Effect of Pre-Strain on the Fatigue Limit of 7:3 Brass Specimens

Abstract

Either with the aim of studying the effect of the pre-strain on the fatigue strength of materials, or for the purpose of increasing fatigue strength, there have been investigators so many who have tested many materials with various amounts of pre-strain under repeated stresses, such as push-pull, rotary or reversed bending, and reversed torsion with some of those having mean stress, and the results from these tests indicate that fatigue limit is generally increased by pre-strain. On the other hand, there have been reports that the fatigue limit of specimens that have been subjected to a small amount of pre-strain (just above yield point) drops below that of the original material.The above-mentioned facts are ascertained in this paper by the experiments with 7:3 brass specimens with electro-polished and pre-strained surface. The amounts of pre-strain are 1.3, 5.3 and 8.7%. With 1.3% pre-strain, the fatigue limit decreases 8.3%. This phenomenon is explained by the fact that slips occurred in relatively weak grains on the surface of the specimen. The damage is retained and there is no artificial strengthening of the material. On the other hand, in the largely pre-strained state, the improvement by artifice is greater than the damaging effect due to the slip, and the fatigue limit is increased. By this consideration, the same phenomenon about notched prestrained specimens can also be explained.