Fibers and Polymers 2013, Vol.14, No.2, 338-344 338 Comparison of Picture Frame and Bias-extension Tests for the Characterization of Shear Behaviour in Natural Fibre Woven Fabrics I. Taha * , Y. Abdin 1 , and S. Ebeid Faculty of Engineering, Ain Shams University, Cairo, Egypt 1 Mechanical Engineering Department, The British University in Egypt, Cairo, Egypt (Received March 2, 2012; Revised July 21, 2012; Accepted July 28, 2012) Abstract: The investigation of the shear behaviour of technical natural fibres is vital for the insurance of aesthetics and performance of light weight, high strength, and eco-friendly composites. In this study, Egyptian jute fibre plain weave fabrics of various areal densities were investigated to describe their shear behaviour in terms of shear forces, shear angles and shear lock angles, using the Bias-Extension and the Picture Frame test methods. Results show that both methods are valid for natural fibres and produce comparable results. Whereas the Bias-Extension test presents a fast and simple test procedure, the analysis of the results is more complex due to the interaction of non-shear components. On the other hand, the Picture Frame test proves to be time consuming and in need of a more complex test rig, but results in pure shear deformations throughout the sample. Keywords: Fabric textiles, Polymer-matrix composites, Textile composites, Shear behaviour, Draping behaviour Introduction The use of fibre reinforced composites has gained a considerable amount of recognition within the last decades. The variations in fibre types (glass, carbon, natural, etc.), shape dimensions and orientation have led to the development of a vast basis for selection allowing for the flexible tailoring of end product properties. Since all processing techniques of fibre reinforced polymer composites are related to moulding operations, the deformation behaviour of the textiles over an open mould or within a closed mould is vital for the guarantee of the aesthetics and performance of the end product. Woven fabric is the most common continuous dry textile material form, where the specific weave pattern affects its deformability characteristics, as well as the handleability and structural properties. The deformation behaviour of textiles, known as “drape”, is considered an important mechanical property that affects the functionality of fabrics [1-5]. The definition of drape has been largely discussed in the literature. Recently, draping has been defined as “the extent to which a fabric will deform when it is allowed to hang under its own weight” (BS 5058:1973; British Standard Institute, 1974b) [1,2]. The draping or deformation behaviour of the woven fabrics is greatly associated with the relative motion of yarns, thus primarily depending on the shear behaviour of the fabric, which determines its performance properties when subjected to a wide variety of complex deformations, as well as its conformance to the required shape. Pure shear consists of a trellising action, whereby the tows in the fabric rotate about the cross-over points [6,7]. Textile reinforcements are favoured for draping over complex surfaces as they offer possibility for large rotations between warp and weft yarns and hence a relatively low in-plane shear resistance [8]. Although this deformation mechanism can accommodate large fibre rotations, at some point, the rotating tows contact each other restricting further shear and leading to subsequent lock up (lock angle) [6,9-11]. The shear resistance increases rapidly when the lock angle is reached, and the assumption of the negligible shear resistance (easy deformation) is no longer valid [11]. While the shear lock angle separates the low and high stiffness parts of the curve, it is not very precise for many fabrics which depict a progressive increase in stiffness [6]. Although there is a considerable amount of literature analysis [6,10,12-23], of the shear behaviour of fabrics, aiming at developing prototype tests, there is no set standard test method for determining the in-plane shear behaviour of textile reinforcements. Nevertheless, there are three main known techniques used to measure fabric shear compliance and locking angle, namely the Direct Shear Force Measurement (DSFM) method, the Bias-Extension (BE) test method, and *Corresponding author: iman_taha@eng.asu.edu.eg DOI 10.1007/s12221-013-0338-6 Figure 1. Different methods for measuring the shear properties of textiles: (a) direct shear force measurement, (b) bias-extension test method, and (c) picture frame test method.