Deformation and failure kinetics of polyvinylidene fluoride: Influence of crystallinity

Abstract

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.

An elasto‐viscoplastic constitutive model for the rate‐dependent behavior of polyvinylidene fluoride

“…It is expected that for higher temperatures, only one relaxation process is required. 13 Nevertheless, the established extension of the constitutive model enables the user to apply a similar procedure at different temperatures.…”

“…Semicrystalline polymers often reveal a thermorheologically complex behavior as is the case for PVDF. 13 Therefore, the remaining equations are given for the multi-process model. Yet, in general they can be applied to all three models in Figure 1.…”

“…Applying the same procedure to PVDF does not result in a satisfactory description as it requires the presence of two molecular processes including strain softening of the secondary process. Although multiple relaxation processes occur in PVDF, 1,26 Pini et al 13 showed that there is no support for the coexistence of two processes over the entire range of tested temperatures and strain rates. Also Figure 3D does not provide evidence for a change in yield kinetics at 23 C. Therefore, a different approach is followed based on Wendlandt et al 18 and Senden et al 19 The plastic deformation rate of a thermo-rheologically simple polymer can be described by the Eyring flow rule 14 as…”

“…The constitutive model described by van Breemen et al, 12 referred to as Eindhoven glassy polymer (EGP)-model, is used as a starting point. In a recent experimental investigation of the yield kinetics of PVDF, Pini et al 13 showed that the yield response in compression and tension can be represented by a modified Ree-Eyring equation. Based on this study, we describe the time-and temperature-dependent behavior of PVDF using the 3D elasto-viscoplastic constitutive model by van Breemen et al, 12 based on the Eyring flow theory.…”

Micromechanical analysis of age‐induced strength reduction in a multiaxially loaded short‐fiber reinforced thermoplastic

“…These factors are governing in determining the physical state of the material; for glassy matrices this is the physical age (governing the yield stress level), [16][17][18] for semicrystalline materials it is the resulting crystallinity and its morphological details. [19][20][21][22][23] The combined effects of orientation and rate-dependence make polymer-based systems complex to describe and their performance hard to predict.…”