Search

This project is based on the study of computational efficiency in crystal plasticity, so first, as an introduction, aspects that help to understand and serve as preliminary knowledge of crystal plasticity are discussed. Issues related to the atomic arrangement of the materials, in what forms they can be arranged, what structures they can form and what defects they present, among other concepts, are explained. Next, it is necessary to define aspects of the solid mechanics theory, which are the basis for the calculations to be carried out in this project. The kinematics of continuous bodies, equilibrium and the constitutive equations are discussed. The role of numerical integration methods and the two main methods to consider in this project are also introduced. In order to put the above knowledge into practice, a simple one-dimensional shear case is studied and the corresponding comparison between the different numerical integration methods is carried out in order to determine their computational efficiency. Finally, a simple two-dimensional elastoplastic shear case is implemented by means of the analysis of the finite element method (FEM) with the different explicit integration schemes and results and conclusions are obtained from all the procedures carried out

α-uranium, the stable phase of uranium up to 670◦C, has a base-centred orthorombic crystal structure. This crystal structure gives rise to elastic and thermal anisotropy, meaning α-uranium exhibits complex deformation and fracture behaviour. Understanding the relationship between the microstructure and mechanical properties is important to prevent fracture during manufacture and usage of components. The lattice of α-uranium corresponds to a distorted close-packed-hexagonal crystal structure and it exhibits twins of both the 1st and 2nd kind. Therefore, detailed examination of the behaviour of α-uranium can also contribute to the general understanding of the interaction between plasticity, twinning and fracture in hcp crystals. Plastic deformation in α-uranium can be accommodated by 4 slip systems and 3 twin systems, previously identified by McCabe et al. These deformation modes are implemented into a crystal plasticity finite element (CPFE) material model. A temperature dependent, dislocation density based law is implemented to describe the critical resolved shear stress on the different slip/twin systems. The strong anisotropic thermal expansion behaviour is taken into account to simulate the development of internal residual stresses following casting of the material. During cooling, the internal stresses in α-uranium are sufficient to induce plasticity. This effect is quantified using polycrystal simulations, in which first the temperature is decreased, then plastic relaxation takes place, followed by application of a mechanical load. The asymmetry between mechanical properties in tension and compression, due to the presence of twins, is investigated. The model is calibrated using stress strain curves and the lattice strain found from published neutron diffraction experiments carried out on textured samples at ISIS. The strength of the slip systems is found to be lower than in fine grained material, while the strength of the twin system is similar to single crystals. The CP

A criterion of sheet metal localized necking under plane stress was established based on the bifurcation theory and the characteristics theory of differential equation. In order to be capable to incorporate the directional dependence of the plastic strain rate on stress rate, Ito-Goya’s constitutive equation which gave a one to one relationship between stress rate component and plastic strain rate component was employed. The hydromechanical deep drawing process of a cylindrical cup part was simulated using the commercial software ABAQUS IMPLICIT. The onset of breakage of the part during the forming process was predicted by combining the simulation results with the local necking criterion. The proposed method is applied to the hydro-mechanical deep drawing process for A2219 aluminum alloy sheet metal to predict the breakage of the cylindrical cup part. The proposed method can be applied to the prediction of breakage in the forming of the automotive bodies.

Dynamic strength tests published in literature have been analysed by structuraltemporal damage criteria. Parameter τ - incubation time - describing material stability behaviour under high-rate influences have been estimated for Kimachi sandstone, Inada granite and Tage tuff. Two types of dynamic tensile experiments have been used: split Hopkinson pressure bar and spalling. Purely dynamic effect of fracture delay have been observed in the case of Kimachi sandstone and discussed.

A proper set of material parameters is one of the most important aspects for a successful simulation of metal forming processes. Several issues must be observed when choosing the constitutive relation and corresponding material parameters, amongst which the most important are: (i) the magnitude of the plastic deformation of the target forming operation must be contemplated by the parameters of the constitutive model, (ii) possibility of failure prediction in fracture-free materials, and (iii) accurate prediction of geometrical changes caused by plastic deformation. Within this framework, the present article discusses techniques to obtain constitutive parameters of a Lemaitre-type material model. The strategy requires compliance of multiple tensile tests with specimens prepared according to different technical standards. Parameter identification is regarded as an inverse problem and solved using optimization methods.

The paper discusses biaxial experiments and corresponding numerical simulations to analyze the effect of non-proportional loading paths on damage and fracture behavior of ductile metals. Newly developed specimens are taken from thin metal sheets and are tested under different biaxial loading conditions covering a wide range of stress states. In this context, an anisotropic continuum damage model is presented based on yield and damage conditions as well as on evolution laws for plastic and damage strain rates. Different branches of the damage criteria are taken into account corresponding to various damage and failure processes on the micro-level depending on stress triaxiality and Lode parameter. Experiments with biaxially loaded specimens have been performed. Results for proportional and corresponding non-proportional loading histories are discussed. During the experiments strain fields in critical regions of the specimens are analyzed by digital image correlation (DIC) technique while the fracture surfaces are examined by scanning electron microscopy (SEM). Numerical simulations of the experiments have been performed and numerical results are compared with experimental data. In addition, based on the numerical analyses stress distributions in critical parts of specimens are detected. The results demonstrate the efficiency of the new specimen’s geometries covering a wide range of stress states in the shear/tension and shear/compression regime as well as the effect of loading history on damage and fracture behavior in ductile metal sheets.

This paper presents analysis methods utilizing the Finite Element Method for spinner straightening, and shows a guideline for optimum conditions. Two types of analysis methods were composed. Model [F-Expl], “full actual model with explicit scheme”, considers the rotational movement of dies as the actual process using the explicit scheme. Model [BndCr], “a model carrying out fundamental analysis on one cross section based on simple bending in the Finite Element Method (FEM)”, uses the FEM only for calculation of simple bending without rotation for obtaining the deformed bar shape. A series of experiments were conducted in an actual production line as well as the analyses by Model [F-Expl] and [BndCr]. The examination mainly focused upon the effect of straightening intensity by changing the die positions. The experimental and analytical results show some mechanism of straightening and a basic guideline for the optimum working condition.

Residual stresses in forming simulations are typically investigated by analyzing the remaining stress state after removing all external loadings. However, the generation of the stress state during forming remains unknown. As a remedy, we use the plastic and elastic dislocation and incompatibility densities - derived from continuum mechanical and differential geometrical considerations - as indicators to track the generation of residual stresses through out a forming operation. Theoretical backgrounds for small and large strain plasticity are highlighted and practical aspects regarding implementation are provided. Two examples demonstrate the functionality of the approach, whereby the plastic incompatibility density in phenomenological, multiplicative large strain plasticity serves as indicator.

A full spectrum of materials responses to dynamic loading and observed temporal effects of plasticity from a united viewpoint are analyzed. The relaxation model of plasticity with characteristic time idea is capable to effectively predict the instability of the stress-strain dependencies on strain rates. It is shown that empirical models cannot simultaneously simulate the appearance and disappearance of the yield drop unlike the relaxation model of plasticity presented in the paper.

Profile overheating and surface defects during hot aluminum extrusion can occur when seeking higher productivity rates at increased ram speed velocities. The incorporation of cooling channels in the die-design allows overcoming this process limitation by keeping the profile temperature below the melting point of the alloy used [1]. Selective laser melting (SLM) of conformal cooling channels provides, in contrast to conventional manufacturing techniques, the opportunity to place the cooling circuit inside the mandrel of a porthole-die in a well-defined position to the critical bearing region [2]. In the framework of this study, a preliminary numerical investigation on the extrusion process under the assumption of liquid nitrogen cooling is analysed. The results show, that by combining conformal cooling channels with liquid nitrogen as a cooling media high cooling rates, which are well beyond the state of the art of conventional dies, can be achieved. In a hybrid extrusion die set-up, a part of the mandrel, that is additively manufactured, is either joined [3] or directly selective leaser melted onto the conventionally manufactured parts [4]. For a proper implementation in the extrusion process, material testing of the welded joint are needed. Thus, in the current study, tensile tests performed at room temperature for hybrid specimens, partially consisting of conventionally processed tool steel 1.2343 and partially additively manufactured 1.2709, will be presented. Moreover, four different heat treatment sequences of the hybrid specimens will be discussed. In addition, for each configuration, micro-structural images are taken to investigate failure at the bonding region. Finally, an optimal manufacturing sequence for a hybrid die with the described material combination is proposed.

Reduced order modeling techniques proposed by the authors are assessed for an industrial case study of a 3D reinforced composite laminate. Essentially, the main dominant strain micro-structural modes are obtained through standard reduced order modeling techniques applied over snapshots of a representative training strain space. Additionally, a reduced number of integration points is obtained by exactly integrating the main energy modes resulting from the training energy snapshots. The outcome consists of a number of dominant strain modes integrated over a remarkably reduced number of integration points which provide the support to evaluate the constitutive behavior of the micro-structural phases. Results are discussed in terms of the consistency of the multiscale analysis, tunability of the microscopic material parameters and speed up ratios comparing a high fidelity simulation and the multiscale reduced order model.

This document provides information and instructions for preparing a Full Paper to be included in the Proceedings of COMPLAS 2019 Conference.

We study the modeling of bilinear and quadratic systems from measured data. The measurements are given by samples of higher order frequency response functions. These values can be identified from the corresponding Volterra series of the underlying nonlinear system. We test the method for examples from structural dynamics and chemistry.

The numerical description of discrete cracks and their propagation remains one of the main difficulties in the modeling of quasi-brittle materials such as rock or concrete. An emerging powerful approach is the use of Configurational Mechanics concepts, in such a way that crack trajectory really corresponds to a structural energy minimum and is not predetermined by the initial mesh lines. In the implementation developed, discrete cracks, represented by zero-thickness interface elements, are reoriented on the basis of configurational or material forces, calculated in a FEM context by an integration over the elements of the Eshelby energy-momentum tensor. The strategy is illustrated with an application example for which the fracture path is known a priori, and the initial mesh layout is chosen such that the lines zig-zag significantly with respect to it. The results show that the procedure implemented works successfully, that is, mesh lines do succeed in reorienting themselves during configurational iterations, so that the developing crack progressively matches the known physical trajectory.

According to the latest assessments made by the world health organization (WHO2016), the atmospheric pollution (air), has become one of the main causes of morbidity and mortality in the world, with a steep growth of respiratory diseases, increase in lung cancer, ocular complications, and dermis diseases [1,2,3]. Currently, there are governments which still underestimate investments in environmental care, turning their countries into only consumers and predators of the ecosystem [1,2,3]. Worldwide, several cities have been implementing different regional strategies to decrease environmental pollution, however, these actions have not been effective enough and significant indices of contamination and emergency declarations persist [1,2,3]. Medellín is one of the cities most affected by polluting gases in Latin America due to the high growth of construction sector, high vehicular flow, increase in commerce, besides a little assertive planting trees system, among other reasons [1,2,3]. With the purpose of providing new researching elements which benefit the improvement of air quality in the cities of the world, it is pretended to mathematically model and computationally implement the behavior of the flow of air, e.g., in zones in the city of Medellín to determine the extent of pollution by tightness, impact of current architectural designs, vehicular transport, high commerce flow, and confinement in the public transport system. The simulations allowed to identify spotlights of particulate tightness caused by architectural designs of the city which do not benefit air flow. Also, recirculating gases were observed in different zones of the city. This research can offer greater knowledge around the incidence of pollution generated by structures and architecture. Likewise, these studies can contribute to a better urban, structural and ecological reordering in cities, the implementation of an assertive arborization system, and the possibility to orientate effective strategies

The flexural stiffness of bamboo is inherently influenced by heterogeneous material characteristic owing to its unique hierarchical structure. In addition, low interfacial strength and unequal distribution of fibres lead to a complex fracture behavior in the material. This research study aims to probe into the limited durability of MADAKE bamboo (Phyllostachys bambusoides) by investigating its fracture mechanism through numerical simulation. The influence of functionally graded material (FGM) on the fracture behavior of bamboo culm was evaluated. A half-solid cylindrical model consisting of a rigid section and a 4-layered wall section was simulated in pure bending mode on LS-DYNA. The effects of material homogeneity and inhomogeneity were replicated by inputting elastic and orthotropic-elastic material data comprising of longitudinal to flexural stiffness ratio. These ratios were derived from experimental results of three-point flexural test. Analysis of results, based on maximum principal strain, showed that the homogeneous model displayed fracture characteristics similar to conventional elastic material. In contrast, the inhomogeneous model displayed maximum principal strain on the lateral surface corresponding to fracture mode of bamboo culms observed in nature. Numerical study of material heterogeneity is a step further in understanding the fracture mechanics of functionally graded materials.

This study presents first the fabrication of a nanocomposite material based on Multi-Walled Carbon Nanotubes, and on a thermoplastic polymer matrix. First, a twin-screw mixer had been employed for preparing polypropylene nanocomposites loaded at 0.1, 1, 2, and 5wt% of MWCNT. Second, a characterization of rheological behavior for polypropylene as well as polypropylene/multi-walled carbon nanotube mixtures, at three temperatures (180, 200, and 220 °C,) has been carried out using cone and plate rheometer. Then, its thermomechanical properties have been studied. The work demonstrates how the addition of functionalized CNTs to a polypropylene will allow it to act as thermal conductor rather than as insulator.

In this work we propose a novel virtual element approach for solving boundary value problems in 2D linear isotropic micropolar elasticity. Following the basic idea of the Virtual Element Method (VEM), the degrees of freedom of each material point, i.e. the displacement and rotation fields, are decomposed into both a polynomial space, either linear or quadratic, and a remaining space that is kept virtual in the formulation. Generalized consistency and stabilization terms are consistently derived. Different patch tests, properly conceived for micropolar continua, are proposed and compared to reference solutions present in literature. The obtained results are in good agreement with these solutions, confirming the capability of the proposed elements in the modelling of the expected responses. The expected applications of this methodology concern the mechanical study of microstructured materials, inherently characterized by nonlocal response, which has been widely proven to be effectively represented by micropolar continua.

The ability to obtain rigorous upper and lower bounds on collapse loads of various structures makes finite element limit analysis an attractive design tool. The increasingly high cost of computing those bounds, however, has limited its application on problems in three dimensions. This work reports on a high-performance homogeneous self-dual primal-dual interior point method developed for three-dimensional finite element limit analysis. This implementation achieves convergence times over 4.5× faster than the leading commercial solver across a set of three-dimensional finite element limit analysis test problems, making investigation of three dimensional limit loads viable. A comparison between a range of iterative linear solvers and direct methods used to determine the search direction is also provided, demonstrating the superiority of direct methods for this application. The components of the interior point solver considered include the elimination of and options for handling remaining free variables, multifrontal and supernodal Cholesky comparison for computing the search direction, differences between approximate minimum degree [1] and nested dissection [13] orderings, dealing with dense columns and fixed variables, and accelerating the linear system solver through parallelization. Each of these areas resulted in an improvement on at least one of the problems in the test set, with many achieving gains across the whole set. The serial implementation achieved runtime performance 1.7× faster than the commercial solver Mosek [5]. Compared with the parallel version of Mosek, the use of parallel BLAS routines in the supernodal solver saw a 1.9× speedup, and with a modified version of the GPU-enabled CHOLMOD [11] and a single NVIDIA Tesla K20c this speedup increased to 4.65×.

A new theoretical method for determining the mechanics properties of ultra-thin elastic materials is proposed in this paper. This method is based on a full contact model and Poisson’s effect. This study consisted of three steps. First, FE model of indentation problem for ultra-thin specimen is developed by elastic constitutive relationship for precise analysis of problem. Second, the simplified model is used to evaluate the result of FEM, and its availability is discussed by comparison with extended Hertzian theory. Third, an equation is proposed after comparing the results of FEM, extended Hertzian theory and full contact model.

In this work an automatic procedure for evaluating the axial force-biaxial bending yield surface of reinforced concrete sections in fire is proposed. It provides an accurate time-dependent expression of the yield condition by a section analysis carried out once and for all, accounting for the strength reduction of the materials, which is a function of the fire duration. The equilibrium state of 3D frames with such yield conditions, once discretized using beam finite elements, is formulated as a nonlinear vectorial equation defining a curve in the hyperspace of the discrete variables and the fire duration. A generalized path-following strategy is proposed for tracing this curve and evaluating, if it exists, the limit fire duration, that is the time of exposure which leads to structural collapse. Compared to the previous proposals on the topic, which are limited to local sectional checks, this work is the first to present a global analysis for assessing the fire resistance of 3D frames, providing a time history of the fire event and taking account of the stress redistribution. Numerical examples are given to illustrate and validate the proposal.

This paper presents analytical, semi-analytical and numerical reference examples which can be employed for code verification of elasto-viscoplastic models under plane stress conditions. Mainly because of the overstress function the algorithms traditionally employed in elasto-plastic implementations must be rewritten to correctly impose the plane stress state along with the viscoplastic flow. The viscoplastic formulation presented here considers the strain-rate hardening effects by means of a hardening law that are assumed to have terms depending on the strain rate, which removed can represent a Voce type hardening. The proposed verification tests were employed for the numerical verification of an in-house implementation of the so-called stress-projected procedure inside the finite element method context. Although the focus of this paper is on the stressprojected algorithms the examples presented here can be employed for the verification of other algorithms intended to impose the plane stress state in viscoplasticity

An energy-based work-softening visco-plastic model for zero-thickness interface elements has been developed as an extension of an existing elastic-perfectly-viscoplastic formulation. In the inviscid limit the model also collapses into a well-established fracture mechanics-based elasto-plastic model. The new model is verified satisfactorily for common loading cases at interfaces such as pure tension (mode I) opening, and shear-compression (mixed-mode) sliding, with results that in the long term match the predictions of the fracture mechanics inviscid model.

Carbon dioxide (CO2) storage in abandoned oil/gas reservoirs is considered a viable alternative to reduce greenhouse gas emissions to the atmosphere. An important element of the risk associated with long-term CO2 storage is the loss of integrity of the cement seals of the abandoned wells in the reservoir. Among others, one possible cause of loss of integrity is the degradation of the oil-well cement due to the acid attack of the carbonated brine in the reservoir. In previous studies, the authors have developed a diffusion-reaction model for simulating this degradation process. In order to study possible coupled Chemo-Mechanical (CM) mechanisms, this model will be coupled with an existing mechanical model. For this purpose, in this paper, an existing constitutive law for zero-thickness interface, based on the theory of elasto-plasticity with concepts of fracture mechanics, is modified to incorporate the effect of chemical degradation on the mechanical strength parameters. Preliminary results obtained with this new constitutive law are presented, in order to illustrate the main aspects of the proposed constitutive law, as well as a possible C-M degradation mechanism that should be considered in the long-term safety assessment of CO2 geological storage projects.

Power-transmitting gears are typically heat-treated, most often case-hardened, to improve the fatigue strength and therefore to ensure higher fatigue life. The heat treatment causes higher hardness in the surface area as well as compressive residual stresses in the hardened layer. The near-surface compressive residual stresses are compensated by tensile stresses in higher depths of the gear volume. Pitting and tooth root breakage are the most common failure modes of gears, which are well researched and are also addressed in ISO 6336 [14]. The assessment of these failure modes provides the basis for the dimensioning of gears in the design phase. However, subsurfaceinitiated failures, like tooth flank fracture (TFF), can also appear at loads below the allowable level of loading for pitting and tooth root bending. TFF is a fatigue damage with crack initiation in the region of the transition between compressive and tensile residual stresses and usually leads to a total loss of drive. The existing calculation models for fatigue strength of gears with regard to TFF consider residual stresses differently. The base of the investigated calculation models is a local comparison of the occurring stresses and the strength value in the gear volume. The outcome of the calculation model from Oster [26] is highly influenced by the residual stress state. However, the material-physical model by Hertter [10] is more tolerant to slightly varying residual stresses. Further approaches such as Weber [34] and Konowalcyk [18] are based on the ideas of Oster and Hertter. The verification of the models is complicated due to the lack of residual stress measurements in larger depths under the gear flank surface. For example, residual stress measurement by Xray diffraction is only possible up to depths of approximately one millimeter. Therefore, tensile residual stresses in the inner tooth volume are considered zero in the common residual stresses calculation of Lang [19] and are not considered i

There have some problems in the press engineering. One of the most representative phenomena is springback. Traditionally, a series of empirical methods were used to obtain target bending angle. However, such methods are relied on the ability and experience of engineer. Therefore, the control of springback is important. According to the viewpoint of plastic processing, it is considered that springback could be controlled by sheet forging method which was added after V-bending process used a punch with a single lump-punch. On the other hand, warp would occur in air bending process when the ratio of width to thickness is relatively small. So, it is considered that width direction deformation would affect springback control to some extent in case of warp is occurred. In this study, V-bending and continuous forging processes were conducted used FE analysis. From the analytical results, occurrence of warp was found. Next, model of these processes in consideration of warp was re-modified. Finally, it was found that the springback was controlled to some extent derived from width direction deformation.

The concept of representative directions allows one to generalize onedimensional uniaxial material models to more general constitutive equations, suitable for arbitrary multi-axial loading scenarios. The procedure preserves the thermodynamic consistency and the resulting material model satisfies the principle of objectivity. In the current paper, the concept is modified by the introduction of new kinematics. Some features of the resulting constitutive equations as well as the applicability of the extended concept to real materials are discussed. For demonstration purposes, the plastic behaviour of an electrospun polymer is modelled under large strain non-monotonic loading.

In recent years, the authors and co-workers have developed a diffusion-reaction model for the degradation process of oil-well cements exposed to carbonated brines in the context of CO2 capture and storage in abandoned oil reservoirs. The model considers two main diffusion-reaction field variables for the concentrations of aqueous calcium and carbon species in the pore solution of the hardened cement paste, complemented by two diffusion-only field variables for chloride and alkalis concentrations. The volume fractions of solid constituents evolve according to the chemical kinetics and chemical equilibrium equations of the reactions involved, determining the diffusivity properties of the material. In this paper, in the framework of an experimental campaign in preparation, this model is used for assessing the effect of different specimen geometries on the kinetics and extent of the acid attack. The results obtained will help to optimize the experimental setup and to the interpretation of the results obtained.

Deep drawing simulation techniques reduce tool design costs and improve tool performance and reliability. In terms of strain hardening, mixed models capturing the kinematic effect are sometimes more accurate than isotropic models. Indeed, nonlinearity in strain paths can lead to inconsistent simulation results. However, the use of such models requires a greater number of tests including strain path changes. Therefore, the use of such mixed models shall be required only if the simulation includes non-linear strain paths and the material exhibits a pronounced Bauschinger effect. New tools to help engineers choose between models could ease the spread of more advanced models in simulation of deep drawing processes when needed. With this in mind, an indicator predicting the influence of kinematic effects could help to select an adequate model. In this study, a new indicator is introduced with the idea of characterising strain path non-linearity in order to assess kinematic hardening influence. The indicator is computed using the forming history taken from a purely isotropic simulation – which is easier to set up and parametrise. The ability of the indicator to predict inconsistencies within the isotropic simulation is investigated using U-channel simulations.

In current research, more and more attention is paid to the understanding of residual stress states as well as the application of targeted residual stresses to extend e.g. life time or stiffness of a part. In course of that, the numerical simulation and analysis of the forming process of components, which goes along with the evolution of residual stresses, play an important role. In this contribution, we focus on the residual stresses arising from the austenite-to-martensite transformation at microscopic and mesoscopic level of a Cr-alloyed steel. A combination of a Multi-Phase-Field model and a two-scale Finite Element simulation is utilized for numerical analysis. A first microscopic simulation considers the lattice change, such that the results can be homogenized and applied on the mesoscale. Based on this result, a polycrystal consisting of a certain number of austenitic grains is built and the phase transformation from austenite to martensite is described with respect to the mesoscale. Afterwards, in a two-scale Finite Element simulation the plastic effects are considered and resulting residual stress states are computed.

In this work, a thermo-mechanically coupled constitutive model for semicrystalline polymers is derived in a thermodynamically consistent manner. In general, the macroscopic material behaviour of this class of materials is dictated by the underlying microstructure, i.e. by the distribution and structure of crystalline regimes, which form up after cooling from the amorphous melt. In order to account for the latter, the total degree of crystallinity is incorporated as an internal variable and its evolution is prescribed by means of a non-isothermal crystallisation kinetics model. The numerically efficient and robust framework is characterised based on experimental data for Polyamide 6 and shows a promising potential to predict the hyperelastic, visco-plastic material behaviour at various temperatures

Residual stresses are an important issue as they affect both the manufacturing processes as well as the performance of the final parts. Taking into account the whole process chain of hot forming, the integrated heat treatment provided by a defined temperature profile for cooling of the parts offers a great potential for the targeted adjustment of the desired residual stress state. However, in addition to elastic, plastic and linear thermal strain components, the complex material phenomena arising from phase transformation effects of the polymorphic steels have to be considered in order to predict the residual stresses. These transformation strains account for the plastic deformation at the phase boundary between the emerging and the parent phase. In addition, they are strongly related to the transformation induced plasticity (TRIP) phenomena which depend on the stress state. The aim of this study is the investigation of TRIP effects and their impact on residual stresses regarding the typical hot forming steels 1.7225 (DIN: 42CrMo4) and 1.3505 (DIN: 100Cr6) by means of an experimental-numerical approach. The TRIP behaviour of the materials under consideration is integrated into an FE simulation model in the commercial software Simufact.forming for the purpose of residual stress prediction. The experimental thermo-mechanical investigations are carried out using a quenching and forming dilatometer. These experiments are numerically modelled by means of FEM which allows TRIP coefficients to be determined phasespecifically by numerical identification. For validation of the improved FE-model, an experimental thermo-mechanical reference process is considered, in which cylindrical specimens with an eccentric hole are hot formed and subsequently cooled by different temperature routes. Finally, the numerical model is validated by means of a comparison between residual stress states determined with X-ray diffraction and predicted residual stresses from the simulation.

In this study, an anisotropic viscoelastic-viscoplastic macro-mechanical model is presented for short-fiber reinforced thermoplastics (SFRT). In injection molding of SFRT, the fiber orientation is influenced by the flow velocity profile which varies throughout the mold. The flow-induced orientation in the microstructure leads to anisotropy in the mechanical response. In addition to the mechanical anisotropy, SFRTs show time dependent behavior because of the thermoplastic matrix. The developed model captures the effects of both material orientation and loading rate on the yield behavior. In this study, uniaxial tests are performed at different strain rates and material orientations with samplescutfrominjectionmoldedplaques. Theexperimentalresultsshowthattheeffects of loading rate and material orientation on the yield are decoupled. The presented model takes advantage of this observation to simplify material characterization. An implicit integration scheme is used for the numerical implementation of the model as a UMAT in ABAQUS. Multiple relaxation times are used in order to capture the nonlinear pre-yield regime. An efficient method for obtaining the model parameters for different modes is proposed. Experimental results are used for validation of the model and a good agreement is observed for the prediction of viscoelastic and viscoplastic behavior.

he authors present a new ring rolling variant that combines a semi-warm forming process of a bearing ring with controlled cooling directly followed by a cold forming process. The aim is to produce near net shape rings with a selected microstructure and high strength without additional consecutive heat treatment. To achieve this, a new and fast control strategy is necessary that not only controls the geometrical forming of the ring, but also considers temperature development and microstructure formation. The proposed control strategy is based on the application of a fast semi-analytical simulation model with a very short response time in combination with a FE-analysis of the thermomechanical ring rolling process. The semianalytical model is used as a predictor and a parallel FEA or experimental results as a corrector for the control model. The aim is to correctly identify transient process parameters needed to achieve defined product properties as a basis for a later implementation in a non-linear modelpredictive-control of thermomechanical ring rolling. The new approach will be described in detail and demonstrated numerically and experimentally.

Residual stresses and fiber orientations in arterial walls can be approximated by means of the simulation of growth and remodeling processes. In order to enable a comparison of different approaches of combined growth and remodeling in one framework, a method based on the optimization of model parameters is developed. The minimization of a mechano-biologically motivated objective function permits to evaluate the approaches with respect to their ability of effectively reducing stress peaks and stress inhomogeneities in the arterial wall. This examination is performed for a simplified, one-layered, rotationally symmetric arterial segment in order to enable the analysis of the fundamental mechanisms included in the individual model variants. Once the most probable growth mechanism is identified, multi-layered segments can be analyzed in more detail.

We compare two homogenized models of the microcirculation which rely on different assumptions. The first model has been derived by the homogenization of the mesoscopic structure with the double-porosity medium represented by the Biot model with large contrasts in the permeability coefficients constituting the Darcy law. The newly developed so-called Biot-Darcy-Brinkman (BDB) model is described in the paper; it arises from a two-stage homogenization of the fluid-structure interaction problem which requires geometric representations of the sinusoidal and the inter-lobular vasculatures associated with venous compartments, the portal and the hepatic veins. An illustrative example shows a good correspondence between the two models.

In the design of sportswear which is expected to modify the performance of athletes, it is important to clarify the effects of the wear's rigidity and wearing pressure on the vibrations during exercise because they have been considered to reduce the vibrations of muscles. Therefore, in this study, the relationship between the vibration generated in cyclic movement of thigh with cloth and the physical properties of the wearing cloth is discussed by using a simple FE model of thigh [1, 2]. In the analysis, the FE model consisted of three parts of the thigh muscle, the femur, and the wear in the cross section of thigh. The thigh muscle is fixed to the femur but it is in contact with the wear cloth ignoring friction. The condition of the thigh cyclical movement is set assuming the athlete's 100 m run. Numerical analysis is performed under these conditions, and the variations of vibration behavior due to changing values of muscle, wear and pressure are evaluated by mechanical consideration. In the results of this FE analysis, it is quantitatively confirmed that more flexible cloth has the effect of restraining vibration, and also its effect can also be observed by applying wearing pressure to thigh.

The paper presents an interpretation of the full-scale ALC1604 in situ heating test carried out in Callovo-Oxfordian claystone (COx) in the Meuse/Haute-Marne underground research laboratory (MHM URL). The MHM URL is a site-specific facility planned to study radioactive waste disposal in the COx. The thermo-hydro-mechanical (THM) behaviour of the host rock is significant for the design of the underground radioactive waste disposal facility and for its long-term safety. When subjected to thermal loading, the Callovo-Oxfordian claystone of low permeability (~10-20-10-21 m2) exhibits a strong pore pressure response that significantly affects the hydraulic and mechanical behaviour of the material. The observations gathered in the in situ test have provided an opportunity to examine the integrated thermo-hydromechanical (THM) response of this sedimentary clay. Coupled THM numerical analyses have been carried out to provide a structured framework for interpretation, and to enhance understanding of THM behaviour of COx. Numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law specially developed for this type of material. The law includes a number of features that are relevant for a satisfactory description of the hydromechanical behaviour. By performing the numerical analysis, it has been possible to incorporate anisotropy of material parameters and of in situ stresses. The performance and analysis of the in situ tests have significantly enhanced the understanding of a complex THM problem and have proved the capability of the numerical formulation to provide adequate predictive capacity.

This paper proposes modifications to the phenomenological model formulation called CDPM2, developed by Grassl et al. [1]. The proposed modifications are designed to enhance model performance with coupling to temperature effects. A very strong coupling between nonlinear elasticity, plasticity, nonlocal damage evolution and temperature gradient is used to simulate arbitrary crack propagation. The use of FVM to model solid damage is a numerical challenge. This approach presents some advantages such as: ensuring that discretization is conservative even when the geometry is changing; providing a simple formulation that can be obtained directly from a difference method; and employing unstructured meshes. Most authors have neglected the nonlinearity of concrete in the elastic domain from the start of loading to the plastic domain. In this paper we confirm that concrete rheology is not linear even under low loading. Also, since the so-called fracture energy is a key parameter needed to determine the size of cracks and how they propagate in space, we consider that the fracture energy is both material and geometrical parameter dependent. For this reason, we developed a new approach which includes adaptive mesh, nonlinear rheology and thermal effects to re-calculate fracture energy at each time step. Many authors use a constant value obtained from experiments to calculate fracture energy; others use a numerical correlation. In this study, the fracture energy parameter is not constant and can vary with temperature or/and with a change in geometry due to concrete failure. As is well known, the mesh quality of complex geometries is very important for making accurate predictions. A new meshing tool was developed using the C++ programming language. This tool is faster, more accurate and produces a high-quality structured mesh. The predictions obtained were compared to a wide variety of experimental data and showed good agreement.

We propose a modification of the Hamiltonian formalism which can be used for dissipative systems, the Brezis-Ekeland-Nayroles principle. The formalism is specialized to the standard plasticity in small strains and dynamics. We apply it to solve the classical problem of a thin tube in plane strain subjected to an internal pressure. The continuum is discretized with mixed finite elements.

Paper deals with the comprehensive methodology for the numerical simulation of potentially unstable slopes combining engineering geological, hydrological, hydrogeological and geotechnical computational model for the assessment of slope stability. Engineering geological model based on available survey data characterizes the rock environment using individual quasi-homogenous units. Model is defined on the basis of documented lithostratigraphic units in exploration probes and field relief documented by advanced methods, including satellite radar interferometry and laser surface scanning. On the basis of engineering geological model, the hydrological model using MIKE SHE software (Finite Difference Method) was performed. Hydrological model includes simulation of surface runoff, evapotranspiration and flow in unsaturated near-surface zone. The model was calibrated on the basis of available field data. Outputs from this model were used as input initial conditions of the following hydrogeological model. Software FEFLOW based on the Finite Element Method was subsequently used to the creation of hydrogeological model focused on the water flow and distribution of pore pressures of groundwater in individual quasi-homogeneous units in saturated zone. The infiltration condition determined by the hydrological model is considered and a flow model with variable saturation is applied. Finally, the geotechnical stability model of slope following the engineering geological, hydrological and hydrogeological models was performed. The occurrence of plastic and failure zones (assuming elastic-perfectly plastic Mohr-Coulomb constitutive model) inside the slope was simulated by using software MIDAS GTS NX based on the Finite Element Method. Stability factor SSRF (Shear Strength Reduction Factor) is evaluated based on the Shear Strength Reduction Method) as the ratio of actual shear strength and minimum shear strength required to maintain stability. Paper deals also with the comparison of st

Colorectal adenocarcinoma is one of the carcinogenic diseases that is increasing the morbidity and mortality rates worldwide. The disease initially occurs through the segregation of biomarker substances in the human system without manifesting symptoms that affect the health of the carrier. Early detection would allow the application of more effective treatments, less invasive procedures and reduce the development of cancer. The purpose of this investigation was the elaboration of a mathematical model and the development of computational simulations to visualize the behavior of biomarker particles in transit through the colon. The flow conditions, properties of the viscous medium and biological regions of interest were established. Constitutive models, numerical conditions and solution strategies were determined. A numerical grid was used to represent the model of the colon and the human feces that carry the bioparticles (biomarkers). The results indicated the trajectories of the bioparticles in the fecal mass and the interactive movement with the natural contractions of the colon. The analysis of the movement of the biomarker particles can provide future less invasive alternatives for the detection in real time of the cancer by means of the implantation of biosensors in the walls of the colon.

A zero-thickness mortar/interface element formulation is briefly described and demonstrated. This element may be considered as an extension of traditional zero-thickness interface element, in order to represent material interfaces located in between subdomains with non-matching FE meshes. In the context of small strain analysis, these elements may be equipped with the same type of constitutive laws as traditional interface elements. Therefore, if friction or fracture-mechanics-based laws are adopted, mortar/interface elements may be used to represent frictional sliding or cracking following the lines (surfaces) along which they have been pre-inserted. Two basic verification examples of this type are presented, showing that the model can correctly represent uniform states of stress and deformation when connecting unmatched mesh subdomains.

This paper is focused on analysis and reliable computations of limit loads in perfect plasticity. We recapitulate our recent results arising from a continuous setting of the so-called limit analysis problem. This problem is interpreted as a convex optimization subject to conic constraints. A related inf-sup condition on a convex cone is introduced and its importance for theoretical and numerical purposes is explained. Further, we introduce a penalization method for solving the kinematic limit analysis problem. The penalized problem may be solved by standard finite elements due to available convergence analysis using a simple local mesh adaptivity. This solution concept improves the simplest incremental method of limit analysis based on a load parametrization of an elastic-perfectly plastic problem.

The macroscopic elastic properties of discrete assemblies are fundamental characteristics of such systems. The contribution uses homogenization procedure based on equivalence of virtual work between the isotropic elastic continuum and the discrete system to develop analytical formulas for estimation of macroscopic elastic modulus and Poisson’s ratio. Such homogenization was recently used to derive formulas for discrete assemblies where (i) there is no vacant space between the discrete units, (ii) the orientation of contacts is uniformly distributed and (iii) the contact normals are parallel to contact vectors (directions connecting centers of discrete units). The third assumption is now removed, three dimensional systems with arbitrary relation between contact vectors and contact normals are studied here. It is shown that the limits of Poisson’s ratio of such system depends on the relation between contact normal and contact vector. The widest limits are however obtained when these two vectors are parallel. This means that arbitrary manipulations with discrete geometry cannot extend Poisson’s ratio of the system outside the known boundaries.

Artificial intelligence and machine learning algorithms have known an increasing interest from the research community, triggering new applications and services in many domains. In geotechnical engineering, for instance, neural networks have been used to benefit from information gained at a given site in order to extract relevant constitutive soil information from field measurements [1]. The goal of this work is to use machine (supervised) learning techniques in order to predict the behaviour of a sheet pile wall excavation, minimizing a loss function that maps the input (excavation’s depth, soil’s characteristics, wall’s stiffness) to a predicted output (wall’s deflection, soil’s settlement, wall’s bending moment). Neural networks are used to do this supervised learning. A neural network is composed of neurons which apply a mathematical function on their input (see Figure 1, left) and synapses which take the output of one neuron to the input of another one. For our purpose, neural networks can be understood as a set of nonlinear functions which can be fitted to data by changing their parameters. In this work, a simple class of neural networks, called Multi-Layer Perceptron (MLP) are used. They are composed of an input layer of neurons, an output layer, and one or several middle layers (hidden layers) (see Figure 1, right). A neural network learns by adjusting the weights and biases in order to minimize a certain loss function (for instance: the mean squared error) between the desired and the predicted output. Stochastic gradient descent or one of its variations are used to adjust the parameters and the gradients are obtained through backpropagation (an efficient application of the chain rule). The interest in neural networks comes from the fact that they are universal function estimators, in the sense that they can approximate any continuous function to any precision given enough neurons. However, this can lead to over-fitting problems where the network learns the n

This paper discusses the plastic behavior of wires in metal mesh for discussing the structure of woven warp and weft with their inhomogeneous and homogeneous by using finite element method (FEM). In the FEM, an isotropic plasticity is adopted as constitutive model of woven wire, but inhomogeneous between warp and weft is discussed to evaluate the mechanical characteristic of the mesh as an industrial products. Here, fundamental relation of power law hardening rule is adopted to represent the plasticity, but physical parameters of it will be controlled for the discussion of plasticity on mesh weaving. The inhomogeneous of mesh structure is one of key technology to control the product quality of metal mesh, and the mechanics of plasticity of metal mesh should be discussed to develop the product. In this report, the difference of material parameters and tension during weaving process is targeted on the discussion. Some conditions on the wires of warp and weft are examined in weaving process by FEM