1,720,966 research outputs found
Effect of the visco-elastic properties of thermoplastic polymers on the flexural and rebound behaviours of ski boots for alpine skiing
No full textThe flexural behaviour and elastic rebound are the main parameters that determine the global performance of a ski boot during skiing. These two parameters are related to the visco-elastic properties of the polymeric materials used. For this reason, the visco-elastic properties of the materials most utilized for the production of ski boots (polyurethanes and polyolefins) have been studied using dynamic mechanical thermal analysis in a temperature range between '30 °C and +50 °C. Also, the flexural and rebound behaviours of the boot have also been tested using specially designed test benches. The dynamic mechanical thermal analysis results and the flexural and rebound tests results were compared, and a significant effect of the visco-elastic properties on the flexural and rebound behaviour of ski boots was seen. Therefore, dynamic mechanical thermal analysis can be used in a knowledge-based design process of new ski boots in order to improve on-snow performances
Thermo-physiological comfort of soft-shell back protectors under controlled environmental conditions
No full textThe aim of the study was to investigate thermo-physiological comfort of three back protectors identifying design features affecting heat loss and moisture management. Five volunteers tested the back protectors in a climatic chamber during an intermittent physical activity. Heart rate, average skin temperature, sweat production, microclimate temperature and humidity have been monitored during the test. The sources of heat losses have been identified using infrared thermography and the participants answered a questionnaire to express their subjective sensations associated with their thermo-physiological condition. The results have shown that locally torso skin temperature and microclimate depended on the type of back protector, whose design allowed different extent of perspiration and thermal insulation. Coupling physiological measurements with the questionnaire, it was found that overall comfort was dependent more on skin wetness than skin temperature: the participants preferred the back protector with the highest level of ventilation through the shell and the lowest level of microclimate humidity
Ski Boot Soles Based on a Glass Fiber/Rubber Composite with Improved Grip on Icy Surfaces
Full text linkAbstractA study on the effect of glass fibers/rubber composites on the grip on ice has been conducted in order to develop new materials for ski boot soles with increased grip in winter environments. The study has been conducted analyzing the friction of a composite material and of a ski boot sole containing an insert made of the composite material and comparing the results with those obtained using rubber and a thermoplastic elastomer. The analysis of the morphology of the composite surface, by Scanning Electron Microscopy, shows a homogenous distribution of glass fibers of approximately 10μm of diameter in the rubber matrix. Moreover, the measure of the contact angle shows that the composite material has a higher water repellency compared to the rubber matrix. The measure of the coefficient of friction indicates a significant effect of the glass fibers on the grip on icy surfaces. The increased grip can be ascribed to the stiffness of the glass fibers that are able to have a mechanical grip on the ice surface and to the increased contact angle and water repellency of the composite that decrease the formation of a water layer below the sole
Thermo-formable Materials for Ski Boots for Improved Comfort and Performance
No full textAbstractFour different materials used for the production of ski boots have been analyzed in order to determine their performance in the thermo-formation process used to modify the shape of ski boots and therefore improve their comfort. As a first step, the chemical composition and the thermo-mechanical properties have been analyzed pointing out that materials based on a blend of nylon with methacrylate ionomers provide the largest decrease of the storage modulus at 80°C. The results of the thermo-formation process indicate that the boot based on the methacrylate ionomer has the larger deformation after the thermo-formation process and the lowest memory effect. These results indicate that the decrease in modulus from 0°C to 80°C is the most important factor to be considered in order to obtain a more consistent and permanent modification of the boot shape
Thermal behaviour of ski-boot liners: effect of materials on thermal comfort in real and simulated skiing conditions
Full text linkThe choice of the appropriate material for the construction of ski-boot liners is of fundamental importance in order to achieve
ergonomic comfort and high thermal insulation. In this work the effect on thermal comfort of different materials used for
commercial ski-boot liners has been analysed. The thermal insulation and the moisture management of liners made of different materials have been tested both in a climatic chamber and in outdoor conditions using wireless sensors combined with infrared thermography. The results obtained show substantial differences in terms of thermal comfort between the liners in the same environmental conditions, showing that closed cell ethylene vinyl acetate foams provide the best thermal comfort
Thermo-mechanical and impact properties of polymeric foams used for snow sports protective equipment
Full text linkThe thermo-mechanical and impact properties of materials used for hard-shell and soft-shell back protectors have been analysed in order to understand the mechanism of action of the foams used for protective equipment. Dynamical mechanical analysis has shown that materials used for soft-shell protectors present frequency-sensitive properties that permit to have a soft response when stressed at low speed and a hard response when subjected to a high-speed impact. Furthermore, by means of drop weight impact tests, the shock absorbing characteristics of the materials have been investigated at two temperatures pointing out the differences between soft and hard-shell protectors; in addition it has been demonstrated that the materials used for soft-shell protectors maintain their protective properties after multi-impacts on the same point
Effect of Compression on Thermal Comfort of Ski Boots
No full textThe effect of compression on the thermal comfort of ski boots has been evaluated comparing the temperature in the toe area of two ski boots with a 10% difference in internal volume, during simulated skiing in a climatic chamber at -10 °C for 60 minutes. The results obtained indicate a more consistent skin temperature decrease (9.15 ± 1.35 °C) using the ski boot with the reduced volume configuration with respect to that observed using the correct volume configuration (2.99 ± 1.10 °C). The most consistent temperature decrease and the feeling of cold discomfort have been ascribed to the restricted blood circulation caused by compression. This effect was proved by the fast temperature increase when the compression was eliminated extracting the liner from the shell after 20 and 50 minutes of test
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effect of material elastic properties and surface roughness on grip performances of ski boot soles under wet and icy conditions
Full text linkA set of thermoplastic materials employed in soles for alpine skiing boots were characterized in terms of chemical composition, cristallinity, hardness, surface roughness, and grip. The results of friction experiments on different substrates reproducing the real environmental scenarios point out that materials provide more grip as they become softer. Moreover, higher roughness results in lower dynamic coefficient of friction (COF). Finite element simulations corroborate the experimental measures of COF and let to rationalize the role of material elasticity and surface roughness on the frictional characteristics of soles. The measure of grip on an inclined wet surface provides analogous results, indicating that COF can be used as key performance indicator in the design of ski-boot soles and of other anti-slip equipments in wet and icy environments
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