Coupled temperature and strain rate effects on non-linear mechanical behaviour of amorphous polymers : Experimental characterisation and modelling of strain rate-temperature superposition

Abstract : The present PhD thesis proposes a simplified and accurate strategy for characterising and modelling the mechanical behaviour of amorphous polymers from the quasi-fluid state up to the solid state.The study was carried out on PMMAs with different molar masses and crosslinking degree.First, we addressed the mechanical behaviour in the linear viscoelastic domain using DMTA and rheological tests. Results showed that increasing the molar mas and crosslinking degree increased the elastic and loss moduli as the α-transition. In parallel, using the time-temperature superposition principle allowed determining “equivalent strain rates at reference temperature”.Then, we performed uniaxial tensile and shear uploading-unloading tests at high temperature and coupled with DIC, to characterise the mechanical behaviour at large strain. Additionally, strain rate and temperature effects were coupled by means of the “equivalent strain rate at reference temperature” extracted from observations in the linear domain. Results showed that targeting the same equivalent strain rate lead to the same stress-strain curves, i.e. same mechanical response. This allows reducing the number of experimental tests needed to characterise the mechanical behaviour of amorphous polymers.Finally, a constitutive modelling based in a thermodynamics framework, was used to reproduce the mechanical response of the PMMAs at large deformation. The model presented a good agreement with the experimental data, being able to reproduce viscoelastoplastic, viscoelastic, hyperelastic and viscohyperelastic behaviours for cyclic loading tensile.
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Carlos Federico. Coupled temperature and strain rate effects on non-linear mechanical behaviour of amorphous polymers : Experimental characterisation and modelling of strain rate-temperature superposition. Materials. PSL Research University, 2018. English. ⟨NNT : 2018PSLEM009⟩. ⟨tel-02096837⟩

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