Full-field strain measurements in textile deformability studies

Abstract

Full-field strain measurements are applied in studies of textile deformability during composite processing: (1) in testing of shear and tensile deformations of textiles (picture frame, bias and biaxial extension test) as an ''optical extensometer'', allowing accurate assessment of the sample deformation, which may differ significantly from the deformation applied by the testing device; (2) to study mechanisms of the textile deformation on the scale of the textile unit cell and of the individual yarns (meso-and micro-scale full-field strain measurements); (3) to measure the 3D-deformed shape and the distribution of local deformations (e.g., shear angles) of a textile reinforcement after draping, providing input data for the validation of material drape models and for the prediction of the consolidated part performance via structural finite element analysis. This paper discusses these three applications of the full-field strain measurements, providing examples of studies of deformability of woven (glass, glass/PP) and non-crimp (carbon) textile reinforcements. The authors conclude that optical full-field strain techniques are the preferable (sometimes the only) way of assuring correct deformation measurements during tensile or shear tests of textile.

Evaluation of normalisation methods for uniaxial bias extension tests on engineering fabrics

“…The kinematics of the UBE test have been analysed in detail using various methods including manual [19] and automated image analysis [20] and also using digital image correlation techniques [22]. For the purposes of normalisation, the kinematics across the test specimen are often described using three distinct regions; A, B and C. Figure 1 shows these regions in a UBE test sample with an aspect ratio of 2; the test can also be conducted using test specimens of higher aspect ratio.…”

Application of digital image correlation at the microscale in fiber-reinforced composites

“…This limitation is due to the presence of strong deformation gradients at the interface between phases, whose evaluation may be compromised by the necessity of averaging displacements and deformations over a certain window. Thus, although DIC is a well-established technique for obtaining the strain fields at the macroscopic scale in composites [2,20,21] and fabrics [9,10,14], this approach has never been used -to the authors' knowledge-at the scale of the fibers due to the differences in stiffness between matrix and fibers.…”

Simulation of 3D interlock composite preforming

“…The bias test is a traction test on a sample oriented at 45°. It is much used and analyzed for the determination of composite reinforcement mechanical behaviour [17,[43][44][45][46][47][48]. At the beginning of the test, yarns make a 45°angle with the deformation direction.…”