Creep

Question 1

What is creep?

Answer 1

With increasing temperature, the strain in a material may increase with time even at a constant applied load, this time dependence of strain is termed CREEP

Question 2

What is stress relaxation?

Answer 2

The complementary time-dependent response to creep, this happens when the strain in a structure is kept constant for a time period.

Question 3

What is the initial strain?

Answer 3

This is the elastic strain before creep occurs, may extend into the plastic range due to first load application

Question 4

What is primary creep?

Answer 4

The slope (creep rate) decreases with time, strain hardening is occurring more rapidly than softening due to the high temperature

Question 5

What is secondary (steady state) creep?

Answer 5

Constant slope as there is equilibrium between strain hardening and thermal softening

Question 6

What is tertiary creep?

Answer 6

Slope increased with time. eventually leads to complete fracture

Question 7

What stage of creep are we interested in?

Answer 7

We are mainly interested in the secondary creep as this is producing the major contribution to total creep strain.

Question 8

How does the strain rate correspond to the temperature and stress?

Answer 8

Strain rate increases for increasing values of stress and temperature

Question 9

What are the parameters in T(C+log t)=L

Answer 9

T=is the temperature in Kelvin
C=constant with values usually around 20
t= rupture time
L=function of applied stress

Question 10

When does stress relaxation occur?

Answer 10

Stress relaxation occurs under constant strain