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Quiz_5_EMA_4714key

# Quiz_5_EMA_4714key - Quiz 5 Key EMA 4714 Materials...

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Quiz 5 Key EMA 4714 - Materials Selection and Failure Analysis March 29, 2007 Name ______________________________________ 1. [10 points] An experiment is conducted to determine whether fracture toughness of a quench and tempered alloy steel has been improved by a decrease in austenitizing temperature. K 1c determinations were made for two groups of samples, one austenitized at A 3 +25 degrees, the other at A 3 +25 degrees. The results of the test are contained within the table shown below. Based upon your analysis, is there a statistically significant improvement in fracture toughness derived from using the lower austenitizing temperature? [Use a significance level of p < 0.05. ************************************************************************ F = 7.52 2 /6.44 2 = 1.364; for ν 1 = 11, ν 2 = 9, F ν 1, ν 2 [ α = 0.05] = 3.10: therefore we assume that σ 1 = σ 2 and use test statistic 6 from Table 10.3 of your text. H o : 1 - 2 = 0; H 1 : 1 - 2 = δ sp 2 = [11*6.44 2 + 9*7.52 2 ] /20 = 48.2; s(x1bar-x2bar) = [48.1[1/12 + 1/10] 1/2 = 2.97 t = [46.31 - 42.79]/2.97 = 1.185; from table, ν = 20, t = 1.725; since calculated value is not in the critical region, the null hypothesis cannot be rejected and we must assume there to be no statistical meaningful effect from the lower austenitizing temperature.

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