Rotating Bending Fatigue Test of Crank Shafts : (Part 1, Effect of Fillet Radius)

Abstract

The authors have carried out statical stress measurements and rotating bending fatigue tests on three model crank shafts (80mm in pin diameter, 45mm in web thickness, 106mm in web breadth) having pin fillet radii of 8.0, 5.0 and 3.0mm respectively. Rotating bending fatigue strengths of plain cylindrical specimens of several sizes taken axially and tangentially from the crank material (0.3% carbon steel) have also studied. The following facts have been revealed by the tests. (1) The nominal fatigue limits of the crank shafts represented in terms of crank-pin (quotient of bending moment devided by the section modulus) are 6.80, 5.50 and 4.25kg/mm² where the fillet radii are 8.0, 5.0 and 3.0mm respectively. (2) The quotients of fatigue limit of 10φ mm plain cylindrical specimens taken from the carnk web perpendicularly to metal flow of forging devided by the stress concentration factors (the ratio of actual stress at fillet to the nominal stress at crank-pin) are nearly equal to the nominal fatigue limits of the crank shafts represented in terms of crank-pin.