GATE Mechanical Engineering (ME) 2019 Shift 1 Solved Paper

Question : 23 of 65

Marks: +1, -0

During a high cycle fatigue test, a metallic specimen is subjected to cyclic loading with a mean stress of

+140 \mathrm{MPa}

, and a minimum stress of

-70 \mathrm{MPa}

. The R-ratio (minimum stress to maximum stress) for this cyclic loading is _________________(round off to one decimal place)

Solution:

Mean stress

= +140

MPa
Minimum stress

= -70

MPa
mean stress

=\;{\;\text " max stress "\;+\;\text " min stress "\;}/{2}

Therefore, max stress

=+350 {\MPa}

So,

R-

ratio (minimum stress to maximum stress)

=\;{\;\text " min stress "\;}/{\;\text " max stress "\;}=\;{-70}/{+350}=-\;{1}/{5}=-0.2

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