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engineering
the science and engineering of materials
The Science And Engineering Of Materials 7th Edition Donald R. Askeland, Wendelin J. Wright - Solutions
Verify that integration of da/dN = C(ΔK)n will give Equation 7-20. N= 2[(a)(2-n)/2 (a)(2-n)/2] (2-n) Cf"A"/2 (7-20)
Explain how fatigue failure occurs even if the material does not see overall stress levels higher than the yield strength.
The following data were obtained from a creep test for a specimen having a gage length of 2.0 in. and an initial diameter of 0.6 in. The initial stress applied to the material is 10,000 psi. The diameter of the specimen at fracture is 0.52 in.Determine(a) The load applied to the specimen during the
What is shot peening? What is the purpose of using this process?
Why is creep accelerated by heat?
A child’s toy was left at the bottom of a swimming pool for several weeks. When the toy was removed from the water, it failed after only a few hundred cycles of loading and unloading, even though it should have been able to withstand thousands of cycles. Speculate as to why the toy failed earlier
Define the term “creep” and differentiate creep from stress relaxation.
What is meant by the terms “stress rupture” and “stress corrosion”?
A stainless steel is held at 705°C under different loads. The following data are obtained:Determine the exponents n and m in Equations 7-22 and 7-23 that describe the dependence of creep rate and rupture time on applied stress. Applied Stress (MPa) 106.9 128.2 1475 160.0 Rupture Time
What is the difference between failure of a material by creep and that by stress rupture?
Using the data in Figure 7-26 for an ironchromium- nickel alloy, determine the activation energy Qr and the constant m for rupture in the temperature range 980 to 1090°C. Stress (psi) 20,000 10,000 6,000 4,000 3,000 2,000 1,000 600 400 300 200 100 760° C 870° C 980° C 1040° C 1090°
Approximate the temperature at which creep deformation becomes an important consideration for each of the following metals: tin, molybdenum, iron, gold, zinc and chromium.
The activation energy for self-diffusion in copper is 49,300 cal/mol. A copper specimen creeps at 0.002 in./in. / h when a stress of 15,000 psi is applied at 600°C. If the creep rate of copper is dependent on self-diffusion, determine the creep rate if the temperature is 800°C.
When a stress of 20,000 psi is applied to a material heated to 900°C, rupture occurs in 25,000 h. If the activation energy for rupture is 35,000 cal/mol, determine the rupture time if the temperature is reduced to 800°C.
A nickel-based alloy component (INCONEL alloy 601) is designed to withstand a service stress of 4000 psi at a temperature of 925°C. Determine the temperature at which the component should be operated in order to double the expected life of the component if the applied stress is to remain the same.
For a temperature of 300°C and a lifetime of three years, what is the maximum stress that the nickel-based component of Figure 7-31 can withstand? 100 Stress (ksi) 10 600 400 200 100 80 60 40 20 10 1 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 Larsen-Miller Parameter = [492 +T(°C)](14.883 +
A 1-in-diameter bar of an iron-chromiumnickel alloy is subjected to a load of 2500 lb. How many days will the bar survive without rupturing at 980°C?
A 5 mm 3 20 mm bar of an ironchrominum- nickel alloy is to operate at 1040°C for 10 years without rupturing. What is the maximum load that can be applied?
An iron-chromium-nickel alloy is to withstand a load of 1500 lb at 760°C for 6 years. Calculate the minimum diameter of the bar.
A 1.2-in-diameter bar of an iron-chromiumnickel alloy is to operate for 5 years under a load of 4000 lb. What is the maximum operating temperature?
A hook (Figure 7-32) for hoisting containers of ore in a mine is to be designed using a nonferrous (not based on iron) material. (A nonferrous material is used because iron and steel could cause a spark that would ignite explosive gases in the mine.) The hook must support a load of 25,000 pounds,
A 1 in. X 2 in. ductile cast-iron bar must operate for 9 years at 650°C. What is the maximum load that can be applied?
A ductile cast-iron bar is to operate at a stress of 6000 psi for 1 year. What is the maximum allowable temperature?
A lightweight rotating shaft for a pump on a plane is to be designed to support a cyclical load of 15,000 pounds during service. The maximum stress is the same in both tension and compression. The endurance limits or fatigue strengths for several candidate materials are shown below. Design the
A support rod for the landing gear of a private airplane is subjected to a tensile load during landing. The loads are predicted to be as high as 40,000 pounds. Because the rod is crucial and failure could lead to a loss of life, the rod is to be designed with a factor of safety of 4 (that is,
A ductile cast-iron bar is to support a load of 40,000 lb in a heat-treating furnace used to make malleable cast iron. The bar is located in a spot that is continuously exposed to 500°C. Design the bar so that it can operate for at least 10 years without failing.
An axially loaded compression member is cold formed from an AISI 10-5 steel plate. A cross-section of the member is shown in Figure K8-1. The metal at the corners of the member was strengthened by cold work. Determine the ultimate and yield strengths of the material prior to forming; the yield
A 0.505-in.-diameter metal bar with a 2-in. gage length l0 is subjected to a tensile test. The following measurements are made in the plastic region:Determine the strain-hardening exponent for the metal. Is the metal most likely to be FCC, BCC, or HCP? Explain.
A 1.33-cm-diameter metal bar with a 3-cm gage length (l0) is subjected to a tensile test. The following measurements are made in the plastic region:Determine the strain-hardening coefficient for the metal. Is the metal most likely to be FCC, BCC, or HCP? Explain.
Using a stress strain diagram, explain what the term “strain hardening” means.
Consider the tensile stress strain curves in Figure 8-20 labeled 1 and 2 and answer the following questions. These curves are typical of metals. Consider each part as a separate question that has no relationship to previous parts of the question.(a) Which material has the larger workhardening
A true stress-true strain curve is shown in Figure 8-22. Determine the strainhardening exponent for the metal. True stress (psi) 90,000 80,000 70,000 60,000 50,000 40,000 0.1 0.2 True strain (in./in.) 0.3 0.4
What is meant by the term “springback”? What is the significance of this term from a manufacturing viewpoint?
What does the term “Bauschinger effect” mean?
What manufacturing techniques make use of the cold-working process?
What is the difference between extrusion and drawing?
Define the terms: strain-hardening exponent (n) and strain-rate sensitivity (m). Use appropriate equations.
What would a strain hardening exponent of zero mean mathematically and practically?
Explain why many metallic materials exhibit strain hardening.
Does a strain-hardening mechanism depend upon grain size? Does it depend upon dislocation density?
Compare and contrast strain hardening with grain size strengthening. What causes resistance to dislocation motion in each of these mechanisms?
Strain hardening is normally not a consideration in ceramic materials. Explain why
Thermoplastic polymers such as polyethylene show an increase in strength when subjected to stress. Explain how this strengthening occurs.
Bottles of carbonated beverages are made using PET plastic. Explain how stress-induced crystallization increases the strength of PET bottles made by the blow-stretch process.
A 3105 aluminum plate is reduced from 1.75 in. to 1.15 in. Determine the final properties of the plate. Note 3105 designates a particular aluminum alloy. Property 30 20 10 0 Tensile strength (ksi) 20 Yield strength (ksi) Elongation (%) 40 60 Percent cold work 80 >
A Cu-30% Zn brass bar is reduced from a 1 in. diameter to a 0.45 in. diameter. Determine the final properties of the bar. Property 100 80 60 40 20 0 Tensile strength (ksi) 20 Yield strength (ksi) Elongation (%) 40 60 Percent cold work 80
Write down the equation that defines percent cold work. Explain the meaning of each term.
We want a copper bar to have a tensile strength of at least 70,000 psi and a final diameter of 0.375 in. What is the minimum diameter of the original bar? Strength (psi) 100,000 90,000 80,000 Tensile strength 70,000 60,000 50,000 40,000 30,000 20,000 10,000 0 0 Yield strength % Elongation 20 40 60
A 0.25-in.-thick copper plate is to be cold worked 63%. Find the final thickness.
A 0.25-in.-diameter copper bar is to be cold worked 63% in tension. Find the final diameter.
A 2-in.-diameter copper rod is reduced to a 1.5 in. diameter, then reduced again to a final diameter of 1 in. In a second case, the 2-in.-diameter rod is reduced in one step from a 2 in. to a 1 in. diameter. Calculate the % CW for both cases.
If the amounts of extrusion in the previous problem were expressed as true strains, (a) Determine the true strain for each of the extrusion steps, and (b) Compare the sum of the true strain for each extrusion to the true strain from 25 mm to 20 mm.
A rolled Cu-30 wt% Zn plate 0.500-in.- thick has 2% elongation as-received by the supplier. The desired specifications for the final sheet are a thickness of 0.125 in., minimum tensile strength of 70,000 psi, and minimum elongation of 7%. Assume that the rolling is conducted so that the width of
A piece of cold-worked Cu-30 wt% Zn brass is identified, but the extent to which it has been cold-worked is unknown. Tensile testing indicates that the tensile strength is 60 ksi with an elongation of 30%. Determine the amount of cold-work and tensile strength of the brass in the annealed condition.
We want a copper sheet to have at least 50,000 psi yield strength and at least 10% elongation, with a final thickness of 0.12 in. What range of original thickness must be used?
Does the yield strength of metallic materials depend upon the crystallographic texture materials develop during cold working? Explain.
Does the Young’s modulus of a material depend upon crystallographic directions in a crystalline material? Explain.
What do the terms “fiber texture” and “sheet texture” mean?
One of the disadvantages of the coldrolling process is the generation of residual stresses. Explain how we can eliminate residual stresses in cold-worked metallic materials.
What is shot peening?
What is the difference between tempering and annealing of glasses?
How is laminated safety glass different from tempered glass? Where is laminated glass used?
What is thermal tempering? How is it different from chemical tempering? State applications of tempered glasses.
Explain factors that affect the strength of glass most. Explain how thermal tempering helps increase the strength of glass.
The electrical conductance of a Cu-40 wt% Zn wire is measured. How much less conductive is it than a 60% cold-worked pure Cu wire? Yield strength (psi) 60,000 Electrical 50,000 conductivity 40,000 30,000 20,000 10,000 0 Yield strength T T 60 50 40 20 I 0 20 40 60 80 Percent cold work (a) Electrical
Residual stresses are not always undesirable. True or false? Justify your answer.
What is cold working? What features does a material have after it has been cold-worked?
Cold working cannot be used as a strengthening mechanism for materials that are going to be subjected to high temperatures during their use. Explain why.
Aluminum cans made by deep drawing derive considerable strength during their fabrication. Explain why.
Such metals as magnesium cannot be effectively strengthened using cold working. Explain why.
Explain the three stages of the annealing of metallic materials
What is the driving force for recrystallization?
In the recovery state, the residual stresses are reduced; however, the strength of the metallic material remains unchanged. Explain why.
What is the driving force for grain growth?
Treating grain growth as the third stage of annealing, explain its effect on the strength of metallic materials.
Why is it that grain growth is usually undesirable? Cite an example where grain growth is actually useful.
What are the different ways one can encounter grain growth in ceramics?
Are annealing and recovery always prerequisites to grain growth? Explain.
A titanium alloy contains a very fine dispersion of Er2O3 particles. What is the effect of these particles on the grain growth temperature and the size of the grains at any particular annealing temperature? Explain.
Explain why a tungsten filament used in an incandescent light bulb ultimately fails.
For a Cu 35% Zn alloy, a tensile strength of not less than 70 ksi and an elongation of 25% are desired. If the metal is cold worked to 75% in forming the desired shape, how high should it be heated when annealing to reach these properties? Property 120 100 80 60 40 20 0 0 25 Tensile
Samples of cartridge brass (Cu-30% Zn) were cold rolled and then annealed for one hour. The data shown in the table below were obtained.(a) Plot the yield strength and grain size as a function of annealing temperature on the same graph. Use two vertical axes, one for yield strength and one for
Is it possible to obtain a single crystal from an initially polycrystalline material a through a process of cold work, recrystallization, and grain growth? Yes or no? Fully explain your reasoning.
What is meant by the term “recrystallization?” Explain why the yield strength of a metallic material goes down during this stage of annealing.
How do we distinguish between the hot working and cold working of metallic materials?
Why is it that the recrystallization temperature is not a fixed temperature for a given material?
Plot the recrystallization temperatures in Table 8-4 as a function of the melting temperatures. Are they proportional and, if they are, what is the proportionality constant? Make sure to convert the temperatures to kelvin first. Melting Metal
Why does increasing the time for a heat treatment mean recrystallization will occur at a lower temperature?
Two sheets of steel were cold worked 20% and 80%, respectively. Which one would likely have a lower recrystallization temperature? Why?
Give examples of two metallic materials for which deformation at room temperature will mean “hot working.”
Add another column to Table 8-4 containing the range (°C) of warm working temperatures. Remember to convert to and from degrees kelvin in performing your calculations. Table 8-4 Typical recrystallization temperatures for selected metals (Repeated for Problem
What is a heat-affected zone? Why do some welding processes result in a joint where the material in the heat-affected zone is weaker than the base metal?
What welding techniques can be used to avoid loss of strength in the material in the heat-affected zone? Explain why these techniques are effective.
The amount of plastic deformation that can be performed during hot working is almost unlimited. Justify this statement.
Compare and contrast hot working and cold working.
Design, using one of the processes discussed in this chapter, a method to produce each of the following products. Should the process include hot working, cold working, annealing, or some combination of these?Explain your decisions.(a) Paper clips;(b) L-beams that will be welded to produce a portion
We plan to join two sheets of cold-worked copper by soldering. Soldering involves heating the metal to a high enough temperature that a filler material melts and is drawn into the joint (Chapter 9). Design a soldering process that will not soften the copper. Explain. Could we use higher soldering
We wish to produce a 1-mm-diameter copper wire having a minimum yield strength of 60,000 psi and a minimum % elongation of 5%. We start with a 20-mmdiameter rod. Design the process by which the wire can be drawn. Include important details and explain.
Design of a Wire Drawing Process. Write a program that will effectively computerize the solution to solving Example 8-4. The program should ask the user to provide a value of the final diameter for the wire (e.g., 0.20 cm). The program should assume a reasonable value for the initial diameter (d0)
What is a viscoelastic material? Give an example.
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