Investigation Of Determination Of Dynamic Fracture Toughness Using A Hopkinson Bar

The testing technology of dynamic fracture toughness using a Hopkinson bar has been studied, the main contents of research as follows:The end of loading bar in the Hopkinson bar apparatus for dynamic fracture test is a wedge which is geometrically similar to the nose of the hammer of the impact pendulum. It is doubtful whether one-dimensional stress wave theory as the application foundation of Hopkinson bar tests can be used because of the shape change of loading bar. The influence of wedge on transmitting of stresss wave and determination of dynamic fracture toughness was analyzed in this article. Three diffierent sizes of wedge were designed, those were:3, 15.5 and 40mm. The tests of no specimens in front of wedge and dynamic fracture tests were finished, it was found that the size of wedge was larger, the oscillations in load-time curve were larger and the error of evaluated crack-initiation time was lager because the reflect time of reflect wave was more ahead. So the influence of wedge on determination dynamic fracture toughenss is smaller for shorter wedge correspond with the precision of test was higher. Additional, two improvement methods for determination of dynamic fracture toughness were put forward, those were dispersion correction for loading bar and inertia correction for wedge.The two methods were validity as the results were good.The loading state of specimen is important for calculation of the temporal evolution of dynamic stress intensity factor. The dynamic fracture tests in a Hopkinson bar were sometimes considered as three-point bending tests. The loss-of-contact between specimen and supports in the dynamic fracture test in a Hopkinson bar was verified by the strain gage on support and this test is one-point bend test not a three-point bend test because cracks are initiated in the period of loss-of-contact. A simple formula for calculated K₁ (t) in one-point bend tests was put forward. The conditions of loss-of-contact were analyzed and obtained based on Timoshenko'beam theory. And a ture three-point bending test was fulfilled by adjustion specimen span. Because crack tip in three-point bending test will suffer a state of one-point bending for a period of time, one-point bending test is better.The incident pulse shaping technique can be used to filter high frequency...