12. A structural component is fabricated from an alloy that has a plane strain fracture toughness of It has been determined that this component fails at a stress of 300 MPa when the maximum length of a surface crack is 0.95 mm. What is the maximum allowable surface crack length (in mm) without fracture for this same component exposed to a stress of 300 MPa and made from another alloy with a plane-strain fracture toughness of 35 MPa m (31.9 ksi in. ). 40 MPa m (36.4 ksi in. ). 45 MPa m. 57.5 MPa m