Graham Warwick/WASHINGTON DC
Lockheed Martin has begun construction of a laser ultrasonics centre which is expected to cut the cost of inspecting composite structures by as much as 90%. The centre is due to be operational by the end of the year, when it will be used to inspect parts for the company's Joint Strike Fighter (JSF) concept demonstrators. The system could save "several hundred million dollars" over the JSF production run, says the company.
Ultrasonic inspection of composite parts is required to detect defects such as inclusions, delamination and porosity, says Tommy Drake, principal engineer on the Laser UT system. Conventional ultrasonic testing requires the part to be immersed in water, or uses a waterjet probe to couple the ultrasound source to the probe. This makes the inspection of complex curved parts difficult, he says.
The Laser UT system uses a pulsed laser beam to heat a point on the surface of a part. The part expands locally, creating a stress wave perpendicular to the surface, which acts as the ultrasound source. A second, coaxial laser beam detects the ultrasound pulse as it bounces off the back of the part - or any defect in its path.
The key to the system, Drake says, is that the laser beam, unlike a waterjet probe, does not have to be kept perpendicular to the part. The beam can be scanned across the surface of a complex curved component, dramatically reducing the time required to inspect the part.
Throughput can be from five to 10 times faster than with conventional ultrasonics, "and up to 20 times with a really complex part", says Drake, who invented the Laser UT system. Lockheed Martin Tactical Aircraft Systems at Fort Worth, Texas, is installing two systems, one of which will be able to inspect parts up to 16.5 x 8.2m.
Other Lockheed Martin divisions may install similar systems. Meanwhile, the Fort Worth plant is to inspect the large composite liquid hydrogen tank for the X-33 re-usable launch vehicle technology demonstrator being built by Lockheed Martin Skunk Works.
Source: Flight International
