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Continuum Mechanics (continuum + mechanic)

Distribution by Scientific Domains

Engineering	50%
Polymers and Materials Science	25%

Selected Abstracts

Run Out of Landslides , Continuum Mechanics versus Discontinuum Mechanics Models

GEOMECHANICS AND TUNNELLING, Issue 5 2008
Rainer Poisel a.o.Univ.-Prof.
In general, a rock slope failure leads to the detachment of a rock mass consisting of a mass of blocks. During the last few years continuum mechanics as well as discontinuum mechanics numerical codes have been developed for modelling the run out of these masses. In order to compare both methods, Punta Thurwieser Rock Avalanche and Frank Slide were modelled by the continuum mechanics numerical code DAN3D as well as by the distinct element method PFC3D modified for run out modelling. The simulations showed that the parameters necessary to get results coinciding with observations in nature are completely different and that Frank run out was a real "slide" of a coherent mass, whereas Punta Thurwieser run out was a rock mass fall with much internal movement. The parameters for a run out simulation, therefore, have to be chosen in such a way that the simulation gives a rock mass fall in one particular case and a slide of a coherent mass in another, corresponding to the real conditions. Therefore, the prediction of the run out kinematics and the fixing of the parameters is a demanding task in each case when modelling run outs. Bergstürze , Vergleich kontinuumsmechanische und diskontinuumsmechanische Rechenmodelle Das Versagen von Felsböschungen und Talflanken führt meist zur Ablösung einer Masse von Blöcken. In den letzten Jahren wurden sowohl kontinuumsmechanische als auch diskontinuumsmechanische Rechenmodelle für die Simulation des Absturzvorgangs solcher Massen entwickelt. Anhand der Modellierung der Bergstürze Punta Thurwieser und Frank Slide mittels DAN3D und PFC3D werden die genannten Ansätze verglichen. Die Ergebnisse zeigen, dass sich die für eine realitätsnahe Modellierung erforderlichen Parameter stark unterscheiden. Während der Frank Slide als weitgehend kohärente Masse abging, war der Bergsturz Punta Thurwieser ein stark turbulenter Trümmerstrom. Die Parameter für die rechnerische Modellierung eines Bergsturzes müssen daher im einen Fall so gewählt werden, dass sich , je nach realen Verhältnissen , eine "laminare" Bewegung, im anderen Fall aber so, dass sich eine turbulente Bewegung ergibt. Die Vorhersage der Kinematik eines Bergsturzes und die darauf aufbauende Auswahl von Rechenparametern stellt daher eine anspruchsvolle Aufgabe dar. [source]

Mechanical Buckling: Mechanics, Metrology, and Stretchable Electronics

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
Dahl-Young Khang
Abstract Mechanical buckling usually means catastrophic failure in structural mechanics systems. However, controlled buckling of thin films on compliant substrates has been used to advantage in diverse fields such as micro-/nanofabrication, optics, bioengineering, and metrology as well as fundamental mechanics studies. In this Feature Article, a mechanical buckling model is presented, which sprang, in part, from the buckling study of high-quality, single-crystalline nanomaterials. To check the mechanical-buckling phenomenon down to the nano-/molecular scale, well-aligned single-walled carbon nanotube arrays and cross linked carbon-based monolayers are transferred from growth substrate onto elastomeric substrate and then they are buckled into well-defined shapes that are amenable to quantitative analysis. From this nano- or molecular-scale buckling, it is shown that the mechanical moduli of nanoscale materials can easily be determined, even using a model based on continuum mechanics. In addition, buckling phenomena can be utilized for the determination of mechanical moduli of organic functional materials such as poly(3-hexylthiophene) (P3HT) and P3HT/6,6-phenyl-C61 -butyric acid methyl ester (PCBM) composite, which are widely used for organic transistors and organic photovoltaics. The results provide useful information for the realization of flexible and/or stretchable organic electronics. Finally, the fabrication and applications of "wavy, stretchable" single-crystal Si electronics on elastomeric substrates are demonstrated. [source]

Run Out of Landslides , Continuum Mechanics versus Discontinuum Mechanics Models

Interfacial Stress Transfer in a Graphene Monolayer Nanocomposite

ADVANCED MATERIALS, Issue 24 2010
Lei Gong
It is demonstrated from stress-induced Raman bands shiftsthat stress can be transferred from a polymer matrix to a graphene monolayer (see image) in a model nanocomposite. It is shown further that the behavior can be modeled using continuum mechanics and that the interface between the graphene and the polymer breaks down at a shear stress of the order of 2,MPa. [source]

Frost heave modelling using porosity rate function

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2006
Radoslaw L. Michalowski
Abstract Frost-susceptible soils are characterized by their sensitivity to freezing that is manifested in heaving of the ground surface. While significant contributions to explaining the nature of frost heave in soils were published in late 1920s, modelling efforts did not start until decades later. Several models describing the heaving process have been developed in the past, but none of them has been generally accepted as a tool in engineering applications. The approach explored in this paper is based on the concept of the porosity rate function dependent on two primary material parameters: the maximum rate, and the temperature at which the maximum rate occurs. The porosity rate is indicative of ice growth, and this growth is also dependent on the temperature gradient and the stress state in the freezing soil. The advantage of this approach over earlier models stems from a formulation consistent with continuum mechanics that makes it possible to generalize the model to arbitrary three-dimensional processes, and use the standard numerical techniques in solving boundary value problems. The physical premise for the model is discussed first, and the development of the constitutive model is outlined. The model is implemented in a 2-D finite element code, and the porosity rate function is calibrated and validated. Effectiveness of the model is then illustrated in an example of freezing of a vertical cut in frost-susceptible soil. Copyright © 2006 John Wiley & Sons, Ltd. [source]

A continuum mechanics-based framework for boundary and finite element mesh optimization in two dimensions for application in excavation analysis

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2005
Attila M. Zsáki
Abstract The determination of the optimum excavation sequences in mining and civil engineering using numerical stress analysis procedures requires repeated solution of large models. Often such models contain much more complexity and geometric detail than required to arrive at an accurate stress analysis solution, especially considering our limited knowledge of rock mass properties. This paper develops an automated framework for estimating the effects of excavations at a region of interest, and optimizing the geometry used for stress analysis. It eliminates or simplifies the excavations in a model while maintaining the accuracy of analysis results. The framework can equally be applied to two-dimensional boundary and finite element models. The framework will have the largest impact for non-linear finite element analysis. It can significantly reduce computational times for such analysis by simplifying models. Error estimators are used in the framework to assess accuracy. The advantages of applying the framework are demonstrated on an excavation-sequencing scenario. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A unified formulation for continuum mechanics applied to fluid,structure interaction in flexible tubes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2005
C. J. Greenshields
Abstract This paper outlines the development of a new procedure for analysing continuum mechanics problems with a particular focus on fluid,structure interaction in flexible tubes. A review of current methods of fluid,structure coupling highlights common limitations of high computational cost and solution instability. It is proposed that these limitations can be overcome by an alternative approach in which both fluid and solid components are solved within a single discretized continuum domain. A single system of momentum and continuity equations is therefore derived that governs both fluids and solids and which are solved with a single mesh using finite volume discretization schemes. The method is validated first by simulating dynamic oscillation of a clamped elastic beam. It is then applied to study the case of interest,wave propagation in highly flexible tubes,in which a predicted wave speed of 8.58 m/s falls within 2% of an approximate analytical solution. The method shows further good agreement with analytical solutions for tubes of increasing rigidity, covering a range of wave speeds from those found in arteries to that in the undisturbed fluid. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Non-local damage model based on displacement averaging

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2005
M. Jirásek
Abstract Continuum damage models describe the changes of material stiffness and strength, caused by the evolution of defects, in the framework of continuum mechanics. In many materials, a fast evolution of defects leads to stress,strain laws with softening, which creates serious mathematical and numerical problems. To regularize the model behaviour, various generalized continuum theories have been proposed. Integral-type non-local damage models are often based on weighted spatial averaging of a strain-like quantity. This paper explores an alternative formulation with averaging of the displacement field. Damage is assumed to be driven by the symmetric gradient of the non-local displacements. It is demonstrated that an exact equivalence between strain and displacement averaging can be achieved only in an unbounded medium. Around physical boundaries of the analysed body, both formulations differ and the non-local displacement model generates spurious damage in the boundary layers. The paper shows that this undesirable effect can be suppressed by an appropriate adjustment of the non-local weight function. Alternatively, an implicit gradient formulation could be used. Issues of algorithmic implementation, computational efficiency and smoothness of the resolved stress fields are discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source]

The play operator on the rectifiable curves in a Hilbert space

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 11 2008
Vincenzo Recupero
Abstract The vector play operator is the solution operator of a class of evolution variational inequalities arising in continuum mechanics. For regular data, the existence of solutions is easily obtained from general results on maximal monotone operators. If the datum is a continuous function of bounded variation, then the existence of a weak solution is usually proved by means of a time discretization procedure. In this paper we give a short proof of the existence of the play operator on rectifiable curves making use of basic facts of measure theory. We also drop the separability assumptions usually made by other authors. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Modelling suspended carbon nanotube resonators

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007
M. Poot
Abstract We study the bending mode vibration in suspended carbon nanotubes. Based on the theory of continuum mechanics, we have developed a model for flexural oscillations of suspended nanotubes. A detailed analysis of the electrostatic force, the scaling behavior of the model and the gate tuning is given. The model is used to fit experimental data and to reconstruct the gate dependence of the tension and strain in the nanotube. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A study of residence time distribution in co-rotating twin-screw extruders.

POLYMER ENGINEERING & SCIENCE, Issue 12 2003
Part I: Theoretical modeling
A theoretical model to determine the residence time distribution (RTD) in a co-rotating twin-screw extruder is proposed. The method consists of coupling a continuum mechanics approach with a chemical engineering one and allows us to obtain the RTD without any adjustable parameter. The process parameters are obtained using Ludovic® twin-screw modeling software, and ideal reactors are chosen to depict the screw profile. The influence of screw speed, feed rate and viscosity on RTD are described on a fictive screw profile. The predictions of the model are in qualitative agreement with literature data. The key point of this procedure is obviously the correct association between an ideal reactor and a screw element. [source]

Mechanical Deformation of Compressible Chromatographic Columns

BIOTECHNOLOGY PROGRESS, Issue 3 2002
R. N. Keener
A one-dimensional model of mechanical deformation of compressible chromatography columns is presented. The model is based on linear elasticity and continuum mechanics and is compared to a more complete two-dimensional model and one-dimensional porosity profiles measured by NMR imaging methods. The model provides a quantitative description of compression and the effects of wall support during scale-up. A simple criterion for the significance of wall support as a function of both diameter and length is also developed. Although the model accounts only for mechanical deformation, flow compression can be included, and validation presented here suggests that a more complete model may be valuable for anticipating the effects of scale and aspect ratio on pressure-flow behavior of compressible columns. [source]