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Homework_5 - Introduction To Materials Science Chapter 1...

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Unformatted text preview: Introduction To Materials Science, Chapter 1, Introduction Composites Thin crystalline platelets grown fromCr,lut-on ,- Mo ihs voldhis crystal structure so !i Fe cha na f e t back and forth: chain-folded model Spring 2007 Engineering Material Polyethylene Polymer composite materials: reinforcing glass fibers in a polymer matrix. University of Virginia, Dept. of Materials Science and Engineering Homework #5 18 The a erag chain l gth is m (for Wednesday, v13 eApril,en2007) uch thickness of the crystallite greater than the University of Virginia, Dept. of Materials Science and Engiineeriing of Virgi24ia, Dept. of Materials Science and Engineering U n v e r s ty n 9 Reading Assignments Chapters 7,9 Problem 1 A tungsten single crystal has a [213] axial orientation. a. Determine cos φ, cos λ and |cos φ cos λ| for each slip system. Consider only the {110} 1 1 0 slip systems. b. Which slip system(s) will be active when plastic yielding occurs? Explain why. c. The critical resolved shear stress is τ0 = 100 MPa. What is tensile stress when yielding occurs? Problem 2 The lower yield point for a mild steel that has an average grain diameter of 5x10-2 mm is 135 MPa. When the grain size is decreased to 8x10-3 mm, the yield point is measured to be 260 MPa. At what grain size will the lower yield point be 205 MPa. Problem 3 Consider the typical engine-block alloy, which is 16%Si, 84% Al a. At what temperature will the first crystals of solid appear upon slow cooling of the melt b. At what temperature will the alloy be completely solid c. Just before the alloy is all solid, at say, 578˚C, what will be the analysis of the β and liquid, respectively d. What will be the phases analyses of the α and β in this alloy at 550˚C Spring 2007 Engineering Material Problem 4 Given the following data, sketch a phase diagram. Be as accurate and as thorough as your knowledge permits. Cooling curves show horizontal temperature arrests @ 715˚F for pure A and 655˚F for pure B. A horizontal arrest in the two component system at 500˚F for 25% A, 75% B indicates that three phases are in equilibrium, the following addition data is available • Melting of A = 715˚F • Melting of B = 655˚F • 501˚F, 25% A and 75% B; all liquid Engineering Material • 499˚F, 25% A and 75% B; 25% of a BCC metal 75% of an FCC metal • 499˚F, 35% A and 65% B; 50% of a BCC metal, 50% of an FCC metal • 400˚F, 40% A and 60% B, 60% of a BCC metal, 40% of an FCC metal • 400˚F, 20% A and 80% B, 20% of a BCC metal, 80% of an FCC metal Problem 5 A contractor has a specification for soldering sections of copper water pipe. recommendation is for 50% Pb, 50% Sn. a. What is the lliquidus and solidus temperatures for the alloy b. What is the primary phase for each alloy c. Calculate the percentage primary phase present in part b for the alloy at 1˚C below the eutectic temperature The Problem 6 Describe the changes that would occur in an alloy of 30% Ag, 70% Cu cooled from the liquid state to room temperature. Sketch the resulting microstructure and give the relative amount of each phase and each microstructural constituents (i.e. primary phase and eutectic) ...
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