Fractography of Mixed Mode I - II Failure in Graphite/Epoxy and Graphite/Thermoplastic Unidirectional Composites.
Final rept. Feb-Aug 84,
AIR FORCE WRIGHT AERONAUTICAL LABS WRIGHT-PATTERSON AFB OH
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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 T3001034C graphiteepoxy 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
- Laminates and Composite Materials