Abstract

Automated Fiber Placement (AFP) enables precise and flexible composite manufacturing but remains sensitive to surface irregularities and disturbances in process parameters. Among common defects, tape overlaps can introduce surface irregularities that create regions of insufficient inter-laminar bonding in the uncured state and promote secondary defects such as wrinkling or bridging during subsequent layup passes. Understanding how overlaps interact with roller behavior and process conditions is therefore essential.
The influence of roller stiffness and geometry on pressure distribution was studied with and without an overlap. Experiments and finite element analyses showed that softer rollers conform more effectively to overlap-induced height variations but deliver reduced pressure, while stiffer rollers maintain higher pressure but leave larger uncovered regions. To capture the effects of process parameters on bonding, an in-house AFP simulation setup was used to fabricate single-lap joint (SLJ) specimens under controlled compaction force, temperature, and feed rate. The resulting shear strength measurements demonstrated that bonding performance arises from the interaction among these variables rather than from any single parameter. A complementary finite element model accurately predicted the shear response of the uncured interfaces, confirming its suitability for representing interlayer bonding.
Motivated by the role of roller behavior near overlaps, new polyurethane compaction rollers with increased shaft diameters (increased from 25 mm to 28, 32, and 35 mm) and softer outer layers were designed to reduce pressure discontinuities while preserving adequate overall compaction force. Captured compaction pressures, microscopic images, SLJ tests, and FEM simulations confirmed that these rollers reduce the width of the affected zone and produce more uniform bonding thickness compared with conventional designs once an overlap is present.
To mitigate overlap-induced disruptions in compaction pressure, further investigations were conducted to examine compaction-roller behavior on complex mold geometries where curvature itself can amplify pressure non-uniformity. Accordingly, concave and convex molds with radii of 100 mm were selected as representative non-flat surfaces. An alternative compaction roller design approach was then introduced to improve conformity while maintaining adequate compaction pressure, with key design parameters (e.g., shaft concave depth and convex height) selected based on FEM results to promote more uniform pressure distribution on both concave and convex geometries.
Overall, the results provide a comprehensive understanding of how overlaps, roller characteristics, and process parameters collectively influence bonding quality in AFP, offering a method to improve pressure distribution and inter-laminar bonding.