Tribology of polymer composites

Tribology of polymer composites

Citation for published version (APA):

Krop, S., Breemen, van, L. C. A., & Meijer, H. E. H. (2012). Tribology of polymer composites. Poster session presented at Mate Poster Award 2012 : 17th Annual Poster Contest.

Document status and date: Published: 01/01/2012 Document Version:

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/ Department of Mechanical Engineering

Sam Krop, Lambert C.A. van Breemen, and Han E.H. Meijer

Tribology of polymer

composites

Polymer Technology

comp. true strain [−]

comp. true stress [MPa]

PC + 9 vol% MBS PC + 10 vol% TiO₂

experiment simulation

undeformed maximal deformed

soft fillers

(PC + 9 vol% MBS) (PC + 10 vol% TiOhard fillers ₂)

0 200 400 600 800 1000 0 50 100 150 200 250 300 350 400 450 scratch distance [µm] lateral force [mN] 9 vol% MBS PC 10 vol% TiO₂ 100 101 102 300 350 400 450 sliding velocity [µm/s]

lateral force [mN] PC_{10 vol% TiO2}

9 vol% MBS Fn = 400 mN v = 100 µm/s lateral force 10−5 10−4 10−3 10−2 40 50 60 70 80 90 100

comp. strain rate [s−1]

comp. true stress [MPa]

PC 10 vol% TiO2 20 vol% TiO2 4.5 vol% MBS 9 vol% MBS 0 0.1 0.2 0.3 0.4 0.5 0 20 40 60 80 100

comp. true strain [−]

comp. true stress [MPa]

PC 20 vol% TiO2 9 vol% MBS 10−2 s−1 10−3 s−1 10−4 s−1

[1] Van Breemen et al., Wear 2012, 274-275, 238-247

Discussion

A macroscopic material model of the heteroge-neous system is constructed, which will be used in the simulation of the scratch test, see Fig. 4a. Apart from the stiffness and the yield stress, fill-ers also change the adhesive interaction with the indenter, which in turn changes the shape of the bow wave in front of the indenter-tip [1]. This adhesive component is the only unknown when relating the simulation to the experimentally measured total response. Imposing the local deformation from the scratch simulation on an RVE gives valuable information about the stress state in the filled system, see Fig. 4b. This enables the definition of a failure criterion that marks the onset of wear.

Simulations

It is impossible to mesh these heterogeneous materials in a scratch simulation. Therefore, representative volume elements (RVEs) are constructed, see Fig. 3a, and subjected to a macroscopic deformation. Although effects like cavitation and particle-matrix adhesion are not taken into account, simulation results show that the mechanical response is captured rather well, see Fig. 3b.

Experiments

To characterize the effect of filler particles on the intrinsic mechanical response, model

sys-tems of PC filled with either hard (TiO₂) or soft

(MBS) particles are tested in uniaxial compres-sion, see Fig. 1a. Although the magnitude of stress changes dramatically, the rate depend-ence is solely determined by the matrix mate-rial, see Fig. 1b. This effect is also observed in the single-asperity scratch test; the addition of soft or hard fillers results in a change in the re-sistance against deformation (Fig. 2a), but the rate effect is still governed by the polymer matrix (Fig. 2b).

Introduction

Polymers play an increasingly important role in tribological applications. The application of a hybrid experimental-numerical approach in the single-asperity scratch test proved a powerful tool in understanding the polymers’ frictional re-sponse [1]. In practice, however, these poly-mers are filled, e.g. with colorants and impact modifiers. Therefore, this strategy is extended to heterogeneous systems.

(b) (a)

Fig. 4: Simulation of a scratch test using the macroscopic constitutive model (a) where the local deformation can be imposed on an RVE to reveal ef-fects on smaller scale (b).

(b) (a)

Fig. 3: Deformed RVE showing local strain level (a) and the macroscopic mechanical response (b).

(a)

(b)

Fig. 2: Effect of filler type (a) and sliding velocity (b) on the scratch response.

(a)

(b)

Fig. 1: Effect of filler type on intrinsic mechanical response (a) and rate-dependent yield stress (b).