A test machine (10, 40, 60) for inducing high-cycle fatigue (at kilohertz vibration rates) in a specimen of a material under test. Each test machine (10, 40, 60) provides both dynamic and static loading. One embodiment is an SEM-compatible machine (10), having an inner frame (11) containing symmetrical components on either side of a stationary node. The specimen is placed at this stationary vibration node. Dynamic loading is the result of vibrations provided by two piezoelectric actuators (16) inside the frame (11), one on each side of the node. Static loading is provided by means of two stress rods (12), each extending from an end plate (11a) into the frame (11). A pair of cylindrical couplers (14) is also inside the frame, one coupler (14) on each side of the node. Each coupler (14) is attached to an associated piezoelectric actuator (16) and stress rod (12) such that the static and dynamic loads are transferred to the couplers (14). The specimen is held between the inner faces of each coupler 14 such that the loading is transferred to the specimen. The static and dynamic loading applied to the specimen are independent of each other and separately controllable.
Thomas E. Owen; David L. Davidson; Andrew Nagy