Enhancement of laminate open-hole tensile strength by considering fiber waviness around holes

Bolted joints are widely used for joining laminated composites despite inducing stress concentrations and potential damage during drilling. This study explores an alternative approach using inserts embedded via vacuumassisted resin transfer molding (VARTM) to mitigate drilling-related issues. Mold-in cylindrical brass inserts were incorporated into the dry fabric and subsequently removed post-fabrication to assess their impact on open-hole tensile and bearing strength compared to drilled counterparts. Results show that non-drilled samples with various ply configurations exhibited significantly higher open-hole tensile loads-up to 54.8 %-compared to drilled samples, with similar bearing load values. A 3D progressive damage model incorporating fiber waviness around the hole was developed and validated by digital image correlation technique. Micro-CT images revealed improved fiber continuity around holes in non-drilled samples, supporting the observed strength improvements. Scanning electron microscope (SEM) images further elucidated failure mechanisms during bearing tests. The failure mechanism involves initial fiber kinking in the linear region (especially for drilled samples), followed by fiber crushing and fracture around the hole. Finally, fiber accumulation is disrupted by shearing. The non-drilling approach presents promising advancements in composite joint strength and durability.