What is stress concentration? Explain any four methods to reduce it.

Stress Concentration: Whenever a machine component changes the shape of its cross-section, the simple stress distribution no longer holds good and the neighborhood of the discontinuity is different. This irregularity in the stress distribution caused by abrupt changes of form is called stress concentration. It occurs for all kinds of stresses in the presence of fillets, notches, holes, keyways, splines, surface roughness or scratches etc.

Causes of stress concentration are as under. i) Abrupt changes in cross-section like in keyway, steps, grooves, threaded holes results in stress concentration. ii) Poor surface finish – The surface irregularities is also one of the reason for stress concentration.

iii) Localized loading – Due to heavy load on small area the stress concentration occurs in the vicinity of loaded area. iv)Variation in material properties – Particularly defects like internal flaws, voids, cracks, air holes, cavities also results in stress concentration.

Two methods of reducing stress concentration :( Any two Methods with sketch 4 Marks ) 1) Introducing additional notches and holes in tension member 2) Fillet radius ,undercutting & notches for member I bending 3) Reduction of stress concentration in threaded portion 4) Drilling additional holes for shaft