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 masstransport 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.

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 Ic , was determined at different temperatures and displacement rates and by applying the time-temperature superposition it was possible to obtain G Ic as a function of crack speed, ܽሶ , 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.

The fracture behaviour of continuous unidirectional carbon fibre composite materials prepared adopting two, one plain and one rubber toughened, thermoplastic acrylic resins as matrices was investigated as a function of temperature and displacement rate. The contributions to fracture toughness of composites given by the matrix and the fibre related mechanisms was analysed by comparing results obtained at crack initiation and during crack propagation stages. It was verified that the transfer of matrix toughness into the composite is only partial when the matrix process zone size is comparable to the interlaminar matrix layer thickness. The effectiveness of fibre bridging mechanism was found to be related to the interfacial strength between the matrix and the fibre

The fracture behaviour of continuous carbon fibre laminates based on plain and rubber-toughened acrylic resins was investigated focusing on the influence of rate and temperature. The tensile behaviour of the two matrices was also characterized for subsequent analysis. In all cases the experimental window was extended by applying the time-temperature equivalence postulate. Fracture toughness at varying crack propagation rate turned out to have opposite trends for the two matrices. For the plain acrylic resin, a monotonically increasing trend with crack rate was found in agreement with viscoelastic fracture theories. For the rubber-toughened resin the change of the failure mechanisms occurring at the crack tip, resulted in a monotonically decreasing trend for increasing crack rate. Rate and temperature effects were analysed in terms of volumetric strain during tensile tests. Composites turned out to be more resistant to crack propagation than the relevant matrices in both cases. Delamination fracture toughness turned out to have the same dependence on crack rate for rubber toughened matrix only. For composites based on the plain resin, no effect of crack\ud rate on delamination fracture toughness was observed

The present study investigates the effect of processing conditions on the yield kinetics, such as rate dependence of the yield stress and creep rupture, of polyvinilidene fluoride. Samples were compression molded with cooling rates varying from 100°C/s to 0.5°C/min, or isothermally crystallized at temperatures varying from 20 to 120°C. Deformation kinetics were studied over a wide range of strain rates and temperatures. It is shown that for all conditions the yield response is well represented by the Ree–Eyring model. Moreover, the activation volumes and activation energies are independent from the processing conditions. The effect of processing is fully covered by a simple relationship between the rate factors and the degree of crystallinity. Subsequently, the versatility of this relationship is demonstrated by experimental validation.