Local Effect on Concrete Containment Due to Pipe Impact - Coupled and Decoupled Analysis

Abstract

This paper first illustrates an analysis of a coupled system comprised of a ruptured high energy system pipe whipping onto a concrete containment wall. using the finite difference computer code PISCES. The results indicate that because of pipe's softness a significant amount of the original kinetic energy has been transformed into strain energy and retained within the pipe Itself. Only a limited concrete area in the vicinity of the Impact was crushed. In this area. elastic unloading occurred due to buckling of the pipe and the subsequent shift of the contact position. A major crack originated from the contact point at the front face of the concrete wall and gradually propagated at approximately a 45 degree angle toward the back face was developed, resembling the sheared plug often seen in experiments. Taking the time derivative of the pipe momentum resulted in the time history of the pipe-wall interaction force. This force was then applied to the second analysis of the decoupled system where only the concrete wall was modelled. Comparison of the coupled and the decoupled analyses reveals that the momentum transfer is quite compatible; whereas, the energy absorbed by the wall in the decoupled model is less than that in the coupled model. Furthermore, the decoupled analysis demonstrated a similar back face cracking due to the reflected tensile shock wave: however, the development of the 45 degree major crack was not as pronounced as in the coupled model. It is also noted that the coupled model induced a higher stress concentration at an earlier stage of impact. The stress distribution became more compatible between the two cases at later stage. These deviations are primary due to the difference in contact area between the two models. Hence, the simulation of the missile/target contact as realistically as possible is very important in a decoupled analysis.