A Study of Shear Stress Intensity Factor of PP and HDPE by a Modified Experimental Method together with FEM

Authors: Md. Shafiqul Islam, Abdullah Khan, Sharon Kao-Walter, Li Jian

Abstract:

Shear testing is one of the most complex testing areas where available methods and specimen geometries are different from each other. Therefore, a modified shear test specimen (MSTS) combining the simple uniaxial test with a zone of interest (ZOI) is tested which gives almost the pure shear. In this study, material parameters of polypropylene (PP) and high density polyethylene (HDPE) are first measured by tensile tests with a dogbone shaped specimen. These parameters are then used as an input for the finite element analysis. Secondly, a specially designed specimen (MSTS) is used to perform the shear stress tests in a tensile testing machine to get the results in terms of forces and extension, crack initiation etc. Scanning Electron Microscopy (SEM) is also performed on the shear fracture surface to find material behavior. These experiments are then simulated by finite element method and compared with the experimental results in order to confirm the simulation model. Shear stress state is inspected to find the usability of the proposed shear specimen. Finally, a geometry correction factor can be established for these two materials in this specific loading and geometry with notch using Linear Elastic Fracture Mechanics (LEFM). By these results, strain energy of shear failure and stress intensity factor (SIF) of shear of these two polymers are discussed in the special application of the screw cap opening of the medical or food packages with a temper evidence safety solution.

Keywords: Shear test specimen, Stress intensity factor, Finite Element simulation, Scanning electron microscopy, Screw cap opening.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1088948

References:

[1] Kristian B. Dahl, and K. A. Malo, “Linear shear properties of spruce softwood”. Wood Sci Technol, vol. 43, 2009, pp.499–525.
[2] Arun Krishnan and L. Roy Xu, “A short-beam shear fracture approach to measure the mode II fracture toughness of materials with preferred interfaces,” International Journal of Fracture, vol. 169, 2011, pp. 15–25
[3] Leslie Banks-Sills and M. Arcan, “Toward a Pure Shear Specimen for KIIc Determination,” International Journal of Fracture, vol. 22, 1983.
[4] F. Gao, L. Gui, and Z. Fan, “Experimental and Numerical Analysis of an In-Plane Shear Specimen Designed for Ductile Fracture Studies,” Experimental Mechanics, vol. 51, Aug. 2011, pp. 891–901.
[5] D. Mohr and S. Henn, “Calibration of Stress-triaxiality Dependent Crack FormationCriteria: A New Hybrid Experimental–Numerical Method,” Experimental Mechanics, vol. 47, 2007, pp. 805–820.
[6] Barnes JA, Kumosa M, and Hull D, “Theoretical and experi-mental evaluation of the Iosipescu shear test,” Compos Sci Technol vol. 28, 1987, pp.251–268.
[7] Abaqus documentation, and suite of manuals, ver 6.11, Dassault Systemes SIMULIA Crop., Providence, USA, (2012).