Instrumented Impact Test Method Based On Acceleration

Charpy impact test is generally used to measure the impact toughness of materials. But the physical meaning of impact energy measured by traditional impact testing machine is not clear. The instrumented impact test is a new development of impact test. It can measure and record the force acting on the specimen during the impact, to give detail information about the elastic, plastic deformation and fracture process of the specimen. This paper used an accelerometer attached to the back of the hammer for Charpy impact test machine and combined with the most advanced virtual instrument technology to built an instrumented impact machine. The program was developed by the Lab VIE software. A series of impact tests were done with the instrumented impact machine. By measuring the acceleration of the pendulum during the test, the dynamic responses of the striker arm was studied. First the force-time curve, energy-time curve and the other impact characteristic curves was calculated to analysis the relationship between the material’s impact properties and the pendulum’s vibration. Second, the vibration of the striker arm was analysis by Euler Bernoulli beam theory, combined with the power spectrum density(PSD) of the accelerometer signal, the relationship between the dynamic response of the striker arm and the toughness of the given material was discussed. The studied results are as follows:(1) The measure using the virtual instrument technology and Lab VIEW software to development instrument impact test system was so simple and quick, and the system ran reliably. It can satisfy the requirements of instrumented impact test method;(2) It was found that the energy calculated with the accelerometer signals agreed well with the dial readings, and the vibration of the striker arm had no influence on the results. The force-time curve and the other impact characteristic curves calculated can give detail information about the elastic, plastic deformation and fracture process of the specimen;(3) The percentage of the energy absorbed by crack propagation for the total impact energy can be used to measure the toughening of material, The greater the percentage, the better toughness of the material;(4) The dynamic response of the striker under impact loading is the superposition of natural vibration of the striker arm. The better the toughness of materials, the higher PSD in the low frequency.