Micro-residual thermal stress

Three-dimensional distributions of the micro-residual stresses are very complicated, and are affected by the elastic properties, local geometry and distribution of the composite constituents within a ply. Many analytical (Daniel and Durelli, 1962 Schapery, 1968 Harris, 1978 Chapman et ah, 1990 Bowles and Griffin, 1991a, b Sideridis, 1994) and experimental (Marloff and Daniel, 1969 Koufopoulos and Theocaris, 1969 Barnes et ah, 1991 Barnes and Byerly, 1994) studies have been performed on residual thermal stresses, A two-dimensional photoelastic study identified that the sign and level of the residual stresses are not uniform within the composite, but are largely dependent on the location (Koufopoulos and Theocaris,... 

Keywords transcrystallization, heterogeneous nucleation, row-nuclei, cylindritic crystallization, interfacial shear strength (ISS), single fiber composites (SFC), mesostructure, micro-Raman spectroscopy (MRS), a-PP, P-PP, residual thermal stresses, composites. 

The first and foremost step in failure analysis of ceramics consists of identifying the fracture origin and the type of cracking, which throws light on the type of failure such as failure due to impact, residual stress combined with load, thermal shock, improper machining, oxidation and corrosion. This is aided by micro- and macrofracto-graphy, examination of microstructure by SEM, chemical analysis and metallographic examination. 

Thermal residual stresses are inherent to fibre reinforced composites due to the heterogeneity of the thermo-mechanical properties of their two constituents. Such stresses build up when composite structures are cooled down from the processing temperature to the test temperature. Residual stresses will be present on both a fibre-matrix scale (micro-scale), and on a ply-to-ply scale (macro-scale) in laminates built up from layers with different orientations. It is recognised that these stresses should be taken into account in any stress analysis. 

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