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A PVDF grade typically used in off-shore applications was annealed at 70, 90 and 120°C. The samples were characterized and it was observed a small change in the crystallinity, but, on the other hand, the Elastic modulus of the sample annealed at 120°C increased from 1.52 to 1.85 GPa. The relaxations observed by Dynamic Mechanical Analysis (DMA) indicate that a morphological change took place at annealing process, which led to a stiffness rises of amorphous phase.

Polyvinylidene fluoride (PVDF) is an engineering thermoplastic having a high degree of sensibility to crack, which affects long-term mechanical behavior. This study evaluates the crack-sensitive of PVDF for one commercial-grade through the development of a numerical model. Firstly, tensile tests using DIC were performed on both uncrack and pre-crack specimens to get experimental tensile as DIC-displacement, displacement-control, and load data. For pre-crack specimens, it was proposed two values of depth: 1.0 and 1.5 mm, opened by razor blade. All specimens were uniaxial tests at 23°C under 5 mm/min. Secondly, tensile tests using extensometer were implemented for uncrack samples to determine material parameters for calibration of the numerical model and comparison with DIC-displacement. Finally, a numerical model based on the FE was implemented using ANSYS-student that inputs PVDF’s material properties, which considered the elastic-plastic behavior in simulation tests. The PVDF demonstrated significant crack sensitivity, as it can be seen in experimental and numerical data. And, the numerical model developed based on MKHP was successfully agreement against experimental data obtained by Blue Hill 3 software. Therefore, the results allowed us to observe that pre-crack acts as a stress concentration and the numerical model got well simulates this influence on the PVDF mechanical behavior.

This study presents the effect of bending strain upon the structure and mechanical behavior of poly(vinylidene fluoride) (PVDF). Using the ISO 22088-3 Bent Strip Method, the PVDF samples were submitted to 3.5 % and 7.0 % strain in bending for 21 days. The unstrained and strained samples were characterized by Fourier Transformed Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) and tensile tests at 23 °C. The applied bending strain of 3.5% and 7.0 % resulted permanent deformation for both strains applied, which curvature was very close to 3.5% and 7%. The 7% strained samples showed stress-whitening, most likely due to the well-known cavitation phenomenon; while 3.5% strained samples no cavitation was seen. Infrared spectroscopy analysis indicates a mechanically induced α to β crystalline phase transition on the outer fibers as the bending strain increases. DSC measurements showed no change on crystallinity volume fraction and melting temperature as deformation increased. The DMA showed a shift on glass transition temperature (TG) to higher temperatures and the Elastic Modulus decreased as the bending strain increased for all temperatures. Reverse deformation had to be applied on the plastically deformed bending samples in order to straight them out to do the tensile tests. The tensile properties measured at room temperature showed the Young’s Modulus and Yield Stress decreasing as the applied bending strain increases. On the other hand, the yield strain rose as the bending strain increased.

The present paper is concerned with the experimental and theoretical investigation of the progressive accumulation of inelastic deformation observed in cyclic tension tests performed on a particular polyamide. The elastic properties are not strongly affected by the strain rate, but the strain hardening induced by the plastic deformation is rate-dependent. Thus, the material behaviour is elasto-viscoplastic rather than viscoelastic or elasto-plastic. For the polymer studied in this paper, the kinematic hardening is much more significant than the isotropic hardening, and a negative plastic strain rate may occur even with a positive stress. The kinematic hardening is strongly dependent, not only on the accumulated plastic strain, but also on the loading rate. An elasto-viscoplastic mechanical model able to describe the cyclic inelastic behaviour for an arbitrary loading history is proposed. All parameters that arise in the theory are identified experimentally. The preliminary theoretical results concerning the modelling of cyclic load-unload tests are in good agreement with the experiments.

Nanocomposites of poly(vinylidene fluoride) (PVDF) with different commercial nanoparticles (rutile-TiO2, SiO2, α-Al2O3, Fe3O4) were prepared by melt extrusion and characterized. The effects of incorporating these nanoparticles in the matrix on the chemical, mechanical, thermal, and morphological properties were investigated. From the FTIR spectra, it was possible to calculate the percentage of α and β-phases of the PVDF matrix. The incorporation of nanoparticles increased the content of the β-crystals when compared with neat PVDF, indicating an improvement in the homogenization of the nanocomposite as observed in SEM images of PVDF/rutile-TiO2. The dynamic-mechanical analysis showed a decrease in storage and loss modulus in PVDF/α-Al2O3, but in both PVDF/rutile-TiO2 and PVDF/SiO2, only a small reduction was observed. The thermal properties also reduced after incorporation of these nanoparticles, except in PVDF/SiO2. For application as a barrier layer in oil ducts, the degradation temperature measured is appropriate to maintain the thermal stability at 130 °C (requested temperature). The experimental results indicated that PVDF/rutile-TiO2 and PVDF/SiO2 exhibited good potential properties, mainly by reducing permeability to CO2 with an increase of lagtime compared to neat PVDF.

The present work is concerned with the thermo-mechanical analysis of a particular aliphatic polyamide with long alkyl chains used in the internal sheath of flexible pipes. The main focus is to analyse the coupled influence of temperature and ageing on its mechanical behaviour and fracture. Fracture and tensile tests were performed over a wide range of temperature (from −5 °C to 90 °C) and of corrected inherent viscosity (between 1.0 dl/g and 1.8 dl/g). For higher values of the CIV, the material presents superplastic behaviour, but the behaviour tends to be brittle for lower values of the inherent viscosity and temperature. A general model is proposed for the uniaxial behaviour (valid for a wide range of temperature and inherent viscosity) and also for the fracture behaviour. Experiments are compared with the model predictions and show good agreement.

This study presents the mechanical properties evaluation of two commercial grades of PVDFs, which were extruded with the same parameters but with different cooling temperatures. After processing, stress relaxation with 7% strain was imposed and tensile properties were measured. The cooling temperature after extrusion were 4°C, 23°C and 80°C. Then, the PVDFs were submitted to stress relaxation at 23°C and 7% strain. The as processed and after relaxation samples were characterized by FTIR, XRD, DSC and tensile tests at 23°C. The stress relaxation at 23 °C resulted in no change in volume fraction of crystallinity for PVDF A and B. The XRD and FTIR, for both PVDFs, showed that the crystalline phases were the same, for all cooling conditions and did not change after the stress relaxation. The tensile properties at room temperature showed that the yield stress was a little affect by the cooling temperature, while Young’s Modulus and yield strain were insensible to the cooling temperature. After the stress relaxation, these three tensile properties were slightly affected for both grades.