Problem:
A tension link shown to the right is used in earth-moving equipment and is subjected to cyclic stresses varying from 10 ksi to 35 ksi. The link contains an internal crack that is 4 in long. If the link is made from A517 steel (σys=110 ksi and Kic= 170 ksi.in1/2), do the following:
a) Determine the factor of safety against net section yield in the presence of the crack.
b) Determine the factor of safety against brittle fracture for the same conditions.
c) If the maximum stress were increased (due to an accidental overload), which would occur first, net section yield or brittle fracture? Explain.
d) For Paris law coefficient of C=0.66 x 10-8 and n = 2.25, where stress is measured in ksi and crack growth in inches, estimate the number of cycles needed to grow the crack by the amount of 0.1 in.
e) If you were the engineer responsible for analyzing the life of this part, what would be your recommendation for continued service of this part (e.g. stopping using it immediately, repair or continue using it until next inspection, etc.)? Justify your decision based on sound engineering principles.
