THERMAL RESIDUAL-STRESSES IN THE ANALYSIS OF FIBER-BRIDGED MATRIX CRACK-GROWTH IN TITANIUM MATRIX COMPOSITES

In this research, thermal residual stresses were incorporated in an an alysis of fiber-bridged matrix cracks in unidirectional and cross-ply titanium matrix composites (TMC) containing center holes or center not ches. Two TMCs were investigated, namely, SCS-6/Ti-15-3 and SCS-6/Time tal-21S laminates. Experimentally, matrix crack initiation and growth were monitored during tension-tension fatigue tests conducted at room temperature and at an elevated temperature of 200 degrees C. Analytica lly, thermal residual stresses were included in a fiber bridging (FB) model. The local R-ratio and stress-intensity factor in the matrix due to thermal and mechanical loadings were calculated and used to evalua te the matrix crack growth behavior in the two materials studied. The frictional shear stress term tau assumed in this model was used as a c urve-fitting parameter to matrix crack growth data. The scatter band i n the values of tau used to fit the matrix crack growth data was signi ficantly reduced when thermal residual stresses were included in the f iber-bridging analysis. For a given material system, lay-up and temper ature, a single value of tau was sufficient to analyze the crack growt h data. It was revealed in this study that thermal residual stresses a re an important factor overlooked in the original FB models.