Correlation between Scratch Behavior and Tensile Properties in Injection Molded and Extruded Polymers

Abstract

This study investigates the validity and applicability of the correlation between scratch and tensile properties for extruded polymer strands. The mechanical properties could be predicted for extruded samples, which allows skipping the step of injection molding and therefore enables a faster material development. Extruded polymer strands and tensile test specimens out of PMMA, PS, POM, PP and PE have been investigated. A correlation of the Young’s modulus and the elastic deformation as well as a correlation of the yield stress and the plastic deformation during scratching is given for both flat molded and cylindrical extruded specimens. SEM images of the scratch grooves are used to analyze the scratch deformation mechanism. The deformation mechanism correlates well to the variation coefficient of the indentation depth. Polarized light microscopy of thin cross sections of both types of specimens provides information about skin layer thickness and morphology. However, the optical analysis could not provide an explanation for the different levels of the indentation depth in the two specimen types. Further investigations should include a study of differences in process induced morphology and the effect of two layers with different mechanical properties, i.e., skin and center, on the stress and strain fields underneath the scratch.

Circular Production, Designing, and Mechanical Testing of Polypropylene-Based Reinforced Composite Materials: Statistical Analysis for Potential Automotive and Nuclear Applications

“…Modern innovation in molding technologies has made injection molding and extrusion techniques suitable for recycling due to excellent control of physical parameters (temperature, pressure, speed, time, etc.) and fast curing [ 89 ]. PP-sisal [ 90 ], PP-wood fibers [ 91 ], PP-hemp + glass fibers [ 92 ], and PP-nylon [ 93 ] are common examples of fabrication of composite materials.…”

Scratch hardness as a quasi-intrinsic parameter to measure the scratch resistance of polymers

“…Several approaches have been proposed in the scientific literature to characterize scratch resistance, widely different in their scope and applicability. The most direct way of evaluating scratch damage is to assess how the optical properties change as a consequence of scratching [2,[17][18][19][20][21][22][23][24][25]. However, scratch visibility is influenced by a huge number of different variables, only partially related to the material: colour, roughness, type and geometry of lighting, angle of observation.…”

“…The measurement of geometrical characteristics of the residual scratch grooves is clearly considerably easier than trying to evaluate the contact area during their formation, something which can be done only via modelling [5,9,[12][13]23,35] and/or using a scratch tester equipped with in-situ observation (and limiting the analysis to transparent materials) [10,13,28,36]. The modelling step introduces the need to characterize the mechanical behaviour of the materials of interest, with additional effort (in particular for viscoelastic materials) and uncertainties; however, it allows to establish a correlation between scratch hardness and the effective contact pressure developed between the indenter and the scratched surface, and eventually with the material bulk mechanical properties [15][16][17]. Scratch hardness measured in such a way makes scratch testing a powerful surface probing technique, applicable to the study of degradation phenomena [37][38] or to the optimization of the composition of materials used for tribological applications [39][40].…”