Modern Practice in Stress and Vibration Analysis VI

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Authors: H. Shahverdi, Cristinel Mares, W. Wang, C.H. Greaves, John E. Mottershead
Abstract: Finite element model updating of a Westland Lynx XZ649 helicopter tail is presented. Eigenvalue sensitivities with respect to Young’s modulus and mass density are used. Large groups based on material input data were divided to form smaller subgroups so that those parts of the model responsible for errors in the predicted eigenvalues were located. A particular new development was the use of parameter clustering based on the similarity of different columns of the sensitivity matrix. Finally the finite element model was updated successfully with regard to the lower frequency tail-bending modes.
Authors: C.M. Chia, Jem A. Rongong, Keith Worden
Abstract: The Hybrid Cellular Automata (HCA) algorithm has been used by several researchers to optimise structures during the last decade. Close observation of their work shows that the proposed optimisation algorithms are sensitive to the controller (local rule), the design variable and the field variable used. The aim of this work is to identify and understand the important parameters when using the HCA algorithm to optimise structures. For static loading, it is shown that the most important parameters are the design variable, the constraints on the design variable, the local rule, and the mesh density of the structure. The choice of the design variable affects the selection of the target value and the homogeneity of the resulting optimum structure. With constraints on the design variable, it is shown that the algorithm cannot always drive the structure to an optimum solution, as stresses in the resulting structure can be significantly higher than expected. Besides, the choice of the local rule and the mesh density of the structure can affect the convergence rate and may cause the algorithm to arrive at a local optimum rather than the global optimum solution.
Authors: S. Quinn, S.S.J. Moy, Keith Piggott
Abstract: The combination of simulation and physical testing is powerful. In this case study Finite Element Analysis (FEA) and a 96 tonne load test were used to prove that the lifting points for a new semi-rigid inflatable rescue craft met their statutory requirements before full manufacture. The FEA was used to optimise the detailed design of the lifting points, without the need to test each different configuration, and the load test was used to prove the final design in practice, before full manufacture. The FEA showed that the bearing stresses in the Glass Reinforced Polymer (GRP) hull of the initial design were unacceptable and appropriate design changes were made from further analysis. However, to suitably risk manage the project a full load test was required to demonstrate that the revised lifting point details met their statutory requirements, before full manufacture of the new craft.
Authors: Lianshan Lin, Haiyan Li, Alex S.L. Fok, Mark Joyce, T. James Marrow
Abstract: A simple finite-element-based inverse method has been devised with the aim of characterizing the properties of isotropic but heterogeneous materials under load. The method has been implemented into the commercial finite element code ABAQUS via its User Material (UMAT) Subroutine to facilitate the process of material characterization. Verification of the method has been carried out using simulated examples and the results showed rapid convergence of the method with good accuracy. The method has also been applied successfully to actual mechanical testing of graphite which has a porous microstructure and hence inhomogeneous distribution of material properties.
Authors: P. Smith Neto, E.S. Palma, V.M. Figueiredo Bicalho
Abstract: The main objective of this work was to introduce Reflexive Photoelasticity Technique in qualifying automotive components at Fiat Automoveis S.A in Brazil. Actual stresses were determined in a simple geometry plate and also in nodes of a body shell of a passenger vehicle by using reflexive photoelasticity methodology. Initially, tests were performed in welded steel plates submitted to traction loads. These plates were previously coated with birrefringent plastic material. External loads were applied through hydraulic MTS actuators. Stress and strain distribution in welded points neighboring areas using reflexive polariscope were quantitative determined. Simultaneously, these stress and strains acting on the welded plate were determined using strain gauges. The results from both experimental techniques (photoelasticity and strain gauges) were compared with those obtained from a numerical model using finite element method. The results were correlated and analyzed. Finally, reflexive photoelasticity technique was used to determine the stresses in nodes of a body shell of a passenger vehicle. Through this analysis it was possible to determine critical points in the structure with peak stresses.
Authors: Fabrice Pierron, Guillaume Vert, Richard L. Burguete, Stephane Avril, René Rotinat, M.R. Wisnom
Authors: Alexander D. Fergusson, Amit Puri, Andrew Morris, John P. Dear
Abstract: Composite sandwich structures are finding increasingly widespread use in fields ranging from aerospace and wind turbines to sports applications such as skis and surfboards. The high specific stiffness that composite sandwich structures can provide lends them well to these applications. However, the operational environment of these structures is frequently aggressive and often results in damage during service. The extent and effect of damage incurred is an important factor in the design and maintenance of composite sandwich structures. Failure of an individual component can be catastrophic for the rest of the structure. The purpose of this investigation was, firstly, to ascertain whether DSP was a viable technique for determining strain fields within composite sandwich structures. Secondly, to determine whether four point flexure would give rise to pure flexure between the central rollers, and if not, to understand what load conditions were present. This investigation was also carried out with a view to extend the investigation into the effect of defects on composite sandwich structures manufactured by RIFT. The grounds for selection of composite sandwich structures normally lie in their flexural performance. Reliable and accurate quantitative testing methods for evaluating the flexural performance of sandwich panels are needed if composite sandwich structures are to be used safely and effectively. In addition, methods to determine the effect of damage and defects on flexural behaviour of sandwich structures is particularly important for designing the repair and maintenance regimes of composite sandwich components.
Authors: Andrew Morris, John P. Dear, Miltiadis Kourmpetis
Abstract: Optical strain measurement techniques have been extensively developed in recent years in order to cope in various environments. Power stations and wind turbine blades can provide challenging environments for the use of a measurement technique. There are, however, many installation problems to be overcome. For example, there is the need to have regard for the hostile environment in steam generating plant and the demanding conditions to which wind turbine blades are subjected. Ideally the outputs from individual sensors would be used for continuous remote monitoring. However, measurements can also be useful each time the plant is shut down during a plant outage; which would be used to complement data from existing proven rugged monitoring methods. This paper addresses the monitoring of pressurized steam pipes as to their micro-strain growth related to time in service. This paper presents the progress made in the developing of a ruggedised digital speckle ‘sensor’ and associated image capture system. The effect of subsurface defects in the strain distribution is examined.
Authors: M. Ciavarella, A. Strozzi, A. Baldini, Matteo Giacopini, S. Rivasi, R. Rosi
Abstract: In pinned connections, the presence of an initial clearance increases the lug stress concentration with respect to a neat fit configuration. By employing a recently proposed loading parameter Φ valid for plane models, the applied load and initial clearance effects on the stress concentration are normalised for a straight-shanked, round-ended, longitudinally loaded pin-lug connection of fixed outer to inner radius ratio. Results are obtained with a Mitchell-type, Fourier series solution and with commercial Finite Elements. The applicability of the loading parameter Φ to pinned connections with small to relevant initial clearances is explored. Two preliminary design charts are presented, which quantify the lug stress concentration factor versus the loading parameter Φ for two lug geometries defined by inner to outer radii ratios of 0.376 and 0.77.
Authors: Jian Ding, J. Madge, Sean B. Leen, Edward J. Williams
Abstract: The prediction of fretting wear and fretting fatigue is a significant issue for the design of high-performance aeroengine spline couplings, due to the potential for slip between the highlyloaded spline teeth under cyclic loads. The work reported here builds on previous work on simpler (Hertzian) laboratory test configurations to take a step towards a unified fretting wear and fatigue modelling approach, which considers the evolution of contact geometry with material removal and consequently the changes in fatigue-pertinent subsurface stresses. The approach calculates the local wear, that it is the wear at each contact node, as a function of local contact pressure and local slip. The influence of wear damage on fretting fatigue behaviour is quantitatively assessed by computing the change of a shear strain based fatigue damage parameter, i.e. the critical-plane Fatemi-Socie parameter. The application of the simulation tool to the complex geometry of a helical spline coupling is discussed.

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