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Study of the Progressive Failure of Composites under Axial Loading with Varying Strain Rates
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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This study investigated the progressive damagefailure of composite panels with open circular holes under progressive axial loading. A series of experiments was carried out to determine the failure in laminated specimens with and without circular holes under tensile and compressive loads, respectively. Different strain rate loading was applied to observe the rate effect on the damage initiation and propagation. Both uniform and non-uniform strain rate loads were applied to the composite specimens in order to understand the varying strain rate effect on the damage initiation and growth. With an increasing load, matrix cracking, surrounded by delamination occurred and lead to fiber breaking at the edge of the hole of high stressstrain concentration. When damage reached a critical state, the laminate failed catastrophically. By utilizing the optical microscope, the matrix cracking and fiber breaking leading to fracture was observed. The fracture strength and strain of composites were varied depending on the applied strain rate loading. When the strain rate was changed halfway from the first rate to the second rate, the failure strength was relatively close to that at the constant second strain rate. However, fracture strain did not match with that of the second strain rate. Finally, the experimental results from the open hole tension was compared against Whitney-Nuiser Failure Prediction Theory, namely the Point Stress Criterion and Average Stress Criterion.
APPROVED FOR PUBLIC RELEASE