The Experts below are selected from a list of 94749 Experts worldwide ranked by ideXlab platform
Stefanie Reese - One of the best experts on this subject based on the ideXlab platform.
-
a Reduced Integration based solid shell finite element formulation for gradient extended damage
Computer Methods in Applied Mechanics and Engineering, 2021Co-Authors: Oliver Barfusz, Tim Van Der Velden, Tim Brepols, Hagen Holthusen, Stefanie ReeseAbstract:Abstract The present contribution is concerned with the incorporation of gradient-extended damage into a Reduced Integration-based solid-shell finite element formulation. To this end, a purely mechanical low-order solid-shell element based on the isoparametric concept is combined with a gradient-extended two-surface damage plasticity model. Due to a tailored combination of the assumed natural strain (ANS) as well as the enhanced assumed strain (EAS) method, the most important locking phenomena are eliminated. A polynomial approximation of the kinematic as well as the constitutively dependent quantities within the weak forms enables the definition of a suitable hourglass stabilization. In this way, the element stiffness contributions coming from the hourglass stabilization can be determined analytically, since they represent polynomials with respect to Cartesian coordinates. Several numerical examples on elastic as well as elasto-plastic plates and shells under various loading scenarios show the ability of the present methodology to predict various degradation processes such as damage initiation, propagation, merging as well as branching.
-
on the use of Reduced Integration in combination with discontinuous galerkin discretization application to volumetric and shear locking problems
Advanced Modeling and Simulation in Engineering Sciences, 2018Co-Authors: Hamid Reza Bayat, Stephan Wulfinghoff, Steffen Kastian, Stefanie ReeseAbstract:In the present work, the discontinuous Galerkin (DG) method is applied to linear elasticity for two-dimensional and three-dimensional settings. A locking-free element formulation based on Reduced Integration and physically-based hourglass stabilization (Q1SP) is coupled for the first time with the DG framework. The incomplete interior penalty Galerkin method is chosen, being one example of different variations of DG methods. Several 2D and 3D typical benchmark problems of linear elasticity are investigated. A selection of numerical Integration schemes for the boundary terms is presented, namely Reduced and mixed Integration schemes. The treatment of the surface terms by means of different rules of Integration shows a significant influence on the performance of the resulting DG method in combination with the standard Q1 element. This intelligent treatment of the surface part leads to a DG variant with very good convergence properties.
-
on an equivalence between a discontinuous galerkin method and Reduced Integration with hourglass stabilization for finite elasticity
Computer Methods in Applied Mechanics and Engineering, 2017Co-Authors: Stefanie Reese, Hamid Reza Bayat, Stephan WulfinghoffAbstract:Abstract Discontinuous Galerkin methods and methods of Reduced Integration with hourglass stabilization have different points of origin. Whereas the discontinuous Galerkin idea was developed to investigate a wide range of applications, among them problems of electrodynamics, fluid and solid mechanics, the Reduced Integration technology started out from the observation of the so-called locking problem in linear elasticity. Today, the two methodologies are still considered separately from each other although it has already been recognized that discontinuous Galerkin methods can be also used to circumvent locking phenomena in elasticity. The idea of the present contribution is to find a direct equivalence between a discontinuous Galerkin method and a finite element technology based on Reduced Integration with hourglass stabilization. The transfer between the two methods is carried out in the context of finite elasticity. Thus the derivation is valid for arbitrarily large deformations. The main advantage of this analysis is that the choice of the “free” parameter in Nitsche’s method (often also called stabilization parameter) is no longer unclear but prescribed by the connection to the hourglass stabilization. Further important in this context is the replacement of the scalar parameter by a symmetric 2 × 2 matrix (if two-dimensional problems are considered which is here the case). The result of the derivation is a discontinuous Galerkin formulation which shows very good convergence behaviour — not only in the limit of incompressibility but also for bending of thin structures.
-
finite element analysis of layered fiber composite structures accounting for the material s microstructure and delamination
Applied Composite Materials, 2015Co-Authors: Bertram Stier, Jaanwillem Simon, Stefanie ReeseAbstract:The present paper focuses on composite structures which consist of several layers of carbon fiber reinforced plastics (CFRP). For such layered composite structures, delamination constitutes one of the major failure modes. Predicting its initiation is essential for the design of these composites. Evaluating stress-strength relation based onset criteria requires an accurate representation of the through-the-thickness stress distribution, which can be particularly delicate in the case of shell-like structures. Thus, in this paper, a solid-shell finite element formulation is utilized which allows to incorporate a fully three-dimensional material model while still being suitable for applications involving thin structures. Moreover, locking phenomena are cured by using both the EAS and the ANS concept, and numerical efficiency is ensured through Reduced Integration. The proposed anisotropic material model accounts for the material’s micro-structure by using the concept of structural tensors. It is validated by comparison to experimental data as well as by application to numerical examples.
-
numerical analysis of layered fiber composites accounting for the onset of delamination
Advances in Engineering Software, 2015Co-Authors: Jaanwillem Simon, Bertram Stier, Stefanie ReeseAbstract:Since delamination is a major failure mode of layered composites, predicting its initiation is essential for the design of composite structures. Evaluating delamination onset criteria based on stress-strength relations requires an accurate representation of the through-the-thickness stress distribution, which is delicate for thin shell-like structures. Therefore, in this paper, a solid-shell finite element is utilized, which allows for incorporating a fully three-dimensional, anisotropic, micro-mechanically motivated material model, still being suited for application to thin structures. Moreover, locking phenomena are cured by using both the enhanced assumed strain (EAS) and the assumed natural strain (ANS) concept, and numerical efficiency is ensured through Reduced Integration.
Marco Schwarze - One of the best experts on this subject based on the ideXlab platform.
-
a Reduced Integration solid shell finite element based on the eas and the ans concept large deformation problems
International Journal for Numerical Methods in Engineering, 2011Co-Authors: Marco Schwarze, Stefanie ReeseAbstract:In this paper we address the extension of a recently proposed Reduced Integration eight-node solid-shell finite element to large deformations. The element requires only one Integration point within the shell plane and at least two Integration points over the thickness. The possibility to choose arbitrarily many Gauss points over the shell thickness enables a realistic and efficient modeling of the non-linear material behavior. Only one enhanced degree-of-freedom is needed to avoid volumetric and Poisson thickness locking. One key point of the formulation is the Taylor expansion of the inverse Jacobian matrix with respect to the element center leading to a very accurate modeling of arbitrary element shapes. The transverse shear and curvature thickness locking are cured by means of the assumed natural strain concept. Further crucial points are the Taylor expansion of the compatible cartesian strain with respect to the center of the element as well as the Taylor expansion of the second Piola–Kirchhoff stress tensor with respect to the normal through the center of the element. Copyright © 2010 John Wiley & Sons, Ltd.
-
sheet metal forming and springback simulation by means of a new Reduced Integration solid shell finite element technology
Computer Methods in Applied Mechanics and Engineering, 2011Co-Authors: Marco Schwarze, Ivaylo N. Vladimirov, Stefanie ReeseAbstract:Abstract The paper deals with the validation of a recently proposed hexahedral solid-shell finite element in the field of sheet metal forming. Working with one Integration point in the shell plane and an arbitrary number of Integration points in thickness direction, highly non-linear stress states over the sheet thickness can be incorporated in an efficient way. In order to avoid volumetric locking and Poisson thickness locking at the level of Integration points the enhanced assumed strain (EAS) concept with only one EAS degree-of-freedom is implemented. A key point of the formulation is the construction of the hourglass stabilization by means of different Taylor expansions. This leads to the advantage that the sensitivity with respect to mesh distortion is noticeably Reduced. The hourglass stabilization includes the assumed natural strain (ANS) concept and a kind of B-Bar method. So transverse shear locking and volumetric locking are eliminated. The finite element formulation incorporates a finite strain material model for plastic anisotropy as well as non-linear (Armstrong–Frederick type) kinematic and isotropic hardening. In this context the plastic anisotropy can be modeled by representing the yield surface and the plastic flow rule as functions of so-called structural tensors. The Integration of the evolution equations is performed by means of an exponential map exploiting the spectral decomposition. The element formulation and material model have been implemented into the commercial code ABAQUS/Standard by means of the UEL interface for user-defined elements. Using an implicit time Integration scheme numerical results for classical deep drawing simulations as well as springback predictions are presented in comparison to experimental measurements.
-
a Reduced Integration solid shell finite element based on the eas and the ans concept geometrically linear problems
International Journal for Numerical Methods in Engineering, 2009Co-Authors: Marco Schwarze, Stefanie ReeseAbstract:In this paper a new Reduced Integration eight-node solid-shell finite element is presented. The enhanced assumed strain (EAS) concept based on the Hu-Washizu variational principle requires only one EAS degree-of-freedom to cure volumetric and Poisson thickness locking. One key point of the derivation is the Taylor expansion of the inverse Jacobian with respect to the element center, which closely approximates the element shape and allows us to implement the assumed natural strain (ANS) concept to eliminate the curvature thickness and the transverse shear locking. The second crucial point is a combined Taylor expansion of the compatible strain with respect to the center of the element and the normal through the element center leading to an efficient and locking-free hourglass stabilization without rank deficiency. Hence, the element requires only a single Integration point in the shell plane and at least two Integration points in thickness direction. The formulation fulfills both the membrane and the bending patch test exactly, which has, to the authors' knowledge, not yet been achieved for Reduced Integration eight-node solid-shell elements in the literature. Owing to the three-dimensional modeling of the structure, fully three-dimensional matenal models can be implemented without additional assumptions.
U Perego - One of the best experts on this subject based on the ideXlab platform.
-
computationally efficient explicit nonlinear analyses using Reduced Integration based solid shell finite elements
Computer Methods in Applied Mechanics and Engineering, 2014Co-Authors: M Pagani, Stefanie Reese, U PeregoAbstract:Abstract Solid-shell formulations based on Reduced Integration with hourglass stabilization have several advantages. Among these are the smaller number of Gauss points and the direct modelling of the thickness stretch, a feature which is usually not present in standard degenerated shell elements. The latter issue is especially important for applications where contact is involved, e.g. for almost all relevant systems in production technology. Obviously this makes solid-shell formulations very attractive for their use in industrial design. A major disadvantage in the context of explicit analyses is, however, the fact that the critical time step is determined by the thickness of the solid-shell element which is usually smaller than the smallest in-plane dimension. Therefore, four-node shells (where the critical time step is determined by the in-plane dimensions) are still often preferred for explicit analysis. In the present paper we suggest several techniques to overcome this difficulty, also in the case of problems dominated by nonlinearities such as finite deformations, elastoplasticity and contact. Reference is made to an 8-node hexahedron solid-shell element recently proposed by Schwarze and Reese (2011) [32] in an implicit context. First of all, the time steps in explicit analyses are so small that it may be not necessary to update the hourglass stabilization and the implicit computation of the internal element degrees-of-freedom in every time step. Performing the update in only every hundredth step or computing an explicit rather than implicit update can reduce the computational effort up to about 50%. Another important issue is selective mass scaling which means to modify the mass matrix in such a way that the speed of sound in thickness direction is Reduced. This enables the choice of a larger time step. The CPU effort can be finally noticeably decreased without changing the structural response significantly. This makes the presently used solid-shell formulation competitive to four-node shells, also for explicit analysis.
-
an explicit dynamics approach to the simulation of crack propagation in thin shells using Reduced Integration solid shell elements
10th World Congress on Computational Mechanics, 2012Co-Authors: M Pagani, U PeregoAbstract:Fracture propagation in laminated shell structures, due to impact or cutting, is a highly nonlinear problem which is more conveniently simulated using explicit finite element approaches. Solid-shell elements are better suited for the discretization in the presence of complex material behavior and delamination, since they allow for a correct representation of the through the thickness stress. In the presence of cutting problems with sharp blades, classi- cal crack-propagation approaches based on cohesive interfaces may prove inadequate. New "directional" cohesive interface elements are here proposed to account for the interaction with the cutter edge. The element small thickness leads to very high eigenfrequencies, which imply overly small stable time-steps. A new selective mass scaling technique is here proposed to increase the time-step without affecting accuracy.
M Pagani - One of the best experts on this subject based on the ideXlab platform.
-
computationally efficient explicit nonlinear analyses using Reduced Integration based solid shell finite elements
Computer Methods in Applied Mechanics and Engineering, 2014Co-Authors: M Pagani, Stefanie Reese, U PeregoAbstract:Abstract Solid-shell formulations based on Reduced Integration with hourglass stabilization have several advantages. Among these are the smaller number of Gauss points and the direct modelling of the thickness stretch, a feature which is usually not present in standard degenerated shell elements. The latter issue is especially important for applications where contact is involved, e.g. for almost all relevant systems in production technology. Obviously this makes solid-shell formulations very attractive for their use in industrial design. A major disadvantage in the context of explicit analyses is, however, the fact that the critical time step is determined by the thickness of the solid-shell element which is usually smaller than the smallest in-plane dimension. Therefore, four-node shells (where the critical time step is determined by the in-plane dimensions) are still often preferred for explicit analysis. In the present paper we suggest several techniques to overcome this difficulty, also in the case of problems dominated by nonlinearities such as finite deformations, elastoplasticity and contact. Reference is made to an 8-node hexahedron solid-shell element recently proposed by Schwarze and Reese (2011) [32] in an implicit context. First of all, the time steps in explicit analyses are so small that it may be not necessary to update the hourglass stabilization and the implicit computation of the internal element degrees-of-freedom in every time step. Performing the update in only every hundredth step or computing an explicit rather than implicit update can reduce the computational effort up to about 50%. Another important issue is selective mass scaling which means to modify the mass matrix in such a way that the speed of sound in thickness direction is Reduced. This enables the choice of a larger time step. The CPU effort can be finally noticeably decreased without changing the structural response significantly. This makes the presently used solid-shell formulation competitive to four-node shells, also for explicit analysis.
-
an explicit dynamics approach to the simulation of crack propagation in thin shells using Reduced Integration solid shell elements
10th World Congress on Computational Mechanics, 2012Co-Authors: M Pagani, U PeregoAbstract:Fracture propagation in laminated shell structures, due to impact or cutting, is a highly nonlinear problem which is more conveniently simulated using explicit finite element approaches. Solid-shell elements are better suited for the discretization in the presence of complex material behavior and delamination, since they allow for a correct representation of the through the thickness stress. In the presence of cutting problems with sharp blades, classi- cal crack-propagation approaches based on cohesive interfaces may prove inadequate. New "directional" cohesive interface elements are here proposed to account for the interaction with the cutter edge. The element small thickness leads to very high eigenfrequencies, which imply overly small stable time-steps. A new selective mass scaling technique is here proposed to increase the time-step without affecting accuracy.
Remko Akkerman - One of the best experts on this subject based on the ideXlab platform.
-
solutions to intra ply shear locking in finite element analyses of fibre reinforced materials
Composites Part A-applied Science and Manufacturing, 2008Co-Authors: R Ten H W Thije, Remko AkkermanAbstract:Intra-ply shear locking results in unrealistic fibre stresses and spurious wrinkling in composite forming simulations. Three remedies were investigated: aligning the mesh, applying Reduced Integration and using multi-field elements. Several triangular and quadrilateral elements were tested on their capability to avoid locking in a two-dimensional bias extension simulation. The resulting locking-free elements were tested in a realistic three-dimensional drape simulation of a biaxial fabric as well. The new triangular multi-field element seems to be the best locking-free element for unaligned meshes. It has a semi-quadratic in-plane and a linear out-of-plane displacement field. This combination improves the accuracy of the element and avoids contact problems in 3D simulations.
-
intra ply shear locking
ESAFORM 2007: 10th ESAFORM Conference on Material Forming, 2007Co-Authors: R Ten H W Thije, Remko AkkermanAbstract:Intra-ply shear locking results in unrealistic fibre stresses and spurious wrinkling in composite forming simulations. Three remedies are investigated: aligning the mesh, applying Reduced Integration and using multi-field elements. The bias extension simulation is used to test several triangular and quadrilateral elements on their capability to avoid locking. Their performance under large deformations is tested as well. The new multi-field element seems to be the best locking free element in random meshes.