Ultrasonic waves in thin plates have a number of interesting properties, such as velocities that vary with frequency and multiple possible modes of vibration at a given frequency. This project will use one particular group of modes, which follow the edges of thin plates, to create a method of monitoring the edges of carbon fibre reinforced polymer (CFRP) aircraft components for damage. Structural health monitoring, whereby engineering structures are continually tested for damage, allows significant improvements in the way that the useful lifetime of engineering structures is managed. Methods based on designing structures to be viable long beyond their planned working life are being replaced by approaches that rely on monitoring for the first signs of deterioration and then repairing or replacing appropriately. This allows lighter structures to be used safely resulting in significant savings in construction materials and, for structures such as aircraft, ships and automobiles, improved efficiency throughout their working life. Ultrasonic waves have been successfully applied to structural health monitoring of plate-like structures and pipes, but structures with complicated geometries and physical properties that vary with direction (anisotropic materials) present particular challenges for ultrasonic structural health monitoring. This work will generate understanding of edge guided waves in anisotropic materials as a method of testing important sections of complicated structures. Ultrasonic waves in thin, plate-like, structures have more complicated behaviour than waves travelling through bulk materials due to the effect of the surfaces of the restricting the possible shapes (or modes) through the thickness of the structure as the wave propagates. These guided waves can travel large distances (up to tens of metres) and are scattered by defects, allowing them to be used to detect damage. They can also have multiple modes at any given frequency, each with a different frequency-dependent velocity and this complicates their use. Substantial work has been done to find methods of applying them to damage detection. The behaviour of ultrasonic waves at the edges of thin structures is further complicated by the edge also acting as a guide to the wave. This leads to modes that propagate along the plate edges, but decay rapidly away from the edge. In addition to representing an interesting physical problem, these modes, collectively referred to as edge waves, are a candidate solution to the problem of inspecting important parts of complicated geometry structures. In particularly they are ideally suited to inspecting for damage on the edges of thin structures such as: the stiffeners of wing panels or control surfaces of aircraft, turbine blades or exposed steel girders. The inspection of wing-panel stiffeners (small plates perpendicular to the panel to prevent it bending) is of interest as they are particularly susceptible to damage and carry significant loads. The following objectives will need to be achieved for this application to be realized: creating numerical models of edge waves in anisotropic materials, designing methods of generating and measuring edge waves, and performing experiments on damaged structures to determine the effect of defects on edge waves. A method of inspecting a specific structure (wing panel stiffeners) will be created and techniques generated to allow application to inspecting the edges of any thin structure for damage. A demonstrator system will be produced that showcases this technique.
|Effective start/end date||1/09/15 → 1/12/17|
- Engineering and Physical Sciences Research Council
Guided electromagnetic wave propagation
Structural health monitoring
Beams and girders