| Popis: |
In this study, two experimental approaches are used to understand fracture mechanisms that govern transverse tensile failure of fiber-reinforced polymer composites at the microscale. These observations are used to directly measure, and indirectly estimate, the magnitude and scatter of the transverse tensile strength, YT, and the associated effective flaw size, a0. To this end, static three-point bend tests are performed on pristine and notched 90° unidirectional IM7/8552 carbon-epoxy samples. In the pristine specimen study, tensile microcracks are observed to initiate well before the ultimate failure load used to compute YT is reached. In the notched specimen study, a comparison is made between experimentally measured strengths with known notch lengths and a linear elastic fracture mechanics solution. The fracture mechanics solution significantly over-predicts the apparent YT for notch lengths less than a ply thickness, suggesting that this approach may not be appropriate for estimation of transverse tensile strength at the microscale. The observations made in this study suggest that YT may not be a true material property, but rather, a structural property dependent on specimen geometry and microstructural variability. |
