Size effect on the contact state between fracture specimen and supports in Hopkinson bar loaded fracture test

To thoroughly understand the dynamic behavior of a fracture specimen under stress wave loading, dynamic fracture test with various three-point bend (3PB) specimens are performed on the Hopkinson bar loaded experimental apparatus. The contact state between the fracture specimen and supports during the loading process is examined via stress wave propagation analysis. The experimental results show that the fracture specimen with usual dimensions does not keep contact with supports in the initial loading stage, i.e. a loss of contact phenomenon occurred. The specimen dimensions and the span of the loading apparatus are important factors affecting specimen's contact state. The loss of contact is more obvious with increasing span under the same specimen dimensions. Conversely, the loss of contact gradually disappears with increasing specimen length or increasing width under a fixed span. Based on experimental investigations, a criterion is established to ensure the fracture specimen keep in contact with supports during dynamic fracture test.