A New Device for Tensile and Compressive Testing at Intermediate Strain Rates

A new device for conducting tensile and compressive tests at strain rates ranging from about 20 s⁻¹ to 250 s⁻¹ is presented. The operation of the device is based on the principles of the Split Hopkinson Bar (SHB) technique, except that the incident bar is replaced by a fast hydraulic actuator and the transmitter bar is very long. One end of the specimen, which is short and has a small cross-sectional area relative to the cross-sectional area of the transmitter bar (like in a SHB test) is attached at one end of the transmitter bar. During a test the actuator applies a force to the specimen. Upon loading the specimen deforms between the actuator and the end of the transmitter bar and a tensile, or compressive, wave starts propagating along the bar. The wave travels to the end of the transmitter bar and reflects back. The force in the specimen is determined from the amplitude of the wave. Digital Image Correlation (DIC) is used to measure the deformation directly on the surface of the specimen. The 40 m long transmitter bar provides 15 ms of time to conduct a test. Stress strain curves from tensile and compression tests with the new device are clean and smooth without any evidence of oscillations or ringing.