A theory for predicting and minimizing the effects of matrix degradation on the thermomechanical properties of general laminates. Ph.D. Thesis
The effects of matrix degradation on the properties of general composite laminates are investigated. The changes in matrix properties due to hygrothermal environment and the presence of microcracking are considered. The matrix-dominated properties of constituent laminate plies are affected by these changes. Laminates dependent on matrix behavior, such as those with coupling, will exhibit the largest variation due to these effects. Models are developed for the effects on ply properties. Hygrothermally-induced effects are modeled as variations in shear modulus. A model for microcracking is developed which considers variations in all ply properties due to microcracking. Both of these models are easily incorporated into laminate analyses based on classical laminated plate theory. A model for predicting the potential distributions of crack density through the laminate thickness for given applied loads is developed. This model is used to analyze laminate behavior. The effects of matrix property variation on laminate moduli and compliances are investigated with an emphasis on extension-shear coupling. Hybrid laminates are presented for which the variation of coupling due to hygrothermal and microcracking effects is reduced or eliminated. Overall variations in properties are reduced with these laminates. The effects of microcracking on laminate coefficients of thermal expansion are investigated. Laminates which are initially thermally isotropic and shear stable may lose these properties due to microcracking. The effects of crack closure on laminate behavior are discussed. As laminate loads (or thermal stresses) vary, ply cracks may be forced open or closed. It is assumed that plies with closed cracks can be treated as uncracked plies. The resulting properties for these laminates become functions of the applied load and may behave nonlinearly. In general, the behavior of laminates changes when cracking develops.
- Research Organization:
- Rensselaer Polytechnic Inst., Troy, NY (United States)
- OSTI ID:
- 102026
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: 1993
- Country of Publication:
- United States
- Language:
- English
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