Midtern 2 Solutions

Midtern 2 Solutions - University of Maryland Honor Pledge:...

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Unformatted text preview: University of Maryland Honor Pledge: “I pledge on my honor that I have not given or received any unauthorized assistance on this exam." My name and signature on page 1 attest that I have read and agree with the above Statement. Printed Name: S0 ( [ONE Signature: ENMA 300 Midterm 2 Friday, April 8, 2011 Instructions. Please: 1. All work must be done on the exam itself, do NOT do caiculations on scrap paper. 2, Read each question carefully and answer the question asked! 3. If it is appropriate, make assumptions to solve the problems. Be sure to state the assumptions you make. . 4. Be consistent within a given problem, 5. Remember you only have 50 minutes to complete the exam. Look at the point values of each question to determine how to spend your time. Point values will not necessarily be split evenly between parts. 6. A person with normal size handwriting should be able to answer each question in the space allotted. If you need more space, continue your answer on the back of the page and indicate which question you are answering. 7. Ifl cannot understand your answer (due to the legibility of your writing or the "English") I will mark the answer wrong. You do not have to write perfect English sentences, "bullet format" is acceptable as long as I can understand what you are saying. 8. Be sure to define terms in any equations you use! 1. (26 points) SHOW YOUR WORK! Figure 7.33 Tensile stress-strain behavior for an alloy steel. l l i 2000 -— 300 —-200 -"“ ._. O O O E Stress (M Pa} Stress (103 ps 100 0 0.000 0.005 0.010 0.015 Strain ‘ 0 0.000 0.020 0.040 0.060 0.080 Strain stored per unit volume in the steel alloy in Fig. 7.33 above? (2pts) . 2 c/ 7 (f _. u = trig”, 2"; : Efl Maj/0006) - b) What is its yield strengtlefi What is its tensile strength?(2pts) A _ - r ' i. e . .1 VS .. I5 00:4 Pr. / «PUTS, {9&0 M P4 [acre]: f'namj c: y ffi‘fiorléwl‘W/E} c) What is thetotal energy required to take the specimen to the point of necking? (2pts) v =. .4 a u MHMZ/ {who/£1“ d) i. Consider a cylindrical specimen of a steel alloy 8.5 mm in diameter and 80 mm long that is pulled in tension. Determine its elongation when a load of 65250N is applied. (4pts) -5: F _ as“,sz - G‘fi/‘b " 777%); ‘ Ti($’LS“X'wr3)'z = [750/431 2. University of Maryland Honor Pledge: “I pledge on my honor that I have not given or received any unauthorized assistance on this exam." My name and signature on page 1 attest that I have read and agree with the above statement. ii) How much elastic strain will be recovered when the toad is released? How much plastic strain if any, will remain when the load is released? (3pts) firi/ 42/22 £192" . iii) Determine Young’s modulus of the steel alloy? (3pts) -— rr' / *0 - 4" IS :- Z/ 3 6 P4 e:-= __H___‘ E (3. act??- e) What is the approximate ductility of the alloy in Fig.7.33 above in terms of percent elongation? (2pts) XE/Qrtfi’a'gwh 1" 7787,}. i) What is the difference between true stress and engineering stress? (2pts) (6" E) ‘1’)"9‘ P ‘71.,= 5‘— =. (no-+5) g) On one plot draw schematic sketches for the stress strain curves for a glassy polymer well below Tg, a covalent solid like GaAs and a semicrystalline polymer well above the Tg. Label the key features and explain why each curve has its shape. On your sketches indicate the relative tensile strength and elastic modulus for each of the three materials. (opts) Q) :Ptl‘fmetp'rg glass? rdllel/Wr 4' T , MWcV/ohaus/ brill/{e say/M @ (713.49 Coma/€146 (‘é‘Wlm/c I _ C33 Palefmé’r‘ > 7%,) ate-Ba: 4m €[Jg‘5‘7lli/MPC’: 914/7 .1th a Niaxm‘iuw mfloL“/w5‘. El>bi ?>63 University of Maryland Honor Pledge: 3 “I pledge on my honor that I have not given or received any unauthorized assistance on this exam.” My name and signature on page 1 attest that I have read and agree with the above statement. 2. (21 points) _ , a) A metal crystal has a Burgers vector of length 0.272nm. If the lattice parameter a is 0.314 nm, is the metal crystal structiire FCC or BCC‘? (5 pts) 37: a [no] Fa: be [NJ 3‘6 .3 éJXZ+YL+21 : F22] g<c; ,%£=67r2¥nma= b) Given the same thermomechanical history, would you expect polycrystalline Cu (a FCC metal) with an average grain size of 25 pm to have a larger yield strength than polycrystalline Cu with an average grain size 10 pm? Why? (3pt5) ‘J {.5}- i" 0}=u“D-+Ikcl'4’- may 4, a: flutter 0;. oi) When a cold worked metal is heated in a temperature range where recrystallization takes place, how are the following affected: (3.) internal residual stresses, (b) strength, (6) ductility, and (d) hardness? (4pts) [995 [Jere/2 519?”?! .l a“. i‘ V . a a it Hxi ii) How is ductility of a metal normally affected by cold working? Why? How is the dislocation density affected? Why? (3pts) DLrtC-"i'r‘li'rl JP" “9475‘”; diS/fiflmlrmm‘ ({megilf inc/1205,93 di) Would you expect dislocations in a network polymer such as bakelite'? Why or why not? (3 pts) My (‘0 3/0 {‘ta‘étmg il/L (“UL/5r {927/ WA’fI'tZ/S" lt-LIE? "/0 / ii) Describe the differences between an edge dislocation and screw dislocation, in terms of directions, type of lattice distortion and directions. (3pts) _ ' ....I‘)_ ".4 a 1' _J_ [D {edge} shear» farm-j 3 ._, .9 . X (i 55m“)! - filamermap University of Maryland Honor Pledge: 4 “I pledge on my honor that I have not given or received any unauthorized assistance on this exam.” ' My name and signature on page 1 attest that 1 have read and agree with the above Statement 3. (10 points) Consider the design of an “I” beam whose strength follows a normal distribution. The beam consists of 316 Stainless steel with a mean yield strength of 240 MPa, which is normally distributed with a standard distribution of the yield strength of 30 MPa. The application environment consists of a load which has mean value of 1.80 We also normally distributed with a standard distribution of the load of 30 MPa. Write the equation which would allow you. to calculate the safety margin. Draw the distribution functions and indicate the location of the means, the standard deviation and the safety margin. Calculate the safety margin for the I beam design. l 5M l 6M; E‘ :- @LWY six/z a. fig "/1; : 24'0th emit/2% VEL'F 027‘ “tea-302‘ _ 60 A éo . _ —- —- /_‘a 1': University of Maryland Honor Pledge: “I pledge on my honor that I have not given or received any unauthorized assistance on this exam." My name and signature on page J attest that I have read and agree with the above statement. Table 6.1 Tabulation of Error Function Values Z 0 0.025 0.05 0.10 0.15 , 0.20 0.25 0.30 0.35 0.40 0.45 0.50 erf (z) 0 0.0282 0.0564 0.1125 0.1680 0.2227 0.2763 0.3236 0.3794 0.4284 0.4755 0.5205 z _ erfu) z 0.55 0.5633 1.3 0.60 0.6039 1.4 0.65 0.6420 1.5 0.70 0.6778 1.6 0.75 0.7112 1.7 0.80 0.7421 1.8 0.85 0.7707 1.9 0.90 0.7970 2.0 0.95 0.8209 2.2 1.0 0.8427 2.4 1.1 0.8802 2.6 1.2 0.9103 2.8 4. (22 points) If boron is diffused into a thick slice of silicon with no previous boron in it at a temperature of 1100°C for 7 hr, what atoms/om3 ? D = 4 x 10'13 cmzls for boron diffusing in silicon at 1100 “C, e00) ‘ 0.9340 0.9523 0.9661 0.9763 0.9838 0.9891. 0.9928 0.9953 0.9981 0.9993 0.9998 0.9999 . is the depth below the surface at which the concentration is 1011 atoms/c1113 if the surface concentration is 1018 I? v H‘ (is =I'C7/S'lenwffm3) (fix-:20 a‘éw%m3/ Clove j )(_ 1: H. . 2.32001 ‘ L9 “7:: ZJW‘ IS” » ' » ’ [0 40/71 , 5c ' 2s- Qrf (~ h ) 70”” 20111410 m“; )(m’zxzu .r 10.7000 :: gar-74 KY (CW) ) = w Z- 2.0.0134 “3‘5' I a 37.7043 2 X (cw) 32 6% 2‘ 2.01‘X/0"?L {ti ,9, 3/302 w__'"”.‘—FML}”W 36 w , 6 00 ix; 2; Hm CM [-2 12.6116; University of Maryland Honor Pledge: 6 ' “I pledge on my honor that I have not given or received any unauthorized assistance on this exam” ' My name and signature on page 1 attest that I have read and agree with the above Statement. 5. (21 points) A stress of 75 MPa is applied in the [001] direction of a unit cell of ECG iron single crystal. Calculate the resolved shear stress for the following slip systems (given as a and b): a) (011)[T T. 1] (9 points) [as A = at = es‘Hc/ A “543”? qb =45?” ‘ a: ruse/7 ms); ‘=-Zs“M_'/>4 ( 0.57¥4X0._ ya} :30, 5 MRI r b) (1 T0)[111] (9 points) COQA‘: a/Jg’p 9i=ri£\qa . 4) E 400 ’c'izm‘esqh C0§/\ : %§“CDK_SEL¥¥)[0) It; 0) Why do pure FCC metals like Ag and Cu have low values of 1m (critically resolved shear stress) and a HCP titanium has high values of Tms ? (3 points) MW?" 3H,; PIQMfiS =3 Tflgasrer ‘74: s/HP f‘ hers six-ear SwFrgs-g I‘S‘ Vfifu/‘H’c‘ls ...
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Midtern 2 Solutions - University of Maryland Honor Pledge:...

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