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Wanlin Guo - One of the best experts on this subject based on the ideXlab platform.
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crack tip opening displacement based description of three dimensional elastic plastic crack border fields
Engineering Fracture Mechanics, 2020Co-Authors: Pengfei Cui, Wanlin GuoAbstract:Abstract Characterization of elastic-plastic crack-tip fields has been great developed in the framework of the classical dominating parameter J-integral, which has a limit of the basic assumptions of small deformation and simple proportional loading. A stable and effective parameter is still a challenge for three-dimensional (3D) elastic-plastic fracture problems. Based on the crack-tip-opening-displacement (CTOD) conception and out-of-plane Stress Constraint factor Tz, a new elastic-plastic Stress intensity factor Kδ-Tz is proposed to dominate the 3D elastic-plastic crack border fields. Detailed 3D finite element simulations are performed for four typical testing specimens, which are the centre-cracked tension specimens, compact specimens, single-edge cracked tension specimens and single-edge-notched bending specimens under three-point bending. It is shown that for specimens with different geometries and thicknesses, Kδ-Tz is proven to be more stable than the classical J-integral via the experiment data and simulation results, in which the maximum change in J-integral can be over 340% while the change in Kδ-Tz is within 7.78%. Good agreements are obtained between the CTOD-based Kδ-Tz description and simulation results for the 3D elastic-plastic crack border Stress fields under all the simulated conditions.
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crack tip opening displacement based description of creep crack border fields in specimens with different geometries and thicknesses
International Journal of Solids and Structures, 2020Co-Authors: Pengfei Cui, Wanlin GuoAbstract:Abstract Creep crack growth is accompanied by strong nonlinear deformation and Stress relaxation. Finding an appropriate parameter to characterize the crack tip fields, as well as the fracture resistance, has long been a challenge. Most previous studies were performed within the framework of the C(t)-integral, which is limited to the assumptions of small deformation and simple proportional loading. By using the crack tip opening displacement (CTOD), we propose a new creep Stress intensity factor Kδ(t)-Tz consisting of the time-dependent CTOD, δ(t) and the out-of-plane Stress Constraint factor Tz to characterize the three-dimensional creep crack tip fields. Four typical specimens, single-edge cracked tension specimens, compact specimens, centre-cracked tension specimens and single-edge-notched bending specimens under three-point bending are comprehensively analysed using the power-law creeping model and three-dimensional finite element analyses. It is found that under both small-scale and large-scale creep conditions, the change in Kδ(t)-Tz along the thickness direction for different specimens is within 8.6%, whereas the change in C(t) can exceed 400%, showing that Kδ(t)-Tz is a stable parameter that governs the creep crack tip fields. With the exception of the centre-cracked tension specimens under large-scale creep conditions, good agreements are obtained between the two-parameter description δ(t)-Tz of crack border Stress fields with the three-dimensional finite element results under small-scale and large-scale creep conditions. These results indicate that the CTOD-based two-parameter description δ(t)-Tz can be taken as the basis of creep fracture criteria.
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the in plane and out of plane Stress Constraint factors and k t tz description of Stress fields near the border of a quarter elliptical corner crack
Fatigue & Fracture of Engineering Materials & Structures, 2007Co-Authors: Junhua Zhao, Wanlin Guo, Chong-min SheAbstract:The elastic T-Stress and Stress intensity factor K for quarter-elliptical corner cracks have been investigated in elastic plates by detailed three-dimensional finite-element calculations. The distributions of normalized K and T-Stress have been obtained along the crack front with aspect ratios (a/c) of 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0, and far-field tension and the effect of Poisson's ratio have also been considered. The normalized K increases and the normalized T-Stress decreases with the increase of Poisson's ratio v. For v = 0.3, the normalized K gradually increases in the range of crack-face angle o≥22.5° and decreases in the range of Φ ≤ 22.5° with the increase of a/c. The normalized T-Stress increases in the beginning and then decreases with increasing 0 except for a/c = 0.2 and a/c = 0.3. By fitting the numerical results with the least squares method, empirical formulae have been given for the convenience of engineering applications. Combining with the corresponding out-of-plane Constraint factor T z , the three-parameter K-T-T z approach has been provided, which can accurately describe the Stress field around the crack front.
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the in plane and out of plane Stress Constraint factors and k t tz description of Stress field near the border of a semi elliptical surface crack
International Journal of Fatigue, 2007Co-Authors: Junhua Zhao, Wanlin Guo, Chong-min SheAbstract:Abstract The elastic T-Stress and Stress intensity factor K for semi-elliptical surface cracks have been investigated in elastic plates by detailed three-dimensional finite element calculations. The distributions of normalized K and T-Stress have been obtained along the crack font with aspect ratios (a/c) of 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0, and far-field tension and the effect of Poisson’s ratio have also been considered. The normalized K increases and the normalized T-Stress decreases with the increase of Poisson’s ratio v. For v = 0.3, the normalized K gradually increases in the range of crack face angle ϕ ⩾ 22.5° and decreases in the range of ϕ ⩽ 22.5° with increasing a/c. When ϕ rises to 90°, the K values tend to maximum for various a/c. The normalized T-Stress increases in the beginning and then decreases with the increase of ϕ except for a/c = 1.0. By fitting the numerical results with the least squares method, empirical formulae have been given for the convenience of engineering applications. Combining with the corresponding out-of-plane Constraint factor Tz, the three-parameter K − T − Tz approach has been provided, which can accurately describe the Stress field around the crack front.
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Theoretical investigation of elastoplastic notch fields under triaxial Stress Constraint
International Journal of Fracture, 2002Co-Authors: Wanlin GuoAbstract:In this paper, an exact elastic-plastic solution has been obtained based on the J2-deformation theory of plasticity for a plate having a circular hole under biaxial tension and triaxial Stress Constraint in linear elastic strain-hardening materials. The theoretical solution shows that a linear elastic solution of the equivalent strain can be used to linear elastic-power hardening plastic situation just by a simple variable replacement. Then a strain equivalent rule (SER) is proposed to predict the elastoplastic notch fields by use of the elastic solution. Validations against theoretical analyses and finite element calculation for various combinations of material properties, triaxial Stress Constraints, load levels show that the SER can be used to predict Stress-strain distributions in the whole plastic zone effectively and conveniently.
Eduardo Alberto Fancello - One of the best experts on this subject based on the ideXlab platform.
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topology optimization with local Stress Constraint based on level set evolution via reaction diffusion
Computer Methods in Applied Mechanics and Engineering, 2016Co-Authors: Hélio Emmendoerfer, Eduardo Alberto FancelloAbstract:Abstract This work focuses the structural topology optimization problem of mass minimization subject to local Stress Constraints. To this aim, two related issues are addressed. The first one is the successful strategy used to define local Stress Constraints by means of an Augmented Lagrangian approach. The second, and main contribution of the present paper, is the use of a reaction–diffusion equation to guide, via evolution of a level set, the design optimization sequence. The advantages of this strategy are twofold: firstly, it allows the creation of new holes during the optimization process, a significant feature for a true topological optimization method. Secondly, reinitialization steps usually found in classical Hamilton–Jacobi based evolution are eliminated with a significant improvement in convergence ease. A set of benchmark examples in two dimensions are presented. Numerical results show the efficiency of the algorithm to create new holes, identify Stress concentrations and to provide stable optimization sequences converging to local minima defined by Stress saturated designs.
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Topology optimization with local Stress Constraint based on level set evolution via reaction–diffusion
Computer Methods in Applied Mechanics and Engineering, 2016Co-Authors: Hélio Emmendoerfer, Eduardo Alberto FancelloAbstract:Abstract This work focuses the structural topology optimization problem of mass minimization subject to local Stress Constraints. To this aim, two related issues are addressed. The first one is the successful strategy used to define local Stress Constraints by means of an Augmented Lagrangian approach. The second, and main contribution of the present paper, is the use of a reaction–diffusion equation to guide, via evolution of a level set, the design optimization sequence. The advantages of this strategy are twofold: firstly, it allows the creation of new holes during the optimization process, a significant feature for a true topological optimization method. Secondly, reinitialization steps usually found in classical Hamilton–Jacobi based evolution are eliminated with a significant improvement in convergence ease. A set of benchmark examples in two dimensions are presented. Numerical results show the efficiency of the algorithm to create new holes, identify Stress concentrations and to provide stable optimization sequences converging to local minima defined by Stress saturated designs.
Andre Teofilo Beck - One of the best experts on this subject based on the ideXlab platform.
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topology optimization of compliant mechanisms considering Stress Constraints manufacturing uncertainty and geometric nonlinearity
Computer Methods in Applied Mechanics and Engineering, 2020Co-Authors: Gustavo Assis Da Silva, Andre Teofilo Beck, Ole SigmundAbstract:Abstract This paper proposes and investigates two formulations to topology optimization of compliant mechanisms considering Stress Constraints, manufacturing uncertainty and geometric nonlinearity. The first formulation extends the maximum output displacement robust approach with Stress Constraints to incorporate the effects of geometric nonlinear behavior during the optimization process. The second formulation relies on the concept of path-generating mechanisms, where not only the final configuration is important, but also the load–displacement equilibrium path. A novel path-generating formulation is thus proposed, not only to achieve the prescribed equilibrium path, but also to take Stress Constraints and manufacturing uncertainty into account during the optimization process. Although both formulations have different goals, the same main techniques are employed: density approach to topology optimization, augmented Lagrangian method to handle the large number of Stress Constraints, three-field robust approach to handle the manufacturing uncertainty, and the energy interpolation scheme to handle convergence issues due to large deformation in void regions. Several numerical examples are addressed to demonstrate applicability of the proposed approaches. The optimized results are post-processed with body-fitted finite element meshes. Obtained results demonstrate that: (1) the proposed nonlinear analysis based maximum output displacement approach is able to provide solutions with good performance in situations of large displacements, with Stress and manufacturing requirements satisfied; (2) the linear analysis based maximum output displacement approach provides optimized topologies that show large Stress Constraint violations and rapidly varying Stress behavior under uniform boundary variation, when these are post-processed with full nonlinear analysis; (3) the proposed path-generating formulation is able to provide solutions that follow the prescribed control points, including Stress robustness.
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Topology optimization of compliant mechanisms with Stress Constraints and manufacturing error robustness
Computer Methods in Applied Mechanics and Engineering, 2019Co-Authors: Gustavo Assis Da Silva, Andre Teofilo Beck, Ole SigmundAbstract:Abstract This work proposes a robust formulation to address the compliant mechanism design problem subject to both Stress Constraints and manufacturing uncertainty. The proposed formulation is an extension of the robust approach for compliant mechanism design based on eroded, intermediate and dilated projections. The novelty in this proposal comes from inclusion of a Stress failure criterion in each projected field, in order to ensure compliant mechanisms that satisfy the Stress failure criterion even in the presence of uniform manufacturing variations. The objective of the optimization problem is the minimization of the maximum displacement at the output port of the mechanism, given eroded, intermediate and dilated designs, subjected to upper and lower volume Constraints and one Stress Constraint per finite element on each of the three projected fields. The objective function is weighted by the volume of the dilated topology, in order to avoid possible numerical instabilities that may occur when the upper volume Constraint is not active. Several examples are solved and the optimized results are post-processed with body-fitted finite element meshes. Numerical results demonstrate that: 1) the proposed Stress-constrained robust approach provides results in which both maximum Stress and output displacements are robust with respect to uniform boundary variations; however, while the maximum Stress is almost insensitive to manufacturing variations, the output displacement does show some degradation when compared with the traditional robust approach; 2) the traditional robust approach, i.e., without the Stress considerations, provides results in which the maximum Stress has unpredictable and non-smooth behavior after uniform boundary variation; and 3) the Stress-constrained deterministic approach, i.e., without considering the manufacturing uncertainty, provides results in which both maximum Stress and output displacements are non-robust with respect to uniform boundary variations.
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Reliability-based topology optimization of continuum structures subject to local Stress Constraints
Structural and Multidisciplinary Optimization, 2018Co-Authors: Gustavo Assis Da Silva, Andre Teofilo BeckAbstract:Topology optimization of continuum structures is a challenging problem to solve, when Stress Constraints are considered for every finite element in the mesh. Difficulties are compounding in the reliability-based formulation, since a probabilistic problem needs to be solved for each Stress Constraint. This paper proposes a methodology to solve reliability-based topology optimization problems of continuum domains with Stress Constraints and uncertainties in magnitude of applied loads considering the whole set of local Stress constrains, without using aggregation techniques. Probabilistic Constraints are handled via a first-order approach, where the principle of superposition is used to alleviate the computational burden associated with inner optimization problems. Augmented Lagrangian method is used to solve the outer problem, where all Stress Constraints are included in the augmented Lagrangian function; hence sensitivity analysis may be performed only for the augmented Lagrangian function, instead of for each Stress Constraint. Two example problems are addressed, for which crisp black and white topologies are obtained. The proposed methodology is shown to be accurate by checking reliability indices of final topologies with Monte Carlo Simulation.
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Topology optimization of continuum structures with Stress Constraints and uncertainties in loading
International Journal for Numerical Methods in Engineering, 2017Co-Authors: G. A. Da Silva, Andre Teofilo Beck, Eduardo CardosoAbstract:Summary Topology optimization using Stress Constraints and considering uncertainties is a serious challenge, since a reliability problem has to be solved for each Stress Constraint, for each element in the mesh. In this paper, an alternative way of solving this problem is employed, where uncertainty quantification is performed through the first order perturbation approach, with proper validation by Monte Carlo Simulation. Uncertainties are considered in the loading magnitude and direction. The minimum volume problem subjected to local Stress Constraints is formulated as a robust problem, where the Stress Constraints are written as a weighted average between their expected value and standard deviation. The augmented Lagrangian method is used for handling the large set of local Stress Constraints, whereas a gradient based algorithm is used for handling the bounding Constraints. It is shown that even in the presence of small uncertainties in loading direction, different topologies are obtained when compared to a deterministic approach. The effect of correlation between uncertainties in loading magnitude and direction on optimal topologies is also studied, where the main observed result is loss of symmetry in optimal topologies. This article is protected by copyright. All rights reserved.
Hélio Emmendoerfer - One of the best experts on this subject based on the ideXlab platform.
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topology optimization with local Stress Constraint based on level set evolution via reaction diffusion
Computer Methods in Applied Mechanics and Engineering, 2016Co-Authors: Hélio Emmendoerfer, Eduardo Alberto FancelloAbstract:Abstract This work focuses the structural topology optimization problem of mass minimization subject to local Stress Constraints. To this aim, two related issues are addressed. The first one is the successful strategy used to define local Stress Constraints by means of an Augmented Lagrangian approach. The second, and main contribution of the present paper, is the use of a reaction–diffusion equation to guide, via evolution of a level set, the design optimization sequence. The advantages of this strategy are twofold: firstly, it allows the creation of new holes during the optimization process, a significant feature for a true topological optimization method. Secondly, reinitialization steps usually found in classical Hamilton–Jacobi based evolution are eliminated with a significant improvement in convergence ease. A set of benchmark examples in two dimensions are presented. Numerical results show the efficiency of the algorithm to create new holes, identify Stress concentrations and to provide stable optimization sequences converging to local minima defined by Stress saturated designs.
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Topology optimization with local Stress Constraint based on level set evolution via reaction–diffusion
Computer Methods in Applied Mechanics and Engineering, 2016Co-Authors: Hélio Emmendoerfer, Eduardo Alberto FancelloAbstract:Abstract This work focuses the structural topology optimization problem of mass minimization subject to local Stress Constraints. To this aim, two related issues are addressed. The first one is the successful strategy used to define local Stress Constraints by means of an Augmented Lagrangian approach. The second, and main contribution of the present paper, is the use of a reaction–diffusion equation to guide, via evolution of a level set, the design optimization sequence. The advantages of this strategy are twofold: firstly, it allows the creation of new holes during the optimization process, a significant feature for a true topological optimization method. Secondly, reinitialization steps usually found in classical Hamilton–Jacobi based evolution are eliminated with a significant improvement in convergence ease. A set of benchmark examples in two dimensions are presented. Numerical results show the efficiency of the algorithm to create new holes, identify Stress concentrations and to provide stable optimization sequences converging to local minima defined by Stress saturated designs.
Eduardo Cardoso - One of the best experts on this subject based on the ideXlab platform.
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Topology optimization of continuum structures with Stress Constraints and uncertainties in loading
International Journal for Numerical Methods in Engineering, 2017Co-Authors: G. A. Da Silva, Andre Teofilo Beck, Eduardo CardosoAbstract:Summary Topology optimization using Stress Constraints and considering uncertainties is a serious challenge, since a reliability problem has to be solved for each Stress Constraint, for each element in the mesh. In this paper, an alternative way of solving this problem is employed, where uncertainty quantification is performed through the first order perturbation approach, with proper validation by Monte Carlo Simulation. Uncertainties are considered in the loading magnitude and direction. The minimum volume problem subjected to local Stress Constraints is formulated as a robust problem, where the Stress Constraints are written as a weighted average between their expected value and standard deviation. The augmented Lagrangian method is used for handling the large set of local Stress Constraints, whereas a gradient based algorithm is used for handling the bounding Constraints. It is shown that even in the presence of small uncertainties in loading direction, different topologies are obtained when compared to a deterministic approach. The effect of correlation between uncertainties in loading magnitude and direction on optimal topologies is also studied, where the main observed result is loss of symmetry in optimal topologies. This article is protected by copyright. All rights reserved.
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Design of Compliant Mechanisms with Stress Constraints Using Topology Optimization
Optimization of Structures and Components, 2013Co-Authors: Luís Renato Meneghelli, Eduardo CardosoAbstract:Compliant mechanisms are mechanical devices that transform or transfer motion, force or energy through a single part. These mechanisms have important applications in micro electromechanical systems (MEMS) and other systems that require great accuracy in motion and micro scale. The compliant mechanisms design is performed by Topology Optimization Method, and the optimization problem is formulated to maximize strain-energy stored by mechanism, eliminating the appearance of hinges. The kinematic behavior of the mechanism is imposed through a set of Constraints over some displacement degrees of freedom of interest. The elastic behavior of the compliant mechanisms is imposed using a global Stress Constraint and some important issues associated to Stress parametrization are discussed in the realm of mechanism design. The characteristics and the feasibility of this proposal, as well as the influence of parameters related to the formulation, are presented with the aid of some examples.