Q1. In a creep test performed on a material at 360ºC under a tensile stress, o, of 100MPa, tensile strains, &, of 0.005

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Q1 In A Creep Test Performed On A Material At 360oc Under A Tensile Stress O Of 100mpa Tensile Strains Of 0 005 1 (78.24 KiB) Viewed 59 times

Q1. In a creep test performed on a material at 360ºC under a tensile stress, o, of 100MPa, tensile strains, &, of 0.005 and 0.007 were recorded at 40,000 hours and 60,000 hours respectively. At 480*C, the material had a rupture life of 12,000 hrs (for the same stress). (a) Describe the phenomenon of creep and briefly explain why the Larson-Miller relationship is useful for engineers. (b) Calculate the Larson-Miller parameter, P, and constant, c, from these test results, where P = T (c + logro tr). Assume that the secondary creep rate is 1/ tr where tr is the rupture life given in hours, (c) If this material were to be used in a turbine under a stress of 100MPa, what would be the maximum operating temperature of the turbine in order for the material to survive 90,000 hrs? (d) Due to a calculation error, it was found that the operating stress was actually 120 MPa. Calculate the new rupture life for the maximum operating temperature found in (c). Assume OP = constant. Comment on your answer comparing the proportional change in stress with the proportional change to rupture life. Discuss its significance in design.