Mechanics of the rate-dependent elastic–plastic deformation of glassy polymers from low to high strain rates

Abstract

A combined experimental and analytical investigation has been performed to understand the mechanical behavior of two amorphous polymers-polycarbonate and poly(methyl methacrylate)-at strain rates ranging from 10 À4 to 10 4 s À1 . This range in strain rates was achieved in uniaxial tension and compression tests using a dynamic mechanical analyzer (DMA), a servo-hydraulic testing machine, and an aluminum split-Hopkinson pressure bar. DMA tension tests were used to characterize the viscoelastic behavior of these materials, with focus on the rate-dependent shift of material transition temperatures. Uniaxial compression tests on the servo-hydraulic machine (10 À4 to 1 s À1 ) and the split-Hopkinson pressure bar (10 3 to 10 4 s À1 ) were used to characterize the rate-dependent yield and post-yield behavior. Both materials were observed to exhibit increased rate sensitivity of yield under the same strain rate/temperature conditions as the btransition of the viscoelastic behavior. A physically based constitutive model for large strain deformation of thermoplastics was then extended to encompass high-rate conditions. The model accounts for the contributions of different molecular motions which become operational and important in different frequency regimes. The new features enable the model to not only capture the transition in the yield behavior, but also accurately predict the post-yield, large strain behavior over a wide range of temperatures and strain rates.

Temperature-dependent mechanical behaviour of PMMA: Experimental analysis and modelling

“…Mechanical behaviour of PMMA in tensile tests exhibited an initial elastic response followed by yielding, strain softening and, finally, non-linear strain hardening, as described by Ref. [27]. As also reported in other studies, polymer glasses deformed beyond their yield stress underwent a drop in the stress level known as strain softening or yield-drop [10,28].…”

“…Over the studied temperature range, the yield stress decreased by 67.7%. It is worth mentioning that various researchers found that yield stress, ultimate tensile strength and Young's modulus decreased with increasing temperature [27,30]. The strain at fracture ε fr (characterising an extent of elongation of the specimen elongated to failure) demonstrated different behaviour described with an exponential regression model:…”

Toughening mechanisms in cellulose nanopaper: the contribution of amorphous regions

“…Yielding in semi-crystalline or amorphous polymers such as polyethylene terephthalate (PET) (Lim et al 2003), polycarbonate (PC) (Mulliken and Boyce 2006), poly(methyl methacrylate) (PMMA) (Mulliken and Boyce 2006), polypropylene (PP) (Alcock et al 2007), poly(vinyl alcohol) (PVA) (Govaert and Peijs 1995) and plasticized starch blend (Chaléat et al 2008) can be attributed to changes of chain conformation in amorphous regions, which depends on chain mobility. Yielding takes place when the molecular plastic strain rate resulting from chain mobility matches the applied strain rate.…”

“…At high temperature, chain mobility increases so that molecular strain rate is easier to match applied strain rate resulting in a lower yield stress. Similarly, low strain rates result in a lowering of the yield stress (Engels et al 2010;Kanters 2015;Mulliken and Boyce 2006;Van Erp et al 2009). The relationship between yield stress and temperature and applied strain rate can be described by the Eyring equation (Chaléat et al 2008;Senden et al 2012;Söntjens et al 2012).…”

Compressive properties of extruded polytetrafluoroethylene

“…Using temperatureestrain rate equivalence, they identified how the different molecular transitions affected the strain rate dependence of material strength. An excellent paper by Mulliken and Boyce [27] further showed how shifting data from DMA curves can be used to develop the physically based understanding behind a predictive model for high strain rate behavior of polymers.…”