Thermal-mechanical and springback behavior of dual-phase steel at warm temperatures

For non-quenchable dual-phase(DP)steel sheet,the warm forming process can effectively reduce the amount of springback,and the mechanical parameters that influence its elastic and inelastic recovery to decrease exhibit a strong temperature dependence,especially under cyclic loading conditions.In this paper,the monotonic and cyclic loading tests of DP980 steel sheets are conducted at the temperatures ranging from 25℃ to 500℃.The temperature-dependent flow stress,nonlinear elastic recovery,and Bauschinger effect are investigated.The results demonstrate that both the elastic modulus and Bauschinger effect show an exponential law with pre-strain,and decrease with the increase of forming temperature,while there will be an abnormal phenomenon of rebound due to the influence of dynamic strain aging effect.Meanwhile,a linear relationship between the Bauschinger effect and inelastic strain is observed at various temperatures,and the weight of the Bauschinger effect in the total strain reduces with temperature increasing,which indicates that the springback is dominated by linear elastic recovery.Furthermore,the U-draw bending tests are carried out to clarify the influence of Vickers hardness distribution and martensite size effect on the springback behavior.

Nanoscale viscoelastic properties and adhesion of polydimethylsiloxane for tissue engineering

It has shown that altering crosslink density of biopolymers will regulate the morphology of Mesenchymal Stem Cells （MSCs） and the subsequent MSCs differentia- tion. These observations have been found in a wide range of biopolymers. However, a recent work published in Nature Materials has revealed that MSCs morphology and differen- tiation was unaffected by crosslink density of polydimethyl- siloxane （PDMS）, which remains elusive. To understand such unusual behaviour, we use nanoindentation tests and modelling to characterize viscoelastic properties and sur- face adhesion of PDMS with different base：crosslink ratio varied from 50：1 （50D） to 10：1 （10D）. It has shown that lower crosslink density leads to lower elastic moduli. De- spite lower nanoindentation elastic moduli, PDMS with lowest crosslink density has higher local surface adhesion which would affect cell-biomaterials interactions. This work suggests that surface adhesion is likely another important physical cue to regulate cell-biomaterials interactions.

Precipitation Behavior in Liesegang Systems under Microwave Irradiation

We studied precipitation patterns in a Liesegang system under microwave irradiation in order to investigate metal salt diffusion in an electrolyte gel. The salt species and microwave irradiation power were varied. Microwave irradiation induced periodic patterns of precipitation because polar molecules vibrate and rotate in an electromagnetic field. For example, the number of patterns increased with the irradiation power. Accordingly, microwave irradiation nonlinearly accelerated the diffusion of ionic molecules.

Mechanical Stress to Cell Nucleus Inhibits Proliferation and Differentiation of Vascular Smooth Muscle Cells

Cells sense the external environment such as a surface topography and change many cellular functions. Cell nucleus has been proposed to act as a cellular mechanosensor, and the changes in nuclear shape possibly affect the functional regulation of cells. This study demonstrated a large-scale mechanical deformation of the intracellular nucleus using polydimethylsiloxane (PDMS)-based micropillar substrates and investigated the effects of nuclear deformation on migration, proliferation, and differentiation of vascular smooth muscle cells (VSMCs). VSMCs spread completely between the fibronectin-coated pillars, leading to strong deformations of their nuclei resulted in a significant inhibition of the cell migration. The proliferation and smooth muscle differentiation of VSMCs with deformed nuclei were dramatically inhibited on the micropillars. These results indicate that the inhibition of proliferation and VSMC differentiation resulted from deformation of the nucleus with high internal stress, and this type of large-scale nuclear mechanical stress might lead the cells to a “quiescent state”.

Microstructural and Mechanical Characterization of Chicken Eggshell-Reinforced Al6061 Matrix Composites

Chicken eggshell (ES) is an aviculture byproduct that has been used as the reinforcement in the present study which is recorded worldwide as one of the vilest environmental problems. The present work deals with development of ES-reinforced Al6061 matrix composites by stir-casting process with 0 to 10 wt% of reinforcement at an interval of 2 wt%. The microstructures of the fabricated composites were examined by optical and scanning electron microscopes with energy dispersive spectrometer (SEM/EDS). Optical micrographs divulge the uniform distribution of reinforcing particles in the matrix while X-ray diffraction (XRD) patterns ensure the dispersion of ES particles reinforcement in Al6061 matrix. The properties measured include density, tensile strength and hardness values. The tensile strength and hardness of composites increase with the addition of ES particles and the maximum values were achieved at 4 wt%. Further increase of ES particles in the matrix leads to decrease in hardness and strength owing to increase in porosity.

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.

齿轮系统振动加剧齿轮磨损毁坏的机理分析

通过齿轮系统的振动运动分析,论证了不计系统振动和考虑系统振动时存在于啮合轮齿齿面间的相对滑动运动,揭示了系统振动加剧齿面磨损毁坏的机理。由于系统振动的原因,齿轮副的实际中心线和理论啮合线是以平面运动方式变化的,实际啮合点的轨迹是一条曲线,啮合点在齿高某些部位(一般是齿高中部)是以进两步退一步的往复运动方式向前移动的。啮合点的这种前进与后退的交替移动,一方面很容易破坏啮合齿面间的润滑油膜,使摩擦增大,另一方面大大增加了冲击作用,使载荷峰值大大增加,同时啮合齿面间的相对滑动距离也大大增加了。这几方面的综合效应必然导致相啮合齿面间发生剧烈滑动磨擦,从而引起齿面的过早磨损。

静高压下邻苯二甲酸二辛酯增塑双酚A型聚碳酸酯体系中立体开放球晶的生长

Bisphenol-A polycarbonate/dioctyl phthalate blend samples crystallized at a hydrostatic pressure were investigated by WAXD,DSC and SEM measurements.Some novel stereo-open spherulitic structures,i.e.,peony-,cabbage-,seaweed-,and lotus-like spherulites,were observed which belong to a three-dimensional structure and were only composed of crystalline region.The foleded-chain lamellar crystal was proved to be the sub-structure of these spherulites.This study also suggests a new route to grow such crystals so as to promote the understanding of the formation process and mechanism of polymer spherulites.

Changes in the Mechanical Environment of the Nucleus with Cell Crowding and Its Effects on DNA Damage Resistance

Nuclear DNA, which is essential for the transmission of genetic information, is constantly damaged by external stresses and is subsequently repaired by the removal of the damaged region, followed by resynthesis of the excised region. Accumulation of DNA damage with failure of repair processes leads to fatal diseases such as cancer. Recent studies have suggested that intra- and extra-nuclear environments play essential roles in DNA damage. However, numerous questions regarding the role of the nuclear mechanical environment in DNA damage remain unanswered. In this study, we investigated the effects of cell confluency (cell crowding) on the morphology of cell nuclei, and cytoskeletal structures, and DNA damage in NIH3T3 skin fibroblasts and HeLa cervical cancer cells. Although nuclear downsizing was observed in both NIH3T3 and HeLa cells with cell crowding, intracellular mechanical changes in the two cell types displayed opposite tendencies. Cell crowding in NIH3T3 cells induced reinforcement of actin filament structures, cell stiffening, and nuclear downsizing, resulting in a significant decrease in endogenous DNA damage, whereas cell crowding in HeLa cells caused partial depolymerization of actin filaments and cell softening, inducing endogenous DNA damage. Ultraviolet (UV) radiation significantly increased DNA damage in NIH3T3;however, this response did not change with cell crowding. In contrast, UV radiation did not cause DNA damage in HeLa cells under either sparse or confluent conditions. These results suggested that cell crowding significantly influenced endogenous DNA damage in cells and was quite different in NIH3T3 and HeLa cells. However, cell crowding did not affect the UV-induced DNA damage in either cell type.

Analysis of Machinable Structures and Their Wettability of Rotary Ultrasonic Texturing Method

Tailored surface textures at the micro- or nanoscale dimensions are widely used to get required functional performances. Rotary ultrasonic texturing （RUT） technique has been proved to be capable of fabricating periodic micro- and nanostructures. In the present study, diamond tools with geometrically defined cutting edges were designed for fabricating different types of tailored surface textures using the RUT method. Surface generation mechanisms and machinable structures of the RUT process are analyzed and simulated with a 3D-CAD program. Textured surfaces generated by using a triangular pyramid cutting tip are constructed. Different textural patterns from several micrometers to several tens of micrometers with few burrs were successfully fabricated, which proved that tools with a proper two-rake-face design are capable of removing cutting chips efficiently along a sinusoidal cutting locus in the RUT process. Technical applications of the textured surfaces are also discussed. Wetting properties of textured aluminum surfaces were evaluated by combining the test of surface roughness features. The results show that the real surface area of the textured aluminum surfaces almost doubled by comparing with that of a flat surface, and anisotropic wetting properties were obtained due to the obvious directional textural features.

Flexible temperature sensor with high sensitivity ranging from liquid nitrogen temperature to 1200℃

Flexible temperature sensors have been extensively investigated due to their prospect of wide application in various flexible electronic products.However,most of the current flexible temperature sensors only work well in a narrow temperature range,with their application at high or low temperatures still being a big challenge.This work proposes a flexible thermocouple temperature sensor based on aerogel blanket substrate,the temperature-sensitive layer of which uses the screen-printing technology to prepare indium oxide and indium tin oxide.It has good temperature sensitivity,with the test sensitivity reaching 226.7μV℃^(−1).Most importantly,it can work in a wide temperature range,from extremely low temperatures down to liquid nitrogen temperature to high temperatures up to 1200℃,which is difficult to be achieved by other existing flexible temperature sensors.This temperature sensor has huge application potential in biomedicine,aerospace and other fields.

Study on Internal Supersonic Flows with Pseudo-shock Wave Using Liquid Crystal Flow Visualization Method

The flow visualization technique using shear-sensitive liquid crystal is applied to the investigation of a Mach 2 internal supersonic flow with pseudo-shock wave （PSW） in a pressure-vacuum supersonic wind tunnel. It provides qualitative information mainly concerning the overall flow structure, such as the turbulent boundary layer separation, reattachment locations and the dimensionalities of the flow. Besides, it can also give understanding of the surface streamlines, vortices in separation region and the corner effect of duct flow. Two kinds of crystals with different viscosities are used in experiments to analyze the viscosity effect. Results are compared with schlieren picture, confirming the effectiveness of liquid crystal in flow-visualization.

Application of multi-dimensional wavelet transform to fluid mechanics

This paper first reviews the application research works of wavelet transform on the fluid mechanics. Then the theories of continuous wavelet transform and multi-dimensional orthogonal(discrete) wavelet transform, including wavelet multiresolution analysis, are introduced. At last the applications of wavelet transform on 2 D and 3 D turbulent wakes and turbulent boundary layer flows are described based on the hot-wire, 2 D particle image velocimetry(PIV) and 3 D tomographic PIV.

Integrated Simulation Method for Interaction between Manufacturing Process and Machine Tool

The interaction between the machining process and the machine tool （IMPMT） plays an important role on high precision components manufacturing. However, most researches are focused on the machining process or the machine tool separately, and the interaction between them has been always overlooked. In this paper, a novel simplified method is proposed to realize the simulation of IMPMT by combining use the finite element method and state space method. In this method, the transfer function of the machine tool is built as a small state space. The small state space is obtained from the complicated finite element model of the whole machine tool. Furthermore, the control system of the machine tool is integrated with the transfer function of the machine tool to generate the cutting trajectory. Then, the tool tip response under the cutting force is used to predict the machined surface. Finally, a case study is carried out for a fly-cutting machining process, the dynamic response analysis of an ultra-precision fly-cutting machine tool and the machined surface verifies the effectiveness of this method. This research proposes a simplified method to study the IMPMT, the relationships between the machining process and the machine tool are established and the surface generation is obtained.

POD analysis of the instability mode of a low-speed streak in a laminar boundary layer

The instability of one single low-speed streak in a zero-pressure-gradient laminar boundary layer is investigated experimentally via both hydrogen bubble visualization and planar particle image velocimetry(PIV) measurement. A single low-speed streak is generated and destabilized by the wake of an interference wire positioned normal to the wall and in the upstream. The downstream development of the streak includes secondary instability and self-reproduction process, which leads to the generation of two additional streaks appearing on either side of the primary one. A proper orthogonal decomposition(POD) analysis of PIV measured velocity field is used to identify the components of the streak instability in the POD mode space: for a sinuous/varicose type of POD mode, its basis functions present anti-symmetric/symmetric distributions about the streak centerline in the streamwise component, and the symmetry condition reverses in the spanwise component. It is further shown that sinuous mode dominates the turbulent kinematic energy(TKE) through the whole streak evolution process, the TKE content first increases along the streamwise direction to a saturation value and then decays slowly. In contrast, varicose mode exhibits a sustained growth of the TKE content,suggesting an increasing competition of varicose instability against sinuous instability.

Manufacturing technologies toward extreme precision

Precision is one of the most important aspects of manufacturing.High precision creates high quality,high performance,exchangeability,reliability,and added value for industrial products.Over the past decades,remarkable advances have been achieved in the area of high-precision manufacturing technologies,where the form accuracy approaches the nanometer level and surface roughness the atomic level.These extremely high precision manufacturing technologies enable the development of high-performance optical elements,semiconductor substrates,biomedical parts,and so on,thereby enhancing the ability of human beings to explore the macroand microscopic mysteries and potentialities of the natural world.In this paper,state-of-the-art high-precision material removal manufacturing technologies,especially ultraprecision cutting,grinding,deterministic form correction polishing,and supersmooth polishing,are reviewed and compared with insights into their principles,methodologies,and applications.The key issues in extreme precision manufacturing that should be considered for future R&D are discussed.

Addition Formulas of Leaf Functions and Hyperbolic Leaf Functions

Addition formulas exist in trigonometric functions.Double-angle and half-angle formulas can be derived from these formulas.Moreover,the relation equation between the trigonometric function and the hyperbolic function can be derived using an imaginary number.The inverse hyperbolic function arsinher(r)■ro 1/√1+t^(2)dt p1tt2 dt is similar to the inverse trigonometric function arcsiner(r)■ro 1/√1+t^(2)dt p1t2 dt,such as the second degree of a polynomial and the constant term 1,except for the sign−and+.Such an analogy holds not only when the degree of the polynomial is 2,but also for higher degrees.As such,a function exists with respect to the leaf function through the imaginary number i,such that the hyperbolic function exists with respect to the trigonometric function through this imaginary number.In this study,we refer to this function as the hyperbolic leaf function.By making such a definition,the relation equation between the leaf function and the hyperbolic leaf function makes it possible to easily derive various formulas,such as addition formulas of hyperbolic leaf functions based on the addition formulas of leaf functions.Using the addition formulas,we can also derive the double-angle and half-angle formulas.We then verify the consistency of these formulas by constructing graphs and numerical data.

粉末注射成形奥氏体不锈钢的疲劳和冲击强度

本文的目的是研究粉末性能对粉末注射成形奥氏体不锈钢的力学性能(特别是疲劳和冲击强度)的影响。试样用混有聚酰氨粘结剂系的水雾化(WA)和气雾化(GA)粉末制成。注射坯在空气中脱粘,而后在不同温度、不同保温时间下真空烧结。粉末性能对烧结体的密度、显微组织和力学性能有显著影响。孔和析出物显示出Ostward时效,而孔和析出物的长大满足Lifshitz-Wagner方程。WA和GA粉末试样的疲劳极限分别约为300MPa和310MPa。它们的疲劳强度略低于常规锻材。烧结体的冲击值随密度增加线性增大。

循环肿瘤细胞在微血管中的膜张力和运动特征分析

目的循环肿瘤细胞在微血管中的细胞膜张力变化和运动特征是影响癌症转移的重要细胞尺度力学微环境。模拟生理状态下微血管中血流与CTCs之间的相互作用,分析CTCs在随血流发生转移时,不同血管直径和红细胞压积条件下循环肿瘤细胞膜张力变化和运动特征的关联。方法采用浸入式边界方法模拟细胞膜和流场的相互耦合作用。结果以血管直径与肿瘤细胞直径之比D_T/D_C=1.25为界,循环肿瘤细胞的膜张力随管径呈现两个不同的分布特性:当D_T/D_C<1.25时。

Effect of Surface Texturing on Lubricating Condition under Point Contact Using Numerical Analysis

The contact fatigue life of machine elements is affected by pitting, wear and so on, under heavier loading conditions. Increasing the fatigue life requires mainly the improvements of lubricating condition, operating condition and materials. In order to improve the lubricating condition, it is necessary to investigate the relation of the microscopic surface texturing and the contact modes of machine elements. In this paper, thus, the pressure and oil film thickness of the contact between sphere and the plate with 5 kinds surface texturing were calculated using a commercial software based on Reynolds equation. There was sufficient evidence to suggest that the dimple shape was the optimum texturing to increase the lubricating condition.