Preliminary study on radar detection and imaging of cavities and cracks of Pinus massoniana

Masson pine (Pinus massoniana), which is a commonly used wood species in ancient timber buildings was studied in this paper, and cavities in the centre and cracks at the edge were artificially made at the end of the wood columns to simulate the common damages in ancient timbers. Radar non-destructive testing technology was adopted to detect the man-made damages, and the influencing factors for radar imaging were studied. By analysis of the specific patterns of the radar waves, rapid identification and characterization of the cavity and crack damages of the wood columns can be realized. The results indicated that the radar non-destructive testing technology can be used to detect the internal cavities and external cracks of wood columns rapidly, although there is a discrepancy between the detected damage area by the radar and the actual damage area. When the cavities inside the column were detected by the radar wave, strong black-white-black patterns will appear at the interface of the radar image and the corresponding reflection waveform is valley-peak-valley. By contrast, when the external damages such as cracks on the surface were detected, longitudinal interference stripes differing from the normal background will appear on the radar image. The detection of internal cavities is not severely affected by the presence of the external cracks, and also the closely attached bark or base coat on the surface will not pose a significant negative influence on the identification of the internal damages. The moisture content of timber was found to have an impact on the radar detection results. With other conditions fixed, the higher the moisture content of the timber is, the smaller the damage area detected by the radar technology is. The estimated boundary of the cavity damages may be offset slightly under the influence of other factors such as the moisture content; therefore, in actual testing, extended analysis in depth direction should be preformed based on the radar image. All of the results illustrated that the radar non-destructive testing technology can be used to detect the cavity and crack damages of timber rapidly, but the quantitative characterization of the damages needs to be further studied.