MECHANICAL MODELING AND ANALYSIS OF THE IMPACT TESTING OF WIRE

A new experimental test method and its associated mechanics descriptio n is reported for the instrumented impact of small diameter rod and wi re. The use of this test lies in its ability to quickly and effectivel y measure impact fracture energy at various dynamic strain rates while indirectly providing a measure of the material's dynamic yield stress . The basic outline of the test is similar to that of an instrumented drop-weight test, albeit with two major differences: (i) the test mate rial (rod or wire) is axially loaded to 60 percent of its yield stress prior to impact and (ii) the rod remains unnotched and is in no other way modified from its original condition. Between the grips, the rod is supported laterally by two hardened steel anvils having a radius of 12.5 mm and is impacted laterally at midspan by a hardened steel tup having a radius of 8 mm. Fracture occurs in a cup and cone manner in t he region directly below the tup. To describe the deformation behavior of the rod during impact, analytical and numerical solutions were dev eloped. Elastic analytical solutions were first investigated and then used to partially verify subsequent nonlinear finite element analyses. Nonlinearities arose as a consequence of both large deformation and e lastic-plastic behavior in the rod during impact. The experimental tes ting program consisted of both quasi-static ((epsilon) over dot = 10(- 4)) and dynamic ((epsilon) over dot = 9) tests on preloaded rods. Exce llent agreement was found between the numerical and experimental resul ts for impact fracture energy and for peak load at failure. Numerical and experimental results indicate that significant strain hardening oc curs in the rod as the strain rate is increased from 10(-4) to 9. Base d on these models, the mechanical behavior of the rod under impact loa ding is discussed.