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.

A nonlinear rate-dependent model for predicting the depth of penetration in ultra-high performance fiber reinforced concrete (UHPFRC)

“…This trend is theoretically reasonable because the static resistance is smaller than its dynamic counterpart, attributing to a larger comminuted area at _ r c ¼ 0. However, this differs with the actual damage distribution in an experimental study [27] that r p is observed to be reduced at the ballistic end. The experimental observation is reported to be caused by the vanished concrete tangential inertial constraints at the end of the penetration process [27].…”

“…However, this differs with the actual damage distribution in an experimental study [27] that r p is observed to be reduced at the ballistic end. The experimental observation is reported to be caused by the vanished concrete tangential inertial constraints at the end of the penetration process [27]. Nevertheless, since the target inertia term in Eq.…”

“…Similarly, the location of the cracked-comminuted regions interface, viz. r p , can be determined by the boundary condition that the radial stress reaches the dynamic compressive strength σ c,d at r p : σ rðr¼rpÞ ¼ σ c;dðr¼rpÞ (27) The dynamic compressive strength σ c,d (r ¼ rp) can be obtained by σ c;dðr¼rpÞ ¼ DIF cðr¼rpÞ � σ c;s (28) where DIF c (r ¼ rp) is calculated by Eq. (5) with…”

“…Impact cratering, penetration tunneling with spherical radiation crack and the rear surface plugging or spalling are the dominant phenomena in a cementitious target under ballistic impacts [8,26,27]. The related mechanisms are quite complex, including wave propagation and reflection, concrete cracking and comminution, and phase change in the target [23].…”

“…The cavity expansion theory is usually used for the tunneling stage, the main characteristic of which can be described by the theory. For example, the concrete spherical radiation cracking and material comminution, which are observed in experimental and numerical studies [27], are reflected by the theoretical response regions surrounding the cavity and described by the material constitutive relations or the yield criteria. Applying the cavity expansion theory, the penetration of the projectile in a target at the penetration tunneling stage is modeled as the expansion of a spherical or cylindrical cavity at a constant velocity.…”