Engineering Stress And Strain Case Study Answers

1) What are engineering stress and strain?
Engineering Stress:
Engineering stress is also called nominal stress, and it is defined as the applied load divided by the original cross sectional area of the material.
Engineering Strain: Engineering strain is defined as the amount of material that deforms per unit length in a tensile test. Engineering strain is also known as nominal strain.

2) In the figure below, graphically show the toughness of three class materials: Ceramics, Metals, and Polymers (un-reinforced)

3) Where is the elastic recovery in the graph below?

4) What is the relation between the yield strength of a material and the size of the grain in polycrystalline metal? What
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Resistance to corrosion
3. Industrial bearings
4. Medical instruments

8) Metals can be extracted from the metal oxide ore by the following methods (1) Reaction of Oxide at High Temperature with Carbon (2) Reaction of Oxide with another Element or by (3) Electrolytic Reduction. Use the Ellingham diagram to illustrate and explain which extraction method is appropriate for which metal.
Answer # 8:

The above graph is plotted between changes in Gibbs free energy for each oxidation reaction vs temperature.
Important features:
1. Lower position of metals in Ellingham diagram, more is the stability of the metals.
2. Metallic oxides in Ellingham diagram are straight lines having slop positive.
3. Metal oxide stability decreases with temperature increases.
4. Huge gap between two lines shows greater effectiveness.
5. High temperature chemical reduction method most widely used.

9) Use the phase diagram of Sugar water shown in class; determine the solubility limit for sugar in water at 80oC. What would happen if that solution is cooled to 40 oC?
Answer # 9:

As shown in above figure at temperature is 800C, then 70 % by wt composition of liquid solution + solid sugar, but when we cool down the temperature up to 400C then 60 % composition by wt % exist, and we come close in the region of liquid solution
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Answer# 10
Part B:
Weight fraction of solid (α-phase) @ 12250C = 42 wt %
Weight fraction of liquid = 26 wt %
c) Under conditions in b), what is the composition of the solid? Answer # 10
Part C:
Under above condition the composition of solid is 28 % by wt.
11) In an ionic crystal, name the two criteria on which the packing of ions depends. How does the coordination number around the cation change with the radius ratio of the cation to the anion? How can you use this to predict if the structure of CsCl to be either BCC or FCC and structure of Nacl to be the other?
Answer # 11:
In ionic crystals, packing of ions depends upon electrostatic attraction and lattice energy, which is released in the form of heat, when two ions come close together. According to the Pauling’s rule the allowed size of the cation for a given structure is determined by the critical radius ratio. Cation –anion radius ration is given by following formula: rc/rA. The structure of CsCl and Nacl both are FCC structures. In ionic crystals, the structure is governed by two principles: positive and negative ions must alternate for electrostatic cohesion; and the ions, which have different sizes, must touch so that the structure does not

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