市售不同結構網線受力機械特性之探討

Mechanical behavior in commercialized tennis strings with different structures

目的：本研究主要在探討不同網線的材料特性，目前最常見的網線與結構包括有心線（Performance）、無心線（Sensation）、實心線（Polyester）及克維拉網線（Kevlar），針對這四種不同結構的網線探討其網線在強度、勁度、勁度變化率及延展性的表現。方法：實驗在溫度及溼度條件相同的實驗室進行，藉萬能測試機分別對四種網球線做拉力測試至網線斷裂，過程中之力量－形變曲線，經過回歸分析，計算其勁度與勁度變化率，以比較不同網線的機械特性。結果：四種網線以Sensation的強度表現最佳而Polyester為最差；Sensation在勁度與勁度變化率方面的測試結果也優於其他三種；但在網線的延展性上，Sensation因受力而產生的形變最少，而Performance則最多。結論：Sensation在強度及勁度表現上優於其他網線，其較小的延展性有助於網壓的維持，而Performance的整體表現則相對最差。然考量運動員不同需求及經濟因素，為達到最佳經濟效益與運動表現，建議初學者選用Performance，隨擊球強度的增加，可選擇Polyester及Kevlar，而對專業選手或強力網球運動者，則推薦使用Sensation，以維持擊球穩定性及增加運動表現。Purpose: This study aimed to discuss the mechanical property of the tennis strings with different structures. The structures of the frequently used strings includes monofilament string (Performance), multifilament string (Sensation), Polyester string (Polymax Ⅱ) and Kevlar string. We investigated the performances in ultimate strength, stiffness, change in stiffness and extensibility of these strings. Methods: The experiments were performed in a laboratory with controlled temperature and humidity. We use the universal testing machine (AG-1, Shimadzu, Japan) to test the tensile load-deformation property of each string. The increasing elongation and loads for each string were recorded for analysis. The ultimate strength, stiffness, and change in stiffness were calculated to compare between different strings. Results: The multifilament string (Sensation) has the highest ultimate strength and stiffness performance while the monofilament string (Kevlar) has the least. However, on the other hand, the extensibility of the Performance string was the best while the Sensation string was the least among the four types of the strings. Conclusion: The mechanical properties of these four types of the strings were significantly different. The multifilament string (Sensation) possessed the highest strength and stiffness performance and the least extensibility, which would help maintaining string tension. However, in order to achieve the optimal economical efficiency and exercise performance, we suggest the novice players should use Performance string. With increasing power stroke, they can change to Polyester and Kevlar. As for the professional tennis players or powerful athletes, Sensation string should be a good choice for maintaining stroke stability and promoting performance.