Residual stresses generated during casting and heat treatment are one of the major challenges faced by piston manufacturing. Therefore, the change of piston residual stress from casting stage to heat treatment stage i...
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Residual stresses generated during casting and heat treatment are one of the major challenges faced by piston manufacturing. Therefore, the change of piston residual stress from casting stage to heat treatment stage is studied by orthogonal experiment and single factor experiment. A finite element model is established to simulate the casting process and heat treatment process, the parameters such as pouring temperature, mold temperature and shake-out temperature are mainly considered in the casting simulation, while the parameters such as heating rate, holding temperature, holding time and cooling rate are mainly studied in the heat treatment simulation. At the same time, the residual stress of the piston after casting and heat treatment is measured by X-ray diffraction to verify the simulation results. The results show that the average residual stress at each measuring point of the piston is 223.6 MPa when there is no sand falling in the casting stage. The residual stress field of the piston is redistributed after sand falling, and the average residual stress value is 161 MPa, which is reduced by 29% before and after sand falling. Heat treatment can significantly reduce or even eliminate the residual stress. The average residual stress of piston is reduced to 15.2 MPa, accompanied by the great release of residual stress. This study provides a cross-software multi-process residual stress analysis method, which is of great significance for reducing and eliminating casting residual stress.
Pyrolysis carbonization of human feces has shown potential for converting feces biomass into a soil amendment. However, little is known about the interactions of DOM derived from feces-based biochar produced at low-te...
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Pyrolysis carbonization of human feces has shown potential for converting feces biomass into a soil amendment. However, little is known about the interactions of DOM derived from feces-based biochar produced at low-temperature with heavy metals (HMs). In this study, the binding properties of Pb(II) and Zn(II) with DOM derived from feces-based biochar produced at low pyrolysis temperatures were investigated using EEM-PARAFAC combined with general, and moving-window two-dimensional correlation analyses (2D-COS). The results revealed that DOM from biochar produced at 280 degrees C exhibited a higher Pb(II) and Zn(II) affinity and more binding sites than DOM produced at 380 degrees C. The fulvic-like and humic-like components exhibited obvious fluorescence quenching after the heavy metal addition, and the complexes formed with Pb(II) and Zn(II) were more stable. C-H groups exhibited the fastest response to Pb(II) and Zn(II) binding in the FB280 DOM, while the COO- groups of carboxylic acids in the FB380 DOM exhibited the fastest response to Pb(II) and Zn(II). Moreover, the mutation concentration range of components and functional groups in DOM, as analyzed by MW2D-COS, was greater for Zn(II) than for Pb(II). These results provide a more detailed molecular-level understanding of the interaction mechanisms between heavy metals and feces-based biochar-derived DOM and the effect of HM concentration on DOM binding. Further, these results will help to provide a reasonable reference for feces management and feces-based biochar in controlling soil HMs.
Two-dimensional SnS holds significant potential in gas-sensing because of its numerous excellent characteristics. Based on first-principles density functional theory (DFT), the adsorption properties of small gas molec...
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Two-dimensional SnS holds significant potential in gas-sensing because of its numerous excellent characteristics. Based on first-principles density functional theory (DFT), the adsorption properties of small gas molecules such as NO2, SO2, and NO on SnS have been thoroughly investigated. The results indicate that SnS can effectively adsorb NO2, SO2, and NO gases, attributed to their higher adsorption energies. Differing from the case of SO2 adsorption, SnS undergoes a transition from a non-magnetic state to a magnetic state upon the adsorption of NO2 and NO gases. To investigate the sensing characteristics of these three adsorption systems, the adsorption densities and I-V curves were calculated using a thermodynamic statistical model and the nonequilibrium Green's function method, respectively. These findings demonstrate that NO2 adsorption not only exhibits the highest adsorption densities but also generates the maximum current at the same voltage. These results highlight the potential of SnS for serving as a selective and reversible NO2 gas sensor.
Direct coal liquefaction in the heating stage of Shenhua Shendong bituminous coal was carried out in a 0.01 t/d continuous tubular facility with iron catalyst and hydrogenated anthracene and wash oil as solvent at a r...
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Direct coal liquefaction in the heating stage of Shenhua Shendong bituminous coal was carried out in a 0.01 t/d continuous tubular facility with iron catalyst and hydrogenated anthracene and wash oil as solvent at a residence time (t) of 3.56.5 min and a reaction temperature (T) of 340-450 degrees C. The results show that when t = 3.5 min and T = 340 degrees C, a cracking reaction of coal occurs, while the oil yield was almost zero. As the residence time and temperature each increase, coal conversion and product yield exhibit different change patterns. Especially when t = 6.5 min and T = 450 degrees C: under these conditions, the coal conversion and oil yield reached 83.67 and 52.27 wt?%, respectively. To investigate the liquefaction kinetics, a 8-lump reaction kinetic model which follow first-order irreversible reactions (r = k(i) dC/dt) was developed to estimate the rate constants. The results indicated that the model is perfectly valid for the heating stage, and the yield of oil and gas were mainly from coal other than preasphaltene (PAA).
In order to improve the fatigue performance of the internal thread of the connecting rod for marine diesel engine, the internal thread cold extrusion technology is introduced into the bolt hole position. Based on the ...
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In order to improve the fatigue performance of the internal thread of the connecting rod for marine diesel engine, the internal thread cold extrusion technology is introduced into the bolt hole position. Based on the three-dimensional finite element model, the residual stress distribution around the cold extrusion internal thread of 42CrMo4 high-strength steel plate hole structure under different edge distance ratios is analyzed in detail. The multiaxial fatigue life prediction model of thread is established based on the stress-strain method;the accuracy and feasibility of the prediction model are further verified by fatigue experiments. The thread surfaces are examined by utilizing the scanning electron microscope and coordinate with the X-ray diffraction method to measure the residual stress of thread. The relationship between the residual stress distribution, surface structure, and fatigue life of the extrusion thread is revealed. The research shows that the improved fatigue prediction model gives a satisfactory accuracy in predicting the fatigue life. Both the tangential residual stress fields around the extrusion thread and the surface structure have a certain influence on its fatigue life, especially when the edge distance ratio is less than 2. The tangential residual compressive stress of the cold extrusion internal thread decreases with the edge distance ratio being smaller, while the depth of the stress zone increases firstly and then decreases. Higher load will greatly reduce the fatigue life and dispersion of the thread;the fatigue life increases linearly with the increase of the edge distance ratio under lower stress level.
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