Prediction of brittle-to-ductile transitions in polystyrene

Abstract

In this study it is attempted to predict brittle-to-ductile transitions (BDTs) in polystyrene blends, induced either by an increase in temperature or by a decrease in inter-particle distance. A representative, two-dimensional volume element (RVE) of a polystyrene matrix with 20% circular voids, is deformed in tension. During deformation a hydrostatic-stress based craze-nucleation criterion [1] is evaluated. The simulations demonstrate that crazes initiate at low temperatures while a transition from crazing to shear yielding (BDT) is found around 75 8C. The numerical results correlate well with tensile tests on similar heterogeneous polystyrene. The presence of an absolute length, as experimentally found, is more difficult to explain. Near a free surface a T g -depression is measured for polystyrene and also the resistance to indentation in polystyrene is lower than expected from bulk properties. Both observations are rationalised by an enhanced segmental mobility of chains near a free surface. As a consequence of these findings, an absolute length-scale could be incorporated in the numerical simulations. For simplicity, the length-scale is modelled by taking a temperature gradient over a thin layer near the internal free surfaces of the RVE. Deformation of the RVE with different absolute length-scales shows that indeed also the experimentally found brittle-to-ductile transition can be predicted if the ligament thickness between the inclusions ('voids') in polystyrene is below a critical value of ca. 15 nm.

Multi‐Scale Analysis of Mechanical Properties of Amorphous Polymer Systems

“…Figure 14 for PS. [35] Simulations of the RVE response at different temperatures reflects this change, [63] as does the development of the hydrostatic stress within the RVE, see Figure 15a. Taking again 40 MPa as critical cavitation stress for PS, we anticipate a brittle-to-tough (B-T) temperature for PS around 80 8C, in accordance with experimental results, see Figure 15b.…”

“…Taking again 40 MPa as critical cavitation stress for PS, we anticipate a brittle-to-tough (B-T) temperature for PS around 80 8C, in accordance with experimental results, see Figure 15b. [63] Effect of Absolute Thickness…”

Processing-induced Properties in Glassy Polymers

“…10 In the last 15 years, a lot of effort has been invested by a number of groups at different universities into the development and validation of 3D constitutive models that can describe this localization behavior of glassy polymers, for example, in the group of Mary Boyce at MIT, [11][12][13] the group of Paul Buckley in Oxford [14][15][16] and in our Eindhoven group. [17][18][19] It was shown in subsequent quantitative studies 10,[19][20][21][22][23][24] that it is the large strain intrinsic behavior (yield, strain softening, and subsequent strain hardening) of the polymer that determines the macroscopic localization behavior, and thus failure. The model developed in our group proved to be capable of also predicting the long term static failure, 25,26 including a static fatigue limit when aging kinetics were taken into account.…”

The effect of physical aging on the embrittlement of steam-sterilized polycarbonate

“…The higher the amount of softening, the more extreme this strain localization will be, and the higher the build-up of hydrostatic stress within the zone [2,21]. A brittle-to-ductile transition is subsequently triggered if the local hydrostatic stress exceeds a (molecular weight dependent) critical level, leading to incipient cavitation and craze initiation [2,25].…”