exam 3 solutions spring _09

exam 3 solutions spring _09 - EMA 3066, Exam 3 April 2,...

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Unformatted text preview: EMA 3066, Exam 3 April 2, 2009 Name: So/U‘l‘r‘ni" First Last I have neither given nor received help on this exam. Signature 1. A polymer with a repeat unit molecular weight of 105 g/mole is 10.0% crosslinked (i.e. a crosslink occurs every 10 repeat units). If the density of this polymer is 1.20 g/cm3, determine its modulus in MPa at 25° C. Note that l J = l N-m. g3 3/3127” .Mc, T - I' k ‘. 3 . 3 f) K D x /C_a~ 3 .-_._ flat: C ‘_ _ _ M °> (rm-a. {2: 3—3/9 J/Wf-K -_._.... 1339‘g:;9<3;< .flzcfi‘ /& X/og— 3/”! r/QS‘C- ’3 fix w. Q, :- E- S 3/ ~ _/(/ I /0 "" “" B'SX/(L £39. 64'“? EMA 3066, Exam 3 April 2, 2009 2. On a single graph, sketch the stress-strain curves for polyethylene with 30 wt% crystallinity and with 80 wt% crystallinity, clearly showing the differences between the two. m L’-€-$::‘\r) C wye‘i‘c-Jh‘n: y (‘ “Jae 5 -‘ "- 7.5 Rx moi-u /v 8 ~— 11: 3 A2: a 17+”bfl _ 0 Mr 5. the"; “:1 (a; Ami?— EMA 3066, Exam 3 April 2, 2009 3. If the stress relaxation modulus for polystyrene is 100 Pa after 10.0 minutes at 150° C, at what time is the stress relaxation modulus equal to 100 Pa at 160° C? Take the glass transition to be 100" C. log) ~h-r . ~17.w(T-'T,e+-3 tn“; 9:. t T (7—7:?(5 ‘lr-‘rasf ngF-l- gst'L a» {ac/(3.. /Os:> 1’(2) Harry : _j7‘VV(?OI\ $ 9—? £115 VH4, 1-?(2 . /0 vs '3 lo”- 66“”‘A 9L3“ "fir-m Ioo‘L -—9 /Gc~“C {orb t;— _ -17-~w(u3 .. ' ‘ __cf_1)tg 3_Y?>*/}cg?.mrn 5-f— 1‘ (90 . {L7- #9:??- 7 2" 3-33 flo MFA tr: yt/o? Mrs) /0H- ‘ -_ WC 12> EMA 3066, Exam 3 April 2, 2009 4. Draw a viseoelastic model (combinations of springs and dashpots) that will exhibit the creep behavior shown in the figure below. On the creep curve, label which spring or dashpot is responsible for each section of the curve. g «- D m , . ‘ t1me stress is applied stress is released EMA 3066, Exam 3 April 2, 2009 5. Sketch the creep compliance versus time for polystyrene under the following two conditions: Mn = 100,000 g/mole at a temperature below its glass transition; Mn = 100,000 g/mole at a temperature above its glass transition. Put both curves on the same graph, clearly showing the differences. The entanglement molecular weight for polystyrene is approximately 18,000 g/mol. You should draw curves corresponding to actual measurements over reasonable time ranges. Do not draw complete master curves. EMA 3066, Exam 3 April 2, 2009 6. a. The cure exothenn for a particular thermoset monomer is 1.23 ka g. The monomer is cured for 40 minutes at 80° C, and the residual cure exotherm that is measured is 0.53 W g. What percentage of polymerizable groups have reacted after 40 minutes at 80° C? b. For the thennoset of part a, at 80° C gelation occurs at 53% reaction and vitrification occurs at 62% reaction. Describe the properties of the material (liquid, etc.) after curing for 40 minutes at 80° C. 7;. aka/“C '— IK / w" \- g /0 Ci» T e was”! At, (De/Ana) 5o l-l 75‘: mi yel vilriier‘lc’tl, 56 Hr 7‘) “l- a 7W??? 7 75 ‘ltrté « 75 (L g,‘.,s/J‘.n}’ecl 39/- EMA 3066, Exam 3 De:l 1'8 [egg =M T 62+(T—Tg) aT _‘_T EMA 3066 Exam 3 Equation Sheet a: oRT[a_;] April 2, 2009 WLF Universal constants are: C1=l7.44 C2=51.6 R = 8.314 meol-K ...
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This note was uploaded on 11/16/2011 for the course EMA 3066 taught by Professor Douglass during the Fall '10 term at University of Florida.

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exam 3 solutions spring _09 - EMA 3066, Exam 3 April 2,...

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