The ability of fabrics to withstand tears can be easily predicted and understood in terms of their yarn and thickness.
Personal protective equipment (such as gloves or clothing) is required by many people for protection (in terms of frequency and severity) from hazards at work. Textiles woven from high-performance synthetic fibers are widely used for the prevention of mechanical risks such as cutting, perforation, and tearing. Various studies have characterized the fracture behavior of textile structures,1, 2 and considerable research has been undertaken into the tearing behavior of materials. Fracture resistance has often been evaluated by determining the maximum force or work required,1, 2 but until now, there has been no analytical model to predict textiles’ tear resistance or determine failure factors.
We have proposed a new tearing criterion based on fracture mechanical theory. The criterion can be used to calculate the fracture energy—also known as the tearing energy or strain energy density—above which textiles will tear.3, 4 Yarn properties determine how cracks propagate,5 and so we have also investigated the relationship of the strain energy density with the yarn properties, and developed and tested an analytical model for the strain energy density of woven fabric.4In standard tearing tests, such as a tongue tear test or tensile crack tear test, a piece of fabric is clamped between jaws of a tensile test machine and pulled (loaded): see Figure 1. A loading/unloading cycle is carried out at various values of the maximum applied crosshead displacement l (that is, the displacement of the clamping jaws). Figure 2 provides an example of typical loading/unloading force-displacement curve measured in a tongue tear test.Figure 1.Configuration of a (a) tongue tear test and (b) tensile crack tear test. We propose calculating the strain energy density G from the change in strain energy ΔW corresponding to a change in the tear surface area ΔA, observed for a set value of the displacement l:We compute the strain energy release rate from the area delimited by the tearing and returns curves and measure the fracture surface area in the undeformed state. In other words, the change in strain energy is given by −ΔW=W1−W2 and corresponds to the change in the tear surface area ΔA=A1−A2, where subscripts 1 and 2 refer to tests performed at two different values of the maximum applied displacement and, therefore, at two different values of the tear crack surface area A (which is the product of the sample thickness and tear length measured in the undeformed state of the sample).To test our criterion, we carried out tongue tear and tensile crack tear tests on cotton, polyester/cotton blend and polyester woven fabrics. The samples included plain and twill weave structures as well as various values of the linear and yarn density in the filling direction: see Figure 1(b). The fracture work, W, seems to be proportional to the tear surface, A, measured in the undeformed state (see Figure 3). This indicates that the proposed fracture energy criterion defined by Equation (1) is valid for tongue tears and tensile crack tears of the tested plan weave fabric.Figure 2.Example of force-displacement curves in the tongue tear for the plain weave cotton fabric for two values of the maximum applied crosshead displacement (l = 30 and 60 mm). Figure 3.Variation of the fracture work (W) as a function of the tear crack surface area (A) for a plain weave fabric tested in the tongue tear and tensile central crack tear configurations. Modeling and calculating the strain energy density G are among the most important steps in understanding the mechanisms of the tearing process for woven materials. We also investigated parameters controlling the mechanisms of crack propagation in textiles, including various characteristics of the fabric required (yarns density, material thickness, etc.) and the main properties that can control the energy dissipated during the textile tearing process (i.e., the breaking force and yarn slippage force).We developed a new model that describes the relationship between the strain energy density and properties of the fabric: where G is the strain energy density, N is the number of inter-yarn spaces, S is spacing between the yarns, t is yarns density, n is number of yarns intersection points, e is thickness of material, FS is slippage force and FYB is breaking force.4We tested our model by carrying out tongue tear and tensile crack tear tests on samples of polyester plain and twill weave structures as well as various values of the linear and yarn density in the filling direction, and compared our results with our model’s predictions. We found the experimental and theoretical results were consistent, which suggests that our model accurately describes textile behavior in tearing tests (see Figure 4).3,4Figure 4.Theoretical strain energy density (line) versus experimental strain energy density (data points).In summary, we have proposed a simple way to calculate the strain energy density of woven fabrics and developed a successful analytical model to relate the strain energy density with fabric properties. We are now developing a model for the strain energy density of textile structures that take into account transverse yarn slippage, a mechanism that has generally been overlooked in previous works on tearing. Such a model will have an additional use in the study of textile-based composite structures, such as coated fabrics and laminates.AuthorsEnnouri TrikiResearch Chair in Protective Materials and Equipment for Occupational Safety and Health School of Advanced Technology of Montreal (ÉTS)Triki Ennouri obtained his PhD in mechanical engineering from ÉTS in 2012. His research interests involve the mechanics and mechanisms of textiles and polymer composites materials. He has published four articles and attended several international conferences. He is now a research associate.Phuong Nguyen-TriResearch Chair in Protective Materials and Equipment for Occupational Safety and Health School of Advanced Technology of Montreal (ÉTS)Phuong Nguyen-Tri received his PhD in materials science from the National Conservatory of Arts and Crafts (Cnam), France, in 2009. He then worked at Cnam for two years as an assistant professor before joining ÉTS. His research interests are agrocomposites, polymer ageing, and personal protective materials. He has published over 20 papers.Toan Vu-KhanhResearch Chair in Protective Materials and Equipment for Occupational Safety and Health School of Advanced Technology of Montreal (ÉTS)Toan Vu-Khanh holds the Research Chair in Protective Materials and Equipment for Occupational Health and Safety at ÉTS. He has authored over 200 scientific publications and is a member of the editorial boards of various international scientific journals.ReferencesN. A. Teixeira, M. M. Platt and W. J. Hamburger, Mechanics of elastic performance of textile materials: part XII: relation of certain geometric factors to the tear strength of woven fabrics, Text. Res. J. 25 (10), pp. 838-861, 1955. W. A. Scelzo, S. Backer and M. C. Boyce, Mechanistic role of yarn and fabric structure in determining tear resistance of woven cloth: part I: understanding tongue tear, Text. Res. J. 64 (5), pp. 291-304, 1994. E. Triki, P. Dolez and T. Vu-Khanh, Tear resistance of woven textiles—criterion and mechanisms, Composites B: Eng. 42 (7), pp. 1851-1859, 2011. E. Triki, T. Vu-Khanh, P. Nguyen-Tri and H. Boukehili, Mechanics and mechanisms of tear resistance of woven fabrics, Theor. Appl. Frac. Mech. 61, pp. 33-39, 2012. E. Triki, P. Nguyen-Tri, H. Boukehili and T. Vu-Khanh, Investigation of tearing mechanisms of woven textile, Polym. Compos. 33 (9), pp. 1578-1585, 2012. DOI: 10.2417/spepro.004671