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Chapter 8: Problem 29

List four measures that may be taken to increase the resistance to fatigue of a metal alloy.

Short Answer

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Question: List four measures that can be taken to increase the fatigue resistance of a metal alloy. Answer: 1. Improve surface finish through methods such as grinding and polishing. 2. Use heat treatment processes like annealing, quenching, tempering, and aging treatments. 3. Introduce compressive residual stresses using techniques like shot peening, cold rolling, and induction hardening. 4. Optimize alloying elements like chromium, nickel, and vanadium to improve the material's properties and fatigue performance.

Step by step solution

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1. Improve surface finish

To increase the fatigue resistance of a metal alloy, it is essential to improve its surface finish. Highly polished surfaces may help reduce the chances of fatigue crack initiation by minimizing surface irregularities and stress concentrations. This can be done through methods such as grinding, polishing, or other surface treatment processes.
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2. Use heat treatment

One of the most effective measures to enhance the fatigue resistance of a metal alloy is heat treatment. Heat treatment can alter the microstructure, mechanical properties and residual stress states of the material in a controlled manner. Some common heat treatment processes include annealing, quenching, tempering, and aging treatments. These processes affect the material's yield strength, tensile strength, and ductility, ultimately increasing its fatigue resistance.
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3. Introduce compressive residual stresses

Introducing compressive residual stresses into the material can help improve its fatigue resistance as it reduces the effective tensile loading applied on the material during service. Some techniques to introduce compressive residual stresses are shot peening, cold rolling, and induction hardening. These methods work by creating a layer of compressively stressed material on the surface, restricting the growth of fatigue cracks that may begin on the surface.
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4. Alloying

Adding alloying elements to a metal can also increase its fatigue resistance. Alloying elements can modify the metal's microstructure and mechanical properties, resulting in improved fatigue resistance. For instance, adding elements like chromium, nickel, or vanadium to steel can form secondary phases, refine the grain size, and optimize the material's properties for enhanced fatigue performance. It is essential to carefully select and optimize the amounts of alloying elements to achieve the desired improvement in fatigue resistance.

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Most popular questions from this chapter

The following tabulated data were gathered from a series of Charpy impact tests on a commercial low-carbon steel alloy. $$ \begin{array}{|cc|} \hline \text { Temperature }\left({ }^{\circ} \boldsymbol{C}\right) & \text { Impact Energy (J) } \\ \hline 50 & 76 \\ \hline 40 & 76 \\ \hline 30 & 71 \\ \hline 20 & 58 \\ \hline 10 & 38 \\ \hline 0 & 23 \\ \hline-10 & 14 \\ \hline-20 & 9 \\ \hline-30 & 5 \\ \hline-40 & 1.5 \\ \hline \end{array} $$ (a) Plot the data as impact energy versus temperature. (b) Determine a ductile-to-brittle transition temperature as the temperature corresponding to the average of the maximum and minimum impact energies. (c) Determine a ductile-to-brittle transition temperature as the temperature at which the impact energy is \(20 \mathrm{~J}\).

A cylindrical 2014-T6 aluminum alloy bar is subjected to compression-tension stress cycling along its axis; results of these tests are shown in Figure \(8.20 .\) If the bar diameter is \(12.0 \mathrm{~mm}\), calculate the maximum allowable load amplitude (in N) to ensure that fatigue failure will not occur at \(10^{7}\) cycles. Assume a factor of safety of \(3.0\), data in Figure \(8.20\) were taken for reversed axial tensioncompression tests, and that \(S\) is stress amplitude.

What is the maximum carbon content possible for a plain carbon steel that must have an impact energy of at least \(200 \mathrm{~J}\) at \(-50^{\circ} \mathrm{C} ?\)

A cylindrical rod of diameter \(6.7 \mathrm{~mm}\) fabricated from a \(70 \mathrm{Cu}-30 \mathrm{Zn}\) brass alloy is subjected to rotating-bending load cycling; test results (as \(S-N\) behavior) are shown in Figure 8.20. If the maximum and minimum loads are \(+120 \mathrm{~N}\) and \(-120 \mathrm{~N}\), respectively, determine its fatigue life. Assume that the separation between loadbearing points is \(67.5 \mathrm{~mm}\).

A cylindrical component constructed from an S-590 alloy (Figure 8.31) has a diameter of \(14.5 \mathrm{~mm}\) (0.57 in.). Determine the maximum load that may be applied for it to survive \(10 \mathrm{~h}\) at \(925^{\circ} \mathrm{C}\left(1700^{\circ} \mathrm{F}\right)\).
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