Chapter 8: Problem 24
Briefly explain the difference between fatigue striations and beachmarks in terms of both (a) size and (b) origin.
Chapter 8: Problem 24
Briefly explain the difference between fatigue striations and beachmarks in terms of both (a) size and (b) origin.
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Get started for freeA polystyrene component must not fail when a tensile stress of \(1.25 \mathrm{MPa}(180 \mathrm{psi})\) is applied. Determine the maximum allowable surface crack length if the surface energy of polystyrene is \(0.50 \mathrm{~J} / \mathrm{m}^{2}\left(2.86 \times 10^{-3}\right.\) in.-lb \(\left._{\mathrm{t}} / \mathrm{in} .^{2}\right)\). Assume a modulus of elasticity of \(3.0 \mathrm{GPa}\) \(\left(0.435 \times 10^{6} \mathrm{psi}\right)\)
A large plate is fabricated from a steel alloy that has a plane strain fracture toughness of \(55 \mathrm{MPa} \sqrt{\mathrm{m}}(50 \mathrm{ksi} \sqrt{\mathrm{in} .})\). If, during service use, the plate is exposed to a tensile stress of \(200 \mathrm{MPa}(29,000 \mathrm{psi})\), determine the minimum length of a surface crack that will lead to fracture. Assume a value of \(1.0\) for \(Y\).
The fatigue data for a brass alloy are given as follows: $$ \begin{array}{cc} \hline \begin{array}{c} \text { Stress Amplitude } \\ \text { (MPa) } \end{array} & \begin{array}{c} \text { Cycles to } \\ \text { Failure } \end{array} \\ \hline 310 & 2 \times 10^{5} \\ 223 & 1 \times 10^{6} \\ 191 & 3 \times 10^{6} \\ 168 & 1 \times 10^{7} \\ 153 & 3 \times 10^{7} \\ 143 & 1 \times 10^{8} \\ 134 & 3 \times 10^{8} \\ 127 & 1 \times 10^{9} \\ \hline \end{array} $$ (a) Make an \(S-N\) plot (stress amplitude versus logarithm cycles to failure) using these data. (b) Determine the fatigue strength at \(5 \times 10^{5}\) cycles. (c) Determine the fatigue life for \(200 \mathrm{MPa}\).
A cylindrical 1045 steel bar (Figure 8.34) is subjected to repeated tension- compression stress cycling along its axis. If the load amplitude is \(22,000 \mathrm{~N}\left(4950 \mathrm{lb}_{\mathrm{f}}\right)\), compute the minimum allowable bar diameter to ensure that fatigue failure will not occur. Assume a factor of safety of \(2.0\).
A specimen of a 4340 steel alloy having a plane strain fracture toughness of \(45 \mathrm{MPa} \sqrt{\mathrm{m}}\) (41 ksi \(\sqrt{\text { in. }})\) is exposed to a stress of 1000 MPa (145,000 psi). Will this specimen experience fracture if it is known that the largest surface crack is \(0.75 \mathrm{~mm}(0.03\) in.) long? Why or why not? Assume that the parameter \(Y\) has a value of \(1.0\).
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