Numerical Simulation Of Dynamic Mechanical Behavior Of Concrete With Two-dimensional Random Distribution Of Coarse Aggregate

Concrete is regarded as a non-homogeneous composite material of cement mortar and coarse aggregate. Due to its raw stuff locally and low cost, concrete is used widely in various civil and military facilities. These concrete structure in its working process in addition to under normal quasi static loading, often have to endure all kinds of rapid changing collision and impact dynamic load. Concrete subjected to impact loading exhibits different mechanical properties under static loading, in order to better design and analysis of the concrete structure, it is necessary to do the further research about the dynamic mechanical properties of concrete materials. There are following works of this paper:(1) The quasi-static uni-axial compression and dynamic impact compression experiments of concrete and cement mortar are carried out by universal testing machine and SHPB experimental apparatus, respectively. From experimental results we can obtain the quasi-static stress-strain curves of concrete and cement mortar, which are divided into the four stages:the first is initial compaction stage, the second is linear elastic stage, the third is nonlinear elastic stage, the forth is the peak failure stage. The peak stress of concrete and cement mortar increases with the enhancement of impact velocity, so concrete and cement mortar is rate-sensitivity materials; at the same impact velocity, the peak stress of concrete is higher than cement mortar, the maximum strain of concrete is lower than cement mortar. Comparing between specimens of concrete an cement mortar after experiments indicates that at impact velocity of 5m/s, they keep perfectly, no obvious crack on their surface; with the impact velocity increasing, the damage of them is more serious, the number of damage pieces is more; at the same impact velocity, the number of damage pieces of concrete is more than cement mortar.(2)On the basis of Fuller gradation curve and Walaraven plane conversion formula, a plane circular aggregate single grading random distribution program of concrete is designed to simulate the dynamic response of concrete in the different impact velocity. It analyzed that impact velocity, specimen dimension, size and distribution of coarse aggregate and volume fraction of aggregate influences on the dynamic mechanical properties of concrete. Numerical simulation shows that the peak stress of concrete increases with the enhancement of impact velocity, so concrete is rate-sensitivity. The peak stress of concrete decreases with the enhancement of specimen dimension, so size effect of concrete is obvious. The peak stress of concrete increases firstly, then declines with the volume fraction of coarse aggregate increasing, the peak stress of concrete is maximum value when the volume fraction of aggregate is equal to 40%. With the increase of the minimum diameter of coarse aggregate, the peak stress of concrete decreases. However, the peak stress of concrete increases firstly, then declines with the increase of the maximum diameter of coarse aggregate.(3)On the basis of Fuller gradation curve and Walaraven plane conversion formula, a plane circular aggregate two grading random distribution program of concrete is designed to simulate the dynamic response of concrete in the different impact velocity. It analyzed that specimen dimension and volume fraction of aggregate influences on the dynamic mechanical properties of concrete. Numerical simulation shows that the peak stress of concrete decreases with the enhancement of specimen(4)dimension, so size effect of concrete is obvious. The peak stress of concrete increases firstly, then declines with the increase of the middle diameter of coarse aggregate, the peak stress of concrete is maximum value when the middle diameter of aggregate is 15mm. The peak stress of concrete declines with the increase of the maximum diameter of coarse aggregate, the peak stress of concrete is maximum value when the maximum diameter of aggregate is 20mm.The peak stress of concrete increases firstly, then declines with the volume fraction of coarse aggregate increasing, the peak stress of concrete is maximum value when the volume fraction of aggregate is equal to 40%.