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Mechanical Behaviour (mechanical + behaviour)

Distribution by Scientific Domains

Engineering	50%
Polymers and Materials Science	25%
Earth and Environmental Science	10%
Medical Sciences	7%
4 Other Domains	8%

Selected Abstracts

Mechanical Behaviour of Internal Reinforced Aluminium Foams,

ADVANCED ENGINEERING MATERIALS, Issue 11 2007
E. Solórzano
The paper presents a new way to improve the mechanical behaviour of aluminum based foams produced by the powder metallurgical (PM) route; the method is based on the use of internal reinforcements. These reinforcements allow an excellent improvement of the mechanical response in compression, tension and bending all at the same time. The produced samples have showed an excellent reproducibly in their mechanical response. [source]

The Influence of Magnetic Fields on the Mechanical Behaviour of Granular Materials Used for Foundry Moulding: Numerical and Experimental Analysis,

ADVANCED ENGINEERING MATERIALS, Issue 8 2006
P.-M. Geffroy
Understanding the mechanical behaviour of granular materials is of financial importance in many industries, including the geotechnical [1], pharmaceutical and foundry sectors. In the latter, granular materials are used as mould elements for lost foam (sand) and magnetic moulding (steel shot) processes. This study focuses on optimising mould geometry and magnetic field characteristics (intensity and orientation) to obtain the desired dimensions of the final product. [source]

Verhalten von hochduktilem Beton unter Impaktbelastung

BETON- UND STAHLBETONBAU, Issue 7 2010
Oliver Millon Dipl.-Ing.
Baustoffe; Versuche; Dynamische Einwirkungen/Erdbeben Abstract In diesem Aufsatz wird das Materialverhalten von Hochduktilem Beton (engl.: Strain Hardening Cementitious Composite , SHCC) bei Impaktbelastung beschrieben. Dazu werden Ergebnisse aus hochdynamischen Spallations-Experimenten an einem Hopkinson- Bar mit Dehnraten > 140 1/s den Resultaten aus quasi-statischen, zentrischen Zugversuchen mit Dehnraten von 0,001 1/s gegenübergestellt. Die Auswirkungen hoher Dehnraten auf das Materialverhalten erfolgt anhand eines Vergleiches der zentrischen Zugfestigkeit, des E-Moduls sowie der Bruchenergie. Die experimentellen Ergebnisse werden zudem mit den Kennwerten anderer Betone in Beziehung gesetzt. Unterschiede im Materialverhalten werden auf Grundlage von Phänomenen der Rissbildung und des Faserauszuges erklärt. Mechanical Behaviour of SHCC under Impact This paper describes the material behaviour of Strain Hardening Cementitious Composite (SHCC) at high strain rates. The results of high dynamic spall experiments using a Hopkinson Bar at strain rates > 140/sec were arrayed against the results of quasistatic, centric tensile tests at strain rates of 0,001/sec. This comparison is based on the parameters of tensile strength, elastic modulus, and fracture energy of the specimens. In addition, the experimental results of SHCC are related to the characteristic values of other concrete types. Differences in material behaviour are explained by the phenomena of crack formation and fibre pullout force. [source]

Mechanical behaviour and quality traits of highbush blueberry during postharvest storage

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 6 2009
Valentina Chiabrando
Abstract BACKGROUND: Berry firmness is one of the most important characteristics for fresh market consumption. Blueberry firmness is also an important attribute because it is considered to be a measure of its freshness. Berries lose their firmness by loss of water and by changes in their structure. RESULTS: The postharvest life of two highbush blueberry cultivars (Bluecrop and Coville) was investigated. Several parameters related to blueberry quality were evaluated during the postharvest storage period. To assess berry texture characteristics (firmness, hardness, cohesiveness, gumminess, chewiness, springiness, resilience), a rapid non-destructive penetrometer test by Durofel® and texture profile analysis (TPA) using a texture analyser were carried out. Low temperature inhibited the decrease of total soluble solids, total titratable acidity and increase of flesh pH value, thereby maintaining good taste quality. There was an increase in fruit firmness (Durofel index) and hardness and a decrease in chewiness and springiness during storage. CONCLUSION: There was a significant correlation among the TPA parameters and Durofel index. The Durofel index could therefore be used as a suitable indicator of fruit quality and storability, and low-temperature storage is beneficial to maintain the taste quality of blueberry fruit after harvest. Copyright © 2009 Society of Chemical Industry [source]

The role of groundwater in cliff instability: an example at Cape Blanc-Nez (Pas-de-Calais, France)

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2006
Guillaume Pierre
Abstract Cliff retreat in northern Boulonnais is described. The distribution of the amount of retreat is related to structural and topographic factors. Both control the runoff,infiltration balance and therefore the mechanical behaviour of the rocks, which determines the modes of failure. The spatial variability of the retreat rate is explained, but predicting the temporal variability of the retreat rate, which is central to risk management, is much more difficult. Rainfall and piezometric surface data enhanced a ,piston flow' mechanism during November 2000. The result of its occurrence on the stability of the cliff and conditions of its recurrence are examined with a view to better understanding the rate of recession of coastal cliffs and wiser management of risk. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Uplift-restraining Friction Pendulum seismic isolation system

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2006
Panayiotis C. Roussis
Abstract This paper extends the scope of seismic isolation by introducing an innovative uplift-restraining Friction Pendulum system. Termed the XY-FP isolator, the new isolation device consists of two orthogonal opposing concave beams interconnected through a sliding mechanism that permits tension to develop in the bearing, thereby preventing uplift. Owing to its distinct configuration, the XY-FP isolator possesses unique properties for a seismic isolator, including uplift restraint, decoupling of the bi-directional motion along two orthogonal directions, and capability of providing independent stiffness and energy dissipation along the principal horizontal directions of the bearing. The study concentrates on introducing the concept and establishing the underlying principles of operation of the new XY-FP isolator, formulating the mathematical model for the XY-FP isolator, and presenting its mechanical behaviour through a displacement-control testing program on a single XY-FP isolator. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Oxidation Resistance of Multilayer SiC for Space Vehicle Thermal Protection Systems,

ADVANCED ENGINEERING MATERIALS, Issue 7 2010
Claudia Milena Vega Bolivar
The oxidation resistances of different kinds of SiC-based laminates are compared. The materials under investigation are produced by tape casting of green ceramic sheets, followed by stacking of the sheets in a multilayer structure and laminate consolidation by de-binding and sintering. Three kinds of specimens are tested: multilayer SiC with fully dense layers, multilayer SiC integrating porous layers and multilayer composites made by stacking SiC/Cf composite layers. Two kinds of chopped carbon fibres (polyamide coated and uncoated) are used for the manufacture of the composite sheets. The oxidation behaviour is investigated by simultaneous TGA,DTA,MS analysis. Specimens are also submitted to a long-term oxidation treatment (30,h at 1,600,°C in flowing air) and their microstructure and mechanical behaviour compared before and after oxidation. This assessment shows that the integration of porous or composite layers in the multilayer architecture does not worsen the oxidation resistance. In every case the formation of a surface passivating layer prevents major degradation phenomena, so that only small changes in the mechanical features are found after oxidation. [source]

Mechanical Behaviour of Internal Reinforced Aluminium Foams,

The Influence of Magnetic Fields on the Mechanical Behaviour of Granular Materials Used for Foundry Moulding: Numerical and Experimental Analysis,

Outstanding Ceramic Matrix Composites for High Temperature Applications

ADVANCED ENGINEERING MATERIALS, Issue 3 2005
L. Vandenbulcke
Accurate deposition of boron and silicon carbides and nitrides permits to improve the oxidation resistance of self-healing matrices of multilayered composites. The uniformity and the microstructure of each layer and of their interfaces induce the final properties of these composites. Their mechanical behaviour in conditions very close to the applications in the energy, space and aeronautic domains, allows to demonstrate the breakthrough enabled by this new composite generation. [source]

Fatigue damage analysis in a duplex stainless steel by digital image correlation technique

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2008
A. EL BARTALI
ABSTRACT Strain field measurements by digital image correlation today offer new possibilities for analysing the mechanical behaviour of materials in situ during mechanical tests. The originality of the present study is to use this technique on the micro-structural scale, in order to understand and to obtain quantitative values of the fatigue surface damage in a two-phased alloy. In this paper, low-cycle fatigue damage micromechanisms in an austenitic-ferritic stainless steel are studied. Surface damage is observed in real time, with an in situ microscopic device, during a low-cycle fatigue test performed at room temperature. Surface displacement and strain fields are calculated using digital image correlation from images taken during cycling. A detailed analysis of optical images and strain fields measured enables us to follow precisely the evolution of surface strain fields and the damage micromechanisms. Firstly, strain heterogeneities are observed in austenitic grains. Initially, the austenitic phase accommodates the cyclic plastic strain and is then followed by the ferritic phase. Microcrack initiation takes place at the ferrite/ferrite grain boundaries. Microcracks propagate to the neighbouring austenitic grains following the slip markings. Displacement and strain gradients indicate probable microcrack initiation sites. [source]

A new methodology to guarantee the structural integrity of Al2O3/SiC composite using crack healing and a proof test

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2007
M. ONO
ABSTRACT Structural ceramics are brittle and sensitive to flaws. As a result, the structural integrity of a ceramic component may be seriously affected by inherent flaws. Self-crack-healing is an excellent answer to this problem. At the moment, however, there is no technique to heal embedded flaws. Therefore, a technique to guarantee the reliability of ceramic components is demanded, and thus a technique using crack healing followed by proof test was developed by K. Ando et al. to accomplish this. With this technique, testing the mechanical behaviour of the crack-healed zone is very important for ensuring the structural integrity of a ceramic component. In this study, first Al2O3/SiC composite with an excellent crack-healing ability was sintered. Second, a crack was introduced on the sample (3 mm × 4 mm × 36 mm), which reduced the bending strength by about 80%, and subsequently the crack was healed. Third, a proof test was carried out on the crack-healed sample. Last, using the crack-healed and proof-tested sample, a fracture test was carried out up to 1373 K. The measured minimum fracture stress (,Fmin) was compared with the theoretical minimum strength (,G) from room temperature (R.T.) to 1373 K. It was concluded that ,G showed good agreement with ,Fmin up to 1373 K and that the crack healing followed by proof test was an excellent technique to increase the survival probability by administering a proof test and to guarantee the reliability of Al2O3/SiC composite. [source]

Damage analysis for structural integrity and durability of composite materials

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2006
R. TALREJA
ABSTRACT Composite structures for mechanical and aerospace applications are designed to retain structural integrity and remain durable for the intended service life. Since the early 1970s important advances have been made in characterizing and modelling the underlying mechanical behaviour and developing tools and methodologies for predicting fracture and fatigue of composite materials. This paper presents a review of the concepts and analyses related to this area, and illustrates these by a few examples. The topics discussed are composite material strength in tension, compression and shear, damage and its progression in monotonic and cyclic loading, fatigue life prediction and damage induced changes in visco-elastic response. [source]

Crack-healing and mechanical behaviour of Al2O3/SiC composites at elevated temperature

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2004
K. ANDO
ABSTRACT Alumina/silicon carbide (Al2O3/SiC) composite ceramics with large self-crack-healing ability, high strength and high heat-resistance limit temperature for strength were developed and subjected to three-point bending. A semicircular surface crack 100 ,m in diameter was made on each sample. Crack-healing behaviour was systematically studied, as functions of crack-healing temperature and healing time, and the fatigue strengths of the crack-healed sample at room temperature and 1373 K were investigated. Four main conclusions were drawn from the present study. (1) Al2O3/SiC composite ceramics have the ability to heal after cracking from 1273to 1673 K in air. (2) The heat-resistance limit temperature for strength of the crack-healed sample is ,1573 K, and ,68% of the samples fractured from outside the crack-healed zone in the testing-temperature range 873,1573 K. (3) The crack-healed sample exhibited very high fatigue limit at room temperature and also 1373 K. (4) The large self-crack-healing ability is a desirable technique for the high structural integrity of ceramic component. [source]

New data for sandwich panels on the correlation between the SBI test method and the room corner reference scenario

FIRE AND MATERIALS, Issue 1 2005
Jesper Axelsson
Abstract Assessment of the fire behaviour of sandwich panels is continuously under discussion. The fire behaviour of these panels is a combination of material characteristics such as the core material and mechanical behaviour of the panels such as joints, dilations etc. The use of small or intermediate scale tests can be questioned for such types of products. Within the proposed European product standard for sandwich panels (prEN 14509) the intermediate scale test method SBI (EN 13823) has been suggested as the fire test method to certify panels. The standard does, however, use quite an artificial mounting procedure, which does not fully reflect the end-use conditions of the panels. In a previous research project conducted by Nordtest it was shown that the correlation between the SBI test method and both the ISO 9705 and ISO 13784 part 1 was insufficient. The test data produced for the SBI test method, however, did not use the above mentioned mounting technique. In this article new data for a number of products are added to the database using the mounting procedure of the product standard. The data are compared with the previous data and show that the mounting method of the product standard results in slightly more severe conditions but that there are still discrepancies with the full-scale test results. The data also show an unacceptable level of repeatability due to the fact that small dilations result in a wide variation of classification result. The new data together with the old data show once more that it is dangerous to make a fire safety assessment of a sandwich panel based on small or intermediate scale tests. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Polyurethane/clay and polyurethane/POSS nanocomposites as flame retarded coating for polyester and cotton fabrics

FIRE AND MATERIALS, Issue 4-5 2002
Eric Devaux
Polyurethane resins (PU) are widely used as coatings for textile fabrics in order to improve some properties (for example mechanical behaviour, water repellency and air impermeability). Two kinds of additives have been added to the polyurethane in order to provide flame retardancy to the coated textile structure: montmorillonite clay and polyhedral oligomeric silsesquioxanes (POSS) have been used to process PU nanocomposites. The paper presents some results obtained with PU/clay and PU/POSS coated polyester or cotton fabrics, using cone calorimetry and thermogravimetric analysis. The efficiency of the additive chosen is clearly demonstrated and discussed. In particular, the great potential of using POSS for fire retardant applications is highlighted. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Analysis of a microcrack model and constitutive equations for time-dependent dilatancy of rocks

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2003
Zuan Chen
SUMMARY Based on experimental observations and theoretical analyses, the author introduces an ideal microcrack model in which an array of cracks with the same shape and initial size is distributed evenly in rocks. The mechanism of creep dilatancy for rocks is analysed theoretically. Initiation, propagation and linkage of pre-existing microcracks during creep are well described. Also, the relationship between the velocity of microcrack growth and the duration of the creep process is derived numerically. The relationship agrees well with the character of typical experimental creep curves, and includes three stages of creep. Then the damage constitutive equations and damage evolution equations, which describe the dilatant behaviour of rocks, are presented. Because the dilatant estimated value is taken as the damage variable, the relationship between the microscopic model and the macroscopic constitutive equations is established. In this way the mechanical behaviour of rocks can be predicted. [source]

Physical and mechanical characterization and the influence of cyclic loading on the behaviour of nickel-titanium wires employed in the manufacture of rotary endodontic instruments

INTERNATIONAL ENDODONTIC JOURNAL, Issue 11 2005
M. G. A. Bahia
Abstract Aim, To analyse the influence of cyclic loading on the mechanical behaviour of nickel-titanium (NiTi) wires employed in the manufacture of ProFile rotary endodontic instruments. Methodology, Nickel-titanium wires, 1.2 mm in diameter, taken from the production line of ProFile rotary endodontic instruments before the final machining step, were tensile-tested to rupture in the as-received condition and after 100 load,unload cycles in the superelastic plateau (4% elongation). The wires were characterized by X-ray energy-dispersive spectroscopy, X-ray diffraction and by differential scanning calorimetry and compared with new size 30, .06 taper ProFile instruments. The fracture surfaces of the wires were observed by scanning electron microscopy. Results, The mechanical properties of the as-received wires, their chemical composition, the phases present and their transformation temperatures were consistent with their final application. Only small changes, which decreased after the first few cycles, took place in the mechanical properties of the cycled wires. The stress at maximum load and the plastic strain at breakage remained the same, while the critical stress for inducing the superelastic behaviour, which is related to the restoring force of the endodontic instruments, decreased by approximately 27%. Conclusions, The mechanical behaviour of the NiTi wires was modified slightly by cyclic tensile loading in the superelastic plateau. As the changes tended towards stabilization, the clinical use of rotary NiTi ProFile instruments does not compromise their superelastic properties until they fracture by fatigue or torsional overload, or are otherwise discarded. [source]

An enhanced constitutive model for crushable granular materials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2010
Ali Daouadji
Abstract Studies in the past have tried to reproduce the mechanical behaviour of granular materials by proposing constitutive relations based on a common assumption that model parameters and parameters describing the properties, including gradation of individual grains are inevitably linked. However successful these models have proved to be, they cannot account for the changes in granular assembly behaviour if the grains start to break during mechanical loading. This paper proposes to analyse the relation between grading change and the mechanical behaviour of granular assembly. A way to model the influence of grain breakage is to use a critical state-based model. The influence of the amount of grain breakage during loading, depending on the individual grain strength and size distribution, can be introduced into constitutive relations by means of a new parameter that controls the evolution of critical state with changes in grain size distribution. Experimental data from a calcareous sand, a quartz sand, and a rockfill material were compared with numerical results and good-quality simulations were obtained. The main consequences of grain breakage are increased compressibility and a gradual dilatancy disappearance in the granular material. The critical state concept is also enriched by considering its overall relation to the evolution of the granular material. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Experimental study and constitutive modelling of elasto-plastic damage in heat-treated mortar

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2010
Xiao-Ting Chen
Abstract This study investigates the effect of a heat-treatment upon the thermo-mechanical behaviour of a model cement-based material, i.e. a normalized mortar, with a (w/c) ratio of 0.5. First, a whole set of varied experimental results is provided, in order to either identify or validate a thermo-mechanical constitutive model, presented in the second paper part. Experimental responses of both hydraulic and mechanical behaviour are given after different heating/cooling cycling levels (105, 200, 300, 400,C). The reference state, used for comparison purposes, is taken after mass stabilization at 60,C. Typical uniaxial compression tests are provided, and original triaxial deviatoric compressive test responses are also given. Hydraulic behaviour is identified simultaneously to triaxial deviatoric compressive loading through gas permeability Kgas assessment. Kgas is well correlated with volumetric strain evolution: gas permeability increases hugely when ,v testifies of a dilatant material behaviour, instead of contractile from the test start. Finally, the thermo-mechanical model, based on a thermodynamics approach, is identified using the experimental results on uniaxial and triaxial deviatoric compression. It is also positively validated at residual state for triaxial deviatoric compression, but also by using a different stress path in lateral extension, which is at the origin of noticeable plasticity. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A numerical method for the study of shear band propagation in soft rocks

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2009
Marta Castelli
Abstract This paper investigates the possibility of interpreting progressive shear failure in hard soils and soft rocks as the result of shear propagation of a pre-existing natural defect. This is done through the application of the principles of fracture mechanics, a slip-weakening model (SWM) being used to simulate the non-linear zone at the tips of the discontinuity. A numerical implementation of the SWM in a computation method based on the boundary element technique of the displacement discontinuity method (DDM) is presented. The crack and the non-linear zone at the advancing tip are represented through a set of elements, where the displacement discontinuity (DD) in the tangential direction is determined on the basis of a friction law. A residual friction angle is assumed on the crack elements. Shear resistance decreases on elements in the non-linear zone from a peak value at the tip, which is characteristic of intact material, to the residual value. The simulation of a uniaxial compressive test in plane strain conditions is carried out to exemplify the numerical methodology. The results emphasize the role played by the critical DD on the mechanical behaviour of the specimen. A validation of the model is shown through the back analysis of some experimental observations. The results of this back analysis show that a non-linear fracture mechanics approach seems very promising to simulate experimental results, in particular with regards to the shear band evolution pattern. Copyright © 2009 John Wiley & Sons, Ltd. [source]

On the capillary stress tensor in wet granular materials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2009
L. Scholtès
Abstract This paper presents a micromechanical study of unsaturated granular media in the pendular regime, based on numerical experiments using the discrete element method, compared with a microstructural elastoplastic model. Water effects are taken into account by adding capillary menisci at contacts and their consequences in terms of force and water volume are studied. Simulations of triaxial compression tests are used to investigate both macro and micro-effects of a partial saturation. The results provided by the two methods appear to be in good agreement, reproducing the major trends of a partially saturated granular assembly, such as the increase in the shear strength and the hardening with suction. Moreover, a capillary stress tensor is exhibited from capillary forces by using homogenization techniques. Both macroscopic and microscopic considerations emphasize an induced anisotropy of the capillary stress tensor in relation with the pore fluid distribution inside the material. Insofar as the tensorial nature of this fluid fabric implies shear effects on the solid phase associated with suction, a comparison has been made with the standard equivalent pore pressure assumption. It is shown that water effects induce microstructural phenomena that cannot be considered at the macro level, particularly when dealing with material history. Thus, the study points out that unsaturated soil stress definitions should include, besides the macroscopic stresses such as the total stress, the microscopic interparticle stresses such as the ones resulting from capillary forces, in order to interpret more precisely the implications of the pore fluid on the mechanical behaviour of granular materials. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A hypoplastic model for mechanical response of unsaturated soils

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2008
David Ma
Abstract A new constitutive model is developed for the mechanical behaviour of unsaturated soils based on the theory of hypoplasticity and the effective stress principle. The governing constitutive relations are presented and their application is demonstrated using several experimental data from the literature. Attention is given to the stiffening effect of suction on the mechanical response of unsaturated soils and the phenomenon of wetting-induced collapse. All model parameters have direct physical interpretation, procedures for their quantification from test data are highlighted. Quantitative predictions of the model are presented for wetting, drying and constant suction tests. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Numerical modelling of regional faults in land subsidence prediction above gas/oil reservoirs

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2008
Massimiliano Ferronato
Abstract The stress variation induced by gas/oil production may activate pre-existing regional faults. This may enhance the expected land subsidence due to the generation of mechanically weak points close to the producing field. A class of elasto-plastic interface elements (IE), specifically designed to address the mechanical behaviour of faults over a regional scale, is integrated into a finite element (FE) geomechanical model and used to investigate the role exerted by active faults in anthropogenic land subsidence. The importance of regional faults depends on a variety of factors including depth of the depleted reservoir, fault number, orientation and size, geomechanical properties of porous medium, pore pressure drawdown induced by fluid production, etc. With the aid of some representative examples, a useful indication is provided as to where and how fault activation may influence both magnitude and extent of the land subsidence bowl above producing gas/oil reservoirs, pointing to a generally limited impact on the ground surface. The simulation of a real faulted gas reservoir in a complex 3-D setting shows that the proposed IE can be simply and efficiently incorporated into a FE geomechanical model, thus improving the quality of the stress and displacement prediction. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Multiscale approach to geo-composite cellular structures subjected to rock impacts

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2007
François Nicot
Abstract Geo-composite cellular structures are an efficient technological solution for various applications in civil engineering. This type of structure is particularly well adapted to resisting rockfalls and can act as a defensive structure. However, the design of such structures is for the most part empirically based; this lack of research-based design stagnates optimization and advanced development. In this paper, the mechanical behaviour of a geo-composite cellular structure is investigated using a multi-scale approach, from the individual cell made up of an assembly of rocky particles contained in a wire netting cage to the entire structure composed of a regular array of cells. Based on discrete modelling of both the cell and structure scales, a computational tool has been developed for design purposes. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A density-dependent elastoplastic hydro-mechanical model for unsaturated compacted soils

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2007
D. A. Sun
Abstract This paper presents a three-dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled-suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water-retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water-retention behaviour is studied using data obtained from controlled-suction wetting,drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress,strain-strength behaviour and the effect of void ratio on the water-retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three-dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka,Nakai criterion. Model predictions of the stress,strain and water-retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd. [source]

On double shearing in frictional materials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2007
J. A. M. Teunissen
Abstract This paper evaluates the mechanical behaviour of yielding frictional geomaterials. The general Double Shearing model describes this behaviour. Non-coaxiality of stress and plastic strain increments for plane strain conditions forms an important part of this model. The model is based on a micro-mechanical and macro-mechanical formulation. The stress,dilatancy theory in the model combines the mechanical behaviour on both scales. It is shown that the general Double Shearing formulation comprises other Double Shearing models. These models differ in the relation between the mobilized friction and dilatancy and in non-coaxiality. In order to describe reversible and irreversible deformations the general Double Shearing model is extended with elasticity. The failure of soil masses is controlled by shear mechanisms. These shear mechanisms are determined by the conditions along the shear band. The shear stress ratio of a shear band depends on the orientation of the stress in the shear band. There is a difference between the peak strength and the residual strength in the shear band. While peak stress depends on strength properties only, the residual strength depends upon the yield conditions and the plastic deformation mechanisms and is generally considerably lower than the maximum strength. It is shown that non-coaxial models give non-unique solutions for the shear stress ratio on the shear band. The Double Shearing model is applied to various failure problems of soils such as the direct simple shear test, the biaxial test, infinite slopes, interfaces and for the calculation of the undrained shear strength. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Influence of liquid bridges on the mechanical behaviour of polydisperse granular materials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2006
F. Soulié
Abstract We investigate a polydisperse granular material in which the particle interactions are governed by a capillary force law. The cohesion force for a grain-pair with unequal diameters is expressed as an explicit function of the inter-particle distance and the volume of the liquid bridge. This analytical relation is validated by experiments on a reference material. Then, it is completed by a rupture criterion and cast in the form of a force law that accounts for solid contact, capillary force and rupture characteristics of a grain-pair. Finally, in order to evaluate the influence of capillary cohesion on the macroscopic behaviour, radial and axial compression tests on cylindrical assemblies of wet particles are simulated using a 3D distinct element method. Copyright © 2005 John Wiley & Sons, Ltd. [source]

On incremental non-linearity in granular media: phenomenological and multi-scale views (Part I)

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2005
Félix Darve
Abstract On the basis of fundamental constitutive laws such as elasticity, perfect plasticity, and pure viscosity, many elasto-viscoplastic constitutive relations have been developed since the 1970s through phenomenological approaches. In addition, a few more recent micro-mechanical models based on multi-scale approaches are now able to describe the main macroscopic features of the mechanical behaviour of granular media. The purpose of this paper is to compare a phenomenological constitutive relation and a micro-mechanical model with respect to a basic issue regularly raised about granular assemblies: the incrementally non-linear character of their behaviour. It is shown that both phenomenological and micro-mechanical models exhibit an incremental non-linearity. In addition, the multi-scale approach reveals that the macroscopic incremental non-linearity could stem from the change in the regime of local contacts between particles (from plastic regime to elastic regime) in terms of the incremental macroscopic loading direction. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Effect of suction on the mechanical behaviour of iron ore rock

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2005
Dragan Grgic
Abstract The effect of suction on the behaviour of iron ore has been studied from both physical and mechanical points of view. The porosity and the suction phenomena have been analysed using different experimental techniques. Uniaxial compressive tests on partially saturated samples have shown that the suction is responsible for strength and cohesion improvement. Considering the theory of partially saturated porous soils of Coussy and Dangla (Mécanique des sols non saturés (2002 edn). Hermès Science: 2002; 390), we have proposed a constitutive law for partially saturated iron ore. The real increase in the apparent cohesion due to the capillary attraction forces is overestimated if the yield function is written in terms of effective stresses. The effect of the capillary cohesion has been modelled with a function in the expression of the apparent cohesion of the yield function. The effect of suction on the mechanical behaviour has been represented in the effective stresses space and in the total stresses space like the Alonso model (Géotechnique 1990; 40:405,430). Copyright © 2005 John Wiley & Sons, Ltd. [source]