Aerospace designers and manufacturers have been turning more frequently to solid-laminate composite materials for major components of commercial aircraft, including wings and fuselages. As an example, 80 percent of a Boeing 787 (by volume), or more than half of the Airbus 350 (by weight), are made from composite materials.
Advanced composites are favored by the aerospace industry because they are lighter than many metals and their structures make them resistance to fatigue stresses. Components made from advanced composites also don’t crack as easily, because they use fewer joints and fasteners where cracks can originate.
Unfortunately, one of the drawbacks to parts made from solid-laminate composites is that they can suffer damage, such as from an impact, that isn’t visible on the surface layer. Oftentimes the visible, external surface pops back into place after an impact, masking any sub-surface damage.
Advanced Composite Materials Create Need for New Inspection Training
This causes unique issues for the aerospace industry when it comes to part inspection and quality assurance. Many of the current, experienced aircraft inspectors working in the industry began their careers at a time when airplanes were made primarily from aluminum, but because composites behave so differently from metals, these inspectors may require additional training.
“We saw people not using the exact equipment setup, procedures or methods that would produce optimum inspection results,” commented Dennis Roach, a senior scientist from Sandia National Lab’s Transportation, Safeguards and Surety Program. “They needed customized training that didn’t exist.”
In an effort to solve this problem, Sandia has developed a new training course for the engineers, technicians and inspectors of the aerospace and aviation industries: the Composite Nondestructive Inspection Training Class. Sandia’s development of the course was sponsored by the Federal Aviation Administration (FAA), and the training is now available to private industry.
The course trains inspectors in aircraft manufacturing essential nondestructive inspection (NDI) techniques for the solid-laminate composite materials in use in these industries.
“We’re trying to improve the proficiency of these inspectors so that they are better able to detect damage in composite structures,” said Roach. “We’re also trying to increase the consistency in inspections across the commercial airline industry.”
The first instance of the course ran this past summer at Delta Airlines, Inc. in Atlanta, Georgia, with 35 engineers and inspectors from six countries.
Engineering Damaged Parts to Help Inspectors Practice
The 2-day course covers the properties of composites, the manufacturing processes and the benefits and shortcomings of these materials. Participants will also learn about nondestructive testing techniques through hands-on exercises, such as:
- Examining custom-built carbon-fiber composite samples that represent various structural configurations common on aircraft which include a variety of engineered defects.
- Using commercial scanners, including phased-array ultrasonic scanners, to “paint” a two-dimensional image of the composite with ultrasound in order to learn how to optimize the scanner settings as well as detect damage.
- Learning how to recognize structural features found in composites, including laminates with substructure such as co-cured bond lines or tapered laminates, and how to recognize signs of damage, including disbands, delaminations, porosity and impact damage.
A key goal of the training program is to help airlines reduce the time and money expenses associated with false calls, where inspectors mistakenly believe they have identified damage.
According to Stephen Neidigk, a Sandia mechanical engineer and principle developer of the Composite NDI Training class, one surprising eye-opener for course participants was noticing that scanner signals decrease in amplitude or intensity due to the presence of the acoustic tiles and sealant used in composite fuselage panels. These are used to mitigate aircraft vibration and noise for passengers, but can create poor readings on detection equipment which could be interpreted as signs of damage to an untrained inspector.
This is why proper training is essential: with practice the course participants were able to learn how to distinguish the effects of the acoustic files from the signals generated by actual defects.
“One of the most valuable things in our view about this class was the opportunity to practice with these materials, because we really don’t get the opportunity and feedback on the aircraft,” said Alex Melton, a Delta manager of quality control and non-destructive testing.
In preparing the course, the engineers at Sandia recorded the best results they obtained in the lab to identify flaws in the course’s engineering samples. Using this information, they produced flaw maps and grading templates.
“After the participants have the chance to inspect the panels, we use our grading templates to point out which ones they hit and missed. Then we show them how the reflected signal changed for a particularflaw, and why they missed it,” Neidigk said.
Both Roach and Neidigk expect that companies will customize the course to their own specific needs, and Sandia will support those efforts as necessary. The team also hopes to develop further non-destructive testing courses, especially for the inspection of composite aircraft repairs.
For more information on composite non-destructive testing training, visit the Sandia National Laboratory website.