混凝土高压状态方程实验与数值模拟研究

Experiment and simulation on high-pressure equation of state for concrete

为研究高压下混凝土冲击压缩特性以及确定HJC本构模型状态方程参数,采用?58 mm火炮加载技术和多普勒探针系统(Doppler probe system,DPS)测速技术,对抗压强度为26.5 MPa(C25)和42.1 MPa(C40)的混凝土进行反向平板撞击实验研究与数值模拟。DPS探针记录TU1无氧铜靶自由面粒子速度历史,根据一维应变弹塑性波理论,计算撞击压力,拟合得到2~11 GPa高压条件下混凝土波速与粒子速度(u_s-u_p)、压力与体积应变(p-μ)关系。实验结果表明:高压条件下,混凝土波速-粒子速度呈线性关系;两种初始密度、孔隙率相近,强度不同的混凝土波速-粒子速度、压力-体积应变关系存在明显差异,相同压力下,混凝土试件强度越高,体积应变越小。基于实验结果,确定了两种强度混凝土HJC本构模型状态方程参数,利用LS-DYNA动力有限元分析软件对平板撞击实验进行了数值模拟,靶板自由面粒子速度历史与实验曲线吻合较好,仿真结果表明混凝土中冲击波的追赶卸载现象仅存在于低速撞击条件下。

To study the dynamic compression characteristics of concrete under high hydrostatic pressure and to determine the equation of state parameters of the HJC constitutive model, inverse flyer-impact tests and numerical simulation analysis were conducted with two kinds of concrete flyers of which the compressive strengths were 26.5 MPa and 42.1 MPa, respectively.The concrete flyers were launched by φ58 mm gun against TU1 copper targets. The particle velocity histories of the TU1 copper target free surface were measured by DPS(Doppler probe system). Based on the one-dimensional strain shock wave theory, the impact pressure was calculated. The relationships of shock velocity vs. particle velocity and pressure vs. volume strain in the pressure range of 2-11 GPa were fitted. The results show that the relationship between shock velocity and particle velocity of concrete is linear. The relationships of shock velocity vs. particle velocity and pressure vs. volume strain for concretes with similar initial density and porosity but different compressive strengths are obviously different. Under the same pressure, the higher the compressive strength of concrete, the smaller the volume strain is. According to the test results, the equation of state parameters of the HJC constitutive model were determined and the plate-impact tests were simulated by LSDYNA. The simulated particle velocity histories of the TU1 target free surface were in good agreement with the experimental results. The simulation results show that the phenomenon of chasing and unloading of shock waves in concrete only exists under low velocity impact conditions.