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Hardwood species are becoming increasingly important with the growing need for a diversity of forests that have recently been facing global temperature changes or conifer pests. This further leads to the growth of its potential as a building material that may originate from sustainable production. As hardwoods need to be properly processed, the article deals with the disintegration of European beech. The influence of wood grain direction, uncut chip thickness and cutting speed on the cutting force magnitudes was experimentally investigated using the device with a rotating arm of approximately 4 m in diameter. Then, the disintegration process was modelled using the finite element method in Abaqus/Explicit. The developed material model consisting of orthotropic elasticity and plasticity with rate-independent and rate-dependent tensile–compressive failure asymmetry was implemented through the user subroutine, while the crack initiation and propagation were realized using the element deletion technique. The computationally predicted average values of cutting forces and chip shapes were, except for a few tests, in good agreement with the experiments. It means that the model may be used for further investigation, such as the influence of tool wear. Druhy tvrdého dřeva začínají být čím dál více důležité s rostoucí potřebou diverzity lesů, které poslední dobou čelí globálním změnám teploty nebo škůdcům jehličnanů. Toto dále vede na růst jeho potenciálu jako stavebního materiálu, který může pocházet z udržitelné produkce. Jelikož tvrdá dřeva je nutné vhodně zpracovat, tak se článek zabývá desintegrací evropského buku. Experimentálně byl zjišťován vliv směru kresby dřeva, tloušťky neodřezané třísky a řezné rychlosti na velikosti řezných sil s použitím zařízení s rotujícím ramenem o průměru přibližně 4 m. Poté byl modelován desintegrační proces s pomocí metody konečných prvků v Abaqus/Explicit. Vyvinutý materiálový model sestávající z ortotropní elasticity a plasticity s časově nezávislou a časově závislou asymetrií porušení v tahu a tlaku byl implementován pomocí uživatelské subrutiny, zatímco iniciace trhliny a šíření byly realizovány pomocí techniky mazání prvku. Výpočtově predikované průměrné hodnoty řezných sil a tvarů třísek byly, až na několik testů, v dobré shodě s experimenty. To znamená, že model může být použitelný pro další výzkum, jako například vlivu opotřebení nástroje.

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.

The plastic behavior of some polycrystalline metals exhibit the Lode dependence. There are many yield criteria, which are capable of such a description. Nevertheless, these criteria predict wrongly the deformation or the stress state or both in some cases. This paper focuses on the comparison of the deformation predicted by a classical von Mises yield criterion and advanced model, which covers the Lode dependence. The comparison was carried out using the tensile tests of two types of specimens manufactured from the aluminum alloy. The numerical simulations were conducted in the Abaqus/Explicit finite element commercial code and the material models were implemented using the user subroutine.

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 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.

The ductile failure predictions have been an issue in many engineering applications. It begins with a design of machines and tools, continues with an evaluation of manufacturing processes, and last but not least ends with the assessment of various structures. The paper deals with a predictability of used criteria for a random structure of aluminum alloy 2024-T351, which was performed under the conditions of room temperature three-point bending. The bi-failure mode creates a space for the numerical studies of various approaches and gives an insight into the model performance. The plasticity was described by Lode-dependent yield criterion, which was coupled with several pressure and Lode-dependent fracture models to form a continuum damage mechanics approach via the material weakening. It was incorporated through a nonlinear damage accumulation, which was finally implemented using Fortran 77 subroutine into abaqus/explicit. All the models exhibited a good ability of crack onset prediction in terms of the force responses and realistic predictability of the crack propagation. The field of deformations was successfully compared with experimental data obtained by an optical method.

Variety of metals are complex materials exhibiting various behavior under different loading. Many metallic materials exhibit Tresca-like behavior rather than von Mises. It means different behavior in tension under plane strain and uniaxial stress conditions. This might be described by Lode dependent plasticity which should result in better prediction in force or torque responses of material tests. Good agreement between computation and experiment is also very important when calibrating the ductile fracture criteria. Several tests under plane strain and uniaxial stress states were carried out on aluminum alloy 2024-T351 where the Lode dependency was significant. The Lode dependent plasticity was implemented along with von Mises and Tresca-like yield criteria, which resulted in improvement of force–displacement responses of plane strain tests simulations. But it also caused significant change in the stress state of tensile flat and grooved plates which wrongly approached uniaxial tension condition. This inconvenience prevents plane strain experiments from using for calibration of ductile fracture criteria under these circumstances.

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.

The aluminium alloy 2024-T351 and AISI 1045 carbon steel was examined in scope of uncoupled ductile fracture criteria calibration using newly designed specimen. Its novel geometry allowed to reach extremely low stress triaxialities. The analysis of fracture envelopes was carried out with comparison of each criteria cut-off regions after the calibration where one novel criterion, KHPS, has been introduced. Ductile fracture criteria implemented into the commercial finite element code Abaqus through user subroutine VUMAT were applied to simulation of compression of newly designed cylinder with specific recess to show the crack prediction ability using the element deletion technique. Crack initiation loci together with force responses were compared to experimental observations.

The hardwood, as a natural composite, may be subjected to the dynamic loading in many applications, such as the high-speed disintegration or structural collapses. The correct material description is needed for finite element modelling that can take place in the design stages of wood manufacturing processes or building the wooden structures. The split Hopkinson pressure (Kolsky) bar test provides the data for high strain rates. The experiments were carried out on the European beech wood in all the principal loading directions. The tests were repeated computationally in order to obtain the material constants of the complex material model, which covered the anisotropy of elasticity, plasticity as well as fracture behaviour. Moreover, the failure was considered non-symmetric with respect to the tension and compression. This was achieved by incorporating the stress triaxiality dependency into the failure model. The crack initiation and propagation were realized through the element deletion technique within LS-DYNA code. The real behaviour was captured quite well including the pulses in the incident and transmission bars.

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.

Forward extrusion is a manufacturing process in which the cross section of product is reduced by forcing it through the die under high pressure. Cold extrusion is most often used in the mass produc...

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.

This paper presents the calibration of three universal ductile fracture criteria with the stress triaxiality and the normalized third invariant of deviatoric stress dependence. Xue-Wierzbicki, Bai-Wierzbicki and Extended Mohr-Coulomb criteria are calibrated using butterfly specimen and newly designed notched tube specimen for an austenitic stainless steel. Different stress states necessary for successful calibration are generated by suitable combination of tension/compression-shear or tension/compression-torsion loading of both specimens, respectively. Suitability of the specimens for ductile fracture criteria calibration is evaluated comparing the range of reached stress states, the homogeneity of stress in process zone and appropriateness for the computational simulation of tests. Possible combination of above mentioned results with tensile testing of standard and notched cylindrical specimens is discussed, too.

Selected ductile fracture criteria are introduced and applied to prediction of chevron crack initiation and development during forward extrusion of long shafts. We present the calibration of selected criteria for carbon steel, simulate the process of forward extrusion and compare the simulation results with real experiments realized in a cooperating industrial company.

The present paper deals with the modelling of ductile fracture which is the result of severe plastic deformation under monotonic loading. It can be the result of a crash or accident or introduced intentionally. There is a need of increasing the safety in many fields of industrial sector or transportation. The aluminium alloy 2024-T351 is widely used for studies of ductile fracture. The material was supplied as a cold-rolled plate for this study and examined within a broad range of stress states. First of all, the flow curve was determined using the standard tensile test of smooth cylindrical bar. Then, the tensile tests of variously notched cylindrical bars were conducted to show the pressure dependence. The tensile and torsion tests of notched tube were added in order to document the dependency on the deviatoric stress state. Finally, the compression test of smooth cylinder was executed. Then, deviatoric stress state dependent plasticity and the original ductile fracture hyperbolic criterion were calibrated. The damage accumulation nonlinearity was examined through loading–unloading experiments. The double damage curve approach, inspired by the fatigue life prediction, was revisited and calibrated using the semi-cyclic testing. Finally, the softening effect was studied aiming to couple the damage with plasticity. The performance and prediction ability was verified after the model was completely calibrated and implemented into the Abaqus finite element software. Three different cases of tension were chosen for this comparative purpose. The tension of notched cylindrical and tubular specimens and flat specimen. The ductile fracture criterion coupled with plasticity should provide the slant fracture in the conditions of plane strain due to localization. Nevertheless, it is shown that the proposed approach has still some drawbacks in prediction of the crack propagation.

This paper deals with ductile fracture criteria calibration process. Choice of calibration tests and their relation to corresponding type of failure is discussed. Further, some of the calibrated criteria are used to simulation of selected technological processes and results are compared with experiments.

The small punch testing technique under quasi-static loading was examined in the view of punch eccentricity role. It might arise especially when the ball is used as the penetrating tool, instead of hemispherical-ended punch. The austenitic stainless steel AISI 316L was chosen to execute several various “large scale” tests in order to calibrate the multi-linear stress–strain relationship along with the ductile fracture criterion KHPS. All the calibration procedure was performed without using the small punch testing. Then, the model was applied to small punch tests to observe the prediction ability when compared to real small punch experiments. Consequently, a numerical study was conducted to see the role of eccentricity in the case of 2 and 2.5 mm ball diameters used as the penetrating tool. The magnitude of eccentricity up to 0.3 mm was numerically tested. The results showed negligible role of eccentricity for 2 mm ball diameter and minor role for 2.5 mm diameter and studied material.

This paper collects experiences from the development of a silicon sensor laser testing setup and from tests of silicon strip modules (ATLAS End-cap SCT), pixel modules (DEPFET) and large-area diodes using semiconductor lasers. Lasers of 1060 and 680 nm wavelengths were used. A sophisticated method of focusing the laser was developed. Timing and interstrip properties of modules were measured. Analysis of optical effects involved and detailed discussion about the usability of laser testing for particle detectors are presented.