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Purposes This work is conducted to achieve the objectives of carbon emission reduction and resource utilization of solid waste. Methods Geopolymer concrete was prepared from red mud and coal-metakaolin, and the effect of four factors on its mechanical properties was investigated with an orthogonal test method. Findings The water-binder ratio was found to have a significant effect on the strength of the geopolymer concrete, followed by Na2O/H2O, while the curing conditions and the aggregate-binder ratio have lesser effect, according to the ANOVA. On the basis of the experimental results, the mathematical model of compressive strength and splitting tensile strength of geopolymer concrete was established, and the fitting effects of the equations were favourable. Further analysis obtained the optimal ratio of geopolymer concrete, and the compressive strength and splitting tensile strengthes of the cube specimens cured for 28 d were 43.6 MPa and 2.87 MPa, respectively. Then, the pore structures of the geopolymer concretes with different W/B ratios were characterised with low-field NMR tests. The results indicate that the geopolymer concrete is predominantly microporous internally. The increased content of evaporable free water increases the porosity and coarsens the pore structure, which macroscopically manifests as a reduction in strength of the material. This study can provide some theoretical guidance for the promotion and engineering application of geopolymer concrete.

Rough-strip energy dissipators (R-SEDs) can be arranged at the bend bottom of curved spillways to dissipate energy and divert flow for bend flow. Using the entropy weight and TOPSIS methods, a multi-criteria evaluation system was established for comprehensive energy dissipation and flow diversion effects of R-SEDs. Orthogonal tests and numerical simulation were conducted to analyze factors affecting these effects (average R-SED height, R-SED angle, R-SED spacing, bend width, bend centerline radius and discharge flow rate). It was found that bend width and bend centerline radius significantly affected R-SEDs' energy dissipation effects. Average R-SED height, R-SED spacing and bend centerline radius significantly affected R-SEDs' flow diversion effects. Bend width, average R-SED height and bend centerline radius significantly affected R-SEDs' combined effects of energy dissipation and flow diversion. Their energy dissipation effects were larger than the flow diversion effects. R-SEDs can effectively alleviate adverse hydraulic phenomena in curved spillways. With the recommended parameters, R-SEDs showed the best performance, with the energy dissipation rate increasing by 18.67% and the water surface superelevation coefficient decreasing by 26.14%. The accuracy of the multi-criteria evaluation system was verified. This study can provide a reference for the R-SED design of similar curved spillways. HIGHLIGHTS R-SEDs can effectively alleviate adverse hydraulic phenomena in curved spillways.; A multi-criteria evaluation system was established to assess R-SEDs’ performance.; Factors affecting energy dissipation and flow diversion of R-SEDs were analyzed.; Energy dissipation rate and water surface superelevation coefficient were constructed.; Optimal parameters were recommended for the best performance of R-SEDs.;

The mechanical properties of Bimrock under different cementation strength are rarely studied, and the cementation strength has an important influence on the mechanical properties and deformation and failure characteristics of Bimrock. In order to explore the influence of different cementation strength on the mechanical properties of Bimrock, the proportion test of Bimrock cementation matrix was conducted by using the orthogonal test design method, and the parameter sensitivity analysis was carried out on the strength mechanical parameters of the samples with different proportions of matrix. Based on the orthogonal test results, the Bimrock samples with different cementation strength were made, and the influence of different cementation strength on the mechanical properties of Bimrock was analyzed through the uniaxial compression test. The results show that the uniaxial compressive strength and elastic modulus of the Bimrock specimens are positively correlated with their cementation strength. From weak cementation to strong cementation, the peak uniaxial compressive strength increases from 11.02 MPa to 34.21 MPa, and the elastic modulus increases from 2.11 GPa to 5.57 GPa, respectively. With the increasing bonding strength, the number of surface cracks in each stage from deformation to failure decreases. The compression failure mode of the strongly bonded specimen is the through failure of a single main crack, with short failure time and obvious brittle failure. The overall and local shear failure occurred in the moderately cemented specimen, which is represented by a shear failure surface that obviously penetrates the whole specimen and a shear failure surface that only penetrates the lower part of the specimen. The weak cementation sample is subject to transverse tensile failure. A number of tensile cracks parallel to the vertical direction can be seen, and the failure characteristics of coexistence of tensile and shear failure can be seen locally. From deformation to failure, there are many cracks that are relatively broken, and the failure time is relatively long. The engineering problems of Bimrock are complex and difficult to deal with. The research on the mechanical properties and deformation and failure characteristics of Bimrock is of great significance for engineering construction and geological disaster prevention.

In order to solve the problem of tooth surface eccentric load caused by shaft deflection angle of large internal meshing gears of the shield machine, the tooth surface equation of comprehensively modified tooth surface is given, and the method of neural network combined with orthogonal test is proposed to screen and predict the tooth surface modification parameters. In this method, the tooth profile modification and tooth direction modification are no longer regarded as independent variables, and the eccentric load on the tooth surface can be transformed into the load evenly distributed on the tooth surface. Through the contact analysis of the modified gear by the finite element method, it is found that this method can effectively reduce the excessive local stress on the tooth surface caused by the shaft deflection angle and reduce the transmission error. The optimal tooth surface modification parameter value can be found at one time, which avoids the high cost of meshing experiment for the internal meshing gear of large shield machines.

In order to design the globoidal cam deceleration mechanism with good performance and improve the transmission performance, the working surface equation and conjugate contact equation are deduced based on the space conjugate contact principle. The constant parameters of globoid cam are preprocessed by using Creo software, and the parametric design of globoid cam deceleration mechanism is completed. According to the finite element method, the first six modes of the reducer mechanism are analyzed. The orthogonal experiment method is used to design the experimental scheme. The influence of pressure angle, rotary pitch radius, roller radius and roller width on the sensitivity of the constraint mode of the reducer mechanism is quantitatively analyzed by statistical theory and variance analysis. The results show that the variances of pitch radius and roller radius of turntable are 0.021 and 0.043 respectively, both of which are less than 0.05 and sensitive to the constraint mode of globoidal cam, followed by the pressure angle and the roller width. The results provide a basis for the study of vibration and noise of globoidal cam mechanism design.

Antarctic krill (Euphausia superba), an important group of marine zooplankton in the Southern Ocean, is the only fishery resource with extremely rich reserves and a low degree of development in the world. Antarctic krill is considered to be the greatest potential source of high-quality marine protein resources due to its abundant biomass and high protein content. Peptides prepared from Antarctic krill exhibit multiple physiological activities, including osteoporosis relief, glucose metabolism regulation, blood pressure amelioration, antioxidation, fatigue alleviation, and anti-aging activity. The production and development of Antarctic krill peptides has recently become an industry focus; however, existing research has been limited to the optimization of enzymatic hydrolysis processes, mainly involving the screening of suitable enzymes and the optimization of enzymatic hydrolysis conditions. Due to the high mineral content of Antarctic krill and the introduction of buffer salt in the process of enzymatic hydrolysis, current Antarctic krill peptides products have a high salt content, which leads to poor sensory experience and health risks. Hence, a process for desalination of Antarctic krill peptides is needed. Desalination methods for bioactive substances include dialysis, ultrafiltration, nanofiltration, electrodialysis, and macroporous resin adsorption. In the field of membrane separation, nanofiltration technology has been widely used in the purification, concentration, and desalination of food components owing to its advantages: low operation cost, no introduction of exogenous substances, no destruction of materials, and low rejection rate of monovalent ions. In order to improve product quality and ensure market expansion, the process of desalination of Antarctic krill peptides using nanofiltration technology was studied and optimized in this study.Defatted Antarctic krill powder was enzymatically hydrolyzed by alkaline protease to obtain Antarctic krill peptides for further use. The main factors affecting the desalination effect of Antarctic krill peptides (peptides concentration, nanofiltration pressure, and cycle times) were optimized by single-factor and orthogonal tests, using the desalination rate and protein loss rate as evaluation indexes. The experimental optimization ranges included peptides concentration of 1%~5%, nanofiltration pressure of 0.6~1.4 MPa and cycle times of 1~5. The salt contents of the samples before and after desalination were quantified using the silver nitrate titration method; the protein contents of the experimental samples were quantified using the Lowry colorimetric method. The quality indexes of the Antarctic krill peptides after treatment (including the basic nutritional composition: moisture content, protein content, ash content, salt content; amino acid composition; and molecular weight distribution) were systematically evaluated by the corresponding national standard methods. All experiments were performed in triplicate, and data were expressed as mean ± standard deviation. Excel 2016, IBM SPSS 20.0, and Origin 2018 were used for data analysis and chart drawing.Single-factor tests revealed that peptides concentration of 3%, nanofiltration pressure of 1.0 MPa and a cycle time of 2 could be selected as the design basis for the L9 (33) orthogonal test. The range value of the orthogonal test indicated that the degree of influence of the three factors on the desalination effect was as follows: peptides concentration > cycle times > nanofiltration pressure. The optimum conditions for desalting Antarctic krill peptides obtained by k value analysis were as follows: peptides concentration of 3.0%, nanofiltration pressure of 1.2 MPa and a cycle time of 3. Under the optimal condition, the desalination rate of the Antarctic krill peptides reached up to (86.35±2.11)%, and the protein loss rate was controlled at (9.10±0.35)%, demonstrating the feasibility of the process. The salt content of the Antarctic krill peptides after desalination was reduced to (1.14±0.12)% and the protein content was (92.73±2.29)%. The molecular weights of the Antarctic krill peptides after desalination were mainly distributed between 189 Da and 6500 Da, of which the proportion of peptides with molecular weight less than 3000 Da was (88.91±2.19)%, conforming to the molecular weight distribution range of bioactive peptides. The amount of essential amino acids in the Antarctic krill peptides after desalination accounted for (40.06±0.10)% of the total amino acids, and the ratio of essential amino acids to nonessential amino acids was (66.82±0.28)%. The amino acid compositions of the Antarctic krill peptides after desalination were ideal and met the standard stipulated by the FAO/WHO. The established nanofiltration desalination process presented good treatment effects, and the obtained peptides were of good quality and high nutritional value.The production of Antarctic krill protein-related products may be the next key development for the processing industry, since the sole high-value products of Antarctic krill at present are Antarctic krill oil and its derivatives. The established nanofiltration desalination process has practical application value and would provide technical support for the development of high-quality Antarctic krill peptides. This research provides scientific support for the efficient utilization of Antarctic krill resources.

To conduct a sensitivity analysis of the relevant parameters that impact the mechanics of tunnel construction in karst areas, firstly, the orthogonal design and range analysis method is applied to sort the 11 kinds of karst-tunnel-influencing factors from high to low according to the sensitivity degree. Secondly, the random forest algorithm based on an orthogonal experimental design is applied to the feature importance ranking of the influencing factors of karst tunnels. Thirdly, according to the results of the sensitivity analysis, the optimum combinations of influencing factors of tunnel construction in karst areas is obtained. The research based on these two methods shows that when taking the vertical displacement as the target variable, the parameters with the highest feature importance are A6 (tunnel diameter) and A10 (tunnel buried depth). When taking the first principal stress as the target variable, the most important influencing factors are A10 (tunnel buried depth) and A9 (location of karst cave). When taking the principal stress difference as the target variable, the most important influencing factors are A10 (tunnel buried depth) and A6 (tunnel diameter). The level combination of the 11 influencing factors obtained by taking the principal stress difference as the target variable was more balanced than the vertical displacement and the principal stress difference as the target variables. The results of this study will provide a theoretical basis to study key parameters in the response of mechanical characteristics to the safe construction of tunnels in karst areas.

To improve the problem of solid waste in phosphate mines, the research on the optimum mix ratio for cemented filling experiment of waste rock and phosphorus tailings was studied by orthogonal tests. Research on the influencing factors of uniaxial compressive strength, bleeding rate and slump constant for the filling body which was based on SPSS multivariate nonlinear regression analysis. Determining the optimal ratio and carry out semi-industrial tests to verify reliability. Results show that the filling to achieve optimal performance when the waste rock and tailings ratio is 6∶4, mass concentration is 78% and cement ratio is 280 kg/m3 for the filling body, the bleeding rate of filling bodyreaches the optimum and meets the pumping requirements of high fluidity, which meets the requirements of the mine filling process.

An orthogonal test method was used to do sensibility analysis on the compressive strength and splitting strength of hybrid fiber-reinforced recycled aggregate concrete (HyFRAC). And a prediction model of compressive strength of HyFRAC based on Convolutional Neural Network (CNN) was proposed. The results show the ratio of recycled brick aggregate (RBA) to recycled concrete aggregate (RCA) has been proved the greatest influence on the compressive strength and splitting tensile strength of HyFRAC, followed by the water reducing agent content, finally the ratio of glass fiber (GF) to polypropylene fiber (PF). When RBA/RCA = 2/8, GF/PF = 7/3, and water reducing agent content is 0%, the compressive strength and splitting tensile strength of HyFRAC are the highest. According to JGJ/T10-2011, when RBA/RCA ≤ 6/4 and water reducing agent content ≥ 0.4%, the HyFRAC slump meets the 50m pumping height requirement; when RBA/RCA ≤ 4/6 and water reducing agent content ≥ 0.6%, the HyFRAC slump meets the 100m pumping height requirement. Compared to back propagation (BP) neural network model and multiple linear regression model, CNN model is more efficient in estimating the compressive strength of HyFRAC. The average relative errors and max relative errors of CNN model are 1.98% and 4.12%, respectively.

Styrene-butadiene-styrene (SBS) is widely used in asphalt modification to obtain superior high-temperature performance. Nevertheless, studies on the low-temperature properties of SBS-modified asphalt are not satisfactory. Orthogonal tests are valid in analysing the results. In this paper, the main factors (SBS content, sulfur content, and the addition of rubber processing oil) for improving the low-temperature performance of SBS-modified asphalt were analyzed base on the orthogonal tests. Firstly, the frequency sweep test, bending beam rheometer (BBR) test, and force-ductility test were conducted to evaluate the low-temperature properties of SBS-modified asphalt. Investigation of low-temperature parameters obtained through these tests was conducted base on the orthogonal analysis method. The G-R parameter was abandoned in the analysis of the orthogonal method for the result that the increase of SBS content was negative to the low-temperature properties by the Glover-Rowe (G-R) parameter, which were contrary to the results of BBR and force-ductility tests. Moreover, the other parameters (ΔTc and toughness) sorted according to the orthogonal analysis method indicated the effect on low-temperature performance of the SBS-modified asphalt as SBS content > rubber processing oil > sulfur. As shown above that both SBS and rubber processing oil play a critical role in improving the low-temperature properties of SBS-modified asphalt, for SBS could resist the generation and subsequent propagation of cracks while the rubber processing oil could supplement the maltene loss.

To improve the strength, shrinkage and erosion resistance of backfill material, the research on the optimum mix ratio was studied by modern material modification technology. Using desulphurized gypsum, lime, fly ash, portland cement and tailings sand coarse aggregate as experimental materials to study the influence of the proportion of several admixtures in aggregate on the strength and shrinkage of the specimen by orthogonal tests. The microscopic mechanism of the modification was investigated by scanning electron microscope. The results show that the optimum mixing ratio of the modified filling material is 56% aggregate, 4% fly ash, 10% lime, 10% gypsum and 20% cement. External admixtures have improved the properties of raw soil materials from physical and chemical aspects, and the change of pore structure and the enhancement of particle adhesion are the fundamental reasons for the improvement of strength, shrinkage and water resistance.

Tribological properties of oleic acid modified natural serpentine ultrafine mineral powders as lubricating oil additive were investigated by a reciprocating sliding wear tester. The effects of the four factors including load, reciprocating frequency, sliding time and concentration of serpentine on the properties of serpentine additive were analyzed. Results indicate that the anti-wear and friction-reducing properties of the base oil are significantly improved by the addition of the modified serpentine powders. The order that affects the friction-reducing performance of the serpentine additive is:concentration, reciprocating frequency, load, sliding time, and the optimal tribological conditions are 100 N, 5 Hz, 180 min, 0.5%(mass fraction). While that affects the anti-wear property is:load, concentration, reciprocating frequency, sliding time, and the optimal conditions are 100 N, 50 Hz, 180 min, 0.3%. Serpentine minerals forms a tribofilm consisting of various oxides, graphite and organic compounds on the friction surface, which is the key to improving anti-wear and friction-reducing properties.

At present, the treatment of tailings is mostly carried out in the form of stacking in tailings ponds, resulting in a huge waste of mineral resources and a major threat to the environment and ecology. Using tailings instead of a part of the cement to make cementitious materials is an effective way to reduce the accumulation of tailings. In this paper, lead–zinc tailings-based cementitious materials were prepared by using lead–zinc tailings, fly ash, and ordinary Portland cement, and the effects of four factors on the mechanical properties of lead–zinc tailings, as well as fly ash content, cement content, and water–binder ratio were studied by orthogonal experiments. The corresponding relationship between the factors and the properties of cementitious materials was determined, and the optimization and prediction of the raw material ratio of lead–zinc tailings-based cementitious materials were realized. The test showed the ratio of raw materials to be at the lowest price ratio. Synchronously the ratio that meets the minimum strength requirements was predicted. When the proportion of fly ash:lead and zinc tailings:cement = 30:40:30 and the water–binder ratio was 0.4, the predicted compressive strength of the prepared cementitious material achieved 22.281 MPa, which meets the strength requirements, while the total content of lead–zinc tailings and fly ash was the highest at this time.

Styrene-butadiene-styrene (SBS) is widely used in asphalt modification to obtain superior high-temperature performance. Nevertheless, studies on the low-temperature properties of SBS-modified asphalt are not satisfactory. Orthogonal tests are valid in analysing the results. In this paper, the main factors (SBS content, sulfur content, and the addition of rubber processing oil) for improving the low-temperature performance of SBS-modified asphalt were analyzed base on the orthogonal tests. Firstly, the frequency sweep test, bending beam rheometer (BBR) test, and force-ductility test were conducted to evaluate the low-temperature properties of SBS-modified asphalt. Investigation of low-temperature parameters obtained through these tests was conducted base on the orthogonal analysis method. The G-R parameter was abandoned in the analysis of the orthogonal method for the result that the increase of SBS content was negative to the low-temperature properties by the Glover-Rowe (G-R) parameter, which were contrary to the results of BBR and force-ductility tests. Moreover, the other parameters (ΔTc and toughness) sorted according to the orthogonal analysis method indicated the effect on low-temperature performance of the SBS-modified asphalt as SBS content > rubber processing oil > sulfur. As shown above that both SBS and rubber processing oil play a critical role in improving the low-temperature properties of SBS-modified asphalt, for SBS could resist the generation and subsequent propagation of cracks while the rubber processing oil could supplement the maltene loss. [ABSTRACT FROM AUTHOR]

We design optimization on the overall blade structure of a vortex pump conducted by using the orthogonal test method to clarify the matching relationship of impeller and casing structures and then improve the hydraulic performance of the vortex pump. Based on two different impeller structures of forward-deflecting (denoted as R1 − F2) and backward-deflecting (denoted as F1 − R2), key parameters describing the impeller structure are calculated through optimization for the objective function of hydraulic efficiency by means of orthogonal tests and computational fluid dynamic simulations. Optimization computations show that the forward-deflecting blade impeller is superior to the backward-deflecting one. Model test of the optimized vortex pump is carried out calculating the error from the comparison of pump efficiencies calculated by model test and numerical simulation is calculated to be less than 6%. The experimental verification shows that the flow simulation has some errors. The weight of structure parameters such as the blade installation angle (α), the blade deflecting angle (β), the position of blade deflecting point (L), the radius (r) of smoothing arc at the deflecting point, the wedge type (W) of blade, to the lift head, the flow rate, and the efficiency of the pump is investigated, through multiparameter optimizations. Visualization observation of flows in the model pump consisted of a back-placed impeller and a front vaneless chamber is further performed. The characteristic of vortex formation predicted by flow simulation agrees with the result of visualization observation. The above results demonstrate that the optimum impeller type of vortex pump is forward-deflecting blade impeller. The optimum combination of the key structure parameters is that the deflection angle of the blade inlet (α) equals 30°, the position of blade deflecting point lM = 2/3 L, the chamfering radius (r) at the deflecting point r = 3 mm, and the best wedge type is axial deflecting blade.

Metakaolin was used as a raw material for the preparation of geopolymers, where two types of alkali activators (Na2SiO3 + NaOH and Na2SiO3 + NaOH) were used to prepare metakaolin geopolymers at room temperature. The mechanical properties and microstructures of the metakaolin geopolymers were analyzed. A three-factor, four-level orthogonal test was designed to investigate the mechanical properties of the metakaolin geopolymer with different ratios. The compressive and flexural strength of different specimens were tested for 7 and 28 days. Both the Na-based and K-based geopolymers exhibited excellent mechanical properties, but the K-based geopolymer had better mechanical properties. The optimal compressive strength and flexural strength of the K-based geopolymer were 73.93 MPa and 9.37 MPa, respectively. The 28-day optimal compressive strength of the Na-based polymer was 65.79 MPa, and the flexural strength was 8.71 MPa. SEM, XRD, and FTIR analyses showed that the mechanical properties of the geopolymers could be greatly improved by using a higher alkaline solution concentration, proper Na2SiO3/MOH mass ratio, and proper mass ratio of alkali exciter to metakaolin. Amorphous silicoaluminate was more favorable for the dissolution of silicon–alumina raw materials, promoted the formation of an amorphous silicoaluminate gel, and caused the internal structure of the geopolymer to be more compact.

To investigate the influence of structural parameters on the performances and internal flow characteristics of partial flow pumps at a low specific speed of 10000 rpm, special attention was paid to the first and second stage impeller guide vanes. Moreover, the impeller blade outlet width, impeller inlet diameter, blade inclination angle, and number of blades were considered for orthogonal tests. Accordingly, nine groups of design solutions were formed, and then used as a basis for the execution of numerical simulations (CFD) aimed at obtaining the efficiency values and heads for each design solution group. The influence of impeller geometric parameters on the efficiency and head was explored, and the “weight” of each factor was obtained via a range analysis. Optimal structural parameters were finally chosen on the basis of the numerical simulation results, and the performances of the optimized model were verified accordingly (yet by means of CFD). Evidence is provided that the increase in the efficiency and head of the optimized model was 12.11% and 23.5 m, respectively, compared with those of the original model. [ABSTRACT FROM AUTHOR]

At present, the treatment of tailings is mostly carried out in the form of stacking in tailings ponds, resulting in a huge waste of mineral resources and a major threat to the environment and ecology. Using tailings instead of a part of the cement to make cementitious materials is an effective way to reduce the accumulation of tailings. In this paper, lead-zinc tailings-based cementitious materials were prepared by using lead-zinc tailings, fly ash, and ordinary Portland cement, and the effects of four factors on the mechanical properties of lead-zinc tailings, as well as fly ash content, cement content, and water-binder ratio were studied by orthogonal experiments. The corresponding relationship between the factors and the properties of cementitious materials was determined, and the optimization and prediction of the raw material ratio of lead-zinc tailings-based cementitious materials were realized. The test showed the ratio of raw materials to be at the lowest price ratio. Synchronously the ratio that meets the minimum strength requirements was predicted. When the proportion of fly ash:lead and zinc tailings:cement = 30:40:30 and the water-binder ratio was 0.4, the predicted compressive strength of the prepared cementitious material achieved 22.281 MPa, which meets the strength requirements, while the total content of lead-zinc tailings and fly ash was the highest at this time.

Styrene-butadiene-styrene (SBS) is widely used in asphalt modification to obtain superior high-temperature performance. Nevertheless, studies on the low-temperature properties of SBS-modified asphalt are not satisfactory. Orthogonal tests are valid in analysing the results. In this paper, the main factors (SBS content, sulfur content, and the addition of rubber processing oil) for improving the low-temperature performance of SBS-modified asphalt were analyzed base on the orthogonal tests. Firstly, the frequency sweep test, bending beam rheometer (BBR) test, and force-ductility test were conducted to evaluate the low-temperature properties of SBS-modified asphalt. Investigation of low-temperature parameters obtained through these tests was conducted base on the orthogonal analysis method. The G-R parameter was abandoned in the analysis of the orthogonal method for the result that the increase of SBS content was negative to the low-temperature properties by the Glover-Rowe (G-R) parameter, which were contrary to the results of BBR and force-ductility tests. Moreover, the other parameters (ΔTc and toughness) sorted according to the orthogonal analysis method indicated the effect on low-temperature performance of the SBS-modified asphalt as SBS content > rubber processing oil > sulfur. As shown above that both SBS and rubber processing oil play a critical role in improving the low-temperature properties of SBS-modified asphalt, for SBS could resist the generation and subsequent propagation of cracks while the rubber processing oil could supplement the maltene loss.

At present, the treatment of tailings is mostly carried out in the form of stacking in tailings ponds, resulting in a huge waste of mineral resources and a major threat to the environment and ecology. Using tailings instead of a part of the cement to make cementitious materials is an effective way to reduce the accumulation of tailings. In this paper, lead–zinc tailings-based cementitious materials were prepared by using lead–zinc tailings, fly ash, and ordinary Portland cement, and the effects of four factors on the mechanical properties of lead–zinc tailings, as well as fly ash content, cement content, and water–binder ratio were studied by orthogonal experiments. The corresponding relationship between the factors and the properties of cementitious materials was determined, and the optimization and prediction of the raw material ratio of lead–zinc tailings-based cementitious materials were realized. The test showed the ratio of raw materials to be at the lowest price ratio. Synchronously the ratio that meets the minimum strength requirements was predicted. When the proportion of fly ash:lead and zinc tailings:cement = 30:40:30 and the water–binder ratio was 0.4, the predicted compressive strength of the prepared cementitious material achieved 22.281 MPa, which meets the strength requirements, while the total content of lead–zinc tailings and fly ash was the highest at this time. [ABSTRACT FROM AUTHOR]

Metakaolin was used as a raw material for the preparation of geopolymers, where two types of alkali activators (Na 2 SiO 3 + NaOH and Na 2 SiO 3 + NaOH) were used to prepare metakaolin geopolymers at room temperature. The mechanical properties and microstructures of the metakaolin geopolymers were analyzed. A three-factor, four-level orthogonal test was designed to investigate the mechanical properties of the metakaolin geopolymer with different ratios. The compressive and flexural strength of different specimens were tested for 7 and 28 days. Both the Na-based and K-based geopolymers exhibited excellent mechanical properties, but the K-based geopolymer had better mechanical properties. The optimal compressive strength and flexural strength of the K-based geopolymer were 73.93 MPa and 9.37 MPa, respectively. The 28-day optimal compressive strength of the Na-based polymer was 65.79 MPa, and the flexural strength was 8.71 MPa. SEM, XRD, and FTIR analyses showed that the mechanical properties of the geopolymers could be greatly improved by using a higher alkaline solution concentration, proper Na 2 SiO 3 /MOH mass ratio, and proper mass ratio of alkali exciter to metakaolin. Amorphous silicoaluminate was more favorable for the dissolution of silicon-alumina raw materials, promoted the formation of an amorphous silicoaluminate gel, and caused the internal structure of the geopolymer to be more compact.

Abstract Titanium alloy with high corrosion resistance, high strength-to-density ratio, and excellent biocompatibility has a wide range of applications in the field of biomedical implants. Polishing experiments of titanium alloy with a small size and complex shapes were investigated using an ultrasonic assisted magnetorheological finishing (UMRF) device excited by a three-pole magnetic field generator. The models of the normal force and the shear force were first proposed based on the Preston equation to analyze the mechanism of material removal in the UMRF process. Subsequently, the single-factor experiments using titanium alloy nuts (M3) and the MR polishing fluid with silicon carbide abrasives were carried out. Furthermore, to improve the surface roughness and the change rate of surface roughness of nuts, orthogonal tests with a standard L9(34) orthogonal array were designed and performed based on the optimized process parameters obtained from the single-factor experiment. The results indicated the effect on surface roughness and change rate of surface roughness as applied current > roller speed > ultrasonic amplitude > spindle speed and applied current > roller speed > spindle speed > ultrasonic amplitude, respectively. Moreover, the surface roughness was improved from an initial 1.247 μm to a final 0.104 μm after the polishing for 80 min under these optimal process parameters.

End milling method is applied to machining of cycloidal gears to improve the cutting quality and efficiency. The influence of milling parameters on the surface roughness is investigated based upon orthogonal tests with the four factors and four levels, as well as analysis of range and variance. A model to predict the surface roughness is built up on basis of the probability statistics and multivariate nonlinear regression analysis. Significance tests are conducted on the prediction model, and the interactive effect of these parameters on the surface roughness is figured out so as to propose optimization schemes. The results show that the shaft inclination angle has the biggest impact on the surface roughness, followed by the feed per tooth, the radial feed and the spindle speed. The prediction model of surface roughness is proved to have high prediction accuracy. This study aims to provide references for the improvement of machining quality of cycloidal gears and optimization of milling parameters. [ABSTRACT FROM AUTHOR]

To provide theoretical basis and practical guidance for preparing composite rods by direct continuous casting, copper-clad aluminum composite rods of external copper layer diameter 12 mm and inner aluminum core diameter 8 mm were manufactured. Orthogonal tests consisted of three factors and three levels were carried out to research the effects of melting copper temperature, continuous casting speed and nitrogen pressure on the performance of composite rods. Results showed that nitrogen pressure is the most important factor in influencing the surface quality; continuous casting speed is the most important factor in influencing copper & aluminum inter diffusion amount. Nitrogen pressure can noticeably improve the surface quality and make the rods easily be drawn out, but the surface quality does not show visible improvement when the nitrogen pressure is above 0.05 MPa. Measured by tests, the compound layer can be divided into three types according to its cladding layer degree: deficient cladding, normal cladding and excess cladding. The diameter of normal copper-clad aluminum composite rods can be successfully drawn less than 0.6 mm without annealing.

We design optimization on the overall blade structure of a vortex pump conducted by using the orthogonal test method to clarify the matching relationship of impeller and casing structures and then improve the hydraulic performance of the vortex pump. Based on two different impeller structures of forward-deflecting (denoted as R1 − F2) and backward-deflecting (denoted as F1 − R2), key parameters describing the impeller structure are calculated through optimization for the objective function of hydraulic efficiency by means of orthogonal tests and computational fluid dynamic simulations. Optimization computations show that the forward-deflecting blade impeller is superior to the backward-deflecting one. Model test of the optimized vortex pump is carried out calculating the error from the comparison of pump efficiencies calculated by model test and numerical simulation is calculated to be less than 6%. The experimental verification shows that the flow simulation has some errors. The weight of structure parameters such as the blade installation angle (α), the blade deflecting angle (β), the position of blade deflecting point (L), the radius (r) of smoothing arc at the deflecting point, the wedge type (W) of blade, to the lift head, the flow rate, and the efficiency of the pump is investigated, through multiparameter optimizations. Visualization observation of flows in the model pump consisted of a back-placed impeller and a front vaneless chamber is further performed. The characteristic of vortex formation predicted by flow simulation agrees with the result of visualization observation. The above results demonstrate that the optimum impeller type of vortex pump is forward-deflecting blade impeller. The optimum combination of the key structure parameters is that the deflection angle of the blade inlet (α) equals 30°, the position of blade deflecting point lM = 2/3 L, the chamfering radius (r) at the deflecting point r = 3 mm, and the best wedge type is axial deflecting blade. [ABSTRACT FROM AUTHOR]