MICRO-IMPACT TECHNIQUE AND ITS APPLICATIONS

A micro-impact tester has been designed and built by using a piezoelec tric impact hammer as an impactor driver. During the course of an impa ct process, force interactions between the impactor and target surface s were monitored continuously by a miniaturized piezoelectric loadcell embedded in the flying head assembly. A 3-sided pyramidal diamond ind enter (Berkovich indenter) was used as an impactor. After having fully characterized such an impact system, the trajectory of the impactor c an be calculated by using the corresponding prerecorded impact force i nteraction in a simulation program. The contact and returning velociti es, kinetic energy loss of the impactor, and the impact penetration cu rve are the key pieces of information obtained from the simulation. Fu rthermore, the impact morphology can reveal failure mechanisms of mate rials by providing details such as indent shapes, coating fragment, ch ipping, crack type and size, and other information which are useful in assessing the fracture toughness of testing materials. The micro-impa ct testing was carried out in the contact velocity ranging from 0.3 to 2.0 m/s. Three types of materials such as metal, glass, and amorphous carbon were used in studying their distinct mechanical behavior under high rate indentations. The correlations among the impact conditions, energy losses, impact morphologies, and material responses are illust rated and discussed.