Villum Centeret

Villum Center and lightweight structures

Future facilities for mechanical testing of lightweight materials and structures
The new Villum Center for Advanced Structural and Material Testing offers entirely new possibilities for basic mechanical research and the development of new structural configurations and materials. The Villum Foundation has donated DKK 76 million to create a new experimental centre which is to acquire and develop unique test facilities and equipment in the next three years.

The centre is run and maintained by DTU Mechanical Engineering, DTU Civil Engineering, and DTU Wind Energy. The three departments make their own equipment available to the centre, and they also bear the costs of running and maintaining existing equipment and facilities, while the DKK 76 million donation is earmarked for new equipment and facilities.

Unique facilities for testing materials and structures
One of the test facilities benefiting from the donation is DTU Structural Lab in Building 119. DTU Structural Lab has a wide range of test facilities used in connection with the basic research conducted at DTU Mechanical Engineering and DTU Civil Engineering. Associate Professor Christian Berggreen from DTU Mechanical Engineering, head of both the Lightweight Structures group of approx. 15 people (at the Section of Solid Mechanics) and the substructure area of the Villum Center, estimates that the new test equipment and facilities from the donation will remain in operation for the next 40-50 years, and DTU Structural Lab will be one of the best-equipped laboratories in the world of this type, once all facilities and equipment have been fully established and installed at the beginning of 2016. This will open up new opportunities for classic mechanical research, for instance in fracture mechanics in composite materials and in lightweight structural components. In this area, researchers are examining how fractures occur and progress in composites used extensively in aircrafts, among other things.

Villum Centeret
Associate Professor Christian Berggreen next to a test set-up in DTU Structural Lab, where images from four digital cameras are used in combination with DIC (Digital Image Correlation) to measure 3D deformation fields on test pieces exposed to compression forces.


From basic research to improving aircraft safety
The Lightweight Structures group is one of the major users of the facilities at DTU Structural Lab for basic research in fracture mechanics and lightweight structures in composite materials in general, including aircraft structures. Among other things, they examine how different composites components and possible damages to these respond when exposed to different load configurations. One of the composite constructions currently being examined is used for aircraft rudders. In this case, low weight and high load-bearing capacity are essential properties, and it is also of particular importance to learn more about how damage caused to the composite construction progresses under cyclic loads throughout the service life of the aircraft. The type of composite construction developed for the aircraft rudder has a beehive-like form made of folded Kevlar paper (also called Honeycomb core material), covered by two very thin carbon fibre layers glued to the Honeycomb core structure, see figure below.

This type of composite construction is also called a sandwich structure, providing lightness and—most importantly—high rigidity and strength, and thereby also a good load-bearing capacity which is essential to aircraft safety and manoeuvrability in the air. Furthermore, it reduces fuel consumption over a given distance. Typical rudder damage is when the rudder is subject to a minor impacts and manufacturing flaws, and the face sheet comes loose in that particular area – also called a disbond. When the face sheet comes loose, the sandwich structure looses its load-bearing capacity. The progression of such rudder damages depend both on the cyclic air pressure variation the aircraft is experiencing between take-off at sea level, flight at typically around 10 km height and landing again at sea level as well as the mechanical loading the rudder is exposed to due to the operation of the aircraft.

The Lightweight Structures group is currently using the new equipment to develop new test methods to provide much more precise information on damage progression in aircraft structures—or similar damages in sandwich components in ships, vehicles, or wind turbine blades for that matter. The work on the test methods in an integrated part of an international aviation collaboration on aircraft design and safety headed by NASA with DTU Mechanical Engineering acting as a core partner. Other collaborative partners include Airbus, Boeing, Dupont, Frauenhofer, FAA (Federal Aviation Administration), and EASA (European Aviation Safety Agency).

 Honeycomb sandwich structure

Honeycomb Sandwich Structure

Villum Centeret
Vishnu Saseendran next to a newly specially designed fracture mechanical test rig (DCB-UBM—Double Cantilever Beam with Un-even Bending Moments) in which a sandwich test specimens from the rudder structure has been mounted.

Villum Centeret
Vishnu Saseendran next to a newly specially designed fracture mechanical test rig (DCB-UBM—Double Cantilever Beam with Un-even Bending Moments) in which a sandwich test specimens from the rudder structure has been mounted.

Villum Centeret
PhD student Marcello Manca, head of the Lightweight Structures group and the substructure area of the Villum Center, Associate Professor Christian Berggreen, and PhD student Vishnu Saseendran together with an Airbus A330 honeycomb sandwich component.

A list of equipment and facilities at DTU Structural Lab granted by the Villum Foundation:

  • Vertical strong wall and floor in connection with a 30 m extension of Building 119 for, e.g., advanced hybrid testing of lightweight structure components and substructures.

     

  • Mobile strong floor towers for flexible test set-ups.

     

  • Hydraulic high-capacity hardline system of 1800 L/min delivered by MTS and operated by three 515.180 MTS hydraulic pump stations with a capacity of 600 L/min each.

     

  • 31 structural actuators from MTS with capacities ranging from 25 kN to 5.000 kN, including HSM stations.

     

  • Three MTS FlexTest 100 multi-axial controller systems with a capacity of up to 40 concurrent load axes, including three MTS FlexDAC data loggers with a total of 192 measuring channels.

     

  • Advanced MTS planar bi-axial testing machine with a capacity of 4 x 250 kN, including a large existing climate chamber for heat/humidity control of the test environment (the climate chamber was previously granted by the Villum Foundation).

     

  • MTS Acumen electro-dynamic fatigue test system with a capacity of 3 kN for, e.g., advanced fracture mechanical tests requiring very accurate test control.

     

  • High-capacity fatigue test system with extra long piston stroke and a capacity of 2.500 kN with the option of extra-high load frequencies.

     

  • Flexible climate chamber for heat/humidity control for use in standard testing machines.

     

  • Advanced Digital Image Correlation (DIC) systems for full-field deformation measurements.

     

  • Two high-speed cameras for ultra high-speed DIC measurements as well as standard high-speed imaging.

     

  • Flexible data logger systems with 100+ measuring channels for laboratory and in-field measurements.


In addition to the above, DTU has granted funds for:

  • A 30 m extension of the test hall in Building 119 and a new annex for the hydraulic pump stations.

     

  • A new cooling system and transformer station running the three large MTS pump stations, among other things.

Contact

Christian Berggreen
Associate Professor
DTU Mechanical Engineering
+45 45 25 13 73
http://www.mek.dtu.dk/english/Research/Feature_Articles/Villum
19 OCTOBER 2018