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.
Highlights
Plastics, especially engineering thermoplastics, need to be mechanically characterized since product designers use material properties such as Young’s modulus, tensile strength and others for choosing appropriate plastics, for first design steps and for structural simulations
This study investigates the validity and applicability of the correlation between scratch and tensile properties for extruded polymer strands
This study investigates the validity and applicability of the correlation between scratch and tensile properties known from injection molded samples for cylindrical, extruded polymer strands
Summary
Especially engineering thermoplastics, need to be mechanically characterized since product designers use material properties such as Young’s modulus, tensile strength and others for choosing appropriate plastics, for first design steps and for structural simulations. The scratch behavior of polymers depends significantly on the indenter geometry, normal load and sliding velocity, besides other influencing factors during scratching [4,5]. Xiang et al [1] linked a lower Young’s modulus to a higher scratch depth for a large number of polymers and the contact radius of the indenter They established the fact that a higher yield stress is accompanied by a lower tendency to plastic flow during scratching. The study has the aim to investigate the relation between the scratch properties of cylindrical, extruded polymer strands and the tensile properties of tensile test specimens To this end, three ductile (PE, PP, POM) and two brittle (PS, PMMA) thermoplastic polymers are scratched. Since the examination is performed on two different types of specimens, further influence factors are identified on the basis of microscopic analysis
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