The Fatigue Limit of Semi Built-Up Type Crankshafts and its Estimation

Abstract

For the estimation of the fatigue limit of semi built-up type crankshaft, the following essential informations have been obtained by means of actual sized crankshafts; a) the distribution of shrink fit stress around pin fillet, b) the change of the residual stress due to the fillet cold rolling before and after loading of cyclic stress, c) the improvement of material properties due to the fillet cold rolling, d) the change in the fatigue limit when shrink fit ratio has been increased.
The both value of the estimated, based on the above informations, and the actually measured have shown a fair agreement. The fatigue limit of semi built-up type crankshaft increases when increased in the shrink fit ratio at the first stage. However, it remains a constant value when the ratio was further increased. The critical area, in this case, moves from the below of pin to 30°-45°angle along the fillet.
The conclusion is that the fatigue limit of semi built-up type crankshafts is estimated by multiplying a strengthening coefficient due to shrink fit with journal by that of a round bar, and this coefficient has been derived.