Enhancing testing for new materials

Because of the constant drive to lower fuel costs and reduce the environmental impact of air travel, OEMs and companies within the aerospace supply chain are continually developing new materials – both composites and alloys – that can provide significant weight reductions with increased strength properties.

These new materials present challenges both for the companies that test them and for the manufacturers of the testing equipment the tests are carried out on.

In aerostructures, such as the wings and fuselage, carbon fibre reinforced plastics (CFRP) are being increasingly employed to reduce the weight of aircraft.

For manufacturers of testing equipment such as the Japanese headquartered Shimadzu, these present particular challenges that have to be overcome.

Tadashi Hasegawa is general manager of the global application development centre for the analytical instrument division of the Shimadzu Corporation.

He says: “The scope of demand is extremely wide, and is not limited to materials evaluations, but also includes evaluations of the parts utilising these materials, their junctions and adhesives, as well as evaluation involving consideration to the conditions under certain temperature and humidity environment.

“In addition to static characteristics, demand for evaluations has heightened in recent years particularly regarding secular change (i.e. clarification of the deterioration process), fatigue and durability, and impact resistance.”

The Element Group is a testing specialist involved in working with materials across a wide range industries, with well proven expertise in the field of aerospace.

Rick Sluiters, Element's executive vice-president for aerospace comments: “Our aerospace industry partners succeed when they are able to transition from R&D phases of materials and components to production phases with confidence in the reliability of the tested material. Element's capabilities in testing are such that it can work seamlessly in both of these two distinct parts of the supply chain process: from the expertise required to characterize the properties of new materials, to the ability to develop and complete high volume, repeatable tests to fit with challenging expectations on the metrics of on-time delivery and right first time.”

Hot stuff 

So what are some of the latest materials that companies such as Element have to evaluate?

“Polymer Matrix Composites (PMCs) have become increasingly commonplace and Ceramic Matrix Composites (CMCs) are also now being developed for use in the industry,” Sluiters continues. “The attraction of CMCs is their ability to withstand very high temperatures, up to 2,400°F, which means that new tests and testing methodologies need to be developed to replicate and repeat extreme conditions.”

Sluiters says CMCs introduction to aero engines has led to new types of heat resistance testing being developed.

“As CMCs can withstand incredibly high temperatures so the increased pressure on the engine's bleed air systems requires new types of product qualification testing to ensure that they can withstand such increased pressures.”

Because of their less homogenous nature composite materials present particular testing challenges.

Hasegawa explains: “From an evaluative viewpoint requirement for testing tends to be more than for metal materials. For example, it is essential to find which are the critical factors, the fibres themselves, the matrix resin, or their interface state to determine the strength of a composite material. Furthermore, with laminated composite materials, peeling between layers is a major issue. Evaluation of the issue requires a variety of measurements (tension, compression, bending, and shearing) and multidimensional strain measurement.”

Sluiters also observes: “Composites properties differ from aluminium alloys in that they are not as isotropic and lack ductility by comparison. As a result, the durability and damage tolerance requires new types of fracture mechanics testing to characterize the properties. Enhanced databases are therefore required to understand the life cycle and costs of use.”

To satisfy the increasing demands for high temperatures and pressures in aerospace testing Sluiters says larger and more powerful hardware, including test frames and chambers has to be used. This is also supported by proprietary software to record data.

Bringing into vision

As well as developing its traditional testing equipment, Shimadzu has developed high speed video camera technology to evaluate composite materials in destructive tests.

“In general, the higher the strength, the more rapidly the destruction of a composite material progresses,” Hasegawa states. “Accordingly, higher-speed observation is preferable in order to acquire the information on the destruction process in more detail.

“High-speed video camera is an indispensable tool not only for Digital Image Correlation (DIC) but also to observe the destruction of fibres and the matrix resin respectively, as well as the behaviour of the laminate layers.

“In terms of non-destructive inspection systems, we are developing higher-resolution observation techniques for low-density materials. Development of image analysis software is an important factor here, so we are investing resource proactively in this area.”

Element has recently invested heavily in its aerospace testing capacity with the acquisition of UK testing company TRaC Global and the opening of a new ISO accredited CMC Centre of Technical Excellence in Cincinnati.

“TRaC Global has six UK laboratories with world leading capabilities in Electromagnetic Compatibility (EMC), Vibration and Environmental Simulation, Safety, Radio, Telecoms, Explosive Atmosphere Testing (ATEX), Finite Element Analysis (FEA) and Early Stage Qualification (ESQ). The acquisition added 30 EMC testing chambers to the Element Group, including a Heavy Vehicle Semi-Anechoic Chamber (HVSAC) with an 18m x 14m working volume and capacity for 70 ton floor loading, which is one of only three in the UK,” Sluiters comments.

Finally, what future aspects of material testing is Shimadzu focusing on in the aerospace sector?

“Recently, we have put the emphasis on strengthening our line-up of advanced evaluation systems including impact testing machines and multiaxial testing machines,” Hesagawa concludes. “We are also reinforcing development of the instruments to reproduce temperature and humidity environments.

“New material development targeting at improving functionality has been accelerating, and increase of demand is expected for the systems capable of evaluating these features. Shimadzu is aiming to strengthen our collaboration with the aviation industry, so that we can meet these demands in a timely and accurate manner.”

www.shimadzu.com

www.element.com