quiz 3 solution

quiz 3 solution - does / does not) change with time. Ficks...

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Name: Solution __ MSE 230 (Spring 2008) Quiz #3 (30 pts) Choose one or fill in the blanks 1. (10 pts) Fatigue is a form of failure that occurs in structures subjected to ( static / dynamic) stresses. ( A ) ( B ) (A) For some Fe and Ti alloys, there is a limiting stress level, called the __ Fatigue Limit _______ . (B) For most other alloys, there is a stress level at which failure will occur for some specified number of cycles. This stress level is called Fatigue Strength . This specified number of cycles is called Fatigue Life . 2. (12 pts) Similar sized atoms diffuse by ( vacancy diffusion / interstitial diffusion) , while small atoms like hydrogen and carbon diffuse by ( vacancy diffusion / interstitial diffusion) . Fick’s 1 st Law is ( steady / non-steady)
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Unformatted text preview: does / does not) change with time. Ficks 2 nd Law is ( steady / non-steady) state diffusion. Concentration ( does / does not) change with time. 3. (8 pts) Ficks first law tells that Diffusion flux dx dC D J = . And the diffusion coefficient ) exp( RT d Q D D = , where Qd is the activation energy. As shown in the following graph, we plot the natural logarithm of D versus the reciprocal of temperature for two materials A and B. From the following graph, which line shows: a. Higher diffusion flux (at the same dC/dx ) (A / B) b. Higher activation energy (at the same temperature) (A / B) c. V a c a n c y d i f f u s i o n (A / B) d. Interstitial diffusion (A / B) A 1/T ln D B...
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