Low-cycle impact fatigue testing based on an automatized split Hopkinson bar device

Preventing fatigue damage and failure in components subjected to repeated impact loading is of great interest in many engineering applications. Quite often, material response during high-rate loading differs from quasi-static response due to the material’s strain rate sensitivity and adiabatic heating effects. Hence, experimental materials testing at realistic loading rates is important in many cases of impact fatigue. Impact loading tests involve an inherent challenge: since force equilibrium does not exist, the dynamic response of the whole load train must be properly accounted for in order to impose the desired loading on the specimen and to measure the specimen response. In the field of monotonic high strain rate materials testing, the Split Hopkinson Bar (SHB) technique has established itself due to its simplicity in terms of structural dynamics. However, traditional SHB setups require a long time to be reset/rearmed after the impact, and therefore they are ill-suited for cyclic impact loading studies. In this contribution, we present a modified SHB technique with fully automatized rapid resetting/rearming of the setup, which allows for controlled cyclic impact loading at a rate of 0.5 Hz. The applicability of the method is demonstrated in this paper with test results for a tempered steel.