Finite Element Software for Rubber Products Design

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Measurement of glass transition in native wheat flour by dynamic mechanical thermal analysis (DMTA)

This work describes a method to study glass transition on native starch powders, based on dynamical mechanical thermal analysis using compression tests, and was applied to wheat flour (13.5% water content). This method will allow the determination of Tg in native (unprocessed) starchy materials, with minimal disturbance of the natural structures. The influence of the test conditions (heating rate, frequency and strain) on the glass transition measurements was determined using factorial designs. The values of Tg determined as the maxima of the energy dissipation (peaks in E ) of native flour and of freezedried pre-gelatinized flour were not statistically different (around 64 C). The heating rate did not affect the measurements in the range tested (0.25 to 1 C min 1). An interactive effect of the strain amplitude and the frequency was detected. The significance of this interaction can be caused by differences in mechanical energy dissipation, which would indicate that not only temperature but also the total energy input may affect this transition. Slight effects of phase separation between gluten and starch were found on native flour

Modeling and simulation in tribology across scales: An overview

This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and micro-scales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions

Realistic tool-tissue interaction models for surgical simulation and planning

Surgical simulators present a safe and potentially effective method for surgical training, and can also be used in pre- and intra-operative surgical planning. Realistic modeling of medical interventions involving tool-tissue interactions has been considered to be a key requirement in the development of high-fidelity simulators and planners. The soft-tissue constitutive laws, organ geometry and boundary conditions imposed by the connective tissues surrounding the organ, and the shape of the surgical tool interacting with the organ are some of the factors that govern the accuracy of medical intervention planning.\ud \ud This thesis is divided into three parts. First, we compare the accuracy of linear and nonlinear constitutive laws for tissue. An important consequence of nonlinear models is the Poynting effect, in which shearing of tissue results in normal force; this effect is not seen in a linear elastic model. The magnitude of the normal force for myocardial tissue is shown to be larger than the human contact force discrimination threshold. Further, in order to investigate and quantify the role of the Poynting effect on material discrimination, we perform a multidimensional scaling study. Second, we consider the effects of organ geometry and boundary constraints in needle path planning. Using medical images and tissue mechanical properties, we develop a model of the prostate and surrounding organs. We show that, for needle procedures such as biopsy or brachytherapy, organ geometry and boundary constraints have more impact on target motion than tissue material parameters. Finally, we investigate the effects surgical tool shape on the accuracy of medical intervention planning. We consider the specific case of robotic needle steering, in which asymmetry of a bevel-tip needle results in the needle naturally bending when it is inserted into soft tissue. We present an analytical and finite element (FE) model for the loads developed at the bevel tip during needle-tissue interaction. The analytical model explains trends observed in the experiments. We incorporated physical parameters (rupture toughness and nonlinear material elasticity) into the FE model that included both contact and cohesive zone models to simulate tissue cleavage. The model shows that the tip forces are sensitive to the rupture toughness. In order to model the mechanics of deflection of the needle, we use an energy-based formulation that incorporates tissue-specific parameters such as rupture toughness, nonlinear material elasticity, and interaction stiffness, and needle geometric and material properties. Simulation results follow similar trends (deflection and radius of curvature) to those observed in macroscopic experimental studies of a robot-driven needle interacting with gels

Planning Framework for Robotic Pizza Dough Stretching with a Rolling Pin

Stretching a pizza dough with a rolling pin is a nonprehensile manipulation. Since the object is deformable, force closure cannot be established, and the manipulation is carried out in a nonprehensile way. The framework of this pizza dough stretching application that is explained in this chapter consists of four sub-procedures: (i) recognition of the pizza dough on a plate, (ii) planning the necessary steps to shape the pizza dough to the desired form, (iii) path generation for a rolling pin to execute the output of the pizza dough planner, and (iv) inverse kinematics for the bi-manual robot to grasp and control the rolling pin properly. Using the deformable object model described in Chap. 3, each sub-procedure of the proposed framework is explained sequentially

Determination of Mechanical Properties of Thin Film Materials Used in Oxide TFTs Toward Advanced Material Models

With an increasing demand for improvement and innovation in the field of microelectronics, flexible electronics, driven by applications that range from displays to medical devices, has gained much relevance in recent years. Thin film transistors (TFTs) are the main building block for flexible microelectronic systems, but a better understanding of the mechanical properties of the constituent thin film materials is necessary to design more reliable microelectronic devices to be used in mechanically harsh environments. This work aims to extract a set of mechanical properties of thin film materials used in flexible oxide TFTs and based on that, parameterize material models for Finite Elements Analysis (FEA). To acquire data for these material models, films from different materials are fabricated on silicon substrates. For assessing the impact of thickness and annealing process on the mechanical properties of the thin films, several samples of the same material are fabricated with distinct specifications. This study is divided into two workflows for extracting two distinct sets of parameters. For films composed of metals (Mo), semiconductors (IGZO) and dielectrics (Ta2O5 and Ta2O5/SiO2), the hardness and, as the main parameter, Young´s modulus, are determined by nanoindentation for describing linear elasticity. For the polymeric films (PI), timedependent parameters such as storage modulus, loss modulus and phase angle, which are necessary to describe viscoelasticity, are determined by nanoscale Dynamic Mechanical Analysis (nano-DMA). Based on these experimental results, the linear elastic and viscoelastic material models are parameterized for the Finite Element Method (FEM). Based on these FEM models, now relevant geometries could be simulated. Beyond that, following the methodology of the dissertation, further thin films used in oxide TFTs could be characterized which paves the way for the acquisition of data from other relevant materials and the obtaining of a complete description of the device for product development.Com uma procura crescente por melhoria e inovação no ramo da microeletrónica, a eletrónica flexível, impulsionada por aplicações que vão desde displays a dispositivos médicos, tem vindo a ganhar muita relevância nos últimos anos. Transístores de filme fino (TFTs) são o principal bloco de construção para sistemas microeletrónicos flexíveis. Mas uma melhor compreensão das propriedades mecânicas dos materiais constituintes de filme fino é necessária para projetar dispositivos microeletrónicos mais confiáveis para serem utilizados em ambientes mecanicamente desafiadores. Este trabalho visa extrair um conjunto de propriedades mecânicas de materiais de filmes finos usados em TFTs de óxidos flexíveis e, com base nestas, parametrizar modelos de materiais para Análise de Elementos Finitos. Para adquirir dados para esses modelos de materiais, filmes de diferentes materiais são fabricados em substratos de silício. Para avaliar o impacto de espessura e do processo de recozimento nas propriedades mecânicas dos filmes, várias amostras são fabricadas com especificações distintas. Este estudo é dividido em dois fluxos de trabalho para a extração de dois conjuntos distintos de parâmetros. Para filmes compostos de metais (Mo), semicondutores (IGZO) e dielétricos (Ta2O5 e Ta2O5/SiO2), a dureza e, como parâmetro principal, o módulo de Young, são determinados por nanoindentação para descrever a elasticidade linear. Para os filmes poliméricos (PI), parâmetros dependentes do tempo, como o módulo de armazenamento, o módulo viscoso e o ângulo de fase, necessários para descrever a viscoelasticidade, são determinados por Análise Mecânica Dinâmica em nanoescala (nano-DMA). Com base nesses resultados experimentais, modelos de materiais lineares elástico e viscoelástico são parametrizados para o Método dos Elementos Finitos (MEF). Com base nesses modelos MEF, geometrias relevantes podem agora ser simuladas. Além disso, seguindo a metodologia da dissertação, outros filmes finos usados em TFTs de óxidos podem ser caracterizados, o que abre caminho para a aquisição de dados de outros materiais relevantes e a obtenção de uma descrição completa do dispositivo para o desenvolvimento de produtos

Experimental Investigation Of Polymer Adhesion Mechanics Using A Blister Contact Test

The adhesion of thin layers of soft polymers is important in many applications, such as tapes, microtransfer printing, and bioinspired adhesives. Traditional adhesion tests based on probe contacts are not suitable for characterizing thin layers and common separation-based specimens, such as the peel test, have well-known limitations. The blister contact test (BCT) was developed in this dissertation to overcome the limitations of current methods and was used to investigate the adhesion and separation of several technologically relevant adhesive systems. In the BCT, a thin sheet was elastically deformed into adhesive contact with a reference substrate and the contact area was optically imaged. Modulated pressure was applied to generate both advancing and receding adhesive contact. Digital image correlation was used to measure the displacements of the specimen. The strain energy release rate at the interface was determined from the measured contact radius, applied pressure, system geometry, and elastic properties of the specimen using a mechanics model. An analytical mechanics model based on von K�rm�n plate theory was developed and used for analysis of the BCT data. Finite element analysis was used to validate and identify the range of applicability of the analytical model. The BCT was used to investigate the adhesion and separation behaviors of three different polymer adhesive systems. First, experiments between a silicone elastomer (polydimethylsiloxane – PDMS) and a stiff substrate were performed to investigate rate effects in adhesion and separation. For the first time, the rate dependence during advancing contact was characterized. Second, the effect of acid-base interactions on performance of pressure sensitive adhesives (PSAs) was examined via a series of BCTs in which adhesion between different formulations of adhesives and multiple substrates was investigated. Viscoelastic contributions to PSA adhesion were also studied. Finally, the effect of layer thickness on rate dependence was investigated through experiments between polyethylene terephthalate (PET) sheets and PDMS films of different thicknesses. The work in this dissertation demonstrates the flexibility and capability of the BCT as a method to characterize adhesion of flat polymer sheets and provides new understanding of several types of polymer adhesive contacts

The role of biomechanics in the assessment of carotid atherosclerosis severity: a numerical approach

Numerical fluid biomechanics has been proved to be an efficient tool for understanding vascular diseases including atherosclerosis. There are many evidences that atherosclerosis plaque formation and rupture are associated with blood flow behavior. In fact, zones of low wall shear stress are vivid areas of proliferation of atherosclerosis, and in particular, in the carotid artery. In this paper a model is presented for investigating how the presence of the plaque influences the distribution of the wall shear stress. In complement to a first approach with rigid walls, an FSI model is developed as well to simulate the coupling between the blood flow and the carotid artery deformation. The results show that the presence of the plaque causes an attenuation of the WSS in the after-plaque region as well as the emergence of recirculation areas