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The effect of temperature on the damage mechanisms occurring in a toughened acrylic resin was investigated by studying volume changes during tensile tests, analyzing the reversibility of the damage after applying proper thermal histories and by direct transmission electron microscope observations. It was found that an increase of temperature, from 0[degrees]C to 60[degrees]C, shifts the predominant mechanism from crazing to cavitation and shear yielding. When the latter occur, the material response is very susceptible to previous thermal treatments; and in particular to the cooling rate from above glass transition temperature. Crazing on the other hand is not influenced by the thermal history of the material., INTRODUCTION Acrylic resins are widely appreciated for their properties such as stiffness, transparency, and good weather resistance but they tend to yield by crazing showing a brittle fracture and this [...]

The time dependence of fracture toughness of two different acrylic resins, one plain and one toughened, intended to be used as continuous fiber composite matrices was studied. By performing fracture tests following the fracture mechanics approach, the energy release rate, [G.sub.Ic], was determined at different temperatures and displacement rates and by applying the time-temperature superposition it was possible to obtain [G.sub.Ic] as a function of crack speed, a, over a wide range of speeds. The trends obtained for the two resins were different. For the plain resin it could be well described by J. G. Williams' viscoelastic fracture theory while for the toughened resin, the trend obtained was attributed to a change in the damage mechanism occurring at the crack tip during fracture. From measurements of the process zone size it was deduced that the damage mechanism at the crack tip for the plain resin was the same irrespective of time and temperature, for the toughened resin instead, different mechanisms seem to take place. This hypothesis was supported by results of volume strain measurements in tensile tests at different temperature and strain rates., INTRODUCTION Acrylic glassy polymers have been widely used in many different applications. These polymers are stiff, transparent and have very good weathering properties but generally yield by crazing and show [...]

To model the engineering performance of components made of polyvinylidene fluoride (PVDF), the 3D elasto‐viscoplastic Eindhoven glassy polymer (EGP) model is extended to describe the rate‐dependent behavior of PVDF. Careful analysis of the intrinsic behavior of PVDF revealed that the postyield compressive response shows a strain rate‐dependence that evolves with increasing deformation. The extension of the constitutive model captures the deformation‐dependent evolution of the activation volume and the rate‐factor, which describes the driving stress. Given the significant temperature‐dependent behavior, the model has been characterized for different temperatures (23, 55 and 75 °C). The accuracy of the model has been validated by means of tension and creep experiments at these temperatures. The constitutive model is implemented in finite element simulations and the results are compared with the experiments. It is shown that the proposed model allows for an accurate prediction of the short‐ and long‐term rate‐dependent behavior of PVDF. [ABSTRACT FROM AUTHOR]

Compressing porous carbon electrodes is a common approach to improve flow battery performance, but the resulting impact on electrode structure, fluid dynamics, and cell performance is not well understood. Herein, microtomographic imaging, load cell testing, and flow cell diagnostics are employed to characterize how compression‐induced changes impact pressure drop, polarization, and mass‐transfer scaling. Five different compressions are tested, spanning ranges typically used in literature, for AvCarb 1071 cloth (0%, 9%, 20%, 25%, 32%) and Freudenberg H23 paper (0%, 8%, 12%, 17%, 22%). It is found that the two electrode structures have distinct responses to compression, resulting in differing optimal conditions identified for each material; specifically, the Freudenberg H23 exhibits lower combined ohmic, charge‐transfer, and mass‐transport values at 8% compression, resulting in improved electrochemical performance across all compressive values, as compared to the optimal AvCarb 1071 compression (20%). Overall, Freudenberg H23 exhibits a greater sensitivity to compression with peak electrochemical activity correlating with increased permeability, whereas AvCarb 1071 is insensitive to compressive loads but produces lower electrochemical performance. Herein, the trade‐offs of mechanical robustness on fluid‐dynamic and electrochemical performance between the two electrodes are demonstrated by the aforementioned findings, suggesting each could be used for specific operating environments. [ABSTRACT FROM AUTHOR]