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This work introduces a novel concept of modular, shape-adaptable sandwich panel with a distributed actuation system based on shape memory alloys (SMA). The panel consists of a modular arrangement of rigid cells connected with compliant active joints. Each joint hosts a SMA wire, which can be controlled independently, enabling the panel to achieve multiple shapes and complex curvatures with a single design. A numerical model of the actuators is developed combining the SMA model proposed by Brinson with a finite element model of the compliant joints, and validated against experimental results. Further, a demonstrator of the panel is manufactured and tested implementing four different actuation patterns and measuring the final shapes with a digital image correlation system. The results prove the capability of the proposed concept to achieve both in plane and out-of-plane deformations in the order of millimeters to centimeters, and to reproduce shapes with double curvatures. With the possibility to integrate sensors and additional components inside the core, the proposed shape-adaptable panel can be used to realize smart structures, which might be used for morphing aerodynamic surfaces or reconfigurable space structures. [ABSTRACT FROM AUTHOR]

Fiber patch placement (FPP) is a manufacturing technique for discrete variable stiffness composites. In the FPP approach, a structural component is assembled from a multitude of discrete fiber patches. However, due to the discontinuous fibers at patch edges, complex stress distributions occur. To date, a holistic FPP design framework that combines a tailored patch placement method with a dedicated mechanical model for the analysis of patched laminates does not exist. This article introduces a novel approach for the design of fiber patched laminates. It is based on the sequential placement of patches on a finite element shell mesh, using a critical element and angle selection routine in order to optimally locate and orientate fiber patches. They are added to the 3D mesh by employing a highly efficient kinematic draping algorithm. Strength-critical regions of the resulting fiber patched laminates are identified by state-of-the-art finite element analysis and extracted to a shear-lag–based mechanical submodel dedicated to the detailed analysis of patched laminates. The patch placement routine terminates once all design optimization criteria are met. The efficiency of applying optimized patch reinforcements on a continuous fiber-reinforced base laminate is demonstrated using the example of an individualized biomedical component. The work at hand presents the first patched laminate design framework combining a patch placement strategy coupled with a dedicated mechanical model. As a consequence, a substantial progress in the design of patch laminated structures is achieved. [ABSTRACT FROM AUTHOR]

For the design of smart composite structures, the placement of piezoelectric patch transducers is a very important issue. For sensing and passive vibration damping applications, the electric charge and the generalized electromechanical coupling coefficient are important parameters. This article presents an approximative but efficient method for the calculation of the generalized coupling coefficient using finite element simulation results. A smart composite turbomachine blade serves as a test structure for the new method. The influence of different laminate integration layers, positions, rotation angles, patch size variations and performance benefits of increased allowable strain is tested with the new procedure. The efficient nature of the method allows for parametric placement studies or even exhaustive search to find the global positioning optimum for the structure under investigation. The proposed method is compared to state-of-the-art procedures for the calculation of the generalized electromechanical coupling factor. The 1:5 scale models of full carbon fabric/epoxy blades were manufactured with structurally integrated piezo modules. Two different piezo placement positions inside the blade were investigated experimentally. The coupling coefficient was determined and compared to the calculated values. [ABSTRACT FROM PUBLISHER]

Abstract Fiber patch placement (FPP) is a manufacturing technique for variable stiffness composites. In the FPP approach, a structural component is assembled from a multitude of discrete fiber patches, thus allowing for an easy tailoring of the layup to the local load state. However, due to the discontinuous fibers at the patch edges, complex stress distributions occur in patched laminates. To date, an efficient method for the analysis of patched laminates on macro-scale does not exist. This article introduces a 2D planar shear-lag model (SLM) based on thin-plate mechanics and a simplified interlaminar shear stress formulation. It is shown how the governing partial differential equation system is assembled and how boundary conditions are set. The model is solved numerically using the Finite Element Method. For verification the 2D SLM is compared to a full 3D linear-elastic solution. It can be shown that the SLM allows for accurate prediction of stress fields disturbed by interrupted fibers with considerably improved numerical efficiency. An application example shows that the SLM resolves the effects of discontinuities significantly better than a state-of-the-art shell element modeling approach. As a consequence, a substantial progress in the design of patch laminated structures is achieved. [ABSTRACT FROM AUTHOR]

The challenge of accomplishing efficient morphing entails providing a vastly anisotropic internal architecture. As a possible solution, selective compliance can be imparted on a larger structural system by embedding its interior with elements exhibiting variable stiffness properties. Multi-stable laminates, which feature markedly different characteristics corresponding to each equilibrium configuration, become promising variable stiffness components. This paper explores the design space of two classes of bi-stable composites specially designed to provide stiffness variability in distributed compliance systems. A further requirement of embeddability is imposed, denoting the ability to constrain two opposite edges of the element without bi-stability loss. Given these two central aspects, the spatial distribution of the piece-wise lamination regions and the overall aspect ratio of the configurations are varied using experimentally validated finite element analysis. Hence characteristic trends are identified, expected to greatly facilitate the design process of shape-adaptable selectively compliant systems based on integrated bi-stable components for stiffness variability. [ABSTRACT FROM AUTHOR]

Composite tape springs are curved shells with the ability to assume two energetically stable states. By carefully selecting layup and mold during manufacturing, these structures can store significant strain energy, making them ideal for deployable systems. Yet, their potential as reversible reconfigurable structures, particularly as adaptive hinges, remains largely unexplored. In structural applications, both stable states of these hinges must exhibit high stiffness to support loads while retaining the capacity for reversible reconfiguration. This paper introduces kinematics-based stacking concepts aimed at enhancing the stiffness of bistable hinges in both states, allowing for specific fold angles without compromising compliance. These designs leverage snap-through kinematics, resulting in unique architectures with customizable stiffness and stability. Additionally, the paper presents a novel energy-based semi-analytical approach for analyzing the stacking concepts. This approach involves constrained exploration of the energy landscape to assess the design space in terms of stiffness and energy barriers. Through comprehensive parametric studies, the research demonstrates significantly increased stiffness and reduced peak stresses compared to single tape spring designs. This research highlights the potential of employing tape springs as reconfigurable load-bearing structures in diverse applications, including precise adjustments of low-mass payloads like solar panels or antennas on space structures. • Kinematically compliant stacking of bistable tape springs is introduced to create high-stiffness bistable hinges without compromising bistability. • New design tools using energy landscape exploration techniques have been developed to generate low-order descriptions of tape spring behavior. • Superposition of these reduced order descriptions correlated by constraints shown as a novel means of designing mechanisms consisting of stacks of bistable elements. • A multistable reconfigurable boom developed for a debris collection satellite using these novel bistable hinges. [ABSTRACT FROM AUTHOR]

Abstract: Aircraft manufacturers are facing several challenges in the pre-design of aircraft structures. This early stage of the aircraft design has a very multi-disciplinary character. Different competence centres need input data, which is at this point in time to a large extent undefined. Therefore, a large variety of specialised tools is used in order to estimate and predict the required data. If these tools are not compatible, interface problems are the consequence. A permanent improvement of the applied processes with regard to the informal value as well as the applicability remains a continuous challenge. The objective of a collaboration project between Airbus Germany GmbH, the DLR Braunschweig, and the ETH Zurich is to find new methods and approaches to improve accuracy, efficiency, and flexibility of data prediction for primary aircraft structures. The use of modern CAE systems together with the integration of finite element methods into the early pre-design process is a very promising approach [F. Bianconi, P. Conti, N. Senin, D.R. Wallace, CAE systems and distributed design environments, in: XII ADM International Conference, Italy, 5–7 September, 2001 ; M. Pellicciari, G. Barbanti, A.O. Andrisano, Functional requirements for a modern CAD system, in: XII ADM International Conference, Italy, 5–7 September, 2001 ; T. Richter, H. Mechler, D. Schmitt, Integrated parametric aircraft design, in: ICAS 2002 Congress, Institute of Aeronautical Engineering, TU Munich]. The modular and knowledge-based architecture of modern CAE systems allows to represent complex assemblies like aircraft structures by parametric associative and very dynamic models. Design knowledge can be integrated into the modelling [M. Mäntylä, S. Finger, T. Tomiyama, Knowledge Intensive CAD, vol. 2, Chapman & Hall, 1997 ] and different characteristics or individuals of the same structure can be mapped through parameters. This document presents concepts, which allow to design comprehensive digital models of novel aircraft structures whereas the level of the modelling detail shall be variegated flexibly [D.E. Whitney, R. Mantripragada, J.D. Adams, S.J. Rhee, Designing assemblies, Res. Engrg. Design 11 (1999) 229–253 ; P. Aspettati, S. Barone, A. Curcio, M. Picone, Parametric and feature-based assembly in motorcycle design: from preliminary development to detail definition, in: XII ADM International Conference, Italy, 5–7 September, 2001]. The strongly parameterised structures allow calculating and assessing different individuals of a given structure in a very efficient and automated way. This makes parametric associative structures very suitable for optimisation. After structural optimisation tasks have successfully been performed with parametric models [U.M. Fasel, O. König, M. Wintermantel, N. Zehnder, P. Ermanni, DynOPS – an approach to parameter optimization with arbitrary simulation software, Centre of Structure Technologies, ETH Zurich; O. König, R. Puisa, M. Wintermantel, P. Ermanni, CAD-entity based evolutionary design optimization, Centre of Structure Technologies, ETH Zurich, and VGTU, Faculty of Mechanics, Vilnius, Lithuania; U.M. Fasel, O. König, M. Wintermantel, P. Ermanni, Using evolutionary methods with a heterogeneous genotype representation for design optimization of a tubular steel trellis motorbike-frame, Centre of Structure Technologies, ETH Zurich], multi-disciplinary optimisations are gaining importance, since they have the potential to find global optima instead of the discipline-dependent optimal configurations and solutions. [Copyright &y& Elsevier]