Failure Initiation and Progression in Internally-Pressurized Elliptical Composite Cylinders

Abstract

The article addresses the influences of the noncircular geometry and material orthotropy on the predictions of initial material failure, and the extent and spatial distribution of subsequent failures, within the walls of internally-pressurized laminated composite cylinders with elliptical cross sections. The work is focused on the potential for leakage through the cylinder walls due to the accumulation of matrix cracking and fiber breakage within the layers. The predictions are based on numerical analyses using the finite-element code STAGS. Three different graphite-epoxy lamination sequences, a quasi-isotropic, a circumferentially stiff, and an axially stiff lamination sequence, are considered to investigate the effects of material orthotropy. Three different failure criteria and several material degradation schemes are considered to determine the sensitivity of the predictions to these steps in the analyses. It is shown that the spatial location of and pressure level to produce the initial failure, which occurs in the form of matrix cracking, is highly dependent on the lamination sequence. The pattern of failure accumulation due to increased pressure levels following initial failure is also dependent on the lamination sequence. No leakage is predicted for pressures to the level to produce first fiber failure. However, leakage is predicted for just a slight increase in pressure beyond that pressure, and the leakage pressure level and location are virtually independent of lamination sequence. The location of the first matrix failure and the spatial pattern of subsequent failures are not overly sensitive to the failure criterion used or the details of material degradation scheme employed. The pressure levels to produce the first matrix and first fiber failures are dependent on the failure criterion used.