Complex Material Behavior Research Articles

A component-based parallel infrastructure for the simulation of fluid–structure interaction

The Uintah computational framework is a component-based infrastructure, designed for highly parallel simulations of complex fluid–structure interaction problems. Uintah utilizes an abstract representation of parallel computation and communication to express data dependencies between multiple physics components. These features allow parallelism to be integrated between multiple components while maintaining overall scalability. Uintah provides mechanisms for load-balancing, data communication, data I/O, and checkpoint/restart. The underlying infrastructure is designed to accommodate a range of PDE solution methods. The primary techniques described here, are the material point method (MPM) for structural mechanics and a multi-material fluid mechanics capability. MPM employs a particle-based representation of solid materials that interact through a semi-structured background grid. We describe a scalable infrastructure for problems with large deformation, high strain rates, and complex material behavior. Uintah is a product of the University of Utah Center for Accidental Fires and Explosions (C-SAFE), a DOE-funded Center of Excellence. This approach has been used to simulate numerous complex problems, including the response of energetic devices subject to harsh environments such as hydrocarbon pool fires. This scenario involves a wide range of length and time scales including a relatively slow heating phase punctuated by pressurization and rupture of the device.

Dielectric relaxation in complex systems: quality sensing and dielectric properties of honeydew melons from 10 MHz to 1.8 GHz

Based on new data treatment methods, it is possible to identify the fitting function for the complex permittivity ε(jω) measured for a complex system representing plant tissues of honeydew melons in the frequency range (107 to 1.8×109 Hz) at 25°C. The identified fitting function contains 9 fitting parameters and well describes the plant tissue permittivity. These parameters vary for different tissues; their correlation behavior with respect to soluble solids content (SSC), tissue density (TD) and moisture content (MC) are found by a new approach based on the statistics of the fractional moments (SFM). These correlation dependencies expressed in the form of correlation functions can be used for quality sensing of different complex systems, in particular, for ripe fruits and vegetables, where direct relationships between molecular and fitting parameters are not easy to find. These correlation functions can be used for practical purposes to construct a desired calibration curve with respect to quality factors, as for example, moisture content or degree of maturity, expressed in terms of SSC value. The discovered common ``universality'' in dielectric behavior of such complex materials as plant tissues opens a possibility to use dielectric spectroscopy as a nondestructive method of control in analysis of electrical behavior (measured in the form of complex permittivity or impedance) for other complex materials.

Neural network constitutive model for rate-dependent materials

Neural network (NN) constitutive model adjusts itself to describe given stress and strain relationship. It is capable of capturing complex material behavior, using stress and strain sets from experiments. This paper presents a rate-dependent NN constitutive model formulation and its implementation in finite element analysis. The proposed NN model is verified for a standard solid viscoelasticity model. The model is then applied to analysis of time-dependent behavior of concrete. The proposed model has potential of capturing any rate-dependent material models, provided enough data sets are given. The issue of what constitutes a sufficient data set to train a neural network constitutive model must be addressed in future research.

Recognition of the “fractional” kinetics in complex systems: Dielectric properties of fresh fruits and vegetables from 0.01 to 1.8 GHz

Based on the new theoretical approach and the self-consistent iteration procedure for calculating the limiting values ( ε( ∞) and ε(0)) of the frequency-dependent permittivity, it becomes possible to recognize the fitting function for the function ε(j ω) measured for a complex system representing plant tissues of fresh fruits and vegetables in the frequency range (10 7–1.8×10 9 Hz). The recognized fitting function is common for all of a set of nine fruits and vegetables (apple, avocado, banana, cantaloupe, carrot, cucumber, grape, orange, and potato) and contains seven fitting parameters. These parameters are varied for different fruits and vegetables, and their behavior with respect to temperature is different but nevertheless exhibits some common features. This fitting function containing power-law exponents and confirming the existence of relaxation processes described in terms of fractional kinetic equations for some complex biological systems can be used for practical purposes to construct a desired calibration curve with respect to quality factors, as for example, moisture content or degree of maturity. The discovered common “universality” in dielectric behavior of such complex materials as plant tissues opens a possibility to use dielectric spectroscopy as a nondestructive method of control in analysis of electrical behavior (measured in the form of complex permittivity or impedance) for other complex materials.

Parameter identification for a TRIP model with backstress

The investigation of complex material behaviour of steel like transformation-induced plasticity (TRIP) is a large field of current research. The simulation of the material behaviour of work-pieces in complex situations requires a knowledge as deep as possible about phenomena like TRIP. In addition, there are effects in the case of non-constant stress which cannot be explained by the widely used Leblond model. Therefore, we consider a TRIP model taking into account backstress due to TRIP itself. Assuming a linear dependence of this backstress from the TRIP strain we derive formulas for calculation of the new TRIP parameters. Based on experimental data we calculate these parameters.

Numerical Simulation of the Application of NiTi Alloys in Medical Technologies

AbstractShape memory alloys are nowadays already established as a material which is able to solve exceptional tasks in practical applications. Particularly, its utilization in the field of medical technologies increases steadily. For example micro tools (staple, catheters) and implants (coronary stents) are made out of Nickel‐Titanium well known as a basic shape memory alloy. Apart from the advantages like the avoidance of auxiliary components and joints in the system and to utilize the high volume specific work of shape memory alloys, NiTi alloys exhibit a good biocompatibility. This property is necessary with regard to either permanent or temporary implants. To optimize the use of NiTi alloys in the scope of medical technologies, the support of the development of applicable tools by numerical simulations is highly recommended. However the complex material behaviour containing a profoundly thermomechanical coupling poses indeed a big challenge to the material modeling and its implementation into a finite element code. Particularly, the material model proposed by Helm [1] proves to be a firm model containing the most common properties of shape memory alloys, as the pseudoelasticity, the shape memory effect and the two‐way effect. In the present contribution the FE modelling of a medical staple used in foot surgery is presented by considering the model of Helm which was investigated by the authors to improve its performance in the finite element method [2]. The foot staple, produced by a group of members of the SFB 459 which is funded by the DFG, avails the shape memory effect to excite the desired clamping effect [3]. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Parallel process system and its application to steam generator structural analysis

A large-scale analysis to evaluate complex material and structural behaviors is one of interesting topic in diverse engineering and scientific fields. Also, the utilization of massively parallel processors has been a recent trend of high performance computing. The objective of this paper is to introduce a parallel process system which consists of general purpose finite element analysis solver as well as parallelized PC cluster. The later was constructed using eight processing elements and the former was developed adopting both hierarchical domain decomposition method and balancing domain decomposition method. Then, to verify the efficiency of the established system, it was applied for structural analysis of steam generator in nuclear power plant. Since the prototypal evaluation results agreed well to the corresponding reference solutions it is believed that, after reinforcement of PC cluster by increasing number of processing elements, the promising parallel process system can be utilized as a useful tool for advanced structural integrity evaluation.

A dissipation-based control method for the multi-scale modelling of quasi-brittle materials

Multi-scale models based on computational homogenisation are nowadays developed for the simulation of complex material behaviour. The use of homogenisation techniques on finite-sized representative volume elements in the presence of quasi-brittle damage may lead to the presence of snap-backs in the macroscopic material response. A methodology to simulate this type of response in the multi-scale technique is proposed, based on the control of the dissipation at the mesoscopic scale. To cite this article: T.J. Massart et al., C. R. Mecanique 333 (2005).

Modelling chemo‐hydro‐mechanical behaviour of unsaturated clays: a feasibility study

AbstractEffective capabilities of combined chemo‐elasto‐plastic and unsaturated soil models to simulate chemo‐hydro‐mechanical (CHM) behaviour of clays are examined in numerical simulations through selected boundary value problems. The objective is to investigate the feasibility of approaching such complex material behaviour numerically by combining two existing models. The chemo‐mechanical effects are described using the concept of chemical softening consisting of reduction of the pre‐consolidation pressure proposed originally by Hueckel (Can. Geotech. J. 1992; 29:1071–1086; Int. J. Numer. Anal. Methods Geomech. 1997; 21:43–72). An additional chemical softening mechanism is considered, consisting in a decrease of cohesion with an increase in contaminant concentration. The influence of partial saturation on the constitutive behaviour is modelled following Barcelona basic model (BBM) formulation (Géotech. 1990; 40(3):405–430; Can. Geotech. J. 1992; 29:1013–1032).The equilibrium equations combined with the CHM constitutive relations, and the governing equations for flow of fluids and contaminant transport, are solved numerically using finite element. The emphasis is laid on understanding the role that the individual chemical effects such as chemo‐elastic swelling, or chemo‐plastic consolidation, or finally, chemical loss of cohesion have in the overall response of the soil mass. The numerical problems analysed concern the chemical effects in response to wetting of a clay specimen with an organic liquid in rigid wall consolidometer, during biaxial loading up to failure, and in response to fresh water influx during tunnel excavation in swelling clay. Copyright © 2005 John Wiley & Sons, Ltd.

Frequency dependence of complex moduli of brain tissue using a fractional Zener model

Brain tissue exhibits viscoelastic behaviour. If loading times are substantially short, static tests are not sufficient to determine the complete viscoelastic behaviour of the material, and dynamic test methods are more appropriate. The concept of complex modulus of elasticity is a powerful tool for characterizing the frequency domain behaviour of viscoelastic materials. On the other hand, it is well known that classical viscoelastic models can be generalized by means of fractional calculus to describe more complex viscoelastic behaviour of materials. In this paper, the fractional Zener model is investigated in order to describe the dynamic behaviour of brain tissue. The model is fitted to experimental data of oscillatory shear tests of bovine brain tissue to verify its behaviour and to obtain the material parameters.

Roll compaction of a pharmaceutical excipient: Experimental validation of rolling theory for granular solids

Roll compaction is widely used in industry to produce free flowing agglomerates from a fine particulate feed. Two of the main advantages of this process are that it is dry and continuous. Despite being superficially a simple process, a quantitative understanding has proved difficult to develop because of the complex behaviour of particulate materials. Sub-optimal design and operation of the equipment can lead to unsatisfactory products. Johanson (1965, ASME, Journal of Applied Mechanics Series E, 32(4), 842–848) developed a theoretical model that enables the surface pressure, torque and separating force of the rolls to be predicted from the physical characteristics of the powder and the dimensions of the rolls. However, a detailed experimental validation of the theory has yet to be accomplished. The current paper describes such a study using a gravity fed instrumented roll press and a microcrystalline cellulose powder. The measured pressure profiles in the nip region of the roll press were comparable to the calculated values. The theory was also found to predict the effect of material properties on the nip angle and the peak pressure but it was unable to account for the influence of roll speed.

The Structure of Vagueness

Around the beginning of the 1990s, Frei Otto and his team at the Institute for Lightweight Structures in Stuttgart studied what they called “optimized path systems.” Previously, similar to the chain modeling technique Gaudi used for the Sagrada Familia, they had experimented with material systems for calculating form. Each of these material machines was devised so that, through numerous interactions among its elements over a certain time span, the machine restructures, or as Frei Otto says, “finds (a) form.” Most of them consist of materials that process forces by transformation, which is a special form of analog computing. Since the materials function as “agents,” it is essential that they have a certain flexibility, a certain amount of freedom to act. It is also essential however, that this freedom is limited to a certain degree set by the structure of the machine itself. In classic analog computing most of the movement is contained in gears, pistons or slots, or often in liquids held by rigid containers, but in the case of Frei Otto’s machines mostly all materials are mixtures of liquids and solids, or start out as liquid and end up as rigid. The material interactions frequently result in a geometry that is based on complex material behaviour of elasticity and variability. Sand, balloons, paper, soap film (including the famous minimal surfaces for the Munich Olympic Stadium), soap bubbles, glue, varnish, and the ones I will be referring to here: the wool-thread machines. This last technique was used to calculate the shape of two-dimensional city patterns, but also of three-dimensional cancellous bone structure or branching column systems. They are all similar vectorized systems that economize on the number of paths, meaning they share a geometry of merging and bifurcating.

Physical characteristics of a waste activated sludge: conditioning responses and correlations with a synthetic surrogate

The efficient and economic management of waste activated sludge (WAS) requires a proper understanding of the sludge's material properties. Though there has been much study of WAS, an adequate linkage between its physical and chemical properties has been elusive. In particular, the conditioning and dewatering of WAS are expensive operations, and the addition of polymer to WAS leads to even more complex material behavior that is difficult to optimize. This paper reports on an extensive characterization of WAS, both with and without polymer conditioning. We combined the classical "jar test" approach with less conventional rheometric and electrokinetic measurements. In addition to the use of sampled WAS, a synthetic surrogate sludge was formulated, attempting to duplicate properties of WAS and allow more extensive characterization of a reproducible surrogate to WAS. Results with both the synthetic surrogate and WAS indicated that the traditional, electrokinetic, and rheological properties were related. However, the dose optima by rheometry were somewhat higher in both cases.

Materials for nuclear energy: towards multi-scale modelling of service properties

The authors introduce the multi-scale modelling approach of service properties and recent results that best reflect the complex behaviour of industrial materials. They describe the main modelling tools and highlight the essence of experimental checking at the appropriate scale. The authors describe in details the progress that has been accomplished in the prediction of the energy of atom-scale defects in steels, as essential input data to model the kinetics of microstructure evolutions under radiation. The authors present the multi-scale prediction of mechanical properties along with the particular issue of the nuclear fuel.

The magic of plutonium: 5f electrons and phase instability

This article was presented at a symposium held in honor of Terence E. (Terry) Mitchell for his many contributions to materials science. Terry Mitchell has explored the magic of materials during his distinguished 40-plus year career, always going back to the fundamentals to understand the behavior of complex materials. He has covered a wide range of materials from metals and alloys, to ceramics, intermetallics, strained-layer superlattices, high-temperature superconductors, and nanostructured materials. In this tribute to the remarkable contributions of Terry Mitchell to the materials field, I will cover the magical world of plutonium—one of the few materials that has escaped his scrutiny to date.

Prediction and control of part distortion during the hot extrusion of titanium alloys

When titanium and steel billets are hot extruded using flat dies and glass lubricant, the extrudate distorts. This distortion is even larger for non-symmetrical shapes and complex billet material behavior. The amount of distortion is often a complex interplay between the die design, glass lubrication and extrusion conditions. Many experimental try-outs are often needed to determine the die design and operating conditions for reduced distortion. In order to investigate distortion, a finite element model for the glass lubricated hot extrusion process was developed that included all relevant aspects of the hot extrusion process such as induction heating, billet transfer, glass lubrication and metal flow. A design strategy was developed that permitted modeling the three-dimensional metal flow field of a complex extrusion by a two-dimensional FEM model. This model was then used to study the effect of die design and process parameters in extrusion of a titanium aerospace structural. Die design strategy was used to modify design for reduced distortion. Model predictions were verified by experiments on an industrial 2000 t hydraulic press.

Air stable copper phosphide (Cu 3P): a possible negative electrode material for lithium batteries

Air stable copper phosphide was synthesized as a thick film over a copper foil by a very simple solid-state reaction at low temperature. X-ray diffraction confirms that the layer is pure Cu 3P. Scanning electron microscopy reveals a porous microstructure consisting of agglomerated particles with 10 μm of diameter. Electrochemical reaction of Cu 3P with lithium leads to an amorphisation of the thick film during the first discharge, and Cu 3P does not seem to recover upon subsequent charge. Structural and microstructural analyses coupled with electrochemical tests emphasize a complex behavior of the copper phosphide material. An initial capacity of 415 mAh/g has been measured with a stable reversible capacity close to 200 mAh/g on subsequent cycles without the help of binder and/or conductive additives. Although the gravimetric capacity values obtained with Cu 3P are slightly below the graphite capacity, the volumetric capacity of Cu 3P (1473 Ah/L) is 80% higher than those of graphite (800 Ah/L).

From snow X-ray microtomograph raw volume data to micromechanics modeling: first results

AbstractThe new approaches in absorption X-ray microtomography allow snow-volume image acquisition in the cm3 range without destroying snow structure, and make it possible to perform micromechanical studies with the real geometry. The main objective of this paper is to introduce the development of a new three-dimensional (3-D) geometry modeling and finite-element analysis simulation package adapted to these scales. These new code modules and procedures are briefly described using an isothermal metamorphism snow experiment (–2°C, 3 months).This sample of aged snow (3.375mm3; 3003 voxels) allows simulation of a simple hypothetical uniaxial compressive stress experiment. The constitutive equations, boundary conditions, basic assumptions and the result showing the stress field over the 3-D data are discussed. The first qualitative results show a maximum stress of 6–9MPa in some small bonds, showing the potential of these codes to simulate the micromechanical behavior of complex materials.

Fatigue characterization of a polymer foam to use as a cancellous bone analog material in the assessment of orthopaedic devices

Analog materials are used as a substitute to cancellous bone for in vitro biomechanical tests due to their uniformity, consistency in properties and availability. To date, only the static material properties of these materials have been assessed, although they are often used in fatigue tests. Cancellous bone exhibits complex material behavior when subjected to fatigue loads, including modulus degradation, accumulation of permanent strain and increasing hysteresis. Analog materials should exhibit similar fatigue behavior to cancellous bone if they are to be used in cyclic loading tests. In our study, a polymer foam (commercial name HEREX C70.55) has been studied for its static and fatigue behavior and compared with that of cancellous bone. In compression, the foam exhibited qualitatively similar mechanical behavior, but the degree of modulus degradation and accumulation of permanent strain was lower than expected for cancellous bone. In general, the tensile properties of the foam were greater than found in compression, the opposite to the mechanical behavior of cancellous bone. The methodology employed here could form the basis of selecting suitable analog materials for cancellous bone in the future.

A theoretical analysis of damage evolution in skeletal muscle tissue with reference to pressure ulcer development.

A theoretical analysis of damage evolution in skeletal muscle tissue with reference to pressure ulcer development.