Effect of thermo-mechanical processing on microstructure and electrochemical behavior of Ti-Nb-Zr-V new metastable β titanium biomedical alloy

The influence of thermo-mechanical processing (TMP) on the microstructure and the electrochemical behavior of new metastableβ alloy Ti?20.6Nb?13.6Zr?0.5V (TNZV) was investigated. The TMP included hot working in belowβ transus, solution heat treatments at the same temperature and different cooling rates in addition to aging. Depending upon the TMP conditions, a wide range of microstructures with varying spatial distributions and morphologies of equiaxed/elongatedα andβ phases were attained, allowing for a wide range of electrochemical properties to be achieved. The corrosion behavior of the studied alloy was evaluated in a Ringer’s solution at 37 °C via open circuit potential?time and potentiodynamic polarization measurements.

Short-and long-term behaviors of drifts in the Callovo-Oxfordian claystone at the Meuse/Haute-Marne Underground Research Laboratory

Since 2000, the French National Radioactive Waste Management Agency （ANDRA） has been constructing an Underground Research Laboratory （URL） at Bure （east of the Paris Basin） to perform experiments in order to obtain in situ data necessary to demonstrate the feasibility of geological repository in the Callovo- Oxfordian claystone. An important experimental program is planned to characterize the response of the rock to different drift construction methods, Before 2008, at the main level of the laboratory, most of the drifts were excavated using pneumatic hammer and supported with rock bolts, sliding steel arches and fiber shotcrete. Other techniques, such as road header techniques, stiff and flexible supports, have also been used to characterize their impacts. The drift network is developed following the in situ major stresses. The parallel drifts are separated enough so as they can be considered independently when their hydromechanical （HM） behaviors are compared. Mine-by experiments have been performed to measure the HM response of the rock and the mechanical loading applied to the support system due to the digging and after excavation. Drifts exhibit extensional （mode I） and shear fractures （modes II and III） induced by excavation works. The extent of the induced fracture networks depends on the drift orientation versus the in situ stress field. This paper describes the drift convergence and deformation in the surrounding rock walls as function of time and the impact of different support methods on the rock mass behavior. An observation based method is finally applied to distinguish the instantaneous and time-dependent parts of the rock mass deformation around the drifts.

Long-term dynamic behavior of monopile supported offshore wind turbines in sand

The complexity of the loads acting on the offshore wind turbines （OWl＇s） structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model are also summarized. The model is supported on monopile, subjected to different types of dynamic loading using an innovative out of balance mass system to apply cyclic/dynamic loads. The test results show the natural frequency of the wind turbine structure increases with the number of cycles, but with a reduced rate of increase with the accumulation of soil strain level. The change is found to be dependent on the shear strain level in the soil next to the pile which matches with the expectations from the element tests of the soil. The test results were plotted in a non-dimensional manner in order to be scaled to predict the orototvoe conseouences usin~ element tests of a soil usin~ resonant column aoDararus.

Prediction of Viscoelastic Behavior of Unidirectional Polymer Matrix Composites

To develop a novel method predicting the viscoelastic behavior of polymer matrix composites according to the viscoelasticity of the matrix, we used the viscoelastic model of the matrix to build new models for unidirectional composites in both 0° and 90° directions. Viscoelastic parameters for both new models were derived, and the obtained equations shared the same form as the viscoelastic constitutive equation of matrix material. The viscoelastic behaviors of matrix material and unidirectional composites were also tested. Results showed that fitting parameters of creep compliance equation were close to the theoretical values of viscoelastic constitutive parameters of the unidirectional composites, proving the validity of the models. A new method was obtained to predict the viscoelastic property of the unidirectional composites based on the viscoelastic property of composite matrix and elastic property of the unidirectional composites. This method provides a theoretical basis for future studies on the viscoelasticity of composite laminates.

Kriging-based reliability analysis of the long-term stability of a deep driftconstructed in the Callovo-Oxfordian claystone

Callovo-Oxfordian(COx)claystone has been considered as a potential host rock for geological radioactive waste disposal in France(Cigéo project).During the exploitation phase(100 years),the stability of drifts(e.g.galleries/alveoli)within the disposal is assured by the liner,which includes two layers:concrete arch segment and compressible material.The latter exhibits a significant deformation capacity(about 50%)under low stress(<3 MPa).Although the response of these underground structures can be governed by complex thermo-hydro-mechanical coupling,the creep behavior of COx claystone has been considered as the main factor controlling the increase of stress state in the concrete liner and hence the long-term stability of drifts.Therefore,by focusing only on the purely mechanical behavior,this study aims at investigating the uncertainty effect of the COx claystone time-dependent properties on the stability of an alveolus of Cigéo during the exploitation period.To describe the creep behavior of COx claystone,we use Lemaitre’s viscoplastic model with three parameters whose uncertainties are identified from laboratory creep tests.For the reliability analysis,an extension of a well-known Kriging metamodeling technique is proposed to assess the exceedance probability of acceptable stress in the concrete liner of the alveolus.The open-source code Code_Aster is chosen for the direct numerical evaluations of the performance function.The Kriging-based reliability analysis elucidates the effect of the uncertainty of COx claystone on the long-term stability of the concrete liner.Moreover,the role of the compressible material layer between the concrete liner and the host rock is also highlighted.

Evolution of macro-meso properties of intact loess under long-term seepage and its influence on irrigation-induced loess flowslides

The loess tableland provides an excellent site for people to live and cultivate.However,flowslides occur frequently on the slope of loess tablelands due to agriculture irrigation,resulting in serious economic losses and casualties.The structure degradation effect of irrigation water seepage on intact loess leads to a weakening of its mechanical properties,which may be responsible for the recurrent occurrence of flowslides in irrigated loess tablelands.In this paper,seepage tests and triaxial tests were carried out to investigate the evolution of the microstructure and undrained shear properties of intact loess during seepage.The results show that water seepage leads to a significant decrease in pore water ion concentration and migration of fine particles with water flow,but no noticeably change in mineral composition.During seepage,the metastable structure of intact loess collapses,the fine particles disperse around the skeleton particle to fill the pores,and the total porosity decreases.The permeability coefficient gradually decreases with seepage time and then tends to a constant.The saturated intact loess shows strongly contractive behavior during undrained shear and has considerable liquefaction potential.After seepage,the intact loess is characterized by more rapid build-up of pore water pressure and more intense strain-softening during shearing and has lower shear strength(including peak strength and steady-state strength).In irrigated loess tablelands,long-term seepage could weaken the shear strength of intact loess and increases its liquefaction potential,which contributes to the initiation of loess flowslide failure and the movement with high-speeds and long run-outs.

A phenomenological memristor model for synaptic memory and learning behaviors

Properties that are similar to the memory and learning functions in biological systems have been observed and reported in the experimental studies of memristors fabricated by different materials. These properties include the forgetting effect, the transition from short-term memory（STM） to long-term memory（LTM）, learning-experience behavior, etc. The mathematical model of this kind of memristor would be very important for its theoretical analysis and application design.In our analysis of the existing memristor model with these properties, we find that some behaviors of the model are inconsistent with the reported experimental observations. A phenomenological memristor model is proposed for this kind of memristor. The model design is based on the forgetting effect and STM-to-LTM transition since these behaviors are two typical properties of these memristors. Further analyses of this model show that this model can also be used directly or modified to describe other experimentally observed behaviors. Simulations show that the proposed model can give a better description of the reported memory and learning behaviors of this kind of memristor than the existing model.

Atom-continuum coupled model for thermo-mechanical behavior of materials in micro-nano scales

In this paper,an atom-continuum coupled model for thermo-mechanical behaviors in micro-nano scales is presented.A representative volume element consisting of atom clusters is used to represent the microstructure of materials.The atom motions in the RVE are divided into two phases,structural deformations and thermal vibrations.For the structural deformations,nonlinear and nonlocal deformation at atomic scales is considered.The atomistic-continuum equations are constructed based on momentum and energy conservation law.The non-locality and nonlinearity of atomistic interactions are built into the thermo-mechanical constitutive equations.The coupled atomistic-continuum thermal-mechanical simulation process is also suggested in this work.

Mathematical model of coupled thermo-mechanical behavior during plane strain compression of 06Cr19Ni9NbN steel

The process of plane strain compression of 06Cr19Ni9NbN steel was carried out in the temperature range of 1000-1200℃ and the reduction ratio range of 10-50%.Combining the finite element numerical simulation,a new constitutive model of thermal deformation was established, which provides the theoretical basis to optimize the plarie strain compression process of the steel.The temperature and grain size at different regions were achieved by experiment and simulation,respectively.According to the results,the mathematical models of stress and temperature during the plane strain compression were established by mathematical analysis method.The new temperature models were established in three regions,respectively,and the stress models took account of the variation of temperature and'st^rain rate.Finally,by comparing the results of calculation,numerical simulation and experiment,the accuracy and validity of these mathematical models were verified.

Long-term spatial memory in Vespula germanica social wasps： the influence of past experience on foraging behavior

Social insects exhibit complex learning and memory mechanisms while for- aging. Vespula germanica （Fab.） （Hymenoptera： Vespidae） is an invasive social wasp that frequently forages on undepleted food sources, making several flights between the resource and the nest. Previous studies have shown that during this relocating behavior, wasps learn to associate food with a certain site, and can recall this association 1 h later. In this work, we evaluated whether this wasp species is capable of retrieving an established association after 24 h. For this purpose, we trained free flying individuals to collect proteinaceous food from an experimental plate （feeder） located in an experimental array. A total of 150 individuals were allowed 2, 4, or 8 visits. After the training phase, the array was re- moved and set up again 24 h later, but this time a second baited plate was placed opposite to the first. After 24 h we recorded the rate of wasps that returned to the experimental area and those which collected food from the previously learned feeding station or the nonlearned one. During the testing phase, we observed that a low rate of wasps trained with 2 collecting visits returned to the experimental area （22%）, whereas the rate of returning wasps trained with 4 or 8 collecting visits was higher （51% and 41%, respectively）. Moreover, wasps trained with 8 feeding visits collected food from the previously learned feeding station at a higher rate than those that did from the nonlearned one. In contrast, wasps trained 2 or 4 times chose both feeding stations at a similar rate. Thus, significantly more wasps returned to the previously learned feeding station after 8 repeated foraging flights but not after only 2 or 4 visits. This is the first report that demonstrates the existence of long-term spatial memory in V. germanica wasps.

Flexural failure experiment on cracked PC simply supported box girders

Long-term load and flexural failure experiments are carried out on two prestressed concrete(PC) simply supported box girders. In the long-term load experiment, girder-1(G1) is in an elastic state, while girder-2(G2) is in a cracking state. To investigate the influence of cracking on the flexural behaviors of PC simply supported box beams, the experiment results are analyzed from many aspects, such as load–deflection, load–strain, and failure mode. Experiment results show the following: 1) the shrinkage and creep of concrete have considerable influences on the long-term deflection and strain of the two girders; 2) in the flexural failure experiment, the cracks and ultimate loads of the two girders are close. The rigidity degeneration of G2 is significantly faster than that of G1, and thus G2 shows nonlinear characteristics earlier; 3) to prove the validity and rationality of the current code, the cracking load and ultimate load of the two girders are calculated according to the current code.

Laboratory creep tests for time-dependent properties of a marble in Jinping Ⅱ hydropower station

In order to investigate the time-dependent behaviors of deep hard rocks in the diversion tunnel of Jinping II hydropower station, uniaxial creep tests were carried out by using the triaxial testing machine RC-2000. The axial compressive load was applied step by step and each creep stage was kept for over several days. Test results show that： （1） The lateral deformation of rock specimens is 2-3 times the axial compressive deformation and accelerates drastically before damage, which may be employed as an indicator to predict the excavation-induced instability of rocks. （2） The resultant deformation changes from compression to expansion when the Poisson＇s ratio is larger than 0.5, indicating the starting point of damage. （3） In the step-loading stages, the Poisson＇s ratio approximately remains constant; under constantly imposed load, the Poisson＇s ratio changes with elapsed time, growing continuously before the specimen is damaged. （4） When the applied load reaches a certain threshold value, the rock deteriorates with time, and the strength of rocks approximately has a negative exponent relation with time. （5） The failure modes of the deep marble are different in long- and short-term loading conditions. Under the condition of short-term loading, the specimen presents a mode of tensile failure; while under the condition of long-term loading, the specimen presents a mode of shear failure, followed by tensile failure.

The Development of Stylolites in Carbonate Formation: Implication for CO_2 Sequestration

The impact of CO2 sequestration on the host formation is an issue occurring over geologic time. Laboratory tests can provide important results to investigate this matter but have limitations due to a relatively short timeline. Based on literature review and core sample observation, naturally occurred geological phenomena, stylolites are studied in this paper for understanding CO2 sequestration in deep carbonate formations. Stylolites are distinctive and pervasive structures in carbonates that are related to water-assisted pressure solution. Pressure solution involving stylolitization is thought to be the main mechanism of compaction and cementation for many carbonates. In parallel, CO2 sequestration in carbonate formation involves extensive chemical reactions among water, CO2 and rock matrix, favoring chemical compaction as a consequence. An analogue between stylolites and CO2 sequestration induced formation heterogeneity exists in the sense of chemical compaction, as both pressure solution in stylolites and CO2 enriched solution in CO2 sequestration in carbonate formations may all introduce abnormal porous regions. The shear and/or tension fractures associated with stylolites zones may develop vertically or sub-vertically; all these give us alert for long-term safety of CO2 sequestration. Thus a study of stylolites will help to understand the CO2 sequestration in deep carbonate formation in the long run.

Fractal and chaotic laws on seismic dissipated energy in an energy system of enginering structures

Fractal and chaotic laws of engineering structures are discussed in this paper, it means that the intrinsic essences and laws on dynamic systems which are made from seismic dissipated energy intensity E d and intensity of seismic dissipated energy moment I e are analyzed. Based on the intrinsic characters of chaotic and fractal dynamic system of E d and I e, three kinds of approximate dynamic models are rebuilt one by one: index autoregressive model, threshold autoregressive model and local-approximate autoregressive model. The innate laws, essences and systematic error of evolutional behavior I e are explained over all, the short-term behavior predictability and long-term behavior probability of which are analyzed in the end. That may be valuable for earthquake-resistant theory and analysis method in practical engineering structures.

Thermomechanical Testing of GGG 40 Spheroidal Graphite Cast Iron Alloy

Spheroidal graphite cast iron GGG 40 was thermo-mechanically tested using thermo-mechanical simulator Gleeble-3500. Three deformation steps were successively applied on test-specimen at temperatures namely;900&deg;C, 850&deg;C and 750&deg;C within the austenitic zone, at the same strain rate of 0.1 s-1. No cracks were observed, up to 50% deformation, after successive deformation steps. Stress-strain relationship obtained is correlated with previous work on SGCI with a different carbon equivalent. It was found that by decreasing the deformation temperature;for the same CE, young’s modulus, yield strength and strain hardening exponent increase. Microstructure of the deformed zone, for a specimen quenched after the final deformation step, reveals fine elongated ferrite and pearlite, as well as elongated graphite. While microstructure of the non-deformed zone subjected to the same treatment, includes coarser ferrite and pearlite with graphite spheres embedded in the matrix.

Support elements in conventional tunneling–Focus on long-term behavior

Owing to increasing traffic and the need for constructing second tunnel tubes including corresponding cross-passages,where only one tube existed thus far,sampling of tunnel-lining materials with an age of 30–40 years has been made possible.Laboratory and in situ tests were carried out to evaluate the long-term effects of the tunnel linings.This paper presents the outcomes regarding the long-term behav-ior of support elements and membranes after performing strength tests on inner and outer lining concrete samples,flat jack tests,rock bolt tests,and tests on re-extracted sheet membranes,as well as geotextiles.Furthermore,the interface connection mechanical behavior in a double-shell-lined tunnel was investigated with laboratory tests.The aim of this research was to determine the characteristics of sheet membranes and geotextiles in the case of reduced load-bearing capacity caused by degradation of the primary lining.The results provide information on the load-sharing effects of the interaction between the primary and secondary lining,depending on the waterproofing sheet membrane and geotextile properties.Based on the results,conclusions for new design approaches for underground infrastructure construction can be formulated.

Creep and Shrinkage Self-Compacting Concrete （SCC） Analytical Models

In the structures whose long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Creep and shrinkage, vary with the constituent and mixtures proportions, and depend on the curing conditions and work environment as well. Self-compacting concrete （SCC） contains combinations of various components, such as aggregate, cement, superplasticizer, water-reducing agent and other ingredients which affect the properties of the SCC including creep and shrinkage of the SCC. Hence, the realistic prediction creep and shrinkage strains of SCC are an important requirement of the design process of this type of concrete structures. In this study, three proposed creep models and four shrinkage models available in the literature are compared with the measured results of 52 mixtures for creep and 165 mixtures for shrinkage of SCC. The influence of various parameters, such as mixture design, cement content, filler content, aggregate content, and water cement ratio （w/c） on the creep and shrinkage of SCC are also compared and discussed.

Effect of Deformation Parameters on Microstructural Evolution of GGG 40 Spheroidal Graphite Cast Iron Alloy

Studying the thermo-mechanical behavior of ductile iron is necessary to develop the rolling process for ductile iron sheet/strip production, thus, extending its application by replacing steel in several fields such as machine casing, constructional applications, etc. In order to predict the safe rolling conditions for producing sheets and strips, the thermo-mechanical behavior of a ductile iron alloy, with CE of 4.48, is studied by physical simulation of hot rolling process using Gleeble-3500 simulator. The test was conducted on specimens at a range of deformation temperatures from 800°C to 950°C while three different strain rates;namely 0.05, 0.1 and 0.5 s-1 were used. The results obtained, show minimum values of flow stresses at 850°C. By increasing the deformation temperature up to 900°C, the flow stresses increased to reach maximum values, beyond which the flow stress decreased again. A remarkable dynamic recrystallization is observed at the deformation temperatures of 850°C and 800°C with applied strain rates of 0.05 and 0.1 s-1. Gleeble test results are correlated with microstructure observations on samples quenched at their deformation temperatures, where the changes in structure and graphite morphology are reported. The deformation process at high temperatures namely 950°C and 900°C result in changing the graphite shape from a spheroidal-like to a saucer-like shape. However, by decreasing the deformation temperature to 850°C as well as 800°C, graphite with lamellar shape is observed. As a conclusion, ductile iron could be successfully deformed without cracking at the applied conditions.

A Framework of Mobile Context-Aware Recommender System

Mobile users can be recommended services or goods precisely according to their actual needs even in different contexts. Therefore, it is necessary to construct a framework integrating following functions: context identification,context reasoning, services or product recommendations and other tasks for the mobile terminal. In this paper, we firstly introduce mobile context awareness theory, and describe the composition of context-aware mobile systems. Secondly, we construct a framework of mobile context-aware recommendation system in line with the characteristics of mobile terminal devices and mobile context-aware data. Then, we build a nested key-value storage model and an up-to-date algorithm for mining mobile context-aware sequential pattern,in order to find both the user’s long-term behavior pattern and the new trend of his recent behavior, to predict user’s next behavior. Lastly, we discuss the difficulties and future development trend of mobile context-aware recommendation system.

Three-dimensional dissipative stress space considering yield behavior in deviatoric plane

Naturally deposited soils are always found in the complex three-dimensional stress state.Constitutive models developed for modeling the three-dimensional mechanical behavior of soils should obey the basic laws of thermo-mechanical principles.Based on the incremental dissipation function,a new deviatoric shift stress is derived and then introduced into the existing constitutive models to describe the yield behavior in the deviatoric plane for geomaterials.By adopting the proposed shift stress,the relationship between dissipative stress tensors and true stress tensors can be established.Therefore,the threedimensional plastic strain can be calculated reasonably through the associated flow rule in the three-dimensional dissipative stress space.At the same time,three methods that are conventionally adopted for generalizing constitutive models to model the three-dimensional stress-strain relationships are examined under the thermo-mechanical framework.The TS(transformed stress)method is shown to obey the thermo-mechanical rules and the TS space adopted in TS method is actually a translational three-dimensional dissipative stress space.However,it is illustrated that the other two approaches,the method of using failure criterion directly and the method of using g()function,violate the basic rules of thermo-mechanical theories although they may bring convenience and simplicity to numerical analysis for geotechnical engineering.Comparison between model predictions and experimental data confirms the validity of the proposed three-dimensional dissipative stress space.