Date

2021-8-13

Author

Hosseinpour Dashatan, Saeid

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In some applications of composite laminates, thickness variation is necessary to fulfill specific design requirements. One way of accomplishing the intentional thickness variation in composite structures is terminating some plies within a layup. Introducing ply drop-offs causes geometrical and material discontinuities, which lead to high localized stresses around drop-off locations. Despite all the progress made in damage analyses of tapered composite laminates, estimating their load-carrying capacity and strength remains a significant challenge.In this study, damage in tapered composite laminates under tensile loading is investigated. The cohesive zone method is used to simulate the delamination failure.For simulation of intralaminar damages, a 3-D continuum damage mechanics-based model with Hashin criteria for damage initiation and bi-linear damage propagation softening is employed. Finite element analyses are implemented in Abaqus/Explicit.Computational results are compared to an experimental study.No significant fiber or matrix damage is detected before and during delaminations. In addition to loads corresponding to delamination onset, both delamination locations and propagation characteristics are also utilized for making comparisons between computational results and experimental observations. Dynamic characteristic of delamination is employed to validate numerical analyses, further. For this purpose, the delamination predictions are compared to images taken by a high-speed camera. Results show that the ply drop-off type influences laminates’ strength and governs the delamination growth to be either dynamic (unstable) or static (stable). A good correlation between experimental and finite element results is observed in terms of delamination onset location, propagation patterns, and stability of delamination growth. For some specimen types, a modified cohesive strength pair is required to enhance these correlations. To further investigate the local delamination behavior around the resin pocket, combinations of unidirectional plies with 0 ◦ and 45◦ orientations for a laminate with a single, double, and three drop-offs are considered as well. In addition to delamination patterns, the load transfer mechanism, especially in the drop-off region, is also studied. A different delamination behavior is detected for each case, which shows the significance of the effect of orientation of each sublaminate on the load transfer mechanism. Also, results show that the progression of delaminations within various interfaces to be similar for both 2-D and 3-D models in laminates with 0 ◦ plies. However, there are some differences in laminates, including 0◦ . Also, the 3-D model clarifies the significance of ply orientation in delamination propagation patterns, which is not detectable in the 2-D model..

Subject Keywords

Tapered Laminate, Cohesive Zone Modeling, Delamination

URI

https://hdl.handle.net/11511/91705

Collections

Graduate School of Natural and Applied Sciences, Thesis