Testing results hitting the target? Complying with Nadcap and beyondJim Hennen of MTS discusses why it is essential for today’s aerospace material suppliers to employ top-quality load frames and grip assemblies for their mechanical testing.
Q: How is the industry changing, and how are material and component suppliers impacted?
Hennen: Aerospace OEMs, including such giants as Airbus, Boeing, GE, Pratt & Whitney, Rolls-Royce and others, have spent considerable energies defining and educating their supply chains with regard to their stringent requirements for purchased materials and components. These OEMs have been purposeful in working with the suppliers to increase confidence in the physical properties of the supplied materials.
Aerospace OEMs are not willing to take a supplier’s word for it in terms of how their products will perform. The risk of liability remains too high to accept anything but empirical evidence.
At the same time, OEMs continue to transition away from doing their own in-house audit testing of incoming materials. This is becoming a widespread practice, as OEMs seek ways to reduce operating costs with faster cycle times. It also makes it more critical than ever to have confidence in the test results provided by suppliers.
OEMs are motivated to tackle this problem through a balanced approach with their supplier community. They are making suppliers prove material performance through robust materials testing, including validating the accuracy of physical test procedures through multiple layers of compliance testing.
Q: What do those layers of compliance entail?
Hennen: The first layer involves passing an audit administered by Nadcap. A key aspect of Nadcap’s charter is to provide international, unbiased, independent certification services for the purpose of adding value, reducing total cost, and facilitating relationships between OEMs and suppliers.
The Nadcap audit will most often follow an OEM’s audit checklist, and will include a collection of test specimens to be used by an auditor for witnessing a laboratory’s proficiency in a test method.
Nadcap’s prominence has been elevated by virtue of OEMs enforcing these audit requirements. But that’s only one element of satisfying OEM requirements. After passing a Nadcap audit, suppliers must then meet additional material testing qualifications set forth by each OEM. This can include participation in the testing of specimens from the same set using the same test method by different laboratories. The cycle continues, as periodic recertification is also required.
This reality raises the stakes for material suppliers to get it right the first time. For example, if a supplier passes Nadcap compliance but falls short of the OEM’s additional requirements, it’s back to the drawing board.
Q: How can material suppliers ensure their tests meet industry requirements?
Hennen:Suppliers have little choice but to integrate precision-engineered load frames and grip assemblies into their testing procedures.
The impact of specimen gripping on alignment should not be understated. Collet-style grips are best for round specimens, and smooth flat grips are best for flat specimens. MTS 646 collet and MTS 647 with surfalloy round or flat-wedge grips are excellent examples of best-in-class grip assemblies.
Once suppliers have invested in these highly precise electromechanical or servohydraulic material test systems and components, the focus can shift to sound maintenance and verification practices to retain this level of test machine precision over time.
Q: What key capabilities should such load frames offer?
Hennen: You get what you pay for in material test system performance. The most important system attributes are precision and repeatability.
ISO 5725 defines precision as ‘the closeness of agreement between independent test results obtained under stipulated conditions. It defines repeatability as conditions ‘where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator, using the same equipment within short intervals of time.’ If a load frame scores well in both repeatability and precision, it also has a high likelihood of scoring well within Nadcap audits, along with the proficiency requirements of the OEM.
Q: How do MTS load frames perform in this regard?
Hennen: Sustained performance in compliance with ever-more stringent industry requirements is one of many areas in which MTS systems excel. Using MTS load frames, material suppliers save time and money by meeting all necessary testing requirements the first time and thereafter.
MTS precision-engineered test machines are also designed to remain aligned, even when subjected to heavy use. By combining these precision machines with regular system maintenance, test labs can achieve a low total cost of ownership over the long term.
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