MAE 20 Homework_3_SOLUTIONS_summer_2008

MAE 20 Homework_3_SOLUTIONS_summer_2008 - (3 We need 60 wt...

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MAE 20 (Summer, 2008) Homework 3 - SOLUTIONS (1) From the figure, the fatigue strength at one million cycles is 22 MPa. The maximum stress is +22MPa, the minimum stress is -22MPa, and the mean stress is 0MPa. A high frequency will cause heating of the polymer. As the temperature of the polymer increases, the fatigue strength will decrease. If the applied stress is not reduced, then the polymer will fail in a shorter time. (2) For copper: r cu = 1.278 Å (a) Au: r = 1.442 Δr = ( r Au - r cu )/( r cu ) = +12.8 % May be Unlimited Solubility (b) Mn: r = 1.12 Δr = -12.4 % Different structure (c) Sr: r = 2.151 Δr = +68.3 % Highest strength (d) Si: r = 1.176 Δr = -8.0 % Different structure (e) Co: r = 1.253 Δr = -2.0 % Different structure The Cu-Sr alloy would be expected to be strongest (largest size difference). The Cu-Au alloy satisfied Hume- Rothery’s conditions and might be expected to display complete solid solubility – in fact it freezes like an isomorphous series of alloys, but a number of solid state transformations occur at lower temperatures.

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Unformatted text preview: (3) We need 60 wt% Ni to obtain the correct liquidus temperature. %Ni = 60 = x / (x+500g)*100% or x = 750 g Ni 1.62 g/mol )/63.54 (500g)(N g/mol )/58.71 (750g)(N atoms Cu atoms Ni A A (4) When the alloy contains 61.9% Sn, it has eutectic composition. Therefore, this binary system has very low melting temperature. So, it is a good material for soldering. (5) 4% % % 96 100 4 100 %α Si 100% : Si 0% : α (e) 21.5% %eutectic Si 12.6% : eutectic 78.5% α %primary Si 1.65% : α primary 2.4% %L 97.6% 1.65 99.83 4 99.83 α Si% 99.83% : β Si 1.65% : α (d) 21.5% %L 78.5% 1.65 12.6 4 12.6 α Si% 12.6% : L Si 1.65% : α (c) Si 1% (b) ic hypoeutect (a) (6) 3.9% 4 pearlite % %C 0.77 : pearlite 6.1% 5 primary % %C 0.0218 : Primary (e) % 9 . 4 %Fe 6.67%C : C Fe % 1 . 95 100 0218 . 67 . 6 0.35-6.67 % C 0.0218% : (d) 3.9% 4 % 0.77%C : % 1 . 56 100 0218 . 77 . 0.35-0.77 % C 0.0218% : (c) ferrite-Primary (b) 795 (a) 3 3 C C (7) oid Hypoeutect 0.53%C x 6.67 x 6.67 0.92 α...
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This note was uploaded on 06/09/2009 for the course MAE 20 taught by Professor Mckittrick during the Summer '08 term at UCSD.

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MAE 20 Homework_3_SOLUTIONS_summer_2008 - (3 We need 60 wt...

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