Numerical and experimental investigation of the structural behavior of a carbon fiber reinforced ankle-foot orthosis

• A multiscale modeling strategy for both UD and textile CFRP is proposed.
• The resulting macromechanical model accounts for the intrinsic micro- and meso-structure of the material.
• The material model is validated on different scales against experimental data.
• Finally, a numerical and experimental investigation of an AFO is performed.
• The comparison shows good agreement of local and global values.

Ankle-foot orthoses (AFOs) are designed to enhance the gait function of individuals with motor impairments. Recent AFOs are often made of laminated composites due to their high stiffness and low density. Since the performance of AFO is primarily influenced by their structural stiffness, the investigation of the mechanical response is very important for the design. The aim of this paper is to present a three dimensional multi-scale structural analysis methodology to speed up the design process of AFO. The multi-scale modeling procedure was applied such that the intrinsic micro-structure of the fiber reinforced laminates could be taken into account. In particular, representative volume elements were used on the micro-scale, where fiber and matrix were treated separately, and on the textile scale of the woven structure. For the validation of this methodology, experimental data were generated using digital image correlation (DIC) measurements. Finally, the structural behavior of the whole AFO was predicted numerically for a specific loading scenario and compared with experimental results. It was shown that the proposed numerical multi-scale scheme is well suited for the prediction of the structural behavior of AFOs, validated by the comparison of local strain fields as well as the global force-displacement curves.