1,721,123 research outputs found
On the mechanics of microsystems
No full textThis work is focused on the mechanical design of MEMS (micro electromechanical systems) and to the most relevant mechanically-coupled fields of interest. The paper represents an overview on some of the research topics investigated by the author in previous studies and provides a good background for the optimization of the mechanics of microsystems. The multiphysics problem is discussed, with reference to the structural-fluidic and the electromechanical coupling and their implications on the dynamic response. The stress and/or strain gradients in the material caused by building processes are introduced, as well as the MEMS reliability related to mechanical fatigue of cyclic loaded components
Mechanical design of microsystems: dynamic and fatigue behavior
No full textThe most relevant issues of mechanical design of microsystems are presented. Micro electro-mechanical systems (MEMS) are characterized by high levels of miniaturization and integration; they base their functioning on many different principles such as mechanical, electrical, optical, thermal, chemical, etc. and can combine a number of functions within an extremely tiny space by providing sensing and actuating performances. The interdisciplinary nature of MEMS introduces many problems for designers because very different competences may be required to define a single device; this evidence is accentuated by the strong coupling among different physical domains (structural, electric, fluidic, magnetic, etc) characterizing microsystems. The theories elaborated in the past for traditional macro-mechanical environments are not completely suitable for microsystems, thus a scientific approach supported by dedicated models and analytic formulations for the microscale become fundamental to provide general tools for the design; then, experimental measurements should be used to validate the proposed theories.
The structural-fluidic coupling was analyzed by means of compact analytic models, numerical simulations and measurements on dedicated samples; a climatic chamber was also fabricated for tests at controlled pressures and temperatures. The dynamic behavior of free vibrating and forced structures was deeply studied and modeled, with particular attention to the effects due to electro-mechanical coupling and to residual stress distribution. The reliability and lifetime of microcomponents under the effect of mechanical fatigue was studied by means of experimental validation on dedicated test structures; an original procedure is introduced for the evaluation of S-N curves at microscale. Finally, the design and fabrication of MEMS energy harvesters able to convert vibrations to electric power was presented as a case study
Additive manufacturing process optimization for innovative aluminium-carbon fibre reinforced polymer co-cured joints
No full textOver the past two decades, significant advancements in production additive technologies allowed the realization of unconventional geometries, that enabled the development of multi-functional (MF), and/or multi-material structures (MM). Integrating these innovative structures into load-bearing applications could revolutionize how mechanical/bio-medical/aerospace components are designed and produced, to maximize, e.g., the final stiffness-to-weight ratio, and/or guarantee a specific degree of compliance [1]. In this study, an overview of the MM joint “Mimosa” [2], is provided. The project involves the design and production of MM joints for commercial aircraft. The bracket is composed of a metal part, manufactured via laser powder bed fusion (L-PBF) with AlSi10Mg, and a carbon fiber reinforced polymer (CFRP) part. The metal part includes a matrix of 3D anchors that can hold the CFRP to form a single lap joint. This solution presents several advantages, such as overall weight reduction, rivets elimination, production process simplification, and reduction of the environmental footprint. On the other hand, to guarantee a high level of structural integrity, several issues need to be addressed, such as the optimization of the anchors’ design and production, understanding the local force transfer mechanism among anchors and fibers, galvanic corrosion, etc. [3]. Given the overall complexity of the MIMOSA component, the present study focuses only on two critical aspects related to the production of the aluminum structure via L-PBF. First, the production parameters optimization for both bulky and relatively thin structures is discussed. Different manufacturing parameters combinations are used to generate cubes (15x15x15mm) and small cylindrical struts (diameter 2mm, height 10mm) to evaluate their correlation with the final members characteristics, in terms of porosity level and surface quality. Archimedes’ density measurements are conducted (range 98-99.95%) to determine the sample density, and μ-CT is used to evaluate the pores topology and distribution, along with the sample external surface morphology. Second, the optimization of a heat treatment that accounts for all the post-processes steps that the plate will undergo to realize the MM-joint, i.e., autoclave curing, is presented. The stress-strain curves on tensile samples are measured to relate the AlSi10Mg mechanical properties with the fabrication parameters and post-treatment profile sequences. Results showed the importance to fine tune the L-PBF process parameters in function of the final part geometry to guarantee high part quality, and the impact of multiple thermal treatments on the final structural strength of the joint
Artificial human joint for the characterization of piezoelectric transducers in self-powered telemedicine applications
No full textThis paper introduces an artificial human joint working as testing machine for the experimental characterization of piezoelectric transducers for wearable applications. The diffusion of portable medical devices and low-power communication systems for telemedicine and telehealth is leading to the development of self-powered diagnostic systems supplied by small wearable generators. Laboratory tests are needed before the validation on human body for instance, to measure electric outputs, material properties and transducers reliability, as well as dedicated test benches must be designed and built. This work contributes to define experimental methodologies and test benches for the characterization of materials and electro-mechanical response of piezoelectric transducers. The proposed testing machine contributes to improve the effectiveness of harvesters design by providing preliminary data about performances, endurance and reliability. The same data are not easy to obtain from direct tests on the body due to the long test duration and the high repeatability and accuracy in imposing the movements. Additionally, the managing and control of multiple testing parameters is also needed, e.g. in design of-experiments approaches. The functionality of the testing machine, which has been previously designed and built, has been proved with some qualitative measurements on piezo foil transducers coated with polyme
MEMS for Sensors and RF Applications: Dynamic Design and Methods for Reliability Assessment
No full text
Analisi matriciale delle strutture
No full textIl testo, destinato prevalentemente agli studenti di ingegneria industriale, ha l'obiettivo di fornire al lettore gli strumenti necessari ad applicare a casi reali le metodologie dell'analisi matriciale delle strutture. Nel corso della trattazione si affrontano i principali problemi di modellazione e formulazione matematica connessi al calcolo di strutture monodimensionali nel piano e si propone una successione di argomenti organizzati con criterio didattico e difficoltà crescente. Partendo da strutture specifiche, i principali aspetti della modellazione agli elementi finiti sono affrontati in modo generale, al fine di fornire indicazioni utili ad applicare i medesimi concetti al numero più ampio possibile di casi. Il testo si compone di 20 capitoli tematici, ognuno dei quali è dedicato a un problema strutturale e di modellazione specifico. I capitoli 1-14 sono rivolti a problemi di tipo statico, mentre i capitoli 15-20 a problemi di analisi modale in ambito dinamico. Al fondo, una sezione è riservata a esercizi per la verifica delle nozioni appres
Experimental analysis of viscous and material damping in microstructures through the interferometric microscopy technique with climatic chamber
Full text linkThis study describes an experimental analysis of energy dissipation due to damping sources in microstructures and micro electro-mechanical systems (MEMS) components using interferometric microscopy techniques. Viscous damping caused by the surrounding air (squeeze film damping) and material damping are measured using variable geometrical parameters of samples and under different environmental conditions. The equipment included a climatic chamber designed (built ad hoc) which was used to modify the surrounding air pressure. Results show the relationship between damping coefficients and sample geometry caused by variation in air flow resistance and the relationship between quality factor and air pressure. The experimental results will provide a useful data source for validating analytic models and calibrating simulations. A thorough discussion about interferometry applied to experimental mechanics of MEMS will also contribute to the reduction of the knowledge gap between specialists in optical methods and microsystem designer
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