Modeling Of Material Behavior Research Articles

Phase field modeling and simulation of coupled fracture and twinning in single crystals and polycrystals

A phase field theory incorporating both fracture and deformation twinning behaviors in crystalline solids is described and implemented in finite element calculations. A variational approach is used to derive governing equations for quasi-static loading. The constitutive theory accounts for possible anisotropy of surface energy of fracture, enabling preferential cleavage on intrinsically weak crystallographic plane(s). Both linear elastic and nonlinear elastic models for bulk material behavior are addressed, the latter via compressible neo-Hookean elasticity. Numerical implementation is undertaken via the finite element method, wherein nodal degrees of freedom are displacement components and order parameters associated with twinning shear and local elastic stiffness reduction from fracture. Three dimensional simulations are reported, with solutions obtained via incremental energy minimization subjected to appropriate boundary and irreversibility constraints. Two sets of calculations are considered: a single crystal with a geometric notch, from which a crack and/or twin may extend upon mode I or mode II loading, and simple tension of a polycrystal consisting of grains with various lattice orientations. Results from the first set of calculations demonstrate a tendency for fracture before twinning when surface energies of the two mechanisms are equal, and a tendency for twinning to delay fracture when the fracture energy substantially exceeds the twin boundary energy. Results from the second set demonstrate effects of relative orientations of cleavage planes to habit planes (parallel or perpendicular), effects of initial orientation distributions, and effects of secondary grain boundary phases differing in strength and stiffness from surrounding crystals.

Identification of ductile damage parameters for pressure vessel steel

The FEM simulations in the field of design and safety assessment represent very powerful tools, but they are strongly limited by available material models and material input data. If states near to ductile fracture are to be considered, more complex material description taking into account multiaxial loading conditions is necessary. As complex material models suitable to include these effects into practical simulations are still mostly phenomenological, experiments with samples of various geometries tested under various loading modes have to be used. On the basis of these tests a complex material behavior model covering elastic and plastic material behavior for various stress states can be obtained. This kind of the material behavior description allows a wide range of application from calculation of component limit loading conditions to material properties conversion for samples of different sizes e.g. This paper deals with ductile damage parameters determination for two typical Reactor Pressure Vessel (RPV) steels ferritic and austenitic. The ferritic steel is used for the RPV vessel and the austenitic one is used for internals. There are chosen appropriate samples geometries based on the preliminary FEM stress state analyses of samples at first. Subsequently, testing of proposed samples is performed and material parameters are evaluated. The obtained material plastic damage parameters are subsequently applied to FEM simulation of sharp notched samples and capabilities of applied models to describe material behavior for high stress concentrations is assessed on the basis comparison with real tests.

Analysis of the tool plunge in friction stir welding - comparison of aluminium alloys 2024 T3 and 2024 T351

Temperature, plastic strain and heat generation during the plunge stage of the friction stir welding (FSW) of high-strength aluminium alloys 2024 T3 and 2024 T351 are considered in this work. The plunging of the tool into the material is done at different rotating speeds. A three-dimensional finite element (FE) model for thermomechanical simulation is developed. It is based on arbitrary Lagrangian-Eulerian formulation, and Johnson-Cook material law is used for modelling of material behaviour. From comparison of the numerical results for alloys 2024 T3 and 2024 T351, it can be seen that the former has more intensive heat generation from the plastic deformation, due to its higher strength. Friction heat generation is only slightly different for the two alloys. Therefore, temperatures in the working plate are higher in the alloy 2024 T3 for the same parameters of the plunge stage. Equivalent plastic strain is higher for 2024 T351 alloy, and the highest values are determined under the tool shoulder and around the tool pin. For the alloy 2024 T3, equivalent plastic strain is the highest in the influence zone of the tool pin.

Primo Levi’s The Periodic Table: Chemistry as Posthumanist Science

This essay positions Primo Levi’s The Periodic Table as an entry point into a larger discussion regarding representations of chemistry as a humanist or posthumanist science in twentieth and twenty-first century culture. In contrast to ideal models of material behavior, which Levi associates with physics, experiments in The Periodic Table do not reach neat conclusions, and these failures call attention to the limited and inevitably inadequate ways that humanist, universalist frameworks model the object world. Levi’s maturation as chemist, I argue, enables him to establish a posthumanist narrative and an accompanying ethics rooted in irregular, material conditions of particularity.

Evaluation of the effects of melting phenomenon on the residual stress formation in ferritic pipeline multi pass girth-weld joints

Coupled thermo-metallurgy-mechanical (TMM) analysis using FEM was carried out to represent a girth welding in ferritic pipeline steel. One of the crucial points to predict residual stress especially in multi pass welding is how to model material behaviour when melting takes place. When elements melt, they lose stiffness and also remaining plastic strain. Based on literature, it is suggested that this stiffness and plastic strain mitigation occurs even below melting temperature, known as annealing temperature. In this paper three FEM models are evaluated: 1) model without omitting stiffness and plastic strain; 2) with mitigating stiffness and plastic strain at melting point (1,400°C); 3) with mitigating stiffness and plastic strain at annealing temperature (970°C). Residual stress of two specimens was measured to validate the FEM models where model with 970°C of omitting stiffness and plastic strain showed best matching results.

Thermo-Mechanical Modeling of Distortions Promoted during Cooling of Ti-6Al-4V Part Produced by Superplastic Forming

In AIRBUS, most of the complex shaped titanium fairing parts of pylon and air inlets are produced by superplastic forming (SPF). These parts are cooled down after forming to ease their extraction and increase the production rate, but AIRBUS wastes a lot of time to go back over the geometric defects generated by the cooling step. This paper investigates the simulations of the SPF, cooling and clipping operations of a part on Abaqus® Finite element software. The different steps of the global process impact the final distortions. SPF impacts the thickness and the microstructure/behavior of material, cooling impacts also the microstructure/behavior of material and promotes distortions through thermal stresses and finally, clipping relaxes the residual stresses of the cut part. An elastic-viscoplastic power law is used to model material behavior during SPF and a temperature dependent elastic perfectly plastic model for the cooling and clipping operations.

A combined grain scale elastic–plastic criterion for identification of fatigue crack initiation sites in a twin containing polycrystalline nickel-base superalloy

Damage initiation during cycling loading of polycrystalline metallic alloys involves localized damage at the scale of individual grains. To better understand damage processes and to build models for material behavior, there is a need for quantitative assessment of the microstructural configurations that favor fatigue crack initiation. In materials that form annealing twins during processing, these special interfaces are often locations of particular interest for their role in strain and damage accumulation. In the present study, fatigue experiments in the very high and low cycle fatigue regime on a René 88DT polycrystalline nickel-base superalloy were performed to statistically evaluate grain-scale features that favor crack initiation. Combined elastic and plastic criteria at the grain scale have been developed. A crack distribution function is defined to compare and assess the effect of the microstructural parameters for the two fatigue regimes.

Introducing the Data descriptor article

C a u w Earlier this year, we announced the launch of a new type of scholarly publication for Integrating Materials and Manufacturing Innovation (IMMI): the Data descriptor article. By introducing the Data descriptor article, we are responding to the growing dependence of research on having access to high-quality materials data. The Data descriptor article aims to provide researchers with the necessary supporting information, or metadata, needed to fully understand and use the data described with a high degree of confidence. A number of compelling needs underpin this new, peer-reviewed forum for the presentation of high-quality, high-value materials data. Most would agree that materials data can be extraordinarily rich in information, but we typically only use a subset of the data collected to explore a fairly focused hypothesis. Thus, it makes good sense, as research budgets are always constrained, to provide a forum to facilitate the reuse of materials data for a more efficient research process. Others can use available data to augment or corroborate their own research, perhaps testing a secondary hypothesis not even considered by the data originator. And as we become more dependent on models of materials behavior to guide advances in science or support engineering design, we have a growing need to develop, refine, and validate these models. Ready access to high-quality data will aid theoreticians and modelers in these pursuits. With the emergence of data analytic techniques, we also have the opportunity to gain new insights into material behavior from complex datasets where we do not yet have robust physics-based models of behavior. And finally, it is just sound scientific practice, and the core of the peer-review process, to allow others to examine the data upon which new scientific claims are based. There are several key elements to the Data descriptor article that are aimed at ensuring the data described is at least as valuable to others as it was to the originator. First and foremost is a requirement for a significantly more detailed description of the materials and experimental and/or simulation techniques and conditions used to generate the data than found in a typical research article. Also, we are asking authors to specifically address attributes of data quality, to appropriate levels, including steps taken in verification, validation, uncertainty quantification, and sensitivity to assumptions and variables. We are requiring the data be made available for peer review prior to publication to ensure the data is interpretable by someone else other than the originator. Finally, we are requiring that the data described be made accessible to all without restriction and that the data be assigned a persistent identifier to ensure it can be more easily discovered and properly cited.

Damage function for historic paper. Part I: Fitness for use

In heritage science literature and in preventive conservation practice, damage functions are used to model material behaviour and specifically damage (unacceptable change), as a result of the presence of a stressor over time. For such functions to be of use in the context of collection management, it is important to define a range of parameters, such as who the stakeholders are (e.g. the public, curators, researchers), the mode of use (e.g. display, storage, manual handling), the long-term planning horizon (i.e. when in the future it is deemed acceptable for an item to become damaged or unfit for use), and what the threshold of damage is, i.e. extent of physical change assessed as damage. In this paper, we explore the threshold of fitness for use for archival and library paper documents used for display or reading in the context of access in reading rooms by the general public. Change is considered in the context of discolouration and mechanical deterioration such as tears and missing pieces: forms of physical deterioration that accumulate with time in libraries and archives. We also explore whether the threshold fitness for use is defined differently for objects perceived to be of different value, and for different modes of use. The data were collected in a series of fitness-for-use workshops carried out with readers/visitors in heritage institutions using principles of Design of Experiments. The results show that when no particular value is pre-assigned to an archival or library document, missing pieces influenced readers/visitors’ subjective judgements of fitness-for-use to a greater extent than did discolouration and tears (which had little or no influence). This finding was most apparent in the display context in comparison to the reading room context. The finding also best applied when readers/visitors were not given a value scenario (in comparison to when they were asked to think about the document having personal or historic value). It can be estimated that, in general, items become unfit when text is evidently missing. However, if the visitor/reader is prompted to think of a document in terms of its historic value, then change in a document has little impact on fitness for use.

Are X-rays the key to integrated computational materials engineering?

An IUCrJ paper by Levine et al. highlights the promise and challenge of 3D X-ray structural microscopy as a unique tool to test predictive models of materials behavior.

New method of the polymeric material properties experimental investigation under powerful energy flux impact

Investigation of the polymeric material properties under powerfull energy flux impact is relevant as for basic research (mathematical modeling of polymeric materials behavior in extreme conditions, testing the state equations), as for practical applications (for testing of protective coatings for space research and laboratory facilities). This paper presents the results of experimental studies of the interaction of polymeric materials with a relativistic electron beam produced by a high-current electron accelerator Calamary. Calamary facility provides a wide range of electron beam parameters: diameter 10-15 mm, the voltage on the diode up to 300 kV, the current through the diode up to 30 kA. New method of beam-target interaction area measurement was developed. The original method for the mechanical kick impulse measuring based on piezoelectric vibration sensor was presented. The dependence of the kick impulse from the power flux was obtained.

Modelling aspects of the design of railway vehicle structures and their crashworthiness

Travelling by rail is considered to be a safe option compared with other types of transport, in terms of the number of accidents. However, there are always opportunities to improve the current safety standards and industrial practices. The aim of this paper is to give a better understanding of the current modelling techniques that could support the design of new railway vehicle structures. The paper highlights the established practices in modelling of proof, fatigue and crashworthiness. It also reviews the state-of-the-art in the modelling of material behaviour, recommends practical modelling solutions that can be used in the railway industry, and demonstrates new modelling techniques for crashworthiness.

Elastic–Brittle–Plastic Analysis of Double-Layered Combined Thick-Walled Cylinder Under Internal Pressure

The elastic–brittle–plastic unified solutions of limit internal pressure are presented for double-layered combined thick-walled cylinder by the triple-shear unified strength criterion. The unified solutions obtained in this paper are especially versatile that can take into account of material brittle softening and intermediate principal stress quantitatively. The conventional existing elastic-perfectly plastic solutions, based on the Tresca yield criterion, Mises yield criterion, or twin-shear strength theory, can be categorized as special cases of the present unified solutions which can overcome their shortages. Parametric studies were carried out to evaluate the influences of various factors such as brittle softening parameter, strength theory parameter, cohesion, internal friction angle, and intermediate principal stress coefficient on the unified solutions. It is shown that proper choices of failure criterion, material behavior model, and brittle softening are significant in combined cylinder design. The new solutions can be naturally degraded to the existing formula and agree well with the results of the prevailing failure criteria. It is concluded that the unified solutions have an important practical value for the optimum design and engineering application of combined thick-walled cylinder.

High resolution mapping of strain localization near twin boundaries in a nickel-based superalloy

Damage during cycling loading of polycrystalline metallic alloys involves localized plastic straining at the scale of individual grains. To better understand damage accumulation processes and to build models for material behavior there is a need for quantitative assessment of the heterogeneous strain fields at the grain and even more microscopic scales. In the present study, a digital image correlation (DIC) approach has been developed to measure the strains at the grain level and at finer scales where plastic strain localization is manifested as physical slip bands. Strain fields have been measured in situ and ex situ on a René 88DT polycrystalline nickel-based superalloy to assess the grain-scale deformation processes during monotonic straining in tension and compression. DIC analysis and transmission electron microscopy demonstrate that slip occurs in a highly localized manner. The highest localized strains developed in slip bands that formed on {111} planes parallel to, and slightly offset from, annealing twins. Enhanced local straining below yield was observed during compression loading. The degree of strain concentration caused by slip bands impinging on grain boundaries was also analyzed. The results are compared to predictions of plasticity models.

On the Bauschinger effect in dual phase steel at high levels of strain

The effect of volume fraction and hardness of martensite on the Bauschinger effect in Dual Phase (DP) steel was investigated for strain levels close to those observed in automotive stamping. Five different grades of DP steel were produced by controlled heat treatment allowing the examination of the Bauschinger effect for three different volume fractions of martensite and three levels of martensite hardness. Compression–tension and shear reversal tests were performed to examine the Bauschinger effect at high levels of forming strain. Good correlation between the shear reversal and the compression–tension test was observed suggesting that for DP steel, shear stress strain data, converted to equivalent stress–strain, may be applied directly to characterize kinematic hardening behavior for numerical simulations. Permanent softening was observed following strain reversal and increased with martensite volume fraction and pre-strain level. While the Bauschinger ratio saturates at 3% pre-strain, the Bauschinger strain increases linearly with forming strain without showing saturation. This suggests that to model material behavior accurately in forming processes involving complex loading paths and high levels of strain, test data generated at high strain is required.

An innovative procedure for characterising a coupled elastoplastic damage model of behaviour using the Virtual Fields Method

The characterisation of material behaviour models can be challenging, especially when dealing with strongly non-linear constitutive laws. Classical procedures are restricted to the treatment of homogeneous mechanical fields. They can therefore not be applied after strain localisation and behaviour model can be characterised only over a very limited strain range. In addition, several tests are generally needed to characterise complex behaviour models. On the contrary, the Virtual Fields Method (VFM) enables the treatment of inhomogeneous mechanical fields. The VFM therefore allows to take advantage of the increasingly powerful full-field measurement techniques. Moreover, its ability to process data enriched by heterogeneities can be used to significantly decrease the number of tests that are required for the identification of complex behaviours. In this paper, the VFM is developed for the characterisation of a fully coupled elastoplastic-damage behaviour model, using one uniaxial tensile test only. The process of identification is assessed using two kinds of thin-specimen geometries (numerically simulated strain fields). Results demonstrate the efficiency of the VFM for the simultaneous identification of plastic and damage parameters from a unique uniaxial tensile test, but also highlight that the definition of a suitable specimen geometry is a key factor for result accuracy.

A Study of Forming Tool Profile Effect in Single Point Incremental Forming by Finite Element Analysis

The Single Point Incremental Forming Process, SPIF, is a forming technique of sheet material based on layered manufacturing principles. The forming tool is moved along the tool path while the edges of sheet material are clamped on fixture by holder. The finished part is performed by the CNC milling machine. The description of the process is more complicated by highly nonlinear boundary conditions, namely contact and frictional effects have been accomplished. Due to the fact that the mathematical analysis of SPIF is complex, numerical approaches dominated by the FEA are now in widespread use. The paper presents the data and main results of a study concerning the effect of forming tool profile on SPIF through FEA, that permits the modeling of complex geometries, material behavior and boundary conditions. SPIF has been studied under certain process conditions referring to the test workpiece, tool, etc., using ANSYS 11.0. The results showed that the model of simulation can predict an ideal profile of processing track, spring back error of SPIF, the behavior of contact tool - workpiece, the accuracy of product by evaluation the strain and the stress distributions between forming tool and workpiece surface interface, and sample of results have been demonstrated.

Material behavior modeling with multi-output support vector regression

Based on neural network material-modeling technologies, a new paradigm, called multi-output support vector regression, is developed to model complex stress/strain behavior of materials. The constitutive information generally implicitly contained in the results of experiments, i.e., the relationships between stresses and strains, can be captured by training a support vector regression model within a unified architecture from experimental data. This model, inheriting the merits of the neural network based models, can be employed to model the behavior of modern, complex materials such as composites. Moreover, the architectures of the support vector regression built in this research can be more easily determined than that of the neural network. Therefore, the proposed constitutive models can be more conveniently applied to finite element analysis and other application fields.As an illustration, the behaviors of concrete in the state of plane stress under monotonic biaxial loading and compressive uniaxial cycle loading are modeled with the multi-output and single-output support regression respectively. The excellent results show that the support vector regression provides another effective approach for material modeling.

Microscopic mechanisms of the shape memory effect in crosslinked polymers

In this work we perform coarse-grained molecular dynamics (MD) simulations to study the molecular origins of the thermal shape memory effect in crosslinked polymer materials. Thermal shape memory polymers (SMPs) are materials able to hold a deformed shape when cooled below the glass transition temperature, and subsequently recover the initial shape when heated. To use SMPs in various applications requires materials which reliably hold and recover their shapes; this has sparked recent synthesis work to create new SMP materials with optimized properties. Here we use coarse-grained MD simulations with different polymer chain models to determine which parameters affect relevant SMP behavior and to investigate the molecular mechanisms at the level of individual chains during temperature cycling. The simulations show how temperature-dependent chain mobility leads to shape memory polymer behavior. In particular, we demonstrate the importance of attractive monomer interactions in leading to ‘good’ SMP behavior. The results suggest promising routes for material development. Additionally, the mechanisms identified with the simple simulation model can be used to inform multi-scale models of SMP material behavior.

Analytical modeling of the extrusion process using the electrostatics concept

Analytical and numerical modeling of metal forming processes has been studied by many researchers during the past decades. So far, several methods have been introduced to model material behavior during forming processes. In this research, the analogy between the classical plasticity theorem and electrostatic field line formation has been investigated for the first time. It is shown that the velocity potential function of movement in the plasticity and the charge-free electrostatic field are both in the form of Laplace’s relation. The aim of the current research is to model the metal forming processes using the equations governing the electrostatic fields. To demonstrate the effectiveness of the proposed method, the extrusion process is used as the benchmark. A three-dimensional CAD model of the deformation region is constructed and two different voltages are applied to the entry and exit sections based on the geometrical and extrusion parameters. Then, the Laplace’s relation is solved numerically and the relative extrusion pressure, particle flow path in the deforming region, and maximum plastic strain are calculated.To verify the proposed method, different sections are modeled and the results are compared with those in the literature. Finally, some experimental tests are conducted for the extrusion process of the round billets to complex sections. Significant agreement has been observed between the experimental results and the analytical ones. It is shown that the extrusion process could be modeled easily and accurately using the mathematical formalism of the electrostatics.