A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method. T...A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method. The composite structure of the growing SiC crystal and graphite lid is considered in the model. The thermal expansion match between the crucible lid and SiC crystal is studied for the first time. The influence of thermal stress on the dislocation density and crystal quality is discussed.展开更多
During quenching, the residual stresses are affected by the crystallographic orientation of martensite, because the nonuniform thermal stresses affect the crystallographic orientation of the lathshaped martensite and ...During quenching, the residual stresses are affected by the crystallographic orientation of martensite, because the nonuniform thermal stresses affect the crystallographic orientation of the lathshaped martensite and induce the anisotropic expansion. To simulate this process, the model of anisotropic transformation induced plasticity(TRIP) was built using the WLR-BM phenomenological theory. The equivalent expansion coefficient was introduced considering the thermal and plastic strains, which simplified the numerical simulation. Furthermore, the quenching residual stresses in carbon steel plates were calculated using the finite element method under ANSYS Workbench simulation environment. To evaluate the simulative results, distributions of residual stresses from the surface to the interior at the center of specimen were measured using the layer-by-layer hole-drilling method. Compared to the measured results, the simulative results considering the anisotropic expansion induced by the crystallographic orientation of martenstic laths were found to be more accurate than those without considering it.展开更多
The deterioration of the microscopic pore structure of concrete under external sulfate attack(ESA)is a primary cause of degradation.Nevertheless,little effort has been invested in exploring the temporal and spatial de...The deterioration of the microscopic pore structure of concrete under external sulfate attack(ESA)is a primary cause of degradation.Nevertheless,little effort has been invested in exploring the temporal and spatial development of the porosity of concrete under ESA.This study proposes a mechanical–chemical model to simulate the spatiotemporal distribution of the porosity.A relationship between the corrosion damage and amount of ettringite is proposed based on the theory of volume expansion.In addition,the expansion strain at the macro-scale is obtained using a stress analysis model of composite concentric sphere elements and the micromechanical mean-field approach.Finally,considering the influence of corrosion damage and cement hydration on the diffusion of sulfate ions,the expansion deformation and porosity space−time distribution are obtained using the finite difference method.The results demonstrate that the expansion strains calculated using the suggested model agree well with previously reported experimental results.Moreover,the tricalcium aluminate concentration,initial elastic modulus of cement paste,corrosion damage,and continuous hydration of cement significantly affect concrete under ESA.The proposed model can forecast and assess the porosity of concrete covers and provide a credible approach for determining the residual life of concrete structures under ESA.展开更多
In this paper, the two-flume method was used to study the change laws of the thermal conductivity and thermal expansion coefficient of diamond/Cu composite materials with 100, 300, and 500 cycle numbers, under the act...In this paper, the two-flume method was used to study the change laws of the thermal conductivity and thermal expansion coefficient of diamond/Cu composite materials with 100, 300, and 500 cycle numbers, under the action of thermal shock load between-196 and 85 °C; the X-ray diffraction method(XRD) was used to study the change of the residual stress in the thermal shock process of the diamond/Cu composite materials; and the evolution of the fracture microstructure with different thermal shock cycle numbers was observed through scanning electron microscopy(SEM). The results of the study show that the increase of the binder residue at the interface reduces the thermal shock stability of the diamond/Cu composite materials. In addition, under the thermal shock load between-196 and 85 °C, the residual stress of the diamond/Cu composite materials increases continuously with the increase of the cycle numbers, the increase of residual stress leads to a small amount of interface debonding, an increase of the interfacial thermal resistances, and a decrease of the constraints of low-expansion component on material deformation, thus the thermal conductivity decreases slightly and the thermal expansion coefficient increases slightly.展开更多
基金The project supported by the National Natural Science Foundation of China (10472126)the Knowledge Innovation Program of Chinese Academy of Sciences
文摘A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method. The composite structure of the growing SiC crystal and graphite lid is considered in the model. The thermal expansion match between the crucible lid and SiC crystal is studied for the first time. The influence of thermal stress on the dislocation density and crystal quality is discussed.
基金Funded by the Creative Research Groups of National Natural Science Foundation of China(No.51221004)the National Natural Science Foundation of China(Nos.51375443,50675200)
文摘During quenching, the residual stresses are affected by the crystallographic orientation of martensite, because the nonuniform thermal stresses affect the crystallographic orientation of the lathshaped martensite and induce the anisotropic expansion. To simulate this process, the model of anisotropic transformation induced plasticity(TRIP) was built using the WLR-BM phenomenological theory. The equivalent expansion coefficient was introduced considering the thermal and plastic strains, which simplified the numerical simulation. Furthermore, the quenching residual stresses in carbon steel plates were calculated using the finite element method under ANSYS Workbench simulation environment. To evaluate the simulative results, distributions of residual stresses from the surface to the interior at the center of specimen were measured using the layer-by-layer hole-drilling method. Compared to the measured results, the simulative results considering the anisotropic expansion induced by the crystallographic orientation of martenstic laths were found to be more accurate than those without considering it.
基金support from the National Natural Science Foundation of China(Grant Nos.11832013,52168030)the Education Department of Jiangxi Province Science and Technology Project(No.211909)K.C.Wong Magna Fund in Ningbo University,and the project of the Key Laboratory of Impact and Safety Engineering(Ningbo University),Ministry of Education(No.202004).
文摘The deterioration of the microscopic pore structure of concrete under external sulfate attack(ESA)is a primary cause of degradation.Nevertheless,little effort has been invested in exploring the temporal and spatial development of the porosity of concrete under ESA.This study proposes a mechanical–chemical model to simulate the spatiotemporal distribution of the porosity.A relationship between the corrosion damage and amount of ettringite is proposed based on the theory of volume expansion.In addition,the expansion strain at the macro-scale is obtained using a stress analysis model of composite concentric sphere elements and the micromechanical mean-field approach.Finally,considering the influence of corrosion damage and cement hydration on the diffusion of sulfate ions,the expansion deformation and porosity space−time distribution are obtained using the finite difference method.The results demonstrate that the expansion strains calculated using the suggested model agree well with previously reported experimental results.Moreover,the tricalcium aluminate concentration,initial elastic modulus of cement paste,corrosion damage,and continuous hydration of cement significantly affect concrete under ESA.The proposed model can forecast and assess the porosity of concrete covers and provide a credible approach for determining the residual life of concrete structures under ESA.
基金financially supported by the Program of National Natural Science Foundation of China (No. 50971020)
文摘In this paper, the two-flume method was used to study the change laws of the thermal conductivity and thermal expansion coefficient of diamond/Cu composite materials with 100, 300, and 500 cycle numbers, under the action of thermal shock load between-196 and 85 °C; the X-ray diffraction method(XRD) was used to study the change of the residual stress in the thermal shock process of the diamond/Cu composite materials; and the evolution of the fracture microstructure with different thermal shock cycle numbers was observed through scanning electron microscopy(SEM). The results of the study show that the increase of the binder residue at the interface reduces the thermal shock stability of the diamond/Cu composite materials. In addition, under the thermal shock load between-196 and 85 °C, the residual stress of the diamond/Cu composite materials increases continuously with the increase of the cycle numbers, the increase of residual stress leads to a small amount of interface debonding, an increase of the interfacial thermal resistances, and a decrease of the constraints of low-expansion component on material deformation, thus the thermal conductivity decreases slightly and the thermal expansion coefficient increases slightly.