Experimental and Numerical Investigation of the Tearing Resistance of a Parachute Woven Fabric using LS-Dyna
Résumé
The performance of a parachute system is conditioned by its ability to sustain the loads applied by its environment during its life. Among others tear resistance is crucial since the unstable propagation of small defects into cracks can lead to the catastrophic loss of load carrying capacity. Defects under consideration are pre-existing notches or cuts. Experimental campaigns of quasi-static tear resistance in the warp and weft directions of parachute woven flexible fabrics have been realized at DGA Aeronautical Systems following the normalized tests defined by NF G07- 145 and NF G 07-149 (‘trousers’ tear or Single Rip Method, and ‘nail’ tear, see Fig. 1). On the contrary to the case of a metallic material, which tear resistance can be related to notch resistance through the yield strength and local plasticity, tear resistance of a tissue involves complex stress and stain distributions in the yarns of the woven fabric. It is shown that sliding of the rip stop yarns are not well handled by the testing standards. A numerical simulation plan has been designed and operated in order to determine the characteristics of a representative numerical model for both the material behavior and the large flexible structure, in the perspective of including it in a full 3D FSI simulation. Results are presented and compared to experimental ones. Using a homogenized anisotropic material, the size of the mesh and the contact algorithm are the critical parameters that handle the crack propagation through the local wrinkles and stresses description. Even though the out of plane deformations are not completely well reproduced for the Single Rip Method, the final numerical model is quite satisfactory regarding the forcedisplacement curve prediction for both test standards. Perspectives are driven for both enhancing the testing standards and deriving a more representative model for future 3D FSI models.