钢琴琴弦在弦枕处的断裂性质研究

FRACTURE PROPERTIES OF PIANO STRINGS ON THE V-BAR

钢琴琴弦在弦枕处最容易断裂,研究琴弦在此处的断裂性质对琴弦的设计及调律具有重要的意义。首先对琴弦的张挂形式以及工作时的受力和振动方式进行了宏观分析。然后在收集到的百组琴弦中选取三组相同键号、相同型号并且已知使用寿命的琴弦的断口为研究对象,利用扫描电子显微镜(SEM)对断口形貌进行分析。结果表明,琴弦和弦枕的相互摩擦造成琴弦表面磨损,使得受损区域应力集中。在交变弯曲载荷的作用下,疲劳裂纹萌生并沿截面向深处发展。当裂纹扩展到超过琴弦的断裂强度时发生了韧性断裂,SEM下可观察到断口呈明显的纤维状。

V-bar is the major fracture location of piano strings. It＇s important to analysis the fracture mechanism of the string in the V-bar for the design and adjustment of the piano string. In this paper,a systematic analysis was performed for the decoration form,loaded modes and vibration of the strings. Three fractures of piano strings under the same key number,figure number and known service life was selected as the objects. A comparative analysis was performed to observe the fracture morphology with the Scanning Electron Microscopes（ SEM）. It is shown that surface abrasion arises because of the wear between the string and V-bar,which causes the stress concentration in this area. The repeated bending loads during playing lead to fatigue initiation and propagation over the string cross section. The final fracture occurred when the stresses exceed the breaking strength of the string. The fibrous fracture was observed under the SEM.