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1
Content available remote Behaviors and modeling of thermal forming limits of AA7075 aluminum sheet
Xiao Wenchao, Wang Baoyu
Archives of Civil and Mechanical Engineering
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2020
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Vol. 20, no. 1
134--143
EN
The aluminum hot stamping process has been widely studied to produce lightweight parts in automobile industry. As forming limit of aluminum sheet at elevated temperatures plays a vital role in judging stamping formability, this study aims at experimentally investigating the forming limits and establishing a constitutive model to predict them. In this study, isothermal deformation test (Nakajima test) of AA7075 was conducted to determine its forming limits at temperatures of 300–450 °C and stamping speeds of 13–40 mm/s. Based on the experimental results, a constitutive model considering continuum damage mechanics was established to predict the forming limits under different deformation conditions. It was found that the formability of the material is best at 400 °C, and a higher strain rate can improve formability slightly. The comparisons between model predictions and experimental results were evaluated; results indicated a good prediction accuracy of the model in describing forming limits of AA7075 at elevated temperatures. Moreover, comparison between different studies on the thermal forming limits of AA7075 was discussed in detail.
2
Content available remote A theory of undamageable graphene
Voyiadjis G. Z., Kattan P. I.
Engineering Transactions
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2018
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Vol. 66, iss. 4
461--470
EN
It is the aim of this work to develop and extend the theory of undamageable materials to graphene. An undamageable material is a material where the value of the damage variable remains zero throughout the deformation process. It is anticipated that the constitutive equations for undamageable graphene can be modeled with differential equations for the case of graphene. The equations are solved for three cases: n = 1, n = 2, and the general case of n. It is hoped that undamageable graphene can be achieved in the laboratory in the near future when the manufacturing technology advances so as to produce such materials.
3
Content available remote Damage characterization of aluminum 2024 thin sheet for different stress triaxialities
Majzoobi G. H., Kashfi M., Bonora N., Iannitti G., Ruggiero A., Khademi E.
Archives of Civil and Mechanical Engineering
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2018
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Vol. 18, no. 3
702--712
EN
Due to its attractive mechanical properties, aluminum 2024 is widely used in aircraft manufacturing industries, especially as fiber metal laminates, such as GLARE. In the present work, a series of experiments for different stress triaxialities are used to study the ductile damage of Al 2024 considering continuum damage mechanics (CDM). Stress triaxiality is produced using notched specimens. The main objective of the present study is to predict the local equivalent plastic strain to fracture and introducing a relation which describes the effect of stress triaxiality factor (TF) on it in the medium range of stress triaxiality. Hence, a nonlinear damage model is utilized for Al 2024 and its parameters are determined by an experimental/numerical/optimization procedure using tensile test on plain specimens. The experiments showed that for large notch specimens (Al-NL) and medium notch samples (Al-NM) fracture started from the center of the notch root of the specimens, whereas for small notched specimens (Al-NS) the failure initiated from the notch root surface. Finite element simulations are performed using the presented nonlinear damage model and are compared with the experimental data. Results show that the proposed damage model can predict the damage evolution for different stress triaxialities.
4
Content available remote Influence of exponent in damage evolution equation on the accuracy of damage modelling in brittle materials
Mika P.
Engineering Transactions
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2015
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Vol. 63, iss. 4
463--479
EN
This paper analyses the influence of nonlinearity of the damage evolution equation that is introduced by exponent to the results obtained in the simulation of elastic-brittle material. Constitutive equation of linear-elastic medium with damages is described by the linear-tensorial function due to damage tensor. The nucleation and growth of microdamages are modelled using a two-parameter equation of damage evolution, in which the current level of damage is expressed by the principal values of Vakulenko-Kachanov and Murakami-Ohno damage tensors. The study examines a relationship between the time of the first macro crack appearance, principal values of damage tensor at the critical moment and the exponent adopted to the equation of damage evolution. The subjects of the analysis are changes in both the qualitative and quantitative variables characterizing the damage.
5
Content available remote Simulation of concrete corrosion and interaction surfaces using cellular automata
Zaborski A.
Czasopismo Techniczne. Budownictwo
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2015
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Y. 112, iss. 2-B
369--378
EN
This paper presents a new approach to determining the synergetic effects of environmental conditions and mechanical loading on the load bearing capacity of structural members. Cellular automata are used to estimate the residual strength of a RC section subjected to concrete corrosion. The evolution of interaction surfaces resulting from bending moments and axial force caused by a continuous degradation process is presented.
PL
W artykule przedstawiono próbę oszacowania skutków oddziaływania środowiska i mechanicznego obciążenia na nośność elementów konstrukcji. Postępy korozji betonu i rezydualną wytrzymałość przekroju żelbetowego określono automatami komórkowymi. Przedstawiono ewolucję powierzchni interakcji momentów gnących i siły osiowej spowodowaną postępującymi procesami degradacji.
6
Content available Porównanie klasycznych metod szacowania niskocyklowej trwałości zmęczeniowej z podejściem CDM
Burak M., Skibicki D.
Postępy w Inżynierii Mechanicznej
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2014
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nr 3(2)
5--12
PL
W pracy skupiono się na porównaniu podejść szacowania trwałości zmęczeniowej metodami tzw. klasycznymi (Morrow, Morrow (σm), SWT) – szeroko wykorzystywanymi w obliczeniach zmęczeniowych – z podejściem kontynualnej mechaniki uszkodzenia (Continuum Damage Mechanics – CDM).
EN
The study focused on a comparison of approaches for estimating the fatigue life of the so-called classical methods (Morrow, Morrow (σm), SWT) widely used in the fatigue calculation with the approach of Continuum Damage Mechanics (CDM).
7
Content available remote Programming of composite plates damage calculation
Dudinsky M., Riecky D., Zmindak M.
Studia i Materiały Informatyki Stosowanej
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2012
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nr 6
11--18
EN
The goal of this paper is to present the numerical results of elastic damage of thin unidirectional fiber-reinforced composite plates. The numerical implementation uses a layered shell finite element based on the Kirchhoff plate theory. Newton-Raphson method is used to solve the system of nonlinear equations and evolution of damage has been solved using return-mapping algorithm. The analysis is performed by finite element method and user own software is created in MATLAB programming language. One problem for two different materials was simulated in order to study the damage of laminated fiber reinforced composite plates.
8
Content available Programming of composite plates damage calculation
Dudinsky Martin, Riecky Daniel, Zmindak Milan
Studia i Materiały Informatyki Stosowanej
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2011
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nr 4
23-29
EN
The goal of this paper is to present the numerical results of elastic damage of thin unidirectional fiber-reinforced composite plates. The numerical implementation uses a layered shell finite element based on the Kirchhoff plate theory. Newton-Raphson method is used to solve the system of nonlinear equations and evolution of damage has been solved using return-mapping algorithm. The analysis is performed by finite element method and user own software is created in MATLAB programming language. One problem for two different materials was simulated in order to study the damage of laminated fiber reinforced composite plates.
9
Content available remote Computational approach for predicting the crack propagation of stainless steel plate using damage mechanics
Yoo B. -M., Lee C. -S., Chun M. -S., Kim M. -H., Lee J. -M.
Computer Methods in Materials Science
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2011
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Vol. 11, No. 2
303-308
EN
The aim of this study is development of numerical method for the prediction for crack propagation of stainless steel plate under cryogenic temperature. Stainless steel is one of the most functional materials at relatively wide temperature ranges. It has strong non-linearities on the mechanical properties under cryogenic temperature such as discontinuous hardening phenomenon induced by the phase transformation, among others. The nonlinear hardening affects significant change of material characteristics, i.e., strength, deformation and fracture phenomenon. This induces some difficulties on the precise evaluation of structural capacity of stainless steel based structures. In the present paper, the crack propagation characteristics of the stainless steel plate under cryogenic temperature have been simulated using a new numerical technique based on a newly proposed damage-coupled constitutive model and orient-purpose user subroutine applicable to commercial FEA code ABAQUS. The numerical results are compared with the experimental results of tensile test and crack propagation tests under cryogenic temperature.
PL
Celem pracy jest opracowanie numerycznej metody przewidywania propagacji pęknięć w blachach grubych ze stali nierdzewnej w temperaturach kriogenicznych. Stal nierdzewna jest jednym z najbardziej funkcjonalnych materiałów w szerokim zakresie temperatur. Charakteryzuje się mocną nieliniowością własności mechanicznych w temperaturach kriogenicznych, między innymi nieciągłym umocnieniem wywołanym przemianą fazową. Nieliniowe umocnienie wpływa znacząco na takie charakterystyki materiału jak wytrzymałość, odksztacalność i pękanie. Zjawisko to powoduje trudności w oszacowaniu możliwości konstrukcyjnych zastosowań stali nierdzewnych. W artykule przeprowadzono symulacje charakterystyk propagacji pęknięć w blachach grubych ze stali nierdzewnych w temperaturach kriogenicznych. Zastosowano w tym celu nową numeryczną technikę opartą o model konstytutywne sprzężony z pękaniem, wprowadzany jako procedura użytkownika do programu ABAQUS. Wyniki symulacji numerycznych porównano z doświadczalnymi próbami rozciągania w temperaturach kriogenicznych.
10
Content available remote Application of viscoplastic-damage models to quasi-static ice failure under compression
Choi H. -Y., Lee C. -S., Yoo B. - M., Lee J. -M.
Computer Methods in Materials Science
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2011
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Vol. 11, No. 1
108-114
PL
W pracy dokonano oceny zachowania się świeżego lodu w aspekcie jego pękania oraz parametrów konstytutywnych. Zastosowano lepkoplastyczny model zniszczenia. Lód jest uważany za jeden z bardziej skomplikowanych materiałów w naturze, ponieważ ma on różną liczbę i długość granic ziaren. Zachowanie się tego materiału różni się znacząco pomiędzy quasi-statycznymi i dynamicznymi prędkościami odkształcenia, to znaczy lód ma w tych stanach odpowiednio plastyczną i kruchą charakterystykę. Zachowanie się lodu w warunkach quasi-statycznych jest znacznie bardziej skomplikowane niż przy obciążeniach dynamicznych, co jest spowodowane wystę-powaniem kruchości a także mięknięciem pod wpływem odkształcenia. W niniejszej pracy przystosowano lepkoplastyczny model do opisu zjawisk zachodzących w lodzie w warunkach quasi-statycznych. Oceniono zjawisko zniszczenia lodu pod wpływem obciążeń ściskających tak aby uniknąć wywołania mechanizmu wzrostu pęknięcia. Zależny od prędkości lepkoplastyczny model pękania został sformułowany i zaimplementowany w programie ABAQUS jako procedura użytkownika. Pozwoliło to na ilościowe przewidywanie pękania lodu. W celu weryfikacji zaproponowanej metody wyniki symulacji pękania lodu porównano z wynikami prób ściskania.
EN
In the present paper, the material behavior characteristics of fresh ice, such as material failure as well as constitutive behavior, have been evaluated based on the viscoplastic-damage mechanism. Ice is considered as one of the most complex materials in naturę since it has various amounts and sizes of grain boundaries. The material behavior also significantly differs between the quasi-static and dynamic strain rates, namely, it has ductile and brittle material characteristics, respectively. In particular, the ice behavior under quasi-static strain rate is more complicated than under dynamic strain rate due to its ductile behavior, strain softening phenomenon, etc. Therefore, in the present paper, the unified viscoplastic model has been adopted to describe this phenomenon of ice under quasi-static strain rate. The material failure phenomenon of ice under compressive loading has been evaluated to avoid the fraction growth damage mechanism. The rate-dependent viscoplastic-damage model has been implicitly formulated and implemented to the ABAQUS user defined sub-routine to simulate the ice failure quantitatively. In order to validate the proposed analysis method, the simulation results of ice failure have been compared to a series of compression tests of ice.
11
Content available remote Modelowanie degradacji betonowych elementów konstrukcyjnych automatami komórkowymi
Zaborski A.
Ochrona przed Korozją
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2010
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nr 6
325-327
PL
Przedstawiono zastosowanie automatów komórkowych do symulacji sprzężonych przepływów dyfuzyjnych czynników agresywnych w ośrodku porowatym. Degradację matrycy betonowej opisano dwoma parametrami skalarnymi: uszkodzeń korozyjnych oraz mechanicznego osłabienia materiałowego. Wyniki przeprowadzonych obliczeń numerycznych potwierdzają synergistyczny charakter oddziaływań obciążenia mechanicznego i agresywnego środowiska.
EN
Cellular automata modeling was applied to conjugated diffusion flows of aggressive substances through porous media. The degradation of concrete matrix is described by means of two scalar parameters of chemical corrosion and strain softening. The results of the numerical calculations prove the synergetic effect between mechanical loading and aggressive environment.
12
Content available remote Zastosowanie automatów komórkowych do numerycznej symulacji korozji betonu pod obciążeniem
Zaborski A.
Czasopismo Techniczne. Mechanika
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2010
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R. 107, z. 3-M
147-158
PL
Przedstawiony model korozji betonu uwzględnia synergistyczne oddziaływanie obciążenia i degradacji chemicznej. Wykazano efektywność zastosowania automatów komórkowych do symulacji sprzężonych przepływów dyfuzyjnych przy zmiennej przepuszczalności ośrodka.
EN
Multiscale simulation by the cellular automata to diffusion in porous material has been applied. Multilevel synergic effect of loading and chemical activity has been considered. The effective stress has been employed for both equilibrium and evolution equations.
13
Content available remote Secant stress/strain relations of orthotropic elastic damage with dual properties
Rizzi E., Carol I.
Archives of Mechanics
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2007
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Vol. 59, nr 2
133-171
EN
A constitutive framework of orthotropic elastic damage in initially-isotropic materials is presented. The constitutive equations are developed within the phenomenological approach of Continuum Damage Mechanics. Focus is made on secant stress/strain relations that can be derived by the application of the so-called damage-effect tensors, namely the fourth-order operators that define the linear transformations between nominal and effective stress and strain quantities. In the attempt to provide selected forms of anisotropic damage approaching general orthotropy, several proposals of damage-effect tensors are formulated. Such fourth-order operators are obtained from the complete orthotropic representations as particular instances that satisfy a duality requirement between compliance- and stiffness-based derivations. A complete family of solutions based on a specific non-singular tensor generator is derived in fuli invariant form.
14
Content available remote Survey of modern trends in analysis of continuum damage mechanics
Ambroziak A., Kłosowski P.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2006
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Vol. 10, No 4
437-454
EN
A brief review of the damage mechanics literature is given. As this area of scientific research is very modern, the authors have restricted themselves to about 100 most impor-tant books and papers. Basic equations to introduce the isotropic model in the framework of thermodynamics are given in a form easily applicable in numerical symulations.
15
A continuum damage mechanics model for multiaxial low cycle fatigue life
Zolochevsky A., Obataya Y.
Inżynieria Materiałowa
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2001
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R. XXII, nr 5
993-995
EN
New multiaxial fatigue damage model based on the critical plane approach is proposed. Two different physical mechanisms of the fatigue damage development on each potential failure plane (critical plane) are considered. In general, each critical plane contains two families of parallel microcracks. The proposed model reproduces simultaneously fatigue damage induced anisotropy, the influence of positive and negative mean stresses, unilateral fatigue damage, microcrack closure effect and fatigue behaviour under variable amplitude loading. The expression for the equivalent stress in the damage evolution equation includes the stress intensity for the amplitudes as well as joint invariants for the mean values of the stress tensor and for the vectors associated with the directions of microcracks. The theoretical predictions are compared with experimental data under uniaxial cyclic loading of brass specimens. The influence of positive and negative mean stresses on the fatigue life of brass is investigated.
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