A material containing cracks of initial length 0.010 mm is subjected to alternating tensil...

A material containing cracks of initial length 0.010 mm is subjected to alternating tensile stresses of 25 and 125 MPa for 350,000 cycles. The material is then subjected to alternating tensile and compressive stresses of 250 MPa. How many of the larger stress amplitude cycles can be sustained before failure? The material has a fracture toughness of 25 MPa  and materials constants of n = 3.1 and C = 1.8 × 10–10 for these units. Assume f = 1.0 for all cracks.