Stress Concentration In almost engineering components and machine have to incorporate design features which introduce changes in thin cross-section. Changes in cross section causes localized stress concentrations and severity depends on the geometry of the discontinuity and nature of the material. Stress concentration factor, K t = S max /S av S max, maximum stress at discontinuity and S av, nominal stress. K t, value depends only on geometry of the part. Applies to brittle & notch sensitive materials. Should consider when using high-strength, low ductility, case-hardened & / or heavily cold work materials.

Stress concentration in fatigue. K f, fatigue stress concentration factor, K f = endurance limit of notch free endurance limit of notched part Notch sensitivity factor, q = K f - 1 K t - 1 Generally, q 1 as material strength increases and sensitive to notches. K f = K t q also depend on component size. Stress-raiser, dangerous in larger masses. Stress Concentration

Guidelines for design. Abrupt changes in cross-section should be avoided. Fillet radii or stress-relieving groove should be provided. Fig. 11.3(d) Slot and grooves should be provided with generous run-out radii and with fillet radii in all corners. Fig. 11.3(b) Stress relieving grooves or undercut should be provided at the end of threads and splines. Fig. 11.3(c) Sharp internal corners and external edges should be avoided Weakening features like bolt and oil holes, identification marks, and part number should not be located in highly stressed areas. Weakening features should be staggered to avoid the addition of their stress concentration effects, Fig. 11.3(d) Stress Concentration