Chinese-fir Non-destructive Testing Based On Ultrasonic Wave

Chinese traditional timber structures were in the service-beyond stage, part of the wood members has been damaged seriously. To detect and assess the residual mechanical properties and internal defects of the wood components is the first step to protect ancient buildings. Non-destructive testing techniques are neither destroy the internal structural, nor damage the external characteristics, has been applied to the detection of timber structure gradually. At present, the application of NDT techniques for the studies of board and dimension lumber of structure is more, but less in the research for structure logs. Without the destruction of the structure, how to evaluate the mechanical properties and internal defects of wood components more quickly and efficiently on site has become a problem urgently to be solved for timber workers.In this paper Chinese fir logs (one typical species fir of south ancient timber buildings) were selected for the study. Using ultrasonic to carry out the testing. Main content can be summarized as follows:1. Firstly, according to the spreading knowledge of ultrasonic wave propagation in solid medium, studied the theories of ultrasonic wave propagation along the radial and longitudinal of logs, the theory of using ultrasonic testing the mechanical properties and defect is also analyzed.2. Sylvatest-Duo ultrasonic detector is used for testing the samples, analyzed the propagation parameter of different directions (radial and longitudinal), different test positions (heartwood area, sapwood area) in logs; axial variation and radial variation of ultrasonic wave propagation are also studied.3. Timber experiment is done to obtain the density, and then obtained the static mechanical properties (parallel to grain compressive strength, tensile strength, flexural strength, parallel to grain compressive modulus of elasticity) by mechanical testing machine. The relationship between the longitudinal ultrasonic wave propagation parameters and mechanical properties were analyzed, to propose a computational model between ultrasonic dynamic elastic modulus and mechanical properties, and strive to evaluate their mechanical properties without damaging the components.4. Using ultrasonic wave tested the defect-free and different degrees defects woods samples, according to the obtained parameters, analyze the relationship between ultrasonic propagation velocity and different types of defects.5. To better for using ultrasonic testing on site, analyzed the experimental data through SPSS statistical analysis software, combined with mathematical statistical methods, a critical velocity determination method of ultrasonic propagation is given, this method provides a basis for ultrasonic inspection on site.Results of this study provides theoretical and experimental basis for the application of ultrasonic nondestructive testing in mechanical properties and internal defects in the inspection on site of wood structure.