Question

a. With the aid of appropriate sketches, explain how the following factors influence material creep behaviour,

i. Exposure time

ii. Applied mechanical load

iii. Exposure temperature

iv. Material mechanical properties.

b. In a typical creep test, load level (typically below material yield strength) and temperature are kept constant while specimen deformation is monitored with time. Three stages may typically be observed.

i. Sketch a typical strain-time curve for the creep life of a component.

ii. On the sketch in (i), indicate instantaneous, primary, secondary and tertiary stages.

iii. For the primary, secondary and tertiary stages, sketch the strain-rate time curve.

iv. Sketch how the sketch in (i) would change when temperature is increased.

Answer 1

11 Creep is the time_dependant phinomenon. Creep depends upon the expouse time.cat -QIKT de dt com db e 1 Effect of Applied load on creep is shown in ng Sex 8270 strain е c time · Stron rate increases with load applied 111] Effect of ecpogure temperature TT2 TzZT Stran 1 Ti Zime .: strain Rate increases with increase in temp

i] Material mechanical property From equu de at com -Q/KT e db as grain size increases Stocein rate due to creeping decreases. creep life of a component With increasein temp, strain rate TEST Increasesin primary straint Region -Tz> Tz primog Seconcey Tertiary DI time Tertiary strain Rate secondary primary time Strain Rate is almost_constant in secondary regios