tungsten concentrate powder is 1%, the micro- hardness and the density of the sintering alloy are both the biggest, which are HK956 and 4.27 g/cm3 respectively, while the porosity and the relative wear rate of the sintering alloy are the lowest, which are 12.2% and 0.05% respectively.
Fe-Al alloy blended with different levels of tungsten concentrate powder was prepared by laser ignition induced self-propagating high-temperature synthesis (SHS). By means of the XRD, SEM, hardness test and abrasion test, the effect of the content of tungsten concentrate powder on the sintered alloy microstructure and macroscopic properties was studied. The experimental results show that through the sintering process, the self-propagating combustion synthesis of the blank was achieved. The structures of the sintered alloy are acicular, which grow up with the increase of the content of tungsten concentrate powder. The product phase of the sintering alloy are AlFe, AlFe3, WO3 and Fe7W6. When the mass fraction of the tungsten concentrate powder is 1%, the micro- hardness and the density of the sintering alloy are both the biggest, which are HK956 and 4.27 g/cm3 respectively, while the porosity and the relative wear rate of the sintering alloy are the lowest, which are 12.2% and 0.05% respectively.
2012, (4): 143-147.
Abstract:
Microwave-assisted method was used to prepare Ag nanorods with uniform sizes. The influence of parameters such as the concentration of catalyst, the concentration ratio of surfactant and precursor was studied. A novel kind of conductive inkjet was prepared by using these Ag nanoreods as conductive filler. The performances of the conductive inkjet such as percolation threshold of the filler, bonding strength and ageing resistant were studied. The results show that a mixture with 95% Ag nanorods can be obtained when the concentration ratio of AgNO3 to NaCl reaches to 5:1. The percolation threshold of the conductive inkjet is 62% when 95% Ag nanorods are included in the filler. The ageing resistant measurements results show that the changes of the electrical conductivity of conductive inkjet are less than 10% after ageing under 85%RH and 80℃ condition for 500 h.
Microwave-assisted method was used to prepare Ag nanorods with uniform sizes. The influence of parameters such as the concentration of catalyst, the concentration ratio of surfactant and precursor was studied. A novel kind of conductive inkjet was prepared by using these Ag nanoreods as conductive filler. The performances of the conductive inkjet such as percolation threshold of the filler, bonding strength and ageing resistant were studied. The results show that a mixture with 95% Ag nanorods can be obtained when the concentration ratio of AgNO3 to NaCl reaches to 5:1. The percolation threshold of the conductive inkjet is 62% when 95% Ag nanorods are included in the filler. The ageing resistant measurements results show that the changes of the electrical conductivity of conductive inkjet are less than 10% after ageing under 85%RH and 80℃ condition for 500 h.
2012, (4): 148-156.
Abstract:
The orthogonal experiment of three factors-four levels and a single factor experiment were conducted to evaluate the effect of compaction force, heating temperature of prepreg, and tool temperature on the mechanical properties of the laminar composite fabricated by fiber placement. The testing results of the mechanical properties and the microstructure images obtained through SEM and light microscope show that the effect of compaction force and heating temperature on interlaminar shear-strength (ILSS) is significant, while the effect of the tool temperature on ILSS is not obvious. The comprehensive mechanical properties of laminar composite are the best at 600 N level of the compaction force, 30℃ of the heating temperature, and 18℃ of the tool temperature. The microstructure results show that the distribution of resin in the cured composite becomes more and more uniform, and the thickness of interlaminar resin-rich area decreases with the increase of compaction force and heating temperature, and accordingly the strong ILSS. When the heating temperature is over 40℃, the distribution of resin in the cured composite material becomes non-uniform because of the action of compaction force, the thickness of interlaminar resin-rich area increases gradually, which results in the decrease of ILSS.
The orthogonal experiment of three factors-four levels and a single factor experiment were conducted to evaluate the effect of compaction force, heating temperature of prepreg, and tool temperature on the mechanical properties of the laminar composite fabricated by fiber placement. The testing results of the mechanical properties and the microstructure images obtained through SEM and light microscope show that the effect of compaction force and heating temperature on interlaminar shear-strength (ILSS) is significant, while the effect of the tool temperature on ILSS is not obvious. The comprehensive mechanical properties of laminar composite are the best at 600 N level of the compaction force, 30℃ of the heating temperature, and 18℃ of the tool temperature. The microstructure results show that the distribution of resin in the cured composite becomes more and more uniform, and the thickness of interlaminar resin-rich area decreases with the increase of compaction force and heating temperature, and accordingly the strong ILSS. When the heating temperature is over 40℃, the distribution of resin in the cured composite material becomes non-uniform because of the action of compaction force, the thickness of interlaminar resin-rich area increases gradually, which results in the decrease of ILSS.
2012, (4): 157-162.
Abstract:
The dynamic properties of 3D orthogonal woven E-glass fiber/epoxy composites were studied experimentally under both the dynamic and static loading conditions, and the stress-strain curves were obtained. The results show that the responses of the composites are of obviously nonlinear and anisotropic characteristics, and of the strain rate sensitivity as well. In theory, a macroscopic damage variable dependent of strain and strain rate is put forward to describe these characteristics, and a nonlinear viscoelastic model is presented for the composites with damage. The stress-strain curves fitted by the modified constitutive equation are in good agreement with the experimental ones.
The dynamic properties of 3D orthogonal woven E-glass fiber/epoxy composites were studied experimentally under both the dynamic and static loading conditions, and the stress-strain curves were obtained. The results show that the responses of the composites are of obviously nonlinear and anisotropic characteristics, and of the strain rate sensitivity as well. In theory, a macroscopic damage variable dependent of strain and strain rate is put forward to describe these characteristics, and a nonlinear viscoelastic model is presented for the composites with damage. The stress-strain curves fitted by the modified constitutive equation are in good agreement with the experimental ones.
2012, (4): 163-169.
Abstract:
Using the incremental plastic damage theory and the phenomenological model for predicting fatigue crack growth in fiber reinforced metal laminates, a predicting model of fatigue crack growth in fiber reinforced aluminium alloy laminates under tension-compressive loading was deduced. The experiments of the fatigue crack growth in the glass fiber reinforced aluminium alloy laminates at the R=-1 and R=-2 were performed in order to verify the predicting model. The results show that the two cases of the effect of compression loading are pointed out that when the effective stress ratio RC>0, it is characterized by counteracting the residual stress in the aluminium alloy layer, and when RC<0, it is characterized by causing the plastic damage in the aluminium alloy layer and the promoting effect on the fatigue crack growth in fiber reinforced aluminium alloy laminates. The effect of compression loading should not be neglected. The model has been obtained good agreements with the experimental data.
Using the incremental plastic damage theory and the phenomenological model for predicting fatigue crack growth in fiber reinforced metal laminates, a predicting model of fatigue crack growth in fiber reinforced aluminium alloy laminates under tension-compressive loading was deduced. The experiments of the fatigue crack growth in the glass fiber reinforced aluminium alloy laminates at the R=-1 and R=-2 were performed in order to verify the predicting model. The results show that the two cases of the effect of compression loading are pointed out that when the effective stress ratio RC>0, it is characterized by counteracting the residual stress in the aluminium alloy layer, and when RC<0, it is characterized by causing the plastic damage in the aluminium alloy layer and the promoting effect on the fatigue crack growth in fiber reinforced aluminium alloy laminates. The effect of compression loading should not be neglected. The model has been obtained good agreements with the experimental data.
2012, (4): 170-177.
Abstract:
The low-velocity impact tests on sandwich structures composed of glass cloth facesheet and different cores which are PMI foams, X-PVC foams, NOMEX honeycomb, stitched PMI foams and grooved PMI foams. The Influential factors, which include different kinds, different thickness of cores and facesheets and interfacial reinforcement techniques on stitching and grooving were studied. The test results show that PMI foam core has higher impact load and energy absorption than X-PVC foam core and NOMEX honeycomb. The impact damage load and energy of sandwich improve with the increase of thickness of facesheets and density of cores. Reasonable stitching and grooving can enhance the strength and rigidity of the sandwich structure, interface property and the resistance of impact.
The low-velocity impact tests on sandwich structures composed of glass cloth facesheet and different cores which are PMI foams, X-PVC foams, NOMEX honeycomb, stitched PMI foams and grooved PMI foams. The Influential factors, which include different kinds, different thickness of cores and facesheets and interfacial reinforcement techniques on stitching and grooving were studied. The test results show that PMI foam core has higher impact load and energy absorption than X-PVC foam core and NOMEX honeycomb. The impact damage load and energy of sandwich improve with the increase of thickness of facesheets and density of cores. Reasonable stitching and grooving can enhance the strength and rigidity of the sandwich structure, interface property and the resistance of impact.
2012, (4): 178-185.
Abstract:
Graded finite elements were proposed for the heat conduction analysis of gradient composites whose thermal properties were described by micromechanics. The spatially varying stiffness matrices of four-node and eight-node graded elements were calculated through linear and high-order interpolations of temperature fields. Several exact steady-state temperature and flux fields of graded composite plates under temperature gradient and thermal flux loads were presented. With reference to the exact solutions, the heat conduction finite element results of continuous gradient models and conventional, step-wise models were compared to validate the graded elements. The effects of some parameters on the graded elements were also discussed. It shows that the temperature fields resulting from graded and homogeneous elements are nearly the same; the graded elements can give more accurate local flux fields than homogeneous elements do when thermal loads are perpendicular to the material gradation; when they are parallel, the eight-node quadrilateral and homogeneous elements are both excellent, nevertheless, the four-node quadrilateral elements are worse.
Graded finite elements were proposed for the heat conduction analysis of gradient composites whose thermal properties were described by micromechanics. The spatially varying stiffness matrices of four-node and eight-node graded elements were calculated through linear and high-order interpolations of temperature fields. Several exact steady-state temperature and flux fields of graded composite plates under temperature gradient and thermal flux loads were presented. With reference to the exact solutions, the heat conduction finite element results of continuous gradient models and conventional, step-wise models were compared to validate the graded elements. The effects of some parameters on the graded elements were also discussed. It shows that the temperature fields resulting from graded and homogeneous elements are nearly the same; the graded elements can give more accurate local flux fields than homogeneous elements do when thermal loads are perpendicular to the material gradation; when they are parallel, the eight-node quadrilateral and homogeneous elements are both excellent, nevertheless, the four-node quadrilateral elements are worse.
Stiffness loss assessment and application based on fracture features of honeycomb sandwich structure
2012, (4): 186-190.
Abstract:
High precision sandwich reflector panels are made of aluminum face sheet and honeycomb core treated by the gap stress releasing process. In order to study the impact of the gap on sandwich structure stiffness loss, a relationship between the gap influence coefficient considering the influence of the area and distribution of gap on the rigidity and stiffness loss coefficient was established with statistical analysis of tests data. A stiffness loss assessment method based on fracture features of sandwich structure was put forward. The experimental analysis results show that gap will cause stiffness loss, which changes slowly after reaching a certain level and the fracture features influence on the stiffness can be limited into 40%. According to the sandwich structure stiffness equivalent principles and the stiffness loss assessment method, the face sheet with gaps can be replaced by the continuous sheet with decreased thickness during the numerical analysis. It has general application value to simulate the sandwich structure with fracture features.
High precision sandwich reflector panels are made of aluminum face sheet and honeycomb core treated by the gap stress releasing process. In order to study the impact of the gap on sandwich structure stiffness loss, a relationship between the gap influence coefficient considering the influence of the area and distribution of gap on the rigidity and stiffness loss coefficient was established with statistical analysis of tests data. A stiffness loss assessment method based on fracture features of sandwich structure was put forward. The experimental analysis results show that gap will cause stiffness loss, which changes slowly after reaching a certain level and the fracture features influence on the stiffness can be limited into 40%. According to the sandwich structure stiffness equivalent principles and the stiffness loss assessment method, the face sheet with gaps can be replaced by the continuous sheet with decreased thickness during the numerical analysis. It has general application value to simulate the sandwich structure with fracture features.
2012, (4): 191-194.
Abstract:
To study the mechanical property of fiber reinforced composite, Reuss-Voigt model and 3D fiber orientation simplified model were utilized to develop the prediction model for elastic modulus of random short fiber reinforced composite (RSFRC). By virtue of this model, elastic modulus of glass fiber reinforced PA6 composite is predicted. The tolerance between calculated results and the tensile test values is less than 5%, which testified the good accuracy of the prediction model for elastic modus of RSFRC.
To study the mechanical property of fiber reinforced composite, Reuss-Voigt model and 3D fiber orientation simplified model were utilized to develop the prediction model for elastic modulus of random short fiber reinforced composite (RSFRC). By virtue of this model, elastic modulus of glass fiber reinforced PA6 composite is predicted. The tolerance between calculated results and the tensile test values is less than 5%, which testified the good accuracy of the prediction model for elastic modus of RSFRC.
2012, (4): 195-203.
Abstract:
A novel design approach was presented to optimizing the winding tension for thick composite pipes in this paper. The theories of filament winding machine control system were introduced, and the factors that influence the forming quality of thick composite pipes were discussed. An approach of calculating the residual inner stress and deformation in tension winding for thick fiber composite pipes according to superposition principle of the elastic theory was advanced. The inner stress distributions in the thick pipes wound with constant tension, constant torque and taper tension patterns separately were compared. A peculiar neural network structure was presented for optimizing the winding tension with error back propagation. Experiments were conducted to identify dominant mechanisms during neural network convergence process. The results show that the winding tension optimized by this network can meet the design requirement with special inner stress distributions such as isostress.
A novel design approach was presented to optimizing the winding tension for thick composite pipes in this paper. The theories of filament winding machine control system were introduced, and the factors that influence the forming quality of thick composite pipes were discussed. An approach of calculating the residual inner stress and deformation in tension winding for thick fiber composite pipes according to superposition principle of the elastic theory was advanced. The inner stress distributions in the thick pipes wound with constant tension, constant torque and taper tension patterns separately were compared. A peculiar neural network structure was presented for optimizing the winding tension with error back propagation. Experiments were conducted to identify dominant mechanisms during neural network convergence process. The results show that the winding tension optimized by this network can meet the design requirement with special inner stress distributions such as isostress.
2012, (4): 204-209.
Abstract:
A method was presented for estimating 3D effective elastic modulus of multidirectional filament-wound hybrid tube. The effective elastic modulus of glass-carbon fibre wound tube was calculated. In order to consider the influence of hybrid effects, the hybrid effect coefficient was introduced. The volume friction of carbon fibre, layered structure, fibre dispersion, etc were considerd for the glass-carbon winding structure. The test results show that effective elastic modulus based on the present method is accurate. The method can greatly reduce the size of problem for stress analysis, because complex structure can be equivalent to homogeneous anisotropic material.
A method was presented for estimating 3D effective elastic modulus of multidirectional filament-wound hybrid tube. The effective elastic modulus of glass-carbon fibre wound tube was calculated. In order to consider the influence of hybrid effects, the hybrid effect coefficient was introduced. The volume friction of carbon fibre, layered structure, fibre dispersion, etc were considerd for the glass-carbon winding structure. The test results show that effective elastic modulus based on the present method is accurate. The method can greatly reduce the size of problem for stress analysis, because complex structure can be equivalent to homogeneous anisotropic material.
2012, (4): 210-216.
Abstract:
Controlling the adjoint coefficient of the first order acoustic radiation mode of vibrating structure can reduce efficiently the total sound power at low frequency. The displacement of laminated composite plates can be obtained by using layerwise finite element models. A preliminary study was conducted for the natural frequency and dynamic response of the laminated composite plates. Based on the acoustic radiation mode, the effects of panel orientation angle, elastic modulus ratio, width-depth ratio and damping ratio on the adjoint coefficient of the first order acoustic radiation mode of the laminated composite plates were discussed. The results show that the natural frequency of laminated composite plates can be analyzed accurately by using the layerwise finite element models. The effects of panel orientation angle and width-depth ratio on the adjoint coefficient of the acoustic radiation mode of the laminated composite plates are significant.
Controlling the adjoint coefficient of the first order acoustic radiation mode of vibrating structure can reduce efficiently the total sound power at low frequency. The displacement of laminated composite plates can be obtained by using layerwise finite element models. A preliminary study was conducted for the natural frequency and dynamic response of the laminated composite plates. Based on the acoustic radiation mode, the effects of panel orientation angle, elastic modulus ratio, width-depth ratio and damping ratio on the adjoint coefficient of the first order acoustic radiation mode of the laminated composite plates were discussed. The results show that the natural frequency of laminated composite plates can be analyzed accurately by using the layerwise finite element models. The effects of panel orientation angle and width-depth ratio on the adjoint coefficient of the acoustic radiation mode of the laminated composite plates are significant.
2012, (4): 217-223.
Abstract:
Using the generalized complex variable method, the plane problem of the piezoelectric strip with semi-infinite collinear cracks penetrating across the material perpendicular to the poling direction is discussed by proposing a new generalized conformal mapping. With the assumption that the surface of the crack was electrically impermeable, the analytical solutions of the field intensity factors are presented. In addition, analytical solutions of some new defects can be derived as the height of the strip and the size of the crack change by a certain tendency. Finally, the influences of the distance of the two cracks, the height of the strip and the loaded crack length on the field intensity factors are obtained through some numerical examples.
Using the generalized complex variable method, the plane problem of the piezoelectric strip with semi-infinite collinear cracks penetrating across the material perpendicular to the poling direction is discussed by proposing a new generalized conformal mapping. With the assumption that the surface of the crack was electrically impermeable, the analytical solutions of the field intensity factors are presented. In addition, analytical solutions of some new defects can be derived as the height of the strip and the size of the crack change by a certain tendency. Finally, the influences of the distance of the two cracks, the height of the strip and the loaded crack length on the field intensity factors are obtained through some numerical examples.
2012, (4): 224-230.
Abstract:
A series of quasi-static compressive experiments of pure foam aluminum, pure epoxy and foam aluminum-epoxy interpenetrating phase composites (IPC) with three kinds of volume fraction of hollow glass bead (HGB) are conducted. The stress relaxation experiments of the three IPC are performed. The deformation process and damage morphology are observed, and their failure mechanisms are analyzed. The stress-strain curves are plotted. Their change rules are discussed. The effective elastic modulus, yield limit and energy absorbing are provided. It is found that the three kinds of IPC all have better mechanical properties than pure foam aluminum. Their specific stiffness and specific strength are more than that of pure foam aluminum. The unit volume energy absorption of foam aluminum-epoxy is the maximum, and it decreases with the increase of HGB’s volume fraction. A good agreement between theoretical and experimental result is found. It is also found that the stress relaxation rate is increases with the increase of HGB’s volume fraction.
A series of quasi-static compressive experiments of pure foam aluminum, pure epoxy and foam aluminum-epoxy interpenetrating phase composites (IPC) with three kinds of volume fraction of hollow glass bead (HGB) are conducted. The stress relaxation experiments of the three IPC are performed. The deformation process and damage morphology are observed, and their failure mechanisms are analyzed. The stress-strain curves are plotted. Their change rules are discussed. The effective elastic modulus, yield limit and energy absorbing are provided. It is found that the three kinds of IPC all have better mechanical properties than pure foam aluminum. Their specific stiffness and specific strength are more than that of pure foam aluminum. The unit volume energy absorption of foam aluminum-epoxy is the maximum, and it decreases with the increase of HGB’s volume fraction. A good agreement between theoretical and experimental result is found. It is also found that the stress relaxation rate is increases with the increase of HGB’s volume fraction.
2012, (4): 231-238.
Abstract:
The influence of interface debonding on matrix cracking of cross-ply SiC/calcium alumino silicate glass (CAS) composites under uniaxial tensile loading was studied by micromechanics approach. The fracture mechanics interface debonding criterion was used to determine the interface debonding length in the 0? ply. When cross-ply ceramic matrix composites are under tensile loading, transverse cracking in the 90? ply and matrix cracking in the 0? ply occur. Based on the difference of the transverse crack and matrix crack, the damage states in cross-ply laminates can be classified into five modes. The mode 3 cracking mode contains transverse cracking, matrix cracking and fiber/matrix interface debonding. The mode 5 cracking mode only contains matrix cracking and fiber/matrix interface debonding. The critical stress of mode 3 and 5 was determined using the energy balance method. The effects of interface shear stress and interface debonding energy on matrix cracking stress have been analyzed. The conclusions that the initial cracking stress of mode 3 and 5 increases as the interface shear stress and interface debonding energy increases was gotten. The analysis was compared with the experimental result of unidirectional fiber-reinforced ceramic matrix composites done by Chiang. The predicted trend of cross-ply ceramic matrix composites is consistent with the experimental results of unidirectional ceramic matrix composites.
The influence of interface debonding on matrix cracking of cross-ply SiC/calcium alumino silicate glass (CAS) composites under uniaxial tensile loading was studied by micromechanics approach. The fracture mechanics interface debonding criterion was used to determine the interface debonding length in the 0? ply. When cross-ply ceramic matrix composites are under tensile loading, transverse cracking in the 90? ply and matrix cracking in the 0? ply occur. Based on the difference of the transverse crack and matrix crack, the damage states in cross-ply laminates can be classified into five modes. The mode 3 cracking mode contains transverse cracking, matrix cracking and fiber/matrix interface debonding. The mode 5 cracking mode only contains matrix cracking and fiber/matrix interface debonding. The critical stress of mode 3 and 5 was determined using the energy balance method. The effects of interface shear stress and interface debonding energy on matrix cracking stress have been analyzed. The conclusions that the initial cracking stress of mode 3 and 5 increases as the interface shear stress and interface debonding energy increases was gotten. The analysis was compared with the experimental result of unidirectional fiber-reinforced ceramic matrix composites done by Chiang. The predicted trend of cross-ply ceramic matrix composites is consistent with the experimental results of unidirectional ceramic matrix composites.
2012, (4): 239-245.
Abstract:
Based on the displacement and potential fields with six degrees of freedom, the equations of motion for piezoelectric composite laminates were established. The closed solutions for cross-ply rectangular piezoelectric composite laminates with simply-supported boundaries are obtained. The present theory is an equivalent single layer theory and contains only six displacement and electric variables, the number of which is independent of the layers. The equations of motion can be solved simply. The displacement and electric potential fields are depicted by the displacement and electric potential distribution functions through thickness, respectively. The three functions are formulated according to particular solutions to the three-dimensional elasticity equilibrium equations and electrostatics charge equation by enforcing interfacial continuity conditions and force and electric conditions at the top and bottom surfaces. The high accuracy of this equivalent single layer theory is demonstrated in the numerical examples.
Based on the displacement and potential fields with six degrees of freedom, the equations of motion for piezoelectric composite laminates were established. The closed solutions for cross-ply rectangular piezoelectric composite laminates with simply-supported boundaries are obtained. The present theory is an equivalent single layer theory and contains only six displacement and electric variables, the number of which is independent of the layers. The equations of motion can be solved simply. The displacement and electric potential fields are depicted by the displacement and electric potential distribution functions through thickness, respectively. The three functions are formulated according to particular solutions to the three-dimensional elasticity equilibrium equations and electrostatics charge equation by enforcing interfacial continuity conditions and force and electric conditions at the top and bottom surfaces. The high accuracy of this equivalent single layer theory is demonstrated in the numerical examples.
2012, (4): 246-250.
Abstract:
To extend Reddy’s theory to accurately analyze the thermal deformations and stresses of laminated composite and sandwich structures, an enhanced Reddy’s theory for laminated composite beams was proposed by using the transverse normal thermal deformation in transverse displacement as well as the free surface conditions. Although transverse normal strain is involved, the number of unknowns in the proposed model is the same as that in Reddy’s theory. Using the principle of virtual work, the equations of equilibrium for laminated composite beams were presented, and the thermal expansion problems of laminated composite and sandwich beams were analyzed. Numerical results show that the enhanced Reddy’s theory can accurately analyze the thermal expansion problems of laminated composite and sandwich structures. However, Reddy’s theory is less accurate for thermal expansion problems.
To extend Reddy’s theory to accurately analyze the thermal deformations and stresses of laminated composite and sandwich structures, an enhanced Reddy’s theory for laminated composite beams was proposed by using the transverse normal thermal deformation in transverse displacement as well as the free surface conditions. Although transverse normal strain is involved, the number of unknowns in the proposed model is the same as that in Reddy’s theory. Using the principle of virtual work, the equations of equilibrium for laminated composite beams were presented, and the thermal expansion problems of laminated composite and sandwich beams were analyzed. Numerical results show that the enhanced Reddy’s theory can accurately analyze the thermal expansion problems of laminated composite and sandwich structures. However, Reddy’s theory is less accurate for thermal expansion problems.
