Boris Jerman

Flexion stiffness of a racing cross-country ski boot

For greater energy efficiency of sports footwear, mass needs to be minimized while preserving other favourable characteristics. In this article, an analysis of the flexion stiffness of the foot region, precisely its middle region, of a specific racing cross-country ski boot for the skating technique regarding its mass was performed. On the basis of a complex finite element model of the ski boot and an existing boot stiffness measuring set-up, flexion stiffness portions, mass portions and flexion stiffness/mass portion ratios were determined for individual boot components regarding the middle boot region. These values were determined for the shoe-upper with strengthening bands and shoelaces (altogether S-U), the sole, the midsole and the glue layer between. The S-U turned out to contribute a high flexion stiffness portion to the boot’s middle region’s flexion stiffness and also its flexion stiffness/mass portion ratio turned out to be the highest. The midsole and the sole present the highest potential for flexion stiffness/mass optimization due to their lowest flexion stiffness/mass ratios and highest mass portions. In order to increase the flexion stiffness/mass ratio of the middle boot region, the sole’s and the midsole’s size portions should be reduced, while the S-U’s size portion should be increased. Beside these findings, other suggestions in order to increase the flexion stiffness/mass ratio of the boot’s middle region are also given.

Advanced finite element cross-country ski boot model for mass optimization directions considering flexion stiffness

Flexion stiffness and mass were recognized as two important parameters of energy efficiency for modern top-class ski boots used in skate cross-country skiing. This article summarizes the study on mass optimization of the front foot region of an existing cross-country ski boot, while considering its flexion stiffness. For this purpose, a finite element model of the boot and an artificial foot for simulation of boot flexion stiffness measurement were made. The boot consists of textiles which require specific measurements for their characterization and special finite element material models for their realization. The finite element model was validated through a three-step validation process, in which flexion stiffness of the complete and stripped versions of the finite element model were compared with experimentally acquired flexion stiffness. Flexion stiffness contributions of individual boot components of the front foot region were acquired from the strain energy accumulated in their finite element. Using flexion stiffness and mass contributions and ratios between them (flexion stiffness to mass contributions), directions for flexion stiffness to mass contribution optimization of the boot’s front region were determined. The shoe-upper and shoe-cap were the most efficient regarding their flexion stiffness to mass contribution ratios and were suggested to be thickened. The soles had the highest potential for the boot’s flexion stiffness to mass contribution optimization due to their high mass contribution and relatively low flexion stiffness to mass contribution ratios. As a result, recommendations were made to reduce the soles’ size and/or increase their flexion stiffness to mass contribution ratios. These recommendations are similar to recommendations from a previous study, despite the higher finite element model accuracy and different method used to determine the flexion stiffness contributions.

Prediction of Load Capacity Behavior of Multi-Stage Formed Construction Elements

The technologies for low-quantity production of sheet metal components and parts are applied mostly for thin single metal sheets. However, such technologies could also be applied as an additional procedure in multi-layer construction element production. Such individually produced construction elements must correspond to required standards, which are usually applied in serial production. Due to the immense testing work expected by custom-made production, it is reasonable to develop a methodology that would be capable of predicting the required results of an individually designed and produced construction block quickly, effectively and with minimal costs. In this investigation, a method of predicting the load capacity behavior of individual construction elements performed by incremental forming as an additional technology in multi-layer construction element production is presented. Special attention is dedicated to the definition of finite element model of a standardized four-point bending test and its correlation to real experimental results.