The Use of Shot Peening to Reduce Weight

Abstract

The object of this investigation was to explore the possibilities of utilizing the shot-peening process on laminated spring leaves from silico-manganese spring steel as a means of increasing the working stresses, and thus reducing weight without loss in fatigue life.

The first part of the investigation showed that so far as fatigue tests alone were concerned it should be possible to increase the working stresses and thus save weight. To do this, however, would involve the bump stress exceeding the primitive elastic limit of the material.

Investigation of the effect of scragging (prestressing) to the British Standards (B.S.) Test Deflexion of L²/900t as at present adopted in manufacture showed that such scragging had practically no effect on the elastic limit, but that if the scrag deflexion was increased to approximately L²/400t an increase in the apparent elastic limit of the order of 40 per cent of the primitive elastic limit could be obtained, and that such scragging also improved the fatigue life in both the plain and shot-peened conditions.

It is considered that with effective scragging and shot peening it is probable that very considerable savings in weight, of the order of at least 20–25 per cent, and under certain conditions even more may be obtainable, provided trouble does not arise due to superimposed stresses of starting and braking torques, and possible embrittlement due to effective scragging. This does not seem to the author to be particularly likely at a weight saving of 20–25 per cent, but can be settled only by service trials which he feels should now be undertaken.