L. Martha - Academia.edu (original) (raw)

Papers by L. Martha

MATEC web of conferences, 2019

Engineering problems that involve fatigue crack growth and fracture frequently can be studied by ... more Engineering problems that involve fatigue crack growth and fracture frequently can be studied by taking into account only mode-I features. However, many important problems that involve combined mode I and II loadings cannot be properly analyzed by a pure mode-I approach, which in particular may not be sufficient to estimate fracture toughness for practical purposes in such cases. Such mixed-mode problems involve crack orientation and/or load conditions that lead to combined local Stress Intensity Factors (SIFs) K I /K II around the crack front. Using multiaxial crack tip condition characterized by the crack inclination angle in a mixed-mode K I /K II modified single edge tension SE(T) specimen, such mixed-mode effects on plastic zone shapes, volumes and plastic work U PL are taken into account to evaluate problems that involve fatigue and fracture.

... Nevertheless, it is worth to use an alternative approach to confirm it, as follows. 60 Page 6... more ... Nevertheless, it is worth to use an alternative approach to confirm it, as follows. 60 Page 66. Z Castro et aIii, Forni eIi Sopra (UD), Itan/, Maren 7-9, Z077," ISBN 978-88-95940-35-9 PLASTIC ZONES ESTIMATED USING THE WESTERGAARD STRESS FUNCTION field [] But since ...

Mecánica Computacional, 2010

This work proposes a methodology, using plugins resources, for configuration of finite element si... more This work proposes a methodology, using plugins resources, for configuration of finite element simulation attributes in geometric modeling. The attributes are necessary additional information for the complete definition of a finite element model, as they constitute specific characterizations of the simulations. The configuration of these attributes allows a relatively simple extension of a given geometric modeler, so that it may be used in other types of finite element simulations. With the plugin methodology, it is possible incorporate to the modeler specific resources that were not initially considered. The strategy adopted in this work consists of using the plugin resource to link, through an interface, a geometric modeler to a library of classes of the module that manages simulation attributes. A simple example is presented to illustrate the proposed methodology.

Proceedings of the 25th International Congress of Mechanical Engineering, 2019

Proceedings of the Sixth International Conference on Computational Structures Technology

This work presents a probabilistic crack approach based on the Monte Carlo method, implemented in... more This work presents a probabilistic crack approach based on the Monte Carlo method, implemented in a 3D fully parallelized finite element code (Paz, [1]). The cracking scheme used is the discrete crack approach. In this approach the heterogeneity of the material is taken into account by considering the properties to vary spatially following a normal distribution determined by the mean and the standard deviation of the considered material properties. Fracturing is modeled by 3D interface elements generated in a previously defined region within the mesh (Paz [1]). The interface elements are triangular base prisms connecting adjacent faces of neighboring tetrahedra. These elements simulate crack opening through relative displacements between the triangular faces.

Revista Interdisciplinar de Pesquisa em Engenharia - RIPE, Feb 8, 2017

Resumo. Este artigo tem como objetivo analisar o comportamento do campo de deslocamentos e de ten... more Resumo. Este artigo tem como objetivo analisar o comportamento do campo de deslocamentos e de tensões em frentes de trincas, a partir de investigações numéricas e comparações com resultados disponíveis na literatura. Para avaliar os efeitos tridimensionais do estado de tensões nas frentes da trinca, dois estudos numéricos utilizando o método dos elementos finitos tridimensional são realizados. O método dos elementos finitos é largamente usado em problemas de mecânica da fratura. Entretanto, as malhas de volume geradas para discretizar o domínio do modelo tridimensional nem sempre é uma tarefa simples, além de sua forma influenciar nos resultados das simulações. Neste trabalho, após estudo do refinamento da malha de domínio, avalia-se os deslocamentos em uma análise linear-elástica e uma análise com comportamento elasto-plástico do material. Como o comportamento do material é estudado com abordagens diferentes, compara-se a eficiência de ambos os métodos em problemas da mecânica da fratura. As comparações são baseadas na avaliação dos deslocamentos na frente da trinca. Os resultados numéricos obtidos são confrontados com os resultados da literatura.

Brazilian Journal of Development

This article aims to present a strategy for multi-objective optimization based on torque distribu... more This article aims to present a strategy for multi-objective optimization based on torque distribution for electrical 4WD (four-wheel drive) vehicles. By considering applications on uneven terrain, common to the navigation of tractors, off-road vehicles, or even mobile robots, an algorithm is developed having as input the vehicle attitude and output the controlled torque on each actuated wheel. The main criterion adopted is to guarantee the execution of a stable trajectory. And, to avoid wheel slippage, which occurs when low torques are applied, as well as vehicle rollover, which can occur in the presence of high torques, it is necessary to use two objective functions. To find the Pareto optimal solutions, the simplified dynamic model of a vehicle is adopted, considering a quasi-static motion. For each vehicle, its electrical, mechanical, and geometric characteristics can be used as formulation constraints. From an optimization performed offline, and adopting a polynomial approximati...

A reliable and cost effective two-phase methodology is proposed to predict crack propagation in g... more A reliable and cost effective two-phase methodology is proposed to predict crack propagation in generic two-dimensional structural components under complex fatigue loading. First, the fatigue crack path and its stress intensity factors are calculated in a specialized finite element software, using small crack increments. At each crack propagation step, the mesh is automatically redefined based on a self-adaptive strategy that takes into account the estimation of the stress analysis numerical errors of the previous step. Numerical methods are used to calculate the crack propagation path, based on the computation of the crack incremental direction, and the stress-intensity factors KI and KII, from the finite element response. An application example presents a comparison between numerical simulation results and those measured in physical experiments. Then, an analytical expression is adjusted to the calculated KI(a) values, where a is the length along the crack path. This KI(a) express...

Abstract. Teaching of applied computer graphics is of great importance in computational simulatio... more Abstract. Teaching of applied computer graphics is of great importance in computational simulation of engineering problems. Currently, many user-friendly computer softwares have improved this work, as it is the case with MATLAB. The generation and manipulation of a geometric model are very important steps in the computational simulation. The use of the mouse allows these steps to become more interactive and easy to understand. For this reason, in this work a generic class is developed in the context of object-oriented programming in the MATLAB environment, which allows managing mouse events in a canvas. The objective of this OOP class is to be used as a base class in the development of graphics and interactive apps in MATLAB, mainly for educational purposes. To meet these expectations, the OOP was adopted, which enables the creation of reusable codes. Allied to this technique, the Unified Modeling Language is used, a graphic language that allows the visualization, construction and d...

Fatigue crack kinking and bifurcation are well-known phenomena capable of inducing significant gr... more Fatigue crack kinking and bifurcation are well-known phenomena capable of inducing significant growth retardation or even crack arrest. However, symmetrically bifurcated crack models available in the literature cannot account for the propagation behavior observed in practice. In this work, specialized Finite Element (FE) and life assessment software are used to predict the reduction in the propagation rates in asymmetrically bifurcated cracks. The crack path and the associated stress intensity factors (SIF) of asymmetrically bifurcated cracks are numerically obtained for several bifurcation angles. A companion life assessment program is used to estimate the number of delay cycles associated with crack bifurcation, allowing for a better understanding of the influence of crack deflection in the propagation life of structural components.

Fatigue crack kinking and bifurcation are phenomena capable of inducing significant growth retard... more Fatigue crack kinking and bifurcation are phenomena capable of inducing significant growth retardation or even crack arrest. However, bifurcated crack models available in the literature cannot account for the subsequent propagation behavior observed in practice. In this work, specialized Finite Element (FE) and life assessment software are used to predict the reduction in the propagation rates in kinked and bifurcated cracks. The crack path and associated stress intensity factors (SIF) of bifurcated cracks are numerically obtained for several bifurcation angles and branch lengths. From these results, empirical crack retardation equations are proposed to model the retardation factor along the crack path, allowing for a better understanding of the influence of crack deflection in the propagation life.

This work presents an interactive graphics computational tool for the verification of prestressed... more This work presents an interactive graphics computational tool for the verification of prestressed concrete beams with post-tensioned bonded tendons to the serviceability limit state (SLS) stress check according to the Brazilian code NBR 6118. The software Autodesk Robot Structural Analysis Professional® is adopted as a structural modeling platform. With data supplied by the user through a graphics user interface, the program calculates the prestressing’s equivalent load considering all relevant prestress losses that occur throughout the structure's life-cycle. In order to adopt an incremental method for the calculation of the differed losses, modifications had to be done to the equations given in the NBR 6118. Examples and results are also presented, validating the adopted methodology. At the end of the software's calculation, the user receives two outputs: the prestress’ equivalent loads in the Robot model and a spreadsheet. The equivalent loads may be used in other calcula...

Revista IBRACON de Estruturas e Materiais, 2015

This work presents an interactive graphics computational tool for the verification of prestressed... more This work presents an interactive graphics computational tool for the verification of prestressed concrete beams with post-tensioned bonded tendons to the serviceability limit state (SLS) stress check according to the Brazilian code NBR 6118:2014. The tool is an add-in for Autodesk Robot Structural Analysis Professional(r), which serves as a structural modeling platform. With data supplied by the user through a graphics user interface, the program here developed calculates all relevant prestress losses that occur throughout the structure's life-cycle, along with the prestress' equivalent loads during this period. The traditional calculation methods, obtained in the NBR 6118, are presented along with the modifications which had to be implemented in order to allow for incremental loss calculations. Usage examples and results are presented, validating the adopted methodology. At the end of the software's calculation, the user receives two outputs: the prestress' equival...

This work describes an automatic algorithm for unstructured mesh regeneration on arbitrarily shap... more This work describes an automatic algorithm for unstructured mesh regeneration on arbitrarily shaped three-dimensional surfaces. The arbitrary surface may be: a triangulated mesh, a set of points, or an analytical surface (such as a collection of NURBS patches). To be generic, the algorithm requires the implementation of three abstract methods. The first, given a point location, returns the desired characteristic size of a triangular element at this position. The second method, given the current edge in the boundary contraction algorithm, locates the ideal apex point that forms a triangle with this edge. And the third method, given a point in space and a projection direction, returns the closest point on the geometrical supporting surface. This work also describes the implementation of these three methods to re-mesh an existing triangulated mesh that might present regions of high curvature. In order to test the efficiency of the proposed algorithm of surface mesh generation and implementation of the three abstract methods, results of performance and quality of generated triangular element examples are presented..

Este trabalho apresenta quatro modelos que consideram o efeito do encruamento no tamanho e na for... more Este trabalho apresenta quatro modelos que consideram o efeito do encruamento no tamanho e na forma de zonas plasticas a frente de trincas. Duas dessas formulacoes sao baseadas na ideia de Irwin, que corrige o tamanho da zona plastica apenas na direcao paralela a trinca, por haver tensoes infinitas na sua ponta e tensoes maiores do que a resistencia ao escoamento dentro da zona plastica original. Os outros dois modelos sao propostos com base na formulacao de Rodriguez, que considera a correcao das zonas plasticas em outras direcoes. Rodriguez analisou uma placa infinita e considerou apenas materiais perfeitamente plasticos, mas usou as tensoes derivadas da funcao completa de tensao de Westergaard, em vez daquelas geradas apenas a partir do Fator de Intensidade de Tensao (FIT) para representar o campo de tensao em regioes proximas a ponta da trinca. As zonas plasticas normalizadas obtidas dessa forma simplificada ficam insensiveis a relacao entre a tensao nominal e a resistencia ao e...

This work presents a methodology for adaptive generation of 3D finite element meshes using geomet... more This work presents a methodology for adaptive generation of 3D finite element meshes using geometric modeling with multi-regions and parametric surfaces, considering a geometric model described by curves, surfaces, and volumes. The adaptive strategy adopted in this methodology is based on independent refinements of these entities. From an initial model, new sizes of elements obtained from numerical error analysis and from geometric restrictions are stored in a global background structure, a recursive spatial composition represented by an octree. Based on this background structure, the model curves are initially refined using a binary partition algorithm. The discretization of curves is then used as input for the refinement of adjacent surfaces. The surface discretization also employs the background octree-based refinement, which is coupled to an advancing front technique for the generation of an unstructured triangulation. Surface meshes are finally used as input for the refinement of adjacent volumetric domains. In all stages of the adaptive strategy, the refinement of curves, surface meshes, and solid meshes is based on estimated numerical errors associated with the mesh of the previous step in the adaptive process. In addition, curve and surface refinement takes into account curvature information. An example is presented in order to validate the methodology proposed in this work.

Several finite element adaptive strategies are available for linear-elastic problems. However, fe... more Several finite element adaptive strategies are available for linear-elastic problems. However, few works deal with adaptive analysis of fracture problems 1,2,3,4. This is due mainly to the singularity at crack tips. An efficient adaptive technique must be able to localize singularity regions, in addition to correctly define element sizes in these regions. The way the singularity is treated differs from author to author. Some 2,4 incorporate the intensity of the singularity in the computation of the characteristic size of elements adjacent to the singularity region, while others 3 clain that this is not necessary. In addition, in fracture problems, elements at the crack tip need to be sufficiently small to capture the existing singularity. Therefore, some requirements are imposed to the mesh generation algorithms such as to provide good mesh transition between regions of different element sizes and to avoid bad shaped elements at the crack tip. Previous work of the authors proposed mesh generation techniques for two-dimensional models with cracks 5. This work describes the adopted adaptive strategy for linear-elastic fracture problems. This strategy is based on a type "h" refinement, with an 'a posteriori' error estimator, which is based on an energy norm 4. To evaluate the proposed strategy, examples of numerical computation of fracture parameters are presented.

Proceeding of the …, 2000

The finite element method has been largely used to analyze mechanical problems and, in particular... more The finite element method has been largely used to analyze mechanical problems and, in particular, to obtain the response of cracked structures. One of the major issues in using the method is mesh generation. Nowadays, several automatic mesh generation algorithms are available for two-dimensional models. Crack analysis imposes severe requirements on automatic mesh generation. It is not uncommon that elements near the cracktip be two orders of magnitude smaller than other elements in the model. Meshing algorithms must be able to provide good size transition capabilities. Previous works of the authors have proposed techniques for automatic, self-adaptive mesh generation of two-dimensional cracked models 1. This work describes the numerical procedures that were developed to numerically estimate fracture parameters both in linear-elastic and elastic-plastic analysis. The article describes three methods to evaluate fracture parameters: Displacement Correlation Technique 2 , Modified Crack Closure Method 3 , and J-integral evaluation accomplished by means of Equivalent Domain Integrals 4. The latter method is also used to evaluate fracture parameters in elastic-plastic analysis. In the mesh generation procedure, special elements with well-formed shape are placed at the crack-tips. For linear-elastic analysis, quarter-point triangular elements are used, forming a rosette of elements with angles of 45°, 40°, or 30°. In elastic-plastic analysis, collapsed Q8 elements are used in the standard rosette. The von Mises yield criterion, with isotropic hardening, is used in the plastic analysis. Some examples are presented to compare the results with analytical and other available numerical results.

tecgraf.puc-rio.br

In recent years several strategies for self-adaptive linear-elastic finite element analysis have ... more In recent years several strategies for self-adaptive linear-elastic finite element analysis have been developed. These methodologies will be available in a near future for the end user in commercial finite element codes. However, adaptive analysis for non-linear plasticity problems is still an on going research effort. This work presents a methodology for self-adaptive analysis of two-dimensional elastic-plastic structures. The self-adaptive process is based on an h-type refinement, with 'a posteriori' error estimation. Two types of error estimators are available. The first is based on effective stress 1 and the second is based on a ratio of plastic work 2. Automatic mesh generation is based on spatial decomposition techniques: binary recursive partition for the refinement of boundary and crack-line curves, and quadtree partition for mesh generation in the model interior. The 'a priori' refinement of the curves has the advantage of generating good transition meshes at boundary regions 3. The system integrates different tools: a geometric modeler to create the model geometry, a preprocessor for mesh generation and attribute assignment, a numerical analysis module to evaluate the finite element response, and a module to manage the self-adaptive procedures. This latter module also incorporates post-processor features for model and response visualization 4. In the non-linear adaptive process for incremental plasticity analysis, a technique for interpolating analysis variables across distinct meshes 5 is used. The von Mises yielding criterion, with isotropic hardening, is adopted. Some examples are presented to evaluate the performance of the adaptive process.

Discretization Methods in Structural Mechanics, 1990

ABSTRACT

MATEC web of conferences, 2019

Engineering problems that involve fatigue crack growth and fracture frequently can be studied by ... more Engineering problems that involve fatigue crack growth and fracture frequently can be studied by taking into account only mode-I features. However, many important problems that involve combined mode I and II loadings cannot be properly analyzed by a pure mode-I approach, which in particular may not be sufficient to estimate fracture toughness for practical purposes in such cases. Such mixed-mode problems involve crack orientation and/or load conditions that lead to combined local Stress Intensity Factors (SIFs) K I /K II around the crack front. Using multiaxial crack tip condition characterized by the crack inclination angle in a mixed-mode K I /K II modified single edge tension SE(T) specimen, such mixed-mode effects on plastic zone shapes, volumes and plastic work U PL are taken into account to evaluate problems that involve fatigue and fracture.

... Nevertheless, it is worth to use an alternative approach to confirm it, as follows. 60 Page 6... more ... Nevertheless, it is worth to use an alternative approach to confirm it, as follows. 60 Page 66. Z Castro et aIii, Forni eIi Sopra (UD), Itan/, Maren 7-9, Z077," ISBN 978-88-95940-35-9 PLASTIC ZONES ESTIMATED USING THE WESTERGAARD STRESS FUNCTION field [] But since ...

Mecánica Computacional, 2010

This work proposes a methodology, using plugins resources, for configuration of finite element si... more This work proposes a methodology, using plugins resources, for configuration of finite element simulation attributes in geometric modeling. The attributes are necessary additional information for the complete definition of a finite element model, as they constitute specific characterizations of the simulations. The configuration of these attributes allows a relatively simple extension of a given geometric modeler, so that it may be used in other types of finite element simulations. With the plugin methodology, it is possible incorporate to the modeler specific resources that were not initially considered. The strategy adopted in this work consists of using the plugin resource to link, through an interface, a geometric modeler to a library of classes of the module that manages simulation attributes. A simple example is presented to illustrate the proposed methodology.

Proceedings of the 25th International Congress of Mechanical Engineering, 2019

Proceedings of the Sixth International Conference on Computational Structures Technology

This work presents a probabilistic crack approach based on the Monte Carlo method, implemented in... more This work presents a probabilistic crack approach based on the Monte Carlo method, implemented in a 3D fully parallelized finite element code (Paz, [1]). The cracking scheme used is the discrete crack approach. In this approach the heterogeneity of the material is taken into account by considering the properties to vary spatially following a normal distribution determined by the mean and the standard deviation of the considered material properties. Fracturing is modeled by 3D interface elements generated in a previously defined region within the mesh (Paz [1]). The interface elements are triangular base prisms connecting adjacent faces of neighboring tetrahedra. These elements simulate crack opening through relative displacements between the triangular faces.

Revista Interdisciplinar de Pesquisa em Engenharia - RIPE, Feb 8, 2017

Resumo. Este artigo tem como objetivo analisar o comportamento do campo de deslocamentos e de ten... more Resumo. Este artigo tem como objetivo analisar o comportamento do campo de deslocamentos e de tensões em frentes de trincas, a partir de investigações numéricas e comparações com resultados disponíveis na literatura. Para avaliar os efeitos tridimensionais do estado de tensões nas frentes da trinca, dois estudos numéricos utilizando o método dos elementos finitos tridimensional são realizados. O método dos elementos finitos é largamente usado em problemas de mecânica da fratura. Entretanto, as malhas de volume geradas para discretizar o domínio do modelo tridimensional nem sempre é uma tarefa simples, além de sua forma influenciar nos resultados das simulações. Neste trabalho, após estudo do refinamento da malha de domínio, avalia-se os deslocamentos em uma análise linear-elástica e uma análise com comportamento elasto-plástico do material. Como o comportamento do material é estudado com abordagens diferentes, compara-se a eficiência de ambos os métodos em problemas da mecânica da fratura. As comparações são baseadas na avaliação dos deslocamentos na frente da trinca. Os resultados numéricos obtidos são confrontados com os resultados da literatura.

Brazilian Journal of Development

This article aims to present a strategy for multi-objective optimization based on torque distribu... more This article aims to present a strategy for multi-objective optimization based on torque distribution for electrical 4WD (four-wheel drive) vehicles. By considering applications on uneven terrain, common to the navigation of tractors, off-road vehicles, or even mobile robots, an algorithm is developed having as input the vehicle attitude and output the controlled torque on each actuated wheel. The main criterion adopted is to guarantee the execution of a stable trajectory. And, to avoid wheel slippage, which occurs when low torques are applied, as well as vehicle rollover, which can occur in the presence of high torques, it is necessary to use two objective functions. To find the Pareto optimal solutions, the simplified dynamic model of a vehicle is adopted, considering a quasi-static motion. For each vehicle, its electrical, mechanical, and geometric characteristics can be used as formulation constraints. From an optimization performed offline, and adopting a polynomial approximati...

A reliable and cost effective two-phase methodology is proposed to predict crack propagation in g... more A reliable and cost effective two-phase methodology is proposed to predict crack propagation in generic two-dimensional structural components under complex fatigue loading. First, the fatigue crack path and its stress intensity factors are calculated in a specialized finite element software, using small crack increments. At each crack propagation step, the mesh is automatically redefined based on a self-adaptive strategy that takes into account the estimation of the stress analysis numerical errors of the previous step. Numerical methods are used to calculate the crack propagation path, based on the computation of the crack incremental direction, and the stress-intensity factors KI and KII, from the finite element response. An application example presents a comparison between numerical simulation results and those measured in physical experiments. Then, an analytical expression is adjusted to the calculated KI(a) values, where a is the length along the crack path. This KI(a) express...

Abstract. Teaching of applied computer graphics is of great importance in computational simulatio... more Abstract. Teaching of applied computer graphics is of great importance in computational simulation of engineering problems. Currently, many user-friendly computer softwares have improved this work, as it is the case with MATLAB. The generation and manipulation of a geometric model are very important steps in the computational simulation. The use of the mouse allows these steps to become more interactive and easy to understand. For this reason, in this work a generic class is developed in the context of object-oriented programming in the MATLAB environment, which allows managing mouse events in a canvas. The objective of this OOP class is to be used as a base class in the development of graphics and interactive apps in MATLAB, mainly for educational purposes. To meet these expectations, the OOP was adopted, which enables the creation of reusable codes. Allied to this technique, the Unified Modeling Language is used, a graphic language that allows the visualization, construction and d...

Fatigue crack kinking and bifurcation are well-known phenomena capable of inducing significant gr... more Fatigue crack kinking and bifurcation are well-known phenomena capable of inducing significant growth retardation or even crack arrest. However, symmetrically bifurcated crack models available in the literature cannot account for the propagation behavior observed in practice. In this work, specialized Finite Element (FE) and life assessment software are used to predict the reduction in the propagation rates in asymmetrically bifurcated cracks. The crack path and the associated stress intensity factors (SIF) of asymmetrically bifurcated cracks are numerically obtained for several bifurcation angles. A companion life assessment program is used to estimate the number of delay cycles associated with crack bifurcation, allowing for a better understanding of the influence of crack deflection in the propagation life of structural components.

Fatigue crack kinking and bifurcation are phenomena capable of inducing significant growth retard... more Fatigue crack kinking and bifurcation are phenomena capable of inducing significant growth retardation or even crack arrest. However, bifurcated crack models available in the literature cannot account for the subsequent propagation behavior observed in practice. In this work, specialized Finite Element (FE) and life assessment software are used to predict the reduction in the propagation rates in kinked and bifurcated cracks. The crack path and associated stress intensity factors (SIF) of bifurcated cracks are numerically obtained for several bifurcation angles and branch lengths. From these results, empirical crack retardation equations are proposed to model the retardation factor along the crack path, allowing for a better understanding of the influence of crack deflection in the propagation life.

This work presents an interactive graphics computational tool for the verification of prestressed... more This work presents an interactive graphics computational tool for the verification of prestressed concrete beams with post-tensioned bonded tendons to the serviceability limit state (SLS) stress check according to the Brazilian code NBR 6118. The software Autodesk Robot Structural Analysis Professional® is adopted as a structural modeling platform. With data supplied by the user through a graphics user interface, the program calculates the prestressing’s equivalent load considering all relevant prestress losses that occur throughout the structure's life-cycle. In order to adopt an incremental method for the calculation of the differed losses, modifications had to be done to the equations given in the NBR 6118. Examples and results are also presented, validating the adopted methodology. At the end of the software's calculation, the user receives two outputs: the prestress’ equivalent loads in the Robot model and a spreadsheet. The equivalent loads may be used in other calcula...

Revista IBRACON de Estruturas e Materiais, 2015

This work presents an interactive graphics computational tool for the verification of prestressed... more This work presents an interactive graphics computational tool for the verification of prestressed concrete beams with post-tensioned bonded tendons to the serviceability limit state (SLS) stress check according to the Brazilian code NBR 6118:2014. The tool is an add-in for Autodesk Robot Structural Analysis Professional(r), which serves as a structural modeling platform. With data supplied by the user through a graphics user interface, the program here developed calculates all relevant prestress losses that occur throughout the structure's life-cycle, along with the prestress' equivalent loads during this period. The traditional calculation methods, obtained in the NBR 6118, are presented along with the modifications which had to be implemented in order to allow for incremental loss calculations. Usage examples and results are presented, validating the adopted methodology. At the end of the software's calculation, the user receives two outputs: the prestress' equival...

This work describes an automatic algorithm for unstructured mesh regeneration on arbitrarily shap... more This work describes an automatic algorithm for unstructured mesh regeneration on arbitrarily shaped three-dimensional surfaces. The arbitrary surface may be: a triangulated mesh, a set of points, or an analytical surface (such as a collection of NURBS patches). To be generic, the algorithm requires the implementation of three abstract methods. The first, given a point location, returns the desired characteristic size of a triangular element at this position. The second method, given the current edge in the boundary contraction algorithm, locates the ideal apex point that forms a triangle with this edge. And the third method, given a point in space and a projection direction, returns the closest point on the geometrical supporting surface. This work also describes the implementation of these three methods to re-mesh an existing triangulated mesh that might present regions of high curvature. In order to test the efficiency of the proposed algorithm of surface mesh generation and implementation of the three abstract methods, results of performance and quality of generated triangular element examples are presented..

Este trabalho apresenta quatro modelos que consideram o efeito do encruamento no tamanho e na for... more Este trabalho apresenta quatro modelos que consideram o efeito do encruamento no tamanho e na forma de zonas plasticas a frente de trincas. Duas dessas formulacoes sao baseadas na ideia de Irwin, que corrige o tamanho da zona plastica apenas na direcao paralela a trinca, por haver tensoes infinitas na sua ponta e tensoes maiores do que a resistencia ao escoamento dentro da zona plastica original. Os outros dois modelos sao propostos com base na formulacao de Rodriguez, que considera a correcao das zonas plasticas em outras direcoes. Rodriguez analisou uma placa infinita e considerou apenas materiais perfeitamente plasticos, mas usou as tensoes derivadas da funcao completa de tensao de Westergaard, em vez daquelas geradas apenas a partir do Fator de Intensidade de Tensao (FIT) para representar o campo de tensao em regioes proximas a ponta da trinca. As zonas plasticas normalizadas obtidas dessa forma simplificada ficam insensiveis a relacao entre a tensao nominal e a resistencia ao e...

This work presents a methodology for adaptive generation of 3D finite element meshes using geomet... more This work presents a methodology for adaptive generation of 3D finite element meshes using geometric modeling with multi-regions and parametric surfaces, considering a geometric model described by curves, surfaces, and volumes. The adaptive strategy adopted in this methodology is based on independent refinements of these entities. From an initial model, new sizes of elements obtained from numerical error analysis and from geometric restrictions are stored in a global background structure, a recursive spatial composition represented by an octree. Based on this background structure, the model curves are initially refined using a binary partition algorithm. The discretization of curves is then used as input for the refinement of adjacent surfaces. The surface discretization also employs the background octree-based refinement, which is coupled to an advancing front technique for the generation of an unstructured triangulation. Surface meshes are finally used as input for the refinement of adjacent volumetric domains. In all stages of the adaptive strategy, the refinement of curves, surface meshes, and solid meshes is based on estimated numerical errors associated with the mesh of the previous step in the adaptive process. In addition, curve and surface refinement takes into account curvature information. An example is presented in order to validate the methodology proposed in this work.

Several finite element adaptive strategies are available for linear-elastic problems. However, fe... more Several finite element adaptive strategies are available for linear-elastic problems. However, few works deal with adaptive analysis of fracture problems 1,2,3,4. This is due mainly to the singularity at crack tips. An efficient adaptive technique must be able to localize singularity regions, in addition to correctly define element sizes in these regions. The way the singularity is treated differs from author to author. Some 2,4 incorporate the intensity of the singularity in the computation of the characteristic size of elements adjacent to the singularity region, while others 3 clain that this is not necessary. In addition, in fracture problems, elements at the crack tip need to be sufficiently small to capture the existing singularity. Therefore, some requirements are imposed to the mesh generation algorithms such as to provide good mesh transition between regions of different element sizes and to avoid bad shaped elements at the crack tip. Previous work of the authors proposed mesh generation techniques for two-dimensional models with cracks 5. This work describes the adopted adaptive strategy for linear-elastic fracture problems. This strategy is based on a type "h" refinement, with an 'a posteriori' error estimator, which is based on an energy norm 4. To evaluate the proposed strategy, examples of numerical computation of fracture parameters are presented.

Proceeding of the …, 2000

The finite element method has been largely used to analyze mechanical problems and, in particular... more The finite element method has been largely used to analyze mechanical problems and, in particular, to obtain the response of cracked structures. One of the major issues in using the method is mesh generation. Nowadays, several automatic mesh generation algorithms are available for two-dimensional models. Crack analysis imposes severe requirements on automatic mesh generation. It is not uncommon that elements near the cracktip be two orders of magnitude smaller than other elements in the model. Meshing algorithms must be able to provide good size transition capabilities. Previous works of the authors have proposed techniques for automatic, self-adaptive mesh generation of two-dimensional cracked models 1. This work describes the numerical procedures that were developed to numerically estimate fracture parameters both in linear-elastic and elastic-plastic analysis. The article describes three methods to evaluate fracture parameters: Displacement Correlation Technique 2 , Modified Crack Closure Method 3 , and J-integral evaluation accomplished by means of Equivalent Domain Integrals 4. The latter method is also used to evaluate fracture parameters in elastic-plastic analysis. In the mesh generation procedure, special elements with well-formed shape are placed at the crack-tips. For linear-elastic analysis, quarter-point triangular elements are used, forming a rosette of elements with angles of 45°, 40°, or 30°. In elastic-plastic analysis, collapsed Q8 elements are used in the standard rosette. The von Mises yield criterion, with isotropic hardening, is used in the plastic analysis. Some examples are presented to compare the results with analytical and other available numerical results.

tecgraf.puc-rio.br

In recent years several strategies for self-adaptive linear-elastic finite element analysis have ... more In recent years several strategies for self-adaptive linear-elastic finite element analysis have been developed. These methodologies will be available in a near future for the end user in commercial finite element codes. However, adaptive analysis for non-linear plasticity problems is still an on going research effort. This work presents a methodology for self-adaptive analysis of two-dimensional elastic-plastic structures. The self-adaptive process is based on an h-type refinement, with 'a posteriori' error estimation. Two types of error estimators are available. The first is based on effective stress 1 and the second is based on a ratio of plastic work 2. Automatic mesh generation is based on spatial decomposition techniques: binary recursive partition for the refinement of boundary and crack-line curves, and quadtree partition for mesh generation in the model interior. The 'a priori' refinement of the curves has the advantage of generating good transition meshes at boundary regions 3. The system integrates different tools: a geometric modeler to create the model geometry, a preprocessor for mesh generation and attribute assignment, a numerical analysis module to evaluate the finite element response, and a module to manage the self-adaptive procedures. This latter module also incorporates post-processor features for model and response visualization 4. In the non-linear adaptive process for incremental plasticity analysis, a technique for interpolating analysis variables across distinct meshes 5 is used. The von Mises yielding criterion, with isotropic hardening, is adopted. Some examples are presented to evaluate the performance of the adaptive process.

Discretization Methods in Structural Mechanics, 1990

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