Research On Phenomenon And Laws When The Specimen Loss Of Contact With Its Supports In The Dynamic Fracture Test

This paper has researched about the contact condition of specimen and its supports when did dynamic fracture tests on Hopkinson pressure bar.In the static three-point bend test with standard impact specimen, the specimen was maintain three-point bend state with its support, but it might be loss contact with its support in the dynamic test because of the high loading speed. That is to say, specimen may be departed from three-point bend state. But at present, there is no unified cognition to the phenomenon and regularity of the specimen and its supports. This paper monitored the loading time by pasted semi-conducting strain gage on the support when the specimen was loaded-on. By comparison, we can found that the specimen was loss of contact with its support rather than been in three-point bend state right in the loading instant. Obviously this change in contact condition significantly influenced the measurement of material's dynamic fracture degree.The divorce phenomenon is contact with the elastic property of the specimen and is supports system. When the installation of the test is constant, the divorce phenomenon is only related to conditions such as sizes of temples, speeds of bullet. By varied the span, the length and width of samples and the speed of bullet, the results showed that the speed of bullet slightly influenced the divorcing time while the span and the length and width of sample showed obvious influence. Critical conditions can be got from the research:S/L- (W-20) /25.15>0.67There is also mathematical model in this paper about the attack instant, use the mathematic analysis critical conditions that specimen loss contact with its supports can also got. Postulate there is no breadth change, the critical condition is: This consequence is the same as the one we got from the test.