不同線徑網球線之機械特性探討

The physical properties of the tennis strings with different diameters

目的：本研究的目的主要是要探討不同線徑大小之合成網球拍網線的材料特性。以市售網線線徑大小為15至18gauge等四種的有心線，實心線，無心線等不同結構設計的網線，探討勁度及最大位移量等機械特性隨線徑大小改變的差異性。方法：實驗藉由萬能材料試驗機將各種網球線分別做拉力測試至拉斷網線，記錄其受力強度與延展性，並計算網線在一般建議穿網線的特定拉力下的勁度，進一步以統計分析加以比較。結果：延展性的表現上，有心線整體表現最佳，而大線徑之實心線最差。三種常見網線種類在不同線徑之強度－位移曲線的表現則十分相似，除了線徑最大的實心線表現與其他線徑相較下有較明顯的差異。在勁度表現上，隨著線徑增加，網線的勁度也隨之增加，並且在不同線徑大小之間有顯著差異。除了1.20mm的無心線在勁度表現上，趨近於1.35mm的無心線。結論：三種常用網線的機械特性測試顯示，當考慮擊球之控球與穩定性，有心線中等線徑（1.25mm與1.30mm）表現較理想。無心線的機械特性整體表現較佳，尤其是細線徑。然而細線徑的實心線擊球穩定性表現可能稍差，建議選用1.30mm線徑網線為佳。在選手或網球運動者選擇網球拍網線時，本研究之結果可做為參考或推薦，以維持擊球時的穩定性及增加操控性及運動表現。Purpose: Monofilament, ployester, and multifilament are the common types of tennis string. In the current study, we intended to discuss the mechanical properties with different string diameters, 15 gauge (1.35mm), 16 gauge (1.30mm), 17 gauge (1.25mm), and 18 gauge (1.20mm), in those strings. Method: The experiments were performed in a laboratory with controlled temperature and humidity. We used the universal testing machine to obtain the tensile load-displacement curve for all strings. The stiffness at 22.7kg, 25kg, 27.3kg, and 29.6kg in the load-displacement curve were calculated, and the nonparametric test was used to compare the differences between different string diameters. Results: The monofilament showed the highest ductility, and the polyester with diameter of 1.30mm showed less ductility. For the same type of strings, different diameters would preserve similar characteristics of the loaddisplacement curve, expect for the polyester. In general, as the diameter of the string increased, the stiffness would also increase. The statistically significant differences in stiffness were found among different diameters of the same type of the strings. One exception was found for the multifilament, the string with 1.20mm diameter showed similar stiffness with the diameter of 1.35mm. Conclusion: The results of this study can be a reference for the novice or expert players in choosing suitable string. And it also can provide the information about properties with different string diameter for optimal exercise performance.