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Fatigue is one of the most common failure modes of structures and components. The prediction of fatigue crack propagation in real structures must take into account realistic boundary conditions. The purpose of this paper is to describe a technique for modelling fasteners through FEM global structure modelling and using the model for stress state analyses and crack growth prediction. The consideration of fastener stiffness during stress analysis is an integral part of the damage tolerance philosophy. The FASTRAN retardation model with a load sequence simulating the real operational service of an aircraft structure was used for crack growth prediction. © 2015 The Authors. Published by Elsevier Ltd. Source


Cecrdle J.,Czech Aeronautical Research and Test Institute
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering | Year: 2015

This paper deals with updating of the aircraft structure finite element (FE) model according ground vibration test (GVT) results. Paper describes possible approaches of flutter analysis as regards to the incorporation of GVT results including: (1) the direct usage of GVT results and (2) updating of analytical FE model. Then the theoretical background of the model updating methods including Bayesian parameter estimation and more generic optimization using powerful nonlinear gradient-based methods are given. Finally, the methodology of an aircraft structure FE model updating is described. The practical application of the procedure is documented on the EV-55M turboprop utility aircraft example. Selected results are shown, evaluated and the conclusions are formulated. © Institution of Mechanical Engineers 2016. Source


Maturkanic D.,Czech Aeronautical Research and Test Institute
Acta Polytechnica | Year: 2015

The quality of the flow field is highly significant wind tunnel measurements are bing made. When an air flow field is formed by a fan, the entire flow field rotates. Moreover, the flow field is deformed at the bends of a wind tunnel with close circulation. Although wind tunnels are equipped with devices that eliminate these non-uniformities, in most cases the air flow field does not have ideal parameters in the test section. In order to evaluate the measured results of the model in the wind tunnel, it is necessary to characterize the deformation of the flow field. The following text describes the possible general forms of the flow field non-uniformity, and their effect on the calculation of the aerodynamic coefficients. © Czech Technical University in Prague, 2015. Source


Cecrdle J.,Czech Aeronautical Research and Test Institute
Journal of Aircraft | Year: 2012

This paper deals with aircraft structure whirl-flutter analysis. It gives a summary of the requirements of airworthiness regulations, the theoretical background, and aircraft certification-related issues. The focus is on the whirl-flutter analyses of the new Czech twin turboprop utility aircraft. Ordinary and optimization-based analytical approaches are described. An optimization-based analytical procedure to determine the whirl-flutter stability boundaries for certification speed is employed. Analyses include nominal state calculation and evaluation of the influence of secondary parameters to whirl-flutter stability. Finally, the propeller-nacelle-wing interference effects (downwash) are evaluated, and future work is outlined. Source


Bohacova M.,Czech Aeronautical Research and Test Institute
Engineering Failure Analysis | Year: 2013

The field of non-destructive inspection (NDI) is an integral part of aircraft maintenance and service. It is optimal to apply the eddy current (EC) method on the complex multi-layered metal aircraft structure to detect cracks and other damage. A range of standard eddy current probes giving satisfactory results with respect to crack detection are available. However, these EC probes are not always suitable for the detection of short fatigue cracks hidden under a rivet head. This article presents a new methodology for eddy current inspection of a critical area on the wing. The development of the new methodology was inspired by a catastrophic glider accident in 2010. Because of this accident, all glider service was prohibited. The critical area is located in the structure of the wing spar, which consists of six layers. The position of the critical area is hidden under the countersunk rivet head in the third layer of the spar flange and under two layers of metal sheets. Thus, the actual location of the area is in the fourth layer, created by the countersunk rivet head. In addition, another rivet of a smaller diameter is inserted into the rivet in the flange. This article presents the work related to the development of a special EC probe that is able to measure in an operating frequency range between 200. Hz and 100. kHz with a single-value interpretation of the individual EC signals. © 2013 Elsevier Ltd. Source

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