Compression of thick laminated composite beams with initial impact-like damage
Breivik, Nicole L
MetadataShow full item record
While the study of compression after impact of laminated composites has been under consideration for many years. the complexity of the damage initiated by low velocity impact has not lent itself to simple predictive models for compression strength. The damage modes due to non-penetrating. low velocity impact by large diameter objects can be simulated using quasistatic three-point bending. The resulting damage modes are less coupled and more easily characterized than actual impact damage modes. This study includes the compression testing of specimens with well documented initial damage states obtained from three-point bend testing. Compression strengths and failure modes were obtained for quasi-isotropic stacking sequences from 0.24 t01.1 inches 'thick with both grouped and interspersed ply stacking. Initial damage prior to compression testing was divided into four classifications based on the type. extent, and location of the damage. These classifications are multiple through-thickness delaminations, isolated delaminations. damage near the surface. and matrix cracks. Specimens from each classification were compared to specimens tested without initial damage in order to determine the effects of the initial damage on the final compression strength and failure modes. A finite element analysis was used to aid in the understanding and explanation of the experimental results. It was found that specimens with multiple through-thickness delaminations experienced the greatest reduction in compression strength, from 50 to 75% below the strength of undamaged specimens. All the sublaminates formed by the delaminations failed at the same time. Individual sublaminate buckling was observed for isolated delaminations near 'the surface of the laminate. Delaminations far from the specimen surface had little effect on the final compression strength. Damage occurring in the outside 00 plies caused a 10 to 200/0 strength reduction according to both analytical and experimental results. The effects of increased interlaminar stresses near the specimen edges caused a reduction in undamaged strength of [05/455/-455/905]55 specimens, while having little effect on the [Osl60sl-605]75 specimens.
- Masters Theses