Laser ultrasound testing (LUT) is typically generated by a very fast laser light pulse (5 to 10ns duration) into a small area (50 to 200 µm) directed to the surface of a sample through a fibre or through free space. This light pulse induces an ultrasonic pulse that propagates into the sample as surface and bulk waves, which in turn interrogates features of interest and then returns to the surface, where it is detected by an LUT receiver. The receiver’s electronic signal can then be processed to produce the measurement of interest. LUT can use all typical detection geometries: pulse-echo, through transmission, and pitch-catch.
Advantages
- Non-contact and remote nature, allows inspection of samples at high temperature and hard to reach. The non-contact nature is also advantageous for applications where surface loading needs to be avoided
- Small footprint due to small laser beam spot size, which allows inspection of small and complex geometries
- Broadband, allows interrogating material properties at a large number of wavelengths, resulting in a richer amount of material and feature information
- High frequencies, a 10 ns laser pulse potentially generates frequencies up to 100MHz, allows the detection of very small flaws
- Laser beam scanning method, alloys decreasing inspection time
Applications
Due to LUT nature, it can be applied to industrial in-process measurements on hot, hazardous, remote samples which may be moving at high speeds. LUT is also useful for high resolution measurement of small parts and fast scans of large components is required. Finally, LUT can be used on inspection of complex structures.
There are several on-going LUT projects at TWI, which involve the inspection of friction stir welds, laser material depositing and composite materials.
For more information about TWI's NDT services, please contact us.
