The aircraft and space industry strives for significantly reduced development and operating costs. Reduction of structural weight at safe design is one possibility to reach this objective which is aimed by the following two running research projects: the EC project "COCOMAT" and the ESA study "Probabilistic Aspects of Buckling Knock Down Factors". These projects develop improved concepts and tools for a fast and reliable simulation of the buckling and the postbuckling behavior of thin-walled structures up to collapse, respectively, which allow the exploitation of considerable reserves in primary fibre composite structures in aerospace applications. For the validation of the concepts and tools, a sound database of experiments is needed which is also performed within these projects. This paper focuses on the experimental activities within these projects performed at the buckling test facility of the Institute of Composite Structures and Adaptive Systems (DLR). It presents an overview about the DLR buckling, postbuckling and collapse tests which are already finished and gives an outlook to the results which are expected until the end of the running projects. This paper explains the working of the buckling test facility, the advanced measurement systems, which are running in parallel to the tests, and gives exemplarily two test results. The structures considered are unstiffened cylinders (ESA study) as well as panels, which are understood as sections of cylinders, stiffened by stringers (COCOMAT project). The unstiffened cylinders are more related to space applications (e.g. Ariane busters or parts of the international space station ISS) and the stiffened panels focus more on aircraft structures (e.g. fuselage). The load case considered for all investigations presented in this paper is axial compression under static loading although the test facility is also ready to apply torsion and internal pressure, as well as dynamic axial impact.

Optically excited Lockin-Thermography is a non-contact NDE-method which found many applications. However, the depth information about thermal boundaries (i.e. defects) which is included in the resulting phase angle images has not been extracted rigorously till now. This paper shows one way to derive from phase angle values depth resolved information on thermal boundaries and perform single-sided thermal wave profilometry.

Ultrasound-Lockin-Thermography ("attenuation mapping") is a defect selective "dark field" NDT-technique with a high probability of defect detection (POD) since only defects produce a signal while other features are suppressed. The basic contrast mechanism is the enhanced local mechanical loss turning a variably loaded defect into a heat source. The method is being applied for quality maintenance e.g. in aerospace and automotive industry to monitor the integrity of thermal features. A variety of examples will be presented to illustrate how well the method is suited to locate defects and to distinguish their depths.

No abstract

No abstract