Abstract
This paper aims at understanding how to model the time-dependent behavior of PMMA during a scratch loading at a constant speed and at middle strain levels. A brief experimental study is first presented, consisting of the analysis of microscratches carried out at various scratching velocities and normal loads. The loading conditions have been chosen in such a way that neither (visco)elasticity nor (visco)plasticity of the PMMA may be neglected a priori. The main analyzed parameter is the tip penetration depth measured during the steady state. Then, a finite element model is used to investigate the potential of classical elastic-viscoplastic constitutive models to reproduce these experimental results. It is mainly shown that these models lead to unsatisfying results. More specifically, it is pointed out here that the time-independent Young modulus used in such models is not suitable. To take into account this feature, a viscoelastic-viscoplastic model based on the connection in series of a viscoelastic part with a viscoplastic part is proposed. It is shown that it leads to more acceptable results, which points out the importance of viscoelasticity in the scratch behavior of solid polymers.
Highlights
The scratch test is one of the most efficient tests to investigate the mechanical resistance of coated and uncoated surfaces [1,2,3]
One can firstly observe that the slope of the decrease of the penetration depth calculated with the FEM is less pronounced than the experimental one. It means that the timedependent behavior of the PMMA is not well reproduced with this elastic-viscoplastic model in these conditions (Fn and V)
That means that the time-dependent behavior of the PMMA in scratch test is better reproduced with this viscoelastic-viscoplastic model
Summary
The scratch test is one of the most efficient tests to investigate the mechanical resistance of coated and uncoated surfaces [1,2,3]. It is well known that the scratch resistance of amorphous polymers depends on the scratching speed and on the load applied on the tip [15, 16]. It points out their complex mechanical behavior which depends strongly on strain and strain rate levels and on the temperature. Three kinds of constitutive models are commonly used: viscoelastic models [17] for low strain levels, elastic-viscoplastic models [18] for large strain levels, and viscoelastic-viscoplastic models [19] for middle strain levels.
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