Experimental Investigation of the Failure of a Stepped Composite Plate

摘要

The progression of damage in a stepped composite plate has been investigated experimentally. This study is intended to provide insight into the failure behavior of co-cured, stringer-reinforced composite plates and shells. The specimens were constructed of four different lay-ups of carbon-fiber- reinforced epoxy and were subjected to various combinations of moment, tension, and shear static loadings. The primary means of damage observation was in situ microscopic inspection of the specimen edges. These observations were supplemented by penetrant-dye inspection, microscopic inspection of the plate face, and ultrasonic C-scanning of specimens which were unloaded prior to catastrophic failure. In addition to providing detailed descriptions of the damage development, this thesis presents hypotheses which attempt to explain the mechanisms involved in the failure process. The immediate goal of this work was to gather the experimental evidence needed to evaluate a recently proposed failure criterion. The criterion attempts to predict failure for an arbitrary lay-up by studying the behavior of the computed stresses within an extremely small vicinity of the singularity. The tests described in this thesis revealed that damage initiation does not always occur on the plate-stringer interface, as assumed in the failure criterion. Furthermore, it was discovered that in some lay-ups, damage initiates at a distance of over one lamina thickness away from the singularity. This fact makes it impossible to predict failure accurately with any criterion which is based solely on a computed stress singularity.