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overallSports1 4; doi: This review summarizes the most significant results reported in the scientific and industrial literature patents in the field of ski-boots for alpine skiing.

A critical analysis of the data has been performed in order to highlight the areas of research and the problems that have not been already addressed, pointing out new possibilities for research and development in this field. The review has been divided in the following sections: Materials used for see more parts cuff, shell and tongue: Full Text Ma Thesis University Ofnew trends and conclusions: Skis have been used for years to permit the motion of people living in countries where the snow was present for several months a year.

The first skis were only plank of woods with laces to link the traditional leather boots used in the Nordic and Alpine regions. At that time skiing was mainly performed in flat areas to help the transportation of loads and for this reason the first recreational activity with skis was cross-country skiing.

Alpine skiing was born only afterwards and, therefore, the first equipment used to ski down the steep terrains of the Alps was developed starting from those already used for skiing in flat snow-fields thin skis, leather boots and heel free bindings.

However, the characteristics of those materials were not satisfactory for the needs of alpine skiers. The development of alpine ski equipment has been done, in the beginning, mainly by trial and error, using on-snow tests. However, in the last few decades, the research in the field of plastic materials and the optimization of new software for the design of sport equipment have permitted the development of new materials and designs that have increased the level of performance, security and comfort of ski-boots [ 1 ].

These improvements have been driven by the growth of alpine skiing as a recreational sport. The new users request lighter materials, more comfort, increased durability and improved performances. With the increasing number of users, new standards and rules for the production of safer materials have also been developed. Despite the large market of ski equipment, not many scientific papers have been published on this subject in the past.

Moreover, most of the scientific work regarding the development of Full Text Ma Thesis University Of materials and designs for ski-boots has been published as patents. However, in the last few years an increasing number of interesting papers have been published on this topic. Some unpublished data will be also reported in order to complete and clarify the results already described in the literature.

Every part of the ski-boot cuff, shell, liner, buckles, soles etc. The materials used for ski-boots dedicated to different skiing disciplines have been correlated with the viscoelastic, chemical and physical properties of the materials used for the different parts of ski-boots.

The sectors that lack scientific studies are also analyzed with suggestions for new studies for the development of boots with improved performances.

On the basis of the results of published papers and patents and on the evolution of ski-boots, a trend for the development of future ski-boots is also provided.

The ISO standards for the construction of ski-boots are also reviewed, highlighting the problems and the lack of international norms dealing with ski-boots. Ski-boot performances have been significantly improved in recent years using new materials and new designs.

In our opinion, in order to deeply understand the reason for these improved read article and to predict new trends, an analysis of the evolution of ski-boot materials and designs in the last century is necessary.

Even if the number of ski-lifts and of alpine skiers was dramatically increasing, Full Text Ma Thesis University Of ski-boots used in the s were essentially unchanged from those used in the previous centuries, having a thick sole with a thinner upper shell of leather similar to a normal winter boot.

However, with the development of new ski bindings like the Kandahar in and of the Head Standard skis which permitted a much stronger control of the edges and a more precise and fast skiing [ 2 ], new boots were necessary. The first changes were made in order to improve the boot stiffness and to allow a greater control by using stiffer and thicker leathers and by soaking the boot in hot water before use.

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Also, the sole was made of harder materials since the boot was clamped on the ski. However, these changes made the boots extremely uncomfortable. The first attempt to use stiffer materials other than leather was made by Robert Lange, who inserted elements made of fiberglass reinforced epoxy resin in [ 3 ].

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Go here the knowledge acquired on reinforced epoxy composites, Lange produced in the first ski-boot completely made of plastic, using acrylonitrile butadiene styrene ABS polymers [ 4 ].

However, the poor low temperature resistance of the plastic used Royalite from Uniroyal gave rise to several mechanical failures. In the same years, Hans Martin of Henke Speedfit patented the levered buckles for the closure of the boot [ 5 ]. The problems connected with the use of ABS plastic were partially solved in using Adiprene, a thermoplastic polyurethane manufactured by Dupont. With this new material it was possible to produce ski-boots by injection molding.

In the same year, Rosemount introduced to the market the first ski-boots completely made of composite materials, using fiberglass epoxy resin composites, with a shell that was made in two separate parts to permit the insertion of the foot [ 6 ].

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The mass production of plastic ski-boots started in with Lange that used an Overlap Full Text Ma Thesis University Of, made of two parts, the lower part called shell and the upper part called cuff Figure 2.

In the same year production was also started by Nordica in Montebelluna Treviso, Italy in collaboration with API Plastic, using a polyurethane made by Bayer for aerospace applications Desmopan [ 7 ] Figure 1.

InHanson introduced the rear entry design that was check this out used by Nordica and Salomon [ 89 ]. Rear entry ski-boots have gained a large commercial market in the 80s and 90s. However, their production has been decreasing in the following years and rear entry boots are currently used only for youth and rental boots [ 10 ]. One of the reasons of this change can be ascribed to the force needed to remove the foot from a rear entry boot that is higher compared to that from an Overlap ski-boot and can be a major problem in case of ankle injuries [ 11 ].

Another reason can be connected with the difficulty to adapt the shape of the front part of the shell of the ski-boot to the foot shape and therefore have a precise control of the skis. Taking inspiration from the joint of spacesuits, he designed a ski-boot that was made of an additional tongue, which was controlling the flex of the boot [ 12 ]. This construction was named Flexon design and now is also known as 3-pieces design or Cabrio Design.

In the last few years, several new models have been introduced to the market; however, the main construction designs have always been related to the Overlapthe 3-pieces designs or to a combination of these two designs. Nowadays, ski-boots are composed of several parts assembled using screws and bolts.

A standard ski-boot with Overlap construction is composed of the parts reported in Figure 2. Other parts such as the footboard a plastic or rubber part between the shell and the sole of the inner boot and the tongue can be also present in the ski-boot. Every part of the ski-boot is made of a different material and the parts are assembled by means of metallic or plastic connectors. The choice of the right material and design is made in order to have: The design of ski-boots is of fundamental importance in order to combine good skiing performances with comfort.

The functional parameters to be taken into account when designing a ski-boot are: Shell Last maximum width of Full Text Ma Thesis University Of inner part of the shell Figure 3. Hinge point between shell and cuff Figure 2. The internal form of the shell and of the cuff must be shaped to follow the anatomical shape of the foot.

However, since foot shapes are different from person to person, a shell shape that can fit all feet does not exist. Continue reading, all ski-boot producers prepare boots with different shapes and Lasts depending on their consumer target.

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For example, a 95 mm Last measured for a size The shell can be modified by grinding the plastic in the points of pressure or by combined heat and pressure boot-fitting. As previously reported, the two main ski-boot designs that are present nowadays in the market are the two-pieces Overlap construction and the three-pieces Cabrio construction developed by Just click for source Giese [ 12 ] Figure 4.

The analysis of the commercial products present on the market shows that the most common design is the Overlap that is composed of a lower part shell connected by metallic screws to the upper part cuff. The forward flex of the boot is controlled by the bending of the upper-back part of the shell spine and by compression of the lower front part of the cuff on the shell. This second interaction can provide the undesired enlargement of the instep of the shell if the boot is not properly designed.

This design provides the best fit in the front part of the shell since the two parts of the shell overlap, and therefore the tightening of the here decreases the internal volume providing a tight and precise fit.

Moreover, this construction provides a fast power transmission from the skier to the ski edge. For these reasons Overlap design is the only one currently used in World Cup racing ski-boots.

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The Overlap construction can sometimes give rise to problems in entry and exit of the foot from the boot in cold weather conditions, especially if stiff plastics are used. Cabrio design is less used with respect to Overlap design, even if for some producers Dalbello and Full Tilt, as reported on their websites and for some skiing disciplines freestyle and mogul skiing is the preferred design. Cabrio design does not use friction to resist the flex. Instead, it uses a separate piece of plastic the tongue that acts as a spring [ 12 ].

This has two advantages: In order to ensure that the flexing force remains under control even with extreme bending, the plastic is formed into the same bellows-like shape used in spacesuits. The result click at this page a smoother flex that starts off soft and progressively stiffens [ 12 ].

When tightened, the mid buckle pulls the foot rearward, which helps keep the ankle in the rear pocket of the boot [ 12 ]. The progressivity of the flex makes this type of ski-boots very efficient in adsorbing shocks during landings or skiing in moguls, and this is the reason it is the design of choice for freestyle and off-piste disciplines.

Moreover, the possibility to move the tongue permits an easier entry and exit of the foot from the shell with respect to the Overlap construction. This has a negative effect on the control of the edges with the front part of the boot and for this reason this type of boots is not used anymore in World Cup races. However, the use of thermo-formable liners Section 7 permits the use of shells with a narrower Lastwithout compromising the comfort and allowing a more precise edge control.

Moreover, since the flex of Cabrio designed boots is mainly governed by the tongue, the flex stiffness of Full Text Ma Thesis University Of boot can be easily modified by changing the tongue with one made of a plastic with different stiffness.

In the last few years a combination of the two designs has been developed, with a tongue and front part with Overlap construction. This new design combines the precise fit and edge control of Overlap construction with the flex progressivity of the Cabrio design. Several design parameters are fundamental in order to improve performances and reduce stresses and injuries.

For example, as widely reported in the literature [ 13141516171819 ], the angles of tibia and foot with respect to the base of the boot and the pressure of the foot on the base of the ski-boot are responsible for ski injuries. Some researchers have studied the correlation between ski-boot design and load at the knee joint [ 2021 ]. It is also reported in the literature [ 19 ] that the injury mechanism for anterior cruciate ligament ACL rupture involves the valgus movement go here with external rotation.

According to other authors [ 15 ], ACL rupture can occur when the skier tries to stand up after or during a fall. The injury mechanism involves the combined valgus movement with deep flexion, which causes internal rotation and anterior displacement of the tibia. Since many skiers have valgus or varus leg alignments, Full Text Ma Thesis University Of skiing posture can be achieved by machine milling the boot sole or moving the position of the cuff with respect to the shell using a canting system positioned in the hinge point between cuff and shell, until a good posture is obtained.

A different approach has been developed by Corazza et al. The loads applied during the turning phase Table 1 have been measured using a boot-board instrumented with four pressure sensors. From the data obtained from the boot-board, a special finite element model FEM was developed in order to design a ski-boot able to decrease the stresses responsible for knee injuries. On the basis of these results, the authors have developed an innovative ski-boot in which the angle between the leg and the ski was not modified by changing the angle between the cuff and the shell, but by changing the angle between the lower part sole and the shell, which were connected with screws.

The method was also implemented using a Motion Capture technique in order to measure the boot deflection patterns under cyclic click. A set of 46 semispherical markers 6 mm diameter was placed on the boot surface to define a reticular mesh of control nodes Figure 8. In this way, the authors have been able to record the torsional Figure 9 and bending moments applied on the ski-boot.

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