Abstract
The current paper is describing the implementation of a multiscale numerical model for prediction of stiffness and strength in braided composites. The model is validated by experimental testing of single-layer braided tubes under torsional loading utilising digital image correlation (DIC). For the numerical model the entire braided structure is modelled at yarn detail level, taking into account the yarn behaviour as well as individual yarn-to-yarn interactions by using cohesive contact definitions. By means of Hashin’s failure criteria and cohesive contact damage, failure of the yarns and failure of the yarn-to-yarn interface is being accounted for. Thereby the material failure behaviour can be predicted. For validation of the model, torsion tests of biaxially braided single-layer composite tubes were performed. The strain distribution at the specimen surface was studied using the DIC system ARAMIS in 3D mode.
Highlights
Aim of this research is the implementation and validation of a numerical tool providing reliable predictions of the mechanical properties of braided composite materials
The presented numerical model accurately predicts stiffness and strength of the braided tubular structure under torsional loading and correlates well with the experimentally obtained data
As buckling under torsional load is generally prone to imperfections, this leads to the assumption that the differences originate mainly from imperfections in the specimens that were not taken into account in the numerical model
Summary
Aim of this research is the implementation and validation of a numerical tool providing reliable predictions of the mechanical properties of braided composite materials. By implementation of failure models, the approach can predict occurring failure mechanisms, distinguishing damage at the yarn level (intra-yarn) and yarn-interface level (inter-yarn). Material properties required as input parameters are obtained by mean-field homogenization (MFH) from the individual constituents behaviour (matrix and fibres). For validation of the model, single layer braided tubes are tested under torsional loading utilising DIC for full-field strain measurement on the surface of the specimen. The global loading response predicted by the numerical model as well as the local strain distribution and occurring instability behaviour is compared to the experimentally obtained results
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