Frequently Asked Questions
Laser bond inspection works on any material: composites of all forms, metals, polymers, and ceramics.
The laser bond inspection process typically requires a reflection from a back surface. This process is most routinely done on relatively flat backed surfaces but can be applied to additional geometries with some calibration. Thicknesses in fiber reinforced polymer composites of up to 1 inch have been tested. The maximum thickness that can be inspected is dependent on the materials and bond strength.
The process was initially developed for the purpose of inspecting bonded joints. As the technology has matured it has been apparent that it can be used for more than just adhesively bonded joints. Any situation in which the response of a material to a stress wave would provide needed information is a candidate for the process. Some examples may include inspecting welded joints for cold (unfused) welds and inspection for the existence of subsurface cracks.
The inspection process as currently configured requires approximately 30 seconds per complete inspection. This is a configurable parameter that can be adjusted to meet specific customer requirements.
No appreciable heating of the structure occurs. The laser beam energy is delivered in such a short duration of time that no significant thermal load is transferred from the plasma to the work piece. In addition, the target surface is protected by an overlay of EMAT stickers and protective tape. The short duration of heating during the laser shock process is insufficient to penetrate these protective layers.
The shockwave magnitudes that the laser bond inspection process can generate are capable of damaging many structures; however, the calibration of the system to specific materials and geometries ensures the actual inspection process is at energies insufficient to damage an acceptable structure.
The laser bond inspection process measures how a material has been affected by a shock wave.
Measurement is completed through analysis of EMAT traces generated by the shockwave. By comparing a known pre-shock trace to a post-shock trace, the effects of the shockwave can be interpreted.
EMAT stands for Electro-Magnetic Acoustic Transducer. It is a subset of the ultrasonic testing field in which ultrasonic waves are generated and then modified by the interaction of magnetic fields. When a surface is moved in response to the shockwave, the magnetic field from that surface will be modified. This change in magnetic field interacting with a known magnetic field generates a change in signal that can be interpreted.
Yes, the process could be applied to 100% of a structure. The current system is designed to perform inspections at critical locations as a verification of bond strength at these locations.
The bond strength is tested by the shockwave. The shockwave magnitude is correlated to the inputs from the laser and can also be determined empirically. In production, the laser bond inspection process would provide you a known minimum bond strength value but not the ultimate strength. Testing to the ultimate strength would be a destructive process.
Laser bond inspection has been proven to provide good results on pi joint inspection capability. There are limitations on thickness of structures that can be inspected based on the attenuation of the shockwave.
Currently there are no standards in place for the application of laser bond inspection. LSP Technologies is working with government and industry to begin the development of standards.
LSP Technologies is constantly working to improve on laser technology and miniaturization of our equipment is a high priority on the list. Substantial R&D activities and funding are required by both LSPT and its suppliers in order to achieve this goal.
The cost per inspection is relatively low requiring only 30 seconds of operator time and an EMAT inspection circuit. Current EMAT inspection circuits are priced around $1.
Inspection of honeycomb and foam has typically been found to be unreliable. Irregular surface bonding of the honeycomb structure prevents adequate transmission and reflection of the shockwave.
Most of the LBI work has been in the inspection of fiber reinforced polymer (FRP) composites. This is the largest market sector of composites and has the greatest demand for the technology at this time. The technology has also been proven on other structures, such as glass adhesively bonded to metal, rubber bonded to metal, and several other combinations.
The sensitivity of the process is a scalable parameter. We have demonstrated the process to be detectable of defects that are less than half a millimeter in size. The custom tailoring of the laser beam, and hence the shockwave, allows the inspection to be almost infinitely customizable.
While a kissing bond may go undetected by conventional ultrasound inspection, the response of a kissing bond to a shockwave will show a different EMAT trace than a good bond. This difference is detectable because of a decoupling event between the kissing bond and mating surface.
The inspection process may or may not leave a void and both results have been observed in practice. There are many contributing parameters related to the material and the inspection process that affect the final outcome.
A pulse laser system is the only reliable means of generating a predictable shockwave with sufficient size, strength and duration to perform complex shockwave processing of components. Shockwave generation requires very high pressures that are difficult to predict, control and generate via any other means.