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Thư viện số Văn Lang: Snow Sports Trauma and Safety: Conference Proceedings of the International Society for Skiing Safety: 21st Volume

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Nguyễn Gia Hào

Academic year: 2023

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No effect of pole diameter on maximum deformation was observed for the "tall" skier. The reason for independence is the low ratio between the weight of the pole (500 g) and the weight of the skier.

5 Limitations

Current impact speeds in World Cup slalom races require advanced research to reduce pole mass. In children's and youth races, the skiing speed and therefore the impact speed is clearly lower than in World Cup races, resulting in a lower impulse of the skier's pole with a lower maximum deflection of the pole and a lower speed of pole damage.

Assuming lower impact speeds of 2 m/s than in World Cup races, bar d27-w2.5 showed the same maximum deflection as the World Cup approved bar d31-w3. However, time loss would be reduced by about 40% in the described seven-gate flat track due to the mass reduction.

Sagittal Plane Helmet Acceleration at Pole Contact of Alpine Ski Racers is Dependent

1 Introduction 1.1 Acceleration

Poles and Training Aids

Poles are used in alpine ski racing to determine the competition line for the skier. The FIS [2] has specifications for the dimensions of the bars used in international competitions, while individual countries set domestic standards. This course was developed to prevent the pole from moving as skiers skied closer and closer to the pole and eventually discovered that they could simply cut the pole with their arm, ski pole or shin, allowing them to make a shorter and therefore faster path.

FIS has two categories of poles: type A; which is for use in any FIS race. However, U14 slalom poles must be 152 cm FIS B, while stubby poles are for non-scoring events [4]. Instead of poles, props, or training aids like Whiskers and Heroes, minimize contact while skiing the intended route.

Furthermore, finish time and subjective feelings of young skiers would be altered by pole length.

2 Methods 2.1 Subjects

Courses

  • Pole Type Used During Each Testing
  • Timing
  • Acceleration
  • Skier Perception

The study was conducted on 12 different slopes at Bridger Bowl Ski Area, Montana, and Park City Mountain Resort, Utah, over 11 separate days in winter conditions. All tracks were frequently skidded to minimize rut development and general track deterioration. All rods, Heroes and Whiskers were manufactured by SPM and were new at the start of the study.

A gyroscopically controlled three-dimensional accelerometer (Electronic Realization, Bozeman, MT) was attached to the crown of the skier's helmet. Sagittal plane, anterior/posterior direction was defined as "x", vertical direction as "y", lateral direction as "z". The subject responded to four statements indicating their perception of speed, aggressiveness, confidence, and line on a 10-point Likert scale.

3 Results 3.1 Time

  • Reliability Between Runs of Same Pole Type (Within Skier)
  • Perception
    • Questionnaire Results (Table 3)
  • Acceleration
    • Mean Acceleration Skilled vs. Less Skilled
  • Peak Acceleration

There were significant differences for mean sagittal plane helmet acceleration between the three pole types and the two training aids. A significant difference was also observed when the skiers were grouped into "skilled" and "less skilled" cohorts (p = 0.0000). There was also a significant difference in average acceleration between the skilled and less skilled in the vertical (p = 0.000) and lateral (p = 0.000) directions.

There were no significant differences in average acceleration in any of the three directions between the five pole types, nor was there any difference when grouped into the two training aids (Whisker and Hero) and the two longer pole lengths (152 and 180 cm) for a of the three directions. 3 Average accelerations in forward/backward (x), vertical (y) and lateral (z) directions for the three pole lengths and two training aids for experienced and less experienced ski racers. Averaged over ten consecutive turns, there were significant differences for the peak acceleration for the skilled group in the z-direction (p = 0.03) when comparing the short supports with the two long poles, and for the less skilled in the y-direction (p=0.05).

When the short props were compared to the two long rods, all other short props vs.

4 Discussion

Possible Explanations

  • Physical Contact with the Pole
  • Anticipatory Postural Control
  • Vestibulo-Ocular Reflex
  • Psychological Factors
  • Ski Pressure Management
  • Movement Decision Under Risk

Reid and colleagues have used kinematic data with elite skiers showing that during a slalom turn, the skier's CoM undergoes a period of negative acceleration followed by a period of positive acceleration between turns [1]. It has been calculated that elite skiers contacting a FIS A bar will use 45 J of work to deform the bar, 108 J to accelerate the bar, and 28 J to overcome hinge resistance for 181 J of work. The more skilled skiers could anticipate the effect of bar contact with their postural muscles.

Less skilled ski racers may not have had enough experience to sufficiently learn this advance postural mechanism, partially explaining the resulting negative acceleration observed in this study. Elite ski racers strive to apply pressure to their skis while in the downslope or downhill part of the turn. Less skilled skiers and recreational skiers who strive to control speed instead of maintaining speed will find themselves under pressure later in the turn.

A risk aversion situation can be postulated by less skilled ski racers having greater variability in most aspects of their skiing technique suggesting increased instability [13].

What Does It Mean for Safety?

Page GD, Telford L, Seidman SH et al (1998) Human vestibulocular reflex and its interactions with vision and fixation distance during linear and angular head movement. Pienciak-Siewert A, Barletta AJ, Ahmed AA (2013) Transfer of postural adaptation depends on context of previous exposure. Ruedl G, Linortner I, Schranz A et al (2009) Distribution of injury mechanisms and related factors in ACL-injured female snowboarders.

Bare T (2011) Mechanisms of anterior cruciate ligament injury in Alpine Skiing World Cup: a systematic video analysis of 20 cases. Kipp RW, Reid RC, Gilgien M et al (2008) Slalom performance in elite alpine ski racing can be predicted by front-to-back motion dynamics. Kipp RW, Reid RC, Gilgien M et al (2009) Fore-aft motion is adapted to gate separation by elite alpine racers in slalom.

Open Access This chapter is distributed under the terms of the Creative Commons Attribution-Noncommercial 2.5 License (http://creativecommons.org/licenses/by-nc/2.5/) which permits any noncommercial use, distribution, and reproduction in any medium, provided that original author(s) and source to be credited.

Auxetic Foam for Snow-Sport Safety Devices

1 Introduction

Auxetic Foam

Despite the wealth of research on auxetic foam, work is needed to determine how best to manufacture and apply it to snow sports safety devices. 34, 38], and highly anisotropic auxetic foams can be obtained by applying different amounts of compression in each direction during fabrication [39]. Producing large samples is challenging as the thermomechanical process can result in inhomogeneous auxetic foam due to non-uniform temperature and compression gradients present during fabrication.

A reliable method for producing large quantities of auxetic foam is therefore required to facilitate production and testing for snow sports safety applications, including monoliths for crash pads and sheets for body armor. This is particularly relevant for snow sports safety devices, which are typically required to absorb energy through compression at relatively high speed. Work exploring snow sports safety applications of auxetic foam should therefore involve testing at high loads and load rates, for both airbags and body armor.

This lateral contraction can cause auxetic foams to deform less in the direction of the applied load during impact [23] and reduce the peak force compared to conventional open cell foams [23, 24].

2 Objective

3 Methods

Body Armour

Concentrated load compression testing (Instron 3369, equipped with a 50 kN load cell) was performed with a PP sheet placed loosely on top of each specimen. The support was supported on a flat plate and a load was applied to the center of the upper face with a stud (Kipsta, aluminum football stud, length 18 mm) as shown in Fig. Pilot testing confirmed the efficiency of the configuration for providing the intermediate behavior between the compression foam in the insulation between two flat plates, and a stud and a flat plate.

Chan and Evans [34] reported slightly lower Poisson's ratios for auxetic foams under tension compared to compression. In this work, Poisson's ratio was measured in tension to avoid problems with (1) contact surface friction when compressing thin sheets [24–26] and (2) positioning and tracking pins in a small sample (from the sheet) under compression. After testing the pads, a sample of auxetic foam of each thickness and porosity was cut into three equal strips (resulting in six measurement mm and six measurement mm in total) and cardboard was taped to the ends so they could be gripped. (Fig. . 2).

Four pins in a 20 × 20 mm square on the face of the specimen were filmed with a camera (JVC Everio Full HD resolution pixels) and the Poisson's ratio was obtained from the linear regression of the true lateral strain vs .

Crash Pad

Three mm samples were cut from the converted foam with a bandsaw, corresponding to the center, corner and center of an edge (Fig. 4). Pins in the front of the sample were filmed with a camera (Sony Handycam HFR-CX410 operating at 25 Hz) to obtain real voltage (Fig. 5) in both directions. Two pins approximately halfway down the sample and approximately 30 mm apart were used for true lateral tension and four pins, arranged in a rectangle around the center, were used for true axial tension.

Density measurements of the samples were used to examine local variations in VCR, and foam images were taken with an optical microscope (Leica S6D) to examine cell structure.

4 Results

Body Armour

Peak power was about four times higher for the thin auxetic pads compared to their conventional counterparts and about five times higher for the thick auxetic pads than their conventional equivalents. Example force-displacement relationships for concentrated load quasi-static compression on composite pads consisting of an R60RF foam skin and 4 mm thick polypropylene shell, (b) 10 mm thick foam and (c) 20 mm thick foam. The thinner pads with auxetic foam absorbed about twice as much energy as their unconverted counterparts, while the thicker auxetic pads absorbed about three times more energy than their conventional equivalents.

Crash Barrier

5 Discussion

Brügger O, Bianchi G, Schulz D et al (2010) Snow sports helmets: injury prevention, rate of wearers and recommendations. Michel FI, Schmitt KU, Greenwald RM et al (2013) White paper: functionality and effectiveness of wrist guards in snowboarding - towards a harmonized international standard. Allen T, Shepherd J, Hewage TAM et al (2015) Low-kinetic energy impact response of auxetic and conventional open-cell polyurethane foams.

Duncan O, Foster L, Senior T, et al (2016) A comparison of new and conventional manufacturing methods for auxetic foams for sports safety applications. Cross TM, Hoffer KW, Jones DP et al (2015) Auxetic structures and footwear with soles with auxetic structures. Grima JN, Attard D, Gatt R et al (2009) A new process for the manufacture of auxetic foams and for their reconversion to conventional form.

Alderson A et al (2005) Processing effects on the topology and mechanical properties of negative Poisson's ratio foams.

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However, it could also raise awareness of the usefulness and the beauty of mathematics, inspiring students to continue taking math courses Open AccessThis chapter is distributed under