Publications

Abstract : Composites have excellent in plane mechanical properties whereas the out of plane properties are poor due to the laminated construction. Delaminations between different stacking plies can occur when a load is applied in the transverse direction or when the structure is subjected to impact loads. Several techniques have been explored to enhance the delamination resistance of polymer matrix composites either by modifying the matrix or having through the thickness reinforcement. Toughening of the matrix is a passive methodology resulting in marginal enhancement of out of plane properties. Stitching is one of the methods for achieving through-the-thickness using one or two needles. The formation of knots and the resulting tensioning of the thread can considerably weaken the mechanical properties due to undulations and constrictions. The other drawback of stitching is the accessing of the needle from the underside to form the stitch. This increases the manufacturing complexity, especially in large composite structures and limits its range of application only to simple and open geometries, with easy access to both sides of the preform. More recently, variations of stitching such one side stitching (OSS) technologies have been explored. Some OSS methods have been borrowed from the textile and cloth production industry and have been adapted to composite reinforcement applications. One of the novel techniques in the OSS technology is called Tufting which was developed at the DLR institute of structural mechanics – German Aerospace Centre, Germany. Tufting is a single-thread and single-needle method in which the formation of loops is possible with a loose and almost tension-free introduction of the threading system that does not adversely affect the material. Results from literature suggest a significant increase in interlaminar fracture toughness, composite ‘T’ Joint pull off strength and compression after impact (CAI) strength. In the present study, the tufted laminated composites have been manufactured using Vacuum Enhanced Resin Infusion Technology (VERITy) process, which was developed and patented by CSIR-National Aerospace Laboratories, Bangalore. To quantify the effect of through-the-thickness reinforcement, extensive experimental studies have been carried out. A comparative assessment of the influence of tufting on the mechanical performance is presented.