Application of acousto-ultrasonics to NDE of timber in the infrastructure

摘要

One of the challenges for the use of acousto-ultrasonics (SU) with timber in service is the relatively high attenuation of ultrasound. However, new transmitter and receiver technologies will open up opportunities to assess large dimension timbers. The major changes in transmitter technology include the use of tone-burst transmission in which the energy input can be maximized and the frequency fixed at specific values within a perticular range. Receiver technology is also changing to provide a better piezoelectric material match with wood and design techniques for higher gain with wideband capability. For wood-based materials, material attenuation requires operation in the low frequency range, from approximately 30 to 120 kHz. AU has been also aided by improvements in A/D converters with higher sampling rates and longer data files, and with state-of-the-art software to process signals in different domains, partition signals, and calculate moments. AU can be applied to bonded material, such as glulam beams, as well as solid beams and columns. In glulam, weakended or delaminated bonds can be detected. In all of the structural materials, AU is very sensitive to even small areas of decay. Two applications that have not been sufficiently tested are the determination of the integrity of fasteners and assessment of residual strength. A major future opportunity exists for the use of AU in developing images of the internal defects in timber.