Q4. A wide panel made of an aluminium alloy was found to contain an 8 mm central through-crack orientated normal to the

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Q4 A Wide Panel Made Of An Aluminium Alloy Was Found To Contain An 8 Mm Central Through Crack Orientated Normal To The 1 (387.51 KiB) Viewed 42 times

Q4. A wide panel made of an aluminium alloy was found to contain an 8 mm central through-crack orientated normal to the applied stress. The panel was designed to withstand four start-up/shut-down cycles per day for 25 years (assuming 300 operating days in a year), the cyclic stress range being -20MPa to 160 MPa. (a) Explain the terms stress intensity factor, fracture toughness and critical crack length. (b) Give the stress range that will contribute to crack opening. (c) If the fracture toughness of the alloy is 68 MPavm, calculate the critical crack length that would cause fast fracture. State any assumptions made. (d) If the growth rate of a crack in this material is defined as da 3.5(10-11)4K3 dN = calculate the number of cycles to failure and compare with its expected design life as defined above. Clearly show your working and define all your variables and any assumptions. Briefly explain why the use of a constant geometry correction factor could lead to errors. (e) If the panel must survive between annual maintenance inspections, what is the largest permissible crack size at each inspection. Comment on a suitable inspection method.