3D strain mapping around fibre breaks using in situ synchrotron computed tomography and digital volume correlation

Abstract

Load redistribution around a single fibre break is a critical mechanism determining longitudinal tensile strength in carbon fibre-reinforced polymer (CFRP) composites, with understanding of this process historically relying on model predictions. Digital Volume Correlation (DVC) combined with high-resolution computed tomography has previously enabled the experimental quantification of strains around fibre breaks, using volumetric speckle patterns generated by the addition of fiducial particles to the composite matrix. Applying fiducial particles to CFRP to interrogate the length scales of single fibre breaks is non-trivial, as micrometre-scale inhomogeneity and particle agglomeration may compromise the broader applicability of the results. The present study extends the potential applicability of DVC, in combination with synchrotron computed tomography, by incorporating silicon dioxide (SiO₂) particles into CFRPs as a practical and improved alternative to barium titanate (BaTiO₃) particles used in previous work. The applicability is assessed in terms of particle distribution, DVC measurement uncertainty, and strain recovery lengths around single fibre breaks. The assessments reveal that SiO₂ particles can produce a reasonably uniformly dispersed speckle patterns with minimal apparent agglomeration, providing the fidelity required for accurate DVC measurements. On this basis, DVC strain mapping around breaks is further applied to two CFRPs with differing interfacial shear strength levels (by ∼17%). DVC results indicated that the strain recovery lengths were insensitive to this change in interfacial strength, which was rationalised by the absence of detectable debonds. Overall, this study provides novel insights into load redistribution under varying interfacial strengths, offering an experimental basis for advancing longitudinal tensile strength models.

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