Study on notched strength of woven C/C composites by means of the modified shear lag analysis method

The notched fracture strength using the double edge notched plate tension specimen of the woven C/C composite was calculated by the modified shear lag analysis method, in combination with the average stress criterion (composite fractures when the average stress over the characteristic distance in the fiber bundle at the notch tip reaches the strength of the fiber bundle). The present method could describe the following features experimentally observed in our former work. (i) The fracture strength was lower than the net strength criterion and decreased with increasing width when the debonding at the notch tip was short. (ii) The fracture strength was well estimated by the net strength criterion when the debonding was long. The results of calculation for wider specimens revealed the following; the notched strength remains nearly constant for any width given by the net strength criterion when debonding length is very long; it decreases with increasing width unless the debonding length is very long; the strength-width curve of the composite with finite debonding length is in the range of the upper bound given by the net strength criterion and the lower bound by the fracture toughness one.