混凝土冲击破坏动态力学及能量特性分析

动强度和能量耗散规律是研究混凝土动力特性的主要内容。为探究混凝土在冲击荷载作用下的动态力学、变形以及能量演化特征,利用直径为100 mm的霍普金森杆装置对骨料率为0、32%、37%和42%的混凝土试样,分别进行了冲击速度为5、6、7 m/s的冲击压缩试验。探讨了冲击速度和骨料率对试样变形、动强度以及分形维数的影响,建立了动强度关于冲击速度和骨料率的表达式,并对试样吸收能和裂纹表面能之间的关系进行了对比分析。结果表明:混凝土试样破坏时出现了变形滞后现象,破坏形式主要以劈裂拉伸破坏为主;动强度随冲击速度、骨料率的增大而增大,用所建动强度公式可以较好地预估混凝土动强度;混凝土破坏碎块分形维数、吸收能和裂纹表面能均随冲击速度的增大而增大,随骨料率的增大而减小,且吸收能始终高于裂纹表面能,当骨料率为37%时,吸收能转化率最高,约91%转化为裂纹表面能。

Analysis of dynamic mechanics and energy characteristics of concrete impact failure

To investigate the mechanics, deformation, and energy evolution characteristics of concrete under dynamic loading, impact compression tests at impact velocities of 5, 6, and 7 m/s, and splitting tensile tests at 4 m/s were carried out on concrete specimens with aggregate volume rates of 0, 32%, 37%, and 42% using a 100 mm diameter split Hopkinson pressure bar (SHPB) device. The failure process of concrete specimens was acquired by a high-speed camera, and the damaged concrete fragments were collected and sorted. Furthermore, the fractal dimension of fragments was calculated by dividing the fragments into different grades. The stress and strain of the concrete specimen were obtained through the corresponding calculation formulas. The relationships between specimen deformation, dynamic strength, and fractal dimension with impact velocity and aggregate rate were studied, and the expression for dynamic strength with respect to impact velocity and aggregate rate was developed. In addition, the fractal dimension was used to characterize the surface roughness of the concrete fragments, and the function expression between crack surface energy and fractal dimension was established. The relationship between sample absorption energy and crack surface energy was analyzed and compared. The results show that deformation hysteresis occurs when concrete specimens are destroyed and the failure is mainly in the form of splitting tensile damage. The dynamic strength increases with the increase of impact velocity and aggregate ratio, the dynamic strength of concrete can be better predicted by using the proposed dynamic strength formula. The fractal dimension of concrete breaking fragments, absorbed energy and crack surface energy all increase with the increase of impact velocity and decrease with the increase of aggregate rate, and the absorbed energy is always higher than the crack surface energy. The highest conversion rate of absorbed energy is achieved when the aggregate rate is 37%, with approximately 91% converts to crack surface energy.