Impact of High-Pressure Gaseous Hydrogen on the Fatigue Behaviour of Austenitic Steel A-286 under Asymmetric Loading Conditions

Ultrasonic techniques are an established means for carrying out fatigue tests at very highnumbers of cycles. These techniques are based on the formation of a standing ultrasonic wave inthe specimen and usually use frequencies around 20 kHz. Although such systems allow testing to avery high number of cycles in a relatively short time, the use of a standing wave for creating thestrains restricts them to symmetric push-pull mode. This limitation can be overcome by coupling an ultrasonic test device to a universal test rig. In this work a different approach is presented that is particularly well suited for studying environmental effects. The load train with the specimen is enclosed in a pressure vessel. An acoustic horn divides this pressure vessel into two separate chambers. Applying a pressure difference between the two chambers then leads to a static stress in the specimenon which the oscillating stress from ultrasonic excitation is superposed. The addition of both stresses allows testing at varying R ratio. The deteriorating effect of high-pressure gaseous hydrogen on the steel A-286 is investigated as function of oscillating and static stresses at room temperature. SEM analysis of the fracture surface is presented.