Abstract
Accurately characterising deformation in fibre-reinforced composites requires specimen geometries that both promote failure within the gauge zone and enable high-quality full-field strain measurements. These demands become even more critical under biaxial loading, where interacting stress states make it challenging to maintain stable and interpretable deformation in the specimen centre. This study systematically evaluates five biaxial cruciform specimen designs for (+45/ 45)S E-glass/epoxy laminates using in-situ interrupted biaxial loading combined with X-ray Computed Tomography (XCT) and Digital Volume Correlation (DVC). Three geometries successfully promoted fracture within the gauge region, while others failed outside the region of interest and were excluded from further analysis. Clear geometry-dependent trends were observed. Specimens with smooth load-path transitions into the gauge section produced the most stable displacement fields, minimal out-of-plane distortion, and the most coherent strain maps. Sharper geometric transitions led to increased strain localisation near the specimen edges, while centrally weakened designs introduced local strain perturbations and amplified XCT artefacts, reducing microstructural visibility despite largely uniform gauge-section deformation. Overall, the results demonstrate how key geometric features govern volumetric strain-field quality, deformation stability, and
damage localisation under biaxial loading. The findings provide practical guidance for the design and selection of cruciform specimens tailored to in-situ XCT–DVC workflows, supporting more reliable volumetric strain characterisation and damage analysis in future multiaxial composite studies. Read more…