Experimental characterization of the volume strain of poly(vinylidene fluoride) in the region of homogeneous plastic deformation

Abstract

Damage to poly(vinylidene fluoride) was studied under uniaxial tension testing at different temperatures and strain rates. A satisfactory accuracy was reached with an original procedure for the assessment of the principal strains and volume strain. The semicrystalline polymer exhibited an increase in the volume strain with the true axial strain caused by material damage. This damage depended on the temperature and strain rate and was related to the whitening phenomenon generally observed. The use of the general ideas of Bucknall's model, based on the decomposition of the whole volume strain into three components, allowed the extraction of the component of the volume strain corresponding to microstructural mechanisms of plastic deformation other than shearing. Therefore, nucleation and growth stages of cavitation were revealed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2516–2522, 2002

Time and temperature effects on Poisson’s ratio of poly(butylene terephthalate)

“…In the author's opinion these high Poisson's ratio values have to be interpreted as scattered around 0.5, and affected by inaccuracies related to the correction of transverse deformation for long times and high temperatures. At the same time, it can not be excluded that the upper plateau could be higher than 0.5, due to non-homogeneity on a microstructural scale, already present in the materials (such as crystalline regions below the melting temperature [1] or porosity [28]) or developed during the deformational process (as cavitational effects [29][30][31][32], although these should have major importance at deformations higher than those investigated here). The decrease of stress was simultaneously monitored, permitting an evaluation of the time evolution of the relaxation modulus E REL , which is reported in Figure 11b in terms of isothermal curves for an axial deformation !…”

Cavitation and morphological changes in polypropylene deformed at elevated temperatures

“…Cavitation process is then initiated in tensile drawing shortly before or at the yield point 11 if the resilience of the amorphous phase is lower than the strength of crystals 3,9,10 . Formation of a cavity changes rapidly the local distribution of stresses in surrounding crystals and initiates their plastic deformation, mainly by crystallographic slips 3 .…”

“…Cavitation is usually studied by small angle X-ray scattering (SAXS) from the nanometer size voids [11][12][13] . Larger cavities, if present in the polymer, scatters light, which is seen as a whitening of a material [14][15][16] .…”

Volume Variation Process of High-Density Polyethylene During Tensile and Creep Tests

“…Although the above techniques are still applied by some researchers, the computerized video techniques developed during the last decade brought a decisive contribution to the assessment of volume strain in polymers. Originally, they were limited to the pre-necking deformation stage [12,[14][15][16][17]. However, the novel video-controlled testing system that was recently developed in this laboratory has several interesting features [18]: -it provides in real time the true stress/strain behavior locally within a representative volume element (RVE) situated at the center of the neck; -it gives access to the volume strain in the same RVE; -it allows the user to regulate dynamically either true strain rate (for tensile tests) or true stress (for creep tests).…”