At present, the demand for ready-mixed concrete (RMC) in construction industry is increasing day by day, and the supply mode of multiple delivery depots corresponding to multiple construction sites has been widely used. In order to further improve the joint distribution efficiency between various delivery depots, this research establishes a multiobjective optimal distribution model with time window constraints and demand postponement attributes for the problem that the subbatching plants need to work together. The model divides the reasons for demand postponement into two types: the constraint for timely unloading of trucks cannot be met on time and the constraint for timely pouring at the construction site cannot be met on time. This work improved the coding method of genetic algorithm based on the characteristics of the distribution model. Using hierarchical real-coding form, the coding operator of each layer can be evolved separately, which ensures the globality of the search, and, at the same time, an improved immune operator is added to ensure the local search performance. By comparison, the results obtained by improved GA are 7.05% higher than those of the standard GA, and the early convergence speed of improved GA is obviously better than that of the standard GA. The simulation experiments show that the total trucks’ waiting time during the process of providing delivery services from 5 concrete plants to 8 construction sites is 769 minutes, and the total waiting time of 8 construction sites is 507 minutes. Through practical case analysis, this work can enable RMC production enterprises and construction sites to effectively reduce the waiting time of corresponding operations, and the obtained results are close to the simulation results. The proposed method indeed improves the efficiency of RMC distribution.
In the welding process of thick-walled titanium alloys, the selection of the wire type is one of the critical factors affecting the welding quality. In this paper, flux-cored and cable wires were used as filler materials in the welding of thick-walled titanium alloys. The macrostructure, microstructure, texture, and grain size of both welded joints were compared by employing an optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM), and the tensile and impact properties were also evaluated. The comparison result showed that the fusion zone microstructure of both welded joints was dominated by a basketweave structure composed of interwoven acicular α′ martensite, whereas the microstructure of flux-cored wire welded joints was finer, and the degree of anisotropy was low. The strength of both welded joints was higher than that of the base metal, ensuring that fracture occurred in the base metal area during tension. The Charpy impact energy of the flux-cored wire welded joint was 16.7% higher than that of the cable wire welded joint, indicating that the welded joint obtained with the flux-cored wire performed better in the welding process of thick-walled titanium alloys.
Laser-MAG (metal active gas) hybrid welding of nickel-saving 08Cr19Mn6Ni3Cu2N stainless steel was carried out by using 98%Ar + 2%N2 and 95%Ar + 5%CO2 as shielding gases. The effect of different shielding gases on the microstructure and properties of the welded joints was investigated. The results showed that arc shrinkage was significant with the addition of nitrogen, weld spatter increased with the expansion of arc volume, and arc stability deteriorated. The ferrite content in the weld decreased by about 60%, the ferrite dendrite also gradually became finer, and the secondary dendrite arm was shorter. Only a small amount of δ and γ phases existed in the weld, and no precipitation of the σ phase and nitride was found. Observing four crystal planes, we found that size of the austenite grains decreased with the addition of nitrogen. The average tensile strength of the welded joints decreased from 712 MPa to 704 MPa, but with improved corrosion resistance, the pitting corrosion rate increased from 19.45 g·m2/h to 18.72 g·m2/h, and the hardness of weld was slightly reduced.
The effects of droplets filling the molten pools during the double-sided laser beam welding (DSLBW) of T-joints was established. The dynamic behavior of the keyhole and the molten pool under different droplet filling modes were analyzed. The results indicated that compared with the contact transition, the stability of metal flow on the keyhole wall was reduced by free transition and slight contact transition. At the later stage of the droplet entering the molten pool via free transition, slight contact transition, and contact transition, the maximum flow velocity of the keyhole wall was 5.33 m/s, 4.57 m/s, and 2.99 m/s, respectively. When the filling mode was free transition or slight contact transition, the keyhole collapsed at the later stage of the droplet entering the molten pool. However, when the filling mode was contact transition, the middle-upper part of the interconnected keyholes became thinner at the later stage of the droplet entering the molten pool. At the later stage of the droplet entering the molten pool via free transition, the flow vortex at the bottom of the keyhole disappeared and the melt at the bottom of the keyhole flowed to the rear of the molten pool, however, the vortex remained during slight contact transition and contact transition.
A self-developed Ti-Al-V-Mo system titanium alloy flux-cored wire was used to join the Ti64 titanium alloy plate via laser welding with filler wire. The microstructure and properties of the obtained welded joint were investigated. The results showed the WM (welded metal) of the welded joint consisted mainly of acicular α’ martensite, and the HAZ (heat affected zone) was comprised of a primary αp phase, Widmanstatten, and a few α’ martensite and a residual β phase. The strength and elongation of the welded joint after breaking are equivalent to that of the BM (base metal). The tensile fracture, presenting as a microvoid coalescence ductile fracture, was encompassed by massive shear lips with deep and uniform dimples. The overall microhardness of the welded joint was sequenced as WM > HAZ > BM. In the WM, large-angle grain boundaries with intragranular misorientation greater than 15° accounted for about 84%. By XRD, it was discovered the welded joint was mainly composed of the α’ martensite, with a modest amount of extremely weak multi-angle α phase diffraction peak. The test results showed the designed welding method of titanium flux-cored wire and laser wire filling is suitable for high-quality welding of titanium alloy plate.
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