Three-dimensional transient stress wave propagation in a plate with application to compressor valve failure analysis.

摘要

Transient stress wave propagations in a valve due to impact and stress wave reflections from its free boundaries account for the fatigue failure near the compressor valve tip. The goals of this research project are to identify the characteristics of the stress wave propagation and reflections in a valve plate in order to obtain some fundamental understanding of valve failures due to impact.; The analytical solution to this problem is based on the method of transformations and the Cagniard method. A Green's function is formulated for a vertical point load on the elastic half-space (Lamb's problem) since the mathematical model of the half-space is easier to handle than that of the infinite plate. A numerical solution is obtained by evaluating the complex integral equations of the Green's function. A simple and efficient convolution scheme is developed for numerically extending this point solution to the problem of impact pressure distribution. A superposition algorithm is developed for the purpose of obtaining the displacements and stresses of the plate interior by utilizing the half-space solutions. The superposition method consists of two steps to satisfy the free boundary conditions of the plate, which is a unique feature of the algorithm. Several numerical results are presented for the half-space and infinite plate.; The three dimensional stress wave solution is compared with the one dimensional solution for certain limiting cases. The agreement of the two solutions is quite excellent.; The stress reversal phenomenon at the free boundary of the plate and the stress fluctuation near the S wave front indicate that the plate may fail earlier than expected by using conventional S-N curves. Thus, it is suggested that new S-N curves which incorporate the impact loading be constructed for a better compressor valve life prediction.