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Ouestion ILB. (30 pts.) (i-10 pts.) A structural component is fabricated from an alloy that has a piane strain fracture toughness of 45 MPaJm. 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 madę from another alloy with a plane-strain fracture toughness of 57.5 MPayjm?', (ii-10 pts.) Suppose that a wing component on an aircraft is fabricated from an aluminum alloy that has a piane strain fracture toughness of 40 MPa4m . It has been determined that fracture results at a stress of 365 MPa when the maximum internal crack length is 2.5 mm. For this same component and alloy, compute the stress level at which fracture will occur for a critical internal crack length of 4.0 mm; (iii-10 pts.) Explain the most salient features of brittle and ductile fracture of engineering materials. Use stress-strain curves in elaborating on your answer.

Griffith ’s Eąuation is given by a_c =

The piane strain fracture toughness is given by Ki_c=Ya_c(7i:a)^1/2