Force based analysis on the instrumented Charpy impact and its industrial application

By determination of characteristic loading points from the instrumented impact testing curve and with the combination of the quasi static tensile test, a series of dynamic testing para- meters including estimated PSF, syd ,F gy/Fm ,J u ,J /syd related to the Force Based Analysis method have been introduced in the study. As a key point to evaluate the dynamic flow yield stress, the confused loading criteria of General Yield point is here clearly marked at the intersection of the steeply rising part of second peak of the force-deflection and KC curves. Moreover, an illustration of FBA method applied to the samples with the same Absorbed Impact Energy, Et, but the distinct Percentage of Shear Fracture, PSF values was discussed in detail as necessary complements for extending the conventional Charpy impact testing into a comprehensive evaluation of the fracture toughness, also revealing the intrinsic fracture mechanism of metals. Since being established by A.G.A. Charpy in 1900s, Charpy impact has been widely used to evaluate the impact toughness of metallic materials under the condition of large deformation and high strain rate loading for its convenience and low cost (1). Two directly measured values could be obtained from the test, the impact energy, Et, standing for the dynamic toughness of material, and the percentage of shear fracture area, PSF, relating to the feature of the fracture mode, brittle or tough. But it is inadequate to describe the dynamic response of material to the dynamic loading, only in dependence of above two values. A confused question is always been asked that what is the different behavior the material experiences for those which have the same Et value but different PSF values, until the application of instrumented impact testing. By recording the change of load signals against time during transient impact period, instru- mentation method (2) differentiates the contribution of impact energy to the crack formation and propagation separately. Further investigation into the series of characteristic loading points on the instrumentation curve output, with Elastic-Plastic-Fracture-Mechanics (EPFM) analysis applied on, will be helpful to study the material response to the dynamic loading. In the present study, Force Based Analysis (FBA) has been illustrated as an industrial application to evaluate the material dynamic toughness.