Cryogenic springback of 2219-W aluminum alloy sheet through V-shaped bending

A V-shaped bending device was established to evaluate the effects of temperature and bending fillet radius on springback behavior of 2219-W aluminum alloy at cryogenic temperatures.The cryogenic springback mechanism was elucidated through mechanical analyses and numerical simulations.The results indicated that the springback angle at cryogenic temperatures was greater than that at room temperature.The springback angle increased further as the temperature returned to ambient conditions,attributed to the combined effects of the “dual enhancement effect” and thermal expansion.Notably,a critical fillet radius made the springback angle zero for 90° V-shaped bending.The critical fillet radius at cryogenic temperatures was smaller than that at room temperature,owing to the influence of temperature variations on the bending moment ratio between the forward bending section at the fillet and the reverse bending section of the straight arm.

《曲径分岔的花园》与电影MR.nobody之时间观比较论

阿根廷作家博尔赫斯的小说《曲径分岔的花园》和比利时导演雅克.范.多梅尔的电影MR.nobody都以颠覆传统线性时间观为叙事前提,这使文本叙事本身和接受者的阐释都呈现出复杂多元的面貌。以比较文学的方法和视野,论析"无限分岔"和"无形无态"这两种时间形态在此类不同艺术形式的文本中或共同或不同的表达方式以及它们对叙事本身与作品哲理性内涵的潜在影响,从而于双向阐释的过程中,更准确和全面地把握两个类乎以多维时间观为叙事前提的叙事文本的深刻内涵。

“原型”理论视角下《曲径通北》中人物的多面人格

小说《曲径通北》以澳大利亚战俘修建泰缅铁路的沉痛历史为背景,揭示了战争对人性的摧残,展现了战争背景下人格的多面性。本文拟用荣格的原型理论来分析小说中的人物形象,重点分析人物多面人格的成因。

博尔赫斯的“中国”

对于博尔赫斯而言，“中国”，一如宇宙间所有玄秘事象，有着无穷的魅力。对于中国读者而言，博尔赫斯的文本中国无疑打开了一扇有趣且有益的文字之窗，为我们提供了一个对我们自身文化传统进行反思的他者视角，同时，也为跨文化对话打通了一条有效的文学通道。

Influence of main site factors on Fraxinus mandshurica (Oleaceae) plantation

the investigation was carried out on 10-year-old plantation of Fraxinus mandshurica in Mao抏r Mountain Experimental Station of Northeast Forest University. Tree height (H), diameter at breast height (D1.3) and the increment of tree height in 5 years (H5), the thickness of humus layer, as well as the soil moisture were measured for the plantation and the growth indexes (H, D1.3, H5) for different site conditions were analyzed. The results showed that main site factors influencing the growth of Fraxinus mandshurica were soil moisture, gradient and location of slope in order. The growth of Fraxinus mandshurica was better on the middle- or up-slope site than on the down-slope site. Soil moisture and late frost caused by terrain are the main reasons that limit the growth of Fraxinus mandshurica plantation.

Significance-based optimization of processing parameters for thin-walled aluminum alloy tube NC bending with small bending radius

Thin-walled aluminum alloy tube numerical control （NC） bending with small bending radius is a complex process with multi-factor coupling effects and multi-die constraints. A significance-based optimization method of the parameters was proposed based on the finite element （FE） simulation, and the significance analysis of the processing parameters on the forming quality in terms of the maximum wall thinning ratio and the maximum cross section distortion degree was implemented using the fractional factorial design. The optimum value of the significant parameter, the clearance between the tube and the wiper die, was obtained, and the values of the other parameters, including the friction coefficients and the clearances between the tube and the dies, the mandrel extension length and the boost velocity were estimated. The results are applied to aluminum alloy tube NC bending d50 mm×1 mm×75 mm and d70 mm×1.5 mm×105 mm （initial tube outside diameter D0 × initial tube wall thickness t0 × bending radius R）, and qualified tubes are produced.

Highly sensitive electronic stethoscope based on non-uniform PVDF curvature structure

Electronic stethoscope is an instrument used for auxiliary determination of patients＇ physical condition by collecting and processing heart sounds and lung sounds.Since traditional electronic stethoscopes have low sensitivity and poor low-frequency response,a novel electronic stethoscope is provided in this paper using curved PVDF clamping structure with non-uniform curvature based on the structure of PVDF and silicone rubber substrate.Theoretical analysis and comparison by means of the corresponding inhomogeneous string vibration model show that sensitivity significantly increases for non-uniform curvature than the uniform one.Furthermore,a new electronic stethoscope pickup is developed based on the optimal parameters at the point of maximum sensitivity of non-uniform curvature.Experiment results show that the sensitivity of the pickup can reach1.7mV/Pa,which increases by 13.3%compared to the one with the structure of uniform curvature PVDF and silicone rubber substrate that has been studied in recent years.Moreover,flat frequency response characteristics can be retained within the frequency band range of 2-2kHz,which covers the frequency response range of cardiopulmonary sound collection,thus provides a strong guarantee for complete acquisition of heart and lung sound signals.

Fluid flow and heat transfer characteristics of spiral coiled tube: Effects of Reynolds number and curvature ratio

Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12n. As the varying radius of curvature became a dominant flow parameter, three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field. From the analysis, centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer. The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube. Even then, friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number. Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.

Non-Darcian Flow Toward a Finite-Diameter Vertical Well in a Confined Aquifer

Non-Darcian radial flow toward a finite-diameter, fully penetrating well in a confined aquifer was analyzed on the basis of the Izbash equation with consideration of the wellbore storage effect. We derived semi-analytical solutions of drawdown by using the Boltzmann transform, and obtained approximate analytical solutions of the drawdown at early and late times. MATLAB programs were developed to facilitate computation of the semi-analytical solutions. The turbulence factor v which was directly related to the pumping rate appeared to have negligible influence upon the wellbore well function at early times, but imposed significant influence at intermediate and late times. However, the turbulence factor v imposed non-negligible influence upon the aquifer well function during the entire pumping period, provided that the observation point was not sufficiently close to the wellbore. Sensitivity analysis indicated that the power index n in the Izbash equation had less influence on the type curves at the face of the pumping wellbore, but had much greater influence upon the well function in the aquifer. As the n values increased, the drawdown in the aquifer decreased at early times and increased at late times. The Boltzmann transformation could only be used in an approximate sense for radial non-Darcian flow problems. This approximation would provide accurate solutions at early times, and introduce small but consistent discrepancies at intermediate and late times for the wellbore well function.

Effect of prestressed ultrasonic peen forming parameters on bending curvature and spherical deformation of plate

The elastic prestressed ultrasonic peen forming(UPF)was adopted in order to solve problems of insufficient bending deformation and large spherical deformation of plate during free UPF.The theoretical analysis of prestressed UPF and the influence of elastic prebending moment on deformation were analyzed.Spherical deformation coefficient was defined to quantificationally describe the spherical deformation.Experiments were conducted to compare the differences between free UPF and prestressed UPF processes and the effects of processing parameters on bending curvature and spherical deformation coefficient were studied.The results show that peening trajectory in chordwise direction is beneficial to enlarging spanwise bending deformation and decreasing spherical deformation coefficient.Large prebending curvature is helpful to increase spanwise bending deformation and decrease chordwise deformation,thereby obviously decreasing spherical deformation coefficient.Large spanwise deformation can be obtained under large firing pin velocity,small plate thickness and small offset distance.Large firing pin velocity plays a positive role in decreasing spherical deformation,while plate thickness and offset distance have little effect on it.Above all,prebending curvature and peening trajectory are the most important factors during prestressed UPF process.This study provides guidance for parameters optimization of prestressed UPF for wing plate with large thickness.

A NURBS Fitting Optimization Method for High⁃Speed Five⁃Axis NC Machining Path Based on Curvature Smoothing Preset Point Constraint

Existing curve fitting algorithms of NC machining path mainly focus on the control of fitting error,but ignore the problem that the original discrete cutter position points are not enough in the high curvature area of the tool path.It may cause a sudden change in the drive force of the feed axis,resulting in a large fluctuation in the feed speed.This paper proposes a new non-uniform rational B-spline(NURBS)curve fitting optimization method based on curvature smoothing preset point constraints.First,the short line segments generated by the CAM software are optimally divided into different segment regions,and then the curvature of the short line segments in each region is adjusted to make it smoother.Secondly,a set of characteristic points reflecting the change of the curvature of the fitted curve is constructed as the control apex of the fitted curve,and the curve is fitted using the NURBS curve fitting optimization method based on the curvature smoothing preset point constraint.Finally,the curve fitting error and curve volatility are analyzed with an example,which verifies that the method can significantly improve the curvature smoothness of the high-curvature tool path,reduce the fitting error,and improve the feed speed.

Kinetics modeling for austenite transformation in AISI 1045 steel during rapid heating under high frequency electromagnetic field

To investigate the effect of alternating magnetic field on austenite transformation process in the case of rapid heating,the austenite kinetics model of AISI 1045 steel was built for spot continual induction hardening(SCIH)process.The results shows that the effect of alternating magnetic field on austenite transformation fraction reaches the maximum(about 3%)when heating rate is the lowest.Relatively low magnetic flux density still has a certain effect on the austenite transformation process during the SCIH process.Concave surface structure can reduce the influence scope of alternating magnetic field on surface in all cases and the minimum influence scope appears when the feed path of inductor is longitudinal.Convex surface structure can minimize the influence scope of alternating magnetic field in depth when the feed path of inductor is longitudinal.The austenite distribution of transitional region on surface for horizontal movement is more uniform than that for longitudinal movement.The austenite distribution of transitional region in depth for longitudinal movement is more uniform than that for horizontal movement.The simulated results are consistent with the experimental results and the austenite transformation kinetics model developed for SCIH process is valid.

Long-term results of small-diameter proximal splenorenal venous shunt:A retrospective study

AIM:To investigate recurrent variceal hemorrhage and long-term survival rates of patients treated with partial proximal splenorenal venous shunt.METHODS:Patients with variceal hemorrhage who were treated with small-diameter proximal splenorenal venous shunt in Ruijin Hospital between 1996 and 2009 were included in this study.Shunt diameter was determined before operation using Duplex Doppler ultrasonography.Peri-operative and long-term results in term of rehemorrhage,encephalopathy and mortality were followed up.RESULTS:Ninety-eight patients with Child A and B variceal hemorrhage received small-diameter proximal splenorenal venous shunt with a diameter of 7-10 mm.After operation,the patients’mean free portal pressure (P<0.01)and the flow rate of main portal vein(P< 0.01)decreased significantly compared with that before operation.The rates of rebleeding and mortality were 6.12%(6 cases)and 2.04%(2 cases),respectively.Ninety-one patients were followed up for 7 mo-14 years (median,48.57 mo).Long-term rates of rehemorrhage and encephalopathy were 4.40%(4 cases)and 3.30% (3 cases),respectively.Thirteen patients(14.29%)died mainly due to progressive hepatic dysfunction.Fiveand ten-year survival rates were 82.12%and 71.24%,respectively.CONCLUSION:Small-diameter proximal splenorenal venous shunt affords protection against variceal rehemorrhage with a low occurrence of encephalopathy in patients with normal liver function.

FEM simulation and experimental verification of roll forming and springback process under complex contact conditions

The application of advanced high strength steel （AHSS） has an important significance in the development of the lightweight of automobile, but the parts made of AHSS usually have defects, such as fracture and large amount of springback, etc. In this paper, a model of multi-pass roll form- ing and springback process of AHSS is established with finite element software ABAQUS. Then a roll forming experiment is performed, and simulation and experimental results have been compared and analyzed. The model is established under complex contact conditions, including self-contact condi- tion. The results shows that during the process of sheet bending, large Mises stresses appear at ben- ding corners. The smaller the bending radius is, the larger the Mises stress and strain are. Thick- ness of sheet metal changes exceeds a certain limit, the differently if the bending radius is different. When the bending radius change tendency of the sheet thickness turns from increase to decrease.

Strengthening and stress drop of ultrafine grain aluminum after annealing

Ultrafine grain pure aluminum was produced by equal channel angular pressing and cold rolling, the deformed aluminum was annealed at 200 ℃ for 1 h. The tensile curves of deformed and annealed aluminum show that yield strength of deformed aluminum increases by 100%-300% and its elongation decreases by about 20%. After low temperature annealing, strength of annealed aluminum increases by 20% and elongation decreases by over 50%, the recovery of dislocations may be the main cause of annealing strengthening. In addition, there is an abrupt stress drop in the tensile curves of annealed aluminum and the formation of shear band is responsible for it.

MPC-based path tracking with PID speed control for high-speed autonomous vehicles considering time-optimal travel

In order to track the desired path as fast as possible,a novel autonomous vehicle path tracking based on model predictive control(MPC)and PID speed control was proposed for high-speed automated vehicles considering the constraints of vehicle physical limits,in which a forward-backward integration scheme was introduced to generate a time-optimal speed profile subject to the tire-road friction limit.Moreover,this scheme was further extended along one moving prediction window.In the MPC controller,the prediction model was an 8-degree-of-freedom(DOF)vehicle model,while the plant was a 14-DOF vehicle model.For lateral control,a sequence of optimal wheel steering angles was generated from the MPC controller;for longitudinal control,the total wheel torque was generated from the PID speed controller embedded in the MPC framework.The proposed controller was implemented in MATLAB considering arbitrary curves of continuously varying curvature as the reference trajectory.The simulation test results show that the tracking errors are small for vehicle lateral and longitudinal positions and the tracking performances for trajectory and speed are good using the proposed controller.Additionally,the case of extended implementation in one moving prediction window requires shorter travel time than the case implemented along the entire path.

AN IMPROVED RADIAL BASIS FUNCTION BASED METHOD FOR IMAGE WARPING

A new image warping method is proposed in this letter, which can warp a given image by some manual defined features. Based on the radial basis interpolation function algorithm, the proposed method can transform the original optimized problem into nonsingular linear problem by adding one-order term and affine differentiable condition. This linear system can get the steady unique solution by choosing suitable kernel function. Furthermore, the proposed method demonstrates how to set up the radial basis function in the target image so as to achieve supports to adopt the backward re-sampling technology accordingly which could gain the very slippery warping image. Theexperimental result shows that the proposed method can implement smooth and gradual image warping with multi-anchor points' accurate interpolation.

Optimization of press bend forming path of aircraft integral panel

In order to design the press bend forming path of aircraft integral panels,a novel optimization method was proposed, which integrates FEM equivalent model based on previous study,the artificial neural network response surface,and the genetic algorithm.First,a multi-step press bend forming FEM equivalent model was established,with which the FEM experiments designed with Taguchi method were performed.Then,the BP neural network response surface was developed with the sample data from the FEM experiments.Furthermore,genetic algorithm was applied with the neural network response surface as the objective function. Finally,verification was carried out on a simple curvature grid-type stiffened panel.The forming error of the panel formed with the optimal path is only 0.098 39 and the calculating efficiency has been improved by 77%.Therefore,this novel optimization method is quite efficient and indispensable for the press bend forming path designing.

Symmetric alteration of four knots of B-spline and NURBS surfaces

Modifying the knots of a B-spline curve, the shape of the curve will be changed. In this paper, we present the effect of the symmetric alteration of four knots of the B-spline and the NURBS surfaces, i.e., symmetrical alteration of the knots of surface, the extended paths of points of the surface will converge to a point which should be expressed with several control points. This theory can be used in the constrained shape modification of B-spline and NURBS surfaces.

Flexible bending of aluminum profiles with polyurethane pad

The high flexibility of profile bending with hyperelastic pad enables it to be a promising method for small lot or single part production, especially for space frame and roof-rail parts in automotive and aerospace industries. Bending of two aluminum profiles with different sections was carried out to investigate the effect of main process parameters on the bending process. Results show that the shape of the cross-section and its relative thickness and section modulus in bending are the main factors that determine the bending properties of the profiles. Roller stroke, properties of polyurethane pad and constraints on profiles are key factors that determine the bending radius and section deformation of bent profiles. Failures and quality problems met in experiments were also analyzed.