In this project we simulate the mechanical properties of leather. This serves as a basis for their specific influencing already during production and processing.

Simulation of Mechanical Properties of Leather with TexMath

AIF Project – Simulation of the Properties of Leather

The microstructure of leather looks like long fiber bundles that are branching out into thinner networks and are interwoven in many places. Macroscopically viewed, leather is a highly anisotropic material. Leather is typically processed in car seats, furniture, clothing and shoes. The project presented here - funded by the German Federation of Industrial Research Associations (AiF) – deals with the prediction of leather properties.

The properties of leather depend on the structural arrangement of the fiber bundles, their thickness, length and viscoelastic properties. Since leather is a natural product, it shows much more non-uniform material properties than plastics and textiles. In view of the industrial mass production, there exists an increasing need to design leather-covered car and furniture seats and to evaluate the corresponding mechanical behavior in advance. In cooperation with our department »Image Processing« and the Research Institute for Leather and Plastic Sheeting (Forschungsinstitut für Leder und Kunststoffbahnen FILK), we simulate the mechanical behavior of leather by means of mathematical modelling and homogenization methods based on micro-CT images of the leather structure and the measured visco-elastic properties of the fibre bundles.
 

Microscopical Simulations Using the Software TexMath

The CT images taken so far show that the leather material consists of many fiber bundles whose orientation along the thickness of the layer varies considerably; the long, curved cylinders are branched, interwoven and crossed at many points. Using the measured properties of the fiber bundles, we simulate the behavior of the structure using our TexMath software. This software allows the efficient calculation of large fiber systems for large deformations with simultaneous contact sliding at millions of nodes. In this case, TexMath correctly considers the influence of frictional sliding in local fiber bundle nodes on the macroscopic leather behavior.

Video: Simulation of Leather with TexMath

Fraunhofer ITWM

The microstructure of leather looks like long fiber bundles that are branching out into thinner networks and are interwoven in many places.

CT Image Leater
© Fraunhofer ITWM
Previous CT images indicate that the leather material consists of many fiber bundles whose orientation (degree of anisortropy) varies greatly along the thickness of the layer.
Scanning electron microscopy (SEM) of leather
© Forschungsinstitut für Leder und Kunststoffbahnen FILK
Scanning electron microscopy (SEM) of leather. The research goal of the project is a 3D FEM structural model for leather that allows realistic load predictions, among others based on CT and such SEM images.

Calculation of the Relaxation Time of Leather

Furthermore, we investigate how the relaxation time of the leather material is related to the relaxation behavior of the fiber bundle. Based on our previous analysis results, we has shown that the macroscopic relaxation behavior can be computed by multiplying the relaxation behavior of a single fiber bundle by the purely structural geometric factor that we determine from the CT images. We were able to confirm this assumption – based on experimental data from tensile tests for leather and fiber bundles. We also carry out macroscopic simulation analyses of leather. We take into account the strength of the yarns, the fibre bundle structure and the calculated homogenised properties and local tensions.

Leather Damage
© Fraunhofer ITWM
Tensile simulation of leather damages near a hole: For example, we predict the anisotropic waxing of a punched hole in the leather that occurs under tensile loads and thus predict realistic material stresses.

Video: Simulation of Leather with TexMath

Fraunhofer ITWM

Another example of microscopic simulation of leather properties with TexMath.