1,720,976 research outputs found
ABS 1.0 (Aircraft Braking Simulation package): Check Manual
No full textReports of the Department of Aerospace Engineering of the University of Pis
Influence of turning parameters on the high-temperature fatigue performance of Inconel 718 superalloy
No full textThe safety-critical rotating parts of aircraft engines are mainly designed using experimental material data, based on standard specimens and procedures, while few data are available on the effect of manufacturing anomalies on fatigue life. In this context, the paper investigates the effects of different machining parameters on the high-temperature fatigue resistance of Inconel 718 superalloy specimens, cut from engine disk forgings, machined by turning on a vertical lathe. An unconventional specimen was designed in order to have the machining marks aligned with the fatigue loading axis, so to reproduce the hoop stresses in engine disks. For the test campaign, three machining parameters were chosen (depth of cut, cutting speed and insert wear) that typically may generate non-geometrical anomalies. A correlation has been found between the machining parameters, the residual stresses, the surface roughness, and the distorted and amorphous layer thicknesses. Correlations of such data with fatigue life are also presented and discussed
Assessment of a numerical strategy for fatigue growth and shape evolution of a corner crack from a pin-loaded hole
No full textThe study investigates fatigue growth and shape evolution of a corner crack in a pin-loaded hole by means of three-dimensional FE analyses. The constraint factor/plasticity-induced crack closure strategy was tuned to reproduce experimentally measured crack front shapes. The study quantitatively determines the LEFM acceptability regions using elastic–plastic simulations. It also assesses the sensitivity of crack propagation and shape evolution to the stress distribution along the front, to the relationship between J-integral and stress intensity factor, and to changing propagation rates along different directions. The proposed approach produces very accurate results in terms of crack propagation rate and shape evolution
Delamination onset in composite materials due to fatigue loading
No full textAn experimental program has been carried out for the evaluation of the delamination onset condition of various composite material systems, under the application of constant amplitude cyclic loading. Standard Double Cantilever Beam End Notch Flexure and Mixed Mode Bending specimens were used; the assessment of resistance to fatigue delamination onset has been performed by means of procedures defined in similitude with the standard static test procedures, introducing appropriate variants, where necessary. Three materials systems have been investigated: two carbon epoxy unidirectional materials and a carbon epoxy 5-harness satin. Normalised curves show a common trend and allow the identification of onset values for the evaluation of defects tolerance in the "no growth" approach. A similitude with the interlaminar fracture toughness measured in static tests, as a function of mode-mix ratio, has been highlighted with a higher influence of the mode I component. A modification of the Benzeggagh-Kenane relationship is proposed, that captures more faithfully the trend of the onset results
A numerical micro-mechanical study on damage induced by the curing process in carbon/epoxy unidirectional material
No full textA numerical framework for the determination of the damage, the stress and the inelastic strain field induced by the curing process for unidirectional carbon/epoxy composite material is proposed. The approach integrates a network model for the estimation of the matrix shrinkage and elastic properties evolution during curing with damageable elasto-plastic constitutive equations. Simulations of the curing process and of the cured material transverse mechanical response are carried out. A sensitivity study is realised for different volume fractions and matrix tensile strengths for single fiber models. Analyses of Representative Volume Elements (RVEs) with randomly distributed fibers are also performed and a comparison with the ideally cured version of the same model is used to highlight the importance of considering the curing process effects in micromechanical models. The proposed framework, with a proper calibration of the constituents, contributes to the enhancement of the fidelity of numerical micromechanics for this class of materials
Multi-scale Least-Weight Design of a Wing-Box Through a Global/Local Modelling Approach
Full text linkIn this work, a multi-scale optimization strategy for lightweight structures, based on a global-local modelling approach is presented. The approach is applied to a realistic wing structure of a civil aircraft. The preliminary design of the wing can be formulated as a constrained optimization problem, involving several requirements at the different scales of the structure. The proposed strategy is characterized by two main features. Firstly, the problem is formulated in the most general sense, by including all design variables involved at each problem scale. Secondly, two scales are considered: (i) the structure macroscopic scale, where low-fidelity numerical models are used; (ii) the structure mesoscopic scale (or component-level), where enhanced models are involved. In particular, the structural responses are evaluated at both global and local scales, avoiding the use of approximated analytical methods. To this end, fully parametric global and local finite element models are interfaced with an in-house genetic algorithm. Refined models are created only for the most critical regions of the structure, and linked to the global one by means of a dedicated sub-modelling approach
Quasi-trivial solutions for uncoupled, homogeneous and quasi-homogeneous laminates with high number of plies
No full textQuasi-trivial (QT) sequences are a class of lamination stacks for which, in the framework of Classical Laminate Theory (CLT), the properties of uncoupling and/or homogeneity are verified in a closed-form solution [1]. These sequences have received great attention from the scientific community as they have proved to be an extremely powerful tool for the design and optimization of composite laminates. Nevertheless, two main reasons limit their adoption: first, to find QT sequences, a complex algorithm is required; second, calculations become computationally intensive for long QT sequences, thus limiting the maximum number of plies attainable. This constrains the use of QT stacks to applications involving only thin laminates. In order to exploit QT stacks for thick laminates new tools are proposed. Firstly, a new and more efficient algorithm for finding QT stacking sequences is developed and an original procedure is devised to effectively code it. The proposed algorithm finds a greater number of QT solutions, with respect to those given in [1]. Additionally, analytical relationships to obtain new QT sequences by superposition of known QT sequences are presented in [2]. Thanks to this new class of closed-form solutions, laminates can be designed using QT stacking sequences without limitations on the maximum number of plies. The results presented in this work open new possibilities for the design and optimisation of thick laminates. In addition, laminates with special requirements may be designed by superposition of QT stacks, thus reaching specific design goals that cannot otherwise be met
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multi-scale optimisation of thin-walled structures by considering a global/local modelling approach
No full textIn this work, a design strategy for optimising thin-walled structures based on a global-local finite element (FE) modelling approach is presented. The preliminary design of thin-walled structures can be stated in the form of a constrained non-linear programming problem (CNLPP) involving requirements of different nature intervening at the different scales of the structure. The proposed multi-scale optimisation (MSO) strategy is characterised by two main features. Firstly, the CNLPP is formulated in the most general sense by including all design variables involved at each pertinent scale of the problem. Secondly, two scales (with the related design requirements) are considered: (a) the structure macroscopic scale, where low-fidelity FE models are used and (b) the structure mesoscopic scale (or component level), where more accurate FE models are involved. In particular, the mechanical responses of the structure are evaluated at both global and local scales, avoiding the use of approximated analytical methods. The MSO is here applied to the least-weight design of an aluminium fuselage barrel of a wide-body aircraft. Fully parametric global and local FE models are interfaced with an in-house metaheuristic algorithm. Refined local FE models are created only for critical regions of the structure, automatically detected during the global analysis, and linked to the global one, thanks to the implementation of a sub-modelling approach. The whole process is completely automated, and once set, it does not need any further user intervention
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