Effect of Crack-Closure by Shrinkage of Embedded Shape Memory TiNi Fiber SMA-FEC under Mixed Mode Loading

Shape memory TiNi fiber reinforced/epoxy matrix composite (SMA-FEC is fabricated to demonstrate the suppression effect of crack-tip stress concentration and the fracture toughness (K value) under mixed mode stresses in the composite. The test specimens have the two types of angled notches to the transverse direction of the tensile-type specimen. i. e. θ=0°, 15°, 30°, 45°, 60° with several crack lengths. The stress intensity factor at the notch tip is experimentally determined by photoelastic fringes. The decreases of K-value are attributed to the compressive stress field in the matrix which is induced when the pre-strain value of TiNi fiber ( T >Af). The dependencies of K value on the pre-strain value of TiNi fibers as well as on the compressive domain size between a crack-tip and are discussed.