Compression Behavior of Single Carbon Filaments Embedded in an Epoxy Polymer

The compression loading of single carbon filaments embedded in an epoxy polymer was investigated to determine the micro-mechanisms of failure. The fibers were observed using transmission polarized light microscopy. Failure invariably occurred by transverse shear with no evidence of microbuckling. A distinctive stress birefringence pattern was observed around the fibers which suggests a systematic variation in fiber modulus but with dimensions much larger than the crystallographic dimensions character istic of carbon fibers. The specimens were etched with acid to reveal the regions of fiber fracture. Although a variety of fracture morphologies were observed, they are all believed to be post-failure damage subsequent to the initial shear failure. The acid etching also revealed etch patterns in the matrix near the fiber/matrix boundary which are probably the result of chemical inhomogeneities in the interphase region.