Behavior of a Composite Material in Compression. A Trident Scholar Project Report No. 163.

摘要

In the study of unidirectional composite materials, the fiber-matrix support mechanism is well understood for the case of a tensile load. Under a purely compressive load, however, the behavior of the fibers in the composite is much less well understood. At present, a widely discussed model of the behavior of the composite is that, under an axial compressive laod, the fibers will deform slightly into the shape of a sine wave of very small amplitude. This model has been termed 'microbuckling'. The objective of the project was to observe and to quantify this phenomenon of microbuckling in a graphite-epoxy composite. It was found that in properly prepared specimens the microbuckling and its associated wavelength were directly observable. From measurements made of the strains in the composite specimen using both surface-mounted resistive strain guages and electrical resistance of the graphite fibers, the amplitude of the observed microbuckling was calculated. As a significant consequence of the this determination of the amplitude and wavelength of the microbuckling, it was learned that the fibers in a composite structure under a compressive load are actually subject to two types of strain. The first is the compressive strain that is read by the usual, resistive strain guage and the other, a strain at the spatial frequency of the microbuckling, is alternately tension and compression. (AW)