Fiber response to pin penetration in dry woven fabric using numerical analysis
A new type of washer with integrated pin structures was developed and presented in a previous study for the use in mechanical joints of fiber-reinforced plastics (FRP) and metal sheets. Thereby, the pin-structured washer significantly increases the load-bearing capacity of mechanically joined FRP-metal combinations. To do so, the FRP hole area is to be relieved by transferring the occurring loads into the laminate via the pin structures. In thermoset FRP, the insertion of the pin-structured washer usually leads to fiber breaks. For fiber-reinforced thermoplastics (FRTP) the chance of fiber failures during the penetration process can be reduced by inserting the pin-structured washer via an ultrasonic-based locally invasive heating system. By doing this, the polymer is locally molten, allowing the fibers to move around the pin structures. However, the ultrasonic-based insertion does not allow visual observation of the fiber movement within the process. With the aim of getting information about the fibers, that are moved, stressed or broken depending on the pin tip geometries, a numerical investigation was carried out. Therefore, a 3 × 3 twill model of a dry woven fabric segment based on a Bézier curve for yarn simplifications was developed. With respect to the molten polymer during the penetration process, the effect of the matrix was neglected. With consideration of necessary simplifications regarding the calculation time, the stress distribution on the dry woven fabric and a regular pattern of the damage situation of the fibers could be investigated. To understand the mechanisms of the fiber behavior within the penetration process, three different pin diameters and pin tip angles were examined and compared in numerical simulations.