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Dissertation
Effects of interlaminar stress gradients on free edge delamination in composite laminates
Doctor of Philosophy (Ph.D.), Drexel University
Jul 2003
DOI:
https://doi.org/10.17918/etd-222
Abstract
Edge delamination in fiber-reinforced composite laminates has been asignificant structural reliability concern. This particular laminate failure mode is caused by the high interlaminar stresses concentrated near the free edges. Due to the complex fiber/matrix microstructure of laminates, an accurate evaluation of these stresses and determining their exact role in laminate failure has been difficult. Traditional approaches to this problem have been based on the "effective-ply" theory in which the plies in the laminate are represented by an elastic homogenized medium. One result of this theory is the presence of stress singularities at bi- material interfaces near the free edge. These stress singularities are thought to be possible causes for edge lamination. In this research, two key issues in the free edge delamination problem are addressed: 1) to identify the physical sources for delamination, and 2) to establish a physical criterion for the onset and growth of delamination. For the first issue, a rigorous numerical stress ana lysis method is devised to accurately determine the full field stress solution, including the stress singularity. Key lamination parameters known to influence the delamination are included in the analysis. The analytical results show that delamination occurs at the largest sized interlaminar stress concentration zone, or zone of dominance (ZOD). The ZOD is shown to be more sensitive to the lamination parameters than the edge singularity is. For the second issue, the "effective flaw concept" is used to model delamination within the confines of linear elastic fracture mechanics. In this concept, an edge flaw is introduced as a starter crack inside the ZOD, and the growth of the flaw is simulated using finite element methods. Good agreement between the simulated results and experiments is achieved provided that the effective flaw is sufficiently large. However, because the crack growth simulation is performed on the "effectiveply", justification of the effective flaw at this point is heuristic. An effort is then made to recover the stress field at the fiber/matrix level near the free edges. Comparisons are made between the macro and micro-stress fields, in hope to provide a rational connection to the effective flaw of the macro-analysis.
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Details
- Title
- Effects of interlaminar stress gradients on free edge delamination in composite laminates
- Creators
- Simon Chung - DU
- Contributors
- Albert S. D. Wang (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Engineering (1970-2026); Mechanical Engineering (and Mechanics) [Historical]; Drexel University
- Other Identifier
- 222; 991014632828304721