Effects of dynamic indentation on the mechanical response of materials

Abstract

Dynamic indentation techniques are often used to determine mechanical properties as a function of depth by continuously measuring the stiffness of a material. The dynamics are used by superimposing an oscillation on top of the monotonic loading. Of interest was how the oscillation affects the measured mechanical properties when compared to a quasi-static indent run at the same loading conditions as a dynamic. Single crystals of nickel and NaCl as well as a polycrystalline nickel sample and amorphous fused quartz and polycarbonate have all been studied. With respect to dynamic oscillations, the result is a decrease of the load at the same displacement and thus lower measured hardness values of the ductile crystalline materials. It has also been found that the first 100 nm of displacement are the most affected by the oscillating tip, an important length scale for testing thin films, nanopillars, and nanoparticles.

The mechanical properties of float glass surfaces measured by nanoindentation and acoustic microscopy

“…In this method the indentation is arrested and a small unload is carried out to determine the contact stiffness at a range of depths before reloading during the indentation experiment. It has been suggested that when CSM is used to measure the mechanical properties of metal specimens, there is an influence of strain rate that results in a difference in hardness values when compared with quasi-static nanoindentation [19]. However, it was explicitly stated that no effect is expected or was observed that influences the elastic properties measured using CSM.…”

Instrumented nanoindentation investigation into the mechanical behavior of ceramics at moderately elevated temperatures

“…However, two recent studies 50,51 have raised questions on the credibility of data obtained by the continuous stiffness measurement technique and underscore vital practical limitations particularly for soft materials such as polymers. For the bulk materials under investigation here, it can be assumed that the stiffness of the material is not a function of indentation depth and therefore a virtual unloading slope can be calculated from the stiffness as determined from the final unloading slope:…”

The Nano-Jackhammer effect in probing near-surface mechanical properties

“…Strain gradient plasticity has been applied by several others to help understand microbend tests (Shi et al, 2008), plasticity (Abu-Al-Rub, 2008;Abu-Al-Rub and Voyiadjis, 2006;Qu et al, 2006;Volokh and Trapper, 2007;Wang et al, 2007), hardening effects (Abu-Al-Rub, 2008;Zhang et al, 2007), interface fracture and plasticity (Abu-Al-Rub, 2008;Siddiq et al, 2007) and the Taylor dislocation model (Hwang et al, 2004;Liu et al, 2005). The main concern is that the dissipative energy associated with even small oscillatory displacements of sharp tips could result in different properties (Cordill, 2007;Cordill et al, 2008), particularly with regard to dislocation nucleation and theoretical shear stress determinations. For example, at the macroscale, it has been known for some time that relatively small resonant-induced displacements on aircraft structures can lead to premature failure.…”