The grain size, textures and grain boundary plane distributions in a cold-rolled and annealed ferritic stainless steel were investigated by means of EBSD techniques. The results show that, following cold rolling with the thickness reduction of 85%, relatively low temperature (780°C) annealing brings an extremely sluggish grain growth and no grain texture develops when the annealing time varies from 5 min to 480 min. The free energy reduction of the system is mainly caused by the grain boundary plane re-orientation in addition to minor grain growth because the distributions of grain boundary planes are moderately preferred on {100} according to the five parameter analyses (FPA) concerning the grain boundary plane characteristics. However, in the case of high-temperature (1 000 °C) annealing, the average grain size does not increase until annealing time is prolonged to 90 min, after which extensive grain growth occurs and strong {100} 〈hkl〉 texture emerges whereas nearly random grain boundary plane distributions are observed. The free energy reduction of the system is most likely attributed to the selective growth.
To investigate the effects of billet geometry on the cold precision forging process of a helical gear, six different billet geometries were designed utilizing the relief-hole principle. And the influences of the billet geometry on the forming load and the deformation uniformity were analyzed by three-dimensional (3D) finite element method (FEM) under the commercial software DEFORM 3D. The billet geometry was optimized to meet lower forming load and better deformation uniformity requirement. Deformation mechanism was studied through the distribution of flow velocity field and effective strain field. The forging experiments of the helical gear were successfully performed using lead material as a model material under the same process conditions used in the FE simulations. The results show that the forming load decreases as the diameter of relief-hole d0 increases, but the effect of d0 on the deformation uniformity is very complicated. The forming load is lower and the deformation is more uniform when d0 is 10 mm.
Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) based composite polymer electrolyte (CPE) modified with CeO2, La2O3 and Y2O3 nano-rare earth oxides was prepared by phase inversion technique. Physical and chemical properties of the modified CPEs were studied by SEM, TG-DSC and electrochemical methods. The results show that the CPE modified with 10% La2O3 (mass fraction) has the best practical applicability, which indicates that the thermal and electrochemical stability can reach over 400 °C and 4.5 V, respectively, and temperature dependence of ionic conductivity follows Vogel-Tamman-Fulcher (VTF) relationship and ionic conductivity at room temperature is up to 3.3 mS/cm. The interfacial resistance Ri reaches a stable value about 557 Ω after 6 d storage.
The CaCu3Ti4O12 xerogels, powders and ceramics were prepared through the sol-gel method using two kinds of organic acid (decanoic acid and decanedioic acid). The xerogels, powders and ceramics were characterized by the methods of TG-DTG, FT-IR, XRD, SEM and TEM. The dielectric properties of the ceramics were also measured. The results indicated that the powders calcined at 850 °C for 2 h are both nanometer scale particles. After sintering, the ceramics mainly consist of the CaCu3Ti4O12 phase. Compared with the powders prepared using monoacid, the particle size of the powders prepared using diacid obviously increases, and the grain size, the relative density and the whole permittivity of the ceramics increase as well. Specially, the ceramic prepared using decanedioic acid has higher relative density (97.3%), dielectric constant (316 808) and lower dielectric loss (0.242 5) at 30 °C (10 kHz)
The leaching results of bismuth sulfide concentrate containing molybdenum and tungsten in air-H2O2-NaOH system, pressure-O2-Na2CO3 system and pressure-O2-NaOH system were investigated. The results show that the extraction of molybdenum, tungsten and sulfur goes up with the increase of NaOH concentration, oxygen partial pressure and reaction time. The extraction of molybdenum and tungsten also rises up with temperature, but the leaching ratio of sulfur increases initially to a peak of 98% at 150°C and then decreases with the increase of temperature. Under the optimal conditions, the extraction of molybdenum, tungsten and sulfur is more than 95.6%, 93.8% and 96.0%, respectively, and the main phases of residue are Bi2O3 and Fe2O3. Therefore, the method of pressure leaching in alkaline solution is provided as an effective separation of molybdenum, tungsten and sulfur from bismuth and a beneficial pretreatment for consequent process.
For physical ozone absorption without reaction, two parametric estimation methods, i. e. the common linear least square fitting and non-linear Simplex search methods, were applied, respectively, to determine the ozone mass transfer coefficient during absorption and both methods give almost the same mass transfer coefficient. While for chemical absorption with ozone decomposition reaction, the common linear least square fitting method is not applicable for the evaluation of ozone mass transfer coefficient due to the difficulty of model linearization for describing ozone concentration dissolved in water. The nonlinear Simplex method obtains the mass transfer coefficient by minimizing the sum of the differences between the simulated and experimental ozone concentration during the whole absorption process, without the limitation of linear relationship between the dissolved ozone concentration and absorption time during the initial stage of absorption. Comparison of the ozone concentration profiles between the simulation and experimental data demonstrates that Simplex method may determine ozone mass transfer coefficient during absorption in an accurate and high efficiency way with wide applicability.
A learning controller of nonhonolomic robot in real-time based on support vector machine (SVM) is presented. The controller includes two parts: one is kinematic controller based on nonlinear law, and the other is dynamic controller based on SVM. The kinematic controller is aimed to provide desired velocity which can make the steering system stable. The dynamic controller is aimed to transform the desired velocity to control torque. The parameters of the dynamic system of the robot are estimated through SVM learning algorithm according to the training data of sliding windows in real time. The proposed controller can adapt to the changes in the robot model and uncertainties in the environment. Compared with artificial neural network (ANN) controller, SVM controller can converge to the reference trajectory more quickly and the tracking error is smaller. The simulation results verify the effectiveness of the method proposed.
In general, the orientation interpolation of industrial robots has been done based on Euler angle system which can result in singular point (so-called Gimbal Lock). However, quaternion interpolation has the advantage of natural (specifically smooth) orientation interpolation without Gimbal Lock. This work presents the application of quaternion interpolation, specifically Spherical Linear IntERPolation (SLERP), to the orientation control of the 6-axis articulated robot (RS2) using LabVIEW® and RecurDyn®. For the comparison of SLERP with linear Euler interpolation in the view of smooth movement (profile) of joint angles (torques), the two methods are dynamically simulated on RS2 by using both LabVIEW® and RecurDyn®. Finally, our original work, specifically the implementation of SLERP and linear Euler interpolation on the actual robot, i.e. RS2, is done using LabVIEW® motion control tool kit. The SLERP orientation control is shown to be effective in terms of smooth joint motion and torque when compared to a conventional (linear) Euler interpolation.
To alleviate the conservativeness of the stability criterion for Takagi-Sugeno (T-S) fuzzy time-delay systems, a new delay-dependent stability criterion was proposed by introducing a new augmented Lyapunov function with an additional triple-integral term, which was firstly used to derive the stability criterion for T-S fuzzy time-delay systems. By the same approach, the robust stability issue for fuzzy time-delay systems with uncertain parameters was also considered. On the other hand, in order to enhance the design flexibility, a new design approach for uncertain fuzzy time-delay systems under imperfect premise matching was also proposed, which allows the fuzzy controller to employ different membership functions from the fuzzy time-delay model. By the numerical examples, the proposed stability conditions are less conservative in the sense of getting larger allowable time-delay and obtaining smaller feedback control gains. For instance, when the allowable time-delay increases from 7.3 s to 12 s for an uncertain T-S fuzzy control system with time-delay, the norm of the feedback gains decreases from (34.299 2, 38.560 3) to (10.073 3, 11.349 0), respectively. Meanwhile, the effectiveness of the proposed design method was illustrated by the last example with the robustly stable curves of system state under the initial condition of x(0)=[3 −1]
An impeller is difficult to machine because of severe collision due to the complex shape, overlapping and twisted shape of the impeller blades. So, most computer aided manufacturing (CAM) software companies have developed CAM module for manufacturing impeller according to their CAM software. But these dedicated modules are difficult to use for inexperienced users. The purpose of this work is to develop a tool-path generation module for impellers. For this purpose, it is based on Visual Basic language and used CATIA graphical environment. The result of simulation for generated tool-path by the module is satisfactory. And it has slow processing speed compared to other commercial modules, but it is easy to use.
Parametric modeling of the impeller which drove a small wind device was built by knowledge fusion technology. NACA2410 airfoil blade was created by KF language. Using technology of UG/KF secondary development for the automatic modeling of wind turbine blade, the program can read in the airfoil data files automatically and the impeller model entity can be generated automatically. In order to modify the model, the aerodynamic characteristics of the impeller were analyzed for getting aerodynamic parameters by Fluent. The maximum force torch and best parameters of impeller were calculated. A physical prototype impeller was manufactured and the correctness of the design was verified, and the error of force torch between simulation and experimental results is about 10%. Parameterization design of the impeller model greatly improves the efficiency of modeling and flexibility of the CAD system.
To solve the problem of stray interference to star point target identification while a star sensor imaging to the sky, a study on space luminous environment adaptability of missile-borne star sensor was carried out. By Plank blackbody radiation law and some astronomic knowledge, irradiancies of the stray at the star sensor working height were estimated. By relative astrophysical and mathematics knowledge, included angles between the star sensor optical axis point and the stray at any moment were calculated. The calculation correctness was verified with the star map software of Stellarium. By combining the upper analysis with the baffle suppression effect, a real-time model for space luminous environment of missile-borne star sensor was proposed. By signal-noise rate (SNR) criterion, the adaptability of missile-borne star sensor to space luminous environment was studied. As an example, a certain type of star sensor was considered when imaging to the starry sky on June 22, 2011 (the Summer Solstice) and September 20, 2011 (August 23 of the lunar year, last quarter moon) in Beijing. The space luminous environment and the adaptability to it were simulated and analyzed at the star sensor working height. In each period of time, the stray suppression of the baffle is analyzed by comparing the calculated included angle between the star sensor optical axis point and the stray with the shielded provided by system index. When the included angle is larger than the shielded angle and less than 90°, the stray is restrained by the baffle. The stray effect on star point target identification is analyzed by comparing the irradiancy of 6 magnitude star with that of the stray on star sensor sensitization surface. When the irradiancy of 6 magnitude star is 5 times more than that of the stray, there is no effect on the star point target identification. The simulation results are identical with the actual situation. The space luminous environment of the missile-borne star sensor can be estimated real-timely by this model. The adaptability of the star sensor to space luminous environment can be analyzed conveniently. A basis for determining the relative star sensor indexes, the navigation star chosen strategy and the missile launch window can be provided.
InGaAs high electron mobility transistors (HEMTs) on InP substrate with very good device performance have been grown by mental organic chemical vapor deposition (MOCVD). Room temperature Hall mobilities of the 2-DEG are measured to be over 8 700 cm2/V-s with sheet carrier densities larger than 4.6×1012 cm−2. Transistors with 1.0 μm gate length exhibits transconductance up to 842 mS/mm. Excellent depletion-mode operation, with a threshold voltage of −0.3 V and IDSS of 673 mA/mm, is realized. The non-alloyed ohmic contact special resistance is as low as 1.66×10−8 Ω/cm2, which is so far the lowest ohmic contact special resistance. The unity current gain cut off frequency (fT) and the maximum oscillation frequency (fmax) are 42.7 and 61.3 GHz, respectively. These results are very encouraging toward manufacturing InP-based HEMT by MOCVD.
A three-dimensional positioning method for global positioning system (GPS) receivers based on three satellites was proposed. In the method, the measurement equation used for positioning calculation was expanded by means of two measures. In this case, the measurement equation could be solved, and the function of positioning calculation could be performed. The detailed steps of the method and how to evaluate the positioning precision of the method were given, respectively. The positioning performance of the method was demonstrated through some experiments. It is shown that the method can provide the three-dimensional positioning information under the condition that there are only three useful satellites.
A roller rack pinion (RRP) system, which consists of a rack-bar and a cam pinion, transforms a rotation motion into linear motion. The rack-bar has a series of roller train and meshes with the cam pinion. First, the exact tooth profile of the cam pinion and the non-undercut condition to satisfy the required performance have been proposed with the introduction of the profile shift coefficient. Then, the load stress factors are investigated under the variation of the shape design parameters to predict the gear surface fatigue limit which is strongly related to the gear noise and vibration at the contact patch. The results show that the pitting life can be extended significantly with the increase of the profile shift coefficient.
We propose a single-poly MTP (multi-time programmable) cell consisting of one capacitor and two transistors based on MagnaChip’s BCD process. The area of a unit cell is 37.743 75 μm2. The proposed single-poly MTP cell is erased and programmed by the FN tunnelling scheme. We design a 256 bit MTP memory for PMICs (power management ICs) using the proposed single-poly MTP cells. For small-area designs, we propose a selection circuit between V10V and V5V, and a WL (word-line) driver by simplifying its logic circuit. We reduce the total layout area by using pumped internal node voltages from a seven-stage cross-coupled charge pump for V10V (=10 V) and V5V (=5 V) without any additional charge pumps. The layout size of the designed 256 bit MTP memory is 618.250 μm × 437.425 μm.
Though the WiMedia supports higher data rates than other WPAN technologies, a WiMedia device cannot reach other devices that are separated from it by more than 10 m, which is the typical limited transmission range of the WiMedia protocol. In this work, we propose a multi-hop QoS routing protocol to enable WiMedia devices to transmit real-time data to devices that are located out of the transmission range. The proposed routing protocol is a hybrid algorithm, which mixes the table-driven and on-demand routing algorithms, searching one or more routes according to the number of hops to a destination device. WiMedia MAC is potentially capable of learning the existence of neighbor devices by using a beacon frame. By utilizing the neighbors’ information, all devices can create routing entries for devices within 2-hops periodically. For devices beyond the 2-hop range, the newly designed on-demand routing algorithm is applied to multi-hop routing. If a routing entry for a destination device is not listed in the routing table, the source device sends a request packet to 2-hop range devices which could be found in the routing table. Since every device maintains routing entries for 2-hop range devices in the routing table, the request packet is replied in advance before its arrival at the destination device. Also, to decide the optimal route for a destination device, the number of medium access slots (MASs), received signal strength indicator (RSSI) and hop count are utilized to establish a QoS-enabled routing table. We perform ns-2 simulation to investigate the performance of the proposed routing protocol with AODV and DSDV. The simulation results show that the proposed protocol has better throughput and lower overhead than other protocols.
A 32 kbit OTP (one-time programmable) memory for MCUs (micro-controller units) used in remote controllers was designed. This OTP memory is used for program and data storage. It is required to apply 5.5 V to BL (bit-line) and 11 V to WL (word-line) for a OTP cell of 0.35 μm ETOX (EEPROM tunnel oxide) type by MagnaChip. We use 5 V transistors on column data paths to reduce the area of column data paths since they require small areas. In addition, we secure device reliability by using HV (high-voltage) transistors in the WL driver. Furthermore, we change from a static logic to a dynamic logic used for the WL driver in the core circuit. Also, we optimize the WD (write data) switch circuit. Thus, we can implement them with a small-area design. In addition, we implement the address predecoder with a small-area logic circuit. The area of the designed 32 kbit OTP with 5 V and HV devices is 674.725 μm×258.75 μm (=0.1745 mm2) and is 56.3% smaller than that using 3.3 V devices.
A differential paired eFuse OTP (one-time programmable) memory cell which can be configured into a 2D (two-dimensional) eFuse cell array was proposed. The sensible resistance of a programmed eFuse link is a half smaller than that of the single-ended counterpart and BL datum can be sensed without a reference voltage. With this 2D array of differential paired eFuse OTP memory cells, we design a 32-bit eFuse OTP memory IP. We use a sense amplifier based D F/F circuit as the BL (bit-line) SA (sense amplifier) and design a sensing margin test circuit with a variable pull-up load. It is confirmed by the function test that the designed 32-bit OTP memory IP functions normally on 30 sample dies.
Artificial bone with porous structure is crucial for tissue scaffold and clinic implants. Scaffold provides structure support for cells and guides tissues regeneration for final tissue structure. A computational aided process of porous bone modeling was developed which described the design and fabrication of tissue scaffolds by considering intricate architecture, porosity and pore size. To simulate intricate bone structure, different constructive units were presented. In modeling process, bone contour was gotten from computed tomography (CT) images and was divided into two levels. Each level was represented by relatively reconstructive process. Pore size distribution was controlled by using mesh generation. The whole hexahedral mesh was reduced by unit structure, when a 3D mesh with various hexahedral elements was provided. The simulation results show that constructive structure of porous scaffold can meet the needs of clinic implants in accurate and controlled way
A new algorithm for segmentation of suspected lung ROI (regions of interest) by mean-shift clustering and multi-scale HESSIAN matrix dot filtering was proposed. Original image was firstly filtered by multi-scale HESSIAN matrix dot filters, round suspected nodular lesions in the image were enhanced, and linear shape regions of the trachea and vascular were suppressed. Then, three types of information, such as, shape filtering value of HESSIAN matrix, gray value, and spatial location, were introduced to feature space. The kernel function of mean-shift clustering was divided into product form of three kinds of kernel functions corresponding to the three feature information. Finally, bandwidths were calculated adaptively to determine the bandwidth of each suspected area, and they were used in mean-shift clustering segmentation. Experimental results show that by the introduction of HESSIAN matrix of dot filtering information to mean-shift clustering, nodular regions can be segmented from blood vessels, trachea, or cross regions connected to the nodule, non-nodular areas can be removed from ROIs properly, and ground glass object (GGO) nodular areas can also be segmented. For the experimental data set of 127 different forms of nodules, the average accuracy of the proposed algorithm is more than 90%.
The problem of the stability analysis and controller design for Lurie networked control systems (NCSs) is investigated, in which the network-induced delays and data dropout problems are simultaneously considered. By considering that the network-induced delays are assumed to be time-varying and bounded, and analyzing the relationship between the delay and its upper bound, employing a Lyapunov-Krasovskii function and an integral inequality approach, an improved stability criterion for NCSs is proposed. Furthermore, the resulting condition is extended to design a less conservative state feedback controller by employing an improved cone complementary linearization (ICCL) algorithm. Numerical examples are provided to show the effectiveness of the method.
A novel and simple technique to control the search direction of the differential mutation was proposed. In order to verify the performance of this method, ten widely used benchmark functions were chosen and the results were compared with the original differential evolution (DE) algorithm. Experimental results indicate that the search direction controlled DE algorithm obtains better results than the original DE algorithm in term of the solution quality and convergence rate.
Thermal performance was the most important factor in the development of borehole heat exchanger utilizing geothermal energy. The thermal performance was affected by many different design parameters, such as configuration type and borehole size of geothermal heat exchanger. These eventually determined the operation and cost efficiency of the geothermal heat exchanger system. The main purpose of this work was to assess the thermal performance of geothermal heat exchanger with variation of borehole sizes and numbers of U-tubes inside a borehole. For this, a thermal response test rig was established with line-source theory. The thermal response test was performed with in-line variable input heat source. Effective thermal conductivity and thermal resistance were obtained from the measured data. From the measurement, the effective thermal conductivity is found to have similar values for two-pair type (4 U-tubes) and three-pair type (6 U-tubes) borehole heat exchanger systems indicating similar heat transfer ability. Meanwhile, the thermal resistance shows lower value for the three-pair type compared to the two-pair type. Measured data based resistance have lower value compared to computed result from design programs. Overall comparison finds better thermal performance for the three-pair type, however, fluctuating temperature variation indicates complex flow behavior inside the borehole and requires further study on flow characteristics.
To investigate the influence of the activated carbon pore structure on the adsorption of volatile organic compounds (VOCs), three commercial activated carbon samples were chosen. The fixed-bed thermostatic adsorption experiments were conducted under certain conditions, where toluene, acetone, and 1, 2-dichloroethane acted as adsorbents. Then, the incidence relation between the experimental results and the activated carbon pore structure was analyzed. After that, the results of the correlation analysis were verified in accordance with fractal theory and adsorption characteristic curve analysis. The results show that the pore diameter gradient is helpful for strengthening the internal diffusion. Under the same condition, the adsorption of organic gases tends to be selective, and the positions of toluene, acetone and 1, 2-dichloroethane adsorbed on the activated carbon are mainly in the ranges of 1.27–1.49 nm, 0.67–0.84 nm and 1.39–1.75 nm, respectively. The relationship between adsorption capacity and activated carbon pore volume can accurately explain the spreading process of the adsorbents in the activated carbon.
The effect of sulfur addition/solids content (SA/SC) ratio on heavy metals (e.g. copper, zinc and lead) obtained from mine tailings by indigenous sulfur-oxidizing bacteria was studied, and the changes in the chemical forms of heavy metals after bioleaching were explored. The results show that the solubilization of metals is significantly influenced by SA/SC ratio, and SA/SC ratio of 2.50 is found to be the best for bacterial activity and metal solubilization among six SA/SC ratios tested (such as 1.00, 1.33, 1.50, 1.67, 2.00 and 2.50) under the chosen experimental conditions. The pH decreases fast and the maximum solubilizations of copper and zinc are respectively 81.76% and 84.35% while that of lead only reaches 40.36%. After bioleaching, the chemical forms of heavy metals have changed. The metals remained in mine tailings are mainly found in residual fractions, which is harmless to the surrounding environment.
An environmentally friendly biodegradable chelant, [S, S]-ethylenediaminedisuccinic acid (EDDS), was used to separate heavy metals from sewage sludge based on chemical extraction technology. The extraction of zinc from sewage sludge with an aqueous solution of EDDS was studied under various conditions. It is found that the extraction efficiency of zinc using EDDS is equivalent to that using ethylenediaminetetraacetic acid (EDTA) at the molar ratio of chelant to total heavy metals of 1:1 over pH range of 5–9. EDDS is capable of extracting zinc from the sludge. The extraction efficiency is improved obviously and reaches a higher value within pH range from 3 to 10. The extraction efficiency maintains at about 65% when pH ≥ 4.5 and the ratio of 10:1. By comparing the species contents of the zinc in sewage sludge before and after the extraction, it is found that the extracted zinc mainly comes from the acid soluble, reducible and oxidizable fractions.
Based on the degradation characteristics of municipal solid waste (MSW) in China, the traditional anaerobic sequencing batch bioreactor landfill (ASBRL) was optimized, and an improved anaerobic sequencing batch bioreactor landfill (IASBRL) was put forward on the basis of leachate self-recirculation. By monitoring MSW composition, leachate characteristics variation and landfill gas (LFG) generation, the effect of IASBRL was comparatively studied by simulation landfill. Based on the adjusting, scouring and carrying effects of leachate self-recirculation, IASBRL can rapidly decrease Eh value to about −500 mV and form a suitable biochemical environment for methanogens, which provides a precondition for stable cooperation between non-methanogens and methanogens. IASBRL can avoid the accumulation of organic acids, make VFA (volatile fatty acid) concentration and CODCr decrease along with the small range fluctuations, and form a stable decomposition-consumption synergy during MSW degradation, therefore, the hydrolysis rate of easy hydrolyze material reaches 71.2% in IASBRL. From the viewpoint of LFG resources in IASBRL, the cumulative LFG production increases to 2 327.0 L, CH4 mass fraction stabilizes at about 50%, and these provide a favorable precondition for LFG development.
Coal slimes are mainly composed of coal and clay particles. The interaction energies among these particles were calculated using extended DLVO (DERJAGUIN-LANDAU-VERWEY-OVERBEEK) theory and the aggregation mechanisms were analyzed based on the settling experiments for coal-kaolinite and coal-montmorillonite suspensions, respectively, under different conditions of water hardness. The results indicate that for coal-kaolinite suspensions, as the water hardness reaches 10.0 mol/L, the coal particles aggregate with each other easily, and then, the coal particles may aggregate with kaolinite particles. However, no aggregation occurs between kaolinite particles. A clay platelet network is formed in coal-montmorillonite suspensions by montmorillonite particles and coal particles are captured into the network. Coal and montmorillonite particles settle completely.
The relationship among the surface fissure ratio, moisture content, seepage coefficient and deformation modulus of field unsaturated expansive soil in Nanning, Guangxi Province, China, was obtained by a direct or indirect method. Digital images of expansive soil of the surface fissure with different moisture contents were analyzed with the binarization statistic method. In addition, the fissure fractal dimension was computed with a self-compiled program. Combined with in situ seepage and loading plate tests, the relationship among the surface fissure ratio, moisture content, seepage coefficient and deformation modulus was initially established. The surface fissure ratio and moisture content show a linear relation, “y=−0.019 1x+1.028 5” for rufous expansive soil and “y=−0.071x+2.610 5” for grey expansive soil. Soil initial seepage coefficient and surface fissure ratio show a power function relation, “y=1×10−9exp(15.472x)” for rufous expansive soil and “y=5×10−7exp(4.209 6x)” for grey expansive soil. Grey expansive soil deformation modulus and surface fissure ratio show a power function relation of “y=3.935 7exp(0.993 6x)”. Based on the binarization and fractal dimension methods, the results show that the surface fissure statistics can depict the fissure distribution in the view of two dimensions. And the evolvement behaviors of permeability and the deformation modulus can indirectly describe the developing state of the fissure. The analysis reflects that the engineering behaviors of unsaturated expansive soil are objectively influenced by fissure.
Based on the results of conventional triaxial compression tests and triaxial compression creep tests on Xiangjiaba sandstone, the failure modes in short-term tests and creep tests, fractography of sandstone after creep failure, short-term and creep failure criterion are analyzed. In the short-term tests and creep tests, the sandstone samples fail in a mix mode consisting of shear failure in a single main plane and tensile failure. Confining pressure can restrict brittle failure and enhance the ductility of sandstone. In the creep tests, brittle fracture is reduced and plastic deformation can fully be developed compared to the condition of short-term tests. And the shear fracture surfaces are flat and they are covered by small particles as a result of friction. When confining pressure increases, particle size decreases while the degree of friction on shear plane increases. On the tensile failure plane, the tensile trace and direction of tearing could be clearly observed. There are obvious tearing steps on the tensile failure plane and tearing laminated structure on the front edge of tearing fracture. The same criterion can be used for the short-term and creep behavior, and the fitting effect using the MOGI criterion is better than the DRUCKER-PRAGER criterion. The cohesion and friction angle calculated by the MOGI criterion are in good accordance with those calculated by the MOHR-COULOMB criterion.
Rehabilitation of existing structures with fiber reinforced plastic (FRP) has been growing in popularity because they offer superior performance in terms of resistance to corrosion and high specific stiffness. The strain coordination results of 34 reinforced concrete beams (four groups) strengthened with different methods were presented including external-bonded or near-surface mounted glass or carbon FRP or helical rib bar in order to study the strain coordination of the strengthening materials and steel rebar of RC beam. Because there is relative slipping between concrete and strengthening materials (SM), the strain of SM and steel rebar of RC beam satisfies the double linear strain distribution assumption, that is, the strain of longitudinal fiber parallel to the neutral axis of plated beam within the scope of effective height (h0) of the cross section is in direct proportion to the distance from the fiber to the neutral axis. The strain of SM and steel rebar satisfies the equation ɛGCH=βɛsteel, where the value of β is equal to 1.1–1.3 according to the test results.
A user-defined micromechanical model was developed to investigate the fracture mechanism of asphalt concrete (AC) using the discrete element method (DEM). A three-dimensional (3D) AC beam was built using the “Fish” language provided by PFC3D and was employed to simulate the three-point bending beam test at two temperature levels: −10°C and 15°C. The AC beam was modeled with the consideration of the microstructural features of asphalt mixtures. Uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. The 3D predictions were validated using laboratory experimental measurements of AC beams prepared by the same mixture design. Effects of mastic stiffness, cohesive and adhesive strength on AC fracture behavior were investigated using the DEM model. The results show that the 3D DEM fracture model can accurately predict the fracture patterns of asphalt concrete. The ratio of stress at interfaces to the stress in mastics increases as the mastic stiffness decreases; however, the increase in the cohesive strength or adhesive strength shows no significant influence on the tensile strength.
A simulation model was proposed to investigate the relationship between train delays and passenger delays and to predict the dynamic passenger distribution in a large-scale rail transit network. It was assumed that the time varying original-destination demand and passenger path choice probability were given. Passengers were assumed not to change their destinations and travel paths after delay occurs. Capacity constraints of train and queue rules of alighting and boarding were taken into account. By using the time-driven simulation, the states of passengers, trains and other facilities in the network were updated every time step. The proposed methodology was also tested in a real network, for demonstration. The results reveal that short train delay does not necessarily result in passenger delays, while, on the contrary, some passengers may get benefits from the short delay. However, large initial train delay may result in not only knock-on train and passenger delays along the same line, but also the passenger delays across the entire rail transit network.
Unmanned aerial vehicle (UAV) was introduced as a novel traffic device to collect road traffic information and its cruise route planning problem was considered. Firstly, a multi-objective optimization model was proposed aiming at minimizing the total cruise distance and the number of UAVs used, which used UAV maximum cruise distance, the number of UAVs available and time window of each monitored target as constraints. Then, a novel multi-objective evolutionary algorithm was proposed. Next, a case study with three time window scenarios was implemented. The results show that both the total cruise distance and the number of UAVs used continue to increase with the time window constraint becoming narrower. Compared with the initial optimal solutions, the optimal total cruise distance and the number of UAVs used fall by an average of 30.93% and 31.74%, respectively. Finally, some concerns using UAV to collect road traffic information were discussed.