Experimental Study On Stress - Related Dynamic Damage Evolution Of Concrete

In this paper, Split Hopkinson Pressure Bar (SHPB) and One - Stage Light Gas Gun are used for study the dynamic damage evolution law of concrete under the different stress states. Impact compression experiments of concrete specimens under one-dimensional stress state with lower speed are carried on the SHPB, including the impact tests of one time under the different pressure and the multi-times (for one specimen) under the same pressure. The experimental results show that the mechanical behaviors of concrete are obviously sensitive to strain rates. The apparent stiffness and the maximum stress that can be achieved both increase with strain rate. The failure strain decreases with increase of cumulative damage. The multi-impact experiments show that the damage accumulation and weakening of properties significantly increase with the impact times. Breaking will be reached by accumulated damage at finally.The dynamic behaviors of concrete are studied under quasi-one-dimensional strain state with high - speed impact by use of One - Stage Light Gas Gun and dynamic testing technique of manganin stress gauge. The voltage-time curves in direction of shock wave propagation are measured. The stress-time curve and the stress-strain curve are resulted by means of analysis the datum. Based on the analysis rule of stress wave propagation, the maximum strain rate of the sample and the propagation rule of pressure decay are obtained. Results show that the peak value of shock wave is rapidly decreases with increases of the propagation time and distance. The concrete has obviously stress relaxation characteristics and dissipation characteristics of viscous material. Results of different impact velocity testing show that the peak value of stress increases with the impact velocity. The overall of stress - strain curve has the phenomenon of hysteretic behavior, the maximum stress increases with the increase of strain rate. The failure of concrete was mainly due to the damage evolution of inherent micro holes and micro cracks of the material. When the impact stress reached to the value of threshold stress of micro - crack nucleation, the micro - crack grown up, micro-hole collapsed, finally, the concrete broken under the development of the damage.LS-DYNA software is used for the numerical simulation in shock compression experiment of One - Stage Light Gas Gun and SHPB. The simulation result is in good agreement with the experimental ones. Numerical results of concrete under different stress states are useful for study dynamic damage evolution and other mechanical behaviors.The project work was a foundation to reveal more about the law of the dynamic damage evolution and damage - modified constitutive relation of concrete.