Study of cracks in concrete target under deep penetration by a projectile

Abstract A large number of cracks occur in concrete structure after projectile penetration. The study of crack distribution and propagation process is the basis of damage assessment, structural repair and high dynamic fracture mechanism. In this paper, wire saw cutting, X-ray computed tomography (X-CT) and mechanical property testing of damaged concrete were carried out on deep penetration targets. According to X-CT images of radial core samples in target and the mechanical properties of damaged concrete, the crack distribution in the target was divided into a plastic damage zone and a brittle damage zone, and the microcracks only existed in the plastic damage zone. The initial growth process of three-dimensional cracks was obtained by X-CT images of axial core samples in target, that is, the cracks in the pure mortar target gradually developed from the radial direction to the tangential direction, and the target containing coarse aggregate directly formed tangential cracks. The propagation progress of cracks was obtained through the target section, that is, the tangential cracks bent in the pure mortar target, and were relatively straight in the target containing coarse aggregate. A crack propagation model was established, and the tangential crack formula and the crack propagation velocity were obtained.弹体侵彻后混凝土结构会产生大量裂纹。对裂纹分布与扩展过程的研究是损伤评估、结构修复及高动态断裂机制研究的基础。本文针对深侵彻靶体，开展了绳锯切割、X射线计算机断层扫描（X-ray computed tomography, X-CT）以及受损混凝土力学性能测试工作。基于靶体径向岩心试样的X-CT图像与受损混凝土的力学性能，将靶体内的裂纹分布划分为塑性损伤区与脆性损伤区，且微裂纹仅存在于塑性损伤区内。通过靶体轴向岩心试样的X-CT图像，得到了三维裂纹的初始萌生扩展过程：纯砂浆靶体中的裂纹由径向逐渐向切向发展，而含粗骨料靶体则直接形成切向裂纹。通过靶体截面得到了裂纹的扩展进程：纯砂浆靶体中的切向裂纹发生弯折，而含粗骨料靶体中的切向裂纹则相对平直。本文建立了裂纹扩展模型，推导得到了切向裂纹公式与裂纹扩展速度。