Pull-Out Resistance of 3D Woven Sandwich Composites

3D woven sandwich composites are being developed for transportation applications such as for light train flooring. For those applications, the joining process of these materials is needed. Mechanical joining is a common and preferable method for this purpose. In mechanical joints, it is critical to consider the pull-out resistance of the joint. This study investigated the pull-out resistance of a fiberglass-polyester 3D woven sandwich composite mechanical joint by adapting ASTM D7332 procedure B. The results indicate that increasing the hole depth and diameter enhances both the failure load and maximum load of the joints. Moreover, inserts significantly enhance failure load and maximum load (292% and 198% respectively) due to increased contact area, leading to improved mechanical joint performance. Specimens without inserts only showcased crack, crazing, and out-of-plane shear failure modes on composite while additional damage on insert and potting material was observed on with-insert specimens. The optimal mechanical joint configuration utilized an insert, featuring a hole depth matching the sandwich composite thickness (20 mm) and a hole diameter of 9 mm resulting in a failure load of 1690 N and a maximum load of 3042 N.