Modified slotted shear test for a thin sheet of solid polymer under large deformations

Abstract

a b s t r a c tA modified slotted shear test based on ASTM B831 is proposed and used for determining the mechanical behavior of a solid polymer at large deformations. The shear stress-strain response of a thin sheet of polytetrafluoroethylene was experimentally investigated and a V-notched rail shear test was carried out to validate the experimental results obtained with the proposed approach. Displacement and strain fields of the test specimens were estimated by the Digital Image Correlation method. The results indicate agreement between both tests for small deformations, while for large deformations significant discrepancies in shear stress-strain responses are observed. These discrepancies can be attributed to unwanted distortions of the gage section observed in the V-notched specimens. The modified slotted shear test provided a uniform shear strain distribution across the gauge section of specimens. In addition, the principal advantages of the proposed approach over V-notched rail shear test are a wide range of shear strains and absence of unwanted distortions.

Mechanical characterization of thin injection-moulded polypropylene specimens under large in-plane shear deformations

“…the V-Notched Rail standard (ASTM D7078) and the V-Notched Beam standard (ASTM D5379) (known also as the modified Wyoming Iosipescu test). In addition, the slotted shear ASTM B831 test modified by Nunes [14] was also investigated because it was successfully applied to a polymer material PTFE. In this study, the capability to measure the mechanical shear behaviour of polypropylene is assessed.…”

“…2b, the left half fixed the sample while the right half of the fixture is forced down, sliding on a bearing post. For the modified B831 test, the commonly used uniaxial tensile test grips were used with a fixture with two separate halves, comprising four 1.5mm thick aluminium holders (designed by Nunes [14]) tightened to the specimen. The top half was pulled at a constant crosshead speed and shear strain was introduced in the centre of the test piece.…”

“…The ASTM D7078 method allowed larger strains under shear stress, which is better suited for stiffer materials. Nunes [14] proposed a modification of the ASTM B831 [15], a standard testing method for thin aluminium alloy specimens, by adding a fixture plate in order to reduce the out-of-plane distortions during shear tests. Since there are a number of sources of uncertainties in finite element simulations for obtaining high quality and reliable material testing data [16], a shear methodology that minimises the non-uniform strain distributions during the experiment needs to be identified, hopefully from the existing tests.…”

“…Therefore, the mechanical response of thin-walled structures can be more accurately predicted using FE codes. The V-notched rail shear test, the V-notched beam test and the slotted shear test modified by Nunes [14] are analysed by using DIC to identify the methodology that can produce a uniform stress state up to large strains.…”

“…Shear specimens produced: a) ASTM D7078; b) ASTM D5379; c) ASTM B831 modified by Nunes[14]. All dimensions in mm.…”