The Fatigue Strength under Bending, Torsional and Combined Stresses of Steel Test Pieces with Stress Concentrations

Abstract

In previous investigations (Gough, Pollard, and Clenshaw 1951)§ under the same general research programme, determinations were made of the intrinsic and vee-notched fatigue strengths of the first seven steels here investigated, under various combinations of bending and torsion. The intrinsic fatigue limits were found to fit reasonably to an ellipse quadrant, and the notched fatigue limits to a two-constant displaced ellipse or ‘ellipse arc’. The bulk of the present paper concerns the behaviour under combinations of bending and torsional stresses of test pieces with transverse holes, for the same seven steels. The fatigue limits under the various stress combinations have been found to fit reasonably to an ellipse arc of the same form as for the vee-Notched Specimens. The similarity in form of the ellipse arcs for the seven materials supports the theoretical conclusion that the shape of the curve is dependent only on the shape of the hole, and is independent of the nature of the material. The information given on strength reduction factors under various combinations of bending and torsion, together with the tables of results of supplementary static tests, should be of use in such problems as crankshaft design. The paper also includes the results of flexural and torsional fatigue tests on an aircraft crankshaft steel, with other forms of stress concentration. These results are compared with those on two other steels of similar composition.