W pracy skonfrontowano trzy wariacyjne sformułowania dla napreżeniowo-przemieszczeniowych elementów skończonych, służących do analizy płaskiego stanu naprężenia. Podprogramy stworzone w środowisku MATLAB z użyciem pakietu CALFEM umożliwiły numeryczną analizę, w której zbadano zachowanie się modeli skończenie-elementowych z różnymi wariantami statycznych i kinematycznych warunków brzegowych.
EN
In this paper three variational formulations for stress-displacement finite elements for pianę stress ana-lysis arę compared. Finite element procedures have been implemented in the environment of MATLAB with its toolbox called CALFEM. The numerical analysis and examination of finite element models with yarious kinds of static and kinematic boundary conditions have been performed.
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At room temperature, the tantalum is shown to exhibit a high and typical strain rate sensitivity. Various experimental tests including uniaxial tensile test in the three plane direction, relaxation and cyclic shear tests have been conducted at room temperature in order to study the mechanical behavior of tantalum. Based on this experimental data, an elasto-viscoplastic model is developped including the initial viscoplastic anisotropy as well as the isotropic ductile damage effects using an enhanced viscosity effect. Using the framework of the thermodynamics with state variables, an appropriate state and dissipation potentials are proposed to account for, the initial viscoplastic flow anisotropy, the mixed non linear isotropic and kinematic hardenings and the isotropic ductile damage effect. Specific developments are made to introduce different isotropic type hardenings thanks to a coupling between cumulative plastic strain and viscous or kinematic hardening effects. The proposed model, implemented into ABAQUS explicit via the user subroutine vumat, is used to simulate different experimental tests in order to determine the accurate values of the overall material parameters. The special treatment of the plane stress case is addressed and shown to describe the anisotropic behavior. Finally, some simple 2D and 3D simulations of deep drawing tests are carried out to validate the accuracy of the proposed model.
PL
W temperaturze pokojowej tantal wykazuje typową wysoką wrażliwość na prędkość odkształcenia. Szereg testów, w tym jednoosiowy test rozciągania, relaksacji i cykliczny test ścinania, zostało przeprowadzonych w temperaturze pokojowej w celu poznania mechanicznych własności tantalu. Bazując na otrzymanych danych eksperymentalnych opracowano sprężyste lepko plastyczny model uwzględniający początkową lepko plastyczną anizotropię jak również izotropowy efekt plastycznego pękania. Wykorzystując termodynamiczne podejście ze zmiennymi stanu zostały zaproponowane zmienne stanu i potencjały dyssypacyjne aby uwzględnić anizotropie w początkowym lepko plastyczny płynięciu, oraz aby połączyć nieliniowe izotropowe i kinematyczne modele umocnienia oraz efekty plastycznego pękania. Szczególny nacisk położono na opracowanie złożonych modeli umocnienia materiału. Opracowany model zaimplementowano w programie ABAQUS/EXPLICIT przez procedurę użytkownika Vumant. Model ten został wykorzystany do symulacji różnych testów w celu identyfikacji dokładnych wartości parametrów materiałowych. W pracy przedstawiono również wyniki prostych symulacji w 2D i 3D testów głębokiego tłoczenia przeprowadzone w celu weryfikacji poprawności proponowanego modelu.
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Purpose: Mechanical behaviour and damage initiation mechanisms in thin rubber sheet composites were investigated under static solicitation at room temperature. Two types of rubber are used in this study; Natural rubber, NR vulcanised and reinforced by carbon black and Synthetic rubber (styrene-butadiene-rubber, SBR). Design/methodology/approach: A comprehensive study has been carried out in order to identify a threshold criterion for the damage mechanism to explain a tearing criterion for the concept of tearing energy of the elastomers and also to give a detail for the damage mechanism depending on the loading conditions. A typical type of specimen geometry of thin sheet rubber composite materials was studied under static tensile tests conducted on the smooth and notched specimens with variable depths. In this way, the effects of the plane stress on the damage mechanism are characterized depending on the rubber materials. Findings: Damage mechanisms during tensile test have been described for both of rubber types and the criteria which characterize the tearing resistance, characteristic energy for tearing (T) was explained. Damage in the specimens were evaluated just at the beginning of the tearing by means of the observations in the scanning electron microscopy (SEM). Practical implications: A tearing criterion was suggested in the case of simple tension conditions by assuming large strain. In the next step of this study, a finite element analysis (FEA) will be applied under the same conditions of this part in order to obtain the agreement between experimental and FEA results. Originality/value: This study propses a threshold criterion for the damage just at the beginning of the tearing for thin sheet rubber composites and gives a detail discussion for explaining the damage mechanisms by SEM results. This type of study gives many facilities for the sake of simplicity in industrial application.
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The back-propagation neural network was trained off line in order to simulate operation of the return mapping algorithm. Selection of patterns and the neural network training as well as testing processes are discussed in detail. The network was incorporated into the FE computer code ANKA as a neural procedure. The hybrid neural-network/finite-element-method program ANKA-H was used for the analysis of two elastoplastic plane stress examples: i) perforated tension strip, ii) notched beam. The results of computations point out quite good accuracy of the hybrid analysis. Some prospects of development of hybrid NN/FEM programs are given at the end of paper.
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Purpose: Mechanical behaviour and damage mechanisms in thin rubber sheet composites investigated under static solicitation at room temperature. Two types of rubber are used in this study; Natural rubber, NR vulcanised and reinforced by carbon black and Synthetic rubber (Styrene-butadiene-rubber, SBR). Design/methodology/approach: A comprehensive study has been carried out in order to identify a threshold criterion for the damage mechanism to explain a tearing criterion for the concept of tearing energy of the elastomers and also to give a detail for the damage mechanism depending on the loading conditions. A typical type of specimen geometry of thin rubber composite materials was studied under static tensile tests conducted on the smooth and notched specimens with variable depths. In this way, the effects of the plane stress on the damage mechanism are characterized depending on the rubber materials. Findings: Damage mechanisms during tensile test have been described for both of rubber types and the criteria which characterize the tearing resistance, characteristic energy for tearing (T) was explained. Damage in the specimens were evaluated just at the beginning of the tearing by means of the observations in the scanning electron microscopy (SEM). Practical implications: A tearing criterion was suggested in the case of simple tension conditions by assuming large strain. In the next step of this study, a finite element analysis (FEA) will be applied under the same conditions of this part in order to obtain the agreement between experimental and FEA results. Originality/value: This study proposes a threshold criterion for the damage just at the beginning of the tearing for thin sheet rubber composites and gives a detail discussion for explaining the damage mechanisms by SEM results. This type of study gives many facilities for the sake of simplicity in industrial application.
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