Papers by Keyword: Correlation Coefficient

Abstract: In this study, Dynamic Shear Rheometer (DSR) and Fourier Transform Infrared (FTIR) spectroscopy tests were performed on 35-50 and 70-100 penetration-graded asphalts. Both tests were performed on specimens at three different ageing states: unaged, short-term aged using the standard rolling thin film oven (RTFO) device, and long term aged by placing RTFO residue in the pressure aging vessel (PAV) apparatus. The tests were accomplished to quantify how ageing affects the results of both tests, namely the complex shear modulus for the DSR test and the carbonyl, sulfoxide, and ageing indices for the FTIR spectroscopy test. Both sets of measurements confirm that the harder asphalt stays harder than the softer asphalt after undergoing ageing, but the rate of hardness is higher for the softer asphalt. For instance, on average, PAV ageing was found to increase the amplitude of the shear complex modulus, from the unaged state, by 4.3 times and by 6.2 times for the 35-50 and 70-100 asphalts, respectively. It was also found that ageing decreases the phase angle for asphalt and the decrease is more pronounced for the softer asphalt (70-100) than the harder one (35-50). This was attributed to more maltenes content in the softer asphalt that transform into asphaltenes during ageing. Correlation coefficient between FTIR signals from the same samples revealed that FTIR spectroscopy as used in this research has an excellent repeatability. The repeatability was also confirmed using measures of dispersion such as the coefficient of variation, which was found not to exceed the 1.2%. The 35-50 asphalt was found to have more C=O and S=O links than the 70-100 asphalt since it showed more absorbance in the carbonyl and sulfoxide bands. These links are thought to make the asphalt physically harder. An analysis of variance study revealed that ageing is a statistically significant factor as measured using ageing indices calculated from FTIR spectroscopy data with the index AI_FTIR being the most sensitive to ageing among all considered indices. Empirical power equations with high coefficient of determination values were established to predict DSR results from FTIR index values, which was possible since both types of measurements show the same trend with ageing.

Abstract: In the article, the interaction of the coefficient of friction for friction pairs operating under conditions of abrasive wear is considered, depending on a number of factors. Thus, the friction coefficient is one of the main indicators characterizing the performance of friction nodes. Analytical expressions obtained based on the calculation of the results of the conducted tests using mathematical statistical and mathematical methods allow to determine the coefficient of friction and allow the designer to effectively choose the material and oils before designing.

Abstract: Most of the structures, parts of machines in the process of operation are subjected to the action of cyclically changing loads, such changes can be judged by the fatigue of the metal. In addition to the influence of mechanical stresses during the service, corrosive environment affects metal structures, machine parts, which leads to the process of gradual accumulation of damage. Corrosive media leads to a decrease in durability. The paper presents results of fatigue tests on a sample of steel X70, selected from the focal zone of destruction of the main gas pipeline. The sample under investigation had numerous cracks typical for corrosion-mechanical destruction. It is shown that with an increase in the number of loading cycles, the electrode potential of the metal decreases, which leads to a decrease in its thermodynamic stability. With the growth of the crack, there is a decrease in the potential, which is not compensated by the relaxation processes. Results of the regression analysis showed that the correlation coefficient is r = 0.99, using the three-parameter logarithmic function.

Abstract: The paper presents the results of the assessment of atmospheric air pollution with fine dust РМ₁₀ studies in the city of Kabul_. The investigation was based on concentration of fine dust РМ₁₀ measurements that were conducted by the national agency on ecology and environmental protection of Afghanistan and by Russian researchers in summer and autumn of 2015. It is shown that, according to the Chi-square and Kolmogorov-Smirnov criteria, the best law for the distribution of the maximum daily dust concentration is the logarithmic normal law. For the maximum daily concentration (РМ₁₀) a density function and an integrated distribution function have been summarized. A mathematical model of the concentration of fine dust (РМ₁₀) dependence of three factors: wind speed, humidity and temperature have been obtained. On the basis of F–Fisher criterion the quadratic model has been chosen for June and August, and the linear model has been chosen for July, September, October and November.

Abstract: This paper presents the modeling of cutting performances in turning of 2017A aluminium alloy at four turning parameters: cutting speed, feed rate, depth of cut, and tool nose radius. These performances include: surface roughness, cutting forces, cutting temperature, material removal rate, cutting power, and specific cutting pressure. The experimental data were collected by conducting turning experiments on a Computer Numerically Controlled lathe and by measuring the cutting performances with forces measuring chain, an infrared camera, and a roughness tester. The collected data were used to develop multiple regression models for the pre-cited cutting performances and investigate the effects of turning parameters and their interactions on responses. To evaluate the accuracy of the developed models, two performance criteria were used: Correlation Coefficient (R²) and Average Percentage Error (APE). It was clearly seen that the multiple regression models estimate the cutting performances with high accuracy: R²>94% and APE<7%. Therefore, this method is an effective tool for modeling the cutting performances in turning process.

Abstract: The present paper describes an investigation of the adsorption of lead ions (Pb²⁺) on graphene-based nanocomposites obtained via exfoliation of hydrolyzed expanded graphite intercalation compound. Three types of these nanocomposites - suspension of graphene nanoplatelets (SGN), paste of multi-layered oxidized graphene (PMOG), and paste of few-layered oxidized graphene (PFOG) - were used to extract Pb²⁺ from 1,040 mg L^-1 aqueous solutions of Pb (NO₃)₂, and the kinetic of the Pb²⁺ adsorption was studied. It was found that the kinetic data are best fitted by the pseudo-second-order model. The adsorption equilibrium was achieved within 30 min under normal conditions. The maximum Pb²⁺ adsorption capacity of SGN, PMOG and PFOG was found to be 457, 103 and 38 mg g^-1, respectively. Considering the obtained results, it can be assumed that the phenolic and hydroxyl oxygen-containing functional groups located at the surface of the adsorption materials under study play an important role in the Pb²⁺ removal process.

Abstract: The adsorption of lead ions (Pb (II)) ions from aqueous solutions was studied. Different types of carbon materials, such as high-porous carbon, BAU-A activated carbon, multi-walled carbon nanotubes (pristine and oxidized), were used as adsorbents. To describe kinetic dependences for the Pb (II) extraction from aqueous solutions with those materials, the following models were implemented: pseudo-first-and pseudo-second-order, intraparticle diffusion, and Elovich. The adequacy of applying the pseudo-second-order equation was presented for characterizing the Pb (II) adsorption on the carbon materials under study. Thus, it was found that the interaction between the adsorbed ions and the functional groups of the adsorbents makes an important contribution to the overall rate of the process. Finally, the time of achieving equilibrium, the adsorption rate constants and the maximum adsorption capacity were empirically determined for all the adsorbents.

Abstract: Silicon nitride ceramic balls are successfully applied in advanced bearings. In order to improve the performance and precision for ball bearings, the research about the material properties of Si3N4 ball is shown in this paper. For the Si3N4 ball, the material properties can be described by the following factors: density, hardness, apparent porosity, crushing load and fracture toughness. In this paper, Si3N4 balls from three different manufacturers are tested to reveal the inherent correlations of the material properties, and the correlation coefficients are calculated. The results indicate that with the increasing of ball diameter, its crushing load increases correspondingly. The higher hardness contributes to the lower crushing load of the Si3N4 ball. Apparent porosity has a greater influence on the crushing load than hardness and the density. Hardness has the closest relevance with fracture toughness among the material characteristics, with the increasing of the hardness, the fracture toughness of Si3N4 ball becomes lower.

Abstract: An indirect type solar dryer is fabricated with the components like evacuated tube collector, drying chamber and blower. The performance of the drier is evaluated by carrying out drying experiments with copra at Coimbatore district Tamilnadu, India. A short survey of these showed that applying the indirect type solar dryer not only significantly reduced the drying time but also resulted in many improvements in the quality of the dried products. The temperature of the drying chamber ranges from 55°C to 75°C while the ambient temperature ranges from 28°C to 38°C. Nine basic solar drying models were used to fit the experimental data of copra. For experimental results, the logarithmic model showed the best curve fitting with highest correlation coefficient (R²⁾ and lowest value of RMSE (Root Mean Square Error). Solar dried copra obtained is free from smoke, dust, bird and rodent damage.

Abstract: At present, both at home and abroad of tunnel surrounding rock classification methods and standards are all aimed at tunnel survey and design phase. It is the cause of that surrounding rock classification are very different between design phase and tunnel construction because of the limits of investigation techniques and geological data. It is the key to the real-time construction design problem that Sentenced to a stable state of surrounding rock based on the monitoring data. This paper determines the influence factors of tunnel convergence value clearance and obtained the tunnel convergence value clearance of principal component factor and power based on the statistical analysis of a lot of tunnel monitoring measurement data. It is put forward correction formula of dynamic classification of surrounding rock according to the theory of probability and statistics. The results show that based on the real-time monitoring of tunnel surrounding rock classification method is quite coincident with the actual situation of tunnel excavation in engineering applications.