GATE 2020 MT – Question 62
A fatigue specimen has constant-amplitude cyclic stress and zero mean stress, with $da/dN\propto(\Delta K)^3$. If crack length doubles, by what factor does growth rate rise? Round to 1 decimal place.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 2.6 to 3.0
Explanation
At unchanged stress range and geometry factor, $\Delta K\propto\sqrt a$. Doubling a multiplies ΔK by √2, so the cubic growth law multiplies da/dN by $(\sqrt2)^3=2\sqrt2=2.828$. The factor is 2.8. This scaling presumes the geometry factor remains effectively constant.