Stress Raiser

Stress Raiser
Stress Raiser

What is stress raiser?

Stress raiser occur at abrupt sectional changes of machine parts or members. They are sometimes referred to as notches. Fillets are made in way of abrupt sectional changes to reduce the abruptness of the change in section.

What are its effect ?

The effect of abrupt changes on the stress pattern across a section of material in way of the section change is such that where the change occurs, the stress is not uniform across the section. It is higher at the corner or shoulder made by the change. Material at the surface will yield earlier than material remote from the shoulder and under conditions of simple or static stress some redistribution of stress occurs. This docs not have time to take place when a machine part is subjected to fluctuating stresses. It is therefore of the utmost importance to design properly and remove all stress raisers. This 1s done by making fillets between shoulders or having easy tapers on section changes with the end of any taper rounded in at its small end. This reduces to a minimum the chances of fatigue failure.

How it can be tackled?

Stress raisers cannot usually be obviated but the effects are reduced by the use of proper fillets which give a better stress distribution and reduce stress concentrations and variations in way of the change of section. An example of a fillet which we have all seen is the radius formed between the coupling flange and the parallel portion of an intermediate shaft. It can be seen then that a close relationship exists between the ability of an engine part or member to resist fatigue failure and the profile of the fillet in way of section changes. As a section change becomes more abrupt by reduction of fillet radius, the risk of fatigue failure is greatly increased.

Where it can occur?

Stress raisers may also occur in welded joints due to bad design, undercut or discontinuities in the way of the joint due to lack of penetration between the filler and the parent material.

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