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8.3 Stress Concentrations
Stress concentrations must be minimised in component design. They are especially important when fluctuating loads are present because fatigue failures are often the result of a geometrical discontinuity (notch), where the local value of stress is greater than the nominal. The severity of the concentration depends entirely on:

The geometrical shape gives rise to a theoretical stress concentration factor, Kt.

Kt = (maximum level of stress attained)/ (average level of stress at section)

Consult standard texts on the subject andthe Engineering Sciences Data Unit Item No. 69021 (Elastic Stress Concentration Factors) for values Kt .

The material sensitivity factor, q, is related to its metallurgical properties. q = (1 + a/r)-l

You can now calculate the fatigue strength reduction factor (Kf). Kf ={ 1 + q (Kt - 1)}-1