Shoulder Radius Research Articles

Effect of test piece length on the fatigue strength of steel in air

1. It is established that the scale factor for short fatigue test pieces is a function of their diameter, length, and shoulder radius, the latter parameter having no effect on the fatigue properties of long test pieces. 2. Our results, demonstrating the dependence of the endurance limit (the principal fatigue strength characteristic) on the length and, consequently, the volume of the test piece, lend support to the statistical theory of the scale factor, the validity of which was doubtful before the existence of such a relationship was established. 3. The results of the present investigation show that the resistance of materials to cyclic stresses should be determined on test pieces of two distinct types: either on test pieces of “zero” length (as recommended by a new draft Soviet standard) which are least affected by the scale factor (Fig. 3), or on specimens long enough to exclude the effect of the shoulder radius.

The Elastic Stress Concentration Factors in Shouldered Shafts

The description of a photoelastic investigation, initiated by the Structures Committee of the Royal Aeronautical Society, into the elastic stress concentration factors associated with shouldered shafts subjected to various simple forms of loading is completed in this part of the paper. A general description of the manufacture of the models, the photoelastic techniques employed to evaluate the s.c.f. and the results of the tests on shouldered shafts subjected to torsion and to bending have been given in the previous two parts.The present paper includes the results of the tests on shafts subjected to axial load, together with details of a supplementary investigation into the limiting value of the s.c.f., for a particular shoulder radius, as the depth of the shoulder is increased to infinity. A summary of the general conclusions for all forms of loading is given at the end of the paper.

The Elastic Stress Concentration Factors in Shouldered Shafts

SummaryThe photoelastic “stress freezing” technique has been employed to evaluate the elastic stress concentration factors associated with the fillet blend radius in a number of shouldered shafts. The full range of practical sizes of blend radius and depth of shoulder has been examined. Comprehensive results for the shaft subjected to torsion, pure bending and axial load are given in this (Part I) and in two subsequent papers (Parts II and III).The accuracy of the graphs of stress concentration factors is better than six per cent. Comparison has been made with the existing theoretical and experimental results for each mode of loading. The results of an investigation into die limiting value of the stress concentration factor (for a particular shoulder radius) as the depth of the shoulder is increased to infinity are included in Part III.