Kinematic study of necking in a semi-crystalline polymer through 3D Digital Image Correlation

Abstract

a b s t r a c tThis study is devoted to the necking phenomenon and to the kinematic aspects associated with this plastic instability. The material studied is a High Density PolyEthylene deformed in tension. Full-field 3D-DIC (Digital Image Correlation) strain measurements were carried out on one face of a tensile specimen. On the opposite face, the longitudinal strain was measured in the central section using video-traction Ò , an extensometer based on marker tracking. This last measurement was used with feedback to control the strain rate in the specimen center. Specific data processing was run on the 3D-DIC measurements to obtain strain and strain rate maps up to true strain levels greater than 1.8. Even with measurements made on a relatively small strain rate range (smaller than 1 decade), we highlighted how much the necking phenomenon depends on the strain rate. In particular, we found that, around the yield point, the strain localization is more pronounced with higher strain rates. By analyzing the evolution of the strain rates in the necking shoulder regions, we carried out direct and original measurements of the strain level corresponding to the onset of necking stabilization (Natural Draw Ratio). This was possible because our original experimental protocol enabled us to obtain such strain maps even when the true strain values were significantly greater than 1. From an experimental point of view, we found that a video-extensometer based on marker tracking cannot efficiently measure the strain rate in the specimen center at large strain levels when the markers are greatly very deformed. In addition, a wide range of new experimental results (2D and 1D strain-rate and velocity data) is presented in this paper and we consider that this data should be particularly useful for the validation of numerical simulations of necking in polymers.

Wide‐angle X‐ray scattering study of the lamellar/fibrillar transition for a semi‐crystalline polymer deformed in tension in relation with the evolution of volume strain

“…The and strain maps were also simultaneously measured on the main and lateral faces. The results are not shown there but available in Ye et al [Fig. (c,d)].…”

“…The 3D‐DIC technique was used to measure the volume strain in the specimen central cross‐section. This article provides a relatively simple summary of the experimental procedure because it has already been described in detail in two previous articles where we provide full analyses of the Poisson's ratio and of the volume strain measurements as well as a study of the kinematics of the necking phenomenon . During a tensile test, simultaneous strain measurements were made on two perpendicular faces of a specimen.…”

Anisotropy development during HDPE necking studied at the microscale with in situ continuous 1D SAXS scans

“…The point located exactly in the middle of the specimen at the beginning of the test (curve X0  ) follows the path which exhibits the maximum strain. During previous synchrotron SAXS/WAXS experiments [Farge et al, 2013[Farge et al, , 2015, microstructural quantitative conclusions concerning deformation mechanisms were raised from the strain path followed by this point only. Thanks to the scanning opportunity at the cSAXS beamline, the present study will be able to follow microstructural evolution during the development of plastic instability.…”

EVALUATION OF FORMABILITY OF THIN SHEETS BASED ON Al-Mg-Si FOR AUTOMOTIVE INDUSTRY

“…On the basis of the change in position of these DOI elements is by software, or manually evaluate the deformation. There are known two types of analysis [15][16][17][18][19]:  postprocessing -manually applied grid -(software Argus, Ncorr, etc.)  online processing analysis -method using the principle of DIC, videoextensometry, ESPI etc.…”

“…For image capturing is using high-speed cameras with high image resolution. This method is seen as a flexible tool that is used not only in the field of experimental mechanics [16][17][18]. Measuring systems which operate on the principle of DIC method have many advantages against conventional method.…”