What is the magnitude of the maximum stress that exists at the tipof an internal crack having a radius of curvature of 5.5 ×10-4 mm ( 2.165 × 10-5 in.) and a cracklength of 5 × 10-2 mm ( 1.969 ×10-3 in.) when a tensile stress of 220 MPa ( 31910 psi)is applied?