Damage Evolution Of Concrete Affected By Stress Triaxiality And Strain Rate

In this paper, Φ74Split Hopkinson Pressure Bar (Φ74SHPB) was used to study the dynamicdamage evolution law of concrete under one-dimensional stress state and tri-axial stress state. TheSHPB experimental results show that the mechanical property of concrete has obvious strain ratesensitivity. As the strain rate increases, the performance stiffness increases, when reaching to thesame strain the stress increases, the maximum stress increases, and the failure strain increases bythe damage.Under tri-axial stress state, ultrasonic velocity of concrete specimen mostly decreases withimpact increasing. However, there is a phenomenon in the process that ultrasonic velocity increasesinstead in some time. Because the existence of two opposite effects under three-dimensional stressstate: the micro-crack damaging effect and the micro-holes compaction effect. Micro-crackgrowing, cumulative and developed until to failure; the original micro-holes crushed, while micro-holes are compacted. The micro-crack damaging effect makes velocity decrease; while the micro-holes compaction effect makes it increase. When the latter plays a significant effect, the velocitywill increase after impact on concrete; on the contrary, the velocity decreases. After several timesimpact loading for the confining specimen encircled by a thin steel sleeve, the stress triaxialitydegree of N remains a constant. The internal damage is accumulated and developed until to failureand the crack on the surface of specimen can be seen. For the thick-walled steel sleeve, the stresstriaxiality degree of N is increasing gradually. The damage variable D is corresponding to thedamage of concrete specimen.Furthermore, we estimated the confining pressure of steel sleeve. In calculate, we found that Eandvin the plane stress solution were separately changed to E/(1-v~2)and v/(1-v). It was theplane strain solution.LS-DYNA software was used to the simulation in impact experiments under tri-axial stressstate. The simulation results with the measured curve of strain-time agree rather well and peakvalue is approaching. Numerical simulation can show the phenomena it is difficult to observe, suchas the cross section of incident bar, two end face of specimen and the stress distribution of steelsleeve. That can improve the experiment in the later.