Experimental determination of out-of-plane shear moduli in woven kenaf composite laminates using a torsional-DIC approach

Accurate characterization of the out-of-plane shear properties of laminated composites is essential for understanding their structural integrity under complex loading. While in-plane shear moduli are well-studied, out-of-plane properties are often challenging to measure, especially in natural fiber-based laminates. This study proposes an experimental method, based on the Mindlin-Reissner plate theory, to determine out-of-plane shear moduli of woven kenaf laminates using a torsional test setup enhanced by three-dimensional digital image correlation (3D-DIC). Rectangular specimens of two lengths (50 mm and 90 mm) were clamped and subjected to quasi-static torsion. The torque was recorded using a load cell, and full-field strain was captured via 3D-DIC. The average in-plane shear modulus (G12) was found to be 1589.5 MPa, while the out-of-plane shear modulus (G13) was 693.85 MPa. A specimen geometry sensitivity analysis revealed that a width-to-thickness ratio below 3 leads to significant overestimation or underestimation of the respective shear moduli. The proposed method is non-destructive, adaptable to relatively thin laminates, and well-suited for characterizing sustainable composites, making it a promising tool for design and performance assessment in bio-based structural applications.