VISION

Integrate cognitive assessment in the design of novel materials and structures

SCIENTIFIC TOPICS

Embedding smart materials and sensitive devices for improving 'feel and control' of sport equipment.

a) Novel "smart" materials with specific microstructures and properties

b) Microstructure's influence on structural (static and dynamic) properties of model and real structures

c) Influence on the athlete's perception: "feel & control"

APPLICATIONS

Skis, tennis raquettes, prosthesis, etc

RESULTS

This work has shown that integrating a shear thickening fluid (STF) with strongly non-linear rheological behaviour into a sandwich structure (Figure) can lead simultaneously to changes in stiffness and damping under dynamic flexural loading as the strain and/or frequency are varied (Figure). Thus, STFs could be used as a tunable damping element for structures exposed to dynamical flexural load. Layers of highly concentrated silica suspensions integrated into the model sandwich structure lead to a 9-fold increase of the damping of the structure's 1^st resonance frequency as the excitation amplitude was continuously increased. Simultaneously, the structure's flexural rigidity increased by over 20%, since the increased viscosity of the STF interlayer lead to an improved stress transfer between the stiff polyvinyl chloride (PVC) layers. Thus, the highly non-linear properties of the STFs observed under oscillatory shear could be transmitted to a dynamically loaded structure when properly integrated. Using this solid background in STF rheology and its effect on the dynamic properties of the model sandwich structure, strategies are being developed to integrate STFs into real structures such as alpine skis, and alternatively at the micro-scale of polymer composites.

Furthermore, using alpine skiing as a case study, a method has been developed to determine how differences in mechanical properties of an item of sports equipment are being perceived by athletes. Using four pairs of slalom race skis specifically designed to differ between each other in static and dynamic properties, we found amongst others that skiers from different levels (expert and advanced level) all preferred the slalom skis with a high torsional- and a low flexural rigidity. This approach was shown to be a powerful method for linking human judgment to the mechanical properties of sports equipment, and should be a powerful tool to evaluate whether the integration of novel materials such as STFs will be beneficial to a certain sports equipment or not.

Schematic representation of the 3-layer PVC sandwich structure used for the vibrating beam testing (VBT).

Compliance vs. frequency for a PVC-STF sandwich structure with different set tip displacements.

MAIN PUBLICATIONS

Fischer C, Braun S A, Bourban P-E, Michaud V, Plummer C J G and Månson J-A E. Dynamic properties of sandwich structures with integrated shear-thickening fluids. Smart Materials and Structures 15, 1467-1475 (2006)

Fischer C, Overney L S, Fauve M, Blanke O, Rhyner H U, Herzog M H and Månson J-A E. What static and dynamic properties should slalom skis possess? Judgments by advanced and expert skiers. accepted for publication in Journal of Sports Sciences