2019 Vol. 36, No. 6
2019, 36(6): 1343-1352.
doi: 10.13801/j.cnki.fhclxb.20180907.001
Abstract:
The compressive performance of fiber reinforced polymer composites is closed associated with the mechanical properties of polymer matrix. In this paper, unidirectional laminates of CF-nano SiO2/Epoxy multi-phase reinforced composites have been prepared using continuous carbon fibers(CF) and epoxy matrix with uniformly-dispersed SiO2 nanoparticles. The systematic experimental study has been carried out. It shows that the incorporation of nanoparticles into matrix contributes to the considerable enhancement of compressive strength of fiber reinforced polymers. The compressive strength of composites is found to be increased by 62.7% with the nanoparticle vlume ratio to nano SiO2/Epoxy of 8.7%. The reinforcing effects of nanoparticles have been theoretically analyzed based on the elasto-plastic micro-buckling model for unidirectional laminates. A method was proposed to construct the constitutive relation during compression for nanocomposite matrix through loading-unloading tests, according to the damage behaviors of epoxy matrix containing nanoparticles. The compressive strength of the prepared multi-phase reinforced composites can be well predicted by combining the classic elaso-plastic micro-buckling model and constructed constitutive relation of nanocomposite matrix. The experimental verification demonstrates the good agreement achieved between the predicted results and the measured data.
The compressive performance of fiber reinforced polymer composites is closed associated with the mechanical properties of polymer matrix. In this paper, unidirectional laminates of CF-nano SiO2/Epoxy multi-phase reinforced composites have been prepared using continuous carbon fibers(CF) and epoxy matrix with uniformly-dispersed SiO2 nanoparticles. The systematic experimental study has been carried out. It shows that the incorporation of nanoparticles into matrix contributes to the considerable enhancement of compressive strength of fiber reinforced polymers. The compressive strength of composites is found to be increased by 62.7% with the nanoparticle vlume ratio to nano SiO2/Epoxy of 8.7%. The reinforcing effects of nanoparticles have been theoretically analyzed based on the elasto-plastic micro-buckling model for unidirectional laminates. A method was proposed to construct the constitutive relation during compression for nanocomposite matrix through loading-unloading tests, according to the damage behaviors of epoxy matrix containing nanoparticles. The compressive strength of the prepared multi-phase reinforced composites can be well predicted by combining the classic elaso-plastic micro-buckling model and constructed constitutive relation of nanocomposite matrix. The experimental verification demonstrates the good agreement achieved between the predicted results and the measured data.
2019, 36(6): 1353-1363.
doi: 10.13801/j.cnki.fhclxb.20190225.001
Abstract:
The mechanically fastened joint specimen tensile test of three kinds of glass fiber reinforced thermoplastic resin composites including glass fiber/polyamide (GF/PA), glass fiber/polyformaldehyde (GF/POM) and glass fiber/polypropylene (GF/PP) were conducted. Additionally, low cycle fatigue tensile test was carried out for three kinds of composite mechanical joints, and the fracture surface of the sample before and after fatigue was observed by SEM, to investigate the effect of joint dimension (sample width/hole diameter(w/d) and edge distance/hole diameter(e/d)) on the failure load of mechanically fastened joint and failure mode. It is found that:The bearing capacity of the mechanically fastened joint of glass fiber reinforced thermoplastic resin composites increases with the increase of e/d at a certain w/d, and tends to be stable when w/d ≥ 3 and e/d ≥ 2. The failure mode is mainly tensile failure. Low cycle tensile fatigue has a certain effect on the tensile strength of GF/POM and GF/PA mechanically jointed specimens, but has no significant effect on that of GF/PP. On the other hand, low cycle fatigue stretch has no obvious effect on the failure mode of the mechanically bonded specimens of glass fiber reinforced thermoplastic resin. SEM observation shows that, with the increase of the fatigue load level, the number of pulled fibers on the fracture surface of GF/POM and GF/PA increases, while there is no significant effect on the existence of fiber and matrix in GF/PP.
The mechanically fastened joint specimen tensile test of three kinds of glass fiber reinforced thermoplastic resin composites including glass fiber/polyamide (GF/PA), glass fiber/polyformaldehyde (GF/POM) and glass fiber/polypropylene (GF/PP) were conducted. Additionally, low cycle fatigue tensile test was carried out for three kinds of composite mechanical joints, and the fracture surface of the sample before and after fatigue was observed by SEM, to investigate the effect of joint dimension (sample width/hole diameter(w/d) and edge distance/hole diameter(e/d)) on the failure load of mechanically fastened joint and failure mode. It is found that:The bearing capacity of the mechanically fastened joint of glass fiber reinforced thermoplastic resin composites increases with the increase of e/d at a certain w/d, and tends to be stable when w/d ≥ 3 and e/d ≥ 2. The failure mode is mainly tensile failure. Low cycle tensile fatigue has a certain effect on the tensile strength of GF/POM and GF/PA mechanically jointed specimens, but has no significant effect on that of GF/PP. On the other hand, low cycle fatigue stretch has no obvious effect on the failure mode of the mechanically bonded specimens of glass fiber reinforced thermoplastic resin. SEM observation shows that, with the increase of the fatigue load level, the number of pulled fibers on the fracture surface of GF/POM and GF/PA increases, while there is no significant effect on the existence of fiber and matrix in GF/PP.
2019, 36(6): 1364-1373.
doi: 10.13801/j.cnki.fhclxb.20180906.001
Abstract:
Quartz fiber reinforced composites are often used in multi-field coupling environments. To ensure enough interlaminar performances, quartz fiber reinforced composites often exist in the form of 2.5D braided structures. In this paper, the three dimensional mechanical properties of a 2.5D quartz fiber reinforced bismaleimide resin composites (shallow bend-joint) were comprehensively tested. The tensile and compressive properties in different directions, and in-plane and out-of-plane shear property were compared and analyzed. It has been found that the tensile and compressive module of the warp direction are slightly higher than those of the weft direction, while the tensile and compressive strenghth of the warp direction are significantly higher than those of the weft direction. Tensile and compressive failure modes of the material in the warp and weft direction are significantly different. In case of tension, the waved warp fibers are pulled out, and the straight weft fibers are split. In case of compression, the straight weft fibers are broken, and the waved warp fibers buckling happen. The material shows high shear deformation capacities in both the in-plane and out-of-plane directions. Besides, a formula for estimating the tensile modulus of the 2.5D material was proposed based on the rule of mixtures of unidirectional composites. Based on the microstructure characteristics of the material, a unit cell containing warp and weft yarns was used as a representative volume unit to establish the finite element model, and the meridional modulus of the 2.5D woven composite was predicted. The prediction results are in good agreement with the experimental results. This study can provide some guidance for the development of the 2.5D quartz fiber/bismaleimide composites.
Quartz fiber reinforced composites are often used in multi-field coupling environments. To ensure enough interlaminar performances, quartz fiber reinforced composites often exist in the form of 2.5D braided structures. In this paper, the three dimensional mechanical properties of a 2.5D quartz fiber reinforced bismaleimide resin composites (shallow bend-joint) were comprehensively tested. The tensile and compressive properties in different directions, and in-plane and out-of-plane shear property were compared and analyzed. It has been found that the tensile and compressive module of the warp direction are slightly higher than those of the weft direction, while the tensile and compressive strenghth of the warp direction are significantly higher than those of the weft direction. Tensile and compressive failure modes of the material in the warp and weft direction are significantly different. In case of tension, the waved warp fibers are pulled out, and the straight weft fibers are split. In case of compression, the straight weft fibers are broken, and the waved warp fibers buckling happen. The material shows high shear deformation capacities in both the in-plane and out-of-plane directions. Besides, a formula for estimating the tensile modulus of the 2.5D material was proposed based on the rule of mixtures of unidirectional composites. Based on the microstructure characteristics of the material, a unit cell containing warp and weft yarns was used as a representative volume unit to establish the finite element model, and the meridional modulus of the 2.5D woven composite was predicted. The prediction results are in good agreement with the experimental results. This study can provide some guidance for the development of the 2.5D quartz fiber/bismaleimide composites.
2019, 36(6): 1374-1380.
doi: 10.13801/j.cnki.fhclxb.20180827.006
Abstract:
With silane coupling agent modified SiO2 as wall material and decanoic acid (DA)-palmitic acid (PA) as call material, the DA-PA@modified SiO2 temperature and humidity control composites were prepared by sol-gel method with ultrasonic wave-assisted. The effects of the content of silane coupling agent, ultrasonic wave power, ultrasonic wave time and ultrasonic wave temperature on the particle size of the DA-PA@modified SiO2 temperature and humidity control composites and related properties were investigated. The results show that the particle size and its distribution of the DA-PA@modified SiO2 temperature and humidity control composites can be significantly reduced using sol-gel method with ultrasonic wave-assisted. With the content of silane coupling agent of 4.0 g, ultrasonic wave power of 120 W, ultrasonic wave time of 100 min and ultrasonic wave temperature of 60℃, the DA-PA@modified SiO2 temperature and humidity control composites has small diameter and narrow particle size distribution, such as d90=87.36 nm, d50=63.34 nm, d10=44.02 nm and d90-d10=43.34 nm. Its equilibrium moisture content in the relative humidity of 40.0%-65.0% is 0.1864-0.2379 g/g, phase change temperature is 20.23-23.59℃, phase change latent heat is 40.91-46.72 J/g, and the stability performance is good.
With silane coupling agent modified SiO2 as wall material and decanoic acid (DA)-palmitic acid (PA) as call material, the DA-PA@modified SiO2 temperature and humidity control composites were prepared by sol-gel method with ultrasonic wave-assisted. The effects of the content of silane coupling agent, ultrasonic wave power, ultrasonic wave time and ultrasonic wave temperature on the particle size of the DA-PA@modified SiO2 temperature and humidity control composites and related properties were investigated. The results show that the particle size and its distribution of the DA-PA@modified SiO2 temperature and humidity control composites can be significantly reduced using sol-gel method with ultrasonic wave-assisted. With the content of silane coupling agent of 4.0 g, ultrasonic wave power of 120 W, ultrasonic wave time of 100 min and ultrasonic wave temperature of 60℃, the DA-PA@modified SiO2 temperature and humidity control composites has small diameter and narrow particle size distribution, such as d90=87.36 nm, d50=63.34 nm, d10=44.02 nm and d90-d10=43.34 nm. Its equilibrium moisture content in the relative humidity of 40.0%-65.0% is 0.1864-0.2379 g/g, phase change temperature is 20.23-23.59℃, phase change latent heat is 40.91-46.72 J/g, and the stability performance is good.
2019, 36(6): 1381-1388.
doi: 10.13801/j.cnki.fhclxb.20180928.001
Abstract:
Carbon fiber reinforced polymer composites were widely used in civil aircraft structures and subjected to complex environments (hydrothermal, corrosion, complex stress, and electro-thermal effects, etc.) during service. But the impact of low-intensity currents on carbon fiber reinforced polymer composites has attracted less attention. In this paper, the carbon fiber/resin composites were taken as the research object. The interface temperature range of the carbon fiber monofilament/epoxy resin composite specimen was calculated based on thermo sensitivity of carbon fibers and the dynamic of resistance change when an electric current was applied. Raman spectroscopy test and monofilament fracture test were used to study the influence of low-intensity current on the interfacial stress and interfacial shear strength of monofilament composite system. The results of the study show that:with increment of the current intensity, the interface temperature of the monofilament composite system is increasing. When the current is up to 8 mA, the interface temperature is as high as about 200℃.With the increase of the current intensity, the interfacial compressive stress of the monofilament composite system increases first and then reduces. When the current is higher than 7 mA, the resin at the interface undergoes ablation degradation and destruction. Monofilament fracture experiment illustrates that with the increase of the current intensity, the interfacial shear strength of the monofilament composite system increases initially and then decreases. The interfacial shear strength reaches a maximum of 62.39 MPa at 6 mA and the interface shear strength is only 34.95 MPa at 8 mA.
Carbon fiber reinforced polymer composites were widely used in civil aircraft structures and subjected to complex environments (hydrothermal, corrosion, complex stress, and electro-thermal effects, etc.) during service. But the impact of low-intensity currents on carbon fiber reinforced polymer composites has attracted less attention. In this paper, the carbon fiber/resin composites were taken as the research object. The interface temperature range of the carbon fiber monofilament/epoxy resin composite specimen was calculated based on thermo sensitivity of carbon fibers and the dynamic of resistance change when an electric current was applied. Raman spectroscopy test and monofilament fracture test were used to study the influence of low-intensity current on the interfacial stress and interfacial shear strength of monofilament composite system. The results of the study show that:with increment of the current intensity, the interface temperature of the monofilament composite system is increasing. When the current is up to 8 mA, the interface temperature is as high as about 200℃.With the increase of the current intensity, the interfacial compressive stress of the monofilament composite system increases first and then reduces. When the current is higher than 7 mA, the resin at the interface undergoes ablation degradation and destruction. Monofilament fracture experiment illustrates that with the increase of the current intensity, the interfacial shear strength of the monofilament composite system increases initially and then decreases. The interfacial shear strength reaches a maximum of 62.39 MPa at 6 mA and the interface shear strength is only 34.95 MPa at 8 mA.
2019, 36(6): 1389-1397.
doi: 10.13801/j.cnki.fhclxb.20180913.003
Abstract:
Based on the failure mechanisms and mechanics of composite, a new degradation model for unidirectional fiber reinforced polymer composites was established to describe the degradation behavior of different failure modes. The difference between the tensile and compressive modulus, the different degradation of damage on the tensile and compressive modulus, the crack closure and the influence of the lateral supports were considered in the proposed model. The proposed model is convenient to use because only fundamental material properties are required. The degradation model for T800/X850 carbon fiber/epoxy composite was established and the progressive failure analyses of typical bolted composite joints were performed. The numerical predictions of failure load, failure patterns, and load-displacement curve were compared with results obtained from static tests. Good agreements between numerical failure predictions and experimental outcomes indicate the effectiveness and suitability of the proposed model.
Based on the failure mechanisms and mechanics of composite, a new degradation model for unidirectional fiber reinforced polymer composites was established to describe the degradation behavior of different failure modes. The difference between the tensile and compressive modulus, the different degradation of damage on the tensile and compressive modulus, the crack closure and the influence of the lateral supports were considered in the proposed model. The proposed model is convenient to use because only fundamental material properties are required. The degradation model for T800/X850 carbon fiber/epoxy composite was established and the progressive failure analyses of typical bolted composite joints were performed. The numerical predictions of failure load, failure patterns, and load-displacement curve were compared with results obtained from static tests. Good agreements between numerical failure predictions and experimental outcomes indicate the effectiveness and suitability of the proposed model.
2019, 36(6): 1398-1412.
doi: 10.13801/j.cnki.fhclxb.20180816.002
Abstract:
Failure evolution in composite structures under compression is a fundamental topic and plays a key role in the strength prediction of composites. Herein, a progressive damage analysis (PDA) model based on continuum damage mechanics (CDM) was proposed to analyze the compression failure of unidirectional fiber reinforced polymer composites. Some essential issues such as the nonlinear behavior of composites, failure judgement, and the degradation of material properties during damage evolution were considered, corresponding respectively to the tension-compression asymmetric elasto-plastic constitutive model, Puck criteria, LaRC05 criteria and a stiffness degradation model considering the direction of fracture plane. The proposed PDA model was implemented in finite element analysis (FEA) by using the interface of user defined materials subroutine (VUMAT) provided by ABAQUS. The result of FEA is in good agreement with the experiment data reported by literatures in the cases of longitudinal, transverse and off-axis compression, which proves the reasonability and effectiveness of this PDA model. This work is of great reference value for compression failure analysis of multidirectional laminates.
Failure evolution in composite structures under compression is a fundamental topic and plays a key role in the strength prediction of composites. Herein, a progressive damage analysis (PDA) model based on continuum damage mechanics (CDM) was proposed to analyze the compression failure of unidirectional fiber reinforced polymer composites. Some essential issues such as the nonlinear behavior of composites, failure judgement, and the degradation of material properties during damage evolution were considered, corresponding respectively to the tension-compression asymmetric elasto-plastic constitutive model, Puck criteria, LaRC05 criteria and a stiffness degradation model considering the direction of fracture plane. The proposed PDA model was implemented in finite element analysis (FEA) by using the interface of user defined materials subroutine (VUMAT) provided by ABAQUS. The result of FEA is in good agreement with the experiment data reported by literatures in the cases of longitudinal, transverse and off-axis compression, which proves the reasonability and effectiveness of this PDA model. This work is of great reference value for compression failure analysis of multidirectional laminates.
2019, 36(6): 1413-1420.
doi: 10.13801/j.cnki.fhclxb.20180821.001
Abstract:
Taking advantages of deep learning in the field of image recognition, the convolutional neural network(CNN) was applied to construct a surrogate model to predict the macroscopic performance of the planar random short fiber reinforced urethane composites, and a data enhancement method was proposed to suppress overfitting occurred in the training process. The accuracy in tensile and shear properties of materials predicted by traditional and CNN surrogate models were compared. Results show that compared with the traditional method, CNN model is much better in learning the internal features of the image samples and obtains more accurate prediction results. Meanwhile, robustness is well maintained in a certain range outside the training sample space. Based on this, the proposed CNN model was combined with Monte Carlo method to study the forward propagation of error in the uncertainty of microgeometric parameters. The simulation result demonstrates that as the fiber aspect ratio increases, the uncertainties of the microgeometric parameters will lead to a nonnegligible error in the prediction of the effective properties of the material.
Taking advantages of deep learning in the field of image recognition, the convolutional neural network(CNN) was applied to construct a surrogate model to predict the macroscopic performance of the planar random short fiber reinforced urethane composites, and a data enhancement method was proposed to suppress overfitting occurred in the training process. The accuracy in tensile and shear properties of materials predicted by traditional and CNN surrogate models were compared. Results show that compared with the traditional method, CNN model is much better in learning the internal features of the image samples and obtains more accurate prediction results. Meanwhile, robustness is well maintained in a certain range outside the training sample space. Based on this, the proposed CNN model was combined with Monte Carlo method to study the forward propagation of error in the uncertainty of microgeometric parameters. The simulation result demonstrates that as the fiber aspect ratio increases, the uncertainties of the microgeometric parameters will lead to a nonnegligible error in the prediction of the effective properties of the material.
2019, 36(6): 1421-1427.
doi: 10.13801/j.cnki.fhclxb.20180827.004
Abstract:
Experimental and numerical works were performed to investigate the mechanical behavior of double scarf-repaired carbon fiber reinforced polymer(CFRP) composite laminates under tensile loading. The load capacity and damage mode of two different thicknesses double scarf-repaired composites were experimentally studied. The results indicate that for double scarf-repaired composites with different thicknesses, the failure strengths are similar and the dominated failure mode is cohesive failure of the adhesive, accompanied by partial 90° matrix crack of composites. A finite element model was established to predict the failure strength and the damage evolution, in which continuum damage model and cohesive zone model were used to describe the composite and adhesive damage respectively. The numerical results show good agreement with the test results and indicate that the matrix crack of the composites initiates prior to the adhesive failure. Based on the validated model, the influences of overlap patch, location of inner tip and adhesive properties were analyzed.
Experimental and numerical works were performed to investigate the mechanical behavior of double scarf-repaired carbon fiber reinforced polymer(CFRP) composite laminates under tensile loading. The load capacity and damage mode of two different thicknesses double scarf-repaired composites were experimentally studied. The results indicate that for double scarf-repaired composites with different thicknesses, the failure strengths are similar and the dominated failure mode is cohesive failure of the adhesive, accompanied by partial 90° matrix crack of composites. A finite element model was established to predict the failure strength and the damage evolution, in which continuum damage model and cohesive zone model were used to describe the composite and adhesive damage respectively. The numerical results show good agreement with the test results and indicate that the matrix crack of the composites initiates prior to the adhesive failure. Based on the validated model, the influences of overlap patch, location of inner tip and adhesive properties were analyzed.
2019, 36(6): 1428-1437.
doi: 10.13801/j.cnki.fhclxb.20180902.001
Abstract:
The penetration of resin along thickness is one of the most crucial factors in liquid composite molding (LCM). The method of continuous loading was used to study the compressive behaviors of non-crimp fabric(NCF) and woven fabrics(WF) during the liquid molding of glass fiber reinforced resin matrix composite respectively and a mathematical model was established to describe this behavior. The through-thickness permeability Kz of the preform under gravity and different injection pressures was tested by a self-made through-thickness permeability testing device. The influence of the preform fiber volume fraction and injection pressure on Kz of the preform was studied. Based on the preform compressive behavior model and the dependence of Kz on injection pressure, the Kozeny-Carman formula was modified and a through-thickness permeability prediction model was presented. The results show that the through-thickness permeability decreases with the increase of the fiber volume fraction of the perform Vf, which agrees with the Kozeny-Carman equation. As the fiber volume fraction varies in the region from 0.42 to 0.58, injection pressure has significant influence on the permeability, and the accuracy of the prediction model presented here is validated experimentally. However, when the fiber volume fraction is higher than 0.58, the injection pressure has little effect on Kz and Kz tends to be constant as Vf increases.
The penetration of resin along thickness is one of the most crucial factors in liquid composite molding (LCM). The method of continuous loading was used to study the compressive behaviors of non-crimp fabric(NCF) and woven fabrics(WF) during the liquid molding of glass fiber reinforced resin matrix composite respectively and a mathematical model was established to describe this behavior. The through-thickness permeability Kz of the preform under gravity and different injection pressures was tested by a self-made through-thickness permeability testing device. The influence of the preform fiber volume fraction and injection pressure on Kz of the preform was studied. Based on the preform compressive behavior model and the dependence of Kz on injection pressure, the Kozeny-Carman formula was modified and a through-thickness permeability prediction model was presented. The results show that the through-thickness permeability decreases with the increase of the fiber volume fraction of the perform Vf, which agrees with the Kozeny-Carman equation. As the fiber volume fraction varies in the region from 0.42 to 0.58, injection pressure has significant influence on the permeability, and the accuracy of the prediction model presented here is validated experimentally. However, when the fiber volume fraction is higher than 0.58, the injection pressure has little effect on Kz and Kz tends to be constant as Vf increases.
2019, 36(6): 1438-1446.
doi: 10.13801/j.cnki.fhclxb.20180906.003
Abstract:
The method of decomposition of deformation gradient and thermodynamics with internal state variables were used to describe the thermo-mechanical behavior of the carbon fiber reinforced shape memory polymer (CF/SMP) composite. A thermo-viscoelastic constitutive model incorporated with stress and structural relaxation was developed in the work. The model can be applied to the finite deformation condition. In the simulation, the CF/SMP lamina was under the unidirectional stress and in the condition of plane stress state. The influence factors of carbon effective strain of the lamina were studied based on the constitutive model. It is proved that the properly ranged carbon fiber can be used in the CF/SMP under the condition of finite deformation condition, though the tolerant strain of the carbon fiber is rather small. In addition, the influence factors of the shape memory effect (SME) of the CF/SMP during a typical thermo-mechanical shape memory cycle were studied here. It is demonstrated that the CF/SMP with the higher volume fraction and smaller inclination angle has the higher stiffness which will result in the lower shape ratio. In addition, the carbon fiber volume fraction and heating rate may also have effect on the recovery process. The research in the paper could provide a basis for design and application of the CF/SMP in engineering.
The method of decomposition of deformation gradient and thermodynamics with internal state variables were used to describe the thermo-mechanical behavior of the carbon fiber reinforced shape memory polymer (CF/SMP) composite. A thermo-viscoelastic constitutive model incorporated with stress and structural relaxation was developed in the work. The model can be applied to the finite deformation condition. In the simulation, the CF/SMP lamina was under the unidirectional stress and in the condition of plane stress state. The influence factors of carbon effective strain of the lamina were studied based on the constitutive model. It is proved that the properly ranged carbon fiber can be used in the CF/SMP under the condition of finite deformation condition, though the tolerant strain of the carbon fiber is rather small. In addition, the influence factors of the shape memory effect (SME) of the CF/SMP during a typical thermo-mechanical shape memory cycle were studied here. It is demonstrated that the CF/SMP with the higher volume fraction and smaller inclination angle has the higher stiffness which will result in the lower shape ratio. In addition, the carbon fiber volume fraction and heating rate may also have effect on the recovery process. The research in the paper could provide a basis for design and application of the CF/SMP in engineering.
2019, 36(6): 1447-1456.
doi: 10.13801/j.cnki.fhclxb.20180905.001
Abstract:
From the perspective of micromechanics, taking into account the in-plane fiber bending and resin-rich defect, an unit cell model was established for stitch damage of the stitching reinforcement for composite laminates containing a large circular hole. The fiber bending function was established and the fiber volume content and fiber bending angle of the fiber bending region were deduced. By applying the method of mechanical analysis of composite materials, the elastic constant of the unit cell was calculated. The study shows that the maximum bending angle of the fibers in the cell surface is never over 20°, the longitudinal Young's modulus decreases while the transverse Young's modulus, shear modulus, and Poisson's ratio increase by not more than -8%-20%; as for composite laminates containing a large circular hole, the variation in material properties caused by changes in needle span is much greater, compared with the edge distance. Based on the calculation results above, a new method for calculating the mechanical properties of the stitching reinforcement for the composite laminates containing a large hole was established. Simultaneously, stitch holes were used to simulate the stress concentration at the stitching. The study results reveal that the stitching may lead to the decrease of the laminates' in-plane mechanical properties, and there is a much stronger influence on the in-plane compress performance than the one of in-plane tensile properties.
From the perspective of micromechanics, taking into account the in-plane fiber bending and resin-rich defect, an unit cell model was established for stitch damage of the stitching reinforcement for composite laminates containing a large circular hole. The fiber bending function was established and the fiber volume content and fiber bending angle of the fiber bending region were deduced. By applying the method of mechanical analysis of composite materials, the elastic constant of the unit cell was calculated. The study shows that the maximum bending angle of the fibers in the cell surface is never over 20°, the longitudinal Young's modulus decreases while the transverse Young's modulus, shear modulus, and Poisson's ratio increase by not more than -8%-20%; as for composite laminates containing a large circular hole, the variation in material properties caused by changes in needle span is much greater, compared with the edge distance. Based on the calculation results above, a new method for calculating the mechanical properties of the stitching reinforcement for the composite laminates containing a large hole was established. Simultaneously, stitch holes were used to simulate the stress concentration at the stitching. The study results reveal that the stitching may lead to the decrease of the laminates' in-plane mechanical properties, and there is a much stronger influence on the in-plane compress performance than the one of in-plane tensile properties.
2019, 36(6): 1457-1463.
doi: 10.13801/j.cnki.fhclxb.20180819.001
Abstract:
In order to study the thermal response of aerospace composites in fire, equations of the composite thermal response were established considering the process of thermal decomposition, the explicit finite difference scheme was derived, and the internal transient thermal response and carbonization of glass fiber/phenolic resin composites were studied. The results show that the equations of nonlinear thermal response established and the method adopted can predict the temperature-time progress of glass fiber/phenolic resin composites, and the temperature of the heating surface at 800 s reaches 1048℃ and the back temperature is 226℃, which are in good agreement with the experimental values. With the increment of the depth, it takes longer for the material to reach the thermal pyrolysis temperature, at the same time, the rate of decrement of material density also decreases, and the carbonization process slows down. The residual mass fraction of materials at different depth in the pyrolysis reaction zone is slightly different at the same temperature, i.e. the deeper the position is, the smaller the residual mass fraction, and the higher the degree of carbonization. As time goes by, the proportion of materials participating in the pyrolysis reaction increases, the carbonization range gradually expands, and the thickness range of the pyrolysis layer gradually expands.
In order to study the thermal response of aerospace composites in fire, equations of the composite thermal response were established considering the process of thermal decomposition, the explicit finite difference scheme was derived, and the internal transient thermal response and carbonization of glass fiber/phenolic resin composites were studied. The results show that the equations of nonlinear thermal response established and the method adopted can predict the temperature-time progress of glass fiber/phenolic resin composites, and the temperature of the heating surface at 800 s reaches 1048℃ and the back temperature is 226℃, which are in good agreement with the experimental values. With the increment of the depth, it takes longer for the material to reach the thermal pyrolysis temperature, at the same time, the rate of decrement of material density also decreases, and the carbonization process slows down. The residual mass fraction of materials at different depth in the pyrolysis reaction zone is slightly different at the same temperature, i.e. the deeper the position is, the smaller the residual mass fraction, and the higher the degree of carbonization. As time goes by, the proportion of materials participating in the pyrolysis reaction increases, the carbonization range gradually expands, and the thickness range of the pyrolysis layer gradually expands.
2019, 36(6): 1464-1470.
doi: 10.13801/j.cnki.fhclxb.20180827.007
Abstract:
Based on the simply analysis of damage mechanism for C/SiC composites and its performance evolution of acoustic emission(AE) during tensile test at room temperature, an analytical research on the AE characterization for one C/SiC thermal structure during static strength experiment at room temperature has been conducted, aimed at the complex characteristics caused by the component assembly design for it. The sort characters of AE parameter were given. The damage evolution patterns were given according to the AE regulation during experimental loading. By the comparison with AE parameter of C/SiC composites, the remaining value was judged between experimental loading to the ultimate damage loading for the thermal structure. So, the AE measure was extended to large C/SiC thermal structure from the research at material level.
Based on the simply analysis of damage mechanism for C/SiC composites and its performance evolution of acoustic emission(AE) during tensile test at room temperature, an analytical research on the AE characterization for one C/SiC thermal structure during static strength experiment at room temperature has been conducted, aimed at the complex characteristics caused by the component assembly design for it. The sort characters of AE parameter were given. The damage evolution patterns were given according to the AE regulation during experimental loading. By the comparison with AE parameter of C/SiC composites, the remaining value was judged between experimental loading to the ultimate damage loading for the thermal structure. So, the AE measure was extended to large C/SiC thermal structure from the research at material level.
2019, 36(6): 1471-1479.
doi: 10.13801/j.cnki.fhclxb.20180906.002
Abstract:
Based on the combined finite-discrete element method (FEM-DEM), the tensile fracture of zirconia toughened alumina particle reinforced Fe45 composites(ZrO2-Al2O3/Fe45) was simulated using axisymmetric representative volume elements. The mesh sensitivity of FEM-DEM models was analyzed. The results show that the second-order solid elements coupling double zero thickness cohesive elements FEM-DEM model reduces the mesh sensitivity. The tensile fracture simulation results of ZrO2-Al2O3/Fe45 show that particle shapes have a great influence on the crack propagation. The crack of ZrO2-Al2O3/Fe45 initiates at the interface which is perpendicular to the direction of tension force, then matrix crack occurs when the interface crack extends to the stress concentration position of the matrix. The cracks of the composites consist of the interfaces crack and matrix crack.
Based on the combined finite-discrete element method (FEM-DEM), the tensile fracture of zirconia toughened alumina particle reinforced Fe45 composites(ZrO2-Al2O3/Fe45) was simulated using axisymmetric representative volume elements. The mesh sensitivity of FEM-DEM models was analyzed. The results show that the second-order solid elements coupling double zero thickness cohesive elements FEM-DEM model reduces the mesh sensitivity. The tensile fracture simulation results of ZrO2-Al2O3/Fe45 show that particle shapes have a great influence on the crack propagation. The crack of ZrO2-Al2O3/Fe45 initiates at the interface which is perpendicular to the direction of tension force, then matrix crack occurs when the interface crack extends to the stress concentration position of the matrix. The cracks of the composites consist of the interfaces crack and matrix crack.
2019, 36(6): 1480-1490.
doi: 10.13801/j.cnki.fhclxb.20180913.001
Abstract:
The plastic deformation behavior of magnesium alloy(AZ91D) and chopped carbon fiber(CFs)/AZ91D composites with different fiber volume fractions were investigated at the condition of 310-430℃ and 10-3-10-1 s-1 using isothermal compression testing. According to the experimental results, the hot processing maps of AZ91D and CFs/AZ91D were constructed to inspect the influence of fiber on the plastic workability and deformation mechanism of CFs/AZ91D composites. The results indicate that the addition of the fiber improves the flow stress as well as the dynamic recrystallization (DRX) and strain softening degree. Nevertheless, the fiber volume fraction has no significant impact on the flow stress and the strain softening degree. The strain rate sensitivity exponent and deformation activation energy of CFs/AZ91D composites are higher than that of AZ91D. It is found there is no deformation instability zone in the processing map of the AZ91D and the power dissipation efficiency exceeds 30% in the deformation safety zone. Due to the stimulation of fiber on the DRX in matrix alloy, the power dissipation efficiency of CFs/AZ91D composite is ultra-high, which exceeds 50%. At the condition of low temperature and high strain rate, the large deformation is liable to induce the interface debonding, which is responsible for the plastic deformation instability of CFs/AZ91D composites.
The plastic deformation behavior of magnesium alloy(AZ91D) and chopped carbon fiber(CFs)/AZ91D composites with different fiber volume fractions were investigated at the condition of 310-430℃ and 10-3-10-1 s-1 using isothermal compression testing. According to the experimental results, the hot processing maps of AZ91D and CFs/AZ91D were constructed to inspect the influence of fiber on the plastic workability and deformation mechanism of CFs/AZ91D composites. The results indicate that the addition of the fiber improves the flow stress as well as the dynamic recrystallization (DRX) and strain softening degree. Nevertheless, the fiber volume fraction has no significant impact on the flow stress and the strain softening degree. The strain rate sensitivity exponent and deformation activation energy of CFs/AZ91D composites are higher than that of AZ91D. It is found there is no deformation instability zone in the processing map of the AZ91D and the power dissipation efficiency exceeds 30% in the deformation safety zone. Due to the stimulation of fiber on the DRX in matrix alloy, the power dissipation efficiency of CFs/AZ91D composite is ultra-high, which exceeds 50%. At the condition of low temperature and high strain rate, the large deformation is liable to induce the interface debonding, which is responsible for the plastic deformation instability of CFs/AZ91D composites.
2019, 36(6): 1491-1500.
doi: 10.13801/j.cnki.fhclxb.20181210.005
Abstract:
The macro-sized macro-mesoporous SiO2 was prepared by using a pillared epoxy resin macroporous polymer as the template and it was used as support to prepare macro-mesoporous TiO2 nanocrystalline-SiO2 composite through an in situ hydrolysis of tetrabutyl titanate and a subsequent calcination at high temperature. The macro-mesoporous TiO2-SiO2 samples were characterized by SEM, TEM, XRD, FTIR and N2 adsorption-desorption. Using azophloxine as a simulated pollutant, the photocatalytic activity of the macro-mesoporous TiO2-SiO2 was studied under the sunlight irradiation simulated by Xenon lamp under different conditions. The results show that the macro-mesoporous SiO2 has 3D continuous pass-through macropore structure and its pore wall is continuous SiO2 nano-film. TiO2 nanocrystallines, in the form of nano-film, in situ grow uniformly on both sides of the nano SiO2 film, and abundant mesopores were observed on the pore wall of the obtained macro-mesoporous TiO2-SiO2 composite. The macro-mesoporous TiO2-SiO2 photocatalyst exhibits the best activity for photocatalytic degradation of pollutant from the macro-mesoporous TiO2-SiO2 composite containing 15.7wt% of TiO2 calcined at 600℃, under the conditions of azophloxine concentration 10 mgL-1 and pH of 3. The macro-mesoporous TiO2-SiO2 photocatalyst also has good reusability.
The macro-sized macro-mesoporous SiO2 was prepared by using a pillared epoxy resin macroporous polymer as the template and it was used as support to prepare macro-mesoporous TiO2 nanocrystalline-SiO2 composite through an in situ hydrolysis of tetrabutyl titanate and a subsequent calcination at high temperature. The macro-mesoporous TiO2-SiO2 samples were characterized by SEM, TEM, XRD, FTIR and N2 adsorption-desorption. Using azophloxine as a simulated pollutant, the photocatalytic activity of the macro-mesoporous TiO2-SiO2 was studied under the sunlight irradiation simulated by Xenon lamp under different conditions. The results show that the macro-mesoporous SiO2 has 3D continuous pass-through macropore structure and its pore wall is continuous SiO2 nano-film. TiO2 nanocrystallines, in the form of nano-film, in situ grow uniformly on both sides of the nano SiO2 film, and abundant mesopores were observed on the pore wall of the obtained macro-mesoporous TiO2-SiO2 composite. The macro-mesoporous TiO2-SiO2 photocatalyst exhibits the best activity for photocatalytic degradation of pollutant from the macro-mesoporous TiO2-SiO2 composite containing 15.7wt% of TiO2 calcined at 600℃, under the conditions of azophloxine concentration 10 mgL-1 and pH of 3. The macro-mesoporous TiO2-SiO2 photocatalyst also has good reusability.
2019, 36(6): 1501-1509.
doi: 10.13801/j.cnki.fhclxb.20180919.001
Abstract:
The NaTaO3-carbon fiber (CF) composite with excellent photocatalytic activity was prepared through sol-gel method combined with dip-coating technique by using TaCl5 and sodium acetate as the raw materials, cetyl trimethyl ammonium bromide (CTAB) as the surfactant. The morphology, crystalline phase and photocatalytic properties of NaTaO3-CF composites were investigated by SEM, TEM and XRD. The dye rhodamine B (RhB) was used as a model contaminant to evaluate the photocatalytic activity of NaTaO3-CF composites. The results indicate that NaTaO3-CF composites have excellent photocatalytic performance and the removal ratio of RhB is achieved 99.35% under dark adsorption for 30 min and irradiation for 80 min. The NaTaO3-CF composites also present favorable stability and photocatalytic activity after recycling, the removal ratio of RhB is remained above 89.17% after five cycles. The photodegradation of RhB is in accordance with the pseudo first order reduction kinetics model and could be described by this kinetic model.
The NaTaO3-carbon fiber (CF) composite with excellent photocatalytic activity was prepared through sol-gel method combined with dip-coating technique by using TaCl5 and sodium acetate as the raw materials, cetyl trimethyl ammonium bromide (CTAB) as the surfactant. The morphology, crystalline phase and photocatalytic properties of NaTaO3-CF composites were investigated by SEM, TEM and XRD. The dye rhodamine B (RhB) was used as a model contaminant to evaluate the photocatalytic activity of NaTaO3-CF composites. The results indicate that NaTaO3-CF composites have excellent photocatalytic performance and the removal ratio of RhB is achieved 99.35% under dark adsorption for 30 min and irradiation for 80 min. The NaTaO3-CF composites also present favorable stability and photocatalytic activity after recycling, the removal ratio of RhB is remained above 89.17% after five cycles. The photodegradation of RhB is in accordance with the pseudo first order reduction kinetics model and could be described by this kinetic model.
2019, 36(6): 1510-1519.
doi: 10.13801/j.cnki.fhclxb.20180907.002
Abstract:
Epoxy polymer-concrete is a kind of composite material prepared by mixing epoxy resin, curing agent and aggregate. It has become a type of novel engineering material with great potential in civil and architectural applications, due to its excellent performance. In this paper, the high performance natural fibers (sisal and ramie) were incorporated into epoxy polymer-concrete to further enhance their mechanical properties. The experimental study shows that the flexural strength of epoxy polymer-concrete can be improved with natural fibers at very low loadings. 0.36vol% natural fibers lead to the increases in flexural strength by 10.5% (ramie fibers) or 8.4% (sisal fibers). The reinforcing effects of natural fibers on the flexural performance of epoxy polymer-concrete can be well described by the parallel model based on the rule of mixture. The theoretical prediction achieves a good agreement with the measured values, with small relative deviation less than 5.1%. The ultraviolet radiation and hygrothermal conditions of natural environment in south China were simulated using a UV accelerated weathering chamber, to the flexural performance decay of natural fiber/epoxy polymer concrete during aging. After the aging of 6 years (equivalent aging time), the flexural strength of natural fiber/epoxy polymer-concrete decreases by 14.3% (sisal fiber) and 15.9% (ramie fiber). The attenuation rule can be described using the residual strength model of fiber reinforced polymer composites in hygrothermal environment.
Epoxy polymer-concrete is a kind of composite material prepared by mixing epoxy resin, curing agent and aggregate. It has become a type of novel engineering material with great potential in civil and architectural applications, due to its excellent performance. In this paper, the high performance natural fibers (sisal and ramie) were incorporated into epoxy polymer-concrete to further enhance their mechanical properties. The experimental study shows that the flexural strength of epoxy polymer-concrete can be improved with natural fibers at very low loadings. 0.36vol% natural fibers lead to the increases in flexural strength by 10.5% (ramie fibers) or 8.4% (sisal fibers). The reinforcing effects of natural fibers on the flexural performance of epoxy polymer-concrete can be well described by the parallel model based on the rule of mixture. The theoretical prediction achieves a good agreement with the measured values, with small relative deviation less than 5.1%. The ultraviolet radiation and hygrothermal conditions of natural environment in south China were simulated using a UV accelerated weathering chamber, to the flexural performance decay of natural fiber/epoxy polymer concrete during aging. After the aging of 6 years (equivalent aging time), the flexural strength of natural fiber/epoxy polymer-concrete decreases by 14.3% (sisal fiber) and 15.9% (ramie fiber). The attenuation rule can be described using the residual strength model of fiber reinforced polymer composites in hygrothermal environment.
2019, 36(6): 1520-1527.
doi: 10.13801/j.cnki.fhclxb.20180913.004
Abstract:
In order to investigate the developing law of flexural strength of cement mortar under sulfate corrosion circumstances with low temperature, the sulfate corrosion tests were carried out under temperature of 20℃, 10℃ and 5℃, and the flexural strength of cement mortar under different ages was also tested. The results show that the flexural strength of mortar specimens increases rapidly first and then decreases, and it is obviously affected by the temperature. The lower the temperature is, the more serious the erosion is, which is mainly manifested by the decrease of the overall strength and the maximum value of the ascending segment decrease, and the beginning time of deterioration becomes earlier. Based on the Irassar model, a prediction model of flexural strength was proposed under sulfate corrosion circumstance at low temperature. The calculated value by the presented model is more consistent with the measured value than the existing model, and the maximum error is 9% and the average error is 2.3%. Therefore, it can be concluded that the proposed model can accurately predict the variation of the flexural strength for cement mortar under sulfate corrosion at a temperature range of 5-20℃.
In order to investigate the developing law of flexural strength of cement mortar under sulfate corrosion circumstances with low temperature, the sulfate corrosion tests were carried out under temperature of 20℃, 10℃ and 5℃, and the flexural strength of cement mortar under different ages was also tested. The results show that the flexural strength of mortar specimens increases rapidly first and then decreases, and it is obviously affected by the temperature. The lower the temperature is, the more serious the erosion is, which is mainly manifested by the decrease of the overall strength and the maximum value of the ascending segment decrease, and the beginning time of deterioration becomes earlier. Based on the Irassar model, a prediction model of flexural strength was proposed under sulfate corrosion circumstance at low temperature. The calculated value by the presented model is more consistent with the measured value than the existing model, and the maximum error is 9% and the average error is 2.3%. Therefore, it can be concluded that the proposed model can accurately predict the variation of the flexural strength for cement mortar under sulfate corrosion at a temperature range of 5-20℃.
2019, 36(6): 1528-1535.
doi: 10.13801/j.cnki.fhclxb.20181210.002
Abstract:
Shrinkage cracking of cement-based materials has become a major cause of its destruction, which has attracted attention at home and abroad. Carbon nanotubes (CNTs), as a nano-fibrous material, may inhibit the shrinkage of cement-based materials. In this paper, CNTs were put into water and dispersed by ultrasonic treatment to form CNTs dispersion liquid. Different CNTs contents was set and added into cement-based materials. The autogenous shrinkage and anti-cracking properties of the new composite were studied through linear shrinkage test and ring test. The results show that the incorporation of CNTs can largely inhibit the self-shrinkage of cement-based materials, with the highest reduction rate reaching more than 40%, and significantly improve the crack resistance of cement-based materials. The increase of water-cement ratio will improve the inhibition effect of CNTs on the shrinkage of cement-based materials. When the content of CNTs is 0.1wt%, the optimal effect can be obtained. Meanwhile, the incorporation of CNTs not only inhibits the self-shrinkage of cement-based materials, but also inhibits the drying shrinkage of cement-based materials to a certain extent. By adding CNTs to cement-based materials in key parts of the building structure, the building safety coefficient can be improved.
Shrinkage cracking of cement-based materials has become a major cause of its destruction, which has attracted attention at home and abroad. Carbon nanotubes (CNTs), as a nano-fibrous material, may inhibit the shrinkage of cement-based materials. In this paper, CNTs were put into water and dispersed by ultrasonic treatment to form CNTs dispersion liquid. Different CNTs contents was set and added into cement-based materials. The autogenous shrinkage and anti-cracking properties of the new composite were studied through linear shrinkage test and ring test. The results show that the incorporation of CNTs can largely inhibit the self-shrinkage of cement-based materials, with the highest reduction rate reaching more than 40%, and significantly improve the crack resistance of cement-based materials. The increase of water-cement ratio will improve the inhibition effect of CNTs on the shrinkage of cement-based materials. When the content of CNTs is 0.1wt%, the optimal effect can be obtained. Meanwhile, the incorporation of CNTs not only inhibits the self-shrinkage of cement-based materials, but also inhibits the drying shrinkage of cement-based materials to a certain extent. By adding CNTs to cement-based materials in key parts of the building structure, the building safety coefficient can be improved.
2019, 36(6): 1536-1545.
doi: 10.13801/j.cnki.fhclxb.20180913.002
Abstract:
In view of the environmental pollution problems caused by the piling up of phosphogypsum and the problems of high filling cost, large amount of cement or other solid materials, and the filling body is unable to contact the top, therefore, a new type of complex phase condensate expansion was prepared. The filling material was optimized by orthogonal test range analysis, variance analysis, multivariate nonlinear regression analysis and data visualization, its formation mechanism was also studied by means of microscopic analysis such as XRD and SEM and so on. The filling composite material is mainly composed of four kinds of materials, namely hemihydrate phosphogypsum (HPG), amorphous phase condensate (SAP), gas phase introduction agent (GPA) and surface hydrophobicity (HA). The filling body is three-phase with solid, liquid and gas. The prominent feature is solidifying under the condition of non-solid volume rate of 87.6%, the compressive strength of 3 days can reach to 1.6 MPa, the expansive rate is above 11%, and the compressive strength is basically stable under the condition of soaking in water for 90 days. The result of microscopic analysis shows that the effect of the SAP is to form the amorphous phase condensate particles, which is a kind of the complex condensate filling material. The main function of the GPA is to introduce the gas phase cavity in the filling body, and the HA is mainly used to form the hydrophobic effect on the surface of the filling body, so that the filling body can be resistant to water for a long time.
In view of the environmental pollution problems caused by the piling up of phosphogypsum and the problems of high filling cost, large amount of cement or other solid materials, and the filling body is unable to contact the top, therefore, a new type of complex phase condensate expansion was prepared. The filling material was optimized by orthogonal test range analysis, variance analysis, multivariate nonlinear regression analysis and data visualization, its formation mechanism was also studied by means of microscopic analysis such as XRD and SEM and so on. The filling composite material is mainly composed of four kinds of materials, namely hemihydrate phosphogypsum (HPG), amorphous phase condensate (SAP), gas phase introduction agent (GPA) and surface hydrophobicity (HA). The filling body is three-phase with solid, liquid and gas. The prominent feature is solidifying under the condition of non-solid volume rate of 87.6%, the compressive strength of 3 days can reach to 1.6 MPa, the expansive rate is above 11%, and the compressive strength is basically stable under the condition of soaking in water for 90 days. The result of microscopic analysis shows that the effect of the SAP is to form the amorphous phase condensate particles, which is a kind of the complex condensate filling material. The main function of the GPA is to introduce the gas phase cavity in the filling body, and the HA is mainly used to form the hydrophobic effect on the surface of the filling body, so that the filling body can be resistant to water for a long time.
2019, 36(6): 1546-1557.
doi: 10.13801/j.cnki.fhclxb.20180816.001
Abstract:
For the assembly gap in composite airframe structure, an optimization method based on genetic algorithm was proposed to optimize the size and layout of pressing force, in which damage caused by pressing force was considered. Combining with finite element analysis, considering the interference between pressing points, with laminates delamination as the constraint condition and elimination rate of gap as the objective function, the optimization model with size and layout of pressing force was established. Taking composite win box as an example, establishing finite element model based on cohesive element, the optimization method was applied to optimize pressing force on composite panel. Then, with the optimum size and layout of pressing force, the elimination rate of gap, delamination damage, stress and strain were calculated and analyzed. The results demonstrate that:the optimum pressing force makes stress and strain distribution more uniform; elimination rate of gap is improved dramatically compared with the traditional one without laminates delamination. When the initial assembly gap is 0.2-0.8 mm, the elimination rate of gap is increased to 77.4%-100%, which is 19.2%-177.8% higher than that before the optimization.
For the assembly gap in composite airframe structure, an optimization method based on genetic algorithm was proposed to optimize the size and layout of pressing force, in which damage caused by pressing force was considered. Combining with finite element analysis, considering the interference between pressing points, with laminates delamination as the constraint condition and elimination rate of gap as the objective function, the optimization model with size and layout of pressing force was established. Taking composite win box as an example, establishing finite element model based on cohesive element, the optimization method was applied to optimize pressing force on composite panel. Then, with the optimum size and layout of pressing force, the elimination rate of gap, delamination damage, stress and strain were calculated and analyzed. The results demonstrate that:the optimum pressing force makes stress and strain distribution more uniform; elimination rate of gap is improved dramatically compared with the traditional one without laminates delamination. When the initial assembly gap is 0.2-0.8 mm, the elimination rate of gap is increased to 77.4%-100%, which is 19.2%-177.8% higher than that before the optimization.
2019, 36(6): 1558-1567.
doi: 10.13801/j.cnki.fhclxb.20180830.001
Abstract:
A calculation model for thermal deformation and thermal stress of orthotropic material was established using Element-free Galerkin method (EFG) and the discreted governing equation for thermoelastic problem of orthotropic material based on EFG method was deduced. The reliability of present model and programs have been verified through a numerical example of composite cooling grid. The total thermal deformation displacement and Mises stress of orthotropic materials turbine impeller with different off-angles, thermal conductivity factors, thermal expansion coefficient factors and primary and secondary Poisson's ratio factors were analyzed using the calculation model. The effects of off-angle and the above orthotropic material factors on total thermal deformation displacement and Mises stress were discussed, and the reasonable ranges of these parameters were provided. A group of parameters were selected to analyze the thermal deformation and thermal stress of orthotropic material by using the proposed calculation model and compared with isotropic materials. The results show that the calculation accuracy of total thermal deformation displacement and Mises stress based on EFG method is higher than the finite element method. The off-angle affects both magnitude and direction of total thermal deformation displacement and Mises stress, while orthotropic factors only affect the magnitude of total thermal deformation displacement and the Mises stress without affecting direction. Reasonable selection of off-angle and orthotropic material factors can effectively reduce the thermal deformation and thermal stress during the design of composite materials.
A calculation model for thermal deformation and thermal stress of orthotropic material was established using Element-free Galerkin method (EFG) and the discreted governing equation for thermoelastic problem of orthotropic material based on EFG method was deduced. The reliability of present model and programs have been verified through a numerical example of composite cooling grid. The total thermal deformation displacement and Mises stress of orthotropic materials turbine impeller with different off-angles, thermal conductivity factors, thermal expansion coefficient factors and primary and secondary Poisson's ratio factors were analyzed using the calculation model. The effects of off-angle and the above orthotropic material factors on total thermal deformation displacement and Mises stress were discussed, and the reasonable ranges of these parameters were provided. A group of parameters were selected to analyze the thermal deformation and thermal stress of orthotropic material by using the proposed calculation model and compared with isotropic materials. The results show that the calculation accuracy of total thermal deformation displacement and Mises stress based on EFG method is higher than the finite element method. The off-angle affects both magnitude and direction of total thermal deformation displacement and Mises stress, while orthotropic factors only affect the magnitude of total thermal deformation displacement and the Mises stress without affecting direction. Reasonable selection of off-angle and orthotropic material factors can effectively reduce the thermal deformation and thermal stress during the design of composite materials.
2019, 36(6): 1568-1573.
doi: 10.13801/j.cnki.fhclxb.20180821.004
Abstract:
The silicon (Si) was mixed with different amounts of asphalt (0%, 10%, 20%, 30% and 50% in mass fraction) as the soft carbon (C) source, respectively, to form the C/Si composites via the thermal decomposition method. As a result, the volume expansion of the Si material during the insertion/deinsertion process is effectively supressed, and the electric conductivity is improved at the same time, leading to the cycling stability and specific capacity increasing. For instance, a first-charge capacity as high as 2 356.7 mAhg-1 is achieved for the C/Si sample synthesized using 20% asphalt. After 50 cycles, 726.4 mAhg-1 of the capacity is retained, which is much higher than that of the commercial graphite and promising for industrial application. Moreover, the synthesis mechanism and effect of different amounts of asphalt on the morphology of obtained materials were also discussed.
The silicon (Si) was mixed with different amounts of asphalt (0%, 10%, 20%, 30% and 50% in mass fraction) as the soft carbon (C) source, respectively, to form the C/Si composites via the thermal decomposition method. As a result, the volume expansion of the Si material during the insertion/deinsertion process is effectively supressed, and the electric conductivity is improved at the same time, leading to the cycling stability and specific capacity increasing. For instance, a first-charge capacity as high as 2 356.7 mAhg-1 is achieved for the C/Si sample synthesized using 20% asphalt. After 50 cycles, 726.4 mAhg-1 of the capacity is retained, which is much higher than that of the commercial graphite and promising for industrial application. Moreover, the synthesis mechanism and effect of different amounts of asphalt on the morphology of obtained materials were also discussed.
