Fractography of Mixed Mode I - II Failure in Graphite/Epoxy and Graphite/Thermoplastic Unidirectional Composites

摘要

The notched off-axis tensile test and the notched three rail shear test were used to produce states of in-plane loading varying from pure Mode I (crack opening) to Mode II (forward shearing). The two material systems tested were Fiberite T300/1034C graphite/epoxy and Imperial Chemical Industries graphite reinforced polyetheretherketone thermoplastic composite (APC-1 PEEK). Using a scanning electron microscope, a detailed examination of the resulting fracture surfaces was conducted. Results at magnification levels of 100X and 800X are presented. Very distinct changes can be observed in each material as the load ratio changes. In addition, for a fixed mode load ratio, large differences can be seen in the matrix deformation patterns between the two material systems. Of particular interest are ductile spike formations seen in the highly shear loaded PEEK specimens. These observations provide some insight as to the increased toughness seen at higher Mode II ratios, and the increased toughness seen in the thermoplastic system. (Author)