Investigation on Thread Forming and Tightening Process of Self Forming Screws on Fiber Reinforced Polymer Composites

ABSTRACT Joining fiber‐reinforced polymer composites (FRPCs) using mechanical fasteners is essential for ensuring structural integrity in lightweight applications. However, their anisotropic nature and susceptibility to localized damage make screw fastening challenging and create uncertainties in joint reliability. Understanding screw–laminate interaction during thread formation and tightening is therefore critical for developing durable fastening solutions. This study examines the screwing behavior of four screw types: metric, self‐tapping, self‐cutting, and self‐drilling in two glass FRPC laminates: bidirectional woven‐mat and chopped strand‐mat. Torque–angle profiles for each screw–laminate combination were established through destructive testing and comparatively evaluated across thread formation, tightening, and failure phases. Woven laminates delivered higher torque capacities due to strong fiber confinement but showed increased delamination risk, while chopped strand‐mat enabled easier thread formation but demonstrated lower torque resistance. Variable‐speed tests indicated that woven laminates sustained torque better at higher speeds, and vertical‐load tests confirmed the need for sufficient push‐force, particularly for self‐forming screws. Overall, the findings demonstrate that optimal screw joining in FRPCs is governed by interaction between screw geometry and fiber‐architecture. Cutting screws suit woven laminates, while displacement screws suit chopped strand‐mat composites. These insights provide a scientific foundation for designing reliable and sustainable screw‐joints in composite structures.