Quiz_1_ S2008_ KEY

Quiz_1_ S2008_ KEY - Quiz 1 Wednesday, January 16, 2008 EMA...

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Quiz 1 EMA 4714 - Materials Selection and Failure Analysis Wednesday, January 16, 2008 Name ________________________________________ 1. [10 points] With respect to the boat lift I-beam support failure case, a question was posed - “If the load on the two cradle support beams was the same [P total /2], why did the I-beam buckle at only one location - the bearing point for the outboard cradle support beam?”. Use representative calculations to back up your answer. Collapse of the beam is predicted to occur when M f = σ f *[I/y m ], where I/y m = 1.11 for bending about the Y-Y axis. For A36 steel, M f = 39,960 in-lbs. Since M = P x-x *a, where a is the distance from the end of the beam to the load bearing point, a left = 5', a right = 4'. This means that P x-x (left) = 666# and P x-x (right) = 832#. Since the critical axis rotation angle, = sin -1 [P x-x /P appl ], and P appl = 0.7*4800/2 = 1680#, α = sin -1 [666/1680] = 23.4 o , or the left support point of the beam will fail when the axis of
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Quiz_1_ S2008_ KEY - Quiz 1 Wednesday, January 16, 2008 EMA...

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