Systematic Study of Ethylene-Vinyl Acetate (EVA) in the Manufacturing of Protector Devices for the Orofacial System

Fracture of facial bones and dental elements, and laceration of soft tissue, have increased in sports over recent years. Dentist is the only professional responsible for the mouth protection design, the knowledge about suitable materials is essential. EVA is a thermoplastic material, available in the market, easy of handling and processing, and low-cost. However, it is important to understand the mechanical properties and ability to absorb and to dissipate the impact energy, when this material is submitted to different environments, such as oral cavity with saliva and different temperatures. This chapter show provides a systematic evaluation of the EVA application in orofacial protectors while focusing on sports. The research comprises two aspects: experimental tests and numerical analyses. During experimental tests, EVA was analyzed in special buccal conditions, concerning temperature and presence of saliva. Regarding the presence of saliva, more specific studies about its influence on the mechanical behavior of EVA were performed. In the numerical analyses of the EVA orofacial protector, the studies focused on its effect on the nasal bone integrity, and in the zygomatic bone protection. However, life cycle should be analyzed, since its performance deteriorates over time. Mainly due to the saliva-originated changes to the EVA mechanical characteristics, it can behave as a rigid material. For facial protection, a better performance is obtained with a combination of rigid and soft EVA material. According to the experimental and numerical results from a systematic study of EVA, its application to orofacial protection can be considered satisfactory

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O plano de trabalho proposto insere-se no âmbito da linha de pesquisas em Mecânica de Materiais com aplicação da Mecânica do dano Contínuo, dando-se ênfase para a questão de localização de deformações decorrente do emprego de modelos constitutivos com encruamento negativo (softening). Em particular, a motivação é oferecer uma contribuição ao estudo de uma das técnicas de regularização da resposta numérica, que objetivam eliminar a dependência dos resultados com relação à discretização adotada. Tal técnica de regularização consiste na consideração de gradientes da variável de dano na formulação dos modelos constitutivos. Tanto aspectos teóricos como de aplicação numérica são explorados, destacando-se nos primeiros uma análise do efeito da inclusão de gradientes de ordem superior na relação constitutiva e o emprego do Método dos Elementos Finitos em sua formulação em variáveis generalizadas no segundo aspecto. Outros aspectos complementares são também discutidos, relacionados à formulação variacional e algoritmos de integração em passo finito dos modelos em estudo. Os exemplos de aplicação consistem de análises estática e dinâmica de estruturas, realizando-se um confronto com resultados disponíveis na literatura ou mesmo com observações experimentais de ensaios de laboratório.This work is inserted in the researches in Material Mechanics with an application in Continuum Damage Mechanics, emphasising the issue about localisation of deformations according to the use of constitutive models with softening. In particular, the motivation is to offer a contribution to one of the regularisation techniques of the numerical response, aiming to eliminate mesh dependence of the results. This regularisation technique consists in considering gradients of the damage variable in the formulation of constitutive models. Theoretical aspects as well as numerical application are explored, highlighting the analysis of the effect of the inclusion of gradients in the constitutive relation in the first aspect, and using Finite Element Methods with generalise variables in the second one. Other complementary aspects will also be discussed associated to the variational formulation and integration algorithms in finite steps of the studied models. The examples consist in dynamic and static analysis of structures, comparing with numerical and experimental results available in the literature

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A microestrutura dos metais e concreto é estudada com o objetivo de caracterizar os mecanismos físicos elementares de deformação e ruptura abordados em modelos constitutivos dedicados à simulação da resposta desses materiais. A fadiga em metais é comentada enfatizando-se o estudo microscópico dos processos de iniciação e propagação de trincas. Um estudo à nível fenomenológico do comportamento do material sob solicitação cíclica é acrescentado. Para o concreto, dá-se ênfase ao estudo da fissuração e das características de comportamento do material sob a ação de solicitação cíclica. Apresenta-se um modelo constitutivo não-linear baseado na mecânica do dano contínuo. O modelo de dano isótropo adotado é analisado em seus aspectos fundamentais: hipóteses básicas, critério de início e propagação de dano, lei de evolução da variável escalar representativa do processo de deterioração. Como o modelo original é limitado ao caso de carregamento proporcional, é apresentada uma extensão para o caso de carregamento cíclico. Destaca-se a implementação numérica do modelo em combinação com a técnica dos elementos finitos. Os resultados fornecidos pelo modelo são apresentados em relação a exemplos teóricos e em vigas de concreto armado das quais se dispõe de resultados experimentais.Metals and concrete microstructure are studied aiming at characterization of the deformation and failure elementary physical mechanisms that are approached by constitutive models dedicated to simulate the response of these materials. Fatigue of metals is commented with emphasis on microscopic study of both the crack initiation and the crack propagation processes. A study at phenomenological level of the behaviour of the material under cyclic loading is added. With reference to concrete, emphasis is given to the study of both cracking and behaviour of the material under cyclic loading. A nonlinear constitutive model based on the Continuum Damage Mechanics is presented. The adopted isotropic damage model is analyzed with respect to its fundamental aspects: basics\' hypothesis, damage threshold, evolution law of the scalar variable representing degradation process. Since the original model is limited to proportional loading an extension for cyclic loading case is presented. The numerical implementation of the model, combined with the finite element technique, is emphasized. Results obtained with the damage model are showed through theoretical examples and reinforced concrete beams for which experimental results are known

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A microestrutura dos metais e concreto é estudada com o objetivo de caracterizar os mecanismos físicos elementares de deformação e ruptura abordados em modelos constitutivos dedicados à simulação da resposta desses materiais. A fadiga em metais é comentada enfatizando-se o estudo microscópico dos processos de iniciação e propagação de trincas. Um estudo à nível fenomenológico do comportamento do material sob solicitação cíclica é acrescentado. Para o concreto, dá-se ênfase ao estudo da fissuração e das características de comportamento do material sob a ação de solicitação cíclica. Apresenta-se um modelo constitutivo não-linear baseado na mecânica do dano contínuo. O modelo de dano isótropo adotado é analisado em seus aspectos fundamentais: hipóteses básicas, critério de início e propagação de dano, lei de evolução da variável escalar representativa do processo de deterioração. Como o modelo original é limitado ao caso de carregamento proporcional, é apresentada uma extensão para o caso de carregamento cíclico. Destaca-se a implementação numérica do modelo em combinação com a técnica dos elementos finitos. Os resultados fornecidos pelo modelo são apresentados em relação a exemplos teóricos e em vigas de concreto armado das quais se dispõe de resultados experimentais.Metals and concrete microstructure are studied aiming at characterization of the deformation and failure elementary physical mechanisms that are approached by constitutive models dedicated to simulate the response of these materials. Fatigue of metals is commented with emphasis on microscopic study of both the crack initiation and the crack propagation processes. A study at phenomenological level of the behaviour of the material under cyclic loading is added. With reference to concrete, emphasis is given to the study of both cracking and behaviour of the material under cyclic loading. A nonlinear constitutive model based on the Continuum Damage Mechanics is presented. The adopted isotropic damage model is analyzed with respect to its fundamental aspects: basics\' hypothesis, damage threshold, evolution law of the scalar variable representing degradation process. Since the original model is limited to proportional loading an extension for cyclic loading case is presented. The numerical implementation of the model, combined with the finite element technique, is emphasized. Results obtained with the damage model are showed through theoretical examples and reinforced concrete beams for which experimental results are known

not available

O plano de trabalho proposto insere-se no âmbito da linha de pesquisas em Mecânica de Materiais com aplicação da Mecânica do dano Contínuo, dando-se ênfase para a questão de localização de deformações decorrente do emprego de modelos constitutivos com encruamento negativo (softening). Em particular, a motivação é oferecer uma contribuição ao estudo de uma das técnicas de regularização da resposta numérica, que objetivam eliminar a dependência dos resultados com relação à discretização adotada. Tal técnica de regularização consiste na consideração de gradientes da variável de dano na formulação dos modelos constitutivos. Tanto aspectos teóricos como de aplicação numérica são explorados, destacando-se nos primeiros uma análise do efeito da inclusão de gradientes de ordem superior na relação constitutiva e o emprego do Método dos Elementos Finitos em sua formulação em variáveis generalizadas no segundo aspecto. Outros aspectos complementares são também discutidos, relacionados à formulação variacional e algoritmos de integração em passo finito dos modelos em estudo. Os exemplos de aplicação consistem de análises estática e dinâmica de estruturas, realizando-se um confronto com resultados disponíveis na literatura ou mesmo com observações experimentais de ensaios de laboratório.This work is inserted in the researches in Material Mechanics with an application in Continuum Damage Mechanics, emphasising the issue about localisation of deformations according to the use of constitutive models with softening. In particular, the motivation is to offer a contribution to one of the regularisation techniques of the numerical response, aiming to eliminate mesh dependence of the results. This regularisation technique consists in considering gradients of the damage variable in the formulation of constitutive models. Theoretical aspects as well as numerical application are explored, highlighting the analysis of the effect of the inclusion of gradients in the constitutive relation in the first aspect, and using Finite Element Methods with generalise variables in the second one. Other complementary aspects will also be discussed associated to the variational formulation and integration algorithms in finite steps of the studied models. The examples consist in dynamic and static analysis of structures, comparing with numerical and experimental results available in the literature

Performance of polymeric reinforcements in vehicle structures submitted to frontal impact

Preformed structural reinforcements have shown good performance in crash tests, where the great advantage is their weight. These reinforcements are designed with the aim of increasing the rigidity of regions with large deformations, thus stabilising sections of the vehicle that work as load path during impact. The objective of this work is to show the application of structural reinforcements made of polymeric material PA66 in the field of vehicle safety, through finite element simulations. Simulations of frontal impact at 50 km/h and in ODB (offset deformable barrier) at 57 km/h configurations (standards such as ECE R-94 and ECE R-12) were performed in the software LS-DYNA R (R) and MADYMO (R). The simulations showed that the use of polymeric reinforcements leads to a 70% reduction in A-pillar intrusion, a 65% reduction in the displacement of the steering column and a 59% reduction in the deformation in the region of the occupant legs and feet. The level of occupant injuries was analysed by MADYMO (R) software, and a reduction of 23.5% in the chest compression and 80% in the tibia compression were verified. According to the standard, such conditions lead to an improvement in the occupant safety in a vehicle collision event

Band-gap structure in two- and three-dimensional cellular locally resonant materials

Wave propagation in periodic locally resonant materials (LRM) is characterized by the presence of band-gaps occurring at relatively low frequencies which can be exploited for vibration attenuation or impact absorption. In this work we consider the dispersion properties of three-components cellular LRM endowed with 2D (cylindrical) or 3D periodicity. Modal analyses on the unit cell, with Bloch-Floquet periodicity conditions, are performed by the finite element methods. For cylindrical LRM, the limits of plane analyses, which consider uncoupled in-plane and out-of-plane modes, are highlighted. Several different geometries for the 3D unit cells are also proposed and their influence on the band-gap width is studied

Experiments on stress-triaxiality dependence of material behavior of aluminum alloys

The paper presents and discusses experimental procedures, visual observations and test results considered important to obtain data that can be used in validation of constitutive relations and failure criteria. The aim is to investigate the combined effects of stress intensity, stress-triaxiality and Lode parameter on the material response and failure behavior of aluminum alloys. Smooth and pre-notched tensile and shear specimens were manufactured from both very thin sheets and thicker plates to cover a wide range of stress triaxialities and Lode parameters. In addition, modified Arcan specimens were designed allowing investigation of the effect of sudden changes in stress states and deformation modes on the material behavior. (C) 2009 Elsevier Ltd. All rights reserved.FAPESP[04/15404-0]FAPESP[06/60511-5]Deutsche Forschungsgemeinschaft (DFG) (German Research Foundation)[BR1793/10-1

Performance of Some Basic Types of Road Barriers Subjected to the Collision of a Light Vehicle

The investigation of the performance of road barriers to the car collision is not very often studied in the literature despite the importance of the topic to the passengers' safety. Indeed, the various road barriers systems are seldom compared in terms of their capabilities in reducing the overall damage in an accident. Here, flexible and rigid road restraint system subjected to a 900 kg car impact is studied in detail via a finite element simulation, with the model being validated against experimental results. The model relies on dynamic material properties for the guardrail, which were measured in Split Hopkinson Pressure Bar. Three severity occupant indexes, ASI, THIV and PHD, are explored and used to infer road barriers behaviour when interacting with a light vehicle. It is also investigated the failure limit of bolted connections and its influence on the guardrail impact result by means of the car trajectory. According to test TB11 from EN 1317 standard, the impact simulation results using a 900 kg car show that the flexible guardrail is safer than any of the analysed concrete barriers