Tailoring the in-plane shear behavior and formability of woven preforms via hybrid slit-tufted modification: Mechanisms and modeling

In-plane shear response governs the formability of woven reinforcements during composite preforming, and its modification is central to defect mitigation in double-curved geometries. This study investigates the coupled effects of controlled slitting and tufting on the shear behavior of plain-woven E-glass fabric through picture frame tests combined with full-field optical measurements. Two slit configurations are examined: a diagonal slit (DS) aligned with the principal shear path, and a corner slit (CS) oriented along the warp/weft directions. Slitting is shown to act as a load-path reconfiguration mechanism rather than a simple stiffness reduction: DS creates a spatially extensive preferential release zone, while CS produces a more confined redistribution. Tufting introduces a deformation-dependent bridging constraint that remains passive at low shear angles and becomes progressively active beyond approximately 35°, partially suppressing slit-edge opening without significantly altering the broader shear angle field. Across all five specimen configurations, the shear locking angle remains invariant at approximately 44.0°, confirming that this geometric limit is governed by the intrinsic yarn packing condition and is insensitive to mesoscale structural modification. To quantify these coupled effects, a spatially weighted slit-opening ratio and a shear enhancement factor are introduced. A semi-empirical framework is developed for the DS configuration and reproduces the measured shear-force evolution with in the pre-locking regime. The CS configuration is excluded from the model because its slit-edge opening is negligible and the tufted and non-tufted responses are nearly indistinguishable. The framework encodes the locking angle invariance as a constitutive constraint, linking the modeling results directly to the experimental finding. These results provide a quantitative basis for mechanism-guided preform design targeting high-curvature composite structures.