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4) Creep (6 Points) Creep is a process that takes place at elevated temperatures. It is is of primary concern to the engineer when designing high-temperature turbines. a) Show schematically the displacement as a function of time (AL vs t) for a creeping polycrystalline material under 3 different tensile stresses, 01<02<03. Please explain where the curves are different and why (1,5 point). b) What is the effect of the grain size on creep behaviour? Elaborate your answer (1 point). c) Describe two (2) ways we can design polycrystalline metallic materials to be strong enough to withstand the typical conditions for high-temperature turbines, using suitable strengthening mechanisms. Explain how each of them contributes to the strength at the microstructural level. Don't to consider the effect of temperature on the microstructure development. (1,5 point) A construction part is loaded in creep and must be able to withstand a tension of 100 MPa at a temperature of 527 °C for 10 years. The plastic strain may become 1 % at most. The material chosen for this shows the following properties during creep tests: creep speed: 1) dɛ = 1. 107/s at 627 °C and 200 MPa stress dt de -= 3,5. 106/s at 727 °C and 200 MPa stress dt 2) Given that the material creeps according to the formula ε = Ao5e-Q/RT, d) Determine Q and A from both creep tests (1 point). e) Does this material meet the requirement of a maximum elongation of 1% (1 point)?