Abstract:High-entropy alloy is a new type of alloy developed in recent years, solving the problem of only one or two main components in traditional metal materials. Through significant increase in the number of components, sluggish diffusion effect and severe-lattice-distortion effect are achieved in high-entropy alloys. It is easy for high -entropy alloys to obtain ideal tensile strength and fracture toughness, which are particularly suitable for welding to improve the service performance of welded joints. The application of high-entropy alloys in welding field has broad prospects. At present, many scholars at home and abroad have tried to apply high-entropy alloys with multi-principal elements to the welding field. Therefore, this paper summarizes the development and research status of high entropy alloys in welding field, from the aspects of welding materials, welding methods, microstructure, hardness and mechanical properties. And the key scientific problems to be solved in the application of high-entropy alloys in welding field are provided. Finally, the prospects for future research direction in this field are proposed.

Abstract:For enterprises whose bulk raw materials are supplied by multiple suppliers, the train departure interval of suppliers may affect their inventory level. This paper focuses on the linkage departure interval of entire direct-trains between multi-suppliers under the target of minimum average inventory of the customer. Due to the fact that the arrival interval will be influenced by the supply volume from different suppliers, freight volume of originating direct train, and the delivery time or path differences in transit, it respectively analyzes the optimization methods of linkage departure interval under four combinations of freight volume for multi-suppliers and the annual supply volume of each supplier. Finally, the corresponding numerical example is given, and the results show that the average inventory level of customer is reduced by 24.2% compared to the random departure interval.

Abstract:To discuss the applicability and dynamic response of HJC model used in the numerical analysis of vehicle-pier collision in LS -DYNA software, the values of key parameters in the HJC model were determined based on the model theory, and a numerical model of drop-hammer impact test was established and validated. On the basis, a vehicle-pier impact analysis model was established, the energy conversion of the system during the collision was verified, and the effects of vehicle speed, vehicle weight and impact position on the impact force and displacement of the pier’s top were discussed. The results show that the HJC model can be used to better simulate the dynamic response of the impact test when the appropriate parameters are selected. The peak values of impact force and the displacement at the pier’s top increase with the increase of impact velocity and impact mass, but gradually weaken with the increase of impact eccentric distance. The increase of impact velocity accelerates the occurrence of peak response, while the increase of impact mass delays the occurrence of peak response. When the speed exceeds 100km/h, two peaks in the time-history curves of impact force and displacement at the pier’s top occur, and the secondary impact response of the carriage should be considered.

Abstract:In order to accurately reflect the influence of external environmental factors and concrete properties on the temperature change in CRTSⅡ track slab of a line in eastern China, considering the time delay of heat flow at different depths caused by hot pressing, the relationship between temperature at different depths of track slab is studied by using the spectrum method. Referring to the thermodynamic theory, the calculation model of temperature at different depths of track slab concrete is established, and the sunshine real-time temperature field and vertical temperature gradient of track slab in this region are studied. The results show that the delay time of heat flow caused by temperature gradient is proportional to the propagation distance in the same medium. The temperature series at different depths of the track slab are relative to the surface layer, and the amplitude decays with an exponential function, and the slab has a linear lag. During the heat transfer process in the track slab, the track slab temperature change delay time is about 1.02 h with each depth of 50 mm. The average relative error of the temperature calculation model based on the heat flow delay track slab is between 1.9% and 2.5%, and the reliability is between 92.85% and 96.53%.

Abstract:Micro-shield machine has complex mechanical properties of the cutterhead tunneling in the complex geological conditions, which puts forward higher requirements on the arrangement of cutterhead structure. Aiming at the typical coastal composite stratum, the cutterhead with a diameter of 600 mm was selected, and the rock breaking model of disc cutters was established based on the principle of dual hobs to collaborate with the rock. Moreover, the dynamic simulation model of the whole cutterhead cutting soil was established according to different cutter layout methods, and three working conditions were considered to analyze the stress and strain of the optimized structure of the cutterhead. The results indicate that the rolling force had the lowest value when the disc cutters spacing was 8 mm, and the rock breaking efficiency was the highest at this time. The cutterheads of Archimedes spiral and single Fermat spiral method could meet the requirements of full excavation of the face, and there was an incomplete cutting phenomenon between the cutterhead cutters of the concentric circular cutter method. However, the maximum and average thrust and torque during the excavation process of the cutterhead of the single Fermat spiral arrangement method were smaller, which was the optimal cutterhead structure. In terms of the cutterhead structure of the single Fermat spiral line knife method, the strength and stiffness check calculation results under the three working conditions all fulfilled the requirements of general mechanical utilization.The research is of reference significance for the optimization design of the cutterhead of the micro shield machine in such projects as pipeline digging.

Abstract:Aiming at the complex and changeable control factors of shield tail clearance, through the positional relationship between the inner wall of shield tail and the outer wall of segment, the geometric relationship between tunnel curve radius, shield elevation angle, shield tail covering segment length and shield tail clearance was established. Based on the above relationship, the theoretical calculation method of the minimum shield tail clearance was obtained. Moreover, the factors such as tunnel curve radius, shield elevation angle and shield tail covering segment length were analyzed. The results show that the shield tail space is significantly affected when the tunnel curve radius is between 50 m and 400 m. The relationship between the shield pitch angle and the minimum shield tail clearance is nearly linear, and it decreases with the increase of the pitch angle. The length of shield tail covering segment has a more significant effect on shield tail clearance, and the influence on shield tail clearance can be balanced by adjusting the tunnel curve radius and shield pitch angle.

Abstract:Based on the research background of the shield tunnel in a parking lot of an urban subway, According to the construction conditions of the new tunnel passing through the existing tunnel, the vertical displacement of the existing shield tunnel in the middle and lower part of the construction is simulated by numerical simulation, and the tunnel deformation value after grouting reinforcement of the existing tunnel is analyzed, Finally, the reinforcement suggestions are put forward. The analysis results show that the excavation of the left line and the right line of the new tunnel has a great difference in the impact on the existing tunnel. At the same time, the crossing angle of the upper tunnel affects the settlement displacement of the existing tunnel. The vertical displacement of the existing tunnel segment directly below the construction tunnel line is 5.3 mm larger than that of the tunnel segment diagonally below. The simulation results show that the maximum deformation of the strengthened tunnel decreases from 3.2 mm to 4.5 mm, which is less than 5 mm of the standard control safety standard. On this basis, a tunnel reinforcement scheme combining steel support ring and arch crown grouting is proposed, and the on-site construction is guided.

Abstract:The electric vibration exciter was used to perform simple harmonic excitation test on the reinforced truss concrete floor to determine the vibration response of the floor under different amplitude and frequency simple harmonic excitation. It used ANSYS to model and analyze the test piece, compared with the test results to verify the feasibility of the finite element method for dynamic analysis of reinforced concrete slabs. Then, a dynamic analysis model of reinforced truss concrete two-way slab under artificial excitation was established, and the influence of bottom steel plate and slab thickness (truss height) on the vibration performance and comfort of the floor was analyzed, and it was combined with the open profiled steel plate-concrete of the same specification. Comparative analysis of floor slabs shows that under the same conditions, the fundamental frequency of reinforced truss concrete floor slab is higher than that of open type composite floor. When pedestrian excitation is applied in the center of the floor slab, the peak vibration acceleration of reinforced truss concrete floor is reduced by an average of 65.65% than that of open type composite floor. After removing the bottom steel plate of the reinforced truss floor bearing slab, the fundamental frequency of the reinforced truss concrete floor is reduced by about 4.37% on average, and the peak acceleration increases by about 19.76% on average. And the thickness of the bottom steel plate also affects the vibration comfort of the floor slab to a certain extent. The increase in the thickness of the floor slab can significantly improve the vibration comfort of the reinforced truss concrete floor and the open profiled steel plate-concrete composite floor.

Abstract:The relationship between residents′ income and ticket prices directly affects the commuting choice of urban rail transit passengers. According to existing researches on the impact of ticket prices on commuting travel, the level of ticket price is defined firstly. Secondly, based on the investigation of Beijing, Guangzhou, Tianjin, Wuhan, Dalian and Changchun, passengers are required to answer the questions based on daily commuting behavior, and a PLS-SEM model and a mediator model are established to analyze the influence mechanism of ticket prices on commuting travel behavior in different types of cities. The result of study shows the influence mechanism that the rationality of ticket prices affects perceived value and then travel intention. Among them, the effect of ticket price per person on perceived value is new first-tier cities(0.862), first-tier cities(0.838), secondtier cities (0.782). Ticket price per person affects perceived value through the ticket price level, namely the affordability of ticket prices, and the affordability of ticket prices plays a mediating role in the impact of the ticket price per person on perceived value. The mediation effect as a proportion of the total impact is first-tier cities(57.3%), new first-tier cities(45.2%), second-tier cities(40.2%).

Abstract:Rainfall affects road conditions and driving environment, which in turn affects the reliability of public transportation. In order to clarify the impact of rainfall on the reliability of urban bus travel time, this paper analyzes the statistical changes of bus travel time affected by rainfall based on the GPS operating data of public transport and hourly rainfall data considering the impact of setting up bus lanes. In order to further explore the influence mechanism of rainfall on bus travel time reliability at the theoretical level, this paper constructs a bus travel time reliability evaluation model, which evaluates the reliability through three parameters including passenger reserved travel time, buffer time, and excess delay. The research results show that rainfall has a negative impact on bus travel time, leading to increased bus travel time and its volatility, and bus lanes can effectively reduce the fluctuation range. Compared with fine weather, passengers need to reserve longer travel time on rainy days to ensure that they can reach their destination on time, the reliability is reduced, and bus lanes can effectively suppress the decline in bus travel time reliability. By constructing a bus travel time reliability evaluationmodel, the bus travel time reliability evaluation system is formed to provide theoretical support for the study of bus operation decision-making and dispatch in bad weather of rainy days.

Abstract:With the panel data of 28 prefecture-level cities in the urban agglomeration in the middle reaches of the Yangtze River from 2006 to 2019 and the PSM-DID model, this paper studied the impacts of high-speed railway on the innovative urban development. According to the results, the opening of the HSR has a significant role in promoting the technological innovation capability in the urban agglomeration in the middle reaches of the Yangtze River. The study also finds that there are obvious temporal dynamics and regional heterogeneity in the impact of the opening of HSR on urban innovation. It’s mainly manifested in two sides. The promotion effect of the opening of HSR on urban innovation shows a trend of first rising and then falling over time. The promotion effect of the opening of HSR on innovation in large and medium-sized cities is not obvious or even negative, while the promotion effect on small cities is significantly positive. In addition, the HSR is further divided into national HSR rail and local HSR rail. The study maintains that compared with local HSR national HSR has a more significant role in promoting urban innovation.

Abstract:The laminated heterogeneous configuration design was applied to improve the strength and toughness of the Cu -Be alloy. The Cu -Be/Cu laminated heterogeneous composite by vacuum hot pressing bonding, hot rolling and subsequent heat treatment was successfully prepared. The microstructure, microhardness and tensile properties of the composites were investigated. During the plastic deformation of the composite, the microstructure evolution, strain distribution and fracture behavior of different metal layers were characterized by in -situ tension under SEM combined with DIC technique. The results show that the Cu-Be/Cu laminated heterogeneous composite is composed of coarse grained Cu layers (with average grain size of 115.3 μm) and fine grained Cu-Be layers (with average grain size of 17.4 μm). The microhardness of Cu-Be layers is approximately 5 times higher than that of Cu layers. The ultimate tensile strength of the composite is between that of the two metals, but theductility of the composite is close to that of the Cu, which is much higher than that of the Cu-Be alloy. During the plastic deformation of the composite, the strain of the Cu-Be layers is mainly coordinated by grain rotation, while the strain of the Cu layers is mainly coordinated by single slip inside the grains. At the initial stage of plastic deformation, the strain concentration first appears in the vicinity to the Cu-Be/Cu interfaces. Then the strain concentration can be transmitted into the metal layers through the interfaces. During the fracture of the composite, the microcracks initiate at the grain boundaries of the Cu-Be layers and propagate along the grain boundaries. Significant crack deflection phenomenon occurs when the cracks propagate to the Cu-Be/Cu interface. The crack propagates transgranular in the Cu layers. The morphology of the fracture of the Cu layer present the characteristics of quasi-cleavage fracture.

Abstract:Since there is no body load data such as core disk and side bearing, the load spectrum of freight car body fatigue simulation analysis is usually converted from the standard load spectrum of similar models, and the calculated results are different from the actual life of the car body. In order to obtain the load spectrum of the actual car body circuit and improve the calculation accuracy of fatigue life, a virtual car body fatigue test bench was introduced. The virtual car body fatigue test rig adopted the driving load data simulated by the real car body circuit to ensure the accuracy of the simulation input. After the virtual test calculation, the calculated load data of body core disk, side bearing and coupler were extracted, and the load spectrum of typical working conditions was constructed according to the damage equivalence principle. The load spectrum was then combined with the main S-N curve method to calculate the life of the welding of the car body. The results show that the fatigue evaluation based on the load spectrum obtained indirectly by the virtual car body bench test and the main S-N curve method solves the problems of inaccurate car body load input and grid sensitivity by the nominal stress method, which is more practical than the traditional car body fatigue evaluation.

Abstract:In order to solve the problem of low frequency vibration and noise of interior panel structure of highspeed train, a "cap type" phononic crystal structure was designed based on local resonance mechanism. Based on the finite element method, the "cap type" phononic crystal unit model was established, and the energy band structure of the unit cell was calculated, and the complete band gap of 183.35~245.14 Hz was obtained. Then, combined with the interior panel, the model of periodically arranged "cap type" phononic crystal trim panel was established. The vibration and sound radiation characteristics of the phononic crystal trim panel under the vertical unit concentrated force excitation and the sound insulation characteristics under the background sound field excitation were analyzed, and the influence of the damping of the trim panel on the sound and vibration characteristics of the phononic crystal trim panel was explored. The results show that: compared with the ordinary trim panel, the vibration acoustic radiation characteristics of the trim panel of phononic crystal have a better suppression effect in the band gap range of 180~210 Hz, and it has a better sound insulation characteristics in the frequency range of 10~500 Hz; the damping loss factor has a more obvious effect on improving some weak points of the acoustic vibration characteristics of the phononic crystal trim panel, which can significantly suppress the vibration control vibration sound radiation peak point and improve sound insulation trough point.