Nano-indentation of scratched poly(methyl methacrylate) surfaces

Abstract

The paper describes an experimental study of the nano-indentation hardness profiling of scratches, of various depths, produced upon the surface of a poly(methyl methacrylate). The method has limited spatial resolution and typically the indent size, and hence the volume of deformed material sensed, was in the worst cases one-tenth of the scratch width; in exceptional cases the resolution was ten times better than this figure. Additionally, the various topographical and morphological features are evaluated using laser profilometry and optical and scanning electron microscopy. The data described indicate that the scratching process introduces damage in subsurface regions, which may be tentatively ascribed to the formation of subsurface crazing or voidage in certain regions of the scratch damage area; in particular within the base of the scratch formation. Such structures could potentially develop in the substrate tensile fields developed at the rear of the indenter. In addition, there is evidence for densification of the polymer adjacent to the primary damage zone-on the ''shoulder'' areas adjacent to the main scratch path. An analysis of the periodic fluctuations of the nanohardness data, in certain zones, allows a speculative description of the topology of the subsurface damage in terms of the induced voidage and its distribution. Such features would naturally lead to a ''positive'' deformation volume; an analysis of an orthogonal topographical trace of a scratch allows a simulation of volume with respect to the unpurturbed surface-a ''positive'' comparison infers an additional volume and vice versa. In the current study, such ''positive'' volume deformation regions were not unequivocally identified with the proposed craze zones using the topographical estimation procedures employed.

One‐Component Intrinsic Self‐Healing Coatings Based on Reversible Crosslinking by Diels–Alder Cycloadditions

“…Due to the experimental “open‐loop” settings, the load decreases during the hold period. The copolymer P7 is a relatively stiff sample comparable with the uncrosslinked PMMA films, which have a hardness of ≈0.3 GPa and an elastic modulus of ≈5 GPa 24 . P7 is a bit more elastic but this can be reasoned by the crosslinking of the film.…”

Nanosurface Mechanical Properties of Polymers Based on Continuous Stiffness Indentation

“…The polymers show delayed response to indenter unloading due to creep, hence, causes uncertainties in surface mechanical properties measurement during the conventional indentation. [14][15][16] The indentation data analysis for a polymeric surface poses further difficulties because of the complex viscoelastic plastic characteristics of these materials. Polymers show different behavior under different contact conditions due to the strain and strain-rate dependence of their properties.…”

Nanoindentation response of poly(ether ether ketone) surfaces—A semicrystalline bimodal behavior

“…The exceptional large variations were seen for hardness values at lower scales specifically at low penetration depths (<50 nm). These values were thought to be because of the errors present in surface determination, the tip geometry defects, and indentation size effects . These values were not regarded as physically significant.…”