Objective As a key load-bearing component in building structures, defects in engineered wooden columns will directly affect the structural safety and durability. However, traditional non-destructive testing methods have certain limitations in terms of detection efficiency and operational space, making it difficult to meet the practical requirements for inspecting engineering timber columns. Currently, the layout of ultrasonic guided wave excitation and reception in the non-destructive testing of engineering timber columns lacks systematic theoretical support, which restricts the effective application of ultrasonic guided wave technology in this field. Therefore, there is an urgent need for in-depth research on the propagation characteristics of ultrasonic guided waves in engineering timber columns to optimize the layout schemes for excitation and reception. This paper aims to investigate the propagation characteristics of ultrasonic guided waves in timber columns to provide a scientific basis for layout schemes of excitation and reception in the non-destructive testing of engineering timber columns.
Method First, the propagation modes of ultrasonic guided waves in solid cylinders were summarized through theoretical analysis. Subsequently, an ultrasonic guided wave detection platform was built, with Pinus sylvestris var. mongolica wooden sticks as test pieces, to carry out three types of tests: single-point lateral excitation, multi-point lateral excitation, and end-face excitation. The effects of excitation-reception point layout on signal characteristics was systematically investigated.
Result (1) Whether excited from the side or the end face, both flexural mode waves (F-waves) and longitudinal mode waves (L-waves) were generated simultaneously in the wooden sticks, but they differed in their dominant positions; side excitation was dominated by F-waves, while end-face excitation was dominated by L-waves. Therefore, the excitation position can be reasonably selected according to the detection requirements of target mode. (2) In the case of single-point lateral excitation, the greater the distance between the excitation point and the reception point was, the more obvious the distinction between F-waves and L-waves was. Hence, during detection, the excitation and reception devices should be arranged at both ends of the stick, or the distance between them should be increased as much as possible to further amplify the mode separation effect. (3) For multi-point lateral excitation, symmetrically increasing the number of excitation points on the circumference of same cross-section can enhance L-waves and suppress F-waves, and the suppression effect can be strengthened with point number invreasing. Therefore, if it is necessary to excite L-waves but it is not possible to arrange an excitation source on the end face, a symmetrical excitation can be arranged on the adjacent side of the end face. (4) In the case of end-face excitation, the ultrasonic guided wave signals measured by the guided wave reception points on the end face or its adjacent side were similar. Thus, when the end face is excited but it is inconvenient to arrange a sensor on the other end face, the reception can be performed on the side adjacent to the other end face.
Conclusion The positions and quantities of excitation-reception points have a significant impact on the composition of modal waves and their amplitude proportions of ultrasonic guided waves in wooden sticks. This characteristic law can directly guide the design of ultrasonic guided wave detection point layouts for engineered wooden columns, laying a methodological foundation for subsequent non-destructive testing of wood.
DownLoad: