Sample records for behavioural mechanisms underlying

  1. Neural mechanisms underlying the evolvability of behaviour

    Katz, Paul S.


    The complexity of nervous systems alters the evolvability of behaviour. Complex nervous systems are phylogenetically constrained; nevertheless particular species-specific behaviours have repeatedly evolved, suggesting a predisposition towards those behaviours. Independently evolved behaviours in animals that share a common neural architecture are generally produced by homologous neural structures, homologous neural pathways and even in the case of some invertebrates, homologous identified neu...

  2. Coping styles and behavioural flexibility: towards underlying mechanisms

    Coppens, Caroline M.; de Boer, Sietse F.; Koolhaas, Jaap M.


    A coping style (also termed behavioural syndrome or personality) is defined as a correlated set of individual behavioural and physiological characteristics that is consistent over time and across situations. This relatively stable trait is a fundamental and adaptively significant phenomenon in the biology of a broad range of species, i.e. it confers differential fitness consequences under divergent environmental conditions. Behavioural flexibility appears to be an important underlying attribu...

  3. Believing versus interacting: Behavioural and neural mechanisms underlying interpersonal coordination

    Konvalinka, Ivana; Bauer, Markus; Kilner, James;

    in joint action has investigated only one of these mechanisms at a time – low-level processes underlying joint coordination, or high-level cognitive mechanisms that give insight into how people think about another. In real interactions, interplay between these two mechanisms modulates how we interact...... into neural mechanisms underlying belief of interacting with another person as well as engaging in interaction with the responsive other....

  4. Mechanical behaviour of an austenitic stainless steel under repeated impacts

    Cyclic indentation tests realised with an energy controlled spherical indenter allow a characterisation of the material behaviour under dynamic solicitations. This solicitation is, for example, able to show erosion and matting phenomenon. This test has been performed on AISI 316 stainless steels samples. Results have shown an increase of the hardness and the depth of the affected area versus the cycles number. With a micrographic optical analysis, we have detected a work hardening effect below the contact area. (authors)

  5. Behaviour of bcc technical superconductors under dynamic mechanical stress

    The behavior of bcc technical superconductors NbTi, NbZr and Nb under dynamic mechanical stress was investigated using two measuring techniques. In shot-sample training experiments the load was measured at which, in wire samples with a transport current applied, normal transitions occured in succesive straining cycles. Complementary, the acoustic emission from superconductors was monitored during strain at 4.2 K. A mechanism based on the formation of a stress induced shear transformation was proposed to account for the training behavior. This partially reversible shearing of the lattice is not sufficient to furnish the required energy for transition in the normal state but it may be detected by means of acoustic emission. On the other hand, a time correlation between acoustic emission and normal transition was found although training behavior and emission responded differently to the same metallurgical treatment. The experiments strongly indicate that the mechanism directly responsible for local energy release is microyielding, induced by the shear transformation. The stress relaxation which accompanies this transformation results in an increased load on the rest of the sample cross-section. Consequently microyielding caused by the transformation could occur in that region of the sample without being detected on the stress-strain curve. This would result in a sufficient release of energy to increase the sample temperature above its critical value. (orig./HP)

  6. Prolonged secretion of cortisol as a possible mechanism underlying stress and depressive behaviour.

    Qin, Dong-Dong; Rizak, Joshua; Feng, Xiao-Li; Yang, Shang-Chuan; Lü, Long-Bao; Pan, Lei; Yin, Yong; Hu, Xin-Tian


    Stress is associated with the onset of depressive episodes, and cortisol hypersecretion is considered a biological risk factor of depression. However, the possible mechanisms underlying stress, cortisol and depressive behaviours are inconsistent in the literature. This study examined the interrelationships among stress, cortisol and observed depressive behaviours in female rhesus macaques for the first time and explored the possible mechanism underlying stress and depressive behaviour. Female monkeys were video-recorded, and the frequencies of life events and the duration of huddling were analysed to measure stress and depressive behaviour. Hair samples were used to measure chronic cortisol levels, and the interactions between stress and cortisol in the development of depressive behaviour were further evaluated. Significant correlations were found between stress and depressive behaviour measures and between cortisol levels and depressive behaviour. Stress was positively correlated with cortisol levels, and these two factors interacted with each other to predict the monkeys' depressive behaviours. This finding extends the current understanding of stress/cortisol interactions in depression, especially pertaining to females. PMID:27443987

  7. Investigating the time-dependent behaviour of Boom clay under thermo-mechanical loading

    Cui, Yu-Jun; Tang, Anh-Minh; Delage, Pierre; Li, Xiang-Ling; 10.1680/geot.2009.59.4.319


    Among the various laboratory studies to investigate the Thermo-Hydro-Mechanical (THM) behaviour of Boom clay, relatively few were devoted to the time dependent behaviour, limiting any relevant analysis of the long-term behaviour of the disposal facility. The present work aims at investigating the time-dependent behaviour of Boom clay under both thermal and mechanical loading. High-pressure triaxial tests at controlled temperatures were carried out for this purpose. The tests started with constant-rate thermal and/or mechanical consolidation and ended with isobar heating and/or isothermal compression at a constant stress rate or by step loading. Significant effects of temperature as well as of compression and heating rates were observed on the volume change behaviour. After being loaded to a stress lower than the pre-consolidation pressure (5 MPa) at a low temperature of 25\\degree C and at a rate lower than 0.2 kPa/min, the sample volume changes seemed to be quite small, suggesting a full dissipation of pore w...

  8. Mechanical behaviour of the T91 martensitic steel under monotonic and cyclic loadings in liquid metals

    The paper deals with the mechanical properties in liquid metals of the T91 martensitic steel, a candidate material for the window of an accelerating driven system (ADS). Two main questions are examined, the risk of liquid metal embrittlement and the accelerated fatigue damage by a liquid metal. It is found that the transition from ductile to brittle behaviour induced by a liquid metal is possible as a result of a decrease in surface energy caused by the adsorbed liquid metal. The embrittlement can occur only with a hard microstructure and a nucleation of very sharp defects inside the liquid metal. Under cycling straining, the fatigue resistance of the standard T91 steel is decreased by a factor of about 2 in the liquid metal as compared to air. It is proposed that short crack growth is promoted by the liquid metal which weakens the microstructural grain boundary barriers and skip the microcrack coalescence stage

  9. Thermo-mechanical behaviour of coolant channels for heavy water reactors under accident conditions

    The objective of nuclear safety research programme is to develop and verify computer models to accurately predict the behavior of reactor structural components under operating and off normal conditions. Indian Pressurised Heavy Water Reactors (PHWRs) are tube type of reactors. The coolant channel assemblies, being one of the most important components, need detailed analysis under all operating conditions as well as during postulated conditions of accidents for its thermo-mechanical behaviour. One of the postulated accident scenarios for heavy water moderated pressure tube type of reactors i.e. PHWRs is Loss Of Coolant Accident (LOCA) coincident with Loss Of Emergency Core Cooling System (LOECCS). In this case, even though the reactor is tripped, the decay heat may not be removed adequately due to low or no flow condition and inventory depletion of primary side. Since the emergency core cooling system is presumed to be not available, the cooling of the fuel pins and the coolant channel assembly depends on the moderator cooling system, which is assumed to be available. Moderator cooling system is a separate system in PHWRs. In PHWRs, the fuel assembly is surrounded by pressure tube, an annulus insulating environment and a concentric calandria tube. In this postulated accident scenario, a structural integrity evaluation has been carried out to assess the modes of deformation of pressure tube-calandria tube assembly in a tube type nuclear reactor. The loading of pressure and temperature causes the pressure tube to sag/balloon and come in contact with the outer cooler calandria tube. The resulting heat transfer could cool and thus control the deformation of the pressure tube thus introducing inter-dependency between thermal and mechanical contact behaviour. The amount of heat thus expelled significantly depends on the thermal contact conductance and the nature of contact between the two tubes. Deformation of pressure tube creates a heat removal path to the relatively

  10. Microstructures of UO2 with controlled properties: understanding of elaboration mechanisms and of the mechanical behaviour under temperature

    The objective of this research work is to develop new UO2 fuel materials, without additive but with microstructure characteristics and mechanical properties controlled at high temperatures. More precisely, it aims at correlating initial powders and their implementation conditions with the microstructures obtained after sintering, and at correlating microstructure characteristics of sintered pellets with their mechanical behaviour at high temperatures. The author described the pellet fabrication process and mentions effects of some powder geometrical characteristics and sintering conditions on granular growth and densification. He gives an overview of knowledge on mechanisms of viscoplastic strain of UO2, on the effect of material parameters and of solicitation conditions on the mechanical behaviour of UO2. He describes and discusses an experimental investigation of industrial UO2 powder sintering which aimed at identifying parameters which influence the final microstructure densification and formation. He reports the development of a 'model' UO2 powder fabrication process with which powder characteristics are better controlled than in the case of industrial powders. These 'model' powders are used to more precisely investigate the effects of powder parameters (quantity of fine particles, specific area and morphology) on densification and grain size after sintering

  11. On the mechanical behaviour of a butt jointed thermoplastic composite under bending

    Baran, I.; Warnet, L.; Akkerman, R.; Thomsen, O.T


    In the present work, the mechanical behavior of a recently developed novel butt jointed thermoplastic composite was investigated under bending conditions. The laminated skin and the web were made of carbon fiber (AS4) and polyetherketoneketone (PEKK). The butt joint (filler) was injection molded fro

  12. CISM course on mechanical behaviour of soils under environmentally induced cyclic loads

    Wood, David; Mechanical Behaviour of Soils Under Environmentally Induced Cyclic Loads


    The book gives a comprehensive description of the mechanical response of soils (granular and cohesive materials) under cyclic loading. It provides the geotechnical engineer with the theoretical and analytical tools necessary for the evaluation of settlements developng with time under cyclic, einvironmentally idncued loads (such as wave motion, wind actions, water table level variation) and their consequences for the serviceability and durability of structures such as the shallow or deep foundations used in offshore engineering, caisson beakwaters, ballast and airport pavements and also to interpret monitoring data, obtained from both natural and artificial slopes and earth embankments, for the purposes of risk assessment and mitigation.

  13. Hydro-mechanical behaviour of two reference Belgian clay formations under non-isothermal conditions

    Document available in extended abstract form only. Two deep clay formations are being investigated in Belgium in connection with the design of a repository for 'High-Level Radioactive Waste': Boom clay BC at Mol (located between 160 and 270 m depths), considered the reference host formation, and Ypresian clay YC at Kallo (located between 300 and 450 m depths) as an alternative one. A comprehensive experimental programme has been carried out on these materials to explore water permeability at different temperatures and sample orientations, as well as to analyse volume change behaviour on loading/unloading at different temperatures and sample orientations (including pre and post-yield compressibility, yield properties and volume changes on drained thermal loading). Table 1 summarises some properties of BC and YC. Figure 1 presents the pore size distribution PSD curves of both clays obtained by mercury intrusion porosimetry. They display contrasting features (bi-modal pore network in YP with larger dominant pore sizes). Larger water permeability values are expected on YC as indicated in Table 1 and Figure 2, not only as a consequence of its higher void ratio but also due to these double porosity features. Water retention properties, of particular concern on sample retrieval from large depths, are also affected due to desaturation processes that are associated with the double porosity network of YP and its effects on air-entry value (a lower initial suction is measured on YP, despite being retrieved from larger depths). Figure 2 shows vertical and horizontal water permeability results under constant volume conditions and different temperatures. BC and YC display small anisotropy at sample scale - permeability is slightly larger on horizontal direction-. With regard to temperature effects, the figure shows that water permeability dependency on temperature in YC is slightly higher than the water viscosity prediction for both orientations. Instead BC displayed a thermal

  14. Mechanical Behaviour under Tensile Loading of Textile Reinforced Concrete with Short Fibres

    Barhum, Rabea; Mechtcherine, Viktor


    This treatise addresses the influence of the addition of short dispersed and integral fibres made of alkali-resistant glass on the fracture behaviour of textile-reinforced concrete (TRC). A series of uniaxial, deformation-controlled tension tests was performed to study the strength-, deformation-, and fracturebehaviour of thin, narrow plates made of TRC both with and without the addition of short fibres. Furthermore, uniaxial tension tests on specimens reinforced with only short fibres and si...

  15. Characterization of the deformation mechanisms and modelling of the mechanical behaviour under multi-axial loadings of SiC/SiC composite tubes

    SiC/SiC composites are candidate materials for in-core components of future nuclear reactors. The analysis of these structures using numerical simulations requires material constitutive laws. The present work focuses on understanding the deformation mechanisms of these materials in order to build a constitutive model able to predict their stress-strain response under complex loadings. An extensive characterization of the mechanical behaviour of SiC/SiC multi-layered tubes - similar to fuel cladding concepts - was carried out, using tension internal pressure, tension-torsion and bending tests, that allowed to build an important experimental basis for the understanding of the mechanisms and the identification of constitutive laws. In-situ and post-failure observations have allowed quantifying the orientation of surface matrix cracks as a function of the loading type. Full-field measurements using Digital Image Correlation at the tow scale brought precise information on the composite surface kinematics, such as the crack opening or the deformation of the matrix fragments. These measurements also evidence the importance of the tow reorientation, that could explain specific features of the macroscopic behaviour because of its coupling with matrix cracking. Finally, these experimental data allowed to build a constitutive model, identified on only four uniaxial tests, able to predict satisfactorily the macroscopic behaviour under several biaxial loadings. The correct prediction of local quantities, such as the characteristics of the matrix cracking in tension, has also been verified. (author)

  16. Fatigue behaviour of coke drum materials under thermal-mechanical cyclic loading

    Jie Chen


    Full Text Available Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. There were some studies on the fatigue life estimation for the coke drums, but most of them were based on strain-fatigue life curves at constant temperatures, which do not consider simultaneous cyclic temperature and mechanical loading conditions. In this study, a fatigue testing system is successfully developed to allow performing thermal-mechanical fatigue (TMF test similar to the coke drum loading condition. Two commonly used base and one clad materials of coke drums are then experimentally investigated. In addition, a comparative study between isothermal and TMF lives of these materials is conducted. The experimental findings lead to better understanding of the damage mechanisms occurring in coke drums and more accurate prediction of fatigue life of coke drum materials.

  17. The behaviour of quantum mechanical systems under continuous measurement: Watchdog effect and master equation

    In this thesis the influence of continuously repeting measurement by the environment on a quantum mechanical system is studied. The interaction with the environment which is in principle present for each physical object can have an important influence on the considered system as the ''watchdog'' effect has clearly demonstrated. These situations are however quite special. Of much more importance is the effect of the environment on macroscopical objects for which only regarding this interaction a derivation of master equations can be founded. (HSI)

  18. High-temperature behaviour of IN 738 LC under isothermal and thermo-mechanical cyclic loading

    Frenz, H. [Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin (Germany); Meersmann, J. [Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin (Germany); Ziebs, J. [Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin (Germany); Kuehn, H.-J. [Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin (Germany); Sievert, R. [Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin (Germany); Olschewski, J. [Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin (Germany)


    The temperature dependence of the cyclic behavior of IN 738 LC was studied. Cyclic iso- and non-isothermal tests were performed with proportional and non-proportional tension/torsion strain paths. It was shown that maximum and minimum stress values measured in isothermal strain controlled tests correspond quite well with results of non-isothermal tests. Thermal-mechanical constitutive equations based on the viscoplastic Chaboche model were used to describe the non-isothermal stress-strain behavior. (orig.)

  19. The impact of flavonoids on spatial memory in rodents: from behaviour to underlying hippocampal mechanisms

    Rendeiro, Catarina; Spencer, Jeremy P. E.; Vauzour, David; Butler, Laurie T.; Ellis, Judi A.; Williams, Claire M.


    Emerging evidence suggests that a group of dietary-derived phytochemicals known as flavonoids are able to induce improvements in memory, learning and cognition. Flavonoids have been shown to modulate critical neuronal signalling pathways involved in processes of memory, and therefore are likely to affect synaptic plasticity and long-term potentiation mechanisms, widely considered to provide a basis for memory. Animal dietary supplementation studies have further shown that flavonoid-rich foods...

  20. Mechanical behaviour of high level nuclear waste overpacks under repository loading and during welding

    One of the concepts for final disposal of high level nuclear waste in Switzerland consists of a mined repository approximately 1200 m deep in the crystalline bedrock of Northern Switzerland. In order to delay the return of the radionuclides to the biosphere, and to reduce their concentration there to acceptable levels, reliance is placed in the multiple safety barrier principle. In addition to the natural barriers the following engineered barriers are envisaged: the waste form itself (vitrified high level nuclear waste), an overpack, and a compacted bentonite backfill within which the overpack is placed horizontally in the axis of the repository gallery. The first part of the present work reports on the participation in the COMPAS project (COntainer Mechanical Performance ASsessment). This project was carried out within the framework of the European Atomic Energy Community's cost-sharing programme on 'Radioactive Waste Management and Disposal'. It was concerned with the mechanical performance of overpacks for vitrified high level nuclear waste. The second part of this work deals with the issue of stress corrosion cracking of the high level nuclear waste overpack from NAGRA which is made out of GS-40 cast steel. After a description of the material properties of GS-40 cast steel, the one-dimensional FIBRE model is discussed, which should give an insight into the parameters involved in a thermomechanical calculation of a welding process. The calculations were performed with the commercially available finite element code ADINA. The output from ADINA was used as input to the postprocessor ORVIRT when fracture calculations are considered. (author) figs., tabs., refs

  1. Mechanical behaviour of a friction stir spot welding lap under static loading

    Herbelot, C.; Hoang, T. Dang; Imad, A.; Benseddiq, N.


    Friction stir spot welding (FSSW) is a recent welding method which takes advantage of being performed in the solid state and presents many benefits such as a lower heat-input, a reduction of residual stresses and an elimination of the solidification defects for example. The present study investigates, for fixed process parameters and tool geometry, the fracture and damage of a single-lap friction stir spot welding joints formed from thin sheets of aluminum alloy 6082 T6. An experimental approach was carried out in order to analyze the sequence of damage mechanisms using acoustic emission (A.E.) and measurement of fields by digital image correlation (D.I.C.) techniques simultaneously. The A.E. technique allows the monitoring of the evolution of acoustic activities by taking into account energy of the events. The D.I.C. technique confirms the damage scenarios after the treatment of strain field at any point near the fastener and especially between the exit hole and the shoulder footprint. The coupling of those two techniques allows to identify characteristic points and a breakdown of the load displacement curve in phases.

  2. Influence of free water content on the compressive mechanical behaviour of cement mortar under high strain rate

    Jikai Zhou; Xudong Chen; Longqiang Wu; Xiaowei Kan


    The effect of free water content upon the compressive mechanical behaviour of cement mortar under high loading rate was studied. The uniaxial rapid compressive loading testing of a total of 30 specimens, nominally 37 mm in diameter and 18.5 mm in height, with five different saturations (0%, 25%, 50%, 75% and 100%, respectively) were executed in this paper. The technique ‘Split Hopkinson pressure bar’ (SHPB) was used. The impact velocity was 10 m/s with the corresponding strain rate as 102/s. Water-cement ratio of 0.5 was used. The compressive behaviour of the materials was measured in terms of the maximum stress, Young’s modulus, critical strain at maximum stress and ultimate strain at failure. The data obtained from test indicates that the similarity exists in the shape of strain–stress curves of cement mortars with different water content, the upward section of the stress–strain curve shows bilinear characteristics, while the descending stage (softening state) is almost linear. The dynamic compressive strength of cement mortar increased with the decreasing of water content, the dynamic compressive strength of the saturated specimens was 23% lower than that of the totally dry specimens. With an increase in water content, the Young’s modulus first increases and then decreases, the Young’s modulus of the saturated specimens was 23% lower than that of the totally dry specimens. No significant changes occurred in the critical and ultimate strain value as the water content is changed.

  3. A mechanical rheological model for the prediction of the creep behaviour of metallic materials under constant loading

    A mechanical rheological model for the prediction of the creep behaviour of metallic materials is presented. The model is based on the time dependence of the material structure during creep. It consists of a Hooke element with constant spring parameter and of a pseudo-Kelvin element with time dependent characteristic parameters for the spring and for the dashpot. The time dependence of the models characteristic parameters is correlated with the time dependence of the material structure parameters. For the time dependence of the model parameters exponential functions were used. Furthermore, these parameters are considered to be functions of stress and temperature. The derived constitutive equation of the proposed mechanical model related with the time dependence of the material structure describes the creep behaviour up to the tertiary creep stage. For the verification of the proposed model numerical results are discussed in connection with experimental results on oxygen free pure copper. The applicability of the model on technical materials has been demonstrated on the austenitic steel X 8 CrNiMoNb 16.16. (orig.)

  4. Multi-scale modeling of the thermo-hydro- mechanical behaviour of heterogeneous materials. Application to cement-based materials under severe loads

    The work of modeling presented here relates to the study of the thermo-hydro- mechanical behaviour of porous materials based on hydraulic binder such as concrete, High Performance Concrete or more generally cement-based materials. This work is based on the exploitation of the Digital Concrete model, of the finite element code Symphonie developed in the Scientific and Technical Centre for Building (CSTB), in coupling with the homogenization methods to obtain macroscopic behaviour laws drawn from the Micro-Macro relations. Scales of investigation, macroscopic and microscopic, has been exploited by simulation in order to allow the comprehension fine of the behaviour of cement-based materials according to thermal, hydrous and mechanical loads. It appears necessary to take into account various scales of modeling. In order to study the behaviour of the structure, we are brought to reduce the scale of investigation to study the material more particularly. The research tasks presented suggest a new approach for the identification of the multi-physic behaviour of materials by simulation. In complement of the purely experimental approach, based on observations on the sample with measurements of the apparent parameters on the macroscopic scale, this new approach allows to obtain the fine analysis of elementary mechanisms in acting within the material. These elementary mechanisms are at the origin of the evolution of the macroscopic parameters measured in experimental tests. In this work, coefficients of the thermo-hydro-mechanical behaviour law of porous materials and the equivalent hydraulic conductivity were obtained by a multi-scales approach. Applications has been carried out on the study of the damaged behaviour of cement-based materials, in the objective to determine the elasticity tensor and the permeability tensor of a High Performance Concrete at high temperatures under a mechanical load. Also, the study of the strain evolution of cement-based materials at low

  5. Fuel thermal/mechanical behaviour under loss of coolant accident conditions as predicted by the FACTAR code

    FACTAR (Fuel And Channel Temperature And Response) is a computer code developed to simulate the transient thennal and mechanical behaviour of 37-element or 28-element fuel bundles within a single CANDU fuel channel for moderate (ie., sheath temperatures less than the melting point of Zircaloy) loss-of-coolant accident (LOCA) conditions including transition and large break LOCAs with emergency coolant injection assumed available. FACTAR's predictions of fuel temperature and sheath failure times are used for subsequent assessment of fission product releases and fuel string expansion. In this paper, model capabilities and calculated quantities of the code are summarised. The results from overly severe test cases are presented in order to clearly demonstrate the effect on calculated fuel channel behaviour of a mechanistic assessment of fuel-to-sheath heat transfer, and the impact of using a diffusion-limited model for Zircaloy/steam reaction (i.e., FROM) as opposed to a reaction rate correlation, coupled with the assumption of unlimited steam supply. (author)

  6. An investigation on thermoelastic behaviour of functionally graded thick spherical vessels under combined thermal and mechanical loads

    D. Karimi


    Full Text Available Purpose: The subject of this paper is to study the thermoelastic behavior of thick functionally graded hollow sphere under thermal and mechanical loads. The mechanical and thermal properties of FG sphere are assumed to be functions of radial position.Design/methodology/approach: In present study, two methods are used to estimate the effective mechanical properties of FG sphere. One of the simplest methods in estimation of the effective mechanical and thermal properties of a mixture of two constituent materials is the Rule of Mixture (R-M scheme. Another scheme for estimating the mechanical properties is due to the work of Mori-Tanaka. When the mechanical properties of FG sphere are estimated by using the Mori-Tanaka scheme, thermal material properties of FG body may be determined utilizing the R-M or the other methods which will be discussed as follows.Findings: Results for the temperature, radial displacement, radial stress and hoop stress fields through the geometry of the sphere are give. The figures reveal that some minor difference may be obtained for two schemes and the difference between the results for displacement distribution is larger than difference of temperature and stress distributions.Practical implications: The thermal material properties are obtained utilizing the Hatta-Taya and Rosen-Hashin relations. Also, the mechanical properties are estimated using the Mori-Tanaka scheme. In addition to the methods of approximation of material properties cited above, the rule of mixture scheme for determination of thermal and mechanical properties is also considered and results of these two schemes are compared for two cases of material composition through the geometry of FG sphere. The FG sphere is assumed to be symmetrically loaded and one-dimensional steady-state analysis of isotropic linear thermoelastic FG sphere under combined thermal and mechanical loads is investigated. Solution of the heat conduction equation and the Navier

  7. Complex associative memory processing and sleep: a systematic review and meta-analysis of behavioural evidence and underlying EEG mechanisms.

    Chatburn, Alex; Lushington, Kurt; Kohler, Mark J


    The beneficial influence of sleep on memory consolidation is well established; however, the mechanisms by which sleep can dynamically consolidate new memories into existing networks for the continued environmental adaptation of the individual are unclear. The role of sleep in complex associative memory is an emerging field and the literature has not yet been systematically reviewed. Here, we systematically review the published literature on the role of sleep in complex associative memory processing to determine (i) if there is reasonable published evidence to support an active role for sleep facilitating complex associative processes such rule and gist extraction and false memory; (ii) to determine which sleep physiological events and states impact these processes, and to quantify the strength of these relationships through meta-analysis. Twenty-seven studies in healthy adults were identified which combined indicate a moderate effect of sleep in facilitating associative memory as tested behaviourally. Studies which have measured sleep physiology have reported mixed findings. Significant associations between sleep electrophysiology and outcome appear to be based largely on mode of acquisition. We interpret these findings as supporting reactivation based models of associative processing. PMID:25452112

  8. CANDU fuel behaviour under transient conditions

    The Canadian R and D program to understand CANDU fuel behaviour under transient conditions is described. Fuel sheath behaviour studies have led to the development of a model of transient plastic strain in inert gas, which integrates the deformation due to several mechanisms. Verification tests demonstrated that on average the model overpredicts strain by 20%. From oxidation kinetics studies a sheath failure embrittlement criterion based on oxygen distribution has been developed. We have also established a rate equation for high-temperature stress-dependent crack formation due to embrittlement of the sheath by beryllium. An electric, simulated fuel element is being used in laboratory tests to characterize the behaviour of fuel in the horizontal. In-reactor, post-dryout tests have been done for several years. There is an axially-segmented, axisymmetric fuel element model in place and a fully two-dimensional code is under development. Laboratory testing of bundles, in its early stages, deals with the effects of geometric distortion and sheath-to-sheath interaction. In-reactor, post-dryout tests of CANDU fuel bundles with extensive central UO2 melting did not result in fuel fragmentation nor damage to the pressure tube. (author)

  9. Strategic Behaviour under Regulation Benchmarking

    Jamasb, Tooraj; Nillesen, Paul; Michael G. Pollitt


    Liberalisation of generation and supply activities in the electricity sectors is often followed by regulatory reform of distribution networks. In order to improve the efficiency of distribution utilities, some regulators have adopted incentive regulation schemes that rely on performance benchmarking. Although regulation benchmarking can influence the ?regulation game?, the subject has received limited attention. This paper discusses how strategic behaviour can result in inefficient behav...

  10. Intermetallic alloys: Deformation, mechanical and fracture behaviour

    The state of the art in intermetallic alloys development with particular emphasis on deformation, mechanical and fracture behaviour is documented. This review paper is prepared to lay the ground stones for a future work on mechanical property characterization and fracture behaviour of intermetallic alloys at GKSS. (orig.)

  11. The mechanical behaviour of packed particulates

    Within the Canadian Nuclear Fuel Waste Management program, the central concept is to package used fuel in containers that would be deposited in an underground vault in a plutonic rock formation. To provide internal mechanical support for the container, the reference design specifies it to be filled with a matrix of compacted particulate material (called 'packed particulate'), such as quartz sand granules. The focus of this report is on the mechanical properties of the packed-particulate material, based on information drawn from the extant literature. We first consider the packing density of particulate matrices to minimize the remnant porosity and maximize mechanical stability under conditions of external pressure. Practical methods, involving vibratory packing, are reviewed and recommendations made to select techniques to achieve optimum packing density. The behaviour of particulates under compressive loading has been of interest to the powder metallurgy industry (i.e., the manufacture of products from pressed/sintered metal and ceramic powders) since the early decades of this century. We review the evidence showing that in short timescales, stress induced compaction occurs by particle shuffling and rearrangement, elastic distortion, plastic yielding and microfracturing. Analytical expressions are available to describe these processes in a semiquantitative fashion. Time-dependent compaction, mainly via creep mechanisms, is more complex. Much of the theoretical and experimental information is confined to higher temperatures (> 500 degrees C), where deformation rates are more rapid. Thus, for the relatively low ambient temperatures of the waste container (∼100 degrees C), we require analytical techniques to extrapolate the collective particulate creep behaviour. This is largely accomplished by employing current theories of creep deformation, particularly in the form of Deformation Mechanism Maps, which allow estimation of creep rates over a wide range of stress

  12. Thermo-mechanical fatigue behaviour of the near-{gamma}-titanium aluminide alloy TNB-V5 under uniaxial and multiaxial loading

    Brookes, Stephen Peter


    With increasing environmental awareness and the general need to economise on the use of fossil fuels, there is growing pressure for industry to produce lighter, more efficient, gas turbine engines. One such material that will help to achieve these improvements is the intermetallic gamma titanium aluminide ({gamma}-TiAl) alloy. At only half the density of current nickel-based superalloys its weight saving capability is highly desirable, however, its mechanical properties have not yet been fully explored especially, when it is to be considered for structural components in aeronautical gas turbine engines. Critical components in these engines typically experience large variations in temperatures and multiaxial states of stress under non-isothermal conditions. These stress states are known as tri-axial thermo-mechanical fatigue (TMF). The work presented here investigates the effects these multi-axial stresses, have on a {gamma}-TiAl, (Ti-45Al-5Nb-0.2B-0.2C) alloy under TMF conditions. The uniaxial, torsional and axialtorsional TMF behaviour of this {gamma}-TiAl alloy have been examined at 400 - 800 C with strain amplitudes ranging from 0.15% to 0.7%. The tests were conducted at both thermomechanical in-phase (IP) and out-of-phase (OP). Selected tests additionally contained a 180 seconds hold period. Fatigue lifetimes are strongly influenced by the strain amplitude, a small increase in amplitude reduces the lifetime considerably. The uniaxial IP tests showed significantly longer fatigue lifetimes than of all the tests performed. Torsional loading although have shorter fatigue lifetimes than the uniaxial IP loading they have longer fatigue lifetimes than the uniaxial OP loading. The non-proportional axial-torsional 90 degree OP test is most damaging which resulted in a shorter lifetime than the uniaxial OP test with the same Mises equivalent mechanical strain amplitude. A hold period at maximum temperatures reduced the lifetime for all tests regardless of the temperature

  13. Prospective and Pavlovian mechanisms in aversive behaviour.

    Rigoli, Francesco; Pezzulo, Giovanni; Dolan, Raymond J


    Studying aversive behaviour is critical for understanding negative emotions and associated psychopathologies. However a comprehensive picture of the mechanisms underlying aversion is lacking, with associative learning theories focusing on Pavlovian reactions and decision-making theoretic approaches on prospective functions. We propose a computational model of aversion that combines goal-directed and Pavlovian forms of control into a unifying framework in which their relative importance is regulated by factors such as threat distance and controllability. Using simulations, we test whether the model can reproduce available empirical findings and discuss its relevance to understanding factors underlying negative emotions such as fear and anxiety. Furthermore, the specific method used to construct the model permits a natural mapping from its components to brain structure and function. Our model provides a basis for a unifying account of aversion that can guide empirical and interventional study contexts. PMID:26539969

  14. Modelling of the mechanical behaviour of a material containing spherical cavities under pressure; example of the aging of a metal tritide

    The study aims at modeling the mechanical behaviour of a material containing spherical cavities under pressure (bubbles) of nano-metric size. This work deals with research on tritium storage in metals. In this way, metal tritides are obtained. During time, helium is generated by tritium decay. Helium appears as a gas, which forms bubbles in the metal tritide. These bubbles subsequently cause damage within the material. The purpose of this work was therefore the following: (i) to determine the overall elastic moduli as a function of the volume fraction of cavities. thus providing an information about material damage, (ii) to analyze the macroscopic inflation of the material in order to solve storage problems, (iii) to determine the local stress fields for predicting the evolutions of the bubbles and the matrix. With the help of the scale change methods (homogenization) the macroscopic mechanical properties of the material can be determined as a function of its morphology on a microscopic scale. Thus the damage of the material can be estimated by experimental measurements of the global elastic moduli. Homogenization also allows the elastic inflation to be evaluated as well as the effects of cavity clusters and local variations of the elastic moduli. The internal stresses are determined on the microscopic scale (cavity scale). Two analytical methods (Eshelby-Mura and Legendre polynomials) and one numerical approach (Abaqus) are used to obtain more information and a best description of the material. It is shown that bubbles should attain the same size and same pressure and the plastic strain zones are determined. (author)

  15. Mechanical behaviour of compacted decomposed granite soil

    Lee, I K


    The purpose of this research was to determine the mechanical behaviour of decomposed granite soil, especially when it is used as a construction material. The soil tested was a completely weathered granite soil (grade V) taken from Seoul, Korea and was a well graded silty sand and gravel. Triaxial compression tests have been carried out on compacted samples and special attention has been given to the determination of the effects of the moisture condition on the behaviour. The test results show...

  16. Preventing Toxic Behaviour through Game Mechanics

    Fahlström, Josefine; Matson, Emma


    Toxic Behaviour, the phenomena where a person behaves in a way meant to intimidate or belittle another person, is an influential issue spreading across the virtual spaces that is online gaming communities. In this thesis we explore the possible correlations between Toxic Behaviour and game mechanics in online multi-player games by analyzing League of Legends (Riot Games, 2009), one of the most prominent online games currently dominating the market (Statista, 2014). We have analysed the game u...

  17. Investigations on mechanical behaviour of dental composites.

    Ilie, Nicoleta; Hickel, Reinhard


    Since a direct comparison of composites efficacy in clinical studies is very difficult, our study aimed to analyse in laboratory tests under standardised and simulated clinical conditions a large variety of commercial composite materials belonging to eight different materials categories. Thus, 72 hybrid, nano-hybrid, micro-filled, packable, ormocer-based and flowable composites, compomers and flowable compomers were compared in terms of their mechanical behaviour. Flexural strength (FS), flexural modulus (FM), diametric tensile (DTS) and compressive strength (CS) were measured after the samples had been stored in water for 24 h at 37 degrees C. Results were statistically analysed using one-way ANOVA with Tukey HSD post hoc test (alpha = 0.05) as well as partial eta2 statistics. Large varieties between the tested materials within the same material category were found. The hybrid, nano-hybrid, packable and ormocer-based composites do not differ significantly among each other as a material type, reaching the highest FS values. Nano-hybrid composites are characterised by a good FS, the best DTS but a low FM. The lowest mechanical properties achieved the micro-filled hybrids. The flowable composites and compomers showed for all properties comparable result. Both flowable material categories do not differ significantly from the micro-filled composites for the most mechanical properties, showing only a higher DTS. The filler volume was shown to have the highest influence on the measured properties, inducing a maximum FS and FM at a level of 60%, whereas such dependence was not measured for DTS or CS. The influence of the type of material on the mechanical properties was significant but very low, showing the strongest influence on the CS. PMID:19242739

  18. Poromechanical behaviour of hardened cement paste under isotropic loading

    Ghabezloo, Siavash; Guédon, Sylvine; Martineau, Francçois; Saint-Marc, Jérémie


    The poromechanical behaviour of hardened cement paste under isotropic loading is studied on the basis of an experimental testing program of drained, undrained and unjacketed compression tests. The macroscopic behaviour of the material is described in the framework of the mechanics of porous media. The poroelastic parameters of the material are determined and the effect of stress and pore pressure on them is evaluated. Appropriate effective stress laws which control the evolution of total volume, pore volume, solid volume, porosity and drained bulk modulus are discussed. A phenomenon of degradation of elastic properties is observed in the test results. The microscopic observations showed that this degradation is caused by the microcracking of the material under isotropic loading. The good compatibility and the consistency of the obtained poromechanical parameters demonstrate that the behaviour of the hardened cement paste can be indeed described within the framework of the theory of porous media.

  19. Mechanical Behaviour of Materials Volume II Fracture Mechanics and Damage

    François, Dominique; Zaoui, André


    Designing new structural materials, extending lifetimes and guarding against fracture in service are among the preoccupations of engineers, and to deal with these they need to have command of the mechanics of material behaviour. This ought to reflect in the training of students. In this respect, the first volume of this work deals with elastic, elastoplastic, elastoviscoplastic and viscoelastic behaviours; this second volume continues with fracture mechanics and damage, and with contact mechanics, friction and wear. As in Volume I, the treatment links the active mechanisms on the microscopic scale and the laws of macroscopic behaviour. Chapter I is an introduction to the various damage phenomena. Chapter II gives the essential of fracture mechanics. Chapter III is devoted to brittle fracture, chapter IV to ductile fracture and chapter V to the brittle-ductile transition. Chapter VI is a survey of fatigue damage. Chapter VII is devoted to hydogen embrittlement and to environment assisted cracking, chapter VIII...

  20. Protective containment behaviour under exceeded design loads

    The contribution describes the calculation results of the behaviour of containment structure if loaded in excess of its design load. The Temelin NPP comprises two WWER 1000 blocks and containment consists of a pre-stressed reinforced concrete structure with a system of unbonded cables. The objective of the calculations was to determine the level of load caused by the internal pressure and temperature at which the containment protective function would fail. In the first step, the maximum overpressure was determined, which may be transferred by the containment structure. In further steps analyses were made of various combinations of simultaneous pressure and temperature loads. The contribution presents relevant calculation results, including the evaluation of containment structure behaviour including liner under loads that exceed its design parameters. (author)

  1. Impact of nutrition on canine behaviour: current status and possible mechanisms

    bosch, G; Beerda, B.; Hendriks, W.H.; Poel, van der, D.; M.W. A. Verstegen


    Each year, millions of dogs worldwide are abandoned by their owners, relinquished to animal shelters, and euthanised because of behaviour problems. Nutrition is rarely considered as one of the possible contributing factors of problem behaviour. This contribution presents an overview of current knowledge on the influence of nutrition on canine behaviour and explores the underlying mechanisms by which diet may affect behaviour in animals. Behaviour is regulated by neurotransmitters and hormones...

  2. Optimal stomatal behaviour under stochastic rainfall.

    Lu, Yaojie; Duursma, Remko A; Medlyn, Belinda E


    Vegetation CO2 uptake is always accompanied by water loss. The balance in this gas exchange is controlled by the stomata, through which CO2 and water vapour diffuse between the leaf and the atmosphere. The optimal stomatal behaviour theory proposes that vegetation should optimise its stomatal behaviour such that, for given water availability, photosynthesis is maximised. In this paper, we optimise stomatal conductance as a function of soil water content for the maximum expected value of photosynthesis rate. This optimisation process is considered under stochastic rainfall. The optimal solution is largely shaped by two constraints: the risks of soil water exhaustion and surface runoff, which results in an inverse S-shaped curve of stomatal conductance along the soil water gradient. We derive the optimal functional relationship between stomatal conductance and soil water content under varying rainfall frequency, mean annual precipitation and atmospheric CO2 concentration. Comparisons with large-scale observational data show that the model is able to broadly capture responses of photosynthesis, transpiration, and water use efficiency along rainfall gradients, although notable discrepancies suggest additional factors are important in shaping these responses. Our work provides a theoretical framework for analysing the vegetation gas exchange under environmental change. PMID:26796317

  3. FRP-to-concrete bond behaviour under high strain rates

    Li, Xiaoqin


    Fibre reinforced polymer (FRP) composites have been used for strengthening concrete structures since early 1990s. More recently, FRP has been used for retrofitting concrete structures for high energy events such as impact and blast. Debonding at the FRP-to-concrete interface is one of the predominant failure modes for both static and dynamic loading. Although extensive research has been conducted on the static bond behaviour, the bond-slip mechanics under high strain rates is n...

  4. Behaviour of concrete filled steel tubular columns under fire

    查晓雄; 钟善桐


    A three dimensional nonlinear FE program is used to calculate the fire resistances of concrete filledsteel tubular columns under fire. The temperature distributions in the circular section fire are decided by solvingthe Fourier Transfer Equation , and the mechanical behaviour and failure of concrete filled steel tubular columnsunder fire are thus investigated, and the effects of several parameters on the fire resistance are analysed. Theresults obtained are in good agreement with the Eurocode.

  5. Simulating farmer behaviour under water markets

    Padula, SIlvia; Erfani, Tohid; Henriques, Catarina; Maziotis, Alexandros; Garbe, Jennifer; Swinscoe, Thomas; Harou, Julien; Weatherhead, Keith; Beevers, Lindsay; Fleskens, Luuk


    Increasing water scarcity may lead water managers to consider alternative approaches to water allocation including water markets. One concern with markets is how will specific sectors interact with a potential water market, when will they gain or loose water and will they benefit economically - why, when and how? The behaviours of different individual abstractors or institutional actors under water markets is of interest to regulators who seek to design effective market policies which satisfy multiple stakeholder groups. In this study we consider two dozen agricultural water users in eastern England (Nar basin). Using partially synthetic but regionally representative cropping and irrigation data we simulate the buying and selling behaviour of farmers on a weekly basis over multiple years. The impact of on-farm water storage is assessed for farmers who own a reservoir. A river-basin-scale hydro-economic multi-agent model is used that represents individual abstractors and can simulate a spot market under various licensing regimes. Weekly varying economic demand curves for water are calibrated based on historical climate and water use data. The model represents the trade-off between current use value and expected gains from trade to reach weekly decisions. Early results are discussed and model limitations and possible extensions are presented.

  6. Effect of water on the mechanical behaviour of shales

    Wakim, J.; Hadj-Hassen, F.; Tijani, M. [Ecole des Mines de Paris - CGES, 77 - Fontainebleau (France); Noirel, J.F. [Charbonnage de France - DTN, 57 - Freyming Merlebach (France)


    This paper aims to presenting the results of a research conducted in order to study the effect of water on the mechanical behaviour of the Lorraine Basin Colliery shale. The work performed can be divided into four main parts. The first part is dedicated to classical tests and it includes geological and mineralogical analysis as well as mechanical laboratory tests. The second part is devoted to the phenomenon of shale swelling under water effect. New procedures and equipment of testing were set up in order to characterise this swelling behaviour and to determine its model parameters. The tests performed in this second part are allowed to develop a phenomenological model which describes the elasto-visco-plastic behaviour of shales before and after saturation. The last phase of the work is dedicated to implement the new model in the finite element code VIPLEF in order to apply in tunnel excavated in swelling anisotropic rocks. (authors)

  7. Mechanical behaviour of nanoparticles: Elasticity and plastic deformation mechanisms

    Celine Gerard; Laurent Pizzagalli


    Nano-objects often exhibit drastically different properties compared to their bulk counterpart, opening avenues for new applications in many fields, such as in advanced composite materials, nanomanufacturing, nanoelectromechanical systems etc. As such, related research topics have become increasingly prominent in recent years. In this review on the mechanical behaviour of nanoparticles, the main investigation approaches are first briefly presented. The main results in terms of elasticity and plastic deformation mechanisms are then reported and discussed.

  8. Analysis of operator's behaviour under accidental transients

    Since 1979, EDF has been conducting intensive test campaigns on full-scale PWR simulators in order to study and improve the operators behaviour under incident as well as accident conditions. This paper presents some results obtained during tests carried out in 1986 on the P4 (1300 MWe power plant series) simulators of the Paluel Training Center. These results essentially concern the observed deviations, the diagnosis and the safety engineer's role. They are compared with the results of previous tests on 900 MWe unit simulators. The test organization and methodology, the result analysis methods and the biases introduced by this kind of test are also discussed. (author). 7 refs, 1 fig., 6 figs

  9. Mechanical behaviour of jute cloth/wool felts hybrid laminates

    Highlights: • New fibre reinforced hybrid composites with wool and jute fibres were manufactured. • Effect of two different stacking sequences on mechanical behaviour was investigated. • The impact performances of wool/jute interply hybrid composites were studied. • Hybridization with jute significantly enhanced mechanical properties of wool composites. - Abstract: This experimental work is aimed at the characterization of new fibre reinforced composites based on epoxy resin with both protein (wool) and lignocellulosic (jute) natural fibres. Wool-based and hybrid (wool/jute) composites with two different stacking sequences (intercalated and sandwich) were developed. Their microstructure has been investigated through optical and scanning electron microscopy, whereas their quasi-static mechanical behaviour has been evaluated in tension and bending. In addition, the impact behaviour under low-velocity impact at three different impact energies, namely 6 J, 8 J and 9 J has been addressed. The tensile and flexural tests have been monitored using acoustic emission (AE) in order to elicit further information about failure mechanisms. AE monitoring showed that development of damage was due to nucleation of matrix microcracks and subsequent debonding and pull-out phenomena in wool fibre composites and that only in hybrid composites a sufficient stress transfer across the jute fibre/matrix interface was achieved. The results confirmed the positive role of hybridization with jute fibres in enhancing both the tensile and flexural behaviour of wool-based composites, though highlighting the need for an improved adhesion between wool fibres and epoxy matrix

  10. Behaviour of Mechanically Laminated CLT Members

    Kuklík, P.; Velebil, L.


    Cross laminated timber (CLT) is one of the structural building systems based on the lamination of multiple layers, where each layer is oriented perpendicularly to each other. Recent requirements are placed to develop an alternative process based on the mechanical lamination of the layers, which is of particular interest to our research group at the University Centre for Energy Efficient Buildings. The goal is to develop and verify the behaviour of mechanically laminated CLT wall panels exposed to shear stresses in the plane. The shear resistance of mechanically jointed CLT is ensured by connecting the layers by screws. The paper deals with the experimental analysis focused on the determination of the torsional stiffness and the slip modulus of crossing areas for different numbers of orthogonally connected layers. The results of the experiments were compared with the current analytical model.

  11. Effectiveness and underlying mechanisms of a group-based cognitive behavioural therapy-based indicative prevention program for children with elevated anxiety levels

    Starrenburg, M.L.A. van; Kuijpers, R.C.W.M.; Hutschemaekers, G.J.M.; Engels, R.C.M.E.


    Background Anxiety is a problem for many children, particularly because of its negative consequences not only on the wellbeing of the child, but also on society. Adequate prevention and treatment might be the key in tackling this problem. Cognitive behavioural therapy (CBT) has been found effective

  12. Chemo-mechanical coupling behaviour of leached concrete

    Nguyen, V.H. [Laboratoire d' Analyse des Materiaux et Identification, Ecole Nationale des Ponts et Chaussees, Institut Navier, 6 et 8, Avenue Blaise Pascal, 77455 Marne la Vallee Cedex 2 (France); Colina, H. [ATILH, 7, Place de la Defense, 92974 Paris-La-Defense Cedex (France); Torrenti, J.M. [LCPC Paris, 58, Boulevard Lefebvre 75732 Paris Cedex 15 (France); LMT, ENS Cachan, 61, Avenue du President Wilson, 94235 Cachan (France)], E-mail:; Boulay, C. [LCPC Paris, 58, Boulevard Lefebvre 75732 Paris Cedex 15 (France); Nedjar, B. [Laboratoire d' Analyse des Materiaux et Identification, Ecole Nationale des Ponts et Chaussees, Institut Navier, 6 et 8, Avenue Blaise Pascal, 77455 Marne la Vallee Cedex 2 (France)


    This paper deals with concrete behaviour under chemical and mechanical degradations. Experimental investigations are described where the effects of the calcium leaching process of concrete on its mechanical properties are highlighted. The calcium leaching and mechanical tests on cement paste, mortar and concrete samples are presented. Because of the slow kinetics of leaching under deionised water, an accelerated method has been chosen by using an ammonium nitrate solution instead. The specimens are immersed into a 6 mol/l ammonium nitrate solution with a controlled pH disposal. To quantify the leaching evolution, the degradation depth is then measured at certain time intervals by means of a phenolphthalein solution. The experimental results show the chemical degradation of the cement-based material and the important role of aggregate in the calcium leaching process of concrete. Compression tests of concrete samples are also performed. We observe that there is a strong coupling between the calcium leaching and the mechanical behaviour; as leaching grows, a loss of stiffness and of strength are observed and a smoother post-peak behaviour is noted.

  13. Effectiveness and underlying mechanisms of a group-based cognitive behavioural therapy-based indicative prevention program for children with elevated anxiety levels

    Starrenburg, M.L.A. van; Kuijpers, R.C.W.M.; Hutschemaekers, G. J. M.; Engels, R. C. M. E.


    Background Anxiety is a problem for many children, particularly because of its negative consequences not only on the wellbeing of the child, but also on society. Adequate prevention and treatment might be the key in tackling this problem. Cognitive behavioural therapy (CBT) has been found effective for treating anxiety disorders. “Coping Cat” is one of the few evidence-based CBT programs designed to treat anxiety symptoms in children. The main aim of this project is to conduct a Randomized Co...

  14. Modelling of the Mechanical Behaviour of Ultra-Fine Grained Titanium Alloys at High Strain Rates

    Halle, T.; Herzig, N.; Krüger, L; Meyer, L.W.; Musch, D.; Razorenov, S. V.; Skripnyak, E. G.; Skripnyak, V. A.


    Results of numerical simulations of the mechanical behaviour of coarse grained and UFG titanium alloys under quasi-static uniaxial compression and plane shock wave loading are presented in this paper. Constitutive equations predict the strain hardening behaviour, the strain rate sensitivity of the flow stress and the temperature softening of titanium alloys with a range of grain sizes from 20 µm to 100 nm. Characteristics of the mechanical behaviour of UFG a and a+ß titanium alloys in wide ra...

  15. Experimental validation of upgraded designs for PERMCAT reactors considering the mechanical behaviour of a Pd/Ag membrane under H2 atmosphere

    The PERMCAT process has been chosen in ITER to be the final clean-up stage of the 3-step Tritium Exhaust Processing system. One of the main critical aspects of such a technology is the mechanical stress of the Pd/Ag membrane due to hydrogen uptake during operation. This hydrogen effect is negligible when the component is operated at the nominal temperature of 400 oC. However in case of hydrogen permeation at lower temperatures it can yield to significant expansion of the lattice parameter, inducing a noticeable macroscopic elongation of the membrane. A dedicated experimental device has been built to study in more details the technical consequences of such off-normal operational conditions. The apparatus comprises a finger-type Pd/Ag membrane (fixed only at one end) enclosed in a quartz tube allowing in-situ observations during operation with hydrogen. By varying the operational conditions (temperature and hydrogen pressure at the feed and permeate sides) some critical aspects are pointed out: membrane elongations of more than 2 % are measured for a temperature of 50 oC and some bending of the membrane takes place once the temperature is below 150 oC. Accordingly the first generation of PERMCAT reactors comprises finger-type membranes fixed only at one end. This can ensure reliability of the component in case of nominal operational conditions. However the design is not considered sufficiently robust for reactor applications. Thus new mechanical designs are proposed so as to improve the robustness of the unit and ensure its integrity even under off-normal operation conditions. Two different upgraded components have been produced using either an additional stainless steel edge welded bellows or a special and dedicated convoluted (corrugated) Pd/Ag membrane. The experimental validation of these new concepts is carried out with gas processing tests using water vapour as the '' contaminated '' species and deuterium as the swamping gas. Results of experiments on the both

  16. Development of a New Experimental Apparatus for the Study of the Mechanical Behaviour of a Rock Discontinuity Under Monotonic and Cyclic Loads

    Ferrero, A. M.; Migliazza, M.; Tebaldi, G.


    The shear behaviour of rock discontinuities in seismic condition is still not fully understood although earthquakes can be an important triggering cause of instability phenomena of rock blocks. For this purpose, a special apparatus was designed and developed at the University of Parma (Italy), which is to be placed inside the MTS press available in the Laboratory of Materials Testing. The press allows the application of monotonic and cyclic loads, in load or in deformation control. Quantitative evaluation of the rock-joint damage is realized by a photogrammetric survey of the discontinuity before and after the tests. The surface comparison enables the identification of the damaged areas. Finally, theoretical and experimental results are interpreted in the light of the damage model developed by Belem et al. (Rock Mech Rock Eng 33(4):217-242, 2001) for a quantitative evaluation of joint roughness and resistance.

  17. Mechanical and frictional behaviour of nano-porous anodised aluminium

    Tsyntsaru, N., E-mail: [Institute of Applied Physics of ASM, 5 Academy str., Chisinau, MD 2028 (Moldova, Republic of); Kavas, B., E-mail: [Istanbul Technical University, Department of Metallurgical and Materials Engineering, 34469 Maslak (Turkey); Ford Otomotiv San A.S., Istanbul (Turkey); Sort, J., E-mail: [Institució Catalana de Recerca i Estudis Avançats (ICREA) and Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Spain); Urgen, M., E-mail: [Istanbul Technical University, Department of Metallurgical and Materials Engineering, 34469 Maslak (Turkey); Celis, J.-P., E-mail: [KU Leuven, Dept. MTM, Kasteelpark Arenberg 44, B-3001 (Belgium)


    The porous structure of anodic aluminium oxide (AAO) can be used in versatile applications such as a lubricant reservoir in self-lubricating systems. Such systems are subjected to biaxial loading, which can induce crack formation and propagation, ultimately leading to catastrophic mechanical failure. In this study, the mechanical and tribological behaviour of AAO, prepared from two different types of electrolytes (sulphuric and oxalic acids), are studied in detail. The electrolytic conditions are adjusted to render highly tuneable average pore diameters (between 16 and 75 nm), with porosity levels ranging from 9% to 65%. Well-ordered porous AAO are produced by two-step anodization at rather low temperatures. Mechanical properties, mainly hardness and Young's modulus, are investigated using nanoindentation. Both the porosity degree and the composition of the electrolytic baths used to prepare the AAO have an influence on the mechanical properties. Ball-on-flat configuration was used to estimate the tribological behaviour under dry conditions. No major cracks were observed by scanning electron microscopy, neither after indentation or fretting tests. In the running-in period of tribology experiments the pores were filled with debris. This was followed by the formation of a highly adherent tribolayer – a third body consisting of fine worn particles originated from both the sample and the counterbody. Pore diameter and porosity percentage are found to strongly affect hardness and Young's modulus, but they do not have a major effect on the frictional behaviour. - Highlights: • Well-ordered porous AAO with pore diameters between 16 and 75 nm were produced. • Porosity and composition of electrolytic baths influence the mechanical properties. • Ball-on-flat configuration was used in tribological testing under dry conditions. • Adherent tribolayer consisting of fine worn particles prevents AAO from cracking. • Testing parameters are moreover essential

  18. Composite fuel behaviour under and after irradiation

    Two kinds of composite fuels have been irradiated in the SILOE reactor. They are made of UO2 particles dispersed in a molybdenum metallic (CERMET) or a MgAl2O4 ceramic (CERCER) matrix. The irradiation conditions have allowed to reach a 50000 MWd/t U burn-up in these composite fuels after a hundred equivalent full power days long irradiation. The irradiation is controlled by a continuous measure of the pellet centre line temperature. It allows to have information about the TANOX rods thermal behaviour and the fuels thermal conductivities in comparing the centre line temperature versus linear power curves among themselves. Our results show that the CERMET centre line temperature is much lower than the CERCER and UO2 ones: 520 deg. C against 980 deg. C at a 300W/cm linear power. After pin puncturing tests the rods are dismantled to recover each fuel pellet. In the CERCER case, the cladding peeling off has revealed that the fuel came into contact with the cladding and that some of the pellets were linked together. Optical microscopy observations show a changing of the MgAl2O4 matrix state around the UO2 particles at the pellets periphery. This transformation may have caused a swelling and would be at the origin of the pellet-cladding and the pellet-pellet interactions. No specific damage is seen after irradiation. The CERMET pellets are not cracked and remain as they were before irradiation. The CERCER crack network is slightly different from that observed in UO2. Kr retention was evaluated by annealing tests under vacuum at 1580 deg. C or 1700 deg. C for 30 minutes. The CERMET fission gas release is lower than the CERCER one. Inter- and intragranular fission gas bubbles are observed in the UO2 particles after heat treatments. The CERCER pellet periphery has also cracked and the matrix has transformed again around UO2 particles to present a granular and porous aspect. (author). 4 refs, 6 figs, 2 tabs

  19. Modelling Traveller Behaviour under Emergency Evacuation Conditions

    Pel, A.J.; Bliemer, M.C.J.; Hoogendoorn, S.P.


    Dynamic traffic simulation models are frequently used to support decisions when planning an evacuation. This paper focuses on limitations in the modelling of travellers’ behaviour with respect to traffic information and compliance to evacuation instructions. More specifically, we propose a model fra

  20. Biochemical mechanisms underlying atherogenesis

    Dr.P.V.L.N. Srinivasa Rao


    Full Text Available Atherosclerosis remains one of the major causes of death and premature disability in developed countries. Though atherosclerosis was formerly considered a bland lipid storage disease, substantial advances in basic and experimental sciences have illuminated the role of endothelium, inflammation and immune mechanisms in its pathogenesis. Current concept of atherosclerosis is that of a dynamic and progressive disease arising from in- jury to endothelium, also known as endothelial dysfunction and an inflammatory response to that injury. The lesions of atherosclerosis occur principally in large and medium sized arteries. Atherosclerosis affects various regions of the circulation preferentially and can lead to ischemia of heart, brain or extremities resulting in in- farction.This produces distinct clinical manifestations depending on the vessel involved. Several predisposing factors to cardiovascular diseases such as diabetes mellitus, hypertension, obesity, infections act as triggers to the devel- opment of atherosclerosis by causing endothelial dysfunction and/or promoting inflammatory response. The evolution of pathogenetic mechanisms has passed through various directions such as oxidative stress, inflam- mation and immune responses. It is now known that all these are not acting independently but are interrelated and getting unified in the current concept of atherogenesis. The following discussion aims at providing an in- sight into these developments which can help in a better comprehension of the disease and management of its clinical complications

  1. Behaviour of high performance concrete under high temperature (60-450 deg C) for surface long-term storage: thermo-hydro-mechanical residual properties

    After various thermal treatments (up to 450 deg C), residual thermo-hydro-mechanical (T-H-M) properties of two OPC high performance concretes (HPC) were analyzed in the context of surface long-term storage. Materials were prepared with silico-calcareous aggregates (standard HPC) and hematite aggregates (heavy HPC). The initial micro structural (porosity =10%) and transport (gas permeability ∼ 10-19 m2) properties are similar for both concretes. As far as the mechanical aspect is concerned, heavy HPC shows a higher compressive strength and elastic modulus than standard HPC (78 and 63 MPa, 81 and 49 GPa, respectively). Heavy HPC is also characterized by a higher thermal conductivity (7.3 W m-1 K-1 compared to 2.7 W m-1 K-1 for standard concrete). Results analysis show that thermo-hydro-mechanical damages are smaller for heavy HPC. Between 60 and 250 deg C, the elastic modulus and the compressive strength of standard HPC decrease by 40% and 16%, respectively. For heavy HPC, these parameters respectively decrease by 10% and 4% A similar trend was observed for thermal conductivity evolution. Gas permeability and porosity data confirm the good behavior of heavy HPC. As a conclusion, hematite HPC seems to provide more interesting T-H-M residual properties than standard HPC. Limited thermal expansion and thermal gradients induced by hematite are probably responsible of this behavior. Copyright (2001) Material Research Society

  2. Mechanical Behaviour of the Wood Masonry

    Fazia FOUCHAL


    Full Text Available In this paper we study the walls wood masonry behaviour. First, we propose a regulatory validation of the walls wood masonry behaviour subjected to vertical and horizontal loads according to Eurocode 5. Then we present the numerical application on the wall wood supported two floors level.

  3. Behaviour of biofilms formed by Pseudomonas fluorescens under different flow regimes when exposed to surfactants : role of the biofilm mechanical stability

    Simões, M; Pereira, M. O.; Vieira, M. J.


    The effectiveness of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) to control biofilms formed by Pseudomonas fluorescens on stainless steel slides under laminar and turbulent conditions, using a flow cell reactor, is compared in this study. The antimicrobial action of the surfactants was evaluated in terms of the activity of the biofilm, the biofilm mass that remained on the surface after treatment and the biofilm morphological characteristics. The mec...

  4. Experimental study of aluminium honeycomb behaviour under dynamic multiaxial loading

    Markiewicz E.


    Full Text Available Split Hopkinson Pressure Bar system (SHPB with large-diameter and Nylon bars introducing a shear-compression loading device is used in order to investigate the dynamic behaviour of aluminium honeycomb under multiaxial loadings conditions. All shear-compression configurations including the loading angle variation from 0∘ to 60∘ are performed with an impact velocity of about 15m/s. The adapted SHPB system with the device are validated numerically and a phenomenon of separation between the input bar and the input beveled bar is observed. Numerical results suggest that this phenomenon provides a cutting of the reflected wave. An electro optical extensometer is employed in experiments. A good agreement between the numerical elastic waves and the experimental ones is obtained. Experimental results show a significant effect of the loading angle on the apparent stress-strain curves. The initial peak value and the plateau stress decrease with the increase of the loading angle. The combined shear-compression device with an enhancement at the alignment set-up provides efficient results for samples dynamically loaded. This device will be used to investigate the influence of the in-plane orientation angle on the deformation mechanisms and multiaxial behaviour of aluminium honeycomb under dynamic and quasi-static loading conditions.

  5. Mechanical behaviour of diamond reinforced metals

    Diamond reinforced metals with a diamond content of 55-60 vol.% were made by gas driven liquid metal infiltration. They were characterized with regard to their stiffness, strength and fracture toughness as a function of diamond particle size and matrix alloy by means of tensile and Chevron notch tests, respectively. The choice of the metal matrix, i.e. pure Al, Al-Cu, Cu-B and Ag-Si alloys was made in view of their application in thermal management where high thermal conductivity is important. For undamaged material Young's moduli, measured in unloading-reloading cycles necessary to measure static Young's modulus, of 250 GPa for Al-based and 300 GPa for Ag-based composites were obtained. The copper-based composites exhibited much lower values indicating that the small deformation necessary to measure Young's modulus induced already considerable damage. Strain to fracture of the composites was found to be a few tenth of a percent. An ultimate tensile strength of approximately 300 MPa was reached for the silver-based composites compared with roughly 150 MPa for the Al-based and below 50 MPa for the Cu-based composites. The size of the diamond particles had little influence on stiffness and strength of the composites but fracture toughness increased with increasing particle size. The differences in the mechanical behaviour of the configurations investigated can be rationalized by observations made during fractographic investigations by scanning electron microscopy. Additionally, the damage evolution in the composites was observed by the repeated determination of the specimen's stiffness during the tensile tests.

  6. Mechanisms of change in human behaviour

    Marchal, Paul; Bartelings, Heleen; Bastardie, François; Batsleer, Jurgen; Delaney, Alyne; Girardin, Raphael; Gloaguen, Pierre; Hamon, Katell; Hoefnagel, Ellen; Jouanneau, Charlène; Mahevas, Stephanie; Nielsen, Rasmus; Piwowarczyk, Joanna; Poos, Jan-Jaap; SCHULZE Torsten


    The scope of this report is to present the science developed within the VECTORS project to improve the understanding of the key processes driving the behaviour of human agents utilising a variety of EU maritime domains. While particular attention has been paid to the spatial interactions between fishing activities and other human uses (e.g., maritime traffic, offshore wind parks, aggregate extractions), the behaviour of non-fishing sectors of activity has also been considered. Various quantit...

  7. The behaviour of fibrous composite materials under nuclear radiations exposure

    The main feature of fibrous composite materials are briefly described, which are constitued by a netwoek of ceramic high performance fiber embebed in a ductile matrix material. These composite materials show such a kind of anisotropic strength that their uses has been widely spreaded in the last times. This philosophy of strengthening was used by the Nature, where are abundant examples of fibrous composites like horn, bamboo tissues, etc. In this paper are collected the published results about behaviour of reinforced dibers and fibrous composites under nuclear radiation exposure. The results show a very wide sort of fenomenae depending on many factors. Are fibers, like the boron one, which shows an inconvenient behaviour and another like graphite fibers which appears to improve its features. Is is concluded that was not achieved enough information about the behaviour of the interface under irradiation in order to build up a theory about the behaviour of the full composite under irradiation exposure. (author)

  8. Numerical modelling investigation of rock mass behaviour under gravity dams

    Alshkane, Younis Mustafa Ali


    The study of rock mass behaviour is a broad subject in the rock mechanics field which still needs more research and investigation, especially for geotechnical issues associated with dam construction. Since it is difficult to study rock mass behaviour at a large scale in the laboratory, the numerical modelling technique is an alternative method which can be used efficiently in this field. In this thesis two codes have been selected for this purpose. The first code was a continuum code FLAC (Fa...

  9. Mechanical Behaviour of Materials Volume 1 Micro- and Macroscopic Constitutive Behaviour

    François, Dominique; Zaoui, André


    Advances in technology are demanding ever-increasing mastery over the materials being used: the challenge is to gain a better understanding of their behaviour, and more particularly of the relations between their microstructure and their macroscopic properties.   This work, of which this is the first volume, aims to provide the means by which this challenge may be met. Starting from the mechanics of deformation, it develops the laws governing macroscopic behaviour – expressed as the constitutive equations – always taking account of the physical phenomena which underlie rheological behaviour. The most recent developments are presented, in particular those concerning heterogeneous materials such as metallic alloys, polymers and composites. Each chapter is devoted to one of the major classes of material behaviour.   As the subtitles indicate, Volume 1 deals with micro- and macroscopic constitutive behaviour and Volume 2 with damage and fracture mechanics. A third volume will be devoted to exercises and the...

  10. Behaviour of fiber reinforced concrete slabs under impact loading

    The behaviour of steel fiber reinforced concrete slabs under impact loads has been investigated. The results obtained show that fracturing and spallation effects are reduced to a large extend due to the high energy absorption and the increased yield strength of this material. Crater depths are comparable to those obtained using normal concrete targets. Systematic tests using different fiber types and dimensions show that the terminal ballistic behaviour is strongly dependent on these parameters. (orig.)

  11. Mechanical behaviour of reactor pressure vessel in severe accident

    The article describes the main achievements in developing methodology for analysing mechanical behaviour of pressure vessels with and without penetrations at high temperatures related to accident scenarios. Validation and applications of the methodology are presented. (orig.)


    Sun, Huichao; Houssin, Remy; Gardoni, Mickael; Jean, Renaud


    The mechanical engineering problems today become more and more complex particularly in the area of new product development. Mechanical product design is usually performed simply taking into consideration system functions and structures, while users’ behaviours in terms of using the system are generally not fully considered enough early in the design phase. This paper covers the multi-trade engineering design, and deals with the development of a behavioural design approach to help designers to...

  13. Analysis of operator's behaviour under accidental transients

    Since 1979, EDF has been conducting intensive test campaigns on full-scale PWR simulators in order to study and improve the operators behavior under incident as well as accident conditions. This paper presents some results obtained during tests carried out in 1986 on the P4 (1300 MWe power plant series) simulators of the Paluel Training Center. These results essentially concern the observed deviations, the diagnosis and the safety engineer's role. They are compared with the results of previous test ou 900 MWe unit simulators. The test organization and methodology, the result analysis methods and the biases introduced by this kind of test are also discussed

  14. Modelling the hydro-mechanical behaviour of swelling unsaturated soils

    The use of compacted swelling soils in engineering practice is very widely spread, especially in geotechnical and environmental engineering. After their setup, these materials are likely to be subject to complex suction/stress paths involving significant variations of their hydro-mechanical properties which can affect their initial behaviour. It is important to be able to predict the hydro-mechanical behaviour of these materials taking into account the significant applications for which they are intended. Barcelona team developed a finite-element code (Code-Bright) for the thermo-hydro-mechanical coupling (THM) integrating the BBM elastoplastic model for unsaturated soils based on the independent variables approach. This model is recognized to correctly describe the hydro-mechanical behaviour of unsaturated soils but fails to take into account some particular observed aspects on swelling soils. A second model BExM was then proposed to address these aspects. The objective of this study is: (i) to implement the elastoplastic model BExM for the unsaturated swelling soils in the finite-element code (Code-Bright); (ii) to check the numerical model validity through the numerical simulation of laboratory tests made on swelling soils; and (iii) to apply this model to some practical problems. For this purpose, a new family of numerical procedures adapted to the BExM model was introduced into the code. The equation of the yield surface of this model for a given deviatoric stress states was given in a manner to facilitate calculations of its derivatives. The model was checked by the numerical simulation of suction-controlled odometric tests made on three different swelling soils. The simulation results showed that the numerical model is able to correctly reproduce the experimental data. Lastly, the model was applied to two practical problems: radioactive waste repository in deep geological layers and a shallow footing under the action of a swelling soil. The results obtained

  15. Undrained Behaviour of Silt under Static and Cyclic Loading

    YANG Shaoli; ROLF Sandven; LARS Grande


    In this study, the undrained behaviour of silt under low stress level is studied. An effective preparation methodfor built in silt samples in the triaxial test was firstly developed. By triaxial testing of samples at low confining pressures itwas found that silt easily loses stability and liquefies. Loose silt may show temporary liquefaction under static loading, anddevelop full liquefaction under cyclic loading. The most important factors influencing the silt behaviour are porosity, confin-ing pressure, consolidation state, cyclic loading level and number of cycles. The maximum obtainable shear stress is primarilya function of the confining pressure and the internal frictional angle. The actual structure of the silt material is the key factorin controlling its behaviour.

  16. Mechanical Behaviour of Phyllosilicate-Rich Faults

    Collettini, Cristiano; Niemeijer, André; Viti, Cecilia; Marone, Chris


    A number of observations indicate that phyllosilicate-rich faults are widespread within the brittle crust. Here, we report on laboratory experiments designed to investigate the frictional behavior of 1) intact foliated solid rocks sheared in their in-situ geometry and 2) powders obtained from crushing and sieving the samples used in the solid experiments; 3) powders obtained from non foliated samples. The samples were collected from the Zuccale low-angle normal fault (Italy) and are characterised by different amounts of phyllosilicates (from 60 to 10 % of talc, smectite biotite and chlorite) plus calcite, hornblende and tremolite. Friction of powders, at room humidity and temperature, is in the range 0.27-0.62 and it is controlled by the abundance of weak phyllosilicates (talc and smectite). Over a range of normal stresses from 10 to 150 MPa and sliding velocities from 1 to 300 μm/s, the powdered material with a) 60% of phyllosilicates exhibits velocity strengthening behaviour associated to calcite grain rotation and translation in a phyllosilicate-rich groundmass; b) powders with identical mineralogical composition. In addition, the solid samples become more and more velocity strengthening with increasing sliding velocity. Field observations along exhumed and phyllosilicate-rich faults worldwide suggest that phyllosilicates-rich strands bound lenses of stronger and non foliated lithologies. Within this fault structure fault creep and aseismic slip along weak and phyllosilicate-rich foliated surfaces (velocity strengthening behaviour) might increase stress on lenses of stronger materials (velocity weakening behaviour) from which a rupture can nucleate. In this view, some crustal faults can behave as weak structures over long timescales (millions of years) and be intermittently seismogenic on shorter timescales.

  17. Behaviourism and the mechanization of the mind.

    Lecas, Jean-Claude


    The significance of Behaviourism is examined in relation to its far conceptual roots, i.e. comparative animal studies initiated by Darwin, mechanistic physiological thinking initiated by Descartes and empiricist associationism. The Behaviourist anti-mentalist position induced neuromechanistic interpretations based on Pavlovian reflexes, stimulus-response connectionism and the very first hypotheses on synaptic plasticity. As a result, the evolutionary tradition was dropped and the two other trends were combined into a new adaptive version of Cartesian automaton, with persisting influences in modern reductionist thinking, from robotics and cognitive science to the neuroscience of learning and memory. PMID:16731496

  18. Modelling the thermo-mechanical volume change behaviour of compacted expansive clays

    Tang, Anh-Minh; 10.1680/geot.2009.59.3.185


    Compacted expansive clays are often considered as a possible buffer material in high-level deep radioactive waste disposals. After the installation of waste canisters, the engineered clay barriers are subjected to thermo-hydro-mechanical actions in the form of water infiltration from the geological barrier, heat dissipation from the radioactive waste canisters, and stresses generated by clay swelling under almost confined conditions. The aim of the present work is to develop a constitutive model that is able to describe the behaviour of compacted expansive clays under these coupled thermo-hydro-mechanical actions. The proposed model is based on two existing models: one for the hydro-mechanical behaviour of compacted expansive clays and another for the thermo-mechanical behaviour of saturated clays. The elaborated model has been validated using the thermo-hydro-mechanical test results on the compacted MX80 bentonite. Comparison between the model prediction and the experimental data show that this model is able...

  19. Creep of uranium dioxide: bending test and mechanical behaviour

    These PhD work in the frame of Pellet-Cladding Interactions studies, in the fuel assemblies of nuclear plants. Electricite de France (EDF) must well demonstrate and insure the integrity of the cladding. For that purpose, the viscoplastic behaviour of the nuclear fuel has to be known and, if possible, controlled. This PhD work aimed to characterize the creep of uranium dioxide, in conditions of transient power regime. First, a literature survey on mechanical behaviour of UO2 revealed that the ceramic was essentially studied with compressive tests, and that its creep behaviour is characterized by two domains, depending on the stress level. To estimate the loadings in a fuel pellet, EDF and CEA developed specific global codes. A simulation during a power ramp allowed the order of magnitude of the loadings in the pellet to be determined (temperature, thermal gradients, strains, strain rate...). The stress calculation using a finite element simulation requires the identification of behaviour laws, able to describe the behaviour under small strains, low strain rates, and under tensile stresses. Starting from this observation, three point bending method has been chosen to test the uranium dioxide. As, for representativeness reasons, testing specimens cut in actual fuel pads was required in our study; a ten millimeters span has been used. For this study, a specific three-point testing device has been developed, that can tests specimens up to 2 000 C in a controlled atmosphere (Ar + 5% H2). A special care has been taken for the measurement of the deflexion of the sample, which is measured using a laser beam, that allow an accuracy of ±2μm to be reached at high temperature. Specimens with 0,5 to 1 mm thickness have been tested using this jig. A Norton's law describe, with respective stress exponent and activation energy values of 1.73 and 540 kJ.mole-1, provided a good description of the stationary creep rate. Then, the mechanical behaviour of the fuel has been modeled

  20. Chemo-mechanical coupling behaviour of leached concrete. Part I : Experimental results

    NGUYEN,VH; COLINA, H; Torrenti, Jean Michel; Boulay, Claude; Nedjar, Boumediene


    This paper deals with concrete behaviour under chemical and mechanical degradations. Experimental investigations are described where the effects of the calcium leaching process of concrete on its mechanical properties are highlighted. The calcium leaching and mechanical tests on cement paste, mortar and concrete samples are presented. Because of the slow kinetics of leaching under deionised water, an accelerated method has been chosen by using an ammonium nitrate solution instead. The specime...

  1. Brain mechanisms underlying sensation-seeking in humans

    Norbury, A. E.


    Sensation-seeking is a personality trait concerned with motivation for intense and unusual sensory experiences, that has been identified as risk factor for a variety of psychopathologies with high social cost; in particular gambling and substance addictions. It has previously proved difficult to tease out neural mechanisms underlying sensation-seeking in humans, due to a lack of cognitive-behavioural paradigms probing sensation-seeking-like behaviour in the lab. The first aim of this thesis w...

  2. Mechanical behaviour of dissimilar metal welds

    This report addresses the problems of dissimilar metal welds connecting an austenitic stainless steel component to a ferritic steel component. In LMFBRs such welds appear at the junction of the austenitic stainless steel vessel with the ferritic steel roof and in sodium and water or steam pipes. The latter are exposed to high temperatures in the creep range. A wide range of austenitic stainless steels and ferritic steels (carbon steels, low allow steels and alloy steels) are covered; the study encompasses more than 20 different weld metals (austenitic stainless steels and nickel base alloys). The report begins with a presentation of the materials, geometries and welding procedures treated in the study, followed by a review of service experience from examinations of dissimilar metal welds after elevated temperature service, in particular failed welds. Results of laboratory tests performed for reproducing service failures are then discussed. A further section is devoted to a review of test results on fatigue behaviour and impact toughness for dissimilar metal welded joints when creep is not significant. Finally, the problem of residual life assessment is addressed. A set of recommendations concludes the report. They concern the material selection, welding procedure, life prediction and testing of dissimilar metal welds. 84 refs

  3. Mechanisms and functions of brain and behavioural asymmetries

    Tommasi, Luca


    For almost a century the field of brain and behavioural asymmetries has been dominated by studies on humans, resting on the evidence that the anatomical structures underlying language functions are asymmetrical, and that human handedness is lateralized at the population level. Today, there is not only evidence of population-level lateralization of brain and behaviour across a variety of vertebrate and invertebrate species, but also a growing consensus that the comparative analysis of the envi...

  4. Multiscale approach of mechanical behaviour of SiC/SiC composites: elastic behaviour at the scale of the tow

    CHATEAU, Camille; Gelebart, Lionel; Bornert, Michel; CREPIN, Jérome; Caldemaison, Daniel


    SiC/SiC composites are candidates for structural applications at elevated temperatures in the context of the development of the 4th generation of nuclear reactors. A multiscale approach is under development to construct a predictive modelling of their complex mechanical behaviour due to their heterogeneous microstructure. This approach is based on two scale transitions: from the fibres/matrix microstructure to the tow and from the tow to the woven composite, each scale presenting a significan...

  5. A strong genetic correlation underlying a behavioural syndrome disappears during development because of genotype-age interactions.

    Class, Barbara; Brommer, Jon E


    In animal populations, as in humans, behavioural differences between individuals that are consistent over time and across contexts are considered to reflect personality, and suites of correlated behaviours expressed by individuals are known as behavioural syndromes. Lifelong stability of behavioural syndromes is often assumed, either implicitly or explicitly. Here, we use a quantitative genetic approach to study the developmental stability of a behavioural syndrome in a wild population of blue tits. We find that a behavioural syndrome formed by a strong genetic correlation of two personality traits in nestlings disappears in adults, and we demonstrate that genotype-age interaction is the likely mechanism underlying this change during development. A behavioural syndrome may hence change during organismal development, even when personality traits seem to be strongly physiologically or functionally linked in one age group. We outline how such developmental plasticity has important ramifications for understanding the mechanistic basis as well as the evolutionary consequences of behavioural syndromes. PMID:26041348

  6. Mechanical behaviour characterizing and simulation of polyacrylate rubber

    D. dos Santos


    Full Text Available Purpose: of this paper is to investigate the influence of EB radiation on the mechanical behaviour of UV curing polyacrylate rubber (ACM and to simulate its behaviour.Design/methodology/approach: The material was irradiated by two different EB doses, 100 kGy and 250 kGy, its mechanical behaviour was investigated with the help of uniaxial, equibiaxial and planar shear experiments. The results were applied to the Ogden’s Model (1972 in order to obtain the parameters to simulate the material behaviour by finite element method (FEM and to compare experimental and FEM curves. The structure molecular changes caused by EB were investigated with the help of infrared spectroscopy.Findings: In most cases the experimental results showed an increase in the strength at rupture and a decrease in the elongation at the rupture with increasing of radiation dose. Equibiaxial and planar shear tests presented similar behaviour like uniaxial results, in terms of elongation decrease and strength increase, with some deviations. Ogden’s Model third order provided simulated curves with similar behaviour in comparison to experimental curves. The infrared spectroscopy showed different chemical group contents in the analyzed regions, surface and middle region.Research limitations/implications: Two doses of EB radiation were applied; higher or lower doses were not investigated.Practical implications: Improved behaviour of UV curing ACM can extend the range of industrial applications, or improve its performance in known applications.Originality/value: Usually EB radiation has been used to modify polymeric structure and to improve thermal and mechanical polymers behaviour. Regarding like rubber materials EB is usually applied as an alternative form of vulcanization. UV is a new type of curing for polyacrylate rubbers, which are usually cured by thermal processes.

  7. Failure behaviour of carbon/carbon composite under compression

    Tushtev, K.; Grathwohl, G. [Universitaet Bremen, Advanced Ceramics, Bremen (Germany); Koch, D. [Deutsches Zentrum fuer Luft- und Raumfahrt, Institut fuer Bauweisen- und Konstruktionsforschung, Keramische Verbundstrukturen, Stuttgart (Germany); Horvath, J.


    In this work the properties of Carbon/Carbon-material are investigated under quasi-static compression and model-like characterized. The investigated material was produced by pyrolysis of a Carbon/Carbon - composite of bidirectionally reinforced fabric layers. For the compression tests, a device to prevent additional bending stress was made. The stress-strain behaviour of this material has been reproduced in various publications. This will be discussed on the fracture behaviour and compared the experimental results from the compression tests with the characteristics of tensile and shear tests. The different compression and tensile properties of stiffness, poisson and strength were assessed. Differences between the tensile and compression behaviour resulting from on-axis tests by micro buckling and crack closure and off-axis experiments by superimposed pressure normal stresses that lead to increased shear friction. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. Mechanical behaviour of aluminium-lithium alloys

    N Eswara Prasad; A A Gokhale; P Rama Rao


    Aluminium-lithium alloys hold promise of providing a breakthrough response to the crying need for lightweight alloys for use as structurals in aerospace applications. Considerable worldwide research has gone into developing a range of these alloys over the last three decades. As a result, substantial understanding has been developed of the microstructure-based micromechanisms of strengthening, of fatigue and fracture as well as of anisotropy in mechanical properties. However, these alloys have not yet greatly displaced the conventionally used denser Al alloys on account of their poorer ductility, fracture toughness and low cycle fatigue resistance. This review aims to summarise the work pertaining to study of structure and mechanical properties with a view to indicate the directions that have been and can be pursued to overcome property limitations.

  9. Prediction of PEC core mechanical behaviour

    A brief description of the original PEC core restraint system is presented. Recent advanced seismic analysis studies have necessitated the introduction of anti-seismic design modifications which have increased the difficulties of fuel handling. Computer codes and numerical methods, used by ENEA to resolve core restraint and fuel handling problems are given together with an outline of mechanical tests and handling experiments in support of the anti-seismic core design. (author)

  10. Morphology and mechanical behaviour of concretes reinforced by amorphous cast fibres

    This research thesis addresses the characterization of the morphology and mechanical behaviour of concretes reinforced by amorphous cast fibres. It first gathers some general characteristics and observations related to the amorphous cast fibre: roughness, failure mode, amorphous structure, X-ray analysis, fire resistance. Experimental methods and techniques developed for morphological analysis and mechanical tests are presented (sample preparation, tensile test, and compression sample) and the use of image automatic analysis techniques is then addressed (void morphology and granulometry analysis, inter-void distance measurement, fibre spatial distribution). The next part reports the study of the mechanical behaviour under axial compression

  11. Post Irradiation Mechanical Behaviour of Three EUROFER Joints

    Lucon, E.; Leenaers, A.; Vandermeulen, W.


    The post-irradiation mechanical properties of three EUROFER joints (two diffusion joints and one TIG weld) have been characterized after irradiation to 1.8 dpa at 300 degrees Celsius in the BR-2 reactor. Tensile, KLST impact and fracture toughness tests have been performed. Based on the results obtained and on the comparison with data from EUROFER base material irradiated under similar conditions, the post-irradiation mechanical behaviour of both diffusion joints (laboratory and mock-up) appears similar to that of the base material. The properties of the TIG joint are affected by the lack of a post-weld heat treatment, which causes the material from the upper part of the weld to be significantly worse than that of the lower region. Thus, specimens from the upper layer exhibit extremely pronounced hardening and embrittlement caused by irradiation. The samples extracted from the lower layer show much better resistance to neutron exposure, although their measured properties do not match those of the diffusion joints. The results presented demonstrate that diffusion joining can be a very promising technique.

  12. Kinesin's backsteps under mechanical load

    Hyeon, Changbong; Onuchic, Jose' N


    Kinesins move processively toward the plus end of microtubules by hydrolyzing ATP for each step. From an enzymatic perspective, the mechanism of mechanical motion coupled to the nucleotide chemistry is often well explained using a single-loop cyclic reaction. However, several difficulties arise in interpreting kinesin's backstepping within this framework, especially when external forces oppose the motion of kinesin. We review evidence, such as an ATP-independent stall force and a slower cycle time for backsteps, that has emerged to challenge the idea that kinesin backstepping is due to ATP synthesis, i.e., the reverse cycle of kinesin's forward-stepping chemomechanics. Supplementing the conventional single-loop chemomechanics with routes for ATP-hydrolyzing backward steps and nucleotide-free steps, especially under load, gives a better physical interpretation of the experimental data on backsteps.

  13. Molecular Mechanisms Underlying Bacterial Persisters

    Maisonneuve, Etienne; Gerdes, Kenn


    All bacteria form persisters, cells that are multidrug tolerant and therefore able to survive antibiotic treatment. Due to the low frequencies of persisters in growing bacterial cultures and the complex underlying molecular mechanisms, the phenomenon has been challenging to study. However, recent...... technological advances in microfluidics and reporter genes have improved this scenario. Here, we summarize recent progress in the field, revealing the ubiquitous bacterial stress alarmone ppGpp as an emerging central regulator of multidrug tolerance and persistence, both in stochastically and environmentally...

  14. Behaviour of fission-product iodine under severe accident conditions

    On account of the radiological properties of I-131 the behaviour of fission-product iodine is of great importance under severe reactor accident conditions. The chemical properties of iodine: Its easy conversion into several oxidation compounds, its capability of forming not only volatile (organo-iodide, elemental iodine), hardly volatile, readily soluble (cesium iodide/iodate) but also insoluble (silver iodide) compounds, and its susceptibility to ionizing radiation, are further aspects of significance. Intensive investigations on iodine behaviour under reactor accident conditions carried out worldwide over the last ten years have shown - even though a number of details have yet to be elucidated - that physicochemical processes form a natural, i.e. passive, barrier against the possible release of iodine. (orig.)

  15. Experimental study of aluminium honeycomb behaviour under dynamic multiaxial loading

    Markiewicz E.; Haugou G.; Chaari F.; Zouari B.; Tounsi R.; Dammak F.


    Split Hopkinson Pressure Bar system (SHPB) with large-diameter and Nylon bars introducing a shear-compression loading device is used in order to investigate the dynamic behaviour of aluminium honeycomb under multiaxial loadings conditions. All shear-compression configurations including the loading angle variation from 0∘ to 60∘ are performed with an impact velocity of about 15m/s. The adapted SHPB system with the device are validated numerically and a phenomenon of separation between the inpu...

  16. Computation of the mechanical behaviour of nuclear reactor components

    A possible limiting factor of the service life of a reactor is the mechanical load carrying margin, i.e. the excess of the load carrying capacity over the actual loading, of the central, heavy section components. This margin decreases during service but, for safety reasons, may not fall below a critical value. Therefore, it is essential to check and to control continuously the factors which cause the decrease. The reasons for the decrease are shown at length and in detail in an example relating to the test which almost achieved failure of a pipe emanating from a reactor pressure vessel, weakened by an artificial crack and undergoing a water-hammer loading. The latter was caused by a sudden valve closure supposed to follow upon a break far downstream. The computational and experimental difficulties associated with the simultaneous occurrence of an extreme weakening and an extreme loading in an already rather complicated geometry are explained. It is concluded that available computational tools and present know-how are sufficient to simulate the behaviour under such conditions as would prevail in normal service, and even to analyse departures from them, as long as not all difficulties arise simultaneously. (author) figs., tabs., refs

  17. Behaviour of gas cooled reactor fuel under accident conditions

    The Specialists Meeting on Behaviour of Gas Cooled Reactor Fuel under Accident Conditions was convened by the International Atomic Energy Agency on the recommendation of the International Working Group on Gas Cooled Reactors. The purpose of the meeting was to provide an international forum for the review of the development status and for the discussion on the behaviour of gas cooled reactor fuel under accident conditions and to identify areas in which additional research and development are still needed and where international co-operation would be beneficial for all involved parties. The meeting was attended by 45 participants from France, Germany, Japan, Switzerland, the Union of Soviet Socialists Republics, the United Kingdom, the United States of America, CEC and the IAEA. The meeting was subdivided into five technical sessions: Summary of Current Research and Development Programmes for Fuel; Fuel Manufacture and Quality Control; Safety Requirements; Modelling of Fission Product Release - Part I and Part II; Irradiation Testing/Operational Experience with Fuel Elements; Behaviour at Depressurization, Core Heat-up, Power Transients; Water/Steam Ingress - Part I and Part II. 22 papers were presented. A separate abstract was prepared for each of these papers. At the end of the meeting a round table discussion was held on Directions for Future R and D Work and International Co-operation. Refs, figs and tabs

  18. Behaviour of organic iodides under pwr accident conditions

    Laboratory experiments were performed to study the behaviour of radioactive methyl iodide under PWR loss-of-coolant conditions. The pressure relief equipment consisted of an autoclave for simulating the primary circuit and of an expansion vessel for simulating the conditions after a rupture in the reactor coolant system. After pressure relief, the composition of the CH3sup(127/131)I-containing steam-air mixture within the expansion vessel was analysed at 80 0C over a period of 42 days. On the basis of the values measured and of data taken from the literature, both qualitative and quantitative assessments have been made as to the behaviour of radioactive methyl iodide in the event of loss-of-coolant accidents. (author)

  19. The behaviour of radioactive waste packages under fire accident conditions

    An experimental study has been made of the behaviour of packaged Intermediate Level Wastes (ILW) subjected to heat. The conditions used represented fire accidents in the transport of the ILW to the repository in shielded transport containers and in the handling of the packages at the repository. The behaviour of four waste materials immobilised in cement and organic resin were studied. Each waste used had features which allowed the results to be applied to a wide range of other waste streams. Samples of these materials have been heated under controlled and well instrumented conditions in furnaces and pool fires. Inactive simulant wastes were used in small and full scale experiments. Fully active waste materials were used in small scale experiments only. Data are presented on the temperature profiles through the packaged ILW and on the release of volatile and particulate materials as a function of time and temperature. (orig.)

  20. Thermal shock behaviour of different tungsten grades under varying conditions

    Thermonuclear fusion power plants are a promising option to ensure the energy supply for future generations, but in many fields of research enormous challenges have to be faced. A major step on the way to the prototype fusion reactor DEMO will be ITER which is build in Cadarache, southern France. One of the most critical issues is the field of in-vessel materials and components, in particular the plasma facing materials (PFM). PFMs that will be used in a device like ITER have to withstand severe environmental conditions in terms of steady state and transient thermal loads as well as high particle fluxes such as hydrogen, helium and neutrons. Candidate wall materials are beryllium, tungsten and carbon based materials like CFC (carbon fibre composite). Tungsten is the most promising material for an application in the divertor region with very severe loading conditions and it will most probably also be used as PFM for DEMO. Hence, this work focuses on the investigation of the thermal shock response of different tungsten grades in order to understand the damage mechanisms and to identify material parameters which influence this behaviour under ITER and DEMO relevant operation conditions. Therefore the microstructure and the mechanical and thermal properties of five industrially manufactured tungsten grades were characterised. All five tungsten grades were exposed to transient thermal events with very high power densities of up to 1.27 GWm-2 at varying base temperatures between RT and 600 C in the electron beam device JUDITH 1. The pulse numbers were limited to a maximum of 1000 in order to avoid immoderate workload on the test facility and to have enough time to cover a wide range of loading conditions. The results of this damage mapping enable to define different damage and cracking thresholds for the investigated tungsten grades and to identify certain material parameters which influence the location of these thresholds and the distinction of the induced damages

  1. Thermal shock behaviour of different tungsten grades under varying conditions

    Wirtz, Oliver Marius


    Thermonuclear fusion power plants are a promising option to ensure the energy supply for future generations, but in many fields of research enormous challenges have to be faced. A major step on the way to the prototype fusion reactor DEMO will be ITER which is build in Cadarache, southern France. One of the most critical issues is the field of in-vessel materials and components, in particular the plasma facing materials (PFM). PFMs that will be used in a device like ITER have to withstand severe environmental conditions in terms of steady state and transient thermal loads as well as high particle fluxes such as hydrogen, helium and neutrons. Candidate wall materials are beryllium, tungsten and carbon based materials like CFC (carbon fibre composite). Tungsten is the most promising material for an application in the divertor region with very severe loading conditions and it will most probably also be used as PFM for DEMO. Hence, this work focuses on the investigation of the thermal shock response of different tungsten grades in order to understand the damage mechanisms and to identify material parameters which influence this behaviour under ITER and DEMO relevant operation conditions. Therefore the microstructure and the mechanical and thermal properties of five industrially manufactured tungsten grades were characterised. All five tungsten grades were exposed to transient thermal events with very high power densities of up to 1.27 GWm{sup -2} at varying base temperatures between RT and 600 C in the electron beam device JUDITH 1. The pulse numbers were limited to a maximum of 1000 in order to avoid immoderate workload on the test facility and to have enough time to cover a wide range of loading conditions. The results of this damage mapping enable to define different damage and cracking thresholds for the investigated tungsten grades and to identify certain material parameters which influence the location of these thresholds and the distinction of the induced

  2. Modelling the mechanical behaviour of heterogeneous Ta/TA6V welded joints: behaviour and failure criteria

    As laser welding of two different materials (heterogeneous welding) leads to a joint having a characteristic size close to the millimetre, i.e. much smaller than that of a structure, and as such a junction displays completely different mechanical properties because of the metallurgical transformations induced by intense thermal loading, the aim of this research thesis is to develop a behaviour model, flexible and robust enough, to represent all together the mechanical behaviours of the Ta, the TA6V and the melted zone. This model must be able to take plasticity and visco-plasticity into account, and also to provide a failure criterion through damage mechanics and its coupling with the behaviour. The author first reports the experimental characterization of the base materials (Ta and TA6V) by using tensile tests under different strain rates and different directions, relaxation tests and fatigue shear tests. He also characterizes the melted zone by describing the influence of a thermal treatment (induced by welding) on the formation of the melted zone, and by using different tests: four point bending on notched specimens, nano-indentation test, and longitudinal tensile test. In a second part, the author develops the model within the framework of continuum thermodynamics, and explores the numerical issues. The last part deals with the validation of the model for the concerned materials (Ta and TA6V) and melted zone

  3. Excavation effect on thermo hydro- mechanical behaviour of geological barrier

    Heat emitted by nuclear waste has great influences on mechanical and hydraulic properties of the surrounded media and also on the movement of water, vapour and air. Due to the complexity of the phenomena that might take place in a waste repository, an adequate understanding of the behaviour of the barriers is not an easy task. The difficulty of the task is increased by the fact that many effect s are coupled. In order to study these effects, series of coupled thermo-hydro-mechanical formulations are used. The first step in a theoretical development of a fully coupled thermo-hydro-mechanical model for an unsaturated soil, is choosing the adequate and independent variables which would be able to present all significant interaction effects among the different components involved in a coupled process in a deformable unsaturated porous medium with three phases (skeleton, water and air)under heating. The phase changes between liquid and gas, evaporation, condensation, induced moisture transfer under thermal and pore pressure gradients and the effects of moisture distribution on the heat flow are important aspects in non-deformable unsaturated porous media. If the deformation of porous media is considered, the coupling effects among deformation, moisture, and heat should be also regarded in addition to all above aspects. The governing equations are the equation of equilibrium and constitutive law for solid skeleton, mass conservation and fluid transfer for water and air, and Fourier law and conservation equation for energy. Due to the fact that water phase consists of liquid and vapour two sets of transfer equations are used for water phase: Philip and de Vries law for vapour and Darcy law for liquid. Darcy law is also used for air transfer. In the presented formulations, due to the fact that the medium is assumed to be deformable, the effects of deformation on the temperature and suction distribution in soil and the inverse effects must be included. In order to include

  4. Evaluation of the AZ31 cyclic elastic-plastic behaviour under multiaxial loading conditions

    V. Anes


    Full Text Available Components and structures are designed based in their material’s mechanical properties such as Young's modulus or yield stress among others. Often those properties are obtained under monotonic mechanical tests but rarely under cyclic ones. It is assumed that those properties are maintained during the material fatigue life. However, under cyclic loadings, materials tend to change their mechanical properties, which can improve their strength (material hardening or degrade their mechanical capabilities (material softening or even a mix of both. This type of material behaviour is the so-called cyclic plasticity that is dependent of several factors such as the load type, load level, and microstructure. This subject is of most importance in design of structures and components against fatigue failures in particular in the case of magnesium alloys. Magnesium alloys due to their hexagonal compact microstructure have only 3 slip planes plus 1 twining plane which results in a peculiar mechanical behaviour under cyclic loading conditions especially under multiaxial loadings. Therefore, it is necessary to have a cyclic elastic-plastic model that allows estimating the material mechanical properties for a certain stress level and loading type. In this paper it is discussed several aspects of the magnesium alloys cyclic properties under uniaxial and multiaxial loading conditions at several stress levels taking into account experimental data. A series of fatigue tests under strain control were performed in hour glass specimens test made of a magnesium alloy, AZ31BF. The strain/stress relation for uniaxial loadings, axial and shear was experimentally obtained and compared with the estimations obtained from the theoretical elastic-plastic models found in the state-of-the-art. Results show that the AZ31BF magnesium alloy has a peculiar mechanical behaviour, which is quite different from the steel one. Moreover, the state of the art cyclic models do not capture in

  5. Thermo-Mechanical Behaviour of Flax-Fibre Reinforced Epoxy Laminates for Industrial Applications

    Giuseppe Pitarresi


    Full Text Available The present work describes the experimental mechanical characterisation of a natural flax fibre reinforced epoxy polymer composite. A commercial plain woven quasi-unidirectional flax fabric with spun-twisted yarns is employed in particular, as well as unidirectional composite panels manufactured with three techniques: hand-lay-up, vacuum bagging and resin infusion. The stiffness and strength behaviours are investigated under both monotonic and low-cycle fatigue loadings. The analysed material has, in particular, shown a typical bilinear behaviour under pure traction, with a knee yield point occurring at a rather low stress value, after which the material tensile stiffness is significantly reduced. In the present work, such a mechanism is investigated by a phenomenological approach, performing periodical loading/unloading cycles, and repeating tensile tests on previously “yielded” samples to assess the evolution of stiffness behaviour. Infrared thermography is also employed to measure the temperature of specimens during monotonic and cyclic loading. In the first case, the thermal signal is monitored to correlate departures from the thermoelastic behaviour with the onset of energy loss mechanisms. In the case of cyclic loading, the thermoelastic signal and the second harmonic component are both determined in order to investigate the extent of elastic behaviour of the material.

  6. The Behaviour of Various Graphites under Neutron Irradiation

    The change of graphite properties under neutron irradiation, which is quite important for reactor designers, has been investigated closely for several years, and results have been reported in detail by several authors. The goal of these irradiation experiments was the quantitative determination of property changes as a function of irradiation dose and temperature. The concern of our own irradiation programme, which is sponsored by the Ministry of Atomic Affairs of the Federal Republic of Germany, was to study the behaviour of a wide range of reactor-grade graphites under controlled irradiation conditions. In the first part of the paper, radiation damage as a function of different types of artificial graphite is dealt with. The graphite types differed only by their degree of crystalline order, even though they were produced under the same graphitizing conditions. The differences are caused by the different graphitizabilities of the raw materials. The dependence oí the radiation damage on the graphite type seems to be of fundamental importance for the development of reactor-grade graphites with respect to various applications. Within one group the physical properties are changed in different ways for different graphite types. The differences of the unirradiated samples remain largely unchanged or are even more pronounced after irradiation. Mechanical properties, such as strength, Young's Modulus and thermal expansion, fall into this group. The well-known Wigner growth of various graphites under irradiation was studied systematically. Furthermore, such properties are reported which are levelled out to a final value under the same irradiation conditions even when the raw materials are different. This is true for the thermal and electrical conductivity, the magnetic susceptibility and to some extent for the lattice dimensions of the graphites. Finally, the effect of irradiation on the pore distribution of the various graphites is discussed. The second section ol the

  7. Analysis of the mechanical behaviour of the ITER magnet system

    The International Thermonuclear Experimental Reactor (ITER) is a tokamak fusion device with the objective of demonstrating controlled ignition and an extended burn for a duration sufficient to achieve stationary conditions. The design of ITER will be based on extensive new design work supported by new physical and technological results. As part of the ITER Engineering Design Activities, the mechanical behaviour of the toroidal field coil (TF coil) system during normal operating conditions and fault conditions has to be analyzed. The displacements and/or stresses in the components must be limited to prevent mechanical failure of parts of the overall structure. These Engineering Design Activities are supported by R and D programs in the European Union. This final report describes the work carried out by ECN to develop a finite element model (FE model) of the TF-coil system which is suitable for the analysis of the mechanical behaviour and presents results obtained with this model. For the analysis of the mechanical behaviour, a large three dimensional (3D) non-linear finite element model has been developed. With this FE model a large number of load cases has been analyzed which correspond with several time points during multiple pulses. (orig./WL)

  8. INPR ACPR utilization in fuel behaviour studies under accidental condition

    Negut, Gheorghe; Popov, Mircea [Institute for Nuclear Power Reactors, Pitesti (Romania)


    This paper is dedicated to the experimental program, investigating CANDU type fuel behaviour in transient condition, as well as the facilities supporting this program. The tests Reactivity Initiated Accident type. The experiments were performed within TRIGA ACPR facility, installed at INSTITUTE for NUCLEAR POWER REACTORS, Pitesti, ROMANIA. Studies of the safety issues took a great international developement during last years. In USA, Japan, owners of the similar reactors, and USSR there are a big commitment to such programs, intended to establish the nuclear fuel behaviour under RIA-conditions. In our country, too, there are programs aiming a complete testing of the CANDU type fuels. As it is known, RIA is not a CANDU specific accident, but the fuel behaviour in such conditions can give useful informations on the fuel cladding failure threshold and about reflooding post LOCA heat transfer condition. Based on some papers and specific requirements it was initiated and developed a safety research program on CANDU type fuel using the ACPR. The paper describes the reactor,test capsule, instrumentation, fuel samples, tests, post irradiation results. (orig.)

  9. Thermo-hydro-mechanical behaviour of Boom clay

    This thesis studied the thermo-hydro-mechanical properties of Boom clay, which was chosen to be the host material for the radioactive waste disposal in Mol, Belgium. Firstly, the research was concentrated on the soil water retention properties and the hydro-mechanical coupling by carrying out axial compression tests with suction monitoring. The results obtained permitted elaborating a rational experimental procedure for triaxial tests. Secondly, the systems for high pressure triaxial test at controlled temperature were developed to carry out compression, heating, and shearing tests at different temperatures. The obtained results showed clear visco-elasto-plastic behaviour of the soil. This behaviour was modelled by extending the thermo-elasto-plastic model of Cui et al. (2000) to creep effect. (author)

  10. Spent HIFAR fuel elements behaviour under extended dry storage

    Previously unpublished observations of the behaviour of HIFAR spent fuel under extended dry storage conditions are reported. The two fuel elements EC802 (Mark III type) were irradiated in 1966, first examined in hot cells in 1967 and again examined in hot cells in 1983 following 16 years of stage, 11 years of which were in the ANSTO engineered dry storage facility. The elements showed negligible deterioration over this extended dry storage period, lending considerable confidence to the viability of dry storage technologies for the long term storage of spent aluminium clad research reactor fuels. 1 tab., 1 fig., 17 ills

  11. Transition in fluctuation behaviour of normal liquids under high pressures

    Postnikov, Eugene B.; Chora&¸zdot; ewski, Mirosław


    We explore the behaviour of the inverse reduced density fluctuations and the isobaric expansion coefficient using α , ω-dibromoalkanes as an example. Two different states are revealed far from the critical point: the region of exponentially decaying fluctuations near the coexistence curve and the state with longer correlations under sufficiently high pressures. The crossing of the isotherms of the isobaric expansion coefficient occurs within the PVT range of the mentioned transition. We discuss the interplay of this crossing with the changes in molecular packing structure connected with the analysed function of the density, which represents inverse reduced volume fluctuations.

  12. Study on Mechanical and Physical Behaviour of Hybrid GFRP

    Nor Bahiyah Baba; Ahmad Syakirin Suhaimi; Muhamad Asyraf Mohd Amin; Alias Mohd


    The paper discusses the mechanical and physical behaviour of hybrid glass fibre reinforced plastic (GFRP). Hybrid GFRP was fabricated by three different types of glass fibre, namely, 3D, woven, and chopped, which were selected and combined with mixture of polyester resin and hardener. The hybrid GFRP was investigated by varying three parameters which were the composite volume fractions, hybrid GFRP arrangement, and single type fibre. The hybrid GFRP was fabricated by using open mould hand lay...

  13. Mechanical behaviour of adhesive joints such as a concrete epoxy

    Aguiar, J. L. Barroso de; Reymond, M. C.; Paillère, A. M.


    The sample DCB is separated in two parts then sticked by epoxy to study adhesion between concrete and epoxy resin. The crack propagation was initiated at a notch in a double cantilever beam. The notch of the test sample was opened by an Instron tensile machin. The crack extension was followed through direct optical observations. The displacement was measured by an extensometer. During the fracture test, mechanical behaviour of the sample was monitored with various techniques: the experimental...

  14. Thermo-mechanical behaviour of a compacted swelling clay

    TANG, Anh Minh; Cui, Yu-Jun; Barnel, Nathalie


    International audience Compacted unsaturated swelling clay is often considered as a possible buffer material for deep nuclear waste disposal. An isotropic cell permitting simultaneous control of suction, temperature and pressure was used to study the thermo-mechanical behaviour of this clay. Tests were performed at total suctions ranging from 9 to 110 MPa, temperature from 25 to 80 °C, isotropic pressure from 0.1 to 60 MPa. It was observed that heating at constant suction and pressure indu...

  15. Nuclear cooling tower submitted to shrinkage; behaviour under weight and wind

    A numerical formulation to analyse nuclear cooling tower submitted to creep and shrinkage of concrete is presented in this paper. Both humidity effects and non-linear mechanical behaviour of the constitutive materials are taken into account. Moisture migration is described using a single diffusion equation in which the relative humidity is the driving force and delayed strains are obtained in a phenomenological way. To capture the time-dependent behaviour, an extension of a continuum plasticity model which incorporates viscous behaviour, has been developed and its main parameters are obtained from experimental results. The effects produced by internal stresses that result from time-dependent deformations are finally presented for nuclear tower under services loading

  16. Behaviour of M30 Grade concrete with confinement under axial compression

    C.Vinil Babu; V.K.Visweswara Rao


    The strength and durability of concrete have undergone continuous improvement. Over the years and these improved materials are now commonly used. In the present experimental investigation the behaviour of M30 grade concrete with and without confinement for different percentages of replacement of silica fume is studied under axial compression as per IS mix design. The 150mm x 300mm cylindrical specimens were cast with and without confinement and investigating the mechanical prop...

  17. Structural and mechanical behaviour of LLDPE/HNT nanocomposite films

    Čermák, M.; Kadlec, P.; Šutta, P.; Polanský, R.


    The paper briefly describes structural and mechanical influences of Halloysite nanotubes (HNT) in different level of fulfilment (0, 1, 3, 7 wt%) in the LLDPE commonly used in the cable industry. The influence of HNT on the polymer has been observed and evaluated through the average crystallite size and the micro- deformation by X-Ray diffractometry and the imaging of SEM. Despite the certain inter-phase tension between the polymer and HNT, the influence on the mechanical and combustion behaviour was observed. Measurement showed a higher content of agglomerates in the sample with 7 wt% HNT fulfilment.

  18. To Cooperate or Not to Cooperate: Why Behavioural Mechanisms Matter.

    Bernard, Arthur; André, Jean-Baptiste; Bredeche, Nicolas


    Mutualistic cooperation often requires multiple individuals to behave in a coordinated fashion. Hence, while the evolutionary stability of mutualistic cooperation poses no particular theoretical difficulty, its evolutionary emergence faces a chicken and egg problem: an individual cannot benefit from cooperating unless other individuals already do so. Here, we use evolutionary robotic simulations to study the consequences of this problem for the evolution of cooperation. In contrast with standard game-theoretic results, we find that the transition from solitary to cooperative strategies is very unlikely, whether interacting individuals are genetically related (cooperation evolves in 20% of all simulations) or unrelated (only 3% of all simulations). We also observe that successful cooperation between individuals requires the evolution of a specific and rather complex behaviour. This behavioural complexity creates a large fitness valley between solitary and cooperative strategies, making the evolutionary transition difficult. These results reveal the need for research on biological mechanisms which may facilitate this transition. PMID:27148874

  19. Study on Mechanical and Physical Behaviour of Hybrid GFRP

    Nor Bahiyah Baba


    Full Text Available The paper discusses the mechanical and physical behaviour of hybrid glass fibre reinforced plastic (GFRP. Hybrid GFRP was fabricated by three different types of glass fibre, namely, 3D, woven, and chopped, which were selected and combined with mixture of polyester resin and hardener. The hybrid GFRP was investigated by varying three parameters which were the composite volume fractions, hybrid GFRP arrangement, and single type fibre. The hybrid GFRP was fabricated by using open mould hand lay-up technique. Mechanical testing was conducted by tensile test for strength and stiffness whereas physical testing was performed using water absorption and hardness. These tests were carried out to determine the effect of mechanical and physical behaviour over the hybrid GFRP. The highest volume fraction of 0.5 gives the highest strength and stiffness of 73 MPa and 821 MPa, respectively. Varying hybrid fibre arrangement which is the arrangement of chopped-woven-3D-woven-chopped showed the best value in strength of 66.2 MPa. The stiffness is best at arrangement of woven-chopped-woven-chopped-woven at 690 MPa. This arrangement also showed the lowest water absorption of 4.5%. Comparing the single fibre type, woven had overtaken the others in terms of both mechanical and physical properties.

  20. Flexural behaviour of selected plants under static load

    F. J. Sutili


    Full Text Available One of the principal purposes of soil bioengineering is the application of vegetation layers from a civil engineering point of view. Living plants are used to reinforce slopes and to control erosion. For a standardised implementation, it is essential to quantify the effectiveness and to assess technical parameters for such bioengineering systems. The objective of this study is to investigate the flexibility of stems and branches of different riparian species of the area of Southern Brazil suitable for soil bioengineering (Phyllanthus sellowianus Müll. Arg., Sebastiania schottiana (Müll. Arg. Müll. Arg., Salix humboldtiana Willd., and Salix×rubens Schrank. Fifty specimens (green stem samples were collected in the surroundings of Santa Maria, state of Rio Grande do Sul, Brazil, and subjected to static bending tests. Their overall deformation behaviour (elastic and plastic is of crucial importance for bioengineering systems. Thus, additional to the state of the art of material parameters, a new parameter is introduced: the "angle of flexibility". This parameter describes the elastic and plastic deformation behaviour of a plant under load in a more engineering practival experience. The results show that the species of Phyllanthus sellowianus is the most flexible species, followed by Sebastiania schottiana, Salix humboldtiana and Salix×rubens.

  1. Behaviour of bituminized ion-exchangers under repository conditions

    This is a final report containing all the research activities and results from the period 13 July 1997-28 February 2001. The purpose of the research was to study the ageing behaviour of bituminized ion-exchanger product under simulated repository conditions. The chosen temperature in this study was 5-8 deg. C and the equilibration solution used was artificial concrete water to simulate the conditions in the final disposal. The aim was to study the properties of wetted product as a release barrier for such important waste nuclides as Sr-90 and Cs-137, which are normal constituents of the bituminized ion-exchangers. All the nine exchanged waters were analysed by ion chromatography (IC) including the follow-up of the water absorption of the samples. All the samples, which were picked up for microscopic examination, have also been analysed. A saturation-elution test was performed with one diffusion sample using tritium (H-3) as a tracer. The results have been presented and further modelling will be performed later. Further two diffusion samples were tested using H-3, Na-22 and Cl-36 as radioactive tracers. The equilibration solution was artificial concrete ground water spiked with H-3 and Na-22 and in the other case with H-3 and Cl-36. Tritium was an internal reference when comparing the results of the equilibration behaviour of Na-22 and Cl-36. From the radioactive input cells samples were taken as a function of time to monitor the equilibration process. Elution of the samples and modelling of the results will be performed later. Na-22 and Cl-36 were chosen to demonstrate the behaviour of a simple anion and cation. Diffusion tests with important waste nuclides Sr-90 and Cs-137 have been scheduled to years 2001-2002. The aim of the performed research project was to study the barrier properties of the bituminized product. The measured parameters and modelling of the results will reflect the behaviour of the wetted product as a part of the multibarrier system providing

  2. Degradation behaviour of fiber reinforced plastic under electron beam irradiation

    Various mechanical properties of four kinds of glass fiber-reinforced plastics irradiated with electron beams were examined at three temperatures; room temperature, 123 K and 77 K. Dynamic viscoelastic properties were measured, and fractography by means of scanning electron microscopy was observed in order to clarify degradation behaviour. A considerable decrease in interlaminar shear strength (ILSS) at room temperature was observed above 60 MGy. On the other hand, the three-point bending strength at 77 K and the ILSS at 123 K decreased with increasing irradiation. Fractography reveals that the degradation of the interface layer between matrix resin and fiber plays an important role in the strength reduction at 123 K and 77 K. These findings suggest that the interface between matrix resin and fiber loses its bondability at 123 K arid 77 K after electron beam irradiation. (author)

  3. Calculation of mechanical strength of the bolts of the flanged joints of LWR-type reactor pressure vessels (with particular emphasis on the behaviour under critical internal excess pressure, acting like a ''safety valve''). 5. Technical report

    The reactor pressure vessel has to be made absolutely fail-safe towards excess primary loads (internal pressure). For this purpose, the vessel is equipped with safety valves (e.g. at the pressurizer) which normally are fully sufficient to master any pressure excursion. Nevertheless, a deterministic safety approach requires additional measures to ensure, in case of safety valve failure, control of the pressure so as to prevent reactor pressure vessel bursting. One way to achieve this is to make the flange joints plastify so strongly in the course of a pressure transient that the flange gap will sufficiently widen and thus behave like a 'safety valve'. In order to keep damage as small as possible, these parts should be easy to replace so that the bolts, or rather the washers, seem to be appropriate for modification. Tests have been made to ascertain whether reduction of bolt cross-sectional area (increase in admissible stress), or insertion of suitable washers is the best way to achieve reliable behaviour under normal conditions and also additional function in terms of a safety valve in case of pressure transients. For this purpose, model calculations have been made for all possible flange joints whith all possible stress variations and bolt dimensions. The event simulated is the ATWS', and the strength computations and stress analyses made for the flange joints of the pressure vessel of the Biblis reactor, unit B, are taken as an example. Main attention has been given to the forces affecting the bolts and to the forces acting between the reactor vessel head flange and the vessel flange under internal excess pressure. For assessment of the thermodynamic processes in case of an ATWS, the calculations made for the Grafenrheinfeld reactor have been taken as a basis. (orig.)

  4. Operational Behaviour of a Complex System Under Priority Repair Echelons

    Anil Kumar


    Full Text Available A mathematical model is set up to evaluate the reliability of a complex system comprising two subsystems (with stand by redundancy in one subsystem. The failure and repair of units for both the subsystems follow exponential and general time distributions respectively. The switching over device for standby subsystem is not perfect and its repair is opportunistic. The repair for both subsystems is carried out under priority. The concept of waiting time for the repair of failed units in staidly subsystem has also been introduced. Supplementary variable and Laplace Transform techniques have been applied to obtain the transient state probabilities for such a system. From these pointwise availability has been evaluated. In the end, a particular case when repair follows exponential time distribution has been derived and asymptotic behaviour of such a system has also been examined.

  5. Molecular Mechanisms Underlying Pituitary Pathogenesis.

    Sapochnik, Melanie; Nieto, Leandro Eduardo; Fuertes, Mariana; Arzt, Eduardo


    During the last years, progress has been made on the identification of mechanisms involved in anterior pituitary cell transformation and tumorigenesis. Oncogene activation, tumor suppressor gene inactivation, epigenetic changes, and microRNAs deregulation contribute to the initiation of pituitary tumors. Despite the high prevalence of pituitary adenomas, they are mostly benign, indicating that intrinsic mechanisms may regulate pituitary cell expansion. Senescence is characterized by an irreversible cell cycle arrest and represents an important protective mechanism against malignancy. Pituitary tumor transforming gene (PTTG) is an oncogene involved in early stages of pituitary tumor development, and also triggers a senescence response by activating DNA-damage signaling pathway. Cytokines, as well as many other factors, play an important role in pituitary physiology, affecting not only cell proliferation but also hormone secretion. Special interest is focused on interleukin-6 (IL-6) because its dual function of stimulating pituitary tumor cell growth but inhibiting normal pituitary cells proliferation. It has been demonstrated that IL-6 has a key role in promoting and maintenance of the senescence program in tumors. Senescence, triggered by PTTG activation and mediated by IL-6, may be a mechanism for explaining the benign nature of pituitary tumors. PMID:26718581

  6. Effect of Microstructure on the Electro-Mechanical Behaviour of Cu Films on Polyimide

    Berger, J.; Glushko, O.; Marx, V. M.; Kirchlechner, C.; Cordill, M. J.


    Metal films on polymer substrates are commonly used in flexible electronic devices and may be exposed to large deformations during application. For flexible electronics, the main requirement is to remain conductive while stretching and compressing. Therefore, the electro-mechanical behaviour of 200-nm-thick Cu films on polyimide with two different microstructures (as-deposited and annealed) were studied by executing in situ fragmentation experiments with x-ray diffraction, under an atomic force microscope, and with 4-point probe resistance measurements in order to correlate the plastic deformation with the electrical behaviour. The three in situ techniques clearly demonstrate different behaviours controlled by the microstructure. Interestingly, the as-deposited film with a bi-modal microstructure is more suited for flexible electronic applications than an annealed film with homogenous 1- µm-sized grains. The as-deposited film reaches a higher yield stress, with unchanged electrical conductivity, and does not show extensive surface deformation during straining.

  7. Experimental study on the hydro-mechanical coupling behaviour of highly compacted expansive clay

    Tang, Anh-Minh; Cui, Yu-Jun


    Highly compacted expansive clays have been usually considered as a possible material for sealing and backfill in deep geological disposal of radioactive waste. In this condition, the material is simultaneously subjected to water infiltration from the geological barrier and stresses generated by the swelling of engineered barriers in confined conditions. Its behaviour under hydro-mechanical loading is essential to the safe design of the whole storage system. In the present work, MX80 bentonite...

  8. Temperature effect on the poro-mechanical or hydraulic behaviour of a carbonated rock and a mortar: experimental studies

    The main objective of this study is to evaluate the temperature effect on the hydraulic and poro-mechanical behaviour of a limestone. Many experimental tests (porosity and permeability measurements, uniaxial and hydrostatic compressions tests) were carried out in order to study the thermal treatments effect and so the thermal microcracking effect on rock behaviour. Moreover, an experimental device for permeability measurements under high temperatures (until 200 C) was realized. This experimental device permitted to study the permeability variation of the limestone under thermal stresses. Finally, the behaviour of cementitious materials was studied; the temperature effect on the permeability of a mortar was examined. (author)

  9. Numerical model for thermal and mechanical behaviour of a CANDU 37-element bundle

    Prediction of transient fuel bundle deformations is important for assessing the integrity of fuel and the surrounding structural components under different operating conditions including accidents. For numerical simulation of the interactions between fuel bundle and pressure tube, a reliable numerical bundle model is required to predict thermal and mechanical behaviour of the fuel bundle assembly under different thermal loading conditions. To ensure realistic representations of the bundle behaviour, this model must include all of the important thermal and mechanical features of the fuel bundle, such as temperature-dependent material properties, thermal viscoplastic deformation in sheath, fuel-to-sheath interactions, endplate constraints and contacts between fuel elements. In this paper, we present a finite element based numerical model for predicting macroscopic transient thermal-mechanical behaviour of a complete 37-element CANDU nuclear fuel bundle under accident conditions and demonstrate its potential for being used to investigate fuel bundle to pressure tube interaction in future nuclear safety analyses. This bundle model has been validated against available experimental and numerical solutions and applied to various simulations involving steady-state and transient loading conditions. (author)

  10. Mechanical behaviour of composite materials made by resin film infusion

    Casavola C.


    Full Text Available Innovative composite materials are frequently used in designing aerospace, naval and automotive components. In the typical structure of composites, multiple layers are stacked together with a particular sequence in order to give specific mechanical properties. Layers are organized with different angles, different sequences and different technological process to obtain a new and innovative material. From the standpoint of engineering designer it is useful to consider the single layer of composite as macroscopically homogeneous material. However, composites are non homogeneous bodies. Moreover, layers are not often perfectly bonded together and delamination often occurs. Other violations of lamination theory hypotheses, such as plane stress and thin material, are not unusual and in many cases the transverse shear flexibility and the thickness-normal stiffness should be considered. Therefore the real behaviour of composite materials is quite different from the predictions coming from the traditional lamination theory. Due to the increasing structural performance required to innovative composites, the knowledge of the mechanical properties for different loading cases is a fundamental source of concern. Experimental characterization of materials and structures in different environmental conditions is extremely important to understand the mechanical behaviour of these new materials. The purpose of the present work is to characterize a composite material developed for aerospace applications and produced by means of the resin film infusion process (RFI. Different tests have been carried out: tensile, open-hole and filled-hole tensile, compressive, openhole and filled-hole compressive. The experimental campaign has the aim to define mechanical characteristics of this RFI composite material in different conditions: environmental temperature, Hot/Wet and Cold.

  11. Metacognitive mechanisms underlying lucid dreaming.

    Filevich, Elisa; Dresler, Martin; Brick, Timothy R; Kühn, Simone


    Lucid dreaming is a state of awareness that one is dreaming, without leaving the sleep state. Dream reports show that self-reflection and volitional control are more pronounced in lucid compared with nonlucid dreams. Mostly on these grounds, lucid dreaming has been associated with metacognition. However, the link to lucid dreaming at the neural level has not yet been explored. We sought for relationships between the neural correlates of lucid dreaming and thought monitoring. Human participants completed a questionnaire assessing lucid dreaming ability, and underwent structural and functional MRI. We split participants based on their reported dream lucidity. Participants in the high-lucidity group showed greater gray matter volume in the frontopolar cortex (BA9/10) compared with those in the low-lucidity group. Further, differences in brain structure were mirrored by differences in brain function. The BA9/10 regions identified through structural analyses showed increases in blood oxygen level-dependent signal during thought monitoring in both groups, and more strongly in the high-lucidity group. Our results reveal shared neural systems between lucid dreaming and metacognitive function, in particular in the domain of thought monitoring. This finding contributes to our understanding of the mechanisms enabling higher-order consciousness in dreams. PMID:25609624

  12. Molecular Mechanisms Underlying Hepatocellular Carcinoma

    Christian Trepo


    Full Text Available Hepatocarcinogenesis is a complex process that remains still partly understood. That might be explained by the multiplicity of etiologic factors, the genetic/epigenetic heterogeneity of tumors bulks and the ignorance of the liver cell types that give rise to tumorigenic cells that have stem cell-like properties. The DNA stress induced by hepatocyte turnover, inflammation and maybe early oncogenic pathway activation and sometimes viral factors, leads to DNA damage response which activates the key tumor suppressive checkpoints p53/p21Cip1 and p16INK4a/pRb responsible of cell cycle arrest and cellular senescence as reflected by the cirrhosis stage. Still obscure mechanisms, but maybe involving the Wnt signaling and Twist proteins, would allow pre-senescent hepatocytes to bypass senescence, acquire immortality by telomerase reactivation and get the last genetic/epigenetic hits necessary for cancerous transformation. Among some of the oncogenic pathways that might play key driving roles in hepatocarcinogenesis, c-myc and the Wnt/β-catenin signaling seem of particular interest. Finally, antiproliferative and apoptosis deficiencies involving TGF-β, Akt/PTEN, IGF2 pathways for instance are prerequisite for cancerous transformation. Of evidence, not only the transformed liver cell per se but the facilitating microenvironment is of fundamental importance for tumor bulk growth and metastasis.

  13. A possible realization of Einstein's causal theory underlying quantum mechanics

    It is shown that a new microscopic mechanics formulated earlier can be looked upon as a possible causal theory underlying quantum mechanics, which removes Einstein's famous objections against quantum theory. This approach is free from objections raised against Bohm's hidden variable theory and leads to a clear physical picture in terms of familiar concepts, if self interactions are held responsible for deviations from classical behaviour. The new level of physics unfolded by this approach may reveal novel frontiers in high-energy physics. (author)

  14. Delamination behaviour of GdBCO coated conductor tapes under transverse tension

    Gorospe, A. [Department of Mechanical Design Engineering, Andong National University, Andong 760-749 (Korea, Republic of); Department of Engineering, Aurora State College of Technology, Baler 3200 (Philippines); Nisay, A. [Department of Mechanical Design Engineering, Andong National University, Andong 760-749 (Korea, Republic of); Dizon, J.R. [Department of Mechanical Design Engineering, Andong National University, Andong 760-749 (Korea, Republic of); College of Engineering and Architecture, Bataan Peninsula State University, Balanga 2100 (Philippines); Shin, H.S., E-mail: [Department of Mechanical Design Engineering, Andong National University, Andong 760-749 (Korea, Republic of)


    Highlights: •Installation of a test frame which gives precisely aligned transverse load. •Investigation of I{sub c} degradation behaviour depending on the type of sample delamination. •Inhomogeneity of the CC tapes caused large variation on delamination strength. •SEM and EDS analysis of delamination sites under transverse loading. -- Abstract: The electromechanical property behaviour of 2G coated conductor (CC) tapes fabricated by multi-layer deposition process both in the in-plane and transverse direction should be understood. The CC tapes are used in the fabrication of epoxy resin-impregnated coils. In such case, the Lorentz force due to the high magnetic field applied as well as the thermal stress due to the difference in coefficient of thermal expansion (CTE) among constituent layers during cooling to cryogenic temperature will induce transversely applied load to the surface of CC tapes in coils. Hence, the CC tape should have a good mechanical property in the transverse direction in order to maintain its superior performance under magnetic field. In this study, a test frame which gives precisely aligned transverse load was devised. Using the fixture, the delamination behaviours including the delamination strength of the GdBCO CC tapes under transverse tensile loading were investigated. Large variation on the delamination strength of the CC tapes was recorded and might have resulted from the slit edge effect and the inhomogeneity of the CC tapes. The I{sub c} degradation behaviour under transverse load was related to the location where delamination occurred in the sample.

  15. Behaviour of M30 Grade concrete with confinement under axial compression

    C.Vinil Babu


    Full Text Available The strength and durability of concrete have undergone continuous improvement. Over the years and these improved materials are now commonly used. In the present experimental investigation the behaviour of M30 grade concrete with and without confinement for different percentages of replacement of silica fume is studied under axial compression as per IS mix design. The 150mm x 300mm cylindrical specimens were cast with and without confinement and investigating the mechanical properties like axial compressive strength and stress – strain behaviour. It was observed that the confinement of concrete has increased the 28days strength for different percentages of confinement and that the peak stress and corresponding strain at peak stress increased with increase in percentages of confinement

  16. Investigation of the hydro-mechanical behaviour of fouled ballast

    Yu-jun CUI; Trong Vinh DUONG; Anh Minh TANG; Jean-Claude DUPLA; Nicolas CALON; Alain ROBINET


    In this study,a fouled ballast taken from the site of Sénissiat,France,was investigated.For the hydraulic behaviour,a large-scale cell was developed allowing drainage and evaporation tests to be carried out with monitoring of both suction and volumetric water content at various positions of the sample.It was observed that the hydraulic conductivity of fouled ballast is decreasing with suction increase,as for common unsaturated soils.The effect of fines content was found to be negligible.For the mechanical behaviour,both monotonic and cyclic triaxial tests were carried out using a large-scale triaxial cell.Various water contents were considered.The results were interpreted in terms of shear strength and permanent axial strain.It appeared that the water content is an important factor to be accounted for since any increase of water content or degree of saturation significantly decreases the shear strength and increases the permanent strain.Constitutive modelling has been attempted based on the experimental results.The model in its current state is capable of describing the effects of stress level,cycle number and water content.

  17. Multi-scale modelling of AISI H11 martensitic tool steel surface anisotropic mechanical behaviour

    Zouaghi Ahmed


    Full Text Available In this work, a numerical investigation is carried out on the anisotropic and heterogeneous behaviour of the AISI H11 martensitic tool steel surface using finite element method and a multi-scale approach. An elasto-viscoplastic model that considers nonlinear isotropic and kinematic hardenings is implemented in the finite elements code ABAQUS using small strain assumption. The parameters of the constitutive equations are identified using macroscopic quasi-static and cyclic material responses by the mean of a localization rule. Virtual realistic microstructures, consisting of laths and grains, are generated using particular Voronoï tessellations. These microstructures consider the specific crystallographic orientations α’/γ. Finite element investigation is then performed. The local heterogeneous and anisotropic behaviour of the surface as well as the subsurface is shown under quasi-static and cyclic mechanical loadings. The laths morphology and crystallographic orientation have an important impact on the local mechanical fields.

  18. Dynamic Behaviour of Concrete Sandwich Panel under Blast Loading

    Dong Yongxiang


    Full Text Available Surface contact explosion experiments were performed to study the dynamic behaviour of concrete sandwich panel subjected to blast loading. Experimental results have shown that there are four damage modes explosion cratering, scabbing of the backside, radial cracking induced failure, and circumferential cracking induced failure. It also illustrates that different foam materials sandwiched in the multi-layered medium have an important effect on damage patterns. Due to the foam material, the stress peak decreases one order of magnitude and the duration is more than four times that of the panel without the soft layer by numerical simulation. Additionally, the multi layered medium with concrete foam demonstrates the favourable protective property compared with that of aluminum foam. Meanwhile, the optimal analysis of the thickness of the foam material in the sandwich panel was performed in terms of experimental and numerical analyseis. The proper thickness proportion of soft layer is about 20 percent to the total thickness of sandwich panel under the conditions in this study.Defence Science Journal, 2009, 59(1, pp.22-29, DOI:  

  19. Corrosion behaviour of fireside materials under oxyfuel conditions

    Tuurna, Satu; Pohjanne, Pekka; Kinnunen, Tuomo; Jauhiainen, Petra [Research Centre of Finland, Espoo (Finland)


    Oxyfuel combustion is widely seen as a major option to facilitate carbon capture and storage (CCS) from future boiler plants utilizing clean coal technologies. Flue gas recirculation can increase the levels of fireside CO{sub 2}, SO{sub 2} and moisture, and thus promote fouling and corrosion. In this work, the oxidation behaviour of typical power plant steels was studied in the simulated oxyfuel conditions (3.6% O{sub 2}-60% CO{sub 2}-30% H{sub 2}O-6,4% Ar). The experiments were carried out in multi-sample furnaces in a temperature range between 580 and 650 C. Test duration was up to 1000 h. Corrosion resistance was evaluated through metallographic examination and mass change measurements. The results are presented and compared to corresponding results from simulated air firing conditions (1.8% O{sub 2}-74.2% N{sub 2}-16% CO{sub 2}O-8%H{sub 2}O Ar). This paper presents the oxidation performance of alloys T22 (10CrMo9-10), X20CrMoV11-1, TP347HFG, HR3C and Sanicro 25 under simulated combustion conditions. (orig.)

  20. Microscopic approaches for understanding the mechanical behaviour of reinforcement in composites

    Durville, Damien


    An approach to the mechanical behaviour of textile composites at the scale of their constituting fibres, using an implicit finite element simulation code, is proposed in this chapter. The approach is based on efficient methods and algorithms to detect and take into account contact-friction interactions between elementary fibres. It allows one to model samples of woven textile composites made of a few hundreds of fibres, with an elastic matrix. The approach is employed first to determine the initial configuration of woven fabric samples, before applying to them various loadings in order to identify their mechanical properties under various solicitations

  1. A review of mechanical behaviour and stress effects in hard superconductors

    The mechanical properties of type II superconducting materials are reviewed as well as the effect of stress on the superconducting properties of these materials. The bcc alloys Nb-Ti and Nb-Zr exhibit good strength and extensive ductility at room temperature. Mechanical tests on these alloys at 4.2 K revealed serrated stress-strain curves, non-linear elastic effects, and reduced ductility. The non-linear behaviour is probably due to twinning and de-twinning or a reversible stress-induced martensitic transformation. The brittle A-15 compound superconductors, such as Nb3Sn and V3Ga, exhibit unusual elastic properties and structural instabilities at cryogenic temperatures. Multifilamentary composites consisting of superconducting filaments in a normal metal matrix are normally used for superconducting devices. The mechanical properties of alloy and compound composites, tapes, as well as composites of niobium carbonitride chemically vapour deposited on high strength carbon fibres are presented. Hysteretic stress-strain behaviour in the metal matrix composites produces significant heat generation, an effect which may lead to degradation in performance of high field magnets. Measurements of the critical current density, Jsub(c), under stress in a magnetic field are reported. Modest stress-reversible degradation in Jsub(c) is observed in Nb-Ti composites while more serious degradation is found in Nb3Sn samples. The importance of mechanical behaviour on device performance is discussed. (author)

  2. Proceedings of a specialist meeting on the behaviour of water reactor fuel elements under accident conditions

    The contributions of this meeting report experimental, numerical and research investigations on the oxidation behaviour of zircaloy in case of a loss-of-coolant accident (LOCA), analysis of the kinetics of the oxidation rate, very high temperature behaviour of fuel rod claddings (failure mechanics, ballooning), the interaction between cladding and fuel, the mechanical behaviour of zircaloy, etc. Numerous experimental and computer code analysis results are given

  3. Behaviour and failure of C-Mn steel in presence of ageing under strain

    As carbon-manganese (C-Mn) steels are largely used in various mechanical applications, and more particularly in secondary circuit pipes of pressurized water nuclear reactors (PWR), this research thesis reports the behaviour and failure modelling of such a steel within a large temperature domain (between 20 and 350 deg C). Tensile tests have been performed on smooth samples and on notches axisymmetric samples, and tear tests have been performed on CT samples. The model of Es trin Kubin-McCormick which takes ageing under strain into account has been used to simulate most of the effects of ageing under strain: negative sensitivity of flow stress to strain rate, Luders bands, PLC effect, modification of tensile mechanical properties, so on. The model is applied to the considered samples. In order to predict the failure of notched specimens, a failure local approach has been applied

  4. Tribological behaviour of conventional Al–Sn and equivalent Al–Pb alloys under lubrication

    J P Pathak; S Mohan


    Two compositions of conventional aluminium base alloys were selected and equal amounts of tin and lead as a soft phase were incorporated separately. Impeller mixing and chill casting technique were employed for the preparation of the alloys. Mechanical properties of as cast alloys were evaluated at room temperature. Frictional behaviour of the alloys was studied in detail under lubrication while creating different frictional states by imposing 5–60 kg of normal load on the bearing (bush) mating surface. It was found that aluminium tin and leaded aluminium alloys slightly differ in mechanical properties. Frictional states created during sliding against steel shaft (hardness 55–60 Rc) under oil lubrication were not much different. Leaded aluminium alloy bushes show marginally lower friction than the conventional ones.

  5. Empathy as a driver of prosocial behaviour: highly conserved neurobehavioural mechanisms across species.

    Decety, Jean; Bartal, Inbal Ben-Ami; Uzefovsky, Florina; Knafo-Noam, Ariel


    Empathy reflects the natural ability to perceive and be sensitive to the emotional states of others, coupled with a motivation to care for their well-being. It has evolved in the context of parental care for offspring, as well as within kinship bonds, to help facilitate group living. In this paper, we integrate the perspectives of evolution, animal behaviour, developmental psychology, and social and clinical neuroscience to elucidate our understanding of the proximate mechanisms underlying empathy. We focus, in particular, on processing of signals of distress and need, and their relation to prosocial behaviour. The ability to empathize, both in animals and humans, mediates prosocial behaviour when sensitivity to others' distress is paired with a drive towards their welfare. Disruption or atypical development of the neural circuits that process distress cues and integrate them with decision value leads to callous disregard for others, as is the case in psychopathy. The realization that basic forms of empathy exist in non-human animals is crucial for gaining new insights into the underlying neurobiological and genetic mechanisms of empathy, enabling translation towards therapeutic and pharmacological interventions. PMID:26644596

  6. Fracture mechanics behaviour of neutron irradiated Alloy A-286

    The effect of fast-neutron irradiation on the fatigue-crack propagation and fracture toughness behaviour of Alloy A-286 was characterized using fracture mechanics techniques. The fracture toughness was found to decrease continuously with increasing irradiation damage at both 24 deg. C and 427 deg. C. In the unirradiated and low fluence conditions, specimens displayed appreciable plasticity prior to fracture, and equivalent Ksub(Ic) values were determined from Jsub(Ic) fracture toughness results. At high irradiation exposure levels, specimens exhibited a brittle Ksub(Ic) fracture mode. The 427 deg. C fracture toughness fell from 129 MPa√m in the unirradiated condition to 35 MPa√m at an exposure of 16.2 dpa (total fluence of 5.2x1022n/cm2). Room temperature fracture toughness values were consistently 40 to 60 percent higher than the 427 deg. C values. Electron fractography revealed that the reduction in fracture resistance was attributed to a fracture mechanism transition from ductile microvoid coalescence to channel fracture. Fatigue-crack propagation tests were conducted at 427 deg. C on specimens irradiated at 2.4 dpa and 16.2 dpa. Crack growth rates at the lower exposure level were comparable to those in unirradiated material, while those at the higher exposure were slightly higher than in unirradiated material. (author)




    Full Text Available Alumina has got some excellent properties like chemical inertness, thermal and mechanical strength against hazardous environment. Alumina is a good ceramic material which is being used for structuralapplications. To enhance the toughness and strength of the body some Zirconia is also used with it. The use of Zirconia in alumina is known as toughening of alumina. One difficulty arises, when alumina and alumina toughened composite are sintered , because the low sinterability of Alumina-Zirconia forced the compact to give very low density body. To overcome this problem alumina and alumina composites are made from slurry method which gives nearly theoretical density. The combined effect of alumina and Zirconia on the phase transformation and microstructure development of heat-treated Alumina-Zirconia composites has been studied. Slurry is prepared by adding water, dispersant, binder and anti-foaming agent. In the present study, Sintering schedule is optimized and kept constant for all samples. After sintering, mechanical behaviour of the composite has been studied.

  8. Microstructural characterisation and constitutive behaviour of alloy RR1000 under fatigue and creep-fatigue loading conditions

    Mechanical behaviour of a nickel-based superalloy, RR1000, has been investigated at 650 deg. C under cyclic and dwell loading conditions. The microstructural characteristics of the alloy have been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the distribution patterns of the dislocations and slip planes have been compared between samples tested under fatigue and creep-fatigue loading conditions. Constitutive behaviour of the alloy was described by a unified constitutive model, where both cyclic plastic and viscoplastic strains were represented by one inelastic strain. The results show that the precipitation state is very stable at 650 deg. C and only minor differences exist in the dislocation arrangements formed under pure fatigue and combined creep and fatigue conditions. Hence, a unified constitutive model seems to be justified in describing and predicting the constitutive behaviour in both cases.

  9. Science under pressure: problematic behaviours and social harms

    Rita Faria


    Full Text Available This paper will suggest the use of the Social Harm Approach (Hillyard, Pantazis, Tobs & Gordon, 2004 to problematic behaviours occurring in scientific research and higher education teaching. By analyzing data collected through interviews to scholars, it is possible to state that fabrication, falsification and plagiarism are the most criticized deviant behaviours in science. It is less common for actors to consider other problematic behaviours arising from the pressure (to publish, to get grants felt by them and originated at the heart of the organizations devoted to science. Or problematic behaviours created on the intersection of universities, corporations and/or the state (ex. commissioned research. Also, those interviewed did not have a coherent view on the rules governing science and higher education. Thus, considering the scattering of (individual and organizational problematic behaviours and rules governing them, a new approach will be put forward, one by which processes of scientific production and dissemination must be considered according to the social harms (financial, economic, physical they may cause.

  10. Mechanical behaviour of PEM fuel cell catalyst layers during regular cell operation

    Al-Baghdadi, Maher A.R. Sadiq [Fuel Cell Research Center, International Energy & Environment Foundation, Al-Najaf, P.O.Box 39 (Iraq)


    Damage mechanisms in a proton exchange membrane fuel cell are accelerated by mechanical stresses arising during fuel cell assembly (bolt assembling), and the stresses arise during fuel cell running, because it consists of the materials with different thermal expansion and swelling coefficients. Therefore, in order to acquire a complete understanding of the mechanical behaviour of the catalyst layers during regular cell operation, mechanical response under steady-state hygro-thermal stresses should be studied under real cell operating conditions and in real cell geometry (three-dimensional). In this work, full three-dimensional, non-isothermal computational fluid dynamics model of a PEM fuel cell has been developed to investigate the behaviour of the cathode and anode catalyst layers during the cell operation. A unique feature of the present model is to incorporate the effect of hygro and thermal stresses into actual three-dimensional fuel cell model. In addition, the temperature and humidity dependent material properties are utilize in the simulation for the membrane. The model is shown to be able to understand the many interacting, complex electrochemical, transport phenomena, and deformation that have limited experimental data.

  11. Mechanical behaviour of PEM fuel cell catalyst layers during regular cell operation

    Maher A.R. Sadiq Al-Baghdadi


    Full Text Available Damage mechanisms in a proton exchange membrane fuel cell are accelerated by mechanical stresses arising during fuel cell assembly (bolt assembling, and the stresses arise during fuel cell running, because it consists of the materials with different thermal expansion and swelling coefficients. Therefore, in order to acquire a complete understanding of the mechanical behaviour of the catalyst layers during regular cell operation, mechanical response under steady-state hygro-thermal stresses should be studied under real cell operating conditions and in real cell geometry (three-dimensional. In this work, full three-dimensional, non-isothermal computational fluid dynamics model of a PEM fuel cell has been developed to investigate the behaviour of the cathode and anode catalyst layers during the cell operation. A unique feature of the present model is to incorporate the effect of hygro and thermal stresses into actual three-dimensional fuel cell model. In addition, the temperature and humidity dependent material properties are utilize in the simulation for the membrane. The model is shown to be able to understand the many interacting, complex electrochemical, transport phenomena, and deformation that have limited experimental data.

  12. Peeling mechanism of tomato under infrared heating

    Critical behaviors of peeling tomatoes using infrared heat are thermally induced peel loosening and subsequent cracking. However, the mechanism of peel loosening and cracking due to infrared heating remains unclear. This study aimed at investigating the mechanism of peeling tomatoes under infrared h...

  13. Influence of the mechanical stress and the filler content on the hydrostatic compression behaviour of natural rubber

    The behaviour of natural rubber (NR) compounds under mechanical stress is often reported in literature. An important and widely discussed effect that occurs is the Mullins effect. During the first loading cycles in a tensile test for example, a stress-softening effect is observed. This and other effects on the mechanical behaviour are investigated for different rubber materials with and without different types of fillers and filler contents. Besides, the hydrostatic compression behaviour is affected by the type and content of filler as well, which is shown for an NR with and without waxes and different contents of carbon black (CB) in this contribution. In contrast to the Mullins effect, there is no dependence of the number of loading cycles on the volumetric behaviour determined in hydrostatic compression tests. Furthermore, the influence of the previous stress-softening due to mechanical stress on the compression behaviour is elaborated. Cyclic uniaxial tensile tests are performed to realize the stress-softening in the rubber materials. The subsequent compression tests are compared to compression tests without any pre-stretching to determine the influence of previous mechanical loading on the compression behaviour of natural rubber with different filler contents

  14. Mechanical behaviour of silicon carbide submitted to high temperature

    Ceramics (composite ceramics) are considered materials for manufacturing structure pieces of future nuclear reactor cores. In condition of nominal running, the temperature of these components is estimated at 500-800 C and could reach 1600 C in accidental condition. On account of its refractory properties and of its good compatibility with neutron flux, silicon carbide is retained for such applications, particularly for fuel cladding material (SiC/SiC composite). A study aiming to specify the mechanical behaviour of the monolithic αSiC (hexagonal structure) between 1000 and 1500 C as well as its evolution after ionic irradiation is presented. This study presents particularly the mechanical characterizations of SiC in three points bending obtained until 1450 C and surface characterizations led on SiC irradiated with ions. The rupture tests in three points bending carried out in temperature on specimens pre-cracked by indentation show an increase of 85% of the SiC rupture stress between 1000 and 1300 C. Above 1300 C, the damage of SiC induces a significant decrease of the rupture stress. Aniso-thermal creep tests on polished specimens show that the SiC presents a viscoplastic behaviour from 1200 C. Surface characterizations by Raman spectroscopy, micro and nano-indentation, acoustic microscopy led at ambient temperature on fresh and irradiated to Xe ions (94 MeV) SiC at 400 C are presented too. The formation of a structural disorder and of Si-Si homonuclear bonds disorder, suggesting a SiC amorphization, are revealed by Raman spectroscopy between 3*1014 and 3.6*1015 ions/cm2 of fluence. These microstructural changes lead to a macroscopic swelling quantifiable by measuring the height of the step formed during irradiations between the non irradiated and irradiated areas. Measurements by profilometry show that between 3*1014 and 1.2*1015 ions/cm2 of fluence, the height of the step increases of 47 nm to 83 nm, and then is stabilized with the fluence increase. The

  15. Selfish-herd behaviour of sheep under threat

    King, A. J.; Wilson, A. M.; Wilshin, S. D.; J. Lowe; Haddadi, H.; Hailes, S; Morton, A. J.


    Flocking is a striking example of collective behaviour that is found in insect swarms, fish schools and mammal herds [1]. A major factor in the evolution of flocking behaviour is thought to be predation, whereby larger and/or more cohesive groups are better at detecting predators (as, for example, in the ‘many eyes theory’), and diluting the effects of predators (as in the ‘selfish-herd theory’) than are individuals in smaller and/or dispersed groups [2]. The former theory assumes that inform...

  16. Mechanical and thermal behaviour of U–Mo and U–Nb–Zr Alloys

    Nuclear fuels composed of uranium alloys in monolithic and dispersed forms are being considered for research and compact power reactors due to their density properties (greater than 15 g-U/cm3) and fast heat transfer. U–Nb–Zr and U–Mo alloys are the most promising systems for plate fuel elements owing to their broad γ-phase stability field, which shows higher ductility and isotropic behaviour, allowing extensive fabrication capability. In the present work, γ-phase stabilized U–7.5Nb–2.5Zr and U–10Mo alloys were characterized by mechanical and thermal analyses for comparison of their behaviour under deformation and heat-treatment. The results demonstrate that the alloys have substantially different properties regarding deformation, kinetics phase transformation and recovery/recrystallization. The main results show that U–Nb–Zr is superior regarding fabrication capabilities although the γ-phase is less stable than U–Mo alloys

  17. Smooth modeling of oblique contact with friction of turbine blades: behaviour analysis under random excitation

    This paper deals with modelling of oblique contact with friction generated by touch of shrouds placed at the blade's end of a pressure turbine of nuclear plant. Two phenomenons emerge from the nonlinearity due to contact between shrouds: contact without sliding and with sliding. The nonlinearity is characterized by a nonlinear differential equation based on smooth hysteresis model proposed by BOUC and generalized by WEN. There is contact without sliding up to a level of contact strength and then sliding. This level is a function of normal strength (at contact point) that is linked to system motion. This contact is considered always hold. Here, the blade is considered as a cantilever beam and the shroud as an oblique support on the beam. The dynamical displacement in two perpendicular directions of axis beam are studied. The smooth hysteresis model equation governing contact behaviour couple up vibrations in 2 transverse directions of beam. The paper presents the setting up of modelization of contact with friction, mechanical behaviour of the smooth hysteresis model with contact strength linked to system motion under random excitation. A sensibility analysis is mode on standard deviation in relation to excitation level by means of MONTE CARLO simulation and NEWMARK step-by-step method of integration. This model allows three contact behaviour types: contact without sliding, sliding with constant step dry friction force and sliding with increasing step dry friction force. Results are compared satisfactorily with experimental results. (authors). 3 refs., 8 figs

  18. Study of mechanical properties of nanomaterials under high pressure

    Sharma, Jyoti; Kaur, Namrat; Srivastava, A. K.


    In the present work, the study of physical properties and behaviour of nanomaterials i.e. n-γ- Al2O3and n-Si3C4 under high pressure is done. For this purpose Murnaghan equation of state is used. The applicability of Murnaghan equation of state is fully tested by calculating mechanical properties of nano materials i.e. volume compression (V/Vo), bulk modulus (KT) and relative isothermal compression coefficient (α(P)/α0) at different pressures. The present calculated values of compression curve for the cited nanomaterials come out to be in reasonable good agreement with the available experimental data.

  19. A study on the mechanical behaviour of WC/Co hardmetals

    Ferreira, J. A. M.; Amaral, M. A. Pina; Antunes, F. V.; Costa, J. D. M.


    The hardmetal cutting tools used in machining are submitted to extreme conditions in terms of temperature and mechanical loading. A better understanding of the failure of cutting tools and capability to predict tool life are key factors in the development of new tool materials with improved mechanical behaviour. Main failure mechanisms are wear, thermal-mechanical fatigue and brittle fracture. The aim of present work is to study the mechanical behaviour of two hardmetals. The properties studi...

  20. Nanoscale grain growth behaviour of CoAl intermetallic synthesized by mechanical alloying

    S N Hosseini; M H Enayati; F Karimzadeh


    Grain growth behaviour of the nanocrystalline CoAl intermetallic compound synthesized by mechanical alloying has been studied by isothermal annealing at different temperatures and durations. X-ray diffraction method was employed to investigate structural evolutions during mechanical alloying and annealing processes. The disordered CoAl phase with the grain size of about 6 nm was formed via a gradual reaction during mechanical alloying. The results of isothermal annealing showed that the grain growth behaviour can be explained by the parabolic grain growth law. The grains were at nanometric scale after isothermal annealing up to 0.7 m. The grain growth exponent remained constant above 873 K indicating that grain growth mechanism does not change at high temperatures. The calculated activation energy indicated that the grain growth mechanism in the disordered CoAl phase at high temperatures was diffusing Co and Al atoms in two separate sublattices. Furthermore, an equation has been suggested to describe the grain growth kinetics of nanocrystalline CoAl under isothermal annealing at temperatures above 873 K (/m ≥ 0.5).

  1. Numerical modelling of the time-dependent mechanical behaviour of softwood

    Engelund, Emil Tang


    When using wood as a structural material it is important to consider its time-dependent mechanical behaviour and to predict this behaviour for decades ahead. For this purpose, several rheological mathematical models, spanning from fairly simple to very complex ones, have been developed over the...... microfibrils. This assumption is incorporated in the numerical model by only allowing non-elastic behaviour in shear deformation modes in the local coordinate system. The rate of shearing is described by deformation kinetics. The results indicate that time-dependent behaviour such as creep and relaxation...... mechanisms causing the observed mechanical behaviour. In this study, the mechanical behaviour of softwood tracheids is described using numerical modelling. The basic composition and orientation of the tracheid constituents is incorporated by establishing a local coordinate system aligned with the...

  2. Chaotic behaviour of Zeeman machines at introductory course of mechanics

    Nagy, Péter; Tasnádi, Péter


    Investigation of chaotic motions and cooperative systems offers a magnificent opportunity to involve modern physics into the basic course of mechanics taught to engineering students. In the present paper it will be demonstrated that Zeeman Machine can be a versatile and motivating tool for students to get introductory knowledge about chaotic motion via interactive simulations. It works in a relatively simple way and its properties can be understood very easily. Since the machine can be built easily and the simulation of its movement is also simple the experimental investigation and the theoretical description can be connected intuitively. Although Zeeman Machine is known mainly for its quasi-static and catastrophic behaviour, its dynamic properties are also of interest with its typical chaotic features. By means of a periodically driven Zeeman Machine a wide range of chaotic properties of the simple systems can be demonstrated such as bifurcation diagrams, chaotic attractors, transient chaos and so on. The main goal of this paper is the presentation of an interactive learning material for teaching the basic features of the chaotic systems through the investigation of the Zeeman Machine.

  3. EDSPA, 1-D Mechanical Displacement for Elastic, Thermoelastic, Viscoelastic Behaviour

    1 - Description of program or function: EDSPA solves the one dimensional mechanical displacement equation in radial (sphere) axisymmetric cylindrical (infinite cylinder, slab) coordinates. The constitutive laws for the material to be considered can comprise the - elastic and/or - thermoelastic and/or - viscoplastic behaviour. The boundary conditions allow to prescribe displacement and/or stress values. The delivered version of EDSPA is especially suitable for the calculation of borehole problems in rock salt (heater boreholes or free converging boreholes or caverns) where convergence rates and/or contact pressures are of interest. 2 - Method of solution: The coarse-mesh method is used to transform the displacement differential equation (quasi-stationary case: second order ordinary differential equation as a two point boundary value problem) into a system of algebraic equations. This three-diagonal system is solved with the Thomas algorithm (direct solver). 3 - Restrictions on the complexity of the problem: Because of EDSPA's simple one-dimensional formulation there are no restrictions for storage allocation and argument ranges

  4. Metallurgical and mechanical behaviours of PWR fuel cladding tube oxidised at high temperature

    Zirconium alloys are used as cladding materials in Pressurized Water Reactors (PWR). As they are submitted to very extreme conditions, it is necessary to check their behaviour and especially to make sure they meet the safety criteria. They are therefore studied under typical in service-loadings but also under accidental loadings. In one of these accidental scenarios, called Loss of Coolant Accident (LOCA) the cladding temperature may increase above 800 C, in a steam environment, and decrease before a final quench of the cladding. During this temperature transient, the cladding is heavily oxidised, and the metallurgical changes lead to a decrease of the post quench mechanical properties. It is then necessary to correlate this drop in residual ductility to the metallurgical evolutions. This is the problem we want to address in this study: the oxidation of PWR cladding materials at high temperature in a steam environment and its consequences on post quench mechanical properties. As oxygen goes massively into the metallic part - a zirconia layer grows at the same time - during the high temperature oxidation, the claddings tubes microstructure shows three different phases that are the outer oxide layer (zirconia) and the inner metallic phases (α(O) and 'ex β') - with various mechanical properties. In order to reproduce the behaviour of this multilayered material, the first part of this study consisted in creating samples with different - but homogeneous in thickness - oxygen contents, similar to those observed in the different phases of the real cladding. The study was especially focused on the β-->α phase transformation upon cooling and on the resulting microstructures. A mechanism was proposed to describe this phase transformation. For instance, we conclude that for our oxygen enriched samples, the phase transformation kinetics upon cooling are ruled by the oxygen partitioning between the two allotropic phases. Then, these materials were mechanically tested at

  5. Mechanical and microstructural behaviour of Y2O3 ODS EUROFER 97

    Two small ingots of the steel EUROFER 97, one containing 0.25 wt% Y2O3 and the other Y2O3 free, have been produced by consolidating mechanically milled powder by hot isostatic pressing at 1373 K for 2 h under 200 MPa. For comparison, a third ingot was consolidated under identical conditions but using un-milled EUROFER powder. Microhardness, tensile and Charpy tests, along with TEM observations, have been performed on these materials in the as-HIPed condition and after different heat treatments. The mechanical behaviour and the microstructural characteristics of these materials suggest that the origin of the reduced impact properties of the oxide dispersion strengthened EUROFER could be the premature formation of carbides during quenching following the HIP process. This would be enhanced by the high density of structural defects produced by milling, as these favour the fast diffusion and segregation of carbon

  6. Sex differences and serotonergic mechanisms in the behavioural effects of psilocin.

    Tylš, Filip; Páleníček, Tomáš; Kadeřábek, Lukáš; Lipski, Michaela; Kubešová, Anna; Horáček, Jiří


    Psilocybin has recently attracted a great deal of attention as a clinical research and therapeutic tool. The aim of this paper is to bridge two major knowledge gaps regarding its behavioural pharmacology - sex differences and the underlying receptor mechanisms. We used psilocin (0.25, 1 and 4 mg/kg), an active metabolite of psilocybin, in two behavioural paradigms - the open-field test and prepulse inhibition (PPI) of the acoustic startle reaction. Sex differences were evaluated with respect to the phase of the female cycle. The contribution of serotonin receptors in the behavioural action was tested in male rats with selective serotonin receptor antagonists: 5-HT1A receptor antagonist (WAY100635 1 mg/kg), 5-HT2A receptor antagonist (MDL100907 0.5 mg/kg), 5-HT2B receptor antagonist (SB215505 1 mg/kg) and 5-HT2C receptor antagonist (SB242084 1 mg/kg). Psilocin induced dose-dependent inhibition of locomotion and suppression of normal behaviour in rats (behavioural serotonin syndrome, impaired PPI). The effects were more pronounced in male rats than in females. The inhibition of locomotion was normalized by 5-HT1A and 5-HT2B/C antagonists; however, PPI was not affected significantly by these antagonists. Our findings highlight an important issue of sex-specific reactions to psilocin and that apart from 5-HT2A-mediated effects 5-HT1A and 5-HT2C/B receptors also play an important role. These findings have implications for recent clinical trials. PMID:26461483

  7. Experimental study of thermo-hydro-mechanical behaviour of Callovo-Oxfordian Clay-stone

    During the different phases of the exothermic radioactive waste deep disposal (excavation, operation) and after permanent closure, the host rock is submitted to various coupled mechanical, hydraulic and thermal phenomena. Hence, a thorough investigation of the thermo-hydro-mechanical behaviour of the rock is necessary to complete existing data and to better understand and model the short and long term behaviour of the Callovo-Oxfordian (COx) clay formation in Bure (Meuse/Haute-Marne - M/HM), considered by ANDRA as a potential host rock in France.In this work, the compression - swelling behaviour of the COx Clay-stone was first investigated by carrying out a series of high-pressure oedometric tests. The results, interpreted in terms of coupling between damage and swelling, showed that the magnitude of swelling was linked to the density of the fissures created during compression. In a second step, the hydro-mechanical and thermo-hydro-mechanical behaviour of the saturated Clay-stone under a mean stress close to the in situ one were investigated by using two devices with short drainage path (10 mm), namely a isotropic cell and a newly designed hollow cylinder triaxial cell with local displacement measurements. These devices helped to solve two majors problems related to testing very low permeability materials: i) a satisfactory previous sample saturation (indicated by good Skempton values) and ii) satisfactory drainage conditions. Some typical constitutive parameters (Skempton and Biot's coefficients, drained and undrained compressibility coefficients) have been determined at ambient temperature through isotropic compression tests that also confirmed the transverse isotropy of the Clay-stone. The consistency of the obtained parameters has been checked in a saturated poro-elastic framework. Two aspects of the thermo-hydro-mechanical behaviour of the COx Clay-stone have then been investigated through different heating tests and through drained and undrained isotropic

  8. Mechanical Buckling of Veins under Internal Pressure

    Martinez, Ricky; Fierro, Cesar A.; Shireman, Paula K.; Han, Hai-Chao


    Venous tortuosity is associated with multiple disease states and is often thought to be a consequence of venous hypertension and chronic venous disease. However, the underlying mechanisms of vein tortuosity are unclear. We hypothesized that increased pressure causes vein buckling that leads to a tortuous appearance. The specific aim of this study was to determine the critical buckling pressure of veins. We determined the buckling pressure of porcine jugular veins and measured the mechanical p...

  9. Study on the mechanical behaviour of the cold forged niobium as function of the cross section reduction

    This work aims to study he mechanical behaviour of commercially pure niobium (99.8 % purity) obtained by means of aluminothermic reduction followed by electron beam melting and refining. Eleven groups of specimens were analyzed under tensile tests, with different degrees of reduction (cold working), using rotary forging. Significant alterations were observed in the mechanical properties in all processing steps. Using electron scanning microscopy, the main characteristics of the fracture surface were studied. (author)

  10. Health Behaviours As a Mechanism in the Prospective Relation between Workplace Reciprocity and Absenteeism: A Bridge too Far ?

    Bart De Clercq

    Full Text Available The persistent lack of evidence on causal mechanisms between social capital and health threatens the credibility of the social capital-health association. The present study aims to address this ongoing problem by investigating whether health behaviours (i.e. smoking, alcohol consumption, and physical activity mediate the prospective relation between workplace reciprocity and future sickness absence.A cohort of 24,402 Belgian employees was followed up during 12 months for sickness absence. Workplace reciprocity was measured with four indicators-colleague help, colleague interest, supervisor help, and supervisor concern. Three types of multilevel mediation models were applied.Overall, workplace reciprocity negatively related to high sickness absence (≥ 10 days mainly independently from health behaviours. Uniquely, colleague interest positively related to smoking (OR = 1.058, 95% CI = 1.019, 1.098 and smoking in turn, positively related to sickness absence (OR = 1.074, 95% CI = 1.047, 1.101. No behavioural pathways could be identified between company-level reciprocity and sickness absence, and company-level health-related behaviours did not mediate the relation between company-level reciprocity and individual sickness absence.These results suggest that both social capital and health behaviours are relevant for employee health, but health behaviours seem not to be the underlying explanatory mechanism between workplace reciprocity and health.

  11. A comparative study of the effects of constructional elements on the mechanical behaviour of dragonfly wings

    Rajabi, H.; Rezasefat, M.; Darvizeh, A.; Dirks, J.-H.; Eshghi, Sh.; Shafiei, A.; Mostofi, T. Mirzababaie; Gorb, S. N.


    Although wings of insects show a large variation in morphology, they are all made from a network of irregular veins interconnected through membranous areas. Depending on their shape, size, and position, wing veins are usually divided into three different groups: longitudinal veins, cross-veins and ambient veins. The veins together with the membrane and some other elements such as spines, nodus and pterostigma can be considered as the wing's "constructional elements". In spite of rather extensive literature on dragonfly wing structure, the role of each of these elements in determining the wing's function remains mostly unknown. As this question is difficult to answer in vivo using biomechanical experiments on actual wings, this study was undertaken to reveal the effects of the constructional elements on the mechanical behaviour of dragonfly wings by applying numerical simulations. An image processing technique was used to develop 12 finite element models of the insect wings with different constructional elements. The mechanical behaviour of these models was then simulated under normal and shear stresses due to tension, bending and torsion. A free vibration analysis was also performed to determine the resonant frequencies and the mode shapes of the models. For the first time, a quantitative comparison was carried out between the mechanical effects selectively caused by different elements. Our results suggest that the complex interactions of veins, membranes and corrugations may considerably affect the dynamic deformation of the insect wings during flight.

  12. An experimental and constitutive investigation on the chemo-mechanical behaviour of a clay

    Witteveen, Paul Joost; Ferrari, Alessio; LALOUI, Lyesse


    Engineering issues for which the understanding of the chemo-mechanical behaviour of soils is relevant include wellbore stability problems, the sali-nification of groundwater and nuclear waste storage, etc. However, despite the vast number of situations in which couplings between chemistry and mechanics occur, the available constitutive models rely on limited experimental evidence. This paper presents the results of an experimental program on the chemo-mechanical behaviour of a non-swelling il...

  13. Modelling of thermal and mechanical behaviour of pebble beds

    FZK (Forshungzentrum Karlsruhe) is developing a Helium Cooled Pebble Bed (HCPB) Blanket Concept for fusion power reactors based on the use of ceramic breeder materials and beryllium multiplier in the form of pebble beds. The design of such a blanket requires models and computer codes describing the thermal-mechanical behavior of pebble beds to evaluate the temperatures, stresses, deformations and mechanical interactions between pebble beds and the structure with required accuracy and reliability. The objective to describe the beginning of life condition for the HCPB blanket seems near to be reached. Mechanical models that describe the thermo-mechanical behavior of granular materials used in form of pebble beds are implemented in a commercial structure code. These models have been calibrated using the results of a large series of dedicated experiments. The modeling work is practically concluded for ceramic breeder; it will be carried on in the next year for beryllium to obtain the required correlations for creep and the thermal conductivity. The difficulties for application in large components (such as the HCPB blanket) are the limitations of the present commercial codes to manage such a set of constitutive equations under complex load conditions and large mesh number. The further objective is to model the thermal cycles during operation; the present correlations have to be adapted for the release phase. A complete description of the blanket behavior during irradiation is at the present out of our capability; this objective requires an extensive R and D program that at the present is only at the beginning. (Y.Tanaka)

  14. Investigations on the lifetime behaviour of a P23 pipe under fatigue loading

    Friedmann, V.; Hartrott, P. von [Fraunhofer IWM, Freiburg (Germany)


    The performance of girth welds on new P23 low chromium steel pipes under cyclic loading at 450 C was investigated. The loading conditions were chosen to be representative for bore crack initiation and growth observed in main steam lines fabricated of 0.5Cr0.5Mo0.25V (CrMoV) steel. The microstructure of the base material and weldments was analysed. A lifetime model, initially set up for the prediction of thermo-cyclic loading, is used to predict the isothermal component behaviour. It is based on a Chaboche-type deformation model and the DTMF crack growth model. The failure mechanism of two component tests was compared to the model assumptions and the component lifetimes and failure locations are compared to the model predictions. (orig.)

  15. Failure mechanisms in thin rubber sheet composites under static solicitation

    E. Bayraktar


    Full Text Available Purpose: Mechanical behaviour and damage mechanisms in thin rubber sheet composites were investigated under static solicitation at room temperature. Two types of rubber are used in this study; Natural rubber, NR vulcanised and reinforced by carbon black and Synthetic rubber (styrene-butadiene-rubber, SBR.Design/methodology/approach: A comprehensive study has been carried out in order to identify a threshold criterion for the damage mechanism to explain a tearing criterion for the concept of tearing energy of the elastomers and also to give a detail for the damage mechanism depending on the loading conditions. A typical type of specimen geometry of thin sheet rubber composite materials was studied under static tensile tests conducted on the smooth and notched specimens with variable depths. In this way, the effects of the plane stress on the damage mechanism are characterized depending on the rubber materials.Findings: Damage mechanisms during tensile test have been described for both of rubber types and the criteria which characterize the tearing resistance, characteristic energy for tearing (T was explained. Damage in the specimens were evaluated just at the beginning of the tearing by means of the observations in the scanning electron microscopy (SEM.Practical implications: A tearing criterion was suggested in the case of simple tension conditions by assuming large strain. In the next step of this study, a finite element analysis (FEA will be applied under the same conditions of this part in order to obtain the agreement between experimental and FEA results.Originality/value: This study propses a threshold criterion for the damage just at the beginning of the tearing for thin sheet rubber composites and gives a detail discussion for explaining the damage mechanisms by SEM results. This type of study gives many facilities for the sake of simplicity in industrial application.

  16. Stress and the social brain: behavioural effects and neurobiological mechanisms.

    Sandi, Carmen; Haller, József


    Stress often affects our social lives. When undergoing high-level or persistent stress, individuals frequently retract from social interactions and become irritable and hostile. Predisposition to antisocial behaviours - including social detachment and violence - is also modulated by early life adversity; however, the effects of early life stress depend on the timing of exposure and genetic factors. Research in animals and humans has revealed some of the structural, functional and molecular changes in the brain that underlie the effects of stress on social behaviour. Findings in this emerging field will have implications both for the clinic and for society. PMID:25891510

  17. Comportamento mecânico de tendões calcâneo bovino sob informações clínicas Mechanical behaviour of bovine calcaneous tendon under ciclic deformations

    Sergio Rocha Piedade


    Full Text Available Este trabalho teve por finalidade analisar o comportamento de tendões calcâneo bovino submetidos a ensaios mecânicos cíclicos. Para cada corpo de prova foram aplicados três ensaios de dez ciclos de tração e três níveis de deformação: 2,5%, 3% e 4%. Ao término de cada ensaio o tendão era mantido em repouso por 300 s. A velocidade de carregamento adotada foi de 10% do comprimento do corpo de prova, por segundo. Os resultados obtidos foram submetidos à análise de variância com delineamento de parcelas subdivididas no tempo e blocos casualizados nas subparcelas. Conclui-se que o pré-tensionamento de tendões realizado através da deformação relativa permanece como parâmetro mais seguro, por atuar dentro dos limites fisiológicos do tendão, evitando os efeitos nocivos do sobretensionamento.This research work reports an experimental study on the mechanical behavior of bovine calcaneous tendons. A total number of 03 cyclic relaxation tests with 10 cycles respectively at 2,5%, 3%, and 4% of deformation were performed for each specimen. The specimens were kept at rest for 300 s between tests. Deformation rates were maintained at 10% of initial length per second. Cyclic relaxation tests carried on all tendons showed that the average force correspondent to the first cycle was statistically significatively greater than the average force correspondent to the tenth cycle. This also emphasizes the occurrence of a force relaxation phenomena. It can be concluded that tendons pre-tensionning by means of specific deformations stands for a safer parameter because it acts within the tendon biological limits avoyding the overtensioning negative effects.

  18. Behavioural, hormonal and neurobiological mechanisms of aggressive behaviour in human and nonhuman primates.

    de Almeida, Rosa Maria Martins; Cabral, João Carlos Centurion; Narvaes, Rodrigo


    Aggression is a key component for social behaviour and can have an adaptive value or deleterious consequences. Here, we review the role of sex-related differences in aggressive behaviour in both human and nonhuman primates. First, we address aggression in primates, which varies deeply between species, both in intensity and in display, ranging from animals that are very aggressive, such as chimpanzees, to the nonaggressive bonobos. Aggression also influences the hierarchical structure of gorillas and chimpanzees, and is used as the main tool for dealing with other groups. With regard to human aggression, it can be considered a relevant adaptation for survival or can have negative impacts on social interaction for both sexes. Gender plays a critical role in aggressive and competitive behaviours, which are determined by a cascade of physiological changes, including GABAergic and serotonergic systems, and sex neurosteroids. The understanding of the neurobiological bases and behavioural determinants of different types of aggression is fundamental for minimising these negative impacts. PMID:25749197

  19. Behaviour of a few mode fiber modal pattern under stress

    Egalon, Claudio O.; Rogowski, Robert S.


    A numerical model was developed to calculate the interference pattern at the end of a multimode weakly guiding optical fiber under stress. Whenever an optical fiber is under stress, the modal phase in the interference term of the intensity formula changes. Plots of the simulated output of a stressed fiber are presented. For multimode fibers, very complicated patterns result. Under stress, lobes in the pattern are generated, displaced and power is exchanged among them.

  20. Fundamentals of soil behaviour

    Gens Solé, Antonio


    The paper reviews in summary form the generalised behaviour of soils under nonisothermal and chemically varying conditions. This generalised soil behaviour underlies the performance of a number of ground improvement techniques. The behaviour of frozen soil is examined first showing that some concepts of unsaturated soil mechanics appear to be readily applicable. Afterwards, the observation that volumetric behaviour of saturated and unsaturated soils at high temperature is similar, leads to th...

  1. The behaviour of ferritic steels under fast neutron irradiation

    Ferritic steels have been irradiated in Rapsodie and Phenix to doses up to 150 dpa F. The swelling and irradiation creep characteristics and the mechanical properties of these materials are reported. (author)

  2. Effect of heat treatment upon the mechanical and poro-mechanical behaviour of cement-based materials: hydraulic properties and morphological changes

    This work investigates the effects of morphological changes of a cement-based material subjected to heat treatment (up to 400 C). For a model W/C=0.5 mortar, we have characterized experimentally hydraulic behaviour (gas permeability), mechanical behaviour (in uniaxial compression, hydrostatic compression with or without deviatoric stress) and poro-mechanical behaviour (incompressibility moduli Kb, Ks and Biot's coefficient b) after a heating/cooling cycle. We have also developed an original experiment aimed at quantifying the accessible pore space volume under hydrostatic compression. The creation of occluded porosity under high confinement is confirmed, which justifies the observed decrease of solid matrix rigidity Ks under high confinement. A gas retention phenomenon was identified under simultaneous thermal and hydrostatic loadings for mortar, and industrial concretes (provided by CERIB and ANDRA). A predictive thermo-elasto-plastic model with isotropic damage and a micro-mechanical approach, which represents micro-cracking, are coupled in order to analyze or predict the evolution of mechanical and poro-elastic properties after heat cycling. (author)

  3. Mechanical characteristics and microcosmic mechanisms of granite under temperature loads

    XU Xiao-li; GAO Feng; SHEN Xiao-ming; XIE He-ping


    The relationships between mechanical characteristics of rock and microcosmic mechanism at high temperatures were investigated by MTS815, as well as the stress-strain behavior of granite under the action of temperatures ranging from room tem-perature to 1200 ℃. Based on a micropore structure analyzer and SEM, the changes in rock porosity and micro'structural mor-phology of sample fractures and brittle-plastic characteristics under high temperatures were analyzed. The results are as follows: 1) Mechanical characteristics do not show obvious variations before 800 ℃; strength decreases suddenly after 800 ℃ and bearing capacity is almost lost at 1200 ℃. 2) Rock porosity increases with rising temperatures; the threshold temperature is about 800 ℃;at this temperature its effect is basically uniform with strength decreasing rapidly. 3) The failure type of granite is a brittle tensile fracture at temperatures below 800 ℃ which transforms into plasticity at temperatures higher than 800 ℃ and crystal formation takes place at this time. Chemical reactions take place at 1200 ℃. Failure of granite under high temperature is a common result of thermal stress as indicated by an increase in the thermal expansion coefficient, transformation to crystal formation of minerals and structural chemical reactions.

  4. A model of multisecond timing behaviour under peak-interval procedures.

    Hasegawa, Takayuki; Sakata, Shogo


    In this study, the authors developed a fundamental theory of interval timing behaviour, inspired by the learning-to-time (LeT) model and the scalar expectancy theory (SET) model, and based on quantitative analyses of such timing behaviour. Our experiments used the peak-interval procedure with rats. The proposed model of timing behaviour comprises clocks, a regulator, a mixer, a response, and memory. Using our model, we calculated the basic clock speeds indicated by the subjects' behaviour under such peak procedures. In this model, the scalar property can be defined as a kind of transposition, which can then be measured quantitatively. The Akaike information criterion (AIC) values indicated that the current model fit the data slightly better than did the SET model. Our model may therefore provide a useful addition to SET for the analysis of timing behaviour. PMID:25539685

  5. Elastic behaviour of terbium metaphosphate glasses under high pressures

    The elastic and nonlinear acoustic vibrational properties of terbium metaphosphate glasses (Tb2O3)x(P2O5) 1-x with x = 0.226, 0.247, 0.263 and 0.271 (x is the mole fraction) have been determined from measurements of the effects of temperature, hydrostatic pressure, and uniaxial stress on ultrasonic wave velocity. At temperatures below about 140 K, the elastic stiffness CSIJ of (Tb2O3)x(P2O5) 1x glasses becomes anomalously dependent upon temperature, a behaviour usually associated with interactions between acoustic phonons and two-level systems. Except for the (Tb2O3) 0.271 (P-2O5) 0.729 glass, the hydrostatic pressure derivatives of the elastic stiffness and als of the bulk modulus BS of terbium metaphosphate glasses are small and negative. The third-order elastic stiffness tensor components CIJK of the (TbSO3)0.247(P205)0.753 glass between 77 K and 400 K have also been determined. Both longitudinal and shear acoustic mode Grueneisen parameters are small and negative: the application of pressure softens the long-wavelength acoustic phonon mode frequencies. The mode softening is enhanced as the temperature is reduced. 33 refs., 2 tab., 7 figs

  6. The behaviour of spherical HTR fuel elements under accident conditions

    Hypothetical accidents may lead to significantly higher temperatures in HTR fuel than during normal operation. In order to obtain meaningful statements on fission product behaviour and release, irradiated spherical fuel elements containing a large number of coated particles (20,000-40,000) with burnups between 6 and 16% FIMA were heated at temperatures between 1400 and 2500 deg. C. HTI-pyrocarbon coating retains the gaseous fission products (e.g. Kr) very well up to about 2400 deg. C if the burnup does not exceed the specified value for THTR (11.5%). Cs diffuses through the pyrocarbon significantly faster than Kr and the diffusion is enhanced at higher fuel burnups because of irradiation induced kernel microstructure changes. Below about 1800 deg. C the Cs release rate is controlled by diffusion in the fuel kernel; above this temperature the diffusion in the pyrocarbon coating is the controlling parameter. An additional SiC coating interlayer (TRISO) ensures Cs retention up to 1600 deg. C. However, the release obtained in the examined fuel elements was only by a factor of three lower than through the HTI pyrocarbon. Solid fission products added to UO2-TRISO particles to simulate high burnup behave in various ways and migrate to attack the SiC coating. Pd migrates fastest and changes the SiC microstructure making it permeable

  7. Loading path effect on the mechanical behaviour and fivefold twinning of copper nanowires

    The effect of loading path on the mechanical behaviour of single crystalline copper nanowires is investigated with molecular dynamics simulations. Different loading conditions including pre-tensile torsion and pre-torsional tension at different temperatures are taken into consideration. It is found that elastic pre-loading conditions can induce a distinct weakening on the resistance against plastic deformation under later applied loads. Meanwhile, coupled thermal and pre-loading effect can also facilitate the transformation from elasticity to plasticity. Formations of fivefold twins are observed in copper nanowires subjected to the loading path with tension after pre-torsion. These fivefold twins all form at the necking stage before fracture, and are found to be pre-torsion- and size-dependent but insensitive to the change in temperature and cross-sectional shape. The results reported here indicate that the loading path effect on the mechanical behaviour plays an important role in the formation of some special microstructures such as multiple twins in metallic nanowires.

  8. DNA under Force: Mechanics, Electrostatics, and Hydration

    Jingqiang Li


    Full Text Available Quantifying the basic intra- and inter-molecular forces of DNA has helped us to better understand and further predict the behavior of DNA. Single molecule technique elucidates the mechanics of DNA under applied external forces, sometimes under extreme forces. On the other hand, ensemble studies of DNA molecular force allow us to extend our understanding of DNA molecules under other forces such as electrostatic and hydration forces. Using a variety of techniques, we can have a comprehensive understanding of DNA molecular forces, which is crucial in unraveling the complex DNA functions in living cells as well as in designing a system that utilizes the unique properties of DNA in nanotechnology.

  9. Effect of dolomite decomposition under CO2 on its multicycle CO2 capture behaviour under calcium looping conditions.

    de la Calle Martos, Antonio; Valverde, Jose Manuel; Sanchez-Jimenez, Pedro E; Perejón, Antonio; García-Garrido, Cristina; Perez-Maqueda, Luis A


    One of the major drawbacks that hinder the industrial competitiveness of the calcium looping (CaL) process for CO2 capture is the high temperature (∼930-950 °C) needed in practice to attain full calcination of limestone in a high CO2 partial pressure environment for short residence times as required. In this work, the multicycle CO2 capture performance of dolomite and limestone is analysed under realistic CaL conditions and using a reduced calcination temperature of 900 °C, which would serve to mitigate the energy penalty caused by integration of the CaL process into fossil fuel fired power plants. The results show that the fundamental mechanism of dolomite decomposition under CO2 has a major influence on its superior performance compared to limestone. The inert MgO grains resulting from dolomite decomposition help preserve a nanocrystalline CaO structure wherein carbonation in the solid-state diffusion controlled phase is promoted. The major role played by the dolomite decomposition mechanism under CO2 is clearly demonstrated by the multicycle CaO conversion behaviour observed for samples decomposed at different preheating rates. Limestone decomposition at slow heating rates yields a highly crystalline and poorly reactive CaCO3 structure that requires long periods to fully decarbonate and shows a severely reduced capture capacity in subsequent cycles. On the other hand, the nascent CaCO3 produced after dolomite half-decomposition consists of nanosized crystals with a fast decarbonation kinetics regardless of the preheating rate, thus fully decomposing from the very first cycle at a reduced calcination temperature into a CaO skeleton with enhanced reactivity as compared to limestone derived CaO. PMID:27253328

  10. Behavioural modelling of irrigation decision making under water scarcity

    Foster, T.; Brozovic, N.; Butler, A. P.


    Providing effective policy solutions to aquifer depletion caused by abstraction for irrigation is a key challenge for socio-hydrology. However, most crop production functions used in hydrological models do not capture the intraseasonal nature of irrigation planning, or the importance of well yield in land and water use decisions. Here we develop a method for determining stochastic intraseasonal water use that is based on observed farmer behaviour but is also theoretically consistent with dynamically optimal decision making. We use the model to (i) analyse the joint land and water use decision by farmers; (ii) to assess changes in behaviour and production risk in response to water scarcity; and (iii) to understand the limits of applicability of current methods in policy design. We develop a biophysical model of water-limited crop yield building on the AquaCrop model. The model is calibrated and applied to case studies of irrigated corn production in Nebraska and Texas. We run the model iteratively, using long-term climate records, to define two formulations of the crop-water production function: (i) the aggregate relationship between total seasonal irrigation and yield (typical of current approaches); and (ii) the stochastic response of yield and total seasonal irrigation to the choice of an intraseasonal soil moisture target and irrigated area. Irrigated area (the extensive margin decision) and per-area irrigation intensity (the intensive margin decision) are then calculated for different seasonal water restrictions (corresponding to regulatory policies) and well yield constraints on intraseasonal abstraction rates (corresponding to aquifer system limits). Profit- and utility-maximising decisions are determined assuming risk neutrality and varying degrees of risk aversion, respectively. Our results demonstrate that the formulation of the production function has a significant impact on the response to water scarcity. For low well yields, which are the major concern

  11. Hybridoma cell behaviour in continuous culture under hyperosmotic stress.

    Cherlet, M; Marc, A


    In this paper, we propose an alternative strategy to the ones proposed before (Oh et al., 1993; Øyaas et al., 1994a) to get real increases of global final antibody titer and production at hyperosmotic stress, by reducing the detrimental effect of such a stress on cell growth, and conserving the stimulating effect on antibody production. It consists of cultivating the cells in continuous culture and increasing the osmolality stepwise. In this way, the cells could progressively adapt to the higher osmolality at each step and antibody titers could be nearly doubled at 370 and 400 mOsm kg-1, compared to the standard osmolality of 335 mOsm kg-1. Surprisingly, the stimulation of antibody production was not confirmed for higher osmolalities, 425 and 450 mOsm kg- 1, despite the minor negative effect on cell growth. Intracellular IgG analysis by flow cytometry revealed at these osmolalities a significant population of non-producing cells. However, even when taking into account this non-producing population, a stimulating effect on antibody production could not be shown at these highest osmolalities. It seems to us that osmolality has a significant effect on the appearance of these non-producing cells, since they were not observed in continuous cultures at standard osmolality, of comparable duration and at an even higher dilution rate. The appearance of the non-producing cells coincides furthermore with modifications of the synthesised antibody, as shown by electrophoretic techniques. It is however not really clear if these two observations reflect actually the same phenomenon. Hyperosmolality affects the cell behaviour in continuous culture in multiple ways, independently of the growth rate, counting all at least partially for the observed stimulation of antibody production: acceleration of the amino acid, and in particular the glutamine metabolism, increase of the cell volume, increase of the intracellular pH and accumulation of cells in the G1 cell cycle phase. PMID

  12. Mechanical Properties and Fracture Behaviour of Multilayer Alumina Composites

    ZHENG Xinguo; ZHAO Fei; ZHANG Jinyong


    Adopting a ceramic/polymer multilayer structure design to simulate the structure of nacre is usually believed to be an effective way to increase the toughness of ceramic composites at the expense of the material's bending strength. However, in this study, we found that both the bending strength and the toughness could be improved simultaneously when using a certain Al2O3/Kevlar multilayer composite design compared to pure alumina samples with the same dimensions. The fracture behaviour of the Al2O3/Kevlar multilayer composite was studied to ifnd a reason for this improvement. The results showed that the complex and asymmetrical stresses occurring in the Kevlar-reinforced layers were the main reason for the differences in fracture behaviour. We expect our results to open up new ways for the design of future high performance ceramic composites.

  13. Aero dynamical and mechanical behaviour of the Savonius rotor

    Aouachria, Z. [Batna Univ., (Algeria). Applied Energetic Physics Laboratory


    Although the Savonius wind turbine is not as efficient as the traditional Darrieus wind turbine, its rotor design has many advantages such as simple construction; acceptance of wind from all directions; high starting torque; operation at relatively low speed; and easy adaptation to urban sites. These advantages may outweigh its low efficiency and make it suitable for small-scale power requirements such as pumping and rural electrification. This paper presented a study of the aerodynamic behaviour of a Savonius rotor, based on blade pressure measurements. A two-dimensional analysis method was used to determine the aerodynamic strengths, which leads to the Magnus effect and the generation of the vibrations on the rotor. The study explained the vibratory behaviour of the rotor and proposed an antivibration system to protect the machine. 14 refs., 1 tab., 9 figs.

  14. The behaviour of Phenix fuel pin bundle under irradiation

    An entire Phenix sub-assembly has been mounted and sectioned after irradiation. The examination of cross-sections revealed the effects of mechanical interaction in the bundle (ovalisations and contacts between clads). According to analysis of the sodium channels, cooling of the pin bundle remained uniform. (author)

  15. Microstructural, mechanical and electrochemical behaviour of a 7017 Al–Zn–Mg alloy of different tempers

    The aim of the investigation is to assess the microstructural features and associated physical, mechanical and electrochemical properties of a 7017 Al–Zn–Mg alloy of various tempers. A 7017 Al–Zn–Mg alloy was subjected to different ageing schedules to produce under-(T4), peak-(T6), over-(T7) and highly over-aged tempers. Optical microscopy, hardness measurement, electrical conductivity measurement, tensile testing and SEM fractographs, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electrochemical polarization studies have been used to characterize the alloy tempers. Hardness measurement and tensile testing showed the characteristic age hardening phenomenon of aluminium alloys. Optical and TEM micrographs have revealed the variation in size of matrix strengthening η′ (MgZn2) and also the size and distribution of grain boundary η (MgZn2) precipitate with ageing time. DSC thermograms exhibiting exothermic and endothermic peaks indicated the characteristic solid state reaction sequence of the 7017 alloy. Potentiodynamic polarization study of the 7017 alloy of various tempers in 3.5 wt.% NaCl solution at near neutral pH showed typical active metal dissolution behaviour, but at pH 12 an active–passive–transpassive transition behaviour has been observed. - Graphical abstract: TEM micrograph of the 7017 aluminium alloy of various tempers (a, b) under aged (T4), (c, d) peak aged (T6), (e, f) over aged (T7) and (g, h) highly over-aged. Display Omitted - Highlights: • 7017 Al-Zn-Mg alloy was subjected to different artificial ageing treatments. • Characterization of 7017 alloy tempers by hardness, tensile, DSC, TEM and electrochemical behaviour. • Structure-properties relationship of the 7017 Al-Zn-Mg alloy of various tempers

  16. Microstructural, mechanical and electrochemical behaviour of a 7017 Al–Zn–Mg alloy of different tempers

    Rout, Prasanta Kumar, E-mail:; Ghosh, M.M.; Ghosh, K.S., E-mail:


    The aim of the investigation is to assess the microstructural features and associated physical, mechanical and electrochemical properties of a 7017 Al–Zn–Mg alloy of various tempers. A 7017 Al–Zn–Mg alloy was subjected to different ageing schedules to produce under-(T4), peak-(T6), over-(T7) and highly over-aged tempers. Optical microscopy, hardness measurement, electrical conductivity measurement, tensile testing and SEM fractographs, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electrochemical polarization studies have been used to characterize the alloy tempers. Hardness measurement and tensile testing showed the characteristic age hardening phenomenon of aluminium alloys. Optical and TEM micrographs have revealed the variation in size of matrix strengthening η′ (MgZn{sub 2}) and also the size and distribution of grain boundary η (MgZn{sub 2}) precipitate with ageing time. DSC thermograms exhibiting exothermic and endothermic peaks indicated the characteristic solid state reaction sequence of the 7017 alloy. Potentiodynamic polarization study of the 7017 alloy of various tempers in 3.5 wt.% NaCl solution at near neutral pH showed typical active metal dissolution behaviour, but at pH 12 an active–passive–transpassive transition behaviour has been observed. - Graphical abstract: TEM micrograph of the 7017 aluminium alloy of various tempers (a, b) under aged (T4), (c, d) peak aged (T6), (e, f) over aged (T7) and (g, h) highly over-aged. Display Omitted - Highlights: • 7017 Al-Zn-Mg alloy was subjected to different artificial ageing treatments. • Characterization of 7017 alloy tempers by hardness, tensile, DSC, TEM and electrochemical behaviour. • Structure-properties relationship of the 7017 Al-Zn-Mg alloy of various tempers.

  17. Behavioural mechanisms behind aggregation in a tritrophic perspective

    Stephan, Jörg


    Gregarious organisms need to handle the trade-off between positive effects of group living and increasing food competition. The gregarious Phratora vulgatissima, a specialist leaf beetle on willow in Europe and Asia, frequently reaches outbreak densities in natural stands and short rotation coppices. Outbreaks threaten the yield and plantations therefore rely on omnivorous predators as biocontrol agents, like Anthocoris nemorum and Orthotylus marginalis. I aimed to elucidate behavioural mecha...

  18. Behaviour of Japanese Quail Eggs Under Mechanical Compression

    Buchar, J.; Nedomová, Š.; Trnka, Jan; Strnková, J.


    Roč. 18, č. 5 (2015), s. 1110-1118. ISSN 1094-2912 Institutional support: RVO:61388998 Keywords : quail egg * compression * rupture force Subject RIV: GM - Food Processing Impact factor: 0.915, year: 2014

  19. Influence of different mechanisms on the constitutive behaviour of textile reinforced concrete

    Hartig, Jens; Jesse, Frank; Häußler-Combe, Ulrich


    Textile Reinforced Concrete shows a complex load-bearing behaviour, which depends on material properties of the composite constituents and load transfer mechanisms in between. These properties cannot be modified arbitrarily in experimental investigations, which complicates identification of the impact of certain mechanisms on composite’s behaviour. In this respect, theoretical investigations offer the possibility to study the influence of individual parameters. At first, experimental results ...

  20. The behaviour of high-temperature steels under thermal load

    The different demands made on plants under thermal stress have been the reason for the development of a multitude of high-temperature steels. Mn, Cr, Ni, Mo and, in small amounts, V, W, Nb, and B are used as alloying metals in order to increase temperature and scaling resistance. They induce structural changes and the formation of finely distributed carbides, nitrides, and intermetallic phases which inhibit creep at higher temperatures. The present report discusses the development of this sort of steel, the high-temperature properties of the materials, the calculation of components under thermal stress, as well as testing and control measures. (GSC)




    Understanding roof behaviour and immediate roof failure patterns of Iongwall face is a prerequisite for establishing correct roof control theory and appplying effective roof control measures. Roof behaviour and immediate roof failure pattern have a close relationship with upper mining boundary conditions of Iongwall face. According to actual situation of Datong Mining Area, upper mining boundary conditions of Iongwall face have been classified into 5 types in this paper. Roof behaviour and immediate roof failure pattern under each upper mining boundary condition are discussed in details.

  2. Investigation on mechanical behaviour of AM60 magnesium alloys

    C. Yan


    Full Text Available Purpose: In this work, tension, impact, bend and fatigue tests were conducted in an AM60 magnesium alloy. The effects of environmental temperature and loading rates on impact and tension behavior of the alloy were also investigated.Design/methodology/approach: The tests were conducted using an Instron universal testing machine. The loading speed was changed from 1 mm/min to 300 mm/min to gain a better understanding of the effect of strain rate. To understand the failure behavior of this alloy at different environmental temperatures, Charpy impact test was conducted in a range of temperatures (-40~35°C. Plane strain fracture toughness (KIC was evaluated using compact tension (CT specimen. To gain a better understanding of the failure mechanisms, all fracture surfaces were observed using scanning electron microscopy (SEM. In addition, fatigue behavior of this alloy was estimated using tension test under tension-tension condition at 30 Hz. The stress amplitude was selected in the range of 20~50 MPa to obtain the S-N curve.Findings: The tensile test indicated that the mechanical properties were not sensitive to the strain rates applied (3.3x10-4~0.1 and the plastic deformation was dominated by twining mediated slip. The impact energy is not sensitive to the environmental temperature. The plane strain fracture toughness and fatigue limit were evaluated and the average values were 7.6 MPa.m1/2 and 25 MPa, respectively. Practical implications: Tested materials AM60 Mg alloy can be applied among others in automotive industry aerospace, communication and computer industry.Originality/value: Many investigations have been conducted to develop new Mg alloys with improved stiffness and ductility. On the other hand, relatively less attention has been paid to the failure mechanisms of Mg alloys, such as brittle fracture and fatigue, subjected to different environmental or loading conditions. In this work, tension, impact, bend and fatigue tests were conducted

  3. The behaviour of weldable strain gauges under nuclear reactor core conditions

    Highlights: • Electrical resistance strain gauges can be used in nuclear reactor environments. • Several in-reactor experiments featuring the use of strain gauges are described. • Static and dynamic strain can be measured under the very hostile conditions of nuclear reactor cores. • Irradiation effects can be corrected if they are well understood and precisely quantified. -- Abstract: Electrical resistance strain gauges are a very useful tool to measure mechanical parameters such as deformation, stress, dynamic strain, vibration, etc. This paper presents our experience with strain gauges in nuclear reactor environments. The nature of nuclear applications and the desirable characteristics of nuclear strain gauges are discussed. Several in-reactor experiments featuring the use of strain gauges are described. The behaviour of weldable strain gauges under intense nuclear radiation is discussed. Experimental results and techniques for the successful applications of strain gauges in nuclear environments are presented. It is concluded that weldable stain gauges can be used successfully under the very hostile conditions of nuclear reactor cores if appropriate procedures are followed

  4. Mechanical behaviour of nitrogen-implanted aluminium alloys

    Guzman, L. [Centro Materiali e Biofisica Medica, Trento (Italy); Bonini, G. [Dipt. di Ingegneria Nucleare del Politecnico, Milano (Italy); Adami, M. [Dipt. di Meccanica Strutturale, Univ. degli Studi di Trento (Italy); Ossi, P.M. [Dipt. di Ingegneria Nucleare del Politecnico, Milano (Italy)]|[Trento Univ., Povo (Italy). Dipt. di Fisica; Miotello, A. [Ist. Nazionale per la Fisica della Materia, Univ. degli Studi di Trento (Italy)]|[Trento Univ., Povo (Italy). Dipt. di Fisica; Vittori-Antisari, M. [ENEA, C.R. Casaccia, Settore Nuovi Materiali, Roma (Italy); Serventi, A.M. [ENEA, C.R. Casaccia, Settore Nuovi Materiali, Roma (Italy); Voltolini, E. [Centro Materiali e Biofisica Medica, Trento (Italy)


    The effect of nitrogen implantation into pure aluminium has been extensively explored, taking into account the variation of several physical and technological properties of the implanted layer. In particular, the formation of aluminium nitride, which occurs under specific choices of the implantation parameters, is associated with an increase in hardness. In this work, we consider two Al alloys (Al-7075 and Al-2011), frequently employed in the mechanical industry, with properties strongly dependent on the thermomechanical treatment. Molecular nitrogen bombardment at 150 keV (75 keV N{sup +}) was employed, up to a total dose of 3.10{sup 17} N cm{sup -2}, varying the substrate temperature from 373 to 473 K. The samples were then characterized with respect to composition, structure, morphology, microhardness, scratch resistance (also performing multi-pass testing) and friction coefficient. The results were interpreted within the framework of micromechanical models describing the hardness of thin coatings deposited onto soft substrates; the microhardness of the implanted layer increased by a factor of five. It appears that nitrogen-implanted aluminium alloy layers, in spite of their shallow thickness, behave better than hard TiN coated surfaces. Care must be taken to implant both alloys at the lowest possible temperature to avoid degradation of the substrate properties. (orig.)

  5. Mechanical behaviour of Bioactive Glass granules and morselized cancellous bone allograft in load bearing defects.

    Hulsen, D J W; Geurts, J; van Gestel, N A P; van Rietbergen, B; Arts, J J


    Bioactive Glass (BAG) granules are osteoconductive and possess unique antibacterial properties for a synthetic biomaterial. To assess the applicability of BAG granules in load-bearing defects, the aim was to compare mechanical behaviour of graft layers consisting of BAG granules and morselized cancellous bone allograft in different volume mixtures under clinically relevant conditions. The graft layers were mechanically tested, using two mechanical testing modalities with simulated physiological loading conditions: highly controllable confined compression tests (CCT) and more clinically realistic in situ compression tests (ISCT) in cadaveric porcine bone defects. Graft layer impaction strain, residual strain, aggregate modulus, and creep strain were determined in CCT. Graft layer porosity was determined using micro computed tomography. The ISCT was used to determine graft layer subsidence in bone environment. ANOVA showed significant differences (p<0.001) between different graft layer compositions. True strains absolutely decreased for increasing BAG content: impaction strain -0.92 (allograft) to -0.39 (BAG), residual strain -0.12 to -0.01, and creep strain -0.09 to 0.00 respectively. Aggregate modulus increased with increasing BAG content from 116 to 653MPa. Porosity ranged from 66% (pure allograft) to 15% (pure BAG). Subsidence was highest for allograft, and remarkably low for a 1:1 BAG-allograft volume mixture. Both BAG granules and allograft morsels as stand-alone materials exhibit suboptimal mechanical behaviour for load-bearing purpose. BAG granules are difficult to handle and less porous, whereas allograft subsides and creeps. A 1:1 volume mixture of BAG and allograft is therefore proposed as the best graft material in load-bearing defects. PMID:26972764

  6. Reactor and fuel behaviour under severe transient conditions in WAGR

    The Windscale prototype advanced gas-cooled reactor (WAGR) closed down in 1981. Following the formal shutdown a collaborative series of safety related experiments were performed, jointly funded by the UKAEA, CEGB and SSEB. Reactor transient tests were carried out, simulating aspects of postulated CAGR faults under conditions far beyond those achievable on commercial plant. Modelling of these tests with a CAGR fault study code has shown that a high degree of confidence can be placed in the predictions of the code. The experiments also included pressurised high temperature transients on individual fuel stringers in a loop of the reactor, which were intended to take the fuel pin cladding close to melting. Post-irradiation examination of the fuel has confirmed the success of the experiments, demonstrating the durability of the present CAGR fuel design under such conditions. (author)

  7. Cellular and molecular mechanisms underlying radiation carcinogenesis

    When considering and analyzing experimental material concerning cellular aspects of the problem of radiation carcinogenesis, the following conclusions can be made: neoplastic transformation of cells in a culture is caused already by small radiation doses, under the effect of which the level of DNA injury is quite insignificant; the frequency of cell transformation depends on the type of radiation, it is particularly pronounced under the effect of radiations with a high linear energy transfer; a correlation between the processes of postradiation recovery and radiogenic transformation of cells is detected, nonrepairable injures of DNA playing the most important role in radiation carcinogenesis; tumour promoters and anticarcinogenic agens produce a modifying effect on the transformation of irradiated cells. Molecular mechanisms of oncogene activation are thoroughly studied using the model of virus carcinogenesis, the problem of the nature of chemical and, in particular, radiation cell transformation remains scantily investigated

  8. Behaviour of Rotating Bose-Einstein Condensates Under Shrinking

    ZHAI Hui; ZHOU Qi


    @@ When the repulsive interaction strength between atoms decreases, the size of a rotating Bose-Einstein condensate will consequently shrink. We find that the rotational frequency will increase during the shrinking of condensate,which is a quantum mechanical analogy to ballet dancing. Compared to a non-rotating condensate, the size of a rotating BEC will eventually be satiated at a finite value when the interaction strength is gradually reduced.We also calculate the vortex dynamics induced by the atomic current, and discuss the difference of vortex dynamics in this case and that observed in a recent experiment carried out by the JILA group [Phys. Rev. Lett.90 (2003) 170405].

  9. How does the composition affect the mechanical behaviour of simulated clay-rich fault gouges?

    Bakker, Elisenda; Spiers, Christopher J.; Hangx, Suzanne J. T.


    CO2 capture and storage (CCS) in depleted oil and gas reservoirs is seen as one of the most promising large-scale CO2-mitigation strategies. Prediction of the effect of fluid-rock interaction on the mechanical integrity and sealing capacity of a reservoir-seal system, on timescales of the order of 1,000 or 10,000 years, is important to ensure the safety and containment of a reservoir in relation to long-term CO2 storage. However, most chemical reactions in rock/CO2/brine systems are slow, which means that long-term effects of fluids on rock composition, microstructure, mechanical properties and transport properties cannot be easily reproduced under laboratory conditions. One way to overcome this problem is to use simulated fault gouges in experiments, investigating a range of possible mineralogical compositions resulting from CO2-exposure. Previous studies have shown that the mechanical and transport properties of clay-rich fault gouges are significantly influenced by the mineralogy, particularly by the presence and relative amount of secondary phases, such as quartz and/or carbonate. In CCS settings, where dissolution and/or precipitation of carbonates may play an important role, the carbonate:clay ratio is expected to influence fault frictional behaviour. This is supported by the different behaviour of phyllosilicates, which generally show stable slip behaviour (aseismic), compared to carbonates, which have shown to become prone to unstable slip (potentially seismic) with increasing temperature. However, little is known about the mechanical and transport properties of carbonate/clay mixtures. We investigated the effect of the carbonate:clay ratio on fault friction, fault reactivation potential and slip stability, i.e. seismic vs. aseismic behaviour, as well as transmissivity evolution during and after fault reactivation. We used two types of starting material, derived from crushed Opalinus Claystone (Mont Terri, Switzerland): i) untreated samples consisting

  10. Mechanical and three-body abrasive wear behaviour of PMMA/TPU blends

    The blends of poly(methyl methacrlate) (PMMA) and thermoplastic polyurethane (TPU) were prepared by a Brabender co-twin screw extruder. The mechanical and three-body abrasive wear behaviour of PMMA/TPU blends has been studied. Three-body abrasive wear tests were conducted using rubber wheel abrasion tester (RWAT) under different abrading distances at 200 rpm and 22 N load. A significant reduction in tensile strength and tensile modulus with an increase in TPU content in the blend formulation was observed. Three-body abrasive wear results indicate that the wear volume increases with increase in abrading distance for all the samples studied. However, neat PMMA showed better wear resistance as compared to PMMA/TPU blends. The worn surface features, as examined through scanning electron microscope (SEM), show matrix cracking and deep furrows in PMMA/TPU blends

  11. Behaviour of concrete under high confinement: study in triaxial compression and in triaxial extension at the mesoscopic scale

    This Ph.D. thesis aims at characterising and modeling the mechanical behaviour of concrete under high confinement at the mesoscopic scale. This scale corresponds to that of the large aggregates and the cementitious matrix. The more general scope of this study is the understanding of concrete behaviour under dynamic loading. A dynamic impact can generate mean pressures around 1 GPa. But the characterisation of a material response, in an homogeneous state of stress, can only be achieved through quasi-static tests. The experimentations led in 3S-R Laboratory have underlined the importance of the aggregates in the triaxial response of concrete. Modeling concrete at the mesoscopic level, as a composite of an aggregates phase and a mortar phase, permits a representation of the aggregates effect. An experimental study of the behaviour of mortar phase is performed. Usual tests and hydrostatic and triaxial high confinement tests are realised. The parameters of a constitutive model that couples plasticity with a damage law are identified from these tests. This model is able to reproduce the nonlinear compaction of mortar, the damage behaviour under uniaxial tension or compression, and plasticity under high confinement. The biphasic model uses the finite element method with a cubic and regular mesh. A Monte-Carlo method is used to place quasi-spherical aggregates that respect the given particle size of a reference concrete. Each element is identified by belonging either to the mortar or to the aggregate phase. Numerical simulations are compared with the experimental tests on this concrete. The parameters for these simulations are only identified on the mortar. The simulations reproduce the different phases observed in hydrostatic compression. The evolution of axial moduli under growing confinement is shown, as is the good reproduction of the limit-states experimentally observed under high confinement. The fracture aspect of numerical simulations is comparable with that of

  12. Corrosion products behaviour under VVER primary coolant conditions

    The aim of this work was to collect data on thermodynamic stability of Cr, Fe, and Ni oxides, mechanisms of hydrothermal corrosion of stainless steels and to compare the real observation with the theory. We found that the electrochemical potential and pH in PWR and VVER are close to the thermodynamic boundary between two fields of stable spinel type oxides. The ways of degradation of the passivating layers due to changes in water chemistry were considered and PWR and VVER systems were found to be potentially endangered by reductive attack. In certain VVER systems the characteristics of the passivating layer on steels and also concentration of soluble corrosion products seem to be in contradiction with the theoretical expectations. (author)

  13. Mechanical behaviour of Nd:YAG laser welded superelastic NiTi

    Highlights: → The main innovations claimed are: understand rolling direction effect on mechanical cycling of laser welded NiTi. → Functionality confirmed by stabilization of hysteretic response up to 8% strain. → Welds tensile cycled exhibited superior functional mechanical behaviour. → For applied stresses of 50 MPa below UTS the joints showed superelastic behaviour. - Abstract: Joining techniques for shape memory alloys (SMA) has become of great interest, as their functional properties, namely shape memory effect (SME) and superelasticity (SE), present unique solutions for state-of-the-art applications, although limited results concerning mechanical properties are reported. This paper reports experimental work performed with Nd:YAG continuous wave laser welding of superelastic cold-rolled plates of NiTi 1 mm thick. The mechanical behaviour was evaluated by means of tensile tests performed both to failure and to cycling. The superelastic behaviour of the welded joints was observed for applied stresses close to about 50 MPa below the ultimate tensile strength of the welds. The functionality was confirmed by analyzing the stabilization of the mechanical hysteretic response to strain levels up to 8%. For tensile cycling involving strain levels larger than 6%, welded specimens were found to exhibit superior functional mechanical behaviour presenting larger recoverable strain levels. The fracture surfaces were observed by scanning electron microscopy (SEM) and the effect of the rolling direction on mechanical properties was evaluated and discussed, reinforcing the importance of joint design when laser welding these alloys.

  14. Biological mechanisms underlying the role of physical fitness in health and resilience

    Silverman, Marni N.; Deuster, Patricia A.


    Physical fitness, achieved through regular exercise and/or spontaneous physical activity, confers resilience by inducing positive psychological and physiological benefits, blunting stress reactivity, protecting against potentially adverse behavioural and metabolic consequences of stressful events and preventing many chronic diseases. In this review, we discuss the biological mechanisms underlying the beneficial effects of physical fitness on mental and physical health. Physical fitness appear...

  15. A nanoscale simulation study of the elastic behaviour in kaolinite clay under pressure

    Highlights: ► Kaolinite is quite compressible compared to the other clays. This reflects the possible uses in several applications including external constraints. ► The elastic constants such as C33, C13, C23 and C34 have a positive slope under pressure with 15%, 6%, 6% and 1.3%, respectively. ► A decrease of the Young modulus is noticed in a and b directions, whereas an increase in c direction appears with a slope equal to 10%. - Abstract: In this paper, Molecular dynamics simulation based on energy minimization technique has been used to study the structural and mechanical properties of kaolinite under pressure from 0 GPa to 25 GPa. Using the shell model, we have optimized the potential parameters according to Newton–Raphson procedure. Various mechanical properties have been calculated, such as the elastic constants, bulk modulus, shear modulus, Young modulus along a, b and c directions. Moreover the S- and P-wave velocities as well as Poisson ratio were also evaluated. Results reveal that kaolinite is quite compressible compared to the other clays. This reflects the possible uses in several applications including external constraints. In addition, we study the pressure effect on the elasticity of kaolinite. Results show that the elastic constants such as C33, C13, C23 and C34 have a positive slope under pressure with 15%, 6%, 6% and 1.3%, respectively. The remaining elastic constants are almost stable with a small change. A decrease of the Young modulus is noticed in a and b directions, whereas an increase in c direction appears with a slope equal to 10%. The ratio of the S- and P-wave velocities, which are key in the interpretation of seismic behaviours, gives Vp/Vs = 1.787, a value in favourable agreement with experimental data.

  16. Effect of the Young modulus variability on the mechanical behaviour of a nuclear containment vessel

    This study aims at investigating the influence of the Young modulus variability on the mechanical behaviour of a nuclear containment vessel in case of a loss of cooling agent accident and under the assumption of an elastic behaviour. To achieve this investigation, the Monte-Carlo Method is carried out thanks to a middleware which encapsulates the different components (random field generation, FE simulations) and enables calculations parallelisation. The main goal is to quantify the uncertainty propagation by comparing the maximal values of outputs of interest (orthoradial stress and Mazars equivalent strain) for each realisation of the considered random field with the ones obtained from a reference calculation taking into account uniform field (equal to the expected value of the random field). The Young modulus is supposed to be accurately represented by a weakly homogeneous random field and realisations are provided through its truncated Karhunen-Loeve expansion. This study reveals that the expected value for the maximal equivalent strain in the structure is more important when considering the Young modulus spatial variability than the value obtained from a deterministic approach with a uniform Young modulus field. The influence of the correlation length is investigated too. Finally it is shown that there is no correlation between the maximal values location of equivalent strain and the ones where the Young modulus extreme values are observed for each realisation.

  17. Characterisation and modelling of anisotropic thermo-mechanical behaviour of oriented polyethylene terephthalate

    The long-term and short-term anisotropic mechanical behaviour of a biaxially stretched polyethylene terephthalate foil is measured. The orientation of the crystalline phase is characterized and the representative foil microstructure is discussed. Using the obtained information, a mean-field model is used to simulate the elasto-viscoplastic behaviour of the oriented polymer foil, taking into account the different constitutive behaviour of the phases. The material is modelled as an aggregate of connected two-phase domains. The parameters of the constitutive behaviour of the crystalline and non-crystalline phases have been determined, and the ability to simulate the large-strain anisotropic behaviour of polyethylene terephthalate in the strain-rate-controlled regime and the long-term creep has been demonstrated. The model is extended to include pre-orientation of the non-crystalline phase. In addition, deformation at the microscopic level is analysed using the model results. (paper)

  18. Behaviour of lindane (gamma HCH) in soil under laboratory conditions

    The degradation of lindane in solid after multiple application was studied. The rate of disappearance of lindane increased at long periods after application. The dissipation of lindane was more rapid in soil collected from treated a plot than an untreated plot, owing to the degradation by micro-organisms suggesting that microorganisms had become adapted to degrade it. The rates of mineralization, mobility and degradation of lindane were also investigated under laboratory conditions using 14C-labelled lindane. The results showed that most of the applied dose remained on the upper 6cm in the soil columns. Over a periods of three months, extractable residues, bound residues and evolution of 14CO2 were recorded. After 12 weeks, the soil contained about 50% of the initially applied 14C and 20% was bound to the soil. The evolution of 14CO2 increased with time, amounting to 3.1% in non-sterile soil and less than 1% in sterile soil. The hexane 14C-extractable residues were shown, by TLC, to contain lindane as the main product. (author). 5 refs, 4 tabs

  19. Modelling of the mechanical behaviour of a material containing spherical cavities under pressure; example of the aging of a metal tritide; Modelisation du comportement mecanique d'un materiau contenant des cavites sous pression; cas du vieillissement d'un tritiure metallique

    Chalon, F


    The study aims at modeling the mechanical behaviour of a material containing spherical cavities under pressure (bubbles) of nano-metric size. This work deals with research on tritium storage in metals. In this way, metal tritides are obtained. During time, helium is generated by tritium decay. Helium appears as a gas, which forms bubbles in the metal tritide. These bubbles subsequently cause damage within the material. The purpose of this work was therefore the following: (i) to determine the overall elastic moduli as a function of the volume fraction of cavities. thus providing an information about material damage, (ii) to analyze the macroscopic inflation of the material in order to solve storage problems, (iii) to determine the local stress fields for predicting the evolutions of the bubbles and the matrix. With the help of the scale change methods (homogenization) the macroscopic mechanical properties of the material can be determined as a function of its morphology on a microscopic scale. Thus the damage of the material can be estimated by experimental measurements of the global elastic moduli. Homogenization also allows the elastic inflation to be evaluated as well as the effects of cavity clusters and local variations of the elastic moduli. The internal stresses are determined on the microscopic scale (cavity scale). Two analytical methods (Eshelby-Mura and Legendre polynomials) and one numerical approach (Abaqus) are used to obtain more information and a best description of the material. It is shown that bubbles should attain the same size and same pressure and the plastic strain zones are determined. (author)

  20. Deformation Mechanisms of Gum Metals Under Nanoindentation

    Sankaran, Rohini Priya

    defect structures to applied loading, we perform ex-situ nanoindentation. Nanoindentation is a convenient method as the plastic deformation is localized and probes a nominally defect free volume of the material. We subsequently characterize the defect structures in these alloys with both conventional TEM and advanced techniques such as HAADF HRSTEM and nanoprobe diffraction. These advanced techniques allow for a more thorough understanding of the observed deformation features. The main findings from this investigation are as follows. As expected we observe that a non-equilibrium phase, o, is present in the leaner beta-stabilized alloy, ST Ref-1. We do not find any direct evidence of secondary phases in STGM, and we find the beta phase in CWGM, along with lath microstructure with subgrain structure consisting of dislocation cell networks. Upon nanoindentation, we find twinning accompanied by beta nucleation on the twin boundary in ST Ref-1 samples. This result is consistent with previous findings and is reasonable considering the alloy is unstable with respect to beta transformation. We find deformation nanotwinning in cold worked gum metals under nanoindentation, which is initially surprising. We argue that when viewed as a nanocrystalline material, such a deformation mechanism is consistent with previous work, and furthermore, a deformation nanotwinned structure does not preclude an ideal shear mechanism from operating in the alloy. Lastly, we observe continuous lattice rotations in STGM under nanoindentation via nanoprobe diffraction. With this technique, for the first time we can demonstrate that the lattice rotations are truly continuous at the nanoscale. We can quantify this lattice rotation, and find that even though the rotation is large, it may be mediated by a reasonable geometrically necessary dislocation density, and note that similar rotations are typically observed in other materials under nanoindentation. HRSTEM and conventional TEM data confirm the

  1. Numerical and experimental investigation of bump foil mechanical behaviour

    Larsen, Jon Steffen; Cerda Varela, Alejandro Javier; Santos, Ilmar


    Corrugated foils are utilized in air foil bearings to introduce compliance and damping thus accurate mathematical predictions are important. A corrugated foil behaviour is investigated experimentally as well as theoretically. The experimental investigation is performed by compressing the foil......, between two parallel surfaces, both statically and dynamically to obtain hysteresis curves. The theoretical analysis is based on a two dimensional quasi static FE model, including geometrical non-linearities and Coulomb friction in the contact points and neglects the foil mass. A method for implementing...... the friction is suggested. Hysteresis curves obtained via the FE model are compared to the experimental results obtained. Good agreement is observed in the low frequency range and discrepancies for higher frequencies are thoroughly discussed....

  2. Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

    The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

  3. Concrete for PCRV's: Mechanical properties at elevated temperatures and residual mechanical behaviour after triaxial preloading

    During the lifetime of reactor vessels stress states will change as a result of changes in loading and heating, shrinkage and creep. For the design of prestressed concrete reactor vessels information is required about the behaviour of concrete under multiaxial short- and long-term loading at elevated temperatures. Therefore, tests were carried out at the Institut fuer Massivbau of the Technical University of Munich to study the properties of mass concrete under uniaxial loading at 353 K. Additionally, biaxial creep of concrete up to 368 K was investigated. Some of the uniaxial test specimens were sealed with a copper foil to avoid drying. The concrete contained calzite gravel. The thermal expansion coefficient of predried concrete was 9.5 x 10-6, of sealed concrete 13.6 x 10-6 and of unsealed concrete 13.2 x 10-6. The modulus of elasticity at 353 K (393 K) was reduced by 10 (13)% for sealed and by 15 (22)% for unsealed specimens. Total shrinkage deformations of heated concrete were 190 to 225 microstrains for sealed and 250 to 350 microstrains for unsealed specimens. Creep deformations were highly dependent upon temperature being about 3 times higher at 353 K for sealed and unsealed concrete. (orig.)

  4. Evolved Mechanisms Versus Underlying Conditional Relations

    Astorga Miguel López


    Full Text Available The social contracts theory claims that, in social exchange circumstances, human reasoning is not necessarily led by logic, but by certain evolved mental mechanisms that are useful for catching offenders. An emblematic experiment carried out with the intention to prove this thesis is the first experiment described by Fiddick, Cosmides, and Tooby in their paper of 2000. Lopez Astorga has questioned that experiment claiming that its results depend on an underlying conditional logical form not taken into account by Fiddick, Cosmides, and Tooby. In this paper, I propose an explanation alternative to that of Lopez Astorga, which does not depend on logical forms and is based on the mental models theory. Thus, I conclude that this other alternative explanation is one more proof that the experiment in question does not demonstrate the fundamental thesis of the social contracts theory.

  5. An Underlying Geometrical Manifold for Hamiltonian Mechanics

    Horwitz, L P; Levitan, J; Lewkowicz, M


    We show that there exists an underlying manifold with a conformal metric and compatible connection form, and a metric type Hamiltonian (which we call the geometrical picture) that can be put into correspondence with the usual Hamilton-Lagrange mechanics. The requirement of dynamical equivalence of the two types of Hamiltonians, that the momenta generated by the two pictures be equal for all times, is sufficient to determine an expansion of the conformal factor, defined on the geometrical coordinate representation, in its domain of analyticity with coefficients to all orders determined by functions of the potential of the Hamilton-Lagrange picture, defined on the Hamilton-Lagrange coordinate representation, and its derivatives. Conversely, if the conformal function is known, the potential of a Hamilton-Lagrange picture can be determined in a similar way. We show that arbitrary local variations of the orbits in the Hamilton-Lagrange picture can be generated by variations along geodesics in the geometrical pictu...

  6. Fatigue behaviour and crack growth of ferritic steel under environmental conditions

    The assessment of fatigue and cyclic crack growth behaviour of safety relevant components is of importance for the ageing management with regard to safety and reliability. For cyclic stress evaluation different codes and standards provide fatigue analysis procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. For the fatigue design curves used as a limiting criteria the influence of different factors like e.g. environment, surface finish and temperature must be taken into consideration in an appropriate way. Fatigue tests were performed in the low cycle fatigue (LCF) und high cycle fatigue (HCF) regime with low alloy steels as well as with Nb- and Ti-stabilized German austenitic stainless steels in air and high temperature (HT) boiling water reactor environment to extend the state of knowledge of environmentally assisted fatigue (EAF) as it can occur in boiling water reactor (BWR) plants. Using the reactor pressure vessel (RPV) steel 22NiMoCr3-7 experimental data were developed to verify the influence of BWR coolant environment (high purity water as well as sulphate containing water with 90 ppb SO4 at a test temperature of 240 C and an oxygen content of 400 ppb) on the fatigue life and to extend the basis for a reliable estimation of the remaining service life of reactor components. Corresponding experiments in air were performed to establish reference data to determine the environmental correction factor Fen accounting for the environment. The experimental results are compared with international available mean data curves, the new design curves and on the basis of the environmental factor Fen. Furthermore the behaviour of steel 22NiMoCr3-7 in oxygenated high temperature water under transient loading conditions was investigated with respect to crack initiation and cyclic crack growth. In this process the stress state of the specimen and the chemical composition of the high

  7. Coupling between chemical degradation and mechanical behaviour of leached concrete

    This work is in the context of the long term behavior of concrete employed in radioactive waste disposal. The objective is to study the coupled chemo-mechanical modelling of concrete. In the first part of this contribution, experimental investigations are described where the effects of the calcium leaching process of concrete on its mechanical properties are highlighted. An accelerated method has been chosen to perform this leaching process by using an ammonium nitrate solution. In the second part, we present a coupled phenomenological chemo-mechanical model that represents the degradation of concrete materials. On one hand, the chemical behavior is described by the simplified calcium leaching approach of cement paste and mortar. Then a homogenization approach using the asymptotic development is presented to take into account the influence of the presence of aggregates in concrete. And on the other hand, the mechanical part of the modelling is given. Here continuum damage mechanics is used to describe the mechanical degradation of concrete. The growth of inelastic strains observed during the mechanical tests is describes by means of a plastic like model. The model is established on the basis of the thermodynamics of irreversible processes framework. The coupled nonlinear problem at hand is addressed within the context of the finite element method. Finally, numerical simulations are compared with the experimental results for validation. (author)

  8. Mechanisms underlying UV-induced immune suppression

    Skin cancer is the most prevalent form of human neoplasia. Estimates suggest that in excess of one million new cases of skin cancer will be diagnosed this year alone in the United States ( Fortunately, because of their highly visible location, skin cancers are more rapidly diagnosed and more easily treated than other types of cancer. Be that as it may, approximately 10,000 Americans a year die from skin cancer. The cost of treating non-melanoma skin cancer is estimated to be in excess of US$ 650 million a year [J.G. Chen, A.B. Fleischer, E.D. Smith, C. Kancler, N.D. Goldman, P.M. Williford, S.R. Feldman, Cost of non-melanoma skin cancer treatment in the United States, Dermatol. Surg. 27 (2001) 1035-1038], and when melanoma is included, the estimated cost of treating skin cancer in the United States is estimated to rise to US$ 2.9 billion annually ( Because the morbidity and mortality associated with skin cancer is a major public health problem, it is important to understand the mechanisms underlying skin cancer development. The primary cause of skin cancer is the ultraviolet (UV) radiation found in sunlight. In addition to its carcinogenic potential, UV radiation is also immune suppressive. In fact, data from studies with both experimental animals and biopsy proven skin cancer patients suggest that there is an association between the immune suppressive effects of UV radiation and its carcinogenic potential. The focus of this manuscript will be to review the mechanisms underlying the induction of immune suppression following UV exposure. Particular attention will be directed to the role of soluble mediators in activating immune suppression

  9. Mechanisms underlying UV-induced immune suppression

    Ullrich, Stephen E. [Department of Immunology, University of Texas, MD Anderson Cancer Center, South Campus Research Building 1, 7455 Fannin St., P.O. Box 301402, Houston, TX 77030-1903 (United States)]. E-mail:


    Skin cancer is the most prevalent form of human neoplasia. Estimates suggest that in excess of one million new cases of skin cancer will be diagnosed this year alone in the United States ( Fortunately, because of their highly visible location, skin cancers are more rapidly diagnosed and more easily treated than other types of cancer. Be that as it may, approximately 10,000 Americans a year die from skin cancer. The cost of treating non-melanoma skin cancer is estimated to be in excess of US$ 650 million a year [J.G. Chen, A.B. Fleischer, E.D. Smith, C. Kancler, N.D. Goldman, P.M. Williford, S.R. Feldman, Cost of non-melanoma skin cancer treatment in the United States, Dermatol. Surg. 27 (2001) 1035-1038], and when melanoma is included, the estimated cost of treating skin cancer in the United States is estimated to rise to US$ 2.9 billion annually ( Because the morbidity and mortality associated with skin cancer is a major public health problem, it is important to understand the mechanisms underlying skin cancer development. The primary cause of skin cancer is the ultraviolet (UV) radiation found in sunlight. In addition to its carcinogenic potential, UV radiation is also immune suppressive. In fact, data from studies with both experimental animals and biopsy proven skin cancer patients suggest that there is an association between the immune suppressive effects of UV radiation and its carcinogenic potential. The focus of this manuscript will be to review the mechanisms underlying the induction of immune suppression following UV exposure. Particular attention will be directed to the role of soluble mediators in activating immune suppression.

  10. Mechanical behaviour of Astm A 297 grade Hp joints welded using different processes

    The influence of different arc welding processes on mechanical behaviour was studied for cast heat resistant stainless steel welded joints, in the as welded conditions. ASTM A 297 grade HP with niobium and niobium/titanium additions were welded following three different welding procedures, using shielded metal arc welding gas tungsten arc welding and plasma arc welding, in six welded joints. The welded joint mechanical behaviour was evaluated by ambient temperature and 870 deg C tensile tests; and creep tests at 900 deg C and 50 MPa. Mechanical test results showed that the welding procedure qualification following welding codes is not suitable for high temperature service applications. (author)

  11. Mechanical buckling of veins under internal pressure.

    Martinez, Ricky; Fierro, Cesar A; Shireman, Paula K; Han, Hai-Chao


    Venous tortuosity is associated with multiple disease states and is often thought to be a consequence of venous hypertension and chronic venous disease. However, the underlying mechanisms of vein tortuosity are unclear. We hypothesized that increased pressure causes vein buckling that leads to a tortuous appearance. The specific aim of this study was to determine the critical buckling pressure of veins. We determined the buckling pressure of porcine jugular veins and measured the mechanical properties of these veins. Our results showed that the veins buckle when the transmural pressure exceeds a critical pressure that is strongly related to the axial stretch ratio in the veins. The critical pressures of the eight veins tested were 14.2 +/- 5.4 and 26.4 +/- 9.0 mmHg at axial stretch ratio 1.5 and 1.7, respectively. In conclusion, veins buckle into a tortuous shape at high lumen pressures or reduced axial stretch ratios. Our results are useful in understanding the development of venous tortuosity associated with varicose veins, venous valvular insufficiency, diabetic retinopathy, and vein grafts. PMID:20094913

  12. Effect of carbonate content on the mechanical behaviour of clay fault-gouges

    Bakker, Elisenda; Niemeijer, André; Hangx, Suzanne; Spiers, Chris


    Carbon dioxide capture and storage (CCS) in depleted oil and gas reservoirs is considered to be the most promising technology to achieve large-scale reduction in anthropogenic emissions. In order to retain the stored CO2 from the atmosphere for the very long-term, i.e. on timescales of the order of 103-104 years, it is essential to maintain the integrity of the caprock, and more specifically of any faults penetrating the seal. When selecting suitable CO2-storage reservoirs, pre-exisiting faults within the caprock require close attention, as changes in the stress state resulting from CO2-injection may induce fault slip motion which might cause leakage. Little is known about the effect of fluid-rock interactions on the mineral composition, mechanical properties and the integrity and sealing capacity of the caprock. Previous studies on the effect of mineral composition on the frictional properties of fault gouges have shown that friction is controlled by the dominant phase unless there is a frictionally weak, through-going fabric. However, the effect on stability is less clear. Since long-term CO2-exposure might cause chemical reactions, potentially resulting in the dissolution or precipitation of carbonate minerals, a change in mineralogy could affect the mechanical stability of a caprock significantly. Calcite, for example, is known to be prone to micro-seismicity and shows a transition from velocity-strengthening to velocity-weakening behaviour around 100-150°C. Therefore, we investigated the effect of varying clay:carbonate ratios on fault friction behaviour, fault reactivation potential and slip stability, i.e. seismic vs. aseismic behaviour. Three types of simulated fault gouges were used: i) carbonate-free, natural clay-rich caprock samples, consisting of predominantly phyllosilicates (~80%) and quartz ~20%), ii) pure calcite, and iii) mixtures of carbonate-free clay-rich caprock and pure calcite, with predetermined clay:carbonate ratios. For the natural clay

  13. Two distinct neural mechanisms underlying indirect reciprocity.

    Watanabe, Takamitsu; Takezawa, Masanori; Nakawake, Yo; Kunimatsu, Akira; Yamasue, Hidenori; Nakamura, Mitsuhiro; Miyashita, Yasushi; Masuda, Naoki


    Cooperation is a hallmark of human society. Humans often cooperate with strangers even if they will not meet each other again. This so-called indirect reciprocity enables large-scale cooperation among nonkin and can occur based on a reputation mechanism or as a succession of pay-it-forward behavior. Here, we provide the functional and anatomical neural evidence for two distinct mechanisms governing the two types of indirect reciprocity. Cooperation occurring as reputation-based reciprocity specifically recruited the precuneus, a region associated with self-centered cognition. During such cooperative behavior, the precuneus was functionally connected with the caudate, a region linking rewards to behavior. Furthermore, the precuneus of a cooperative subject had a strong resting-state functional connectivity (rsFC) with the caudate and a large gray matter volume. In contrast, pay-it-forward reciprocity recruited the anterior insula (AI), a brain region associated with affective empathy. The AI was functionally connected with the caudate during cooperation occurring as pay-it-forward reciprocity, and its gray matter volume and rsFC with the caudate predicted the tendency of such cooperation. The revealed difference is consistent with the existing results of evolutionary game theory: although reputation-based indirect reciprocity robustly evolves as a self-interested behavior in theory, pay-it-forward indirect reciprocity does not on its own. The present study provides neural mechanisms underlying indirect reciprocity and suggests that pay-it-forward reciprocity may not occur as myopic profit maximization but elicit emotional rewards. PMID:24591599

  14. The thermal and mechanical behaviour of structural steel piping systems

    Fonseca, E.M.M.; F. J. M. Q. de Melo; Oliveira, C.A.M de


    The temperature, the deformation and the stress field in thermo-mechanical problems play a very important role in engineering applications. This paper presents a finite element algorithm developed to perform the thermal and mechanical analysis of structural steel piping systems subjected to elevated temperatures. The new pipe element with 22 degrees of freedom has a displacement field that results from the superposition of a beam displacement, with the displacement field associated w...

  15. Effect of microstructure on the mechanical and damping behaviour of dragonfly wing veins.

    Rajabi, H; Shafiei, A; Darvizeh, A; Dirks, J-H; Appel, E; Gorb, S N


    Insect wing veins are biological composites of chitin and protein arranged in a complex lamellar configuration. Although these hierarchical structures are found in many 'venous wings' of insects, very little is known about their physical and mechanical characteristics. For the first time, we carried out a systematic comparative study to gain a better understanding of the influence of microstructure on the mechanical characteristics and damping behaviour of the veins. Morphological data have been used to develop a series of three-dimensional numerical models with different material properties and geometries. Finite-element analysis has been employed to simulate the mechanical response of the models under different loading conditions. The modelling strategy used in this study enabled us to determine the effects selectively induced by resilin, friction between layers, shape of the cross section, material composition and layered structure on the stiffness and damping characteristics of wing veins. Numerical simulations suggest that although the presence of the resilin-dominated endocuticle layer results in a much higher flexibility of wing veins, the dumbbell-shaped cross section increases their bending rigidity. Our study further shows that the rubber-like cuticle, friction between layers and material gradient-based design contribute to the higher damping capacity of veins. The results of this study can serve as a reference for the design of novel bioinspired composite structures. PMID:26998340

  16. Mechanical behaviour of textile-reinforced thermoplastics with integrated sensor network components

    Highlights: → Consideration of two types of integrated bus systems for textile-reinforced thermoplastics with embedded sensor networks. → Specimens with bus systems made of flexible printed circuit boards show good mechanical performance compared to the reference. → Inhomogeneous interface and reduced stiffnesses and strengths for specimens with bus systems basing on single copper wires. -- Abstract: The embedding of sensor networks into textile-reinforced thermoplastics enables the design of function-integrative lightweight components suitable for high volume production. In order to investigate the mechanical behaviour of such functionalised composites, two types of bus systems are selected as exemplary components of sensor networks. These elements are embedded into glass fibre-reinforced polypropylene (GF/PP) during the layup process of unconsolidated weft-knitted GF/PP-preforms. Two fibre orientations are considered and orthotropic composite plates are manufactured by hot pressing technology. Micrograph investigations and computer tomography analyses show different interface qualities between the thermoplastic composite and the two types of bus systems. Mechanical tests under tensile and flexural loading indicate a significant influence of the embedded bus system elements on the structural stiffness and strength.

  17. Modelling and experimental contrast of the mechanical behaviour of structural laminated glass

    Sanz-Ablanedo, E.


    Full Text Available This paper presents a numerical simulation of the mechanical behaviour of laminated glass plates (glass- PVB-glass and its experimental verification. The viscoelastic characterization of the intermediate layer of PVB has been done by means of stress relaxation tests at various temperatures. The consideration of PVB as a viscoelastic material permits to analyze the real response of the structural element of laminated glass under time variations of temperature, of application of loading, of stress state, etc. Displacements obtained with the numerical analysis have been verified experimentally with laminated glass plates under lateral load using close range photogrammetry and dial gauges indicators. The analysis of results confirms the time dependent behaviour of the glass-PVB-glass laminate and suggests the validity of the proposed model.

    Este trabajo presenta la simulación numérica del comportamiento mecánico de placas de vidrio laminado (vidrio-PVB-vidrio y su comprobación experimental. La caracterización viscoelástica de la lámina intermedia de PVB se ha realizado mediante ensayos de relajación de tensiones a diversas temperaturas. La consideración del PVB como material viscoelástico permite analizar la respuesta real del elemento estructural de vidrio laminado ante variaciones en el tiempo de la temperatura, de la velocidad de aplicación de las cargas, del estado tensional, etc. Los desplazamientos obtenidos numéricamente han sido contrastados experimentalmente en placas de vidrio laminado sometidas a carga lateral mediante fotogrametría de objeto cercano y relojes comparadores. Del análisis de los resultados se confirma el comportamiento variable en el tiempo del conjunto vidrio-PVB-vidrio y se deduce la validez de la modelización propuesta.

  18. The behaviour of irradiated fuel under RIA transients: Interpretation of the CABRI experiments

    Paper presents the results of investigation of highly irradiated PWR fuel behaviour under fast power transients conducted in a sodium loop of CABRI reactor, as well as the results on development and validation of computer code SCANAIR. (author). 8 refs, 9 figs, 2 tabs

  19. Microstructural evolutions and mechanical behaviour of the nickel based alloys 617 and 230 at high temperature

    properties at 850 C and 950 C have been evaluated using several stress levels (creep), strain rates (tensile) and relaxation duration (fatigue). The effects of initial treatments have also been studied, i.e. ageing treatments effects on creep and tensile properties and cold-work effects on creep properties. At high temperature, the as received Inconel 617 does not show classical creep behaviour. This study shows the importance of the fast carbides precipitation on their mechanical properties, despite the fact that the Inconel 617 and the Haynes 230 are listed as solid solution alloys. Low cycle fatigue tests with and without holding time have been performed at 850 C under air and under vacuum on both alloys. The results showed that cyclic hardening, cyclic stability and life time are closely related to the duration of the holding time. Furthermore, a single thermally activated mechanism operates over a very wide range of strain rates, corresponding to tensile tests, creep and relaxation. The link between microstructure and mechanical behaviour presented in this thesis helps to determine the advantages as the operation limits of each alloy in order to manufacture a nuclear power plant heat exchanger. (author)

  20. Critical current behaviour of superconducting Chevrel phase wires under tensile stress and pressure

    The Chevrel-phase superconductors PbMo6S8 and SnMo6S8 with the critical magnetic fields Bc2 (4.2 K) = 51 T or 31 T, resp., currently are the most promising materials for applications as superconducting wires in very high magnetic fields, B > 20 T. A new process for industrial-scale production of the Chevrel-phase material using the HIP technique now is available, and the wires made of this material are competitive with otherwise fabricated wires in terms of critical currents: Jc (20 T) ≅ 104 A/cm2. The conductor configurations currently in use need some reinforcing steel in the cladding to guarantee the required mechanical stability. This reinforcing steel proportion and the pre-stressing of the filament have been varied by tests with the PbMo6S8 wires and the SnMo6S8 wires, for examining the critical current behaviour under external, axial tensile stress and transversal pressure, in magnetic fields up to 20 T. The results are compared with corresponding test results obtained with Nb3Sn wires, and are discussed with a view to applications in high magnetic fields. (orig.)

  1. Behaviour of rock-like oxide fuels under reactivity-initiated accident conditions

    Pulse irradiation tests of three types of un-irradiated rock-like oxide (ROX) fuel - yttria-stabilised zirconia (YSZ) single phase, YSZ and spinel (MgAl2O4) homogeneous mixture and particle-dispersed YSZ/spinel - were conducted in the Nuclear Safety Research Reactor to investigate the fuel behaviour under reactivity-initiated accident conditions. The ROX fuels failed at fuel volumetric enthalpies above 10 GJ/m3, which was comparable to that of un-irradiated UO2 fuel. The failure mode of the ROX fuels, however, was quite different from that of the UO2 fuel. The ROX fuels failed with fuel pellet melting and a part of the molten fuel was released out to the surrounding coolant water. In spite of the release, no significant mechanical energy generation due to fuel/coolant thermal interaction was observed in the tested enthalpy range below∼12 GJ/m3. The YSZ type and homogenous YSZ/spinel type ROX fuels failed by cladding burst when their temperatures peaked, while the particle-dispersed YSZ/spinel type ROX fuel seemed to have failed by cladding local melting. (author)

  2. Mechanical behaviour of ferritic ODS steels - Temperature dependancy and anisotropy

    Fournier, B.; Steckmeyer, A.; Rouffie, A.-L.; Malaplate, J.; Garnier, J.; Ratti, M.; Wident, P.; Ziolek, L.; Tournie, I.; Rabeau, V.; Gentzbittel, J. M.; Kruml, T.; Kubena, I.


    Ferritic 14%Cr and 18%Cr ODS steels produced at CEA in round bars or plates were tested mechanically. The present paper reports results obtained in tension, impact, fatigue, creep and toughness tests. These tests were carried out at various temperatures and in different directions. These materials show a pronounced anisotropy at all tested temperatures. No matter the loading, the transversal direction is always found to be far less resistant than the longitudinal one. This anisotropy is mainly observed in terms of damage mechanisms, with intergranular fracture preferentially occurring along the extrusion direction. This intergranular fracture mode leads to very low and anisotropic toughness values and to the absence of tertiairy creep stage, pointing out the unstable nature of fracture, even at high temperature. The unrealistically high values of the Norton exponent measured in creep suggests the existence of a threshold stress, which is consistent with the mainly kinematic nature of the stress as revealed by fatigue tests.

  3. Rat behaviour reactions and brain synaptic membrane lipids under the chronical gamma-irradiation

    The effects of low level chronical ionising irradiation (12.9 cGy/day on the sensory attention to the stimuli of different modalities (somatosensor, visual, odor) of Wistar rats were studied. Analysis of animals behaviour was made after they had received the different doses of irradiation: 4, 6, 8, 10, 15 and 20 Gy. It was founded, that the attention and exploratory activity of rats is significantly decreased up to 20-30% after 4-6 Gy. The irradiation doses 8 Gy did not change animal behaviour as compared to control animals, but doses 10, 15 and 20 Gy decreased the exploratory activity as well as sensory attention of rats to 3-5-times as compared to previous dose. Such a wave-like way of behaviour reflects the functioning of an adaptive mechanism. Biochemical data indicated that after 5 months of the irradiation (dose 20 Gy) the level of phospholipids, lysophosphatidylcholine, phosphatdylethanolamine, phosphatidylcholine, cholesterol were decreased

  4. Experimental creep behaviour determination of cladding tube materials under multi-axial loadings

    Cladding tubes are structural parts of nuclear plants, submitted to complex thermomechanical loadings. Thus, it is necessary to know and predict their behaviour to preserve their integrity and to enhance their lifetime. Therefore, a new experimental device has been developed to control the load path under multi-axial load conditions. The apparatus is designed to determine the thermomechanical behaviour of zirconium alloys used for cladding tubes. First results are presented. Creep tests with different biaxial loadings were performed. Results are analysed in terms of thermal expansion and of creep strain. The anisotropy of the material is revealed and iso-creep strain curves are given.

  5. Mechanical behaviour of composite materials made by resin film infusion

    Casavola C.; Pappalettere C.; Barile C.; Tursi F.


    Innovative composite materials are frequently used in designing aerospace, naval and automotive components. In the typical structure of composites, multiple layers are stacked together with a particular sequence in order to give specific mechanical properties. Layers are organized with different angles, different sequences and different technological process to obtain a new and innovative material. From the standpoint of engineering designer it is useful to consider the single layer of ...




    Alumina has got some excellent properties like chemical inertness, thermal and mechanical strength against hazardous environment. Alumina is a good ceramic material which is being used for structuralapplications. To enhance the toughness and strength of the body some Zirconia is also used with it. The use of Zirconia in alumina is known as toughening of alumina. One difficulty arises, when alumina and alumina toughened composite are sintered , because the low sinterability of Alumina-Zirconia...


    J. Sahari; S. M. Sapuan; Zainudin, E. S.; Maleque, M A


    A new Sugar Palm Starch (SPS) based biopolymer was successfully developed using glycerol as plasticizer. The effect of glycerol concentration (viz., 15, 20, 30 and 40 by weight percent) to the mechanical properties of plasticized SPS biopolymer was investigated. From this investigation, it was found that the 30% glycerol concentrated biopolymer showed the highest flexural strength and impact with the value of 0.13 MPa and 6.13 kJ/m2 respectively. Later, the above 30% gl...

  8. Simulation of disordered systems of cylinders. II. mechanical behaviour

    Stauffer, D.; Herrmann, H. J.; Roux, S


    A model is simulated, with non-linear relaxation methods close to molecular dynamics, describing the mechanical behavior of a random array of hard and soft parallel cylinders. Moreover, the hard cylinders fluctuate slightly in their radii. The relation between compression and force is about the same for the whole system as it is for two cylinders (Hertz law), if only soft cylinders exist. Instead, the radius fluctuations of the hard cylinders produce drastic deviations between the macroscopic...

  9. Mechanical behaviour of copper 15% volume niobium microcomposite wires

    Marcello Filgueira


    Full Text Available Cu-Nb microcomposites are attractive in magnet pulsed field technology applications due to their anomalous mechanism of mechanical strength and high electrical conductivity. In this sense, recently it was conceived the use of Cu 15% vol. Nb wires to operate as a high tensile strength cable for a diamond cutting tool (diamond wires for marble and granite slabbing. The multifilamentary Cu 15% vol. Nb composite was obtained using a new processing route, starting with niobium bars bundled into copper tubes, without arc melting. Cold working techniques, such as swaging and wire drawing, combined with heat treatments such as sintering and annealing, and tube restacking were employed. The tensile property of the composite was measured as a function of the niobium filaments dimensions and morphology into the copper matrix, in the several processing steps. An ultimate tensile strength (UTS of 960 MPa was obtained for an areal reduction (R = Ao/A, with Ao-initial cross section area, and A-final cross section area of 4x10(8 X, in which the niobium filaments reached thickness less than 20 nm. The anomalous mechanical strength increase is attributed to the fact that the niobium filaments acts as a barrier to copper dislocations.


    Telmo F. M. Morgado,


    Full Text Available Generation of virtual poles, based on the statistical distribution of selected visual and physical properties, and the estimation of their mechanical properties are of great help for predicting the quality of the roundwood that a forest stand can provide. With this objective in mind, an algorithm, SIMPOLE (SIMulator of POLEs, was developed. This algorithm allows the generation of pole’s geometry, as well as the mechanical properties of clear wood and the distribution of knots along its length. This generation is made through statistical distributions. The generated poles are simulated, either according to standard EN14251 or according to EN14229, for testing with simple supported beam conditions or with cantilever beam conditions, respectively. The algorithm outputs are: the bending strength, the modulus of elasticity, the location, and cause of failure. The algorithm was calibrated with a sample of 56 maritime pine utility poles and validated with another sample of 57 small diameter maritime pine poles. The results for the validation sample show: for bending strength, a mean error of 16.9%, and for modulus of elasticity, a mean error of 17.2%. Based on these results, the algorithm shows potential to estimate mechanical characteristics of small diameter poles from a forest.