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There has been growing interest in enhancing the properties of machine components to improve their reliability in recent years. Surface barrel finishing is one of the most widely used surface processes to decrease the surface roughness of components and improve mechanical properties. However, the effect of barrel finishing parameters on surface integrity such as residual stress and hardness distribution is still unclear, which needs an in-depth understanding. This study experimentally investigated the effect of different barrel finishing media and finishing time on the surface integrity including surface morphology, residual stress, microhardness and microstructure of 18CrNiMo7-6 carburized rollers. Experiment results demonstrate that the surface roughness Sa can be decreased to less than 0.2 μm with the surface barrel finishing, and the surface compressive residual stress (SCRS) can be increased by 500 MPa compared with shot peening process. In addition, the surface microhardness increased by 20 HV and the grain size of the surface layer was refined. The improvement of the surface integrity should be of interest for engineers when designing against rolling contact fatigue.

During the last twenty years, the complex network modeling approach has been introduced to assess the reliability of rail transit networks, in which the dynamic performance involving passenger flows have attracted more attentions during operation stages recently. This paper proposes the passenger-flow-weighted network reliability evaluation indexes, to assess the impact of passenger flows on network reliability. The reliability performances of the rail transit network and passenger-flow-weighted one are analyzed from the perspective of a complex network. The actual passenger flow weight of urban transit network nodes was obtained from the Shanghai Metro public transportation card data, which were used to assess the reliability of the passenger-flow-weighted network. Furthermore, the dynamic model of the Shanghai urban rail transit network was constructed based on the coupled map lattice (CML) model. Then, the processes of cascading failure caused by network nodes under different destructive situations were simulated, to measure the changes of passenger-flow-weighted network reliability during the processes. The results indicate that when the scale of network damage attains 50%, the reliability of the passenger-flow-weighted network approaches zero. Consequently, taking countermeasures during the initial stage of network cascading may effectively prevent the disturbances from spreading in the network. The results of the paper could provide guidelines for operation management, as well as identify the unreliable stations within passenger-flow-weighted networks.

In this work, the unbalanced phase ratio and the adverse secondary austenite generally discovered in the wire arc additive manufactured duplex stainless steel were modified using post-manufacturing heat-treatment. The pitting corrosion resistance was significantly improved, which could be comparable to the hot-rolled 2205 duplex stainless steel after the heat-treatment at 1300 °C for an hour. The crystalline and microstructural investigation revealed that the striking corrosion resistance of the 1300 °C heat-treated sample was the result of the balanced phase ratio, the non-existence of chromium nitride, the 〈111〉//X texture of austenite, the decrease of crystalline defect density and the recrystallization of austenite.

Submerged arc additive manufacturing (SAAM) with high deposition efficiencies and unique cyclic re-heating was firstly introduced to fabricate the low-carbon steel product in this work. The microstructure and mechanical properties of the SAAM product was studied. The results showed that the intermediate zone of the as-deposited component was mainly composed of equiaxed α-Fe grains and possessing obvious homogeneous characteristics along the building direction. The impact energy of the component was vastly improved to over 300 J at −60 °C with little loss of strength. The tensile yielding strength ~346 MPa, elongation ~39% in vertical direction were competitive to that in horizontal direction, showing a fancy isotropic characteristic. The exclusive intrinsic heat treatment of SAAM holds the decisive role for this dramatic phenomenon.

A novel welding process named molten metal filler welding aimed to control heat input precisely was investigated in this paper. The process used molten metal which was high in both speed and temperature as a heat source. The filler metal was heated to a temperature above the melting point preliminary at a graphite crucible. The molten filler metal was jetted as a flow by pressure to achieve a big depth-to-width ratio of bead. A new welding system was designed to fulfill the requirements of the process. The relation between the flow speed and the input pressure was calculated. Tests using tin-lead alloy (63 % Sn-37 % Pb) plates showed that the distance between the nozzle and workpiece had an important influence on the joint quality. When the distance was 2 mm or less, an ideal joint could be obtained. The penetration increased with the heat input proportionally, and increasing input pressure was the most efficient way to increase penetration. The weld profile was mainly affected by the travel speed. A novel conception to limit the flow of the weld pool was proposed. If the weld pool flowed in a limited space, it was easy to get an ideal joint in which the depth-to-width ratio could reach 6. Meanwhile, the heat distribution of the process could be investigated using the microstructures of the samples.

The microstructure evolution of Mg96−xGd3Zn1Zrx (at%) (x=0, 0.1, 0.2, 0.4) alloys with long period stacking ordered (LPSO) structures prepared by conventional permanent mold casting were investigated by XRD, EDS, SEM and TEM. Also, the deformation behavior and microstructure evolution of Mg95.8Gd3Zn1Zr0.2 (at%) alloy subjected to equal channel angular pressing (ECAP) were examined. The results show that the LPSO structure phases observed in as-cast Mg96Gd3Zn1 alloy did not notably improve the mechanical properties of the alloy owing to their low volume fraction. In contrast, the mechanical properties of the alloy after heat treatment were raised significantly because of the transformation from eutectic structures to LPSO structure phases. Furthermore, moderate Zr addition into Mg–Gd–Zn alloys refined and homogenized α-Mg grains, changed the morphology and distribution of LPSO structure phases and promoted the precipitation of strengthening phases, and hence strengthened the alloys. Besides, tensile test results showed that aging-treated Mg95.8Gd3Zn1Zr0.2 alloy subjected to 2-pass ECAP processing exhibited high ultimate tensile strength (UTS) of 418 MPa, yield strength (YS) of 330 MPa and elongation of 7.5%. Such excellent mechanical properties could be attributed to complex strengthening of kinking LPSO phases and the dispersion strengthening of tiny spherical phases.

Appropriate depth of weld penetration is required in many precision joining application but the weld penetration underneath the work-piece is not directly/conventionally measurable during the welding process. This work aims at establishing an analytic model to correlate the measurable weld pool surface to the development of the weld pool. To this end, the analytical solution of single-ellipsoidal static heat source in finite thick plate is used to calculate the temperature filed that provides the penetration of the developing weld pool. However, the analytical solution may not be as accurate as expected because the convection, radiation etc. have been omitted in order to obtain the analytic solution. A 3D measurement of the weld pool surface is thus used to calibrate the size and shape of the calculated weld pool such that the analytical model after the calibration will provide weld pool boundary and penetration to control the welding parameters. It is found that such calibration that combines analytic model and on-line weld pool surface can provide an estimation for the weld pool underneath the work-piece with an accuracy better than 90% in all three dimensions. As a result, the weld pool development will be able to be dynamically controlled to assure the desired weld penetration for the desired weld integrity as well as for future optimal control of the welding process.

With the shortage of water resources in China, water-saving agriculture has been highly addressed and developed by the government. This paper studies the channel structure of a helical micro pressure drip irrigation emitter, focusing on the tilt and tooth chamfer’s angles within eight different combinations of structure parameters. By comparison of hydraulic performances, it show a small discrepancies between CFD software simulating results and testing results on 6 selected real trial prototype samples of flaky emitters and inlaid drip pipes. A conclude is made that under various flow coefficient K and pressure sensitive coefficient X, in the section of minimum flow, the smaller angle θ the better hydraulic performance, the bigger angle r the better anti clogging ability.

This study was primarily involved with the experimental determination of the dynamic mechanical properties of five different sheet steels. The nominal yield strengths of these five types of sheet steels ranged from 172 to 690 MPa (25–100 ksi) and the range of strain rates varied from 10 −4 to 1.0 mm/mm/s. All these five materials were studied in both longitudinal and transverse directions under various strain rates, and some materials were also tested under different strain rates and different amounts of prior cold stretching. In addition, two types of steels were tested to estimate the aging effect on the mechanical properties of sheet steels. The test results showed that the proportional limit, yield strength, and ultimate tensile strength increase with increasing strain rate. In general, the amount of increase was found to be dependent on the static yield stress of sheet steel, the amounts of prior cold stretching, and the strain rates used in the tests, and independent on the test directions (longitudinal or transverse), test types (tension or compression), and material aging conditions (aged or nonaged). General equations were also derived to predict the tensile and compressive yield stresses for strain rates ranging from 10 −4 to 10 2 mm/mm/s.