Question

Which of the following is not true?

• Creep rate increases at higher temperatures:

• Creep rate increase with higher applied load

• Creep rate increase with decrease of temperature.

• Creep rate increase with increase of time

Answer 1

Creep Rate : When a material is subjected to a stress that is at higher temperature relatively plastic deformation can occur even when the stress is lower than the yield stress. This deformation is time-dependent and is known as creep. The rate of deformation is called the creep rate. It is the slope of the line in a Creep Strain vs. Time curve.

Primary Instantaneous Secondary Tertiary - - - - - - Rupture

There are three stage of Creep:

Primary Creep: starts at a rapid rate and slows with time.

Secondary Creep: has a relatively uniform rate.

Tertiary Creep: It has an accelerated creep rate and terminates when the material breaks or ruptures. It is associated with both necking and formation of grain boundary voids.

Therefore 4th Option i.e. " Creep rate increases with increase of time" is true except for primary creep, but overall we can say Creep rate increases with increase of time.

Effect of Temperature & Stress/load:

The equation governing the rate of steady state creep is:

Creep Ratelė) = Ao"experten

Where,Q = activation energy;   n = stress exponent;    A = constant and T= temperature

From the above equation we can conclude that Creep rate increases with increase of Temperature and Creep rate also increases with stress component or load

Therefore 1st Option i.e. "Creep rate increases at higher temperatures" is true

2nd Option i.e. "Creep rate increases at higher applied load." is true

3rd Option i.e. " Creep rate increases with decreases of temperature" is not true

rather creep rate increases with increase of temperature,

Therefore your correct answer is the 3rd Option

Answer 2

ANSWER :

Creep rate increases at higher temperatures and higher applied load.

So, option 1 and 2 are true.

Creep rate also increases with time. So, option 4 is also true.

Creep rate does not increase with decrease of temperature. So, option 3 is NOT TRUE.

Hence, answer is : OPTION 3 is NOT TRUE .