The fracture toughness of a carbon/carbon composites oxidized at different temperature for 1 h was measured. The fracture surfaces were examined by scanning electron microscopy (SEM). The results indicate that oxida...The fracture toughness of a carbon/carbon composites oxidized at different temperature for 1 h was measured. The fracture surfaces were examined by scanning electron microscopy (SEM). The results indicate that oxidation temperature has significant effects on the fracture toughness. Fracture toughness decreases with the increase of the weight loss. The SEM images reveal that the decrease of fracture toughness was mainly attributed to the oxidation of the interface in the composite.展开更多
Polymer bonded explosives (PBXs) are highly particle-filled composite materials.This paper experimentally studies the tensile deformation and fracture behavior of a PBX simulation by using the semi-circular bending (S...Polymer bonded explosives (PBXs) are highly particle-filled composite materials.This paper experimentally studies the tensile deformation and fracture behavior of a PBX simulation by using the semi-circular bending (SCB) test.The deformation and fracture process of a pre-notched SCB sample with a random speckle pattern is recorded by a charge coupled device camera.The displacement and strain fields on the observed surface during the loading process are obtained by using the digital image correlation method.The crack opening displacement is calculated from the displacement fields,the initiation and propagation of the crack are analyzed.In addition,the damage evolution and fracture mechanisms of the SCB sample are analyzed according to the strain fields and the correlation coefficient fields at different loading steps.展开更多
Recently, quasimolecular dynamics has been successfully used to simulate the deformation characteristics of actual size solid materials. In quasimolecular dynamics, which is an attempt to bridge the gap between atomis...Recently, quasimolecular dynamics has been successfully used to simulate the deformation characteristics of actual size solid materials. In quasimolecular dynamics, which is an attempt to bridge the gap between atomistic and continuum simulations, molecules are aggregated into large units, called quasimolecules, to evaluate large scale material behavior. In this paper, a 2-dimensional numerical simulation using quasimolecular dynamics was performed to investigate laminar composite material fractures and crack propagation behavior in the uniform bending of laminar composite materials. It was verified that under bending deformation laminar composite materials deform quite differently from homogeneous展开更多
The dynamic tensile processes of silicon carbide whisker reinforced Al composite(SiC_w/Al) with 22% V_f have been in situ observed with a scanning electron microscope equipped with a tensile stand.The results show tha...The dynamic tensile processes of silicon carbide whisker reinforced Al composite(SiC_w/Al) with 22% V_f have been in situ observed with a scanning electron microscope equipped with a tensile stand.The results show that a number of microcracks have formed as the tensile stress increases to 180~190 MPa.Microcracks form in most cases at the whisker ends.The frac- ture behaviour of SiC_w/Al composite observed has been explained theoretically.展开更多
Solidification microstructure and mechanical property are explored.Furthermore,tensile fracture and microstructure are analyzed by using SEM and JXA 840A electron probe.The results indicate that SiC particles in SiC...Solidification microstructure and mechanical property are explored.Furthermore,tensile fracture and microstructure are analyzed by using SEM and JXA 840A electron probe.The results indicate that SiC particles in SiCp/ZA27 composite are mainly distributed on interfaces or between dendrites and surrounded by primary α phase.The dendrite of α phase is fined by SiCp.The tensile strength at room temperature decreases with the increasing of SiCp addition.The tensile strength at elevated temperature increases with the addition of SiCp.The fracture of SiCp/ZA27 composites is the mixture of tough and brittle fracture.The carck is prone to extend along the interface and the region of dispersed shrinkage.展开更多
The fracture toughness and fracture work of A12O3/SiC prismatic ceramic composites was evaluated in this paper, which showed the fracture energy was improved greatly. Based on the observation ’for crack propagation a...The fracture toughness and fracture work of A12O3/SiC prismatic ceramic composites was evaluated in this paper, which showed the fracture energy was improved greatly. Based on the observation ’for crack propagation and fracture morphology, the fracture behavior of the prismatic composites was analyzed. In the bending test, the composites displayed a non-catastrophic behavior and a graceful failure with reasonable load-carrying capability.展开更多
This paper reports some results obtained in an investigation to see how increasing the corundum dispersoid content from 0% to 7% in a matrix of as-cast and wrought hiduminium alloy affects the hardness. wear resistanc...This paper reports some results obtained in an investigation to see how increasing the corundum dispersoid content from 0% to 7% in a matrix of as-cast and wrought hiduminium alloy affects the hardness. wear resistance and fracture toughness of the composite. The results show that as the corundum content is increased, the hardness and the wear resistance increase remarkably,whereas the fracture toughness drops significantly. It was found that Just a minute amount of corundum is sufficient to cause a fairly large change in these mechanical properties. The hardness of the material is also affected signifIcantly by the aging time. Moreover, if other factors are kept constant, hot extrusion improves both its hardness and its wear resistance. whereas the fracture toughness is decreased展开更多
The strengthening effect of a Zn alloy reinforced by SiC particulate was examined. Based on the results of SEM in-situ fracture observation and stress field analysis by finite element method, it is believed that the r...The strengthening effect of a Zn alloy reinforced by SiC particulate was examined. Based on the results of SEM in-situ fracture observation and stress field analysis by finite element method, it is believed that the reinforcing effect of this composite is due to the combination of strain and stress hardening in the matrix.展开更多
Theoretical consideration was conducted on a relation between pore diameter and interfacialarea between pores and fibers when pores uniforinly distribute in C/C composites. It was shownthat bonding at the fiber/matrix...Theoretical consideration was conducted on a relation between pore diameter and interfacialarea between pores and fibers when pores uniforinly distribute in C/C composites. It was shownthat bonding at the fiber/matrix interface apparently decreased with decreasing a pore diameter,and consequently a new idea of microspace modification concept was proposed for controllingfracture behavior of C/C composites. Four types of C/C composites with various pore structureswere fabricated by hot-pressing, and their fracture behavior was investigated by three pointbending tests. The fracture behavior of the C/C composites was changed from brittle one topseudo ductile one with decreasing the pore diameter. This result supported the validity of themicrospace modification concept proposed in this paper.展开更多
The solidification processing of SiCp/ZL108 composite material developed by mechanical stirring molten matrix alloy containing flux treated SiC particles is studied. The criterion and model of particles well distrib...The solidification processing of SiCp/ZL108 composite material developed by mechanical stirring molten matrix alloy containing flux treated SiC particles is studied. The criterion and model of particles well distributed in matrix are discussed. The bonding structure of interface between SiC particles and ZL108 matrix and the morphology of tensile fracture are analysed by using JXA-840A electron-probe. The mechanism of crack propagating is explored preliminarily.展开更多
The strength of rockmass from two aspects is analyzed.Firstly,the strength of the rockmass is mainly controlled by the critical stress value of rock,and the contribution of joints is to increase the effective stresses...The strength of rockmass from two aspects is analyzed.Firstly,the strength of the rockmass is mainly controlled by the critical stress value of rock,and the contribution of joints is to increase the effective stresses of rock and to decrease the damage strength of rockmass according to the macro damage mechanics of rockmass.Secondly,the strength of rockmass is mainly controlled by the fracture strength of joints.Based on the comprehensive analysis and comparison for the damage strength of rockmass and the fracture strength of joints,a composite damage theory of rockmass may be established.展开更多
In this study, magnesium matrix composites reinforced with different loading of AlN particles were fabricated by the powder metallurgy technique. The microstructure, bending strength and fracture behavior of the resul...In this study, magnesium matrix composites reinforced with different loading of AlN particles were fabricated by the powder metallurgy technique. The microstructure, bending strength and fracture behavior of the resulting Mg-Al/Al N composites were investigated. It showed that the 5 wt% AlN reinforcements led to the highest densification and bending strength. The total strengthening effect of AlN particles was predicted by considering the contributions of CTE mismatch between the matrix and the particles,load bearing and Hall-Petch mechanism. The results revealed that the increase of dislocation density,the change of Mg17Al12 phase morphology, and the effective load transfer were the major strengthening contributors to the composites. The fracture of the composites altered from plastic to brittle mode with increasing reinforcement content. The regions of clustered particles in the composites were easy to be damaged under external load, and the fracture occurred mainly along grain boundaries.展开更多
2D carbon fiber reinforced AZ91 D matrix composites(2D-C_f/AZ91 D composites) were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique(LSEVI). In order to modify the interface between ...2D carbon fiber reinforced AZ91 D matrix composites(2D-C_f/AZ91 D composites) were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique(LSEVI). In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon(Py C) coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition(CVD). Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_(17)Al_(12) precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.展开更多
基金Funded by National Natural Science Foundation of China(No.50702045)the Program for New Century Excellent Talents in University(No.NCET-08-0460)Basic Research Foundation of NWPU(No.JC20100227)
文摘The fracture toughness of a carbon/carbon composites oxidized at different temperature for 1 h was measured. The fracture surfaces were examined by scanning electron microscopy (SEM). The results indicate that oxidation temperature has significant effects on the fracture toughness. Fracture toughness decreases with the increase of the weight loss. The SEM images reveal that the decrease of fracture toughness was mainly attributed to the oxidation of the interface in the composite.
基金supported by the National Natural Science Foundation of China (10832003)the National Basic Research Program of China (613830202),the NSAF (11076032)
文摘Polymer bonded explosives (PBXs) are highly particle-filled composite materials.This paper experimentally studies the tensile deformation and fracture behavior of a PBX simulation by using the semi-circular bending (SCB) test.The deformation and fracture process of a pre-notched SCB sample with a random speckle pattern is recorded by a charge coupled device camera.The displacement and strain fields on the observed surface during the loading process are obtained by using the digital image correlation method.The crack opening displacement is calculated from the displacement fields,the initiation and propagation of the crack are analyzed.In addition,the damage evolution and fracture mechanisms of the SCB sample are analyzed according to the strain fields and the correlation coefficient fields at different loading steps.
文摘Recently, quasimolecular dynamics has been successfully used to simulate the deformation characteristics of actual size solid materials. In quasimolecular dynamics, which is an attempt to bridge the gap between atomistic and continuum simulations, molecules are aggregated into large units, called quasimolecules, to evaluate large scale material behavior. In this paper, a 2-dimensional numerical simulation using quasimolecular dynamics was performed to investigate laminar composite material fractures and crack propagation behavior in the uniform bending of laminar composite materials. It was verified that under bending deformation laminar composite materials deform quite differently from homogeneous
文摘The dynamic tensile processes of silicon carbide whisker reinforced Al composite(SiC_w/Al) with 22% V_f have been in situ observed with a scanning electron microscope equipped with a tensile stand.The results show that a number of microcracks have formed as the tensile stress increases to 180~190 MPa.Microcracks form in most cases at the whisker ends.The frac- ture behaviour of SiC_w/Al composite observed has been explained theoretically.
文摘Solidification microstructure and mechanical property are explored.Furthermore,tensile fracture and microstructure are analyzed by using SEM and JXA 840A electron probe.The results indicate that SiC particles in SiCp/ZA27 composite are mainly distributed on interfaces or between dendrites and surrounded by primary α phase.The dendrite of α phase is fined by SiCp.The tensile strength at room temperature decreases with the increasing of SiCp addition.The tensile strength at elevated temperature increases with the addition of SiCp.The fracture of SiCp/ZA27 composites is the mixture of tough and brittle fracture.The carck is prone to extend along the interface and the region of dispersed shrinkage.
文摘The fracture toughness and fracture work of A12O3/SiC prismatic ceramic composites was evaluated in this paper, which showed the fracture energy was improved greatly. Based on the observation ’for crack propagation and fracture morphology, the fracture behavior of the prismatic composites was analyzed. In the bending test, the composites displayed a non-catastrophic behavior and a graceful failure with reasonable load-carrying capability.
文摘This paper reports some results obtained in an investigation to see how increasing the corundum dispersoid content from 0% to 7% in a matrix of as-cast and wrought hiduminium alloy affects the hardness. wear resistance and fracture toughness of the composite. The results show that as the corundum content is increased, the hardness and the wear resistance increase remarkably,whereas the fracture toughness drops significantly. It was found that Just a minute amount of corundum is sufficient to cause a fairly large change in these mechanical properties. The hardness of the material is also affected signifIcantly by the aging time. Moreover, if other factors are kept constant, hot extrusion improves both its hardness and its wear resistance. whereas the fracture toughness is decreased
基金This project is supported by the National Natural Science Foundation of China(No.59971017).
文摘The strengthening effect of a Zn alloy reinforced by SiC particulate was examined. Based on the results of SEM in-situ fracture observation and stress field analysis by finite element method, it is believed that the reinforcing effect of this composite is due to the combination of strain and stress hardening in the matrix.
文摘Theoretical consideration was conducted on a relation between pore diameter and interfacialarea between pores and fibers when pores uniforinly distribute in C/C composites. It was shownthat bonding at the fiber/matrix interface apparently decreased with decreasing a pore diameter,and consequently a new idea of microspace modification concept was proposed for controllingfracture behavior of C/C composites. Four types of C/C composites with various pore structureswere fabricated by hot-pressing, and their fracture behavior was investigated by three pointbending tests. The fracture behavior of the C/C composites was changed from brittle one topseudo ductile one with decreasing the pore diameter. This result supported the validity of themicrospace modification concept proposed in this paper.
文摘The solidification processing of SiCp/ZL108 composite material developed by mechanical stirring molten matrix alloy containing flux treated SiC particles is studied. The criterion and model of particles well distributed in matrix are discussed. The bonding structure of interface between SiC particles and ZL108 matrix and the morphology of tensile fracture are analysed by using JXA-840A electron-probe. The mechanism of crack propagating is explored preliminarily.
文摘The strength of rockmass from two aspects is analyzed.Firstly,the strength of the rockmass is mainly controlled by the critical stress value of rock,and the contribution of joints is to increase the effective stresses of rock and to decrease the damage strength of rockmass according to the macro damage mechanics of rockmass.Secondly,the strength of rockmass is mainly controlled by the fracture strength of joints.Based on the comprehensive analysis and comparison for the damage strength of rockmass and the fracture strength of joints,a composite damage theory of rockmass may be established.
基金financially supported by the State Key Laboratory for Mechanical Behavior of Materials (No. 20151712)
文摘In this study, magnesium matrix composites reinforced with different loading of AlN particles were fabricated by the powder metallurgy technique. The microstructure, bending strength and fracture behavior of the resulting Mg-Al/Al N composites were investigated. It showed that the 5 wt% AlN reinforcements led to the highest densification and bending strength. The total strengthening effect of AlN particles was predicted by considering the contributions of CTE mismatch between the matrix and the particles,load bearing and Hall-Petch mechanism. The results revealed that the increase of dislocation density,the change of Mg17Al12 phase morphology, and the effective load transfer were the major strengthening contributors to the composites. The fracture of the composites altered from plastic to brittle mode with increasing reinforcement content. The regions of clustered particles in the composites were easy to be damaged under external load, and the fracture occurred mainly along grain boundaries.
基金supported by the National Nature Science Foundation of China (Nos. 51472203, 51521061, 51575447 and 51432008)
文摘2D carbon fiber reinforced AZ91 D matrix composites(2D-C_f/AZ91 D composites) were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique(LSEVI). In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon(Py C) coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition(CVD). Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_(17)Al_(12) precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.