What is stress concentration? Explain the methods to reduce stress concentration.

 Whenever a machine part suddenly changes its geometrical shape, the simple stress no longer remains the same but increases.This increase in stress due to sudden change in geometrical shape is called stress concentration.

Geometric discontinuities cause on object to experience a local increase in the intensity of a stress filed.

The stress concentration occur near cracks, sharp corners, holes and changes in the cross sectional area of the object.

It should also be noted that tool marks. Porosity in casting etc. may also give rise to stress concentration effect.

High local stresses can cause the object to fail more quickly than if it wasn't there.                                      Engineers must design the geometrical shapes of the objects to minimize stress concentrations.

In many design situations , it is not possible to altogether avoid the effect of stress concentration, but it can be minimized by making logical changes in the design of the parts.

   

                                              Stress Concentration in a shaft due to change                                                                                                         in geometrical shape

                                            

   

                                          Poor design                   Better design                                           

For example a stepped shaft can be gradually reduced in diameter than abrupt reduction.Another example to reduce one of the worst types of stress concentrations a crack is to drill a large hole at the end of the crack. the drilled hole with its relatively large diameter, causes a smaller stress concentration than the sharp end of a crack.

In mechanical design, stress concentration effect can be reduced by placing these geometric features in a non critical stress zone.