Solid Mechanics: Stress Relaxation and Creep Rupture Strength

Solid Mechanics:
1) Stress relaxation:
Creep is said to be the increase in the plastic strain by having the stress as the constant factor. A
good contact force could be achieved by having elastic strain with the maximum stress achieved.
The material selected should have the sufficient elastic modulus with the yield strength. The
stress-strain curve could serve as an indication of stress and strain relationship. Creep and stress
relaxation have two similar yet distinct mechanism through which there is an increase of plastic
strain over a period of time.
Stress relaxation is defined as the decrease in stress by having the strain as the constant factor.
The principle of creep could be best understood with the help of the elastic rubber band. When a
rubber band is stretched with the nominal weight then it tends to return back to its original
position. Suppose the rubber band is hung by the weight with the elevated temperature then there
occurs deformation with the occurrence of creep (weight is not varied) [1]. During unloading, the
tendency of the material that fails to come back to its original shape then it is known as the stress
relaxation. During stress relaxation the part remains unchanged. It could partially regain its
position after removing the deflection. Hence it is noted until the load is removed while the stress
relaxation is invisible [2]. The contact performance will decline steadily without any visual
effect.
ii) Creep Rupture Strength:
The stress applied to a material causing it to rupture at a constant temperature within a specified
time is known as creep rupture strength [3]. Similar to the creep test, the rupture test is also
carried out but at a higher stress level until the material fails and the failure time should be noted.
The sufficient chart is also plotted.
iii) Creep Life:
All the components are basically designed based on the reasonable life operation. Creep life is
defined as the life of the material at which the material could sustain above which causes certain
problem and failures.
iv) Factors affecting creep:
The following are the factors that affect the creep that are as follows: (Here the creep nature of
the concrete has been mentioned)
 Intensity of stress
 Loading age
 Temperature
 Coarse aggregate