4.Vaulting pole characteristics PDF

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4. Vaulting Pole Characteristic 4.1 Introduction Fiberglass composites are light and hard, with one larger failure strain than bamboo [9]. Carbon fiber composites usually have higher hardness (The elastic modulus of carbon fiber is 235Gpa compared with the 76GPa of fiberglass, it can store more energy for the same strain. So if athletes can bend carbon fiber rods to the same extent as fiberglass rods, they will benefit from greater energy released so there can be a greater final height arrivals. But this means that the recoil time is shorter, athlete swing and rotate for a shorter time before the pole is straightened. Therefore, the athlete needs have greater technical ability to succeed treasury. The strength of the carbon fiber sheet is higher than glass fiber sheet with a typical carbon laminate fiber in epoxy resin, volume fraction of 50%, with strength 1000MPa compared with 700Mpa polyester and fiberglass laminates [10]. This is potential safety advantage because the pole is unlikely rest and death occurred in this movement. Most athlete still use fiberglass rods and quite large the use of carbon fiber rods requires experience.

4.2 Stiffness The stiffness of the dome affects its ease of use. The athlete can bend it in the vault. Incase stiffness is too low, the rod is not enough support, if the rod is too stiff, the athlete can "Bounce" without getting the proper vault. The stiffness of the rod is related to the stiffness of the material it is made of (the modulus of elasticity of the material, E) its shape (diameter and wall thickness). Relatively the stiffness of the rod is shown as "weight class", where athletes should not exceed. Weight rating is calculated by the manufacturer and related to how when the center is full 50lb, the rod will bend a lot at pound (22.3 kg) mass. Test methods may vary between manufacturers (example free or limited support) extremely long, free span, and etc. Hunt chose one weight class is suitable for its physical characteristics ability [11]. For GFRP vault rods, the modulus of the material is elasticity, E, related to the volume fraction, and fiber orientation. If there were a change in fiber orientation, for example to be more parallel to the pole axis in order to increase bending stiffness, this would also reduce the torsional stiffness of the pole, which is not desired.

4.3 The Selection The selection is using the data that we get, for formula for contours of constant index M for slope 1 is:

Limits on

is:

For the chart is shown on figure above and the selection is shown on the table 1 for the CFRP, bamboo and GFRP.

The chart showing from formula.

plotted against

using the generic database that we get

Table 1: Materials for vaulting poles. MATERIAL

COMMENT

CFRP

Good control over properties and easily shaped

BAMBOO

Efficient due to tubular shape and taper, cheap but this not easily controlled.

GFRP

Good control over properties, cheaper than CFRP and easily shaped.

4.4 Microstructure Microstructure of GFRP vault rod figure 6 shows the different existence composite layer: inner layer, about 200μm thick, fiber bundle, embedded in polymer resin the matrix consists of a thin layer of approximately 10-20μm. Figure 6 shows a GFRP composite vault with five the area of the fiber bundle is separated only by a thin layer two of them are clearly visible. Check carefully microstructure on figure 7 that shows about 300 fibers in each bundle, oriented approximately 45° to the rod length. While the inner layer and the fibers in the layer angle of the split beam is approximately 80°-85° with the length of the rod, if they are almost running vertical to the length of the rod. Fiber angle is 45° provide bending stiffness and torsional stiffness the requirements of the vault rod. Fiber at 80°-85° it provides hoop stiffness and can also be used as a crack stopper. For example, in figure 6, cracks can be observed microstructure extending from the outer surface of the rod pass through two fiber bundles and then stop reaching the layer the fiber runs around the circumference of the rod [18].

Figure 6: Optical micrograph of a transverse section through a GFRP vaulting pole showing the different composite layers [17]

Figure 7: Optical micrograph showing individual glass fibers in the fiber bundles [17]

The observation of the crack indicates that the pole can damage experienced during use will not result disastrous failure. This illustrates the bar composition design multiple layers with different fiber orientation don't just optimize bending stiffness, but also there is also the torsional stiffness and the breaking strength of the rod. The presence of cracks will make the rod more be tempted to fail under pressure bend. Therefore, athletes should not use their poles can be suspected to be damaged (example rough processing, etc.)....