抄録
The present writers have investigated the accelerated testing for predicting the fatigue limit of hard drawn steel wire by means of stepwise load increase test with Haigh-Robertson wire fatigue testing machine, and have cleared the simplified method for predicting the fatigue limit with only one loading rate.
The principal results of this investigation can be summarized as follows:
1) The modified Prot method that takes the exponent n=0.40 in equation σR=σW+k·αn, produces better agreement with conventional Wöhler fatigue limit than does the original Prot method based n=0.50.
2) Stepwise load increase test using four loading rates with three specimens can reduce the fatigue testing time to one third as compared with conventional Wöhler procedure.
3) Simplified method for predicting the fatigue limit with only one loading rate can be performed by increasing the division plate reading of head stock by 0.1 degree to every 50000 cycles until the specimen (l=150d) breaks down. The starting stress is taken about 10% lower than the experientialy expected fatigue limit. For 0.6% carbon hard drawn steel wire, if the mean value of the stresses at failure for three specimens is divided by 1.09, a value close to Wöhler fatigue limit, with an error less±3.2%, may be obtained. The testing time can be reduced to one sixth as compared with that of conventional Wöhler procedure.
