Response and Failure Characteristics of Internally Pressurized Elliptical Composite Cylinders

Abstract

The characteristics of the response of internally pressurized thin-walled elliptical composite cylinders, including failure, are discussed. The influence of the elliptical geometry on response is illustrated by comparison with a circular cylinder. It is shown that with internal pressure elliptical cylinders tend to become more circular by exhibiting inward normal displacements at some circumferential locations and by the existence of circumferential displacements. The influence of material orthotropy is illustrated by considering axially stiff, circumferentially stiff, and quasi-isotropic laminates. The results show that orthotropy can he used to counter the influence of the circumferentially varying curvature by producing circumferential strains at the midcylinder axial location of a circumferentially stiff cylinder that are almost independent of the circumferential coordinate, much like the axisymmetric response of a circular cylinder. The influence of geometric nonlinearities is studied by inclusion of the von Karman terms in the strain-displacement relations, and it is shown that one of the primary effects is flattening of the ellipse in the regions near the ends of the minor diameter. Because of varying curvature in the circumferential direction, there can be, effectively, a stress concentration at certain circumferential locations, which are sites of failure initiation, the exact location depending on material orthoropy. To study failure initiation, two failure criteria are considered: the interactive Hashin criterion and the noninteractive maximum stress criterion. These criteria are used to compute the pressures to cause first matrix cracking and first fiber failure. It is demonstrated that the predictions of the two criteria are not that different, and the pressure to cause first fiber failure is about twice the pressure to cause first matrix failure. Additionally, it is shown that matrix cracking begins in the circumferentially stiff cylinder at lower pressures than in the axially stiff and quasi-isotropic cylinders, and the location of failure is different.