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Shear dominated failure mechanisms in high temperature graphite/polymer matrix composites

Kumosa M.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2001

Vol. 269, z. 67

147-162

This presentation summarizes recent activities in the Center for Advanced Materials and Structures at the University of Denver toward the development of experimental and computational methodologies to facilitate the analyses of failure/fracture mechanisms and residual thermal stresses in unidirectional and woven graphite/PMR-15 composites subjected to biaxial shear dominated loads. Over the last three years, both the losipescu and off axis tests have been applied to determine the mechanical response of unidirectional and woven graphite/polyimide composites. The most recent experimental and computational results are presented in this paper. In addition, a new methodology developed to evaluate residual thermal stresses in unidirectional and woven polymer matrix composites is demonstrated. This method is based on the X-ray diffraction measurements of residual strains inside metallic particles/inclusions embedded in the composites. Interlaminar residual stresses in unidirectional and woven graphite/polyimide composites are presented.

Fracture analysis of composite high voltage insulators

Kumosa M.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2001

Vol. 269, z. 67

125-145

In this presentation, fracture mechanisms caused by the combined effect of mechanical, electrical and environmental stresses in composite high voltage insulators are discussed. In particular, the effect called brittle fracture as well as damage/fracture mechanisms caused by improper crimping are demonstrated. Several experimental procedures developed to simulate the brittle fracture process under laboratory conditions are shown and discussed. In addition, comprehensive non-linear finite element models of crimped composite insulators developed to optimize crimping and to increase the mechanical strength of crimped composite insulators are presented. 1 The effect of crimping on the mechanical strength of composite high voltage insulators is discussed in this presentation.