Indentation Size Effect in Pressure-Sensitive Polymer Based on A Criterion for Description of Yield Differential Effects and Shear Transformation-Mediated Plasticity

Abstract

Indentation size effects in poly(methyl methacrylate) (PMMA) were studied through nanoindentation. Two factors of indentation size effects in PMMA, namely yield criterion and shear transformation-mediated plasticity, were analysed in detail. The yield criterion that considers strength differential (SD) effects and pressure sensitivity was constructed by performing the combined shear-compression experiments. The relationship between hardness and normal stress can then be obtained based on Tabot’s relation. Shear transformation-mediated plasticity was also applied to model the measured hardness as a function of the indentation depth at different strain rates. Results show that the yield criterion contains the terms of SD effects and pressure sensitivity gives the best description of the yielding of PMMA. Additionally, the volume of single shear transformation zone calculated through the presented criterion agrees well with simulation and exhibits increases with increasing strain rate. Indentation size effects in PMMA under different strain rates were discussed and an appropriate indentation depth range was suggested for calculating the hardness and modulus.

Macro-, Micro- and Nanomechanical Characterization of Crosslinked Polymers with Very Broad Range of Mechanical Properties

“…During the indentation experiments, hardness, modulus and other properties change not only with the hold time (or dwell time, i.e., the time of maximum load), but also with loading and unloading rate [ 17 , 18 ]. Moreover, the indentation properties tend to change with the maximum loading force, which is usually denoted as the indentation size effect [ 19 , 20 , 21 , 22 ]. In dynamic experiments the indentation moduli and damping factors depend on the frequency of force oscillations; this is analogous to dynamic mechanical analysis in macroscale [ 8 , 18 , 23 ].…”

Investigation on the Influences of Hygrothermal Aging on the Indentation Size Effects and Micro-Indentation Measurements of PMMA. Part I: Experimental Results

“…Sci. 2020, 10, 5454 3 of 13 in our previous paper [1]. The principle of the CSM technique of nanoindentation has been widely reported in various studies [1,31,32] and will not be repeated in this paper.…”

“…Polymethyl methacrylate (PMMA) is extensively applied in different industrial areas, such as aircraft, automotive industries, and biomedical materials, for its excellent properties [1][2][3][4][5][6]. For these widely used materials, mechanical strength is the first and foremost characteristic to ensure safety [7][8][9][10][11][12].…”

“…Therefore, the dislocation-mediated plasticity may not be suitable for describing the ISE in GPs. By contrast, the cooperative-localized rearrangement of atomic or molecular clusters in small distinct regions, defined as shear transformation-mediated plasticity, is a widely accepted mechanism for plastic deformation in GPs [1]. As displayed by Voyiadjis et al [17,23,25], shear transformation-mediated plasticity has been successfully applied in the modeling of ISE in PMMA and PC (College of automobile).…”

Physicochemical and Mechanical Performance of Freestanding Boron-Doped Diamond Nanosheets Coated with C:H:N:O Plasma Polymer

“…The greatest restriction to their possible application is their moisture sensitivity [25], which limits their physical and transport properties [26]. Therefore, the mechanical behavior of polymers is a crucial property that should be analyzed prior to usage [27]. Essentially, the yield stress decreases with increasing moisture content [28].…”