The microstructural evolution and performance of diamond/Al composites during thermal cycling has rarely been investigated.In the present work,the thermal stability of diamond/Al composites during thermal cycling for ...The microstructural evolution and performance of diamond/Al composites during thermal cycling has rarely been investigated.In the present work,the thermal stability of diamond/Al composites during thermal cycling for up to 200 cycles was explored.Specifically,the thermal conductivity(λ)of the composites was measured and scanning electron microscopy of specific areas in the same samples was carried out to achieve quasi-in situ observations.The interface between the(100)plane of diamond and the Al matrix was well bonded with a zigzag morphology and abundant needle-like Al4C3 phases.By contrast,the interface between the(111)plane of diamond and the Al matrix showed weak bonding and debonded during thermal cycling.The debonding length increased rapidly over the first 100 thermal cycles and then increased slowly in the following 100 cycles.Theλof the diamond/Al composites decreased abruptly over the initial 20 cycles,increased afterward,and then decreased monotonously once more with increasing number of thermal cycles.Decreases in theλof the Al matrix and the corresponding stress concentration at the diamond/Al interface caused by thermal mismatch,rather than interfacial debonding,may be the main factors influencing the decrease inλof the diamond/Al composites,especially in the initial stages of thermal cycling.展开更多
Peeling-off phenomena in FRP strengthened concrete beams are investigated in this paper. Based on the beam theory and the fracture mechanics, a new theoretical model is proposed to analyze the peeling-off behavior nea...Peeling-off phenomena in FRP strengthened concrete beams are investigated in this paper. Based on the beam theory and the fracture mechanics, a new theoretical model is proposed to analyze the peeling-off behavior near FRP-concrete interfaces, which is governed by residual thermal stresses. Numerical examples are presented to provide a clear insight into the failure mechanism. Some suggestions are provided for the optimal design of FRP strengthened structures.展开更多
The thermal expansion mismatch between cement mortar and aggregate at high temperature is one of the main reasons causing the deterioration of concrete at high temperature.In this study,the thermal damage of concrete ...The thermal expansion mismatch between cement mortar and aggregate at high temperature is one of the main reasons causing the deterioration of concrete at high temperature.In this study,the thermal damage of concrete caused by the thermal expansion mismatch between aggregate and cement mortar was investigated using a meso-scale concrete model.The meso-scale concrete model is composed of mortar,aggregate and the interfacial transition zone(ITZ).Laboratory tests on the mechanical properties of cement mortar at high temperature were conducted to provide the necessary mechanical parameter for the meso-scale concrete model.The simulation results show that the particle size,content,distribution and mechanical properties of the aggregate have an effect on the thermal damage of concrete at high temperature.The smaller the particle size of concrete aggregate and the higher the elastic modulus of aggregate,the greater the damage of concrete under high temperature.Due to the increasing thermal expansion difference between aggregate and cement mortar,and the deterioration of the cement mortar with the increasing temperature,the damage of concrete increased sharply after 500℃.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.1871072,51871073,52171136,51771063,61604086,and U1637201)the China Postdoctoral Science Foundation(Nos.2016M590280 and 2017T100240)+1 种基金the Heilongjiang Postdoctoral Foundation(Nos.LBH-Z16075 and LBH-TZ2014)the Fundamental Research Funds for the Central Universities,China(Nos.HIT.NSRIF.20161 and HIT.MKSTISP.201615).
文摘The microstructural evolution and performance of diamond/Al composites during thermal cycling has rarely been investigated.In the present work,the thermal stability of diamond/Al composites during thermal cycling for up to 200 cycles was explored.Specifically,the thermal conductivity(λ)of the composites was measured and scanning electron microscopy of specific areas in the same samples was carried out to achieve quasi-in situ observations.The interface between the(100)plane of diamond and the Al matrix was well bonded with a zigzag morphology and abundant needle-like Al4C3 phases.By contrast,the interface between the(111)plane of diamond and the Al matrix showed weak bonding and debonded during thermal cycling.The debonding length increased rapidly over the first 100 thermal cycles and then increased slowly in the following 100 cycles.Theλof the diamond/Al composites decreased abruptly over the initial 20 cycles,increased afterward,and then decreased monotonously once more with increasing number of thermal cycles.Decreases in theλof the Al matrix and the corresponding stress concentration at the diamond/Al interface caused by thermal mismatch,rather than interfacial debonding,may be the main factors influencing the decrease inλof the diamond/Al composites,especially in the initial stages of thermal cycling.
基金supported by the National Basic Research Program of China(No.2007CB714102)the National Natural Science Foundation of China(No.50979048)
文摘Peeling-off phenomena in FRP strengthened concrete beams are investigated in this paper. Based on the beam theory and the fracture mechanics, a new theoretical model is proposed to analyze the peeling-off behavior near FRP-concrete interfaces, which is governed by residual thermal stresses. Numerical examples are presented to provide a clear insight into the failure mechanism. Some suggestions are provided for the optimal design of FRP strengthened structures.
基金supported by the open Fund of State Key Laboratory of Disaster Reduction in Civil Engineering(Grant No.SLDRCE15-03)Beijing major science and technology projects(Grant No.Z191100008019002).
文摘The thermal expansion mismatch between cement mortar and aggregate at high temperature is one of the main reasons causing the deterioration of concrete at high temperature.In this study,the thermal damage of concrete caused by the thermal expansion mismatch between aggregate and cement mortar was investigated using a meso-scale concrete model.The meso-scale concrete model is composed of mortar,aggregate and the interfacial transition zone(ITZ).Laboratory tests on the mechanical properties of cement mortar at high temperature were conducted to provide the necessary mechanical parameter for the meso-scale concrete model.The simulation results show that the particle size,content,distribution and mechanical properties of the aggregate have an effect on the thermal damage of concrete at high temperature.The smaller the particle size of concrete aggregate and the higher the elastic modulus of aggregate,the greater the damage of concrete under high temperature.Due to the increasing thermal expansion difference between aggregate and cement mortar,and the deterioration of the cement mortar with the increasing temperature,the damage of concrete increased sharply after 500℃.
