Buckling Test Facility
The buckling test facility has been continuously developed over the past 20 years and is especially designed for buckling tests on thin walled composite structures such as cylinders and panels. Due to its extreme stiffness, careful load introduction and shortening control, buckling tests of high precision can be conducted under well defined boundary conditions. The hydraulic cylinder is equipped with a small servo valve for static tests and additionally with a second valve for high dynamics. Axial compression up to 1,000 kN, torsion up to 20 kNm as well as internal pressure between 1 hPa (simulating external pressure) and 10 hPa can be applied simultaneously. The load history of axial compression ranges from static loading to shock loading. Tests of panels and shells with up to 1,600 millimeters in length and 1,200 millimeters in width (diameter) can be performed. The high-precision buckling test results serve as a reference for the development of fast computational procedures to simulate buckling and post buckling behavior of thin walled structures, as they are required for concurrent/integrated engineering. In addition, proof tests of real structural components with respect to their buckling and post-buckling behavior can be conducted. So far, several buckling tests were conducted within ESA contracts and EU projects such as DEVILS (Design and Validation of Imperfection-Tolerant Laminated Shells), POSICOSS (Improved Post-buckling Simulation for Design of Fiber Composite Stiffened Fuselage Structures) and the current project COCOMAT (Improved Material Exploitation at Safe Design of Composite Airframe Structures by Accurate Simulation of Collapse).
The capacity of the axial load is 1,000 kN. The hydraulic cylinder is equipped with a small servo-valve for quasi-static tests which enables very smooth controlling of the displacement. Additionally, a second valve is provided for very high dynamics as required for dynamic buckling or shock tests. Axial compression = 1,000 kN, Piston acceleration = 1,500 m/s2, Piston velocity = 0.675 m/s, Piston frequency (ampl.1 mm) = 100 Hz, Torsion moment = 50 kNm, Shear load (for panels) = 200 kN, Specimen length =1,600 mm, Specimen width = 1,200 mm.
200 measurement points for strain gauges and displacement transducers are scanned by 1 kHz for static tests, and 72 measuring points by 400 kHz for dynamic tests. Four self-sustaining fast ARAMIS systems, each of which is able to measure the 3-dimensional deformation field at a speed of 1,000/sec, can be coupled, resulting in a maximum speed of 4,000/sec. This system provides much more information on the dynamics of buckling deformations than previously achieved.