New insights in stressing leather – multi-scale simulation of macroscopic structure-property relations

The naturally grown leather structure is the origin of both the uniqueness of each leather product as well as the inherent variance inside the material. For optimal exploitation of the leather's potential during processing and utilisation, an extensive material characterisation is imperative. However, the qualification of leather properties remains a challenge as conventional testing methods often require the destruction of the test material. In addition, non-destructive computer-aided design and numerical analysis of the physical and mechanical behaviour of components are increasingly essential for industrial mass production. Dedicated software solutions for leather materials are not yet available. As part of ongoing research activities, imaging analysis methods using micro-computed tomography (µCT) were utilised to analyse leather structure areas and corresponding sub-structural elements. The extraction of hierarchical leather structures was facilitated by the use of automated segmentation and parameterisation algorithms. The creation of a stochastic leather structure model was achieved. This pioneering approach enabled the multi-scale simulation of elastic and viscoelastic structural properties, exemplified by the tensile strain testing of leather, using advanced mathematical-numerical simulation techniques. The macroscopic simulation results were validated using classical mechanical and single-fibre tensile tests. These tests showed excellent agreement for the elastic but not for the viscoelastic deformation scales. It is hypothesised that an unexpected loss of anisotropy in the macroscopic leather structure composite occurred during sample preparation for the µCT studies.