2. Suppose that a wing component on an aircraft is fabricated from an aluminium alloy that has a plane-strain fracture toughness of 26 MPa. It has been determined that fracture results at a stress of 112 MPa when the maximum internal crack length is 8.6 mm. For this same component and alloy, compute the stress level at which fracture will occur a critical surface crack length of 3.0 mm.