面向木结构的螺栓连接松动检测系统

Bolt Connection Looseness Detection System for Wood Structures

螺栓是一种临时连接件,螺栓连接是目前木结构的主要连接方式,广泛应用于建筑、运输等领域。木结构螺栓连接产生松动问题的原因主要有冲击力、应力集中、裂纹、腐蚀等,冲击力容易导致木结构螺栓连接松动问题。设计了一种基于压电时间反演法的木材连接螺栓松动检测系统。利用NI-ELVIS II+数据采集卡并设计LabVIEW程序,发生Lamb波冲击信号。利用粘贴在木板上的两片压电陶瓷分别产生振动,对发射的超声波信号进行两次测量,其中第一次测量的信号经时间反演后作为二次超声波信号的发生。由于冲击信号持续的时间很短,约10 ms,因此检测系统设计了二次数字触发以确保信号的完整记录。应用设计的检测系统测试了几组不同螺栓预紧力作用下的超声波信号,结果表明聚焦信号的幅值随着螺栓预紧力的增大而增大。因此,该检测系统可通过测试聚焦信号的幅值反映螺栓的松动状态,通过观察聚焦信号的幅值可以分析预紧力的大小,确保轴向力施加适当,系统同时具有精度高、响应迅速等优点。

A bolt is a kind of temporary connector.Bolt connection is the main connection mode of wood structures which is widely used in construction,transportation and other fields.The main causes of the loosening of wood structure bolt connection are impact force,stress concentration,crack,corrosion,etc.The impact force easily leads to the loosening of wood structure bolt connection.In this paper,a wood connecting bolt looseness detection system based on piezoelectric time inversion method was designed.Using NI-ELVIS II+data acquisition card and LabVIEW program,Lamb wave shock signal was generated.Two pieces of piezoelectric ceramics pasted on the wood board were used respectively to generate vibration and measure the transmitted ultrasonic signal twice,in which the first measured signal was used as the generation of secondary ultrasonic signal after time inversion.Because the duration of the impact signal was very short,about ten milliseconds,the detection system designed a secondary digital trigger to ensure the complete recording of the signal.Using the detection system designed in this paper,several groups of ultrasonic signals under different bolt preload were tested.The results show that the amplitude of the focusing signal increased with the increase in the bolt preload.Therefore,the detection system can reflect the loosening state of the bolt by testing the amplitude of the focus signal.By observing the amplitude of the focus signal,the preload can be analyzed to ensure that the axial force is applied properly.At the same time,the system has such advantages as high precision and rapid response.