Abstract
The safety diagnostic inspection of large plate structures, such as nuclear power plant containment liner plates and aircraft wings, is an important issue directly related to the safety of life. This research intends to present a more quantitative defect imaging in the structural health monitoring (SHM) technique by using a wide range of diagnostic techniques using guided ultrasound. A noncontact detection system was applied to compensate for such difficulties because direct access inspection is not possible for high-temperature and massive areas such as nuclear power plants and aircraft. Noncontact systems use unstable pulse laser and air-coupled transducers. Automatic detection systems were built to increase inspection speed and precision and the signal was measured. In addition, a new Difference Hilbert Back Projection (DHB) algorithm that can replace the reconstruction algorithm for the probabilistic inspection of damage (RAPID) algorithm used for imaging defects has been successfully applied to quantitative imaging of plate structure defects. Using an automatic detection system, the precision and detection efficiency of data collection has been greatly improved, and the same results can be obtained by reducing errors in experimental conditions that can occur in repeated experiments. Defects were made in two specimens, and comparative analysis was performed to see if each algorithm can quantitatively represent defects in multiple defects. The new DHB algorithm presented the possibility of observing and predicting the growth direction of defects through the continuous monitoring system.
Highlights
It is well known that Lamb waves can propagate long distances with little energy loss
Using an automatic detection system, the precision and detection efficiency of data collection has been greatly improved, and the same results can be obtained by reducing errors in experimental conditions that can occur in repeated experiments
The automatic detection system was developed based on the hybrid application of a pulse laser and an air-coupled transducer
Summary
It is well known that Lamb waves can propagate long distances with little energy loss. Lamb waves have been shown to be sensitive to most types of defects They are efficient for detecting tiny subsurface damages and inspecting large areas. The RAPID algorithm has the advantage of being able to visualize faults with small transmission and reception points, but due to some negative influences such as shape factor (factor of influence), there is a limit to quantifying the defects It is not suitable for multidefect imaging. The automatic detection system was developed based on the hybrid application of a pulse laser and an air-coupled transducer. This is one of the best combinations among many different kinds of noncontact NDT methods. The imaging quality has been improved to a great extent compared with other methods used in earlier studies
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