Mechanical damping in instrumented impact testing

Instrumented impact testing is an effective tool for the study of high-speed fracture of polymeric materials. The evaluation of force signals is usually impeded by dynamic effects. These can be compensated by mechanical damping which, however, leads to additional energy absorption. A model and a technique were developed for the determination of the viscoelastic properties of the damper. Correction of the force versus deflection traces obtained in the instrumented impact test is carried out automatically during the evaluation of the test. Unbiased force versus deflection correlations are recovered and the most important fracture parameters are determined. Comparison of different correction techniques has shown the validity of the method. The agreement between K-c values calculated from the maximum force and fracture energy proved to be excellent. The developed technique greatly facilitates the evaluation of instrumented impact tests and increases the reliability of the measurement.