Guided waves in long range nondestructive testing and structural health monitoring: Principles, history of applications and prospects

The early work on long range guided wave nondestructive testing (NDT) was largely done in industry, and multiple applications were developed before a surge in academic interest starting in the early 1990s. This paper reviews the history of the field, covering the topics that must be addressed in the design of a test procedure, as well as applications in both NDT and Structural Health Monitoring (SHM). The use of guided waves in long range NDT is relatively mature, and largely limited to simple structures in applications that are difficult or impossible to address by conventional point inspection methods. Point methods are impractical in most large area SHM applications where it is necessary to detect isolated defects since it is not possible to cover the whole area of interest with transducers. Guided waves therefore have great potential in SHM as they enable a large area of structure to be monitored from a limited number of transduction locations, so reducing the added weight, cost and complexity of the attachment to the structure. It is also possible to improve the sensitivity of the test relative to that obtained in one-off inspection by monitoring the change in signals with time using baseline subtraction. Current SHM deployments are largely in the same types of structure as those where guided wave NDT is used, but there is substantial potential for increasing the range of applications. The paper concludes with a review of the research and development needs for this potential to be realised.