Predicting crack initiation in composite material systems due to a thermalexpansion mismatch

Residual stresses due to curing and thermal stresses due to differences bet ween the thermal expansion coefficients of the matrix and fiber may have a major effect on the micro-stresses within a composite material system and m ust be added to the stresses induced by the external mechanical loads. Such microstresses are often sufficient to produce micro-cracking even in the a bsence of external loads, example during the cooling process. In this investigation, a micro-mechnics approach is used in which the fiber s of a composite material system are modeled as cylindrical inclusions that are embedded into a matrix plate. The model is then used to predict, analy tically, the residual stresses due to a thermal expansion mismatch, e.g. du ring a cooling process. Additionally, some critical effects due to a load t ransverse to the direction of the fibers are examined. The analysis provide s a better understanding of how residual stresses are developed and how the y may be controlled in material systems where small strains are present. Moreover, the results are used to identify locations of possible crack fail ure and to derive a fracture criterion for crack initiation at the local le vel. Comparison with experimental evidence for matrix cracking in intermeta llic composites caused by thermal expansion mismatch shows a good agreement .