Residual Stresses in Ceramic Fiber Composites: Effect of Non-Uniform Fiber Distribution
Residual stresses evolve in ceramic fiber composites during cool down from a stress free state. These stresses play a very important role in the overall mechanical behaviour of the composites, and may lead to microcracking by themselves or when aided by thermomechanical loadings. In this paper, the residual stresses in unidirectional fiber composites are computed by the three dimensional finite element analysis. We investigate the effect of fiber volume fraction and fiber distribution effects such as fibers touching and fibers enclosing matrix (short range effects) as well as matrix and fiber rich domains (long range effects). The effect of thermal expansion mismatch is studied by examining two ceramic composite systems: SiC fibers (Nicalon) reinforced by LithiumAluminumSilicate (LAS) and CalciumAluminumSilicate (CAS) glass-ceramics. It is shown that the residual stress state varies with fiber distribution: The analysis of small range effects shows that the local stresses may differ considerably from the average stresses. The analysis of long range effects shows that the residual stress states are affected both inside and outside the domains. Due to differences in the thermal expansion mismatch, the residual stress state in SiClLAS and Sic/CAS are very different. Therefore, different damage modes are expected in the two systems. Partial debonding is likely in SiC/LAS at locations where fibers are in contact, whereas matrix cracks may initiate in Sic/CAS.
Unable to display preview. Download preview PDF.
- 4.Chen T., Dvorak G.J., Benveniste Y., Thermal stresses in coated fiber composites. Symp. High Temp. Comp. 1989, 139–47.Google Scholar
- 6.Zhu H., Achenbach J.D., Effect of Fiber-Matrix Interphase Defect at Micro Stress State at Neighbouring Fibers, J. Comp. Mats 1991, 25, 224–38.Google Scholar
- 7.Zhu H., Achenbach J.D., Radial Matrix cracking and Interphase Failure in Transversely Loaded Fibre Composite, Mech. of Mats. 1991 (submitted)Google Scholar
- 11.Evans A.G., Marshall D.B., The Mechanical Behaviour of Ceramic Matrix Composites, Acta Metall., 37, 2567–83.Google Scholar
- 12.Karandikar P., Talreja R., Chou T.-W., Evolution of Damage and Mechanical Response of Ceramic Matrix Composites, J. Mats. Sci., 1991 (submitted)Google Scholar
- 13.FEMGEN Users Manual version 8.6, 1987, Femgen AB, Lund, SwedenGoogle Scholar