Centre of Structure Technologies

ETH Zurich - Swiss Federal Institute of Technology

Keywords: smart materials, active structures, sensors, actuators, piezoelectric fibers, composite materials, numerical and analytical analysis, finite element modeling.

The engineering vision is to be able to design and build smart structures with the inherent ability to sense changes in their surroundngs and adapt their shape accordingly (eg. airfoils that change shape like a bird's wing). Such a concept would benefit greatly lightweight structures in terms of performance, weight and reliability.

This smart structures concept is described by the synergistic integration of active materials into a passive structure connected by a control system to enable an automatic adaptation to changing environmental conditions.

Among a plethora of smart materials, my research project considered the idea of integrating thin piezolectric fibres (sensors and actuators) within plies of composite layers both as sensors and actuators. Such fibres are actuated longitudinally by a specially designed interdigitated electrode pattern and exhibit a high frequency response and relatively large deformations.

Aim of this study was to identify key issues related to materials, fabrication, experimental procedures and modeling of active structures, particularly those activated by anisotropic piezoceramic actuators. The results were compared both with theoretical analyses and numerical simulations (finite elements) to evaluate the validity of existing mathematical models found.

Automatic Control Lab

ETH Zurich -Swiss Federal Institute of Technology

 

Keywords: CAD/CAM, mechanical design, static and dynamic analysis.

 

Task-oriented repetitive movements can improve muscular strength and movement coordination in patients with impairments due to neurological or orthopaedic problems. Arm therapy is used for patients with paralysed upper extremities after stroke or spinal cord injury. ARMin - designed at the Rehabilitation Engineering Group at ETH Zurich - is a device that supports spatial movements of the shoulder and elbow joint with innovative, cooperative control strategies which allow the patient effort to be taken into consideration.

My work focused on the mechanical behaviour of the robot's forearm exoskeleton, which for control performance and for safety reasons, must have low inertia, low friction and negligible backlash. The first prototype was built with four active DoF (three for shoulder and one for elbow actuation).

Hellenic Air Force Research & Technology Center and University of Patras

 

Keywords: aeronautical structures, stress analysis, fatigue, fracture mechanics, composite materials, numerical and analytical analysis, finite element modeling.

Aircraft structures experience fatigue loading which may lead to serious damage. Fatigue loading arises from internal pressurization of the fuselage shell during each flight and results in the growth of large longitudinal cracks in fuselage skins, which are often formed by the coalescence of many smaller cracks. Aircraft accidents caused by crack growth which lead to explosive decompression prove the importance of studying crack growth and propagation in fuselages.

The aircraft must be tolerant to the cracks thus formed.A knowledge of the stress field around the tip of such cracks is of big importance for the economic design of the new aircraft and the estimation of the structure's residual strength. Research in the field of fracture mechanics in aeronautical structures has not taken into consideration parameters such as plasticity and curvature at the crack tip yet. This project was a first approach to address such parameters, by introducing a computational methodology which incorporates the plasticity effects and the influence of curvature at the crack tip.

The methodology consists of a hierarchical modeling of the cracked fuselage, involving three stages of analysis. Each succeeding stage in the hierarchy accounts for more complex behavior but which is dominant in a smaller portion of the fuselage structure.

©2020 Manolis Kelaidis

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