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MECHANICAL ENGINEERING DESIGN
TUTORIAL 4-14: STRESS CONCENTRATION
ORIGIN OF STRESS CONCENTRATIONS
Machine members often have regions in which the state of stress is significantly greater than
theoretical predictions as a result of:
1. Geometric discontinuities or stress raisers such as holes, notches, and fillets;
2. Internal microscopic irregularities (non-homogeneities) of the material created by such
manufacturing processes as casting and molding;
3. Surface irregularities such as cracks and marks created by machining operations.
These stress concentrations are highly localized effects which are functions of geometry and
loading. In this tutorial, we will examine the standard method of accounting for stress
concentrations caused by geometric features. Specifically, we will discuss the application of a
theoretical or geometric stress-concentration factor for determination of the true state of stress in
the vicinity of stress raisers.
THEORETICAL (GEOMETRIC) STRESS-CONCENTRATION FACTOR, Kt AND Kts
In order to predict the “actual” stress resulting from a geometric stress raiser, a theoretical stress-
concentration factor is applied to the nominal stress. For a part subjected to a normal stress, the true
stress in the immediate neighborhood of the geometric discontinuity