Dog-bone versus Gaussian gigacycle fatigue specimens for size effect evaluation

Gigacycle fatigue properties of materials are strongly affected by the specimen risk volume (region subjected to a stress amplitude above the 90% of the maximum stress). Gigacycle fatigue tests, performed with ultrasonic fatigue testing machines, are commonly carried out by using hourglass shaped specimens with a small risk volume. The adoption of traditional dog-bone specimens allows for increasing the risk volume, but the increment is however limited. In order to obtain larger risk volumes, a new specimen shape is proposed (Gaussian specimen). The dog-bone and the Gaussian specimens are compared through Finite Element Analyses. The range of applicability of the two different specimens in terms of available risk volume and stress concentration effects due to the cross section variation is determined. Finally, the Finite Element model is validated experimentally by means of strain gages measurements.