A simulação numérica de componentes estmturais necessita de dados do material que são obtidos por ensaios mecânicos. Materiais não-lineares, como termoplásticos, podem apresentar em ensaios de tração estricção quando submetidos à deformações firútas. Este fenômeno normalmente ainda está associado a campos de deformações heterogêneos que possuem uma cinemática particular, se propagando ao longo do corpo. A formação e propagação da estricção podem mascarar o real comportamento mecârúco do material quando obtido por um ensaio de tração, levando o processo de caracterização da curva tensão-deformação real do material a um procedimento não-trivial. Através de um ensaio de tração de um termoplástico, dados experimentais de força e do campo de deslocamentos da região de estricção, obtido através de métodos ópticos, são utilizados em um procedimento numérico-experimental de otimização para a deternúnação dos parâmetros (FEMU) de alguns modelos constitutivos capazes de representar a tendência do comportamento de termoplásticos. De modo a estudar a capacidade representativa da resposta mecânica do ensaio, um modelo constitutivo multi linear e um modelo constitutivo variacional, são estudados. Uma função objetivo conveniente que utiliza dados experimentais e numéricos é usada para considerar a cinemática da estricção, responsável pela mudança geométrica que diferencia as respostas nonúnais e reais da curva tensão-deformação. Por meio dos resultados obtidos neste trabalho verificou-se que a caracterização dos modelos constitutivos utilizando somente a resposta de força, não garante uma caracterização constitutiva adequada, sendo necessária a resposta de deslocamento para garantir a representação da cinemática da região de estricção. / Numerical simulation of structural components requires material data obtained from mechanical testing. Nonlinear materials, like thermoplastics, submitted to tensile testing presents necking undergoing finite strain. This phenomenon is still typically associated to heterogeneous strain fields which possess a particular kinematic, propagating through the body. Necking and colddrawing may mask the actual mechanical behavior measured by a tensile testing machine, turning the real stress-strain curve characterization process into a non-trivial procedure. Through a thermoplastic tensile testing, force experimental data and displacement experimental data from the necking region, obtained by optical methods, are used in a numerical-experimental optimization procedure in order to determine the constitutive parameters (FEMU) from some constitutive models which are able to represent the thermoplastic behavior tendency. In order to study the representative capacity of the mechanical testing response, a multilinear constitutive model and a variational constitutive model, are studied. A suitable objective function which uses experimental and numerical data is used to consider the necking kinematics, responsible for geometric change that distinguishes the nominal and real responses of the stress-strain curve. Through the obtained results, it can be seen that the model parameters determination using, in addition to force, the displacement field in the objective function is necessary to represent the kinematic behavior in the necking region.

National and international crises in the early 21st Century, whether natural, technological or man-made, emphasize the need for highly reliable organizations (HROs) to conduct emergency response in a relatively error-free way. Urban search and rescue units provide a pivotal intermittent role in these high-risk environments. Traditional HRO research focuses on a concept known as "collective mind" -- heedful interactions of responders that accomplish reliability. Rather than focusing on collective mind, this study uses a practice-based communication approach to examine the material interplay of bodies, objects, and sites using ethnography and grounded theory. In-depth interviews, participant observations, and organizational documents were coded and contrasted to find patterns in material interplay. More specifically, this study examines how these material features interact to orchestrate reliable practices through ecological coherence, a bonding of multiple forces to construct meaning and improvisation. The study has implication for HRO theory through focusing on the role of the body rather than emphasizing cognitive judgment in collective action. Collective body shifts the discussion of mindful processes to embodied practices and offers insights into the ways responders enact safety and perform responses in dynamic, high-risk environments.

A simulação numérica de componentes estmturais necessita de dados do material que são obtidos por ensaios mecânicos. Materiais não-lineares, como termoplásticos, podem apresentar em ensaios de tração estricção quando submetidos à deformações firútas. Este fenômeno normalmente ainda está associado a campos de deformações heterogêneos que possuem uma cinemática particular, se propagando ao longo do corpo. A formação e propagação da estricção podem mascarar o real comportamento mecârúco do material quando obtido por um ensaio de tração, levando o processo de caracterização da curva tensão-deformação real do material a um procedimento não-trivial. Através de um ensaio de tração de um termoplástico, dados experimentais de força e do campo de deslocamentos da região de estricção, obtido através de métodos ópticos, são utilizados em um procedimento numérico-experimental de otimização para a deternúnação dos parâmetros (FEMU) de alguns modelos constitutivos capazes de representar a tendência do comportamento de termoplásticos. De modo a estudar a capacidade representativa da resposta mecânica do ensaio, um modelo constitutivo multi linear e um modelo constitutivo variacional, são estudados. Uma função objetivo conveniente que utiliza dados experimentais e numéricos é usada para considerar a cinemática da estricção, responsável pela mudança geométrica que diferencia as respostas nonúnais e reais da curva tensão-deformação. Por meio dos resultados obtidos neste trabalho verificou-se que a caracterização dos modelos constitutivos utilizando somente a resposta de força, não garante uma caracterização constitutiva adequada, sendo necessária a resposta de deslocamento para garantir a representação da cinemática da região de estricção. / Numerical simulation of structural components requires material data obtained from mechanical testing. Nonlinear materials, like thermoplastics, submitted to tensile testing presents necking undergoing finite strain. This phenomenon is still typically associated to heterogeneous strain fields which possess a particular kinematic, propagating through the body. Necking and colddrawing may mask the actual mechanical behavior measured by a tensile testing machine, turning the real stress-strain curve characterization process into a non-trivial procedure. Through a thermoplastic tensile testing, force experimental data and displacement experimental data from the necking region, obtained by optical methods, are used in a numerical-experimental optimization procedure in order to determine the constitutive parameters (FEMU) from some constitutive models which are able to represent the thermoplastic behavior tendency. In order to study the representative capacity of the mechanical testing response, a multilinear constitutive model and a variational constitutive model, are studied. A suitable objective function which uses experimental and numerical data is used to consider the necking kinematics, responsible for geometric change that distinguishes the nominal and real responses of the stress-strain curve. Through the obtained results, it can be seen that the model parameters determination using, in addition to force, the displacement field in the objective function is necessary to represent the kinematic behavior in the necking region.

A simulação numérica de componentes estmturais necessita de dados do material que são obtidos por ensaios mecânicos. Materiais não-lineares, como termoplásticos, podem apresentar em ensaios de tração estricção quando submetidos à deformações firútas. Este fenômeno normalmente ainda está associado a campos de deformações heterogêneos que possuem uma cinemática particular, se propagando ao longo do corpo. A formação e propagação da estricção podem mascarar o real comportamento mecârúco do material quando obtido por um ensaio de tração, levando o processo de caracterização da curva tensão-deformação real do material a um procedimento não-trivial. Através de um ensaio de tração de um termoplástico, dados experimentais de força e do campo de deslocamentos da região de estricção, obtido através de métodos ópticos, são utilizados em um procedimento numérico-experimental de otimização para a deternúnação dos parâmetros (FEMU) de alguns modelos constitutivos capazes de representar a tendência do comportamento de termoplásticos. De modo a estudar a capacidade representativa da resposta mecânica do ensaio, um modelo constitutivo multi linear e um modelo constitutivo variacional, são estudados. Uma função objetivo conveniente que utiliza dados experimentais e numéricos é usada para considerar a cinemática da estricção, responsável pela mudança geométrica que diferencia as respostas nonúnais e reais da curva tensão-deformação. Por meio dos resultados obtidos neste trabalho verificou-se que a caracterização dos modelos constitutivos utilizando somente a resposta de força, não garante uma caracterização constitutiva adequada, sendo necessária a resposta de deslocamento para garantir a representação da cinemática da região de estricção. / Numerical simulation of structural components requires material data obtained from mechanical testing. Nonlinear materials, like thermoplastics, submitted to tensile testing presents necking undergoing finite strain. This phenomenon is still typically associated to heterogeneous strain fields which possess a particular kinematic, propagating through the body. Necking and colddrawing may mask the actual mechanical behavior measured by a tensile testing machine, turning the real stress-strain curve characterization process into a non-trivial procedure. Through a thermoplastic tensile testing, force experimental data and displacement experimental data from the necking region, obtained by optical methods, are used in a numerical-experimental optimization procedure in order to determine the constitutive parameters (FEMU) from some constitutive models which are able to represent the thermoplastic behavior tendency. In order to study the representative capacity of the mechanical testing response, a multilinear constitutive model and a variational constitutive model, are studied. A suitable objective function which uses experimental and numerical data is used to consider the necking kinematics, responsible for geometric change that distinguishes the nominal and real responses of the stress-strain curve. Through the obtained results, it can be seen that the model parameters determination using, in addition to force, the displacement field in the objective function is necessary to represent the kinematic behavior in the necking region.

The experimental identification of mechanical properties is crucial in mechanics for understanding material behavior and for the development of numerical models. Classical identification procedures employ standard shaped specimens, assume that the mechanical fields in the object are homogeneous, and recover global properties. Thus, multiple tests are required for full characterization of a heterogeneous object, leading to a time consuming and costly process. The development of non-contact, full-field measurement techniques from which complex kinematic fields can be recorded has opened the door to a new way of thinking. From the identification point of view, suitable methods can be used to process these complex kinematic fields in order to recover multiple spatially varying parameters through one test or a few tests. The requirement is the development of identification techniques that can process these complex experimental data. This thesis introduces a novel identification technique called the constitutive compatibility method. The key idea is to define stresses as compatible with the observed kinematic field through the chosen class of constitutive equation, making possible the uncoupling of the identification of stress from the identification of the material parameters. This uncoupling leads to parametrized solutions in cases where 5 the solution is non-unique (due to unknown traction boundary conditions) as demonstrated on 2D numerical examples. First the theory is outlined and the method is demonstrated in 2D applications. Second, the method is implemented within a domain decomposition framework in order to reduce the cost for processing very large problems. Finally, it is extended to 3D numerical examples. Promising results are shown for 2D and 3D problems

No description available.

Constitutive modeling is a method that is useful in providing precise predictions of material response in components subjected to a variety of operating conditions. A process for optimizing the material constants of the Miller constitutive model for uniaxial modeling was developed and implemented in an automated optimization routine. Generally, up to twenty experiments simulating a range of conditions are needed to identify the material parameters for the model. The research sought to minimize the amount of empirical data that is necessary for optimization, aiming to reduce the costs and time necessary to carry out this procedure for more expensive classes of materials. The ultimate goal was to develop a robust method for determining the material constants of a viscoplastic model using a minimum amount of experimental data. An automated optimization routine was implemented into a program, referred to as uSHARP, developed as part of the research to determine constitutive model parameters. Central to the method was the use of more complex stress, strain, and temperature histories than are traditionally used, allowing for the effects of all material parameters to be captured using as few tests as possible. By carrying out successive finite element simulations and comparing the results to simulated experimental test data, the material constants were determined from 75% fewer experiments. By reducing monetary costs and time required, this procedure will allow for a more widespread application of advanced constitutive models in industry, allowing for better life prediction modeling of critical components in high temperature applications.

A novel constitutive characterization method for uncured rubber behaviour has been developed in this article. A systematic measuring procedure was designed to fully investigate the uncured rubber complex stress–strain behaviour under different deformation patterns, which integrated three kinds of tests – the uniaxial tensile, the compression test and the shear test. It can be found from the observed behaviour that the uncured rubber has similar but much pronounced non-elastic stress–strain relationship, which is highly non-linear and highly rate dependent. A generalized Maxwell model with modified Yeoh model is developed to constitutively describe the observed phenomena in which parameters are identified by an evolution optimization scheme. Good agreement can be found between the model and the test data. Another finding is that, similar to vulcanized rubber, multi-test data are needed to obtain compatible constitutive models. The test results, findings and the developed model help rubber engineers deeply understand the uncured rubber’s mechanical behaviour and provide a base for rubber manufacturing simulation.

<p align="justify">The conservation of structures of the historical heritage is an increasing concern nowadays for public authorities. The technical design phase of repair operations for these structures is of prime importance. Such operations usually require an estimation of the residual strength and of the potential structural failure modes of structures to optimize the choice of the repairing techniques.</p> <p align="justify">Although rules of thumb and codes are widely used, numerical simulations now start to emerge as valuable tools. Such alternative methods may be useful in this respect only if they are able to account realistically for the possibly complex failure modes of masonry in structural applications.</p> <p align="justify">The mechanical behaviour of masonry is characterized by the properties of its constituents (bricks and mortar joints) and their stacking mode. Structural failure mechanisms are strongly connected to the mesostructure of the material, with strong localization and damage-induced anisotropy.</p> <p align="justify">The currently available numerical tools for this material are mostly based on approaches incorporating only one scale of representation. Mesoscopic models are used in order to study structural details with an explicit representation of the constituents and of their behaviour. The range of applicability of these descriptions is however restricted by computational costs. At the other end of the spectrum, macroscopic descriptions used in structural computations rely on phenomenological constitutive laws representing the collective behaviour of the constituents. As a result, these macroscopic models are difficult to identify and sometimes lead to wrong failure mode predictions.</p> <p align="justify">The purpose of this study is to bridge the gap between mesoscopic and macroscopic representations and to propose a computational methodology for the analysis of plane masonry walls. To overcome the drawbacks of existing approaches, a multi-scale framework is used which allows to include mesoscopic behaviour features in macroscopic descriptions, without the need for an a priori postulated macroscopic constitutive law. First, a mesoscopic constitutive description is defined for the quasi-brittle constituents of the masonry material, the failure of which mainly occurs through stiffness degradation. The mesoscopic description is therefore based on a scalar damage model. Plane stress and generalized plane state assumptions are used at the mesoscopic scale, leading to two-dimensional macroscopic continuum descriptions. Based on periodic homogenization techniques and unit cell computations, it is shown that the identified mesoscopic constitutive setting allows to reproduce the characteristic shape of (anisotropic) failure envelopes observed experimentally. The failure modes corresponding to various macroscopic loading directions are also shown to be correctly captured. The in-plane failure mechanisms are correctly represented by a plane stress description, while the generalized plane state assumption, introducing simplified three-dimensional effects, is shown to be needed to represent out-of-plane failure under biaxial compressive loading. Macroscopic damage-induced anisotropy resulting from the constituents' stacking mode in the material, which is complex to represent properly using macroscopic phenomenological constitutive equations, is here obtained in a natural fashion. The identified mesoscopic description is introduced in a scale transition procedure to infer the macroscopic response of the material. The first-order computational homogenization technique is used for this purpose to extract this response from unit cells. Damage localization eventually appears as a natural outcome of the quasi-brittle nature of the constituents. The onset of macroscopic localization is treated as a material bifurcation phenomenon and is detected from an eigenvalue analysis of the homogenized acoustic tensor obtained from the scale transition procedure together with a limit point criterion. The macroscopic localization orientations obtained with this type of detection are shown to be strongly related to the underlying mesostructural failure modes in the unit cells.</p> <p align="justify">A well-posed macroscopic description is preserved by embedding localization bands at the macroscopic localization onset, with a width directly deduced from the initial periodicity of the mesostructure of the material. This allows to take into account the finite size of the fracturing zone in the macroscopic description. As a result of mesoscopic damage localization in narrow zones of the order of a mortar joint, the material response computationally deduced from unit cells may exhibit a snap-back behaviour. This precludes the use of such a response in the standard strain-driven multi-scale scheme.</p> <p align="justify">Adaptations of the multi-scale framework required to treat the mesostructural response snap-back are proposed. This multi-scale framework is finally applied for a typical confined shear wall problem, which allows to verify its ability to represent complex structural failure modes.</p>

Recent experiences from the Darfield and Canterbury, New Zealand earthquakes have shown that the soft soil condition of saturated liquefiable sand has a profound effect on seismic response of buildings, bridges and other lifeline infrastructure. For detailed evaluation of seismic response three dimensional integrated analysis comprising structure, foundation and soil is required; such an integrated analysis is referred to as Soil Foundation Structure Interaction (SFSI) in literatures. SFSI is a three-dimensional problem because of three primary reasons: first, foundation systems are three-dimensional in form and geometry; second, ground motions are three-dimensional, producing complex multiaxial stresses in soils, foundations and structure; and third, soils in particular are sensitive to complex stress because of heterogeneity of soils leading to a highly anisotropic constitutive behaviour. In literatures the majority of seismic response analyses are limited to plane strain configuration because of lack of adequate constitutive models both for soils and structures, and computational limitation. Such two-dimensional analyses do not represent a complete view of the problem for the three reasons noted above. In this context, the present research aims to develop a three-dimensional mathematical formulation of an existing plane-strain elasto-plastic constitutive model of sand developed by Cubrinovski and Ishihara (1998b). This model has been specially formulated to simulate liquefaction behaviour of sand under ground motion induced earthquake loading, and has been well-validated and widely implemented in verifcation of shake table and centrifuge tests, as well as conventional ground response analysis and evaluation of case histories. The approach adopted herein is based entirely on the mathematical theory of plasticity and utilises some unique features of the bounding surface plasticity formalised by Dafalias (1986). The principal constitutive parameters, equations, assumptions and empiricism of the existing plane-strain model are adopted in their exact form in the three-dimensional version. Therefore, the original two-dimensional model can be considered as a true subset of the three-dimensional form; the original model can be retrieved when the tensorial quantities of the three dimensional version are reduced to that of the plane-strain configuration. Anisotropic Drucker-Prager type failure surface has been adopted for the three-dimensional version to accommodate triaxial stress path. Accordingly, a new mixed hardening rule based on Mroz’s approach of homogeneous surfaces (Mroz, 1967) has been introduced for the virgin loading surface. The three-dimensional version is validated against experimental data for cyclic torsional and triaxial stress paths.