Analysis on the turning point of dynamic in-plane compressive strength for a plain weave composite

Experimental investigations on dynamic in-plane compressive behavior of a plain weave composite were performed using the split Hopkinson pressure bar. A quantitative criterion for calculating the constant strain rate of composites was established. Then the upper limit of strain rate, restricted by stress equilibrium and constant loading rate, was rationally estimated and confirmed by tests. Within the achievable range of 0.001/s-895/s, it was found that the strength increased first and subsequently decreased as the strain rate increased. This feature was also reflected by the turning point(579/s) of the bilinear model for strength prediction. The transition in failure mechanism, from local opening damage to completely splitting destruction, was mainly responsible for such strain rate effects. And three major failure modes were summarized under microscopic observations: fiber fracture, inter-fiber fracture, and interface delamination. Finally, by introducing a nonlinear damage variable, a simplified ZWT model was developed to characterize the dynamic mechanical response. Excellent agreement was shown between the experimental and simulated results.

High-sensitive state perception method for inverter-fed machine turn insulation based on FrFT-Mel

Amidst the swift advancement of new power systems and electric vehicles,inverter-fed machines have progressively materialized as a pivotal apparatus for efficient energy conversion.Stator winding turn insulation failure is the root cause of inverter-fed machine breakdown.The online monitoring of turn insulation health can detect potential safety risks promptly,but faces the challenge of weak characteristics of turn insulation degradation.This study proposes an innovative method to evaluate the turn insulation state of inverter-fed machines by utilizing the fractional Fourier transform with a Mel filter(FrFT-Mel).First,the sensitivity of the high-frequency(HF)switching oscillation current to variations in turn insulation was analyzed within the fractional domain.Subsequently,an improved Mel filter is introduced,and its structure and parameters are specifically designed based on the features intrinsic to the common-mode impedance resonance point of the electrical machine.Finally,an evaluation index was proposed for the turn insulation state of inverter-fed machines.Experimental results on a 3kW permanent magnet synchronous machine(PMSM)demonstrate that the proposed FrFT-Mel method significantly enhances the sensitivity of turn insulation state perception by approximately five times,compared to the traditional Fourier transform method.

Numerical Study of a Three-Dimensional Laminar Flow in a Rectangular Channel with a 180-Degree Sharp Turn

This study presents a numerical analysis of three-dimensional steady laminar flow in a rectangular channel with a 180-degree sharp turn. The Navier-Stokes equations are solved by using finite difference method for Re = 900. Three-dimensional streamlines and limiting streamlines on wall surface are used to analyze the three-dimensional flow characteristics. Topological theory is applied to limiting streamlines on inner walls of the channel and two-dimensional streamlines at several cross sections. It is also shown that the flow impinges on the end wall of turn and the secondary flow is induced by the curvature in the sharp turn.

TURNING LIGNIN INTO VALUABLE PRODUCTS

In a study published in Nature Catalysis on May 28,Chinese scientists unveiled a nove l approach to transforming lignin,a major component of woody biomass,into valuable chemical products(doi:10.1038/s41929-024-01165-w).This discovery could pave the way for more sustainable and efficient use of renewable resources.

SURFACE ROUGHNESS PREDICTION MODEL FOR ULTRAPRECISION TURNING ALUMINIUM ALLOY WITH A SINGLE CRYSTAL DIAMOND TOOL

A surface roughness model utilizing regression analysis method is developedfor predicting roughness of ultra-precision machined surface with a single crystal diamond tool. Theeffects of the main variables, such as cutting speed, feed, and depth of cut on surface roughnessare also analyzed in diamond turning aluminum alloy. In order to predict the optimum cuttingconditions during process planning. A lot of experimental results show that the model can predictthe surface roughness effectively under a certain cutting conditions.

Experimental Study on Hard Turning Hardened GCr15 Steel with PCBN Tool

This paper discusses experimental results of turnin g experiments on GCr15 bearing steel hardened to 60～64 HRC. The objective was to d etermine the effect of the cutting parameters on cutting force, chip morphology and resultant workpiece surface quality, more specifically surface texture, micr ostructure alterations, changes in microhardness and residual stresses distribut ion. The changing rules of the main cutting force was shown in this paper which feature a increasing tendency with the improvement of the workpiece hardness wit hin the cutting parameter scope. The rule of cutting force changing with the wor kpiece hardness is accord to the traditional metal cutting theory. Stress value decrease with increasing cutting speed and workpiece hardness. The comparison of the machined surface roughness and harden layer depth of machined surface for d ifferent hardness is shown in Fig.1. The machined surface roughness is the worst when the workpiece hardness is around 50HRC. When the workpiece hardness is ove r 50HRC, the surface roughness value shows a descending tendency with the additi on hardness. The machined superficial harden layer depth shows an increasing ten dency with the improvement of the workpiece hardness. When the workpiece hardnes s is 50HRC the machined superficial harden layer depth is tiptop. When the workp iece hardness is over 50HRC the depth changes little with the addition of workpi ece hardness. The remnant stress status of the machined surface is shown in Fig. 2, which is press stress status both in surface and in base for less cutting par ameters under two kinds of cutting condition. But experiment results show that t ensile stress can be produced under uncomfortable cutting conditions. The deform ation created by the chip formation is reduced whereduce with [TPP126A,+35mm77mm,Z,PY#]Depth from surface (μm) ■ v=200m/min,f=0.24mm/r,ap=0.8mm,60HRC ● v=200m/min,f=0.15mm/r,ap=0.5mm,60HRC Fig.1 The subsurface residual stress between the two experimentsHardness (HRC) Fig.2 The surface finish vs. workpiece hardness the workpiece hardness is improved.

Returning Chinese school-aged children and adolescents to physical activity in the wake of COVID-19: Actions and precautions

The Coronavirus disease-2019(COVID-19)pandemic is still spreading globally.As of April 7,2020,it has reached 184 countries and territories,infecting more than 1.4 million people worldwide with more than 82,000 deaths.1 The situation in China has improved significantly since December 31,2019.2 Owing to the unprecedented and effective quarantine measures taken across the country,Chinese health authorities reported on March 18,2020,that for the first time since the outbreak no new locally transmitted COVID-19 cases had been reported,marking a major turning point in the fight against the highly contagious coronavirus.3 Since then,the daily number of new cases in the mainland of China has dropped to double digits,with new infections primarily originating from incoming air passengers from outside China.

Ultra-high voltage 4H-SiC gate turn-off thyristor for low switching time

An ultra-high voltage 4H-silicon carbide(Si C) gate turn-off(GTO) thyristor for low switching time is proposed and analyzed by numerical simulation. It features a double epitaxial p-base in which an extra electrical field is induced to enhance the transportation of the electrons in the thin p-base and reduce recombination. As a result, the turn-on characteristics are improved. What is more, to obtain a low turn-off loss, an alternating p^+/n^+region formed in the backside acts as the anode in the GTO thyristor. Consequently, another path formed by the reverse-biased n^+–p junction accelerates the fast removal of excess electrons during turn-off. This work demonstrates that the turn-on time and turn-off time of the new structure are reduced to 37 ns and 783.1 ns, respectively, under a bus voltage of 8000 V and load current of 100 A/cm^2.

Research of a fractional-turn ratio saturable pulse transformer and its application in a microsecond-range pulse modulator

As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is constructed and analyzed in this paper.Preliminary experimental results show that if the primary energy storage capacitors are charged to 300 V,an output voltage of about 19 kV can be obtained across the capacitor connected to the secondary windings of a fractional-tum ratio saturable pulse transformer.Theoretical and experimental results reveal that this kind of pulse transformer is not only able to integrate a step-up transformer and a magnetic switch into one device,but can also lower the saturable inductance of its secondary windings,thus leading to the relatively high step-up ratio of the pulse transformer.Meanwhile,the application of the fractional-turn ratio saturable pulse transformer in a μs range pulse modulator as a voltage step-up device and main switch is also included in this paper.The demonstrated experiments display that an output voltage with an amplitude of about 29 kV,and a 1.6 μs pulse width can be obtained across a 3500 Ω resistive load,based on a pulse modulator,if the primary energy storage capacitors are charged to 300 V.This compact fractional-turn ratio saturable pulse transformer can be applied in many other fields such as surface treatment,corona plasma generation and dielectric barrier discharge.

Migrant Workers Age-Group Productivity Gap Is Key to Verifying Lewis Turning Point in Chin＊

This paper uses age-related productivity gaps to analyze the Lewis turning point in China. The age-related productivity gap implies that under same wage rate, older and less productive rural laborers working in cities will earn less than the reservation wage. Thus, they may elect instead to return to the countryside. Therefore, this paper argues that while the supply of younger, high-productivity migrant workers fails demand and Lewis turning point emerges, there still exists a high volume of lower-productivity rural surplus labor.

Effect of PCBN cutting tools wear on surface integrality in high-speed hard turning

In this paper, the effect of of flank wear polycrystalline cubic boron nitride （PCBN） tools on residual stresses, white layer and roughness of machined workpiece surfaces is studied. Experimental results indicate that with the increase of the tool wear, the surface of the machined workpiece tends to generate tensile residual stresses, and white layer becomes clearly thicker and uneven on the workpiece surface. The effect of the flank wear on the surface roughness is less within some range of flank wear value. The results show that it is possible to produce ideal surface integrality levels by controlling the tool flank wear.

The Homotopy Perturbation Renormalization Group Method to Solve the WKB Problem with Turn Points

In this paper,we give the homotopy perturbation renormalization group method,this is a new method for turning point problem.Using this method,the independent variables are introduced by transformation without introducing new related variables and no matching is needed.The WKB approximation method problem can be solved.

A COMPLETE EXPRESSION OF THE ASYMPTOTIC SOLUTION OF DIFFERENTIAL EQUATION WITH THREE_TURNING POINTS

In this paper, a second order linear ordinary differential equation with three-turning points is studied. This equation is as follows (dx2)/(d2y) + [lambda(2)q(1)(x) + lambda q(2)(x, lambda)]y = 0, where q(1) (x) = (x - mu(1))(x - mu(2))(x - mu(3))f(x), f(x) not equal 0, mu(1) < mu(2) < mu(3) and lambda is a large parameter, but q(2)(x, lambda) = Sigma(i = 0)(epsilon a) g(i)(x)lambda(-i) (here g(0)(x) not equivalent to 0). By using JL function, the complete expression of the formal uniformly, valid asymptotic solutions of the equation near turning point is obtained.

ASYMPTOTIC SOLUTIONS OF BOUNDARY VALUE PROBLEMS FOR THIRD-ORDER ORDINARY DIFFERENTIAL EQUATIONS WITH TURNING POINTS

Boundary value problem; for third-order ordinary differential equations with turning points are studied as follows : epsilon gamma ' ' + f(x ; epsilon) gamma ' + g(x ; epsilon) gamma ' +h(x ; epsilon) gamma = 0 (- a < x < b, 0 epsilon 1), where f(x ; 0) has several multiple zero points in ( - n, b). the necessary conditions for exhibiting resonance is given, and the uniformly valid asymptotic solutions and the estimations of remainder terms are obtained.

Application of Machine Learning for Tool Condition Monitoring in Turning

The machining process is primarily used to remove material using cutting tools.Any variation in tool state affects the quality of a finished job and causes disturbances.So,a tool monitoring scheme(TMS)for categorization and supervision of failures has become the utmost priority.To respond,traditional TMS followed by the machine learning(ML)analysis is advocated in this paper.Classification in ML is supervised based learning method wherein the ML algorithm learn from the training data input fed to it and then employ this model to categorize the new datasets for precise prediction of a class and observation.In the current study,investigation on the single point cutting tool is carried out while turning a stainless steel(SS)workpeice on the manual lathe trainer.The vibrations developed during this activity are examined for failure-free and various failure states of a tool.The statistical modeling is then incorporated to trace vital signs from vibration signals.The multiple-binary-rule-based model for categorization is designed using the decision tree.Lastly,various tree-based algorithms are used for the categorization of tool conditions.The Random Forest offered the highest classification accuracy,i.e.,92.6%.

White Layer of Hard Turned Surface by Sharp CBN Tool

White layers in hard turned surfaces were identified and measured as a function ot turning parameters based on the Taguchi method. It reveals that white layers generate on the machine surface in the absence of tool flank wear, and white layer depth varies with the different combinations of hard turning parameters. Turning speed has the most important impact on white layer depth, feed rate follows, and cutting depth at last. The white layer generation consequently suggests a strong couple relation to the heat generation and thermal process of hard turning operation. White layer disappears under an optimal combination of turning parameters by Taguchi method. It suggests that a superior surface integrity without white layer is feasible under some selected combinations of turning parameters by a sharp CBN cutting tool.

A COMPLETE EXPRESSION OF THE ASYMPTOTIC SOLUTION OF DIFFERENTIAL EQUATION WITH A∩-TH ORDER TURNING POINT

A second order linear ordinary differential equation has been studied,and thecomplete expression.of the formal uniformly valid asymptotic solutions to the equationnear turning point is obtained by using extended Airy function.

Experimentation on Tool Wear and Surface Roughness in AISI D2 Steel Turning with WC Insert

The Taguchi method, based on an orthogonal arrangement (L9, 33), the vari-ance analysis, the signal-to-noise ratios and the response surface methodol-ogy have been used to optimize maximum flank wear (VBmax) and surface roughness (Ra) of the cutting tool when turning a hardened steel AISI D2 (65 HRC) with PVD—TiAlN coated WC insert upon dry environment. By em-ploying regression models;cutting speed, cutting depth and feed rate, which optimize maximum flank wear and surface roughness were validated. Results of relation signal-to-noise ratios, showed that with cutting speed of 200 m/min, cutting depth of 0.2 mm and feed rate of 0.20 mm/rev, Ra is opti-mized. With cutting speed of 150 m/min, cutting depth of 0.4 mm and feed rate of 0.3 mm/rev, VBmax is optimized. Through the variance analysis it was concluded that the depth of cut was the main parameter that affected on the surface roughness;whereas, the feed rate was the most influential parameter on the flank wear. Confirmation test results showed that the Taguchi method was very successful in the optimization of machining parameters for mini-mum surface roughness and flank wear in the turning of the D2 steel.

Neck Motion Restriction Negatively Affects Turning Stability in Community-Dwelling Older Adults with and without a History of Falls

Background: Many older adults fall while turning. During the turning maneuver, rotation of the head precedes the rest of the body, creating a spatial frame of reference. Limitations of the neck rotation, may interfere with the turning mechanism, affect stability, and lead to recurrent falls. However, the association between the range of the neck rotation and turning stability was not explored yet. Purpose: To compare the impact of restricting the neck rotation by a brace, on the turning stability of adults with and without a history of falls. Methods: An observational, cross-sectional study consisting of 59 adults (average age 76 ± 6.9). A group (N = 29) with at least 2 falls (FL) in the last year and a group (N = 30) without a history of falls in the last year (NFL). All participants performed three tests: Timed up and Go (TUG), 180° Turn Test (180 TT) and 360° Turn Test (360 TT) with and without a neck brace. Results: All the scores of the FL were lower than those of the NFL (p Application of the brace worsened the performance of the 180 TT and the 360 TT of both groups (p < 0.05) but there was no interaction between group and bracing. The TUG score of only the NFL was affected by the brace (p < 0.004). Interestingly, only the range of the right neck rotation was correlated with balance tests and number of falls (r = 0.272;p Conclusions: Restricting of the neck mobility worsened the turning stability of both groups but without interaction. The study reinforces the need of considering the neck range of motion when addressing adult stability. A decrease in the range of right neck rotation was identified as a risk factor for loss of balance.

Grey Relational Optimization of Turning Parameters in Dry Machining of Austenitic Stainless Steel Using Zr Based Coated Tools

The present work aims at the microstructural characterization of TiAlZrN/ Al2O3 and TiAlZrN/Si3N4 coatings deposited via lateral rotating cathodes. The coatings were deposited using Lateral Rotating Cathodes (LARC) technology. The deposited coatings were studied for its cross sectional morphology using scanning electron microscopy. Energy Dispersive Spectrometry was also conducted along the cross section to determine the elemental composition. Micro Vickers hardness test was conducted to determine the hardness of the coatings. The scanning electron microscope images showed that TiAlZrN/Al2O3 coatings showed preferred columnar grain orientation with multilayered structure while TiAlZrN/Si3N4 coatings exhibit a dense grain structure. The TiAlZrN/Si3N4 coating shows a hardness of 31.58 GPa while TiAlZrN/Al2O3 coating shows a hardness of 25.40 GPa. Dry turning tests were performed on AISI 304 stainless steel. The TiAlZrN/Si3N4 coatings show reduced flank wear. Both the coatings even under severe cutting conditions impart surface roughness of less than 1.5 μm.