This paper presents an analytical approach to predict the machining force, temperature and residual stress under minimum quantity lubrication (MQL) condition. Both the lubrication and cooling effects are considered to change the tribological and thermal properties in the modified Oxleys model, which is capable to predict the cutting force and temperature in MQL machining directly from cutting conditions. The machining-induced residual stress is predicted by modified McDowell hybrid algorithm. The predicted cutting forces and residual stresses are verified by orthogonal cutting tests for C45 steel and TC4 alloy steel.
Hardened AISI 1045 steel implemented in machine tool spindle was previously ground using grinding operation. This research aims to address the feasibility of hard turning AISI 1045 using PCBN tool with chip breaker under dry condition. Chip morphology, cutting force and temperature were measured, analyzed and correlated with machining parameters. Experimental results demonstrate that serrated chips are generated at high speeds, high feed rate is an assistant to promote serrated chips, and chip breaker can help break chip into acceptable lengths. Cutting forces were characterized with periodic fluctuation along three directions as chips are serrated. Temperature at machined zone can reach as high as 1200°C, which indicates that adiabatic shear bands can be successfully achieved during the machining of hardened AISI 1045 steel without applying lubricants.
Hard turning has been recognized as a substitute for abrasive-based processes not only due to its flexibility, economic benefit and environmental consciousness, but also its determinate surface integrity (surface roughness, micro hardness and residual stress), which is superior and more consistent than ground surfaces. Residual stress is of considerable industrial importance because they can affect failure by fatigue, creep or cracking. It is believed that compressive residual stresses are more favorable for fatigue life than tensile residual stresses. Hard turning generally generates compressive residual stress, which is the dominant role in determining both the variance and average value of fatigue life. This paper focus on the published data, especially C.R.Liu’s research, which address the residual stresses by hard turning in terms of experimental approaches， theoretical modeling，numerical simulation by Finite Element Analysis (FEA) and the correlation with its fatigue life and performance. The potential trends and key technologies for residual stresses are predicated and discussed so as to capture the most effective approach to investigate residual stress by hard turning.
Since the volume of hippocampal formation has been found to be an early biomarker for MCI and Alzheimer's disease, hippocampus segmentation plays a significant role in clinical diagnosis. Because hippocampus in MR images presents features of low contrast, low signal-to-noise ratio and discontinuous boundaries, accurate segmentation still remains a challenging task. We presented a survey of the methods used to segment the hippocampal formation in MR images of human brain and concluded with a discussion on the trend of the future research in hippocampus segmentation.
An explicit dynamic coupled thermal-mechanical Arbitrary Lagrangian Eulerian (ALE) model was established to simulate orthogonal cutting AISI 52100 bearing steel, and its temperature and stress distribution. Based on ABAQUS, The ALE approach effectively simulates plastic flow around round edge of the cutting tool without employing chip separation criteria. The calculation results reveal that cutting speed and cutting depth have great impact on chip morphology, stress and temperature distribution in the finished surface and subsurface, the predicted temperature agrees well with experiment data obtained under the similar cutting conditions as well as the change in chip morphology from continuous to sawtooth as the cutting speed increases.
It is well known that there is a lager deviation in the fatigue life of machined components even under nominally identical loading conditions. Understanding and controlling fatigue life variance are essential to enhance reliability. However, few research focus on the impact of machining processes on the fatigue life variance of machined components. In this study, surface residual stress distributions of bearing rings randomly selected from a production line by super-finishing grinding, are measured by X-ray diffraction method in cutting and feed direction, and its scatter is analyzed by statistical tools. Based on the variance prediction theories, build a simplified fatigue life variance prediction model incorporating the resultant residual stresses scatter induced by machining process. Based on the Basquin equation, the model is validated by experimental data published in literature. The predicted fatigue life agrees well with the experimental average fatigue life. Statistical analysis shows that the predicted variances of fatigue life are equal to those estimated from experimental fatigue life.
In this paper, the cell potential method is used to determine the average activity coefficients of the NaBr–Na2SO4–H2O ternary system at 318.15 K. The ion-selective electrode and electrolyte solution are used to form a liquid-free battery. The ionic strength in the mixed solution is in the range 0.01–1.0 mol·kg–1 with different ionic strength fractions of Na2SO4, that is, y b = (0, 0.2, 0.4, 0.6, and 0.8). First, in a single salt solution, the response curve of Nernst can be obtained according to the Nernst equation. The standard cell potential E 0 = 251.03, electrode response slope k = 27.124, and linear correlation coefficient R 2 = 0.9998 are obtained in this work. In the same way, the average activity coefficients of NaBr in mixed electrolyte solution at 318.15 K were also determined by using the Nernst equation. Finally, the mixed ion interaction parameters θBr, SO4 and φNa, Br, SO4 of Pitzer equations can be fitted by the multilinear regression method combined with the average activity coefficients of mixed salt solution. In addition, the osmotic coefficients, water activity, excess Gibbs free energy, and activity coefficient of Na2SO4 can also be calculated using Pitzer equations based on the fitted θBr, SO4 and φNa, Br, SO4.
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