Instrumented Indentation

Numerous advances in solid mechanics and materials science have been possible through instrumented indentation, a technique now widely used to probe the mechanical properties of materials ranging from metals and ceramics to polymers and biological materials.  Instrumented indentation is conducted with a specified force-displacement history, where the penetration depth and the indent force are controlled and measured continuously over a complete loading cycle.  The indentation technique has been applied to study the dislocation behavior in metals, fracture behavior in ceramics, strength of bone, mechanical behavior of thin films and coatings, residual stresses, interface adhesion, time-dependent behavior in soft metals and polymers, as well as novel small material structures such as the colloidosome particles and carbon nanotubes.

Unfortunately, there are several shortcomings in evaluating the test-results from indentation and scratch testing.  The extent to which these techniques can be used to quantify material properties is limited by the current understanding of the complicated material response – often accompanied with finite plastic deformation – during indentation and scratch test experiments.  For example, obtaining constitutive equations from indentation techniques have traditionally been limited to stress-free elastic-perfectly plastic material, thus not giving critical information regarding residual stress and strain hardening.  Fracture and cracking induced by normal indentation have also not been systematically investigated.

We are working towards releasing some of these restrictions and are investigating the effect of residual stress and strain hardening, along with studying cracks in brittle materials.  The results will be used for evaluating the mechanical properties of the materials we are investigating in our laboratory.  

University of Delaware, Newark, Delaware 19716-3140