STRESS CONCENTRATIONS : CAUSE,EFFECT AND SOLUTION EXPLAINED !!

Stress concentration is the accumulation of stress in a body due to sudden change in its geometry. When there is a sudden change in the geometry of the body due to cracks sharp corners, holes and decrease in the cross section area, then there is an increase in the localised stress near these cracks, sharp corners, holes, and decreased cross section area. The body tends to fail from these places where the stress concentration is more. So to prevent a body from getting failed, the stress concentration should be avoided or reduced.It is also called as stress raisers or stress risers.

Cause:

The stress concentration in a body happens because of sudden change in the geometry of the body due to cracks, sharp corners, holes, decrease in the cross section area. Due to these irregularities, there is an increase in the intensity of stress in the body.

Effect

When a body has stress concentration in it, the chances of its failure increases. The body tends to fail from the place where it is has more concentration of stress. A body has less life that has more irregularities within it. In order to increase the life of the body, the intensity of stress should be reduced.

Stress concentration factor

The stress concentration factor is defined as the ratio of highest stress in the body to the reference stress. It is denoted by Kt.

Mathematically,

Where
σmax = Highest stress or maximum stress
σref = Reference stress

The value of stress concentration factor for
(i) A body free from irregularities is 1.
(ii) A body that has maximum irregularities or discontinuity is greater than 1.

Methods to Reduce Stress Concentration

1. There are no of ways to reduce stress concentration in a body and some of these are:

Avoiding sharp corners by providing a fillet radius at the sharp corners. By providing the fillet radius at sharp corners, the cross section area decreases gradually instead of suddenly. And this distributes the stress in the body more uniformly. This is shown in the figure given below.

2. By providing small holes near big hole. If we have an object, that has an internal hole within it. Then the intensity of stress near that hole is more. To avoid this, some smaller holes are created near that hole. This distributes the stress more uniformly than it was before. This is shown in the figure given below.

3. By decreasing the nominal diameter of a threaded object and make it equal to the core diameter. Suppose we have a threaded object. And the intensity of stress at threaded part is more. The chances of object may fail is more at the threaded part. This can be avoided by decreasing the nominal diameter of the shank and make it equal to the core diameter. This will distribute the stress more uniformly in the object with threads.

4. By providing notches or undercut at the sharp corners.