Analysis and optimization of riveting processon relay’s components

O processo de rebitagem é um dos métodos mais importantes para unir duas ou mais peças. O sucesso da xação dessas peças dependerá de diferentes variáveis, como a geometria das peças envolvidas, os seus materiais, as restrições e a magnitude da carga exercida sobre o sistema. Neste estudo, tendo em consideração um problema industrial real, nomeadamente a deformação de um rebite numa única peça de forma a criar um contacto, um modelo numérico de elementos nitos foi desenvolvido com o auxílio do software ABAQUS, de forma a ser possível comparar os resultados obtidos da simulação com a realidade em termos de força e deformação plástica. A comparação desses resultados irá validar a abordagem e criar uma forma de optimizar este processo de forma a minimizar defeitos indesejáveis no material como por exemplo o fender do rebite devido a excesso de força ou deformação; Analysis and optimization of riveting process on relay's components Abstract: The riveting process is one of the most signi cant methods to join/fasten two or more parts. The success of fastening these parts will depend on di erent variables such as the geometry of the parts involved, its materials, constraints and the magnitude of the load exerted onto the system. In this study, taking into account a real industrial problem, which is the deformation of a rivet onto a single metal sheet in order to create a contact, a nite element numerical model is developed with the aid of the software ABAQUS, in a way to compare our results with the reality in terms of force and plastic deformation. The comparison of these results will validate our approach and create a form to optimize this process in order to minimize undesirable defects on the material such as the cracking of the rivet due to excess of force or over deformation

A computational and experimental analysis of impact to aircraft structures

The modelling and analysis of high energy impact on aircraft structures is highly complex. Traditional methods give only a limited understanding of what occurs and it is evident from the continuing problem of uncontained engine failure and other debris impact that a more accurate way of predicting the results of such impacts is needed. Finite element techniques can provide that solution. This work attempts to model accurately impacts to existing aircraft structures. Of particular interest is the behaviour at the ballistic velocity as this is where the problem is most difficult to predict. Initially the model consisted of a simple sheet subject to impact by a cylindrical projectile. This was used to develop the modelling techniques for the more complex model. Issues that arose included the mesh density, the material model and the penalty stiffness factor used. Experimental testing was carried out using a gas fired projectile launcher to validate the finite element model. The geometry of the second model was more complex, a right angled stringer was riveted to a plate using four rivets. Two different approaches were used in modelling here, that of modelling the rivets in 3D and that o f modelling the rivets using 2D approximations. Modelling the rivets in 3D proved to be impractical and o f the 2D approximations the model where the rivets were not allowed to fail proved the most accurate. Experimental testing was again used for validation. Finally a new gas powered projectile launcher was designed and built. Improvements over its predecessor included the ability to accommodate a half metre squared test plate, impact this plate anywhere on its surface and tilt the plate through 45°. Also included were modifications to the barrel so that projectiles of any shape or size up to a maximum of 50mm in diameter could be used

Optimization study of hybrid spot-welded/bonded single-lap joints

Joining of components with structural adhesives is currently one of the most widespread techniques for advanced structures (e.g., aerospace or aeronautical). Adhesive bonding does not involve drilling operations and it distributes the load over a larger area than mechanical joints. However, peak stresses tend to develop near the overlap edges because of differential straining of the adherends and load asymmetry. As a result, premature failures can be expected, especially for brittle adhesives. Moreover, bonded joints are very sensitive to the surface treatment of the material, service temperature, humidity and ageing. To surpass these limitations, the combination of adhesive bonding with spot-welding is a choice to be considered, adding a few advantages like superior static strength and stiffness, higher peeling and fatigue strength and easier fabrication, as fixtures during the adhesive curing are not needed. The experimental and numerical study presented here evaluates hybrid spot-welded/bonded single-lap joints in comparison with the purely spot-welded and bonded equivalents. A parametric study on the overlap length (LO) allowed achieving different strength advantages, up to 58% compared to spot-welded joints and 24% over bonded joints. The Finite Element Method (FEM) and Cohesive Zone Models (CZM) for damage growth were also tested in Abaqus® to evaluate this technique for strength prediction, showing accurate estimations for all kinds of joints

Multifunctional vertical interconnections of multilayered flexible substrates for miniaturised POCT devices

Point-of-care testing (POCT) is an emerging technology which can lead to an eruptive change of lifestyle and medication of population against the traditional medical laboratory. Since living organisms are intrinsically flexible and malleable, the flexible substrate is a necessity for successful integration of electronics in biological systems that do not cause discomfort during prolonged use. Isotropic conductive adhesives (ICAs) are attractive to wearable POCT devices because ICAs are environmentally friendly and allow a lower processing temperature than soldering which protects heat-sensitive components. Vertical interconnections and optical interconnections are considered as the technologies to realise the miniaturised high-performance devices for the future applications. This thesis focused on the multifunctional integration to enable both electrical and optical vertical interconnections through one via hole that can be fabricated in flexible substrates. The functional properties of the via and their response to the external loadings which are likely encountered in the POCT devices are the primary concerns of this PhD project. In this thesis, the research of curing effect on via performance was first conducted by studying the relationship between curing conditions and material properties. Based on differential scanning calorimetry (DSC) analysis results, two-parameter autocatalytic model (Sestak-Berggren model) was established as the most suitable curing process description of our typical ICA composed of epoxy-based binders and Ag filler particles. A link between curing conditions and the mechanical properties of ICAs was established based on the DMA experiments. A series of test vehicles containing vias filled with ICAs were cured under varying conditions. The electrical resistance of the ICA filled vias were measured before testing and in real time during thermal cycling tests, damp heat tests and bending tests. A simplified model was derived to represent rivet-shaped vias in the flexible printed circuit boards (FPCBs) based on the assumption of homogenous ICAs. An equation was thus proposed to evaluate the resistance of the model. Vias with different cap sizes were also tested, and the equation was validated. Those samples were divided into three groups for thermal cycling test, damp heat ageing test and bending test. Finite element analysis (FEA) was used to aid better understanding of the electrical conduction mechanisms. Based on theoretical equation and simulation model, the fistula-shape ICA via was fabricated in flexible PCB. Its hollow nature provides the space for integrations of optical or fluidic circuits. Resistance measurements and reliability tests proved that carefully designed and manufactured small bores in vias did not comprise the performance. Test vehicles with optoelectrical vias were made through two different approaches to prove the feasibility of multifunctional vertical interconnections in flexible substrates. A case study was carried out on reflection Photoplethysmography (rPPG) sensors manufacturing, using a specially designed optoelectronic system. ICA-based low-temperature manufacture processes were developed to enable the integration of these flexible but delicate substrates and components. In the manufacturing routes, a modified stencil printing setup, which merges two printing-curing steps (vias forming and components bonding) into one step, was developed to save both time and energy. The assembled probes showed the outstanding performance in functional and physiological tests. The results from this thesis are anticipated to facilitate the understanding of ICA via conduction mechanism and provide an applicable tool to optimise the design and manufacturing of optoelectrical vias

Multiphysics Modeling and Numerical Simulation in Computer-Aided Manufacturing Processes

The concept of Industry 4.0 is defined as a common term for technology and the concept of new digital tools to optimize the manufacturing process. Within this framework of modular smart factories, cyber-physical systems monitor physical processes creating a virtual copy of the physical world and making decentralized decisions. This article presents a review of the literature on virtual methods of computer-aided manufacturing processes. Numerical modeling is used to predict stress and temperature distribution, springback, material flow, and prediction of phase transformations, as well as for determining forming forces and the locations of potential wrinkling and cracking. The scope of the review has been limited to the last ten years, with an emphasis on the current state of knowledge. Intelligent production driven by the concept of Industry 4.0 and the demand for high-quality equipment in the aerospace and automotive industries forces the development of manufacturing techniques to progress towards intelligent manufacturing and ecological production. Multi-scale approaches that tend to move from macro- to micro- parameters become very important in numerical optimization programs. The software requirements for optimizing a fully coupled thermo-mechanical microstructure then increase rapidly. The highly advanced simulation programs based on our knowledge of physical and mechanical phenomena occurring in non-homogeneous materials allow a significant acceleration of the introduction of new products and the optimization of existing processes.publishedVersio

Efficient multiscale methodology for local stress analysis of metallic railway bridges based on modal superposition principles

This paper presents an advanced submodelling methodology for local stress analysis of complex details of existing metallic railway bridges. The fatigue assessment of connections of large structures based on local methods leads inherently to a multiscale problem that can only be solved by adopting efficient numerical procedures. Aiming to overcome such limitations that influence the analysis process, submodelling techniques and modal superposition principles are combined to fully represent numerically the local geometrical, material and contact properties of the fatigue-critical details. The results of experimental in situ tests are proposed to characterise the numerical models and respective multiscale relation, implementing optimisation and validation procedures. In this work, the suggested efficient multiscale methodology for stress analysis aims to allow the subsequent local fatigue assessment, according to the real mechanism of loading transference, reducing sources of conservatism. All numerical procedures and respective validation thru experimental techniques are illustrated using a real case study.This work was financially supported by: Base Funding - UIDB/04708/2020 of the CONSTRUCT - Institute of R&D In Structures and Construction - funded by national funds through the FCT/MCTES (PIDDAC) and by national funds through FCT - Fundação para a Ciência e a Tecnologia; PD/BD/114101/2015. This work was also carried out in the framework of Shift2Rail projects IN2TRACK2 [826255-H2020-S2RJU-CFM-2018] and IN2TRACK3 [101012456-H2020-S2RJU-CFM-2020].info:eu-repo/semantics/publishedVersio