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.

摘要 弹体侵彻混凝土结构后，结构内部会产生大量裂缝。研究裂缝分布与扩展过程，是开展损伤评估、结构修复以及深入探究高动态断裂机理的基础。本文针对深侵彻靶体开展了受损混凝土的绳锯切割、X射线计算机断层扫描（X-ray computed tomography, X-CT）以及力学性能测试。基于靶体径向岩心样品的X-CT图像与受损混凝土的力学性能，本文将靶体内的裂缝分布划分为塑性损伤区与脆性损伤区，且微裂缝仅存在于塑性损伤区内。通过靶体轴向岩心样品的X-CT图像，本文获取了三维裂缝的初始萌生扩展过程：纯砂浆靶体中的裂缝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缝。通过靶体截面分析得到了裂缝的扩展路径：纯砂浆靶体中的切向裂缝发生弯折，而含粗骨料靶体中的切向裂缝则相对平直。本文建立了裂缝扩展模型，推导得到了切向裂缝计算公式与裂缝扩展速率。