Composite Materials and Structures in Aerospace Engineering

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作者: Wenbin Yu
摘要: This article provides a brief introduction to micromechanics using linear elastic materials as an example. The fundamental micromechanics concepts including homogenization and dehomogenization, representative volume element (RVE), unit cell, average stress and strain theories, effective stiffness and compliance, Hill-Mandel macrohomogeneity condition. This chapter also describes the detailed derivations of the rules of mixtures, and three full field micromechanics theories including finite element analysis of a representative volume element (RVE analysis), mathematical homogenization theory (MHT), and mechanics of structure genome (MSG). Theoretical connections among the three full field micromechanics theories are clearly shown. Particularly, it is shown that RVE analysis, MHT and MSG are governed by the same set of equations for 3D RVEs with periodic boundary conditions. RVE analysis and MSG can also handle aperiodic or partially periodic materials for which MHT is not applicable. MSG has the unique capability to obtain the complete set of 3D properties and local fields for heterogeneous materials featuring 1D or 2D heterogeneities.
作者: Paul M. Weaver, Zhang Ming Wu, Gangadharan Raju
摘要: Variable angle tow (VAT) describes fibres in a composite lamina that have been steered curvilinearly. In so doing, substantially enlarged freedom for stiffness tailoring of composite laminates is enabled. VAT composite structures have been shown to have improved buckling and postbuckling load carrying capability when compared to straight fibre composites. However, their structural analysis and optimal design is more computationally expensive due to the exponential increase in number of variables associated with spatially varying planar fibre orientations in addition to stacking sequence considerations. In this work, an efficient two-level optim isation framework using lamination parameters as design variables has been enhanced and general ised to the design of VAT plates. Explicit stiffness matrices are found in terms of component material invariants and lamination parameters. The convex hull property of B-splines is exploited to ensure point-wise feasibility of lamination parameters. In addition, a small set of explicit closed-form expressions is used to define the feasible region of two in-plane and two out-of-plane lamination parameters, which are used for the design of orthotropic laminates. Finally, numerical examples of plates under compression loading with different boundary conditions and aspect ratios are investigated. Reliable optimal solutions demonstrate the robustness and computational efficiency of the proposed optimisation methodology.
作者: Steffen Czichon, Jessica Köhnke, Andreas Preisler, Henrik Herranen
摘要: This article provides an overview over some current challenges in industrial composite product development with a main focus on numerical analysis. Three main subjects are covered. Firstly, sizing of composite joining techniques is discussed with an emphasis on the joining of thin ply laminates. Secondly, multi scale analysis, determination of nesting factors and optimization of braided composite structures is discussed. Finally, a shape optimization approach for embedded SHM sensors, aiming at improving the mechanical properties of monitored laminates, is presented.
作者: Adrian P. Mouritz, Fabio Pegorin, Mohd Dali Isa, Khomkrit Pingkarawat
摘要: This paper presents an experimental study into the effect of through-thickness z-pin reinforcement on the in-plane and out-of-plane (delamination) fatigue properties of carbon-epoxy composites used in aerospace structures. The in-plane fatigue strength and fatigue life (load cycles-to-failure) of aerospace composite materials are reduced by z-pins. The in-plane compressive fatigue properties decrease when the volume content of z-pins is increased. Reductions to the in-plane fatigue properties are due to microstructural damage caused by the z-pins. However, the out-of-plane (delamination) fatigue properties of composites are increased greatly by z-pins. The mode I, mode II and mixed mode I/II delamination fatigue properties increase rapidly with increasing volume content of z-pins. The improvement is due to the z-pins forming a large-scale bridging zone along the delamination which resists fatigue crack growth. The work clearly reveals that a trade-off exists between the in-plane and out-of-plane fatigue properties of z-pinned composites. Improvements to the delamination fatigue properties come at the expense of lower in-plane fatigue performance, and this is a key consideration for the design of z-pinned aerospace composite structures.
作者: Marco Gigliotti, Yannick Pannier, Marie Christine Lafarie-Frenot, Jean Claude Grandidier
摘要: This paper presents, discusses and review some recent results concerning the interaction between mechanics and the environment during fatigue tests carried out under accelerated environmental conditioning of laminated and woven Organic Matrix Composites (OMC) for high temperature aircraft parts, the synergy between electrical and mechanical fields during electro-mechanical fatigue of composite laminates for fuselage applications the damage behavior of 3D woven OMC under thermal cycling.For all case studies, the capabilities of the PPRIME Institute to perform such tests reproducing “multi-physical” fatigue environment and characterizing the phenomenology associated to multi-physics coupling at several scales will be highlighted. The main issues related to the development of “multi-physics” models for proper interpretation of test results are also reviewed.
作者: Vincenzo Oliveri, Andrea Alaimo, Alberto Milazzo
摘要: A Rayleigh-Ritz approach for the analysis of buckling and post-buckling behavior of cracked composite stiffened plates is presented. The structure is modeled as the assembly of plate elements modeled by the first order shear deformation theory and taking geometric nonlinearities into account through the von Karman’s theory assumptions. Continuity along the plate elements connected edges and the enforcement of rigid and elastic restraints of the plate boundaries are obtained by using penalty techniques, which also allow to straightforwardly implement efficient crack modeling strategies. General symmetric and unsymmetric stacking sequences are considered and numerical procedures have been developed and used to validate the present solution by comparison with FEA results. Original results are presented for post-buckling solution of multilayered stiffened plates with through-the-thickness cracks, showing the effects of large displacements on the cracked plate post-buckling behavior.
作者: Frederic Dau, J. Girardot, B.D. Le
摘要: A promising way to model fracture mechanics with the use of an original Discrete Element Method (DEM) is proposed. After proving the ability of the method to capture kinetic damage induced by cracking phenomena in brittle materials such as silica [1], taking advantage of the method for composite materials applications is the main purpose of this work. This paper highlights recent and current developments to prove abilities of the DEM to give some answers to challenges : i) use the present DEM to model damage mechanisms (matrix cracking, debonding, fiber break and delamination) in a composite material ii) deal with impact applications on dry fabrics using the DEM. All developments are made in the home made software GRANOO (GRANular Objet Oriented) [2]. The promising results are commented and the on going developments are exposed.
作者: Gaetano Giunta, Salim Belouettar, Erasmo Carrera
摘要: This paper investigates the mechanical behaviour of three-dimensional beams subjected to thermal stresses.The temperature field is obtained by exactly solving Fourier's heat conduction equation and, as classically done by a staggered solution approach, it is considered as an external load within the mechanical analysis.Several higher-order beam models are derived thanks to a compact notation for the a-priori approximation of the displacement field upon the cross-section.The governing differential equations and boundary conditions are obtained in a compact nuclearform using the Principle of Virtual Displacement.The final form does not depend upon the order of approximation of the displacement fieldover the cross-section (this latter being a free parameter of the proposed modelling approach).The obtained problem is solved by means of two strong form solutions: an analytical Navier-type solution andpoint collocation (using Wendland's radial basis functions).Isotropic, functionally graded and laminated beams are considered.Results are validated towards three-dimensional FEM solution obtained by ANSYS.The proposed models yield accurate results characterised by smooth stresses thanks to the used solution methods.Furthermore, computational costs are very attractive when compared to the reference three-dimensional solutions.
作者: Marco Petrolo, Erasmo Carrera
摘要: The Component-Wise approach (CW) is a novel structural modeling strategy that stemmed from the Carrera Unified Formulation (CUF). This work presents an overview of the enhanced capabilities of the CW for the static and dynamic analysis of structures, such as aircraft wings, civil buildings, and composite plates. The CW makes use of the advanced 1D CUF models. Such models exploit Lagrange polynomial expansions (LE) to model the displacement field above the cross-section of the structure. The use of LE allows the improvement of the 1D model capabilities. LE models provide 3D-like accuracies with far fewer computational costs. The use of LE leads to the CW. Although LE are 1D elements, every component of an engineering structure can be modeled via LE elements independently of their geometry, e.g. 2D transverse stiffeners and panels, and of their scale, e.g. fiber/matrix cells. The use of the same type of finite elements facilitates the finite element modeling to a great extent. For instance, no interface techniques are necessary. Moreover, in a CW model, the displacement unknowns are placed along the physical surfaces of the structure with no need for artificial lines and surfaces. Such a feature is promising in a CAD/FEM coupling scenario. The CW approach can be considered as an accurate and computationally cheap analysis tool for many structural problems. Such as progressive failure analyses, multiscale, impact problems and health-monitoring.