### Creep

• Understand the phenomenon of creep when a material is loaded at elevated temperature.

• Define creep and specify the conditions under which it occurs.

• Given the absolute melting temperature of a metal, estimate the temperature at which creep becomes important.

• Calculate the strain rate depending upon stress, stress sensitivity and time.

Creep is the time-varying plastic deformation of a material stressed at high temperatures.
The creep rate can be calculated by the following equation:

$\dfrac{d\epsilon }{dt} = A \sigma ^{n}e^{\frac{-Q}{RT}}$

where
$\displaystyle \large \epsilon$ = strain
t = time
A = Pre-exponential constant
$\displaystyle \large \sigma$ = Applied stress
n = stress sensitivity
Creep (Thermal failure) takes place where there is stress combined with high temperature. e.g. turbine blades, nuclear reactors, etc.

### Solved Example:

#### 59-1-01

Time dependent permanent deformation is called _____________ (AFCAT EKT Mech Paper I- Set 2 2016)

### Solved Example:

#### 59-1-02

Slow plastic deformation of metals under a constant stress is known as: (CIL MT Mech 2020)