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Advanced simulations are needed in the industry nowadays for reliable design of various machine parts. A complex computation is presented here to describe the whole manufacturing process, apart from the machining, of forged spur gear for a reverse transmission from a car gearbox. A coupled thermomechanical analysis was realized through the explicit finite element method, while the stress–strain analysis was conducted in all phases of the production with time- and temperature-dependent constitutive law. The influence of process parameters was assessed, and the magnitudes of forging load were compared for selected dimensions of intermediate product (blank) and its initial temperature (preheating). The numerical simulation was finished with the flash trimming along the circumference, so the temperature-dependent ductile failure criterion proposed by Johnson and Cook was accounted for as well.

The ductile fracture has been observed in large as well as small scales. Three chosen Lode and pressure dependent phenomenological ductile fracture criteria with cut-offs were calibrated for aluminium alloy EN AW 2024-T351 using an enhanced hybrid experimental–numerical technique. It consisted of calibrating all the material constants of fracture criteria altogether. This enabled ready determination of the cut-off related constant for one of those criteria. Moreover, a non-quadratic Lode dependent plasticity model was coupled with the ductile failure criteria to form the damage plasticity approach in the numerical analysis. The fracture criteria were calibrated using the standard – large – sized specimens including a non-standard upsetting test. The specimens used for the calibration of failure criteria are usually ten times larger than that of a specimen for the small punch test. The transferability of calibrated parameters was tested and fair predictability was observed for all numerical models when applied to small scales.

Accurate material behaviour and its response to loading are needed for a reliable calibration of ductile failure criteria. Non-quadratic yield functions are often necessary for such a description. Nevertheless, it leads to the prediction of stress states that are inconsistent with the expected behaviour and deformations that are in contradiction with the experiments when the associated flow rule is adopted. These problems may be solved by applying a less restrictive non-associated flow rule. Therefore, an isotropic non-associated non-quadratic phenomenological plasticity model was developed as a function of the second and third invariants of deviatoric stress tensor. The yield function that is convex was proposed to allow for different yield stresses in tension, compression and shear. For simplicity, the same function was used for the plastic potential. Each of these functions is described by seven material parameters. The scheme of the so-called next increment corrects error method was adopted for the implementation of the proposed model within finite elements. Above that, three additional plasticity models were calibrated for 2024-T351 aluminium alloy. It is shown how the non-associated flow rule resolves the above-mentioned problems. Moreover, the possible extensions of the proposed yield function are described to include the hydrostatic stress dependence. Přesný popis chování materiálu a jeho odezva na zatěžování jsou potřeba pro věrohodnou kalibraci kritérií tvárného porušování. Pro takový popis jsou často potřeba nekvadratické funkce plasticity. To vede nicméně k predikci napěťových stavů, které nejsou konzistentní s očekávaným chováním a deformací, které jsou v rozporu s experimenty, pokud je přijatý sdružený zákon tečení. Proto byl vyvinut izotropní nesdružený nekvadratický fenomenologický model plasticity jako funkce druhého a třetího invariantu deviátoru tenzoru napětí. Funkce plasticity, která je konvexní, byla použita i pro plastický potenciál. Každá z těchto funkcí je popsána sedmi materiálovými parametry. Schéma takzvané metody další přírůstek koriguje chybu bylo přijato pro implementaci navrženého modelu v rámci konečných prvků. Navíc byly kalibrovány tři další modely plasticity pro slitinu hliníku 2024-T351. Je ukázáno, jak nesdružený zákon tečení řeší výše zmíněné problémy. Mimoto jsou popsána možná rozšíření funkce plasticity o zahrnutí závislosti na hydrostatickém napětí.

Cyclic plasticity models for the description of the deformation characteristics of austenitic stainless steel 304 at a room temperature have been studied with the focus on its industrial use. The main objective of this work is to investigate the capabilities of the classical Chaboche model with four terms which is commonly used in practice, and to compare those capabilities with the same model enriched with the evolution of some kinematic hardening parameters. The incorporation of parameters evolution brings significant number of necessary parameters to be determined, compared to the classical Chaboche model with four terms. To overcome excessive number of necessary parameters, also two terms Chaboche model with parameters evolution is used. Presented paper evaluates the time and temperature independent modeling possibilities of Chaboche combined nonlinear kinematic hardening model and isotropic hardening model with von Mises yield criterion.

This paper deals with a small punch test and ductile failure prediction of austenitic stainless steel 316L. Comprehensive investigation of fracture surfaces was conducted as well as examination of δ-ferrite and σ-phase present in the material in order to reveal the reason of occurrence of nonstandard type of fracture. Three phenomenological ductile fracture criteria were selected for comparative simulations regarding the prediction of crack initiation and propagation during the SPT. These criteria were calibrated by using the fracture tests of smooth cylindrical specimens, notched cylindrical specimens, notched tube specimens and cylinders with spherical recess. The whole material model including the fracture criteria with von Mises plasticity and element deletion technique for simulation of the crack initiation was implemented by using the user subroutine Vectorised User MATerial into the commercial finite element code of Abaqus. Finally, the simulation results with three ductile fracture criteria are compared and discussed based on the experimental results. Only one of the failure criteria captured the displacement at fracture correctly.

Notched specimen was designed for testing in compression. It was manufactured from the aluminium alloy 2024-T351, which is widely used in the aerospace, aeronautical and automotive industry. The test, among others, was used for the calibration of three uncoupled ductile fracture criteria dependent on the first invariant of stress tensor and third invariant of deviatoric stress tensor. The yielding was described by three plasticity models dependent on the second invariant of deviatoric stress tensor – proposed by von Mises, dependent on the second and third invariants of deviatoric stress tensor, and the most complex yield criterion dependent on the first invariant of stress tensor and second and third invariants of deviatoric stress tensor. All models were implemented into Abaqus commercial finite element code using VUMAT user subroutine. The ductile fracture prediction was carried out by widely used element deletion technique for specimen under compression. In the aftermath, the results were compared to experiments to see the performance of complex plasticity models with uncoupled fracture criteria.

The paper provides extensive experiments on aluminium alloy 2024-T351. Those cover the uniaxial strain- and stress-controlled tests using cylindrical specimens. Then, multiaxial tests were conducted via strain- and stress-controlled tensile–torsional loading on tubular specimens, which also cover the following non-proportional test – the 3-step experiment carried out in order to document the additional hardening. The paper also provides a fractography using the scanning electron microscopy and the life assessment. A novel approach to fatigue life prediction is presented, based on replacing the plastic part of the strain-life curve by the non-linear term in order to provide more variability and approximation ability. The broad experimental base will serve as a basis for future calibration and simulation using advanced cyclic plasticity models within the finite elements.

The hardwood is a natural composite, which finds applications in many fields such as an important building material. Attention was paid to the accurate description of the European beech wood under high strain rates in order to constitute a reliable input for the finite element method. It was done on the basis of split Hopkinson tensile bar tests, taking also into consideration the previously reported pressure bar tests to capture the tensile–compressive failure asymmetry, which was incorporated through the stress triaxiality. Strains measured on the steel bars for specimens oriented in all principal loading directions were used to calibrate the fully orthotropic behaviour of elasticity, plasticity and fracture. The concept of continuum damage mechanics was applied to the damage accumulation in order to simulate the crack propagation within explicit finite elements realistically.

The paper presents a complex material model which covers the elastic-plastic behavior, material deterioration and ductile fracture. The calibration of such model was conducted for Aluminum Alloy (AA) 2024-T351 using specimens with various geometries and loading which covers various stress states. The model was then applied to the simulations of tensile test of plates. The computations were carried out in Abaqus/Explicit using the user subroutine Vectorized User MATerial (VUMAT), where the crack initiation and subsequent propagation was realized using the element deletion technique. The results were compared to the experimental observation in the end.

The experimental program was designed and proportional tests carried out at a room temperature on aluminium alloy 2024-T351. These concerned tension, torsion and compression, in order to investigate the damage accumulation nonlinearity and to reliably calibrate new phenomenological ductile fracture criterion. This fracture model, KHPS2, expressed through the fracture strain, was dependent on the stress triaxiality and normalized third invariant of deviatoric stress tensor. The ductile fracture model was then coupled with the yield criterion, as in the continuum damage mechanics, using the material softening. The plasticity model was considered in the form of taking into account the Lode dependence for investigated material, through normalized third invariant of deviatoric stress tensor. The whole approach, fully applicable to multiaxial ductile fracture related problems, was implemented using the user subroutine into the commercial software, based on the explicit finite element method. In the end, the proposed approach was verified using chosen realized fracture tests, which were used in the calibration, and newly designed KHPS2 criterion along with an existing one—modified Hosford–Coulomb model. The latter model showed better performance in simulations despite worse approximation ability, which can be attributed to its micromechanically-motivated formulation. Keywords: Al–Mg–Cu alloy, Failure, Finite element, Elastic–plastic material, Weakening, Polycrystalline material

Two alternative methods for the stress–strain curve determination in the large strains region are proposed. Only standard force–elongation response is needed as an input into the identification procedure. Both methods are applied to eight various materials, covering a broad spectre of possible ductile behaviour. The first method is based on the iterative procedure of sequential simulation of piecewise stress–strain curve using the parallel finite element modelling. Error between the computed and experimental force–elongation response is low, while the convergence rate is high. The second method uses the neural network for the stress–strain curve identification. Large database of force–elongation responses is computed by the finite element method. Then, the database is processed and reduced in order to get the input for neural network training procedure. Training process and response of network is fast compared to sequential simulation. When the desired accuracy is not reached, results can be used as a starting point for the following optimization task.

A new finite element formulation, aimed at the modeling of cross roll straightening of circular bars is presented. It is based on Eulerian description of elastoplastic material flow through a stationary finite element mesh, which is fixed in space and coupled with the multi-roller straightening machine. This approach leads to extremely effective computational algorithm which provides the relation between input parameters like curvature, diameter and material of the bar, straightening rollers geometry and intermeshing on one hand and output bar curvature and residual stress distribution on the other. Using this strategy, multiple repetition of the straightening process analysis for variable intermeshing scheme is a feasible task, aimed to optimization of roller intermeshing. Basic features of the algorithm are described, some verification results presented and compared with real experiments realized in industrial conditions. The industry was also a motivation for the optimization study, presented in the last part of paper. The results prove that the suggested solution strategy is a mighty tool for effective analysis of cross roll straightening and show a great potential for other types of straightening processes as well.

The performance of ductile fracture criteria often depends on the accuracy of material constants identification. Calibration process of three uncoupled phenomenological models was analysed. All of them contain the strain hardening exponent which is related to material plasticity as one of the fracture criteria parameter. More flexibility, better approximation of the fracture locus and more convenient shape of the fracture envelope might be reached when the strain hardening exponent is considered as another independent parameter of the fracture criteria in the identification process. Results are illustrated on the example of two structural steels, AISI 316L and AISI 1045, respectively.

The cutting process is now combined with machining, milling, or drilling as one of the widespread manufacturing operations. It is used across various fields of engineering. From an economical point of view, it is desirable to maintain the process in the most effective way in terms of the fracture surface quality or minimizing the burr. It is not possible to manage this experimentally in mass production. Therefore, it is convenient to use numerical computation. To include the crack initiation and propagation in the computations, it is necessary to implement a suitable ductile fracture criterion. Uncoupled ductile fracture models need to be calibrated first from fracture tests when the test selection is crucial. In the present article, there were selected widespread uncoupled ductile fracture models calibrated with, among others, an extremely low-stress triaxiality test realized through the compression of a cylinder with a specific recess. The whole experimental program together with the cutting process experiment were carried out on AISI 1045 carbon steel. After the fracture models were calibrated and the cutting process was simulated with their use, fracture surfaces and force responses from computations were compared with those experimentally obtained and concluding remarks were made.

Phenomenological ductile fracture criteria represent, among others, one of powerful tools for prediction of ductile fracture. These criteria are based on evaluating damage throughout the solid body as a response to straining. The damage is influenced by plasticity but not vice versa. Therefore, these criteria are often called uncoupled as they do not mutually couple the damage and plasticity. One of immense advantages of such criteria is a possibility not only to predict the crack initiation but also to follow the propagation based on the damage. Moreover, it is not restricted for one specific locus but the damage is evaluated in the entire solid body and one or more cracks can be tracked simultaneously or sequentially. Ductile fracture criteria are calibrated on the basis of several independent calibration tests under various stress states. One way how to verify calibrated model is to simulate numerically an experimental tests and follow the crack initiation and propagation. In the present study, selected phenomenological criteria were calibrated using various calibration tests. Then, selected calibration tests were simulated together with implemented ductile fracture criteria. In our case, the verification is carried out on tensile cylindrical specimens. Finally, computationally obtained results were compared to the experimentally observed ones and the prediction ability and reliability of selected phenomenological criteria is discussed.

Extended Mohr–Coulomb criterion which is uncoupled, therefore the plasticity is not influenced by the damage, was selected and calibrated. Experiments on the aluminum alloy 2024-T351 were carried out. Further, the impact of the damage rule proportionality was investigated. The damage exponent was sequentially held 1, 2 and 3, respectively. Therefore, the influence of the damage rate on the damage failure in finite element simulations was examined. Numerical simulations of the tensile test of smooth and notched cylindrical specimens and flat grooved specimen were performed. It is also shown that there is inability to predict slant fracture by uncoupled models for flat grooved specimen and in the final phase of tensile tests of cylindrical specimens.

Presented paper summarizes the weld assessment on the basis of national standards. The approach concerning the static loading has been still not adequately developed in standards. The standard of American Institute of Steel Construction was considered as the best candidate for implementation into the finite element method using post-processing of a particular weld. A comparative analysis of maximum allowable loadings of weld connection models loaded in-plane and out-of-plane has been performed. Results obtained by the finite element method and American and Czech standards were compared and the conclusions of applicability and reliability were made. Předložený článek shrnuje hodnocení svarů podle národních norem. Přístup týkající se statického zatížení stále nebyl v normách dostatečně vyvinut. Norma Amerického ústavu pro ocelové konstrukce byla za nejlepšího kandidáta pro implementaci do metody konečných prvků pro zpracování konkrétního svaru. Byla provedena srovnávací analýza maximálních dovolených zatížení modelů svarových spojů zatěžovaných v rovině a mimo rovinu. Byly srovnány výsledky získané pomocí metody konečných prvků pro Americkou a Českou normu a byly formulovány závěry o použitelnosti a spolehlivosti.