In order to clarify the fatigue damage evolution of concrete exposed to flexural fatigue loads,ultrasonic pulse velocity(UPV),impact-echo technology and surface electrical resistance(SR) method were used.Damage variab...In order to clarify the fatigue damage evolution of concrete exposed to flexural fatigue loads,ultrasonic pulse velocity(UPV),impact-echo technology and surface electrical resistance(SR) method were used.Damage variable based on the change of velocity of ultrasonic pulse(Du) and impact elastic wave(Di)were defined according to the classical damage theory.The influences of stress level,loading frequency and concrete strength on damage variable were measured.The experimental results show that Du and Di both present a three-stages trend for concrete exposed to fatigue loads.Since impact elastic wave is more sensitive to the microstructure damage in stage Ⅲ,the critical damage variable,i e,the damage variable before the final fracture of concrete of Di is slightly higher than that of Du.Meanwhile,the evolution of SR of concrete exposed to fatigue loads were analyzed and the relationship between SR and Du,SR and Di of concrete exposed to fatigue loads were established.It is found that the SR of concrete was decreased with the increasing fatigue cycles,indicating that surface electrical resistance method can also be applied to describe the damage of ballastless track concrete exposed to fatigue loads.展开更多
Investigation was to study the influence of pulse-impact on microstructure of Liquid-Phase-Pulse-Impact Diffusion Welding (LPPIDW) welded joints of aluminum matrix composite SiCp/A356, SiCp/6061Al, Al2O3p/6061Al. Resu...Investigation was to study the influence of pulse-impact on microstructure of Liquid-Phase-Pulse-Impact Diffusion Welding (LPPIDW) welded joints of aluminum matrix composite SiCp/A356, SiCp/6061Al, Al2O3p/6061Al. Results showed that under the effect of pulse-impact: 1) the interface state between reinforcement particle (SiC, Al2O3) and matrix was prominently;2) the initial pernicious contact-state of reinforcement particles was changed from reinforcement (SiC, Al2O3)/reinforcement (SiC, Al2O3) to reinforcement (SiC, Al2O3)/matrix/ reinforcement (SiC, Al2O3);3) the density of dislocation in the matrix neighboring to and away from the interface in the matrix was higher than its parent composite;and 4) the intensively mutual entwisting of dislocation was occurred. Studies illustrated that: 1) deformation was mainly occurred in the matrix grain;and 2) under the effect of pulse-impact, the matrices around reinforcement (SiC, Al2O3) particles engendered intensive aberration offered a high density nucleus area for matrix crystal, which was in favor of forming nano-grains and improved the properties of the successfully welded composite joints.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.U1934206,52208299,and 52108260)the 2021 Tencent XPLORER PRIZE。
文摘In order to clarify the fatigue damage evolution of concrete exposed to flexural fatigue loads,ultrasonic pulse velocity(UPV),impact-echo technology and surface electrical resistance(SR) method were used.Damage variable based on the change of velocity of ultrasonic pulse(Du) and impact elastic wave(Di)were defined according to the classical damage theory.The influences of stress level,loading frequency and concrete strength on damage variable were measured.The experimental results show that Du and Di both present a three-stages trend for concrete exposed to fatigue loads.Since impact elastic wave is more sensitive to the microstructure damage in stage Ⅲ,the critical damage variable,i e,the damage variable before the final fracture of concrete of Di is slightly higher than that of Du.Meanwhile,the evolution of SR of concrete exposed to fatigue loads were analyzed and the relationship between SR and Du,SR and Di of concrete exposed to fatigue loads were established.It is found that the SR of concrete was decreased with the increasing fatigue cycles,indicating that surface electrical resistance method can also be applied to describe the damage of ballastless track concrete exposed to fatigue loads.
文摘Investigation was to study the influence of pulse-impact on microstructure of Liquid-Phase-Pulse-Impact Diffusion Welding (LPPIDW) welded joints of aluminum matrix composite SiCp/A356, SiCp/6061Al, Al2O3p/6061Al. Results showed that under the effect of pulse-impact: 1) the interface state between reinforcement particle (SiC, Al2O3) and matrix was prominently;2) the initial pernicious contact-state of reinforcement particles was changed from reinforcement (SiC, Al2O3)/reinforcement (SiC, Al2O3) to reinforcement (SiC, Al2O3)/matrix/ reinforcement (SiC, Al2O3);3) the density of dislocation in the matrix neighboring to and away from the interface in the matrix was higher than its parent composite;and 4) the intensively mutual entwisting of dislocation was occurred. Studies illustrated that: 1) deformation was mainly occurred in the matrix grain;and 2) under the effect of pulse-impact, the matrices around reinforcement (SiC, Al2O3) particles engendered intensive aberration offered a high density nucleus area for matrix crystal, which was in favor of forming nano-grains and improved the properties of the successfully welded composite joints.
