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
The elastoplastic mechanical behaviour of an epoxy-impregnated REBCO pancake winding under cryogenics and high magnetic field is investigated in the frame of finite element(FE)modelling.A two-dimensional axisymmetric ...The elastoplastic mechanical behaviour of an epoxy-impregnated REBCO pancake winding under cryogenics and high magnetic field is investigated in the frame of finite element(FE)modelling.A two-dimensional axisymmetric electromagnetic-thermal-structure multi-physics multi-layer FE model with main layers of the coated conductor and insulation materials is developed.The radial stress and hoop stress on each constituent layer induced by thermal mismatch stress during cooling are investigated.The mechanical behaviour of each constituent material is also analysed by considering the thermal mismatch stress and electromagnetic force under 20 T background field.The results show that discrete stresses appear in all the constituent materials indicating that the multi-layer winding model containing the main constituent materials is necessary for the accurate stress analysis in an epoxy-impregnated REBCO winding.The stress of each constituent material induced by thermal mismatch during cooling process are too high to be ignored in the subsequent electromagnetic structure analysis.The mechanical-magnetic coupling analyses show that the stresses of all the constituent materials increase with the transport current.The plastic failure mainly induced by hoop stress successively occurs on copper stabilizer and Hastelloy substrate of the innermost turn,and the plastic region propagates from the inner turns to the outer turns with the increase of transport current.The failure of the superconducting layer occurs before the yield in Hastelloy due to the direct action of Lorentz force on the superconducting layers.The transverse tensile stress increases with the increasing transport current,indicating that the risk of transverse delamination failure increases with the increase of transport current.The mechanical failure modes including delamination within the conductor,plastic deformation in substrate and crack in superconducting layer should be seriously considered.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
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
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the National Natural Science Foundation of China(11902129,11932008)the China Postdoctoral Science Foundation(2019T120963)the Fundamental Research Funds for the Central Universities(lzujbky-2020-pd03,lzujbky-2021-kb06).
文摘The elastoplastic mechanical behaviour of an epoxy-impregnated REBCO pancake winding under cryogenics and high magnetic field is investigated in the frame of finite element(FE)modelling.A two-dimensional axisymmetric electromagnetic-thermal-structure multi-physics multi-layer FE model with main layers of the coated conductor and insulation materials is developed.The radial stress and hoop stress on each constituent layer induced by thermal mismatch stress during cooling are investigated.The mechanical behaviour of each constituent material is also analysed by considering the thermal mismatch stress and electromagnetic force under 20 T background field.The results show that discrete stresses appear in all the constituent materials indicating that the multi-layer winding model containing the main constituent materials is necessary for the accurate stress analysis in an epoxy-impregnated REBCO winding.The stress of each constituent material induced by thermal mismatch during cooling process are too high to be ignored in the subsequent electromagnetic structure analysis.The mechanical-magnetic coupling analyses show that the stresses of all the constituent materials increase with the transport current.The plastic failure mainly induced by hoop stress successively occurs on copper stabilizer and Hastelloy substrate of the innermost turn,and the plastic region propagates from the inner turns to the outer turns with the increase of transport current.The failure of the superconducting layer occurs before the yield in Hastelloy due to the direct action of Lorentz force on the superconducting layers.The transverse tensile stress increases with the increasing transport current,indicating that the risk of transverse delamination failure increases with the increase of transport current.The mechanical failure modes including delamination within the conductor,plastic deformation in substrate and crack in superconducting layer should be seriously considered.
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℃.
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.