RELATIONSHIP BETWEEN STRUCTURE AND MECHANICAL PROPERTIES OF BRAIDING GOLF SHAFTS AND KANSEI M. OHARA, A. OHTANI, A. NAKAI, H. HAMADA, M. SAKATA, T. TANAKA, M. KUME, Y. YOSHIDA, T. YOSHIDA Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan, E-mail: nakai@kit.ac.jp In this paper, in order to develop the new custom-made golf shaft with the braiding technique, mechanical properties of the carbon fiber braided composite pipes with different fiber orientation angle, and the quantitative swing data of the golf shaft were investigated. The 3-point bending test was carried out for these different pipes, and the mechanical properties were obtained. The swing data was measured by EMG (electromyogram) analysis. From these data, the characteristics of the braided golf shaft were clarified. 1. Introduction Golf playing skill depends on not only personal s skill but also golf club performance and golf ball efficiency. The golf club is consisted of grip, shaft and head among three many different requirements required on the shaft rather than the grip and the head. Particularly, high level golf player s demand for the shaft is severe and these are quite personal issue. Therefore, Custom-made shaft requirements naturally are arisen, which is fit the personal skill and feeling. The golf shafts have been made by using carbon fiber reinforced plastics called Black shaft. Normally, reinforcement configuration is unidirectional aligned fibers. It is difficult that the fiber orientation angle is changed partially. Also, the diameter of the shaft near the grip is larger than that near the head. In the case of fabricating custom made golf shaft, change of bending rigidity along the longitudinal direction should be suitable for that person, so that we need more fabrication flexibility of fiber orientation angle. From this view point, unidirectional prepreg sheet does not posses fabrication flexibility on the other hand braiding technique has much freedom in fiber orientation state. The fiber orientation state, braiding angle in braided fabric can be determined by the velocity ratio between spindle movement on the circle and picking up movement to the vertical direction. Therefore desired fiber orientation angle can be decided and it is easy to change the angle. Our purpose of this study is to develop a new braided golf shaft which can be regarded as Custom made shaft. In this report, the effects of braiding angle on bending properties of braided composites at the first section. Next, actual golf swing was performed by the expert golf player, and the electromyogram (EMG) activity was measured. At the end of this report, Kansei and feeling of the player was evaluated by questionnaire. The characteristics of braided golf shaft would be clear.
2. Braided tubular composite The schematic drawing of braided fabric is shown in Figure 1. One of the important features is continuity of the fiber bundle in the braided fabric. The all fiber bundles are continuously oriented, so that the seamless composite tube can be fabricated with tubular braiding technique. Moreover, the excellent mechanical properties were expected because of the continuity of fiber bundle. Other characteristic is capability of changing the braiding angle. Using woven fabric or unidirectional prepreg sheet for fabricating the composite tube, the fiber orientation angle is fixed uniformly in a layer. On the other hand, in braided fabric, all fiber bundles are diagonally oriented in longitudinal direction, and the angle of the fiber bundle to the longitudinal direction can be adjusted freely. Therefore, the mechanical properties can be variously designed according to the requirement. Figure 2 show the braided fabric with 30, 45, and 60 degrees fabricated using same filament and bundle number of carbon fibers. Braiding angle Braiding yarn Middle end fiber Figure 1. Braiding structure Figure 2. Braided fabric with different braiding angle
3. Experiments 3.1 Fabrication The composite tubes were fabricated by tubular braiding machine (Murata Machinery, Ltd.) using 48 carbon prepreg yarns (Nippon oil corporation, in which fiber is the carbon yarn (TORAYCA T700-6k) and the resin is modified epoxy (Nippon oil corporation; resin impregnated ratio is 35wt%)). For the fabricating process, prepreg yarns were braided around the mandrel with 20mm diameter. Then PP tape was wrapped around the preforms stacked with a few layer up to the predefined thickness of the braided tube and it was cured in an oven at 80oC for half an hour and at 130oC for 1.5 hours. The photograph and specification of the fabricated tubes are shown in Figure 3 and Table 1, respectively. The number of stacking layers is decreased with increase in the braiding angle to keep the same thickness of composite tube with different braiding angle since the thickness of one layer increases with increase in the braiding angle. N30 N45 N60 Figure 3. Specimens N30 Table 1 Specification for braided tubes Braiding Inner and Outer Number of angle ( o ) diameter (mm) layers 30 20.023.3 5 Vf (%) 54.9 N45 45 20.023.3 4 53.8 N60 60 20.023.6 3 55.2 3.2 Bending test The four-point bending test was performed by using the pulley unit and the metal solid-core bar as shown in Figure 4. The pulley unit and the round bar are capable of decreasing the stress concentration generated at the point of support and loading nose.
The rosette gage was stuck on the surface of the center and bottom part of the specimen to measure the local tensile strain of the tube and to calculate the principal strain. The bending test was performed by using an INSTRON universal testing machine with a span length of 300mm and cross-head speed of 5mm/min. 100 Pulley unit with V-shaped groove Metal solidcore bar 200 300 Figure 4. 4 point bending test 3.3 Results of bending test The results of bending test were shown in Table 2. The bending modulus and strength were decreased with increase in the braiding angle. N30 Table 2. Results of bending tests Bending modulus Eg (GPa) 39.5 Strength (MPa) 318.5 N45 N60 15.2 9.6 236.2 137.6 4. Measurement of golf swing A male who has golf playing experiences is a subject. Two different golf shafts were prepared; one was sheet winding shaft and another was braided shaft. EMG signal was measured by using telemeter (web-7000, Nihon Kohden Corporation) position of infrared EMG sensor were attached at biceps brachii muscle, triceps brachii muscle, extensor muscle of the forearm, flexor muscles of the forearm, erector spinae muscles, lateral great muscle, and medial great muscle. Figure 5 and Figure 6 shows wave pattern of EMG of the right and left biceps brachii muscle.in each figure, original wave pattern, full-wave rectification which was absolute value conversion from original wave pattern and the integration of EMG activity were shown.the total EMG activity was calculated by using these figures. Figure 7 shows the EMG activity of biceps brachii muscle, triceps brachii muscle, extensor muscle of the forearm, flexor muscles of the forearm, erector spinae muscles, lateral great muscle, and medial great muscle.
Here, A was results of braided shaft and D was those of sheet winding shaft (commercial shaft). In each parts the values of A were larger than those of D. This results means that by using Braided golf shaft the player can exert their own power sufficiently. RAW EMG RECTIFIED & ENVELOPED EMG INTEGRATED EMG iemg(mvs) Figure 5. EMG patterns of right biceps brachii muscle with braided shaft A RAW EMG RECTIFIED & ENVELOPED EMG INTEGRATED EMG iemg(mvs) Figure 6. EMG patterns of left biceps brachii muscle with braided shaft A
120 100 iemg(mvs) 80 60 40 A D 20 0 5. Kansei evaluation Figure 7. The mean EMG for each muscle In this section, Kansei evaluation was described by using pair comparison method for D to A. Figure 8 shows the results of the evaluation. Here, in Weight, Balance, and Direction, the shaft D got high mark, however, the other evaluation item such as stiffness, flexibility, easy to swing, the distance of ball, the height of ball, timing at impact, easy to catch the ball and total evaluation had high score in the case of shaft A. From these evaluation results the player who uses the braided shaft better feeling, thus they can enjoy playing golf. 2 1 Point 0 Weight, Balance -1 Stiffness of shaft Viscous behavior of shaft Easiness of swing Distance Altitude of hit ball Directional accuracy Duration of impact Timing Holding time at the impact Total impression -2 Figure 8. Organoleptic assessment of A against D 6. Conclusion (1) Fabrication of braided golf shaft was established. (2) The players can exhibit their own physical power efficiently by using braid golf shaft. (3) The braided golf shaft gave better feeling to the players.