Contact mechanics of isotactic polypropylene: Effect of pre-stretch on the frictional response

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Abstract

Polymers are increasingly used in applications where relative moving parts are in contact. The dissipation of energy due to friction, i.e. heat production, reduces a product's lifetime significantly. Since in processing often an extrusion or injection moulding step is used in product formation, the induced anisotropic microstructure leads to a spatial variation of mechanical properties, for example frictional resistance. In this work we compare the scratch response of isotropic isotactic polypropylene (iPP) to the response of various oriented iPP systems. Subjected to single-asperity contact with a rigid diamond, the surface penetration and lateral force are measured. For various combinations of applied normal load and sliding velocity, the surface penetration and lateral force are measured. Optical profilometry measurements are used to explain the (large) differences in residual scratch profile between tests performed in the direction parallel and transverse to the orientation direction, respectively. As the anisotropy increases with the amount of orientation, both the maximum tensile stress and the strain hardening increase substantially. The penetration depth, for oriented systems governed by the transverse viscoelasticity and yield stress, is comparable for all loading angles and decreases with increasing amount of orientation. The direction of lowest frictional resistance is shown to be the direction parallel to the oriented crystals. The combination of decreasing global deformation and friction reduction as a result of pre-stretch decelerates strain localization, therewith delaying crack initiation which eventually leads to abrasive wear. Along with that, the substantial amount of elastic recovery after scratching in the transverse direction is related to the pre-tension of the perpendicular crystal network.

Original languageEnglish
Pages (from-to)183-190
Number of pages8
JournalWear
Volume398-399
Early online date5 Dec 2017
DOIs
Publication statusPublished - 15 Mar 2018

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Polypropylenes
polypropylene
Mechanics
Extrusion molding
Friction
Crystals
Profilometry
Viscoelasticity
Strain hardening
Crack initiation
Abrasion
Injection molding
Tensile stress
penetration
Yield stress
Diamonds
Anisotropy
Recovery
Mechanical properties
Microstructure

Keywords

  • Contact mechanics
  • Polymers
  • Scratch testing
  • Sliding friction

Cite this

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abstract = "Polymers are increasingly used in applications where relative moving parts are in contact. The dissipation of energy due to friction, i.e. heat production, reduces a product's lifetime significantly. Since in processing often an extrusion or injection moulding step is used in product formation, the induced anisotropic microstructure leads to a spatial variation of mechanical properties, for example frictional resistance. In this work we compare the scratch response of isotropic isotactic polypropylene (iPP) to the response of various oriented iPP systems. Subjected to single-asperity contact with a rigid diamond, the surface penetration and lateral force are measured. For various combinations of applied normal load and sliding velocity, the surface penetration and lateral force are measured. Optical profilometry measurements are used to explain the (large) differences in residual scratch profile between tests performed in the direction parallel and transverse to the orientation direction, respectively. As the anisotropy increases with the amount of orientation, both the maximum tensile stress and the strain hardening increase substantially. The penetration depth, for oriented systems governed by the transverse viscoelasticity and yield stress, is comparable for all loading angles and decreases with increasing amount of orientation. The direction of lowest frictional resistance is shown to be the direction parallel to the oriented crystals. The combination of decreasing global deformation and friction reduction as a result of pre-stretch decelerates strain localization, therewith delaying crack initiation which eventually leads to abrasive wear. Along with that, the substantial amount of elastic recovery after scratching in the transverse direction is related to the pre-tension of the perpendicular crystal network.",
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Contact mechanics of isotactic polypropylene : Effect of pre-stretch on the frictional response. / Looijmans, S.F.S.P.; Anderson, P.D.; van Breemen, L.C.A.

In: Wear, Vol. 398-399, 15.03.2018, p. 183-190.

Research output: Contribution to journalArticleAcademicpeer-review

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