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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,
Kt = Smax/Sav
Smax, maximum stress at discontinuity and Sav, nominal stress.
Kt, 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
Stress concentration in fatigue.
Kf, fatigue stress concentration factor,
Kf = endurance limit of notch free
endurance limit of notched part
Notch sensitivity factor, q = Kf - 1
Kt - 1
Generally , q
1 as material strength increases and sensitive to
notches.
Kf = Kt
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)

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