MAT exam2_2001 - II Tensile Test(25 pts The following...

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Unformatted text preview: II. Tensile Test (25 pts.) The following questions pertain to the stress—strain curve from a tension test on a hot- rolled 1095 steel shown below. The diameter of the cylindrical test specimen was 9.07 mm before the test, and the gauge length was 250 mm. L Sum ‘Curve 2 0 0.04 0.08 O 12 a.) What is the Young's modulus, E? E b.) What is the yield strength? Yield strength c.) What is the percent elongation? % elongation d.) What is the load supported at the maximum stress? Load e.) If y0u were given the data stress-strain data set for this graph in the form of a spreadsheet, bn'efly explain haw you would estimate the toughness of this steel? m. Fe-C System (20 pts.) The following questions pertain to the Fe—C phase diagram shown below. 0mm» (me C) 0 5 H500 ‘0 '5 20 25 X, I400 2500 1200 E3 _. 2000 D g 1000 a II E 800 k A Y MO 500 «gamma-,0) — 1000 400 ' o I 2 3 4 5 s 6.70 “" Wonmx c) a.) What phase(s) are present in the region marked "X" on the phase diagram? Phase(s) 10.) Circle the eutectoid point on the diagram and write the eutectoid reaction upon cooling. Reaction A specimen of 98.5 wt % Fe - 1.5 wt % C is cooled from 1000 °C under equilibrium conditions. When the alloy is cooled to 730 °C (denoted by "Y") c.) What is the carbon-rich phase and what is its relative amount (by weight)? Carbon-rich phase Relative amount d.) Which of these microstmctures corresponds to point "Y"? (Circle one.) none of these Proeutectoio a proeutectoid Fe3C e.) If the alloy is slowly cooled to 720 “C (denoted by "2") what is the corresponding microstmcture? (Circle one.) none of these Proeutectmu «2 Proeutectoid F83C IV. Strengthening Mechanisms, Etc. (30 pts.) a.) Two previously undeformed cylindrical specimens of an alloy are to be strain hardened by reducing their cross—sectional areas. The aim is to create two deformed specimens with the same hardness. The initial and deformed radii for one specimen are16 mm and 11mm, respectively. If the second specimen has an initial radius of 12 mm, what is its radius after deformation? Radius The graph below shows the dependence of the yield strength, tensile strength and percent elongation on percent cold work for a 70 wt % Cu - 30 wt % Zn brass alloy. b.) Place the appropriate label (i.e., yield strength, ultimate tensile strength and percent elongation) next to each curve. TOKCuMZn l ‘l I-nsilt- stri-nglh and yin-III hlil'lttzllu, kNl' .l_ .b O I'Ilnngntiun pen-em -‘l'20 > 0 K) 20 30 4o 50 60 Percent cold work c.) Suppose that a brass sheet having this composition is cold-rolled from 0.09 in to 0.064 in. What is the ductility of the sheet after rolling? Ductility d.) List two strengthening mechanisms discussed in class and, for one of them, briefly discuss the strengthening mechanism in terms of the motion of line defects (dislocations). Strengthening Mechanism 1 Strengthening Mechanism 2 Discussion of Mechanism e.) Identify each attribute as being associated with either recovery, recrystallization or grain growth by writing the appropriate term(s) in the blanks. New strain-free, equiaxed grains are formed. Low-energy dislocation configurations are produced. Mechanical properties are restored to precold~worked values. It occurs by the migration of grain boundaries. I. PinseDiagi-am (25 pls.) The following questions pertain to the Al—Ni phase diagram shown below. Atomic Percent Nickel 20 an 1100 Temperature 'C 3 5 § figi § § 8 8 § 0 13 20 so in 50 so 70 A} Weight. Percent Nickel Ni a.) Identify any eutectic points at temperatures below 1200 °C by circling them on the phase diagram. Write the corresponding eutectic reaction(s)? Eutectic reaction(s) b.) Suppose that a 60 wt %Al - 40 wt % Ni alloy is slowly cooled from 1200°C to [000°C What is the first solid phase to form during this process? What is the initial composition of the solid phase? Phase Composition c.) For a 20 wt % Al - 80 wt % Ni alloy in equilibrium at 710°C, what phases are present and what are their compositions? Which phase comprises the larger (largest) fraction by weight? Phase(s) present Composition(s) Phase with larger (largest) weight fraction (1.) What is the stoichiometric compound for the phase labeled 7? Y ...
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