Comment on ?the compression yield behaviour of polymethyl methacrylate over a wide range of temperatures and strain-rates?

206

164

A robust physically consistent three-dimensional constitutive model is developed to describe the finite mechanical response of amorphous polymers over a wide range of temperatures and strain rates, including the rubbery region and for impact loading rates. This thermomechanical model is based on an elastic-viscoplastic rheological approach, wherein the effects of temperature, strain rate, and hydrostatic pressure are accounted for. Intramolecular, as well as intermolecular, interactions under large elastic-inelastic behavior are considered for the mechanisms of deformation and hardening. For a wide range of temperatures and strain rates, our simulated results for poly(methyl methacrylate) (PMMA) and polycarbonate (PC) are in good agreement with experimental observations.

Section: Flow Rulementioning

confidence: 70%

Modeling and validation of the large deformation inelastic response of amorphous polymers over a wide range of temperatures and strain rates

Richeton¹,

Ahzi²,

Vecchio³

et al. 2007

206

164

“…(4) for T < T g and by Eq. (6) for T P T g , is a continuous function of T. For the determination of r i (T P T g ), it was suggested by Fotheringham and Cherry (1976) to use a vanishing internal stress above T g :…”

Section: Extension Of the Model Through The Glass Transition Regionmentioning

confidence: 99%

Influence of temperature and strain rate on the mechanical behavior of three amorphous polymers: Characterization and modeling of the compressive yield stress

Richeton¹,

Ahzi²,

Vecchio³

et al. 2006

473

362

Uniaxial compression stress-strain tests were carried out on three commercial amorphous polymers: polycarbonate (PC), polymethylmethacrylate (PMMA), and polyamideimide (PAI). The experiments were conducted under a wide range of temperatures (À40°C to 180°C) and strain rates (0.0001 s À1 up to 5000 s À1 ). A modified split-Hopkinson pressure bar was used for high strain rate tests. Temperature and strain rate greatly influence the mechanical response of the three polymers. In particular, the yield stress is found to increase with decreasing temperature and with increasing strain rate. The experimental data for the compressive yield stress were modeled for a wide range of strain rates and temperatures according to a new formulation of the cooperative model based on a strain rate/temperature superposition principle. The modeling results of the cooperative model provide evidence on the secondary transition by linking the yield behavior to the energy associated to the b mechanical loss peak. The effect of hydrostatic pressure is also addressed from a modeling perspective.

“…Richeton et al (2007) proposed constitutive equations for glassy polymers capable of predicting the response of PMMA and PC over a wide range of temperatures and strain rates. The flow rules in the glassy and the rubbery states were based on the cooperative model of Fotheringham and Cherry (1976) and the free volume theory of Williams et al (1955) respectively. They considered the temperature rise in a PC and a PMMA due to adiabatic heating and material properties like the mass density and the specific heat as functions of temperature.…”

Section: Review Of Existing Constitutive Equationsmentioning

confidence: 99%

Constitutive equations for thermomechanical deformations of glassy polymers

Varghese

Batra

2009

Keywords:Material models High strain rate Thermo-viscoplasticity Material softening a b s t r a c t Poly-Carbonate (PC) and Poly-Methyl-Methacrylate (PMMA) are lightweight and mechanically tough transparent glassy polymers. Their mechanical behavior at low to moderate strain rates has been well characterized; however, that at high strain rates needs additional work. We propose two modifications to existing pressure-dependent viscoplastic constitutive equations that enable one to simulate better mechanical deformations of PC and PMMA at high strain rates. First, the elastic moduli are taken to depend upon the current temperature and the current effective strain rate. Second, two internal variables are introduced to better characterize the strain softening of the material at high strain rates. A technique to find values of newly introduced material parameters is described. We compute the local temperature rise due to energy dissipated during plastic deformations. The true axial stress vs. the true axial strain curves in uniaxial compression from numerical simulations of the test configurations at high strain rates using the proposed constitutive equations are found to agree well with the experimental results available in the literature.