1,721,014 research outputs found
Study of the structural behavior of a membrane wing: retrospective analysis of the 1917 biplane Ansaldo SVA5
No full textIn the present paper, a numerical investigation and simulation of the cable-membrane wing of the 1917 biplane Ansaldo SVA5 is shown. This activity was mainly sug-gested by a renewed interest about membrane wings, that are currently proposed for specific classes of UAV planes as MAV and HALE aircraft. The study was also performed to evaluate the structural behavior of a such type of wing configuration from an historical point of view. Preliminarily, a procedural FEM model, able to accurately describe wing geometry, topol-ogy and materials, was developed. In order to properly simulate the wing structure subjected to tensile preloads (shrinking dope effects and cable pre-tension), manoeuvre loads and ai-leron deflection, a specific solution procedure, consisting of several non linear analyses, was performed. Some preliminary results, related to fabric skin, wooden parts and steel-wire ca-bles have been finally reported in terms of overall displacements, strain and stress distribution
Influence of Damage Onset and Propagation on The Tensile Structural Behaviour of Protruding Composite Joints
No full textIn the present paper, a detailed numerical investigation of the structural behaviour of single-lap protruding composite joints under tensile loading has been carried out using a three-dimensional progressive damage FEM model. The adopted FEM model is based on a combination of Hashin’s failure Criteria, ply-discount material’s degradation rules and penalty method (for contact-friction phenomena).
Some joints’ configurations with different hole’s diameter and different interfaces (composite/composite and composite/aluminium) have been analysed. The numerical results in terms of strain curves, load-displacement curves and damage propagation have been compared with experimental data in order to point out the effectiveness and the weak points of the proposed progressive damage approach. Comparisons between the numerical damage and no-damage approach for each configuration have been carried out in order to analyse the influence of progressive damage approach on the numerical simulation of the overall structural behaviour. Also the influence of penalty contact stiffness on the damage onset and damage propagation inside the joints has been investigated. Finally, particular emphasis has been given to the damage onset and damage propagation inside the joints critically discussing the differences among the analysed geometrical configuration
Analisi cineto-statica e dinamica di strutture spaziali estensibili a dispiegamento ibrido telescopico-pantografico
No full textA bit-masking oriented data structure for evolutionary operators implementation in genetic algorithms
No full textOptimal design of deployable pantograph space structures via a hybrid genetic-deterministic technique
No full textInterlaminar and intralaminar damage evolution in composite stiffened panels under compressive loads: a global/local approach
No full textThe damage phenomenology of composite laminate is extremely complex and may involve different geometric scales in the initiation and progression of damage, and different typologies of failure. In recent years, delaminations and intralaminar damage onset and propagation have been extensively investigated separately [1-3] both numerically and experimentally and when possible analytical models have been developed. However, results of a few works [4-5] have shown that the correct simulation of the damage phenomenology for composite laminate structure can be achieved only by considering interlaminar and intralaminar damage interaction. In fact, to neglect this interaction would mean not only an incorrect prediction of the structural stiffness in presence of damage but also a significant overestimation of the residual structural strength.
A numerical procedure has been developed and implemented in the parametric language of the ANSYS © finite element code. Within this procedure both delamination growth and progressive damage onset and evolution have been taken into account.
The interlaminar damage evolution is based on the evaluation of the Strain energy Release Rate at the delamination front [7] computed by means of the modified virtual crack closure technique (MVCCT) and on releasable connections which allow the debonding between adjacent sub-laminates to be simulated. Furthermore, an iterative numerical procedure has been introduced to simulate the progressive matrix and fibre breakage by adopting respectively the Hashin’s failure criteria [8] to check the stress state and instantaneous degradation rules for the reduction of the damaged material properties [3].
The effectiveness of this procedure has just been proved on flat composite laminate plates [4]. In the present work the interlaminar-intralaminar interaction phenomenon is analysed for a more complex structure: a stiffened composite panel with a circular embedded delamination.
In order to reduce the computational efforts requested for the numerical analysis a global/local approach has been used to connect differently modeled substructures.
Results obtained by numerical approaches characterised by a different degree of accuracy (only interlaminar damage, damage interaction) are compared with experimental results [9] thus highlighting the intralaminar/interlaminar damage interaction effects on the residual stiffness and strength of the structure under consideration
Skin Stringer Debonding Evolution in Stiffened Composite Panels under compressive load: A novel Numerical Approach
No full textIn this paper, a numerical study, on the compressive behaviour of stiffened composite
panels with skin-stringer debonding has been carried out. The analysis has been performed by
adopting a novel robust (mesh and time step independent) finite elements based numerical model on
a single stiffener panel with an artificial debonding. In order to prove the effectiveness of the
proposed numerical tool, the results in terms of debonded area growth and compressive load versus
applied displacement, have been compared with experimental data available in literatur
A Study on Skin Delaminations Growth in Stiffened Composite Panels by a Novel Numerical Approach
No full textIn this paper, a study on skin delamination growth in stiffened composite panels made of carbon fibres reinforced polymers and subjected to compressive load is presented. A robust (mesh and time step independent) numerical finite elements procedure, based on the Virtual Crack Closure Technique (VCCT) and on the fail release approach, is used here to investigate the influence of skin delamination size and position on the damage tolerance of stiffened composite panels. Four stiffened panels configurations with skin delaminations differently sized and positioned are introduced. Bay delaminations and delaminations under the stringer foot are considered. The novel numerical procedure has been used to simulate the delamination growth for all the investigated panel configurations and to evaluate the influence of the delaminations' geometrical parameters on the growth development. As a confirmation of the applicability and effectiveness of the adopted numerical tool, the numerical results, obtained for all the analysed configurations, in terms of grown delaminated area, displacements and strains measured in various panel locations, have been compared with experimental data available in literature. © 2012 Springer Science+Business Media B.V
Three-Dimensional Progressive Damage Analysis of Composite Joints”, presentato alla conferenza internazionale
No full textThe laminated composites were analyzed by three-dimensional progressive damage approach. This approach is based upon geometrically non-linear finite element formulation for stress calculation. The analysis showed that the choice of the penalty parameter for contacts and the choice of the reduction factor for the degraded material properties are the key factors for the further development of composite joint
Influence of Contact Phenomena on Embedded Delamination Growth in Composites
No full textNumerical geometrically nonlinear analyses have been performed to investigate the influence of contact phenomena on multiple embedded delamination growth in composite panels under compressive load. An in-house finite element method code based on the modified virtual crack closure technique, which analyses delamination growth, combined with the penalty method approach, which takes into account contact phenomena, was used for computations. Compressed composite panels with two embedded delaminations have been investigated for various geometrical configurations with different delaminations' sizes and positions. Comparisons with a single embedded delamination model introduced in previous papers are presented. Finally a comparison between contact and no-contact approaches is shown for a significant geometrical configuration
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