A tension member in service has been inspected and a
fatigue crack has been discovered as shown in sketch f.
A proposed solution is to drill a hole at the tip of the
crack, the intent being to reduce the stress concentration
at the crack tip. The material is 30-mm-thick annealed
AISI 1040 medium carbon steel, and was produced
through forging. If the load is a completely reversing
15 kN and the original design is as shown,
(a) What was the original factor of safety? Ans. ns =
2.9
(b) What is the smallest drilled hole which restores the
safety factor to that of the original design? (Use the
nearest 5 mm increment that is satisfactory.) Use a
reliability of 90%. Ans. 5 mm