IRIS Politecnico di Milanohttps://re.public.polimi.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Sun, 16 Jan 2022 10:50:50 GMT2022-01-16T10:50:50Z10241Sviluppo di un approccio ad elementi finiti per la simulazione del taglio di strutture sottilihttp://hdl.handle.net/11311/783920Titolo: Sviluppo di un approccio ad elementi finiti per la simulazione del taglio di strutture sottili
Abstract: Viene proposta una strategia computazionale per la simulazione del taglio di strutture sottili. Lâ€™attenzione `e posta, in particolare, sullâ€™implementazione di elementi finiti di tipo solid-shell in ambiente esplicito. Lâ€™adozione di un criterio per la propagazione della frattura e lâ€™utilizzo di un approccio coesivo direzionale sono brevementi discussi.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11311/7839202013-01-01T00:00:00ZComputationally efficient explicit nonlinear analyses using reduced integration-based solid-shell finite elementshttp://hdl.handle.net/11311/783917Titolo: Computationally efficient explicit nonlinear analyses using reduced integration-based solid-shell finite elements
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 non- linearities such as finite deformations, elastoplasticity and contact. Reference is made to an 8-node hexahedron solid-shell element recently proposed by Schwarze and Reese (Schwarze, M., Reese, S., 2011, International Journal for Numerical Methods in Engineering 85, 289-329) 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 solidshell formulation competitive to four-node shells, also for explicit analysis. Keywords: reduced
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11311/7839172014-01-01T00:00:00ZExplicit Simulation of Forming Processes Using a Novel Solid-Shell Concept Based on Reduced Integrationhttp://hdl.handle.net/11311/636915Titolo: Explicit Simulation of Forming Processes Using a Novel Solid-Shell Concept Based on Reduced Integration
Abstract: The contribution deals with the simulation of sheet metal forming processes by means of a recently developed hexahedral solid-shell finite element. In contrast to this earlier work, we pursue here explicit integration. The element formulation has the following features. In order to avoid undesired effects of locking an enhanced assumed strain (EAS) concept using only one EAS degree-of-freedom has been implemented. In addition, by means of the assumed natural strain (ANS) method an excellent performance in bending situations is obtained. A key point of the element formulation is the construction of the hourglass stabilization by means of different Taylor expansions. This procedure leads to the important advantage that the sensitivity of the results with respect to mesh distortion is noticeably reduced. Further the hourglass stabilization is in this way designed that locking is eliminated and numerical stability guaranteed. The finite strain material model for plastic anisotropy and non-linear kinematic and isotropic hardening is motivated by a rheological model including Armstrong-Frederick kinematic hardening. The element formulation has been implemented into the academic code FEAP. Some standard benchmark examples are computed.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11311/6369152012-01-01T00:00:00ZSOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTUREShttp://hdl.handle.net/11311/668167Titolo: SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES
Abstract: Crack propagation in thin shell structures due to cutting is conveniently simulated
using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell
elements are usually preferred for the discretization in the presence of complex material
behavior and degradation phenomena such as delamination, since they allow for a correct
representation of the thickness geometry. However, in solid-shell elements the small thickness
leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new
selective mass scaling technique is proposed to increase the time-step size without affecting
accuracy. New ”directional” cohesive interface elements are used in conjunction with selective
mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile
shells.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11311/6681672012-01-01T00:00:00ZEXPLICIT SIMULATIONS WITH REDUCED INTEGRATION SOLID-SHELL ELEMENTS: STABILIZATION AND SELECTIVE MASS SCALINGhttp://hdl.handle.net/11311/668165Titolo: EXPLICIT SIMULATIONS WITH REDUCED INTEGRATION SOLID-SHELL ELEMENTS: STABILIZATION AND SELECTIVE MASS SCALING
Abstract: Explicit approaches are usually preferred for the simulation of thin walled structural
problems, which are often highly nonlinear due to large deformations and possible material
inelasticity. Solid-shell elements can describe the correct thickness geometry and are
therefore more suitable than standard shell elements for the implementation of complex 3D
material models. However, their poor kinematic formulation requires computationally expensive
corrections which suggest the use of reduced integration with hourglass stabilization.
Furthermore, a high element maximum eigenfrequency is implied by the small thickness, leading
to overly small stable time-steps. These two issues are addressed in this paper where a
stabilized reduced integration solid-shell element and a selective mass scaling technique for
the reduction of the maximum eigenfrequency are proposed.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11311/6681652012-01-01T00:00:00ZEXPLICIT DYNAMICS SIMULATIONS OF ELASTOPLASTIC AND BRITTLE FAILURE OF THIN SHELL STRUCTUREShttp://hdl.handle.net/11311/668166Titolo: EXPLICIT DYNAMICS SIMULATIONS OF ELASTOPLASTIC AND BRITTLE FAILURE OF THIN SHELL STRUCTURES
Abstract: Fracture propagation in elastoplastic shell structures, due to impact or cutting, is conveniently simulated using explicit finite
element approaches, in view of the high nonlinearity of the problem. Solid-shell elements are usually preferred for the discretization in
the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation
of the thickness geometry. Solid-shell elements require time consuming corrections to the element kinematics to avoid locking.
Reduced integration with hourglass stabilization is used to reduce the computational cost. New "directional" cohesive interface elements
are used to account for the interaction with a sharp blade in cutting problems. The element small thickness leads to very high
eigenfrequencies, which imply very small stable time-steps. A new selective mass scaling technique is used to increase the time-step
without affecting accuracy.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11311/6681662012-01-01T00:00:00ZAN EXPLICIT DYNAMICS APPROACH TO THE SIMULATION OF CRACK PROPAGATION IN THIN SHELLS USING REDUCED INTEGRATION SOLID-SHELL ELEMENTShttp://hdl.handle.net/11311/668164Titolo: AN EXPLICIT DYNAMICS APPROACH TO THE SIMULATION OF CRACK PROPAGATION IN THIN SHELLS USING REDUCED INTEGRATION SOLID-SHELL ELEMENTS
Abstract: 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.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11311/6681642012-01-01T00:00:00ZA finite element approach to blade cutting of thin sheetshttp://hdl.handle.net/11311/602904Titolo: A finite element approach to blade cutting of thin sheets
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11311/6029042011-01-01T00:00:00ZShell and Solid-Shell Finite Element Models for the Simulation of Blade Cutting of Thin Sheetshttp://hdl.handle.net/11311/643331Titolo: Shell and Solid-Shell Finite Element Models for the Simulation of Blade Cutting of Thin Sheets
Abstract: The finite element simulation of cutting of a thin shell by a sharp blade is considered. Among the various sources of difficulty one can list contact, crack propagation, large displacements, material nonlinearities, possible delamination. When cohesive interface elements are used to describe crack propagation, an additional difficulty is represented by the blade sharpness. A new type of "directional" cohesive element, to be used in conjunction with solid-shell elements, is proposed and discussed for the simulation of this type of problems.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11311/6433312012-01-01T00:00:00ZElementi ‘coesivi direzionali’ per la modellazione del taglio di strutture sottilihttp://hdl.handle.net/11311/602897Titolo: Elementi ‘coesivi direzionali’ per la modellazione del taglio di strutture sottili
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11311/6028972011-01-01T00:00:00Z