Stress Concentration Factor Calculator (Kt, Kf, q)

Your details

Choose the geometry that matches your part. All four follow classic Peterson / Pilkey curve fits.
Full width of the plate including the hole.
mm
Diameter of the central circular hole.
mm
Plate thickness (out-of-plane dimension).
mm
Tensile or compressive force applied to the bar or plate.
kN
Material Sut is used to compute Peterson material constant a and notch sensitivity q. Leave at 0 to skip Kf.
MPa
Theoretical stress concentration factor (Kt)Moderate concentration
2.307

Ratio of maximum stress to nominal stress based on geometry alone.

Diameter / width ratio (d/w)0.333
Nominal stress (sigma_nom)37.5MPa
Maximum stress (sigma_max)86.5MPa
Notch sensitivity (q)0.977
Fatigue notch factor (Kf)2.277
Peterson material constant (a)0.236mm
2.307
Low (< 1.5)<1.5Moderate (1.5 - 2.5)1.5-2.5High (> 2.5)2.5+

Kt = 2.307 - moderate stress concentration

  • Kt = 2.307 means the local peak stress is 2.31 times the nominal stress at the notch in your plate with central circular hole under axial load.
  • Nominal stress is 37.5 MPa; peak stress at the notch is 86.5 MPa.
  • Notch sensitivity q = 0.977: the material responds to 98% of the theoretical concentration in fatigue.
  • Fatigue notch factor Kf = 2.277 is used to reduce the endurance limit in fatigue life calculations (Kf < Kt because real materials are not fully sensitive).

Next stepModerate Kt values are acceptable in low-stress applications but should be accounted for in any fatigue life assessment using the computed Kf.

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