Bending behavior of fabrics made of flax/PA12 comingled yarns
Topic(s) : Material science
Co-authors :
Théo PERRIN (FRANCE), Gilles ARNOLD (FRANCE), Karine GAUTIER (FRANCE), Michel TOURLONIAS (FRANCE), Peng WANG (FRANCE)Abstract :
With current environmental conditions and in a context of scarcity of raw materials, the composite industry is turning towards bio-sourced reinforcements and thermoplastic matrices. However, the manufacturing processes remain generally the same and stamping shaping techniques are widely used. During the forming process, the main deformation mode is in-plane shear. Nevertheless, bending behavior is critical to take into account the defects such as wrinkles and tow buckling during the simulation of the forming of non-developable shapes[1],[2]. In this work, the influence of the fabric’s structure on the bending behavior is studied, should it be the weaving pattern or the angle formed by warp and weft yarns.
Three fabrics made of the same hybrid yarns are selected: a plain weave, and two different twills. The yarns are made of flax comingled with PA12 and wrapped with a PA12 multifilament.
The yarns and fabrics bending behavior are investigated using a modified protocol for the bending tester of the Kawabata Evaluation System of Fabrics, initially developed for clothing textiles. In order to test yarns out of the fabric, a yarn-holder was designed to extract the yarn orthogonal to the tested direction (warp or weft), to ensure the orientation of the yarns and to control their tension and torsion (Fig. 1.a). The yarns are straightened one by one with a fixed mass. A benchmark with a standard cantilever test is conducted to show the reliability of the new protocol. In order to test the fabric in different configurations, a 3D printed guide is used to shear the samples to a given shear angle (Fig. 1.b) prior to the bending test. The samples are then glued in a paper frame to keep the yarn orientation, before being set up in the clamps of the bending tester. The bending stiffness was measured according to the Kawabata’s standard theory [3].
The comparison between bending stiffnesses of the yarn and the fabric in the same direction shows that the fabric is more rigid than the yarns that compose it (Fig.2). It can also be noted that the warp and weft yarns have different stiffnesses, even if the yarn used is the same. These results can be explained by the weaving process that induces different undulations in each direction and the storage on a roll that induces a pre-existing curvature.
Several configurations are tested from no shear between the warp and the weft, to a shear of 40° (which is close to the locking angle of the tested fabrics). One can observe that the measured bending rigidity increases with the shear angle.
Finally, bending models are considered to fit the behavior. Generally, the most used is the Grosberg model [4] for its simplicity but for a better description, Dahl [5] and Lahey’s [6] models seem more suitable.
Three fabrics made of the same hybrid yarns are selected: a plain weave, and two different twills. The yarns are made of flax comingled with PA12 and wrapped with a PA12 multifilament.
The yarns and fabrics bending behavior are investigated using a modified protocol for the bending tester of the Kawabata Evaluation System of Fabrics, initially developed for clothing textiles. In order to test yarns out of the fabric, a yarn-holder was designed to extract the yarn orthogonal to the tested direction (warp or weft), to ensure the orientation of the yarns and to control their tension and torsion (Fig. 1.a). The yarns are straightened one by one with a fixed mass. A benchmark with a standard cantilever test is conducted to show the reliability of the new protocol. In order to test the fabric in different configurations, a 3D printed guide is used to shear the samples to a given shear angle (Fig. 1.b) prior to the bending test. The samples are then glued in a paper frame to keep the yarn orientation, before being set up in the clamps of the bending tester. The bending stiffness was measured according to the Kawabata’s standard theory [3].
The comparison between bending stiffnesses of the yarn and the fabric in the same direction shows that the fabric is more rigid than the yarns that compose it (Fig.2). It can also be noted that the warp and weft yarns have different stiffnesses, even if the yarn used is the same. These results can be explained by the weaving process that induces different undulations in each direction and the storage on a roll that induces a pre-existing curvature.
Several configurations are tested from no shear between the warp and the weft, to a shear of 40° (which is close to the locking angle of the tested fabrics). One can observe that the measured bending rigidity increases with the shear angle.
Finally, bending models are considered to fit the behavior. Generally, the most used is the Grosberg model [4] for its simplicity but for a better description, Dahl [5] and Lahey’s [6] models seem more suitable.