Define stress concentration. Explain any four methods to reduce it with neat sketch.
4 Answers
Answer :
Stress Concentration: Whenever the machine component changes the shape of its cross section the stress distribution pattern no longer holds good and the neighborhood of the discontinuity is different. The stresses induced in the neighborhood are much higher than the stress induced in the other part of the component. This abrupt change in cross section or the discontinuity form is called stress concentration. It is for all kinds of stresses caused due to keyways, grooves, notches, roughness or scratches.
The effect of stress concentration cannot be completely eliminated but its effect can be reduced by altering the geometry of the component.
So the following methods are adopted to reduce the effect of stress concentration:
1. Providing additional holes and notches.
a. Use of multiple notches.
b. Drilling additional holes.
c. Removing roughness.
2. By providing fillet radius to the corners of the members and under and notches for the members in bending.
3. Reduction in stress concentration of the threaded component.
4. By drilling small holes near the large holes or providing additional holes in the shafts.
5. By providing taper cross sections to the members having sharp corners.
Answer :
Whenever there is a change in cross section of machine components, it causes high localized stresses. This effect is called as stress concentration.
Causes of Stress Concentration: i) Variation in properties of material from point to point due to cavities, cracks or air pockets. ii) Abrupt changes of shape and cross section. iii) Concentrated loads applied at points or small areas of machine elements. iv) Force flow line is bent as it passes from the shank portion to threaded portion of component due to changes in cross section. This results in stress concentration in transition plane. v) Local Pressures
The methods of reducing stress concentration:
1. The methods of reducing stress concentration in cylindrical members subjected to tensile load.
In Fig. (a) it is seen that stress lines tend to bunch up and cut very close to the sharp re-entrant corner. In order to improve the situation, fillets may be provided, as shown in Fig. (b) and (c) to give more equally spaced flow lines. It may be noted that it is not practicable to use large radius fillets as in case of ball and roller bearing mountings. In such cases, notches may be cut as shown in Fig.(d)
2. The methods of reducing stress concentration in cylindrical members with shoulders subjected to bending moment.
3. The methods of reducing stress concentration in cylindrical members with shoulders hole, subjected to tensile load.
4. Methods of reducing stress concentration in cylindrical members with threads.
5. Methods of reducing stress concentration of a press fit