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A ductile damage theory is presented by coupling the covariant formulation of finite deformation plasticity with the phase field modeling of fracture, including kinematic hardening for the ductile response of the materials. A phase field coupled nonlinear kinematic hardening equation is proposed in the reference configuration having equivalent representation through the Lie derivative of the kinematic hardening tensor by push‐forward operation in the spatial configuration, thus ensuring the satisfaction of frame invariance. To capture the correct physical response of the material by the phase field evolution equation, the fracture driving function, that is, the difference between the sum of elastic and plastic energies and threshold energy, after the damage initiation is modified by an energy release controlling function, which is an empirical relation of equivalent plastic strain. In defining the energy release controlling function, well‐defined points with physical significance in the experimental load versus displacement curve are used. To simulate the response of the material in relatively large time steps, a modified staggered scheme is presented, evaluating the fracture driving and energy release controlling functions from the previous converged step and using the updated phase field variable in the weak form of the momentum balance equation. To quantify different material parameters from available experimental results in the literature, the developed phase field coupled elasto‐plastic model uses a neural network optimization procedure consisting of neural network training together with optimization in MATLAB and finite element model evaluation in Abaqus user element subroutine UEL. Model capabilities are demonstrated by simulating the crack propagation in complex 3D geometries such as the second and third Sandia Fracture Challenges. [ABSTRACT FROM AUTHOR]

In this study, anisotropic non-proportional hardening behaviour of the sheet metals with different crystalline structures is investigated. The investigated materials particularly exhibit the Bauschinger effect and complex transient hardening behaviour during loading path change. Furthermore, the finite element simulations are carried out to evaluate the performance of the distortional and multi-surface-kinematic hardening models in flow stress prediction under loading path change. Both models can well reproduce the measured anisotropic hardening, but the distortional hardening concept shows better predictive capability for flow stresses. The improved accuracy of the flow stress prediction with the distortional hardening model compared to the kinematic hardening is attributed to its flexibility in distortion of the yield surface following microstructure deviator independent on the initial yield surface. In contrast, the initial size of the yield surface in the kinematic hardening significantly affects the determination of the re-yielding stress at load reversal. [ABSTRACT FROM AUTHOR]

In this present work, a damage-coupled cyclic plasticity model has been developed for more accurate ratcheting–fatigue life estimation under strain and stress controlled ratcheting. Ratcheting–fatigue damage behavior under uniaxial multistep strain-controlled ratcheting shows that the incremental mean ratcheting strain deteriorates the elastic slopes cycle by cycle, by means of ratcheting damage. Severe ratcheting strain accumulation rate has been observed in tertiary region under uniaxial stress controlled ratcheting. The proposed damage-coupled model has been constructed which incorporates both fatigue damage and damaging effect of the accumulated mean plastic strain. The proposed model incorporates a critical fatigue damage parameter which can predict effects of early fatigue crack nucleation due to combined ratcheting and fatigue damages. The performance of the proposed damage-coupled model has been investigated in the present study based on the critical fatigue damage parameter. The proposed model is calibrated on experimental data of SA333 Gr. 6 carbon steel and SA508 Gr. 3 steel. The proposed formulations have been applied in user material subroutine UMAT of finite element software, ABAQUS. The proposed model has been validated by comparing predicted ratcheting behavior with experiments for the two different steels. All the predicted number of cycles to failure are located within 0.5 times error band. The proposed damage-coupled model has demonstrated excellent capabilities of predicting ratcheting–fatigue life under cyclic loading with ratcheting damage. [ABSTRACT FROM AUTHOR]

The present study aims to thoroughly investigate the edge‐cracking phenomenon in high‐strength sheets. Hence, the edge crack sensitivity of three dual‐phase steels is studied in various combinations of edge manufacturing and forming processes. Finite element simulations are performed to elaborate the study. In this regard, the Yoshida–Uemori kinematic hardening model is employed to describe the plasticity behavior of the materials under multistep processes. A stress‐state fracture model is coupled with this plasticity model to illustrate the distinguished local fracture strains of each material. Moreover, the effects of strain rate and the consequent temperature rise on hardening and damage are taken into account, which play significant roles during shear‐cutting. The results show that although the shear‐cutting processes are applied at very low speed, the strain rate and induced temperature are still high at the cutting area. The hole expansion results show different fracture behaviors for different cases. In brief, cracking is initiated at a location, which shows the highest damage accumulation during edge manufacturing plus the subsequent forming process. Such a complicated situation can only be successfully predicted by using a computer‐aided approach along with proper material modeling, like the applied model in this study. [ABSTRACT FROM AUTHOR]

The classical deviatoric hardening models are capable of characterizing the mechanical response of granular materials for a broad range of degrees of compaction. This work finds that it has limitations in accurately predicting the volumetric deformation characteristics under a wide range of confining/consolidation pressures. The issue stems from the pressure independent hardening law in the classical deviatoric hardening model. To overcome this problem, we propose a refined deviatoric hardening model in which a pressure-dependent hardening law is developed based on experimental observations. Comparisons between numerical results and laboratory triaxial tests indicate that the improved model succeeds in capturing the volumetric deformation behavior under various confining/consolidation pressure conditions for both dense and loose sands. Furthermore, to examine the importance of the improved deviatoric hardening model, it is combined with the bounding surface plasticity theory to investigate the mechanical response of loose sand under complex cyclic loadings and different initial consolidation pressures. It is proved that the proposed pressure-dependent deviatoric hardening law is capable of predicting the volumetric deformation characteristics to a satisfactory degree and plays an important role in the simulation of complex deformations for granular geomaterials.

Indentation is a versatile method to assess the hardness of different materials along with their elastic properties. Recently, powerful approaches have been developed to determine further material properties, like yield strength, ultimate tensile strength, work-hardening rate, and even cyclic plastic properties, by a combination of indentation testing and computer simulations. The basic idea of these approaches is to simulate the indentation with known process parameters and to iteratively optimize the initially unknown material properties until just a minimum error between numerical and experimental results is achieved. In this work, we have developed a protocol for instrumented indentation tests and a procedure for the inverse analysis of the experimental data to obtain material parameters for time-dependent viscoplastic material behavior and kinematic and isotropic work-hardening. We assume the elastic material properties and the initial yield strength to be known because these values can be determined independently from indentation tests. Two optimization strategies were performed and compared for identification of the material parameters. The new inverse method for spherical indentation has been successfully applied to martensitic steel. [ABSTRACT FROM AUTHOR]

The work presented in this paper focuses on modeling the welding process to develop a numerical model able to perform a good prediction of welding distortions. The model is developed for a butt welded joint using S235 steel as the base metal and an electrode (AWS E6013) as the filler metal. To assess accuracy, numerical and experimental results are compared. The present work makes it possible to identify the main factors influencing the accuracy of the numerical model, which must be taken into account to obtain satisfactory results. To carry out this analysis, the effect of the mechanical properties of deposited metal and the effect of the deposition process were taken into account. The effect of the variation of the mechanical properties of the filler metal on the distortions is illustrated. The model was developed by using APDL language, and the birth and death technique is used to model the deposition process. Distortion results obtained by numerical models approach properly the experimental measurement. Further analysis of the numerical data reveals considerable fluctuation of the obtained results by modifying the models used to describe the plastic behavior and the work hardening process. Regarding this strong correlation, numerical modeling of the welding process needs a vigilant identification of the work hardening mode appropriate for the used materials. [ABSTRACT FROM AUTHOR]

Drag link is one of the important parts in steering system used in automotive. The ball joint, ball joint housing, and pipe compose the drag link. In this study, finite element analysis is used to simulate the deformation process. St 52 steel material is used. A yield criterion, an associated flow rule, and Chaboche's kinematic hardening rule were used in the finite element simulations of processes involving high plastic deformation. A series of low-cycle tensile/compression tests is performed to determine the parameters of Chaboche's kinematic hardening rule. The success of the simulation results depends on the more accuracy of the finding parameters. Some optimization methods are used in the calibration progression of these parameters and the results are compared. For the purpose of optimization, the angle of the pipe after bending is set as 16.6° as soon as possible. As design variables, the Chaboche kinematic hardening rule parameters were adjusted. Consequently, calibrated parameters were obtained for St52 pipe bending. By analysing and verifying the candidate points, optimization methods are compared. The optimum parameters are determined as YS=350 MPa, C=2984.3 MPa, and γ=l00 while their initial values are YS=373.806 MPa, C=4016 MPa, and γ=94. It is concluded that the optimization process gives more consistency in the bending process. [ABSTRACT FROM AUTHOR]

This article presents an experimental evaluation of electro-welded wire meshes featuring bars ranging from 6 to 8 mm in diameter, focusing on their monotonic tensile and cyclic behavior. Microstructure and hardness characteristics are analyzed, and their correlation with tensile and cyclic properties is investigated. Results are contrasted against industry standards and previous research. The study delves into the cyclic stress-strain response, assessing energy dissipation capacity, material cyclic degradation, and kinematic hardening. Additionally, two methods are employed to evaluate the potential for bar buckling. The findings underscore limited ductility capacity hindering earthquake-resistant structural applications.

This article describes a dataset used to calibrate a finite element model of a thick circular hollow section (CHS) with varying d/t (diameter to thickness) ratio under cyclic loading which may be used as a computational model validation benchmark by researchers working on similar problems in structural and mechanical engineering. The test data consists of seven cold-formed S335J2H steel CHS tube specimens tested to buckling failure in low-cycle fatigue under a three-point bending arrangement, instrumented with discrete strain gauges, displacement transducers and string potentiometers together with continuous surface deformation fields obtained by two pairs of digital image correlation (DIC) cameras. ‘Half-cycle’ material data from the uniaxial tensile testing of dog-bone coupons is also provided. Comparisons between measured and simulated entities such as midspan forces, moments, displacements and mean curvatures can be obtained with MATLAB processing scripts. Complete ABAQUS model input files are also provided to aid in benchmarking.

Introduction: Most standard texts on structural dynamics deal with elasto-plastic dynamic response considering only the simplest model, namely, the elastic perfectly plastic material model. Method: In the present article, a numerical evaluation algorithm is attempted by phenomenologically modeling the general elasto-plastic models, including strain hardening models, namely, kinematic hardening and isotropic hardening, in a coherent manner. The models are presented in a simple manner yet conforming to the unified theory of plasticity. Concluding Remarks: The main purpose of the article is to aid research-minded students and instructors in the study of the subject and encourage the development of more unique material models in an incremental fashion and integrate them into dynamic analysis platforms. Secondly, a tutorial-like approach is adopted for students to implement the material models in any dynamic problem. By modifying the easily modifiable supplied code, students and instructors can themselves try out their models or load cases and hence enhance the overall teaching-learning experience. [ABSTRACT FROM AUTHOR]

In the cup drawing process, the tensile stress in the radial direction is dominant during the drawing. However, the sheet bends around the punch and die radiuses, and the fibers touching the punch and die are exposed to compression, while the outer surfaces are exposed to tension. Therefore, the stress state at the radius regions of punch and die becomes complicated to overcome due to the bending and may influence the final earing form. The present study investigates the influence of a plasticity model involving an advanced yield criterion coupled with a combined hardening model on the earing prediction in the cup drawing process of AA6016-T4 aluminum alloy. Therefore, isotropic hardening and combined hardening models are implemented, respectively so as to show the kinematic hardening effect on the earing prediction performance. The combined hardening model comprises Armstrong-Frederic kinematic hardening and isotropic hardening rules together to characterize the hardening behavior of the sheet, and the parameters of the hardening model were obtained by considering a reversal shear test. A sixth-order polynomial-based yield criterion was implemented to represent the anisotropic response of the sheet successfully. The Hill48 yield criterion was also considered in the present study for comparison purposes. The analyses were conducted based on the additive plasticity approach and using the implicit stress update scheme in Marc commercial software. The punch force-displacement responses and earing profile predictions were obtained numerically and compared with the experimental outcomes. It was seen that introducing the combined hardening model enhances the earing prediction capability for both yield criteria. With the incorporation of the combined hardening rule, the improvement in the prediction of the earing profile was more apparent in HomPol6 results compared to Hill48. The HomPol6 yield criterion coupled with the combined hardening rule led to a better agreement in the prediction of ear formation. [ABSTRACT FROM AUTHOR]

The Chaboche-Lemaitre combined isotropic-kinematic hardening model (CKIH) gives an overall information about the material behaviour under cyclic loading. The identification of hardening parameters is a difficult and time-consuming problem. The procedure of the parameters identification using the experimental hysteresis curve obtained in a cyclic loading test under strain control is presented in details here for a S235JR construction steel. The last stabilized cycle extracted from the hysteresis curve is required for the identification of hardening parameters. The model with three backstresses is tested here. The optimization algorithm is also used for the improvement of the agreement between experimental and numerical data. In order to include some uncertainty of experiment and the identification procedure, the authorial algorithm written on the basis of the fuzzy logic soft-computing method is applied here. The results obtained show that the identification procedure presented in this paper ensures the good agreement between the experimental tests and numerical calculations. The correct selection of parameters associated with the hardening is essential for the right description of material behaviour subject to loading in different engineering problems, including in metal forming processes. [ABSTRACT FROM AUTHOR]

This study evaluates the performance of a user-defined combined hardening modeling method for advanced high-strength steels (AHSS) under monotonic and reversal loading conditions. The plastic behavior of TWIP980 and TRIP980 AHSS sheet metals is investigated using a cyclic plasticity modeling approach. The model incorporates an isotropic von Mises yield criterion and a single-term Chaboche nonlinear kinematic hardening rule. Monotonic and reversal loading stress-strain curves are predicted and compared with experimental results. The model accurately captured the Bauschinger effect for both materials, but it needs help to effectively model the permanent softening behavior observed in TWIP980 steel. Overall, the proposed modeling method agrees well with experimental results for monotonic loading and accurately represents the Bauschinger effect and transient behavior during reversal loading. However, better improvements are needed to capture the permanent softening behavior of TWIP980 steel.

The choice of material behavior models, as well as the forming procedures such as loadings and their sequences are essential in plastic flow and springback. In this study, the combined torsion and bending of a thick-walled tube under an internal pressure is simulated to predict bending and torsion springback. Continuum Damage Mechanics and the nonlinear kinematic hardening models are assumed and a numerical tool is developed to predict the springback analytically. The numerical model is verified by comparing the experimental results of simultaneous bending and torsion of a pure aluminum tube conducted by Wu et al. (Int J Mech Sci 131–132:191–204, 2017) with the numerical results. The experimental results of Sorour et al. (Thin-Walled Struct 144:106336, 2019), which studied the bending of a tube with internal pads, are also modelled with the present numerical model. The effects of loading sequences on the springback are also investigated. [ABSTRACT FROM AUTHOR]

By blending the primal‐dual interior point method (PDIPM) and the return mapping algorithm, we propose a hybrid strategy of implicit stress update for a class of hypoelastic‐plastic models with the hardening rule whose evolution is restricted by the memory surface. The inequality constraint relevant to the memory surface is replaced by the equality constraint by the introduction of a slack variable, and the duality gap is gradually reduced by using path‐following method. First, we formulate an optimization problem corresponding to the principle of maximum plastic dissipation for the standard von‐Mises plasticity with isotropic and kinematic hardening rules and its variant for the model with the memory surface. Next, after function forms employed for the elastic‐plastic model are specified, the PDIPM to realize an implicit stress update is briefly reviewed and then applied to the model involving the memory surface to replace the relevant inequality constraint by the equality constraint by the introduction of a slack variable. Then, we present a hybrid scheme that combines the standard return mapping algorithm with the PDIPM. The numerical accuracy of the proposed stress update algorithm for the conventional elastic‐plastic model is verified in comparison with the standard return mapping algorithm using iso‐error map. Also, targeting a notched round steel bar under cyclic loading with three different amplitudes, we demonstrate the performance for the stress update using the elastic‐plastic model with the memory surface. Finally, the capability of the proposed algorithm is proven through a typical real‐life example such that a steel bridge is subjected to earthquake for which the residual load carrying capacity must be estimated. [ABSTRACT FROM AUTHOR]

Constitutive models constructed within the combined framework of kinematic hardening and bounding surface plasticity have proved to be successful in describing the rate-independent deformation of soils under non-monotonic histories of stress or strain. Most soils show some rate-dependence of their deformation characteristics, and it is important for the constitutive models to be able to reproduce rate- or time-dependent patterns of response. This paper explores a constitutive modelling approach that combines multiple viscoplastic mechanisms contributing to the overall rate-sensitive deformation of a soil. A simple viscoplastic extension of an inviscid kinematic hardening model incorporates two viscoplastic mechanisms applying an overstress formulation to a 'consolidation surface' and a 'recent stress history surface'. Depending on the current stress state and the relative 'strength' of the two mechanisms, the viscoplastic mechanisms may collaborate or compete with each other. This modelling approach is shown to be able to reproduce many observed patterns of rate-dependent response of soils. [ABSTRACT FROM AUTHOR]

The description of cyclic plasticity requires experimental determination of the constants entered into respective resulting equations. In this paper, a method is proposed for determining the parameters and constants of a Lemaitre-type damage accumulation model on the example of P2M rotary steel. The model is based on the Voce isotropic and the Armstrong–Frederick kinematic hardening law. The method of experimental determination involves standard uniaxial tension tests as applied to the parameters of isotropic hardening, and low-cycle fatigue tests, to the constants of damage accumulation and parameters of kinematic hardening. The method is applicable to any alloy that fits the model representations. Using the constants and parameters found, the behavior of cylindrical P2M steel specimens under cyclic loading is modeled by finite element simulation and their fatigue curve is plotted. The predicted fatigue life of P2M steel correlates well with experimental data. [ABSTRACT FROM AUTHOR]

Constitutive models are essential for assessing the mechanical response of complex materials, yet uncertainties in model forms and parameters persist due to the influence of micromechanisms and microstructural features. We develop Bayesian protocols to iteratively refine both model forms and the associated material properties for complex constitutive models. Our aim is to provide rigorous, probabilistically informed evaluations of improvements achieved with increasing model complexity. Leveraging high-throughput experimental microindentation data, the protocols involve three steps: (i) emulating FE simulations using multi-output Gaussian process surrogate models, (ii) calibrating an initial simple constitutive model against experimental data, and (iii) progressively enhancing model complexity by iteratively improving agreement between simulations and experiments. The various model forms are compared using model form probabilities and aggregate discrepancies. Sobol indices are used to quantify the identifiability of material properties, aiming to prevent parameter proliferation. We apply this protocol to identify the optimal form of cyclic plasticity models for duplex Ti-6Al-4V. Although tailored for cyclic plasticity models, these protocols hold promise for calibrating and refining nonlinear constitutive models across diverse material classes. • A Bayesian framework is developed to systematically refine constitutive model forms. • The framework is used to optimize the Ohno–Wang model for Ti-6Al-4V. • Model form probability and discrepancy are used to balance fidelity and complexity. • The framework achieves similar levels of fidelity with 50% fewer material properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Although the prediction of earing in the cup drawing process is considerably related to the yield surface shape, the yield surface evolution is also essential for the final ear form. The bending-unbending issue is a fundamental subject occurring on the die and punch shoulders. Since the yield stress is loading path dependent in reversal loadings, the conventional hardening models used in the monotonic loading conditions bring about inaccurate outcomes for predicting the ultimate earing profile, and a kinematic hardening model should be incorporated into the constitutive equations. This study elucidates the yield surface evolution effect involving expansion and translation simultaneously on the ear formation. A sixth-order polynomial yield function was employed to precisely characterize the yield surface shape, while a combined isotropic-kinematic hardening model was implemented to represent the evolution of the yield surface. The translation of the yield surface position was defined by the Armstrong-Frederic hardening model. Punch force-stroke responses and the ear form profiles were predicted by the implemented plasticity model in Marc using the Hypela2 user subroutine and compared with the experimental results. The combined hardening assumption yielded an increase in the mean cup height when compared to the isotropic hardening assumption. Moreover, The HomPol6 coupled with the combined hardening showed a better agreement with the experimental results.

In order to better describe the uniaxial ratcheting behavior of Z2CDN18.12N austenitic stainless steel, the Abdel-Karim-Ohno model was improved under the framework of the unified viscoplastic cyclic constitutive theory. By introducing a plastic strain memory surface into the isotropic hardening rule, the model parameters were determined. Further, the Abdel-Karim-Ohno model and the improved Abdel-Karim-Ohno model were used to predict the uniaxial ratcheting effect behavior of Z2CDN18.12N austenitic stainless steel at the room temperature. The influences of mean stress, stress amplitude, stress rate and loading history on the uniaxial ratcheting strain of Z2CDN18.12N austenitic stainless steel were studied by the two models, respectively. The uniaxial ratcheting strain level increased with the increasing mean stress and stress amplitude, decreased with the increasing stress rate, being more sensitive to the lower stress rate, and the loading history had great influence on the ratcheting behavior. Comparison of the prediction results of the two models with the experimental data proved the effectiveness of the improved model. [ABSTRACT FROM AUTHOR]

The aim of this paper is to model the elastic–plastic uniaxial behaviour of a quenched and tempered steel. The common Chaboche isotropic kinematic hardening model (CIKH) is introduced, and a physics-based procedure is proposed to determine its parameters. This procedure is based on strain- and stress-controlled tests and is focused on the stabilized cycles. The imposed cycle properties are the hysteresis area, the stress range, the slope at the inversion points, obtained from the stabilized cycles of strain-controlled tests, and the ratcheting rate extracted from a stress-controlled test. The novelty of the algorithm is to determine the hardening parameters from the global properties of the cycle rather than imposing a pointwise fitting, which is also implemented to calculate the parameters for a comparison. The Bouc–Wen model showed great flexibility in describing nonlinear behaviours, corresponding to different physical phenomena, through an appropriate tuning of its parameter values. In this paper, another optimization approach is developed to estimate the Bouc–Wen coefficients and accurately describe the same experimental cycles. The performances of the Bouc–Wen model are compared with the predictions of the Chaboche model, and a discussion comparing the techniques used to reproduce cyclic plastic behaviour is provided. [ABSTRACT FROM AUTHOR]

Several constitutive models had been developed by other researchers to cover the main features of mechanical behaviour of natural overconsolidated clays, such as the nonlinear stress–strain response at small and large strains, and the recent stress history effect. Kinematic hardening models include these features to facilitate realistic predictions of soil–structure interaction. This paper presents the further development of a kinematic hardening model BRICK that includes anisotropy and the influence of soil structure on the mechanical behaviour of a natural clay. High quality laboratory tests were used to calibrate the input parameters of the model in a single element configuration, and a documented boundary value problem of tunnel excavation was used to validate the model in finite element calculations. A comprehensive comparative study between the predictions of different kinematic hardening models, using two different software packages, was carried out. It was observed that the SA_BRICK model is in fair agreement with the observed data and gives improved predictions in comparison to other kinematic hardening models, particularly in terms of narrowness of the settlement trough above the tunnel. Advanced predictions of ground deformations caused by tunnel excavations can be effectively used to mitigate possible damage of existing structures affected by tunnelling in an urban environment. [ABSTRACT FROM AUTHOR]

This paper presents a constitutive model enabled to simulate monotonic and cyclic behaviour of clay and sand in a unified framework. The bounding surface concept has been utilized to predict a smooth transition from elastic to plastic state of the soil. A new dilatancy relation is proposed to capture the volumetric behaviour of sand and clay in a unified manner. Moreover, closed hysteresis loops and accumulation of the plastic strain during cyclic loading have been regarded appropriately by transmitting the similarity centre of the loading and bounding surfaces in the stress space through a kinematic hardening rule. Furthermore, in order to improve the accuracy and convergence property of the model, an implicit integration scheme is introduced. Finally, the accuracy and performance of the model are verified using several experimental data from the literature. Both drained and undrained behaviours under monotonic and cyclic loading for sand and clay are considered, and the characteristic features of the behaviour are captured. [ABSTRACT FROM AUTHOR]

Understanding the effect of thermomechanical loads during finish cutting processes, in our case hard milling, on the surface integrity of the workpiece is crucial for the creation of defined quality characteristics of high-performance components. Compared to computationally generated modifications by simulation, the measurement-based determination of material modifications can only be carried out selectively and on a point-by-point basis. In practice, however, detailed knowledge of the changes in material properties at arbitrary points of the high-performance component is of great interest. In this paper, a modification of the well-known Johnson–Cook material model using the finite element software Abaqus is presented. Special attention was paid to the kinematic hardening behavior of the used steel material. Cyclic loads are relevant for the chip formation simulation because, during milling, after each cut, the material under the surface is loaded plastically several times and not necessarily in the same direction. Therefore, in analogy, multiple bending was investigated on samples made of 42CrMo4. A pronounced Bauschinger effect was observed in the bending tests. An adaptation of the material model to the results of the bending tests was only possible to a limited extent without kinematic hardening, which is why the Johnson–Cook model was supplemented by the Armstrong–Frederick hardening approach. The modified Johnson–Cook–Armstrong–Frederick material model was developed for practical use as a VUMAT and verified by bending tests for simulation use.

This article investigates the relevance, for material parameter identification, of substituting a set of 3 experiments (uniaxial tension, monotonous shear and reverse shear tests) by a test performed by a Computer Numerical Control (CNC) machine, where a spherical tool replacing the cutting tool performs a simple path on a fixed square sheet. This tool path is defined by one indent, one go linear path, one further indent and one return linear path. This so called line test is a simple version of Single Point Incremental Forming (SPIF) process where the depth of the produced part is however usually smaller. Completed by a uniaxial tensile test, this line test allows identifying the parameters of both kinematic and isotropic hardening models. This CNC test provides an easy alternative to tensile-compression test or reverse shear test. It generates non uniform cyclic loadings in sheets which are necessary to accurately identify kinematic hardening laws. This identification method of isotropic and kinematic hardening is applied on a brass CuZn37 sheet of 1 mm thick. It uses only the experimental measured force during the line test and a classical tensile test. The Levenberg–Marquardt algorithm is used to determine the optimal hardening material set of parameters, through inverse modelling based on finite element (FE) simulations. The sensitivity of the identification method is evaluated and the approach is validated by the capacity of the identified hardening material data set to simulate an experimental reverse shear test and a second “SPIF like test” having a more complex shape. [ABSTRACT FROM AUTHOR]

Large diameter welded pipes are amongst the most cost-effective transportation means for oil and gas. The production of those pipes involves different cold forming steps, as a result of which the mechanical properties on pipe will be different from the plate or coil properties. The steel manufacturer has several parameters at hand to control the properties of his final product. However, the pipe manufacturer only has a narrow process window, but eventually he is responsible for the properties of his product, i.e. the pipe. Furthermore, for some pipeline applications, the properties in both the transverse and longitudinal pipe direction must be within certain limits. This paper presents a Finite Element model which allows simulating pipe forming and subsequent mechanical testing and thus could be adopted to predict pipe properties from coil/plate properties. The complex hardening behaviour exhibited by pipeline grades is described by an extended version of the Levkovitch-Svendsen model, a constitutive model which accounts for isotropic, kinematic and distortional hardening. To validate the model, numerical predictions were compared to experimental results obtained from mechanical tests conducted on 32″ × 16 mm X65 HSAW (Helical Submerged Arc-Welding) pipes. The properties on pipe were evaluated by means of ring expansion tests and tensile tests on (flattened) full-thickness dog-bone samples and non-flattened round bar samples. Furthermore, tensile tests were performed in the transverse and longitudinal pipe direction and tests were conducted before and after hydrotesting. In general, the numerical predictions are in good agreement with the experimental data.

Laser shock peening (LSP) is investigated as a potential tool for reducing tensile back stress, shown here applied to rolled and annealed 304L austenitic steel. The back stress of treated and untreated dog-bone samples is extracted from hysteresis tensile testing. Electron back-scatter diffraction (EBSD) and orientation imaging microscopy (OIM) analysis quantify the geometrically necessary dislocation (GND) density distribution of unstrained and strained as well as unpeened and peened conditions. Finite element analysis (FEA) simulation models back stress and residual stress development through tensile testing and LSP treatment using known LSP pressure models and Ziegler's nonlinear kinematic hardening law. Nonlinear regression fitting of tensile testing stress-strain in as-received specimens extracts the kinematic hardening parameters that are used in numerical study. This research shows LSP may be used to overcome manufacturing design challenges presented by yield asymmetry due to back stress in rolled steel. [ABSTRACT FROM AUTHOR]

The aim of this paper is to develop a linear kinematic elastoplastic model for simulating the mechanical behavior of a heat-affected zone under low-cycle fatigue for welded S355J2 low-carbon steel. First, an experimental procedure is developed by means of a Gleeble machine for creating macroscopic tensile specimens with different homogeneous metallurgical compositions according to a welding continuous cooling transformation diagram. Then, cyclic tensile tests are carried out by prescribing different strain amplitudes up to 1%. By considering the stabilized behavior at mid-life, the yield stress and hardening modulus are identified as functions of the metallurgical composition by means of a linear mixture rule. Comparisons with numerical simulations are presented to show the efficiency of the multi-phase cyclic linear kinematic elastoplastic model proposed in this work.

In finite deformation inelasticity, one often has to deal with the incompressibility constraint. In the past, this was dealt with using, for example, an exponential mapping approach, which yields exact volume preservation in plastic deformations. In this article however, the special‐linear update approach by Hurtado et al. The special‐linear update: An application of differential manifold theory to the update of isochoric plasticity flow rules, Int J Numer Methods Eng. 2014;97(4):298‐312, which utilizes a projection method to fulfill the incompressibility constraint is used. The model is applied to isotropic plasticity by a novel approximation of the logarithm and treats kinematic hardening without losing the symmetry of the internal variables. The model results are compared to models utilizing an exponential mapping approach in numerical experiments. [ABSTRACT FROM AUTHOR]

In this study, a combination of Chaboche's nonlinear kinematic hardening model and Lemaitre's anisotropic continuum damage mechanics (CDM) model is used to predict ratcheting strain of different loading paths. The fictitious continuum domain is considered, and the consistent relations are developed between real and fictitious materials. The return mapping algorithm is developed to obtain the plastic strain of different loading paths. Non-proportional loading paths are simulated by the combined model. The ratcheting strain of the stress-strain controlled loading paths is obtained numerically and compared with the experimental results of the cyclic loading tests of Corona et al. [ABSTRACT FROM AUTHOR]

The aim of this paper is to model the elastic–plastic uniaxial behaviour of a quenched and tempered steel. The common Chaboche isotropic kinematic hardening model (CIKH) is introduced, and a physics-based procedure is proposed to determine its parameters. This procedure is based on strain- and stress-controlled tests and is focused on the stabilized cycles. The imposed cycle properties are the hysteresis area, the stress range, the slope at the inversion points, obtained from the stabilized cycles of strain-controlled tests, and the ratcheting rate extracted from a stress-controlled test. The novelty of the algorithm is to determine the hardening parameters from the global properties of the cycle rather than imposing a pointwise fitting, which is also implemented to calculate the parameters for a comparison. The Bouc–Wen model showed great flexibility in describing nonlinear behaviours, corresponding to different physical phenomena, through an appropriate tuning of its parameter values. In this paper, another optimization approach is developed to estimate the Bouc–Wen coefficients and accurately describe the same experimental cycles. The performances of the Bouc–Wen model are compared with the predictions of the Chaboche model, and a discussion comparing the techniques used to reproduce cyclic plastic behaviour is provided.