Quantitative analysis of the morphing wing mechanism of raptors:IMMU-based motion capture system and its application on gestures of a Falco peregrinus

This paper presented a novel tinny motion capture system for measuring bird posture based on inertial and magnetic measurement units that are made up of micromachined gyroscopes, accelerometers, and magnetometers. Multiple quaternion-based extended Kalman filters were implemented to estimate the absolute orientations to achieve high accuracy.Under the guidance of ornithology experts, the extending/contracting motions and flapping cycles were recorded using the developed motion capture system, and the orientation of each bone was also analyzed. The captured flapping gesture of the Falco peregrinus is crucial to the motion database of raptors as well as the bionic design.

Measuring the flexibility matrix of an eagle’s flight feather and a method to estimate the stiffness distribution

Flight feathers stand out with extraordinary mechanical properties for flight because they are lightweight but stiff enough.Their elasticity has great effects on the aerodynamics, resulting in aeroelasticity.Our primary task is to figure out the stiffness distribution of the feather to study the aeroelastic effects.The feather shaft is simplified as a beam, and the flexibility matrix of an eagle flight feather is tested.A numerical method is proposed to estimate the stiffness distributions along the shaft length based on an optimal Broyden–Fletcher–Goldfarb–Shanno(BFGS) method with global convergence.An analysis of the compressive behavior of the shaft based on the beam model shows a good fit with experimental results.The stiffness distribution of the shaft is finally presented using a 5 th order polynomial.

Quantitative analysis of the morphing wing mechanism of raptors:Morphing kinematics of Falco peregrinus wing

Raptors are getting more attention from researchers because of their excellent flight abilities.And the excellent wing morphing ability is critical for raptors to achieve high maneuvering flight,which can be a good bionic inspiration for unmanned aerial vehicles(UAV)design.However,morphing wing motions of Falco peregrinus with multi postures cannot be consulted since such a motion database was nonexistent.This study aimed to provide data reference for future research in wing morphing kinetics.We used the computed tomography(CT)approach to obtain nine critical postures of the Falco peregrinus wing skeleton,followed with motion analysis of each joint and bone.Based on the obtained motion database,a six-bar kinematic model was proposed to regenerate wing motions with a high fidelity.

Survey and Analysis on the Status Quo of Occupational Risk Perception of Teachers in Public Vocational Colleges in an Underdeveloped Area

This paper selects the teachers of public higher vocational college(College A)in underdeveloped areas to participate in the analysis,and conducts a questionnaire survey using the occupational risk perception questionnaire of higher vocational teachers.A total of 223 higher vocational teachers were selected to participate in the survey in order to understand the status quo of occupational risk perception of higher vocational teachers.The survey results show that the Cronbach’sαcoefficient of occupational risk perception scale for higher vocational teachers is 0.846,and the Kaiser-Meyer-Olkin(KMO)is 0.871.The education legal liability risk,workload risk,and career development risk are the highest average occupational risk perception of higher vocational teachers.In conclusion,the occupational risk perception scale of higher vocational teachers compiled in this study has good reliability and validity.The occupational risk perceived by teachers in public higher vocational colleges is relatively high.

High-Strength and High-Plasticity TWIP Steel for Modern Vehicle

In this paper new high-strength and high-plasticity twinning induced plasticity (TWIP) steel for modern automobile body was investigated. Some basic experimental results were given. The results indicate the TWlP steel has excellent properties. It exhibits high ultimate tensile strength (600～1100 MPa) and extremely large elongation of 60% to 90%. In the future it would be capable of satisfying the requirements of new generation of vehicle.

Microstructures and mechanical properties of C-Mn-Cr-Nb and C-Mn-Si-Nb ultra-high strength dual-phase steels

The microstructures and mechanical properties of C-Mn-Cr-Nb and C-Mn-Si-Nb ultra-high strength dual-phase steels were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM),and tensile test.The results show that Si can promote the transformation of austenite(γ) to ferrite(α),enlarge the(α+γ) region,and increase the aging stability of martensite by inhibiting carbide precipitation.Adding Cr leads to the formation of retained austenite and martensiteaustenite(MA) constituents,as well as the decomposition of martensite during the overaging stage.Both of the steels show higher initial strain-hardening rates and two-stage strain-hardening characteristics.The C-Mn-Si-Nb steel shows the higher strain-hardening rate than the C-Mn-Cr-Nb steel in the first stage;however,there is no significant difference in the second stage.Although the tensile strength and elongation of the two steels both exceed 1000 MPa and 15%,respectively,the comprehensive mechanical properties of the C-Mn-Si-Nb steel are superior.

Texture and stretch formability of rolled Mg–Zn–RE(Y, Ce, and Gd) alloys at room temperature

To develop a new magnesium alloy with excellent formability at room temperature,the effect of Y,Ce,and Gd addition on texture and stretch formability of Mg–1.5Zn alloys was carried out.The result shows that Y,Ce,and Gd addition in Mg–1.5Zn alloys can effectively weaken and modify the basal plane texture,characterized by TD-split texture in which the position of basal is titled from normal direction(ND)toward transverse direction(TD).When Mg–1.5Zn alloy with Gd addition appears low texture intensity and TD-split texture,where the position of basal poles is tilted by about±35°from ND toward to TD,the largest Erichsen value of 7.0 and the elongation rate reaches 29.1%in TD direction.However,Y and Ce addition in Mg–1.5Zn alloys promote a large number of second phase particles,which cancel the contribution of the unique basal texture to stretch formability and ductility.

Effect of interface morphology on the mechanical properties of titanium clad steel plates

Interface morphology has important influence on the bond quality of titanium clad steel plates.The mechanical properties of titanium clad steel plates with wavy and straight interfaces were investigated by tensile-shear tests and bending tests.The interface morphology of the plates was examined by optical microscopy(OM) and scanning electron microscopy(SEM).The experimental results show that the shear strength of a wavy interface is higher than that of a straight interface.A wavy interface is the guarantee for obtaining high shear strength to provide a greater shear resistance.During the macrobending process,cracks appear in the swirl of the wave tip and ferrotitanium intermetallics.For in-situ observing the bending process by SEM,the wave tip of a wavy interface and the massive ferrotitanium intermetallics of a straight interface are places where cracks initiate and propagate.The results are the same as those observed in the macrobending process.Because of high hardness,the wave tip and the massive ferrotitanium intermetallics are hard in terms of compatible deformation.

Corrosion behavior of high-strength spring steel for high-speed railway

The corrosion resistance and evolution of corrosion products in medium-carbon high-strength spring steels were investigated in a neutral salt spray(5 wt% Na Cl solution). A formation model of γ-Fe OOH and a transformation model describing the conversion of γ-Fe OOH to α-Fe OOH were constructed. The results indicated that, at the initial corrosion stage, the corrosion resistance was gradually improved with the addition of Cr; however, with the addition of alloying element V, the corrosion resistance decreased. These results were attributed mainly to the initial corrosion stage being closely related to the matrix microstructure parameters such as grain-boundary character and dislocation density. After the rust layer was formed at a later corrosion stage, the corrosion resistance was reinforced with the addition of Cr and V because Cr strongly influenced the composition, structure, and morphology of the corrosion products. The results presented herein show that Cr was conducive to the transformation of γ-Fe OOH into α-Fe OOH. Moreover, V and Cr exhibited obvious synergy and were enriched in the inner layer of the corrosion products.

Precipitation behaviors of X80 acicular ferrite pipeline steel

The precipitation behaviors of X80 acicular ferrite pipeline steel were investigated by using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The results show that dendritic precipitates in the as-cast steel slabs precipitate mainly in grain boundaries, and these dendritic precipitates dissolve and re-precipitate to two kinds of carbonitrides: Ti- and Nb-rich (Ti, Nb)(C, N) carbonitrides during reheating. Four types of precipitates mainly exist in the hot rolled plate: Ti-rich carbonitrides resulted from the dendritic carbonitrides undissolved during the reheating process; Ti-rich carbonitrides re-precipitated along austenite grain boundaries during the re-heating process; NbC carbides mainly heterogeneously nucleated on the small pre-existing Nb-rich carbonitrides in the hot rolling process; and NbC carbides precipitated on dislocations during hot rolling.

Research and development of 780 MPa cold rolling TRIP-aided steel

As an industry-university cooperative project, an experimental research was conducted to develop a new cold-rolled transformation-induced plasticity (TRIP) steel with a tensile strength of 780 MPa and an elongation of 25% under the conditions that some processing parameters were preestablished according to the actual conditions of factory production lines. The optimal heat treatment conditions for obtaining excellent strength-ductility balance, specifically in intercritical annealing temperature and isothermal treatment temperature, were investigated by means of thermal simulation tests. Ultimately the desirable mechanical properties were attained successfully, and the microstructure and retained austenite stability were studied by optical microscopy (OM) and electron back-scattered diffraction (EBSD). It has been discovered that the sizes of retained austenite grains are generally proportional to the sizes of carbon-clear space (ferrite and bainite) around them, and there is marked selectivity in their transition sequences under stress-strain.

Mechanical Properties and Degradability of Electrospun PCL/PLGA Blended Scaffolds as Vascular Grafts

In our study, the mechanical properties and degradability of vascular grafts made from poly(ε-caprolactone)(PCL) and poly(lactic-co-glycolic acid)(PLGA) at different ratios were investigated. The results showed that the electrospun PCL/PLGA grafts possess good mechanical properties and biodegradability. The tensile and burst strength of the scaffolds met the demands of vascular grafts. In vitro degradation tests indicated that the degradation rate of the materials increased with the percentage of PLGA, and in vivo tests showed that increasing the amount of PLGA is an effective way to promote cell infiltration. Particularly, the electrospun PCL/PLGA blended scaffold with 10% PLGA exhibited a balance of mechanical and degradation properties, making it a promising tissue engineering material for vascular grafts.

A combined airfoil with secondary feather inspired by the golden eagle and its influences on the aerodynamics

Bird flight is a remarkable adaption that has allowed thousands of species to colonize all terrestrial habitats. A golden eagle has impressive flying abilities, such as hovering, perching, preying and attacking. To reveal the flying abilities, avian geometry of a golden eagle was extracted based on noncontact surface measurements using a ROMBER three-dimensional laser scanner. Distributions of a camber line, thickness and a secondary feather line of the extracted point cloud were fitted using convenient analytical expressions. A traditional airfoil was established with the camber line and thickness, then a combined airfoil was constructed by combining the traditional airfoil with a secondary feather. Oscillations of an airfoil as well as rapid pitch up were simplified as a sine wave around the quarter chord axis. Thereafter, both steady and unsteady aerodynamic performances of the airfoil are computed, the influences of the secondary feather on the steady and unsteady aerodynamics were further studied.

Leakage of an eagle flight feather and its influence on the aerodynamics

We investigate how the barb of bird feathers is changed along both the rachis and barb.To investigate the microstructures and the mechanical behaviors of barbs,a series of barbs are manually cut from an eagle’s primary feather to observe the cross sections.Aλ-like cross section with a tiny hook is observed at the right feet at each section.Afterwards,a measurement of the setup system is developed to evaluate the leakage ratio of a feather followed by a numerical predicting approach based on the CFD method.It is found that the air leakage increases linearly against the pressure,and the predicted results coincide well with the experimental results.Finally,the influences of leakage of the flight feather on both steady and unsteady aerodynamics are studied.

Shape reconstructions and morphing kinematics of an eagle during perching manoeuvres

The key to high manoeuvre ability in bird flight lies in the combined morphing of wings and tail.The perching of a wild Haliaeetus Albicilla without running or wing flapping is recorded and investigated using a high-speed digital video.A shape reconstruction method is proposed to describe wing contours and tail contours during perching.The avian airfoil geometries of the Aquila Chrysaetos are extracted from noncontact surface measurements using a ROMBER 3D laser scanner.The wing planform,chord distribution and twist distribution are fitted in convenient analytical expressions to obtain a 3D wing geometry.A three-jointed arm model is proposed to associate with the 3D wing geometry,while a one-joint arm model is proposed to describe the kinematics of tail.Therefore,a 3D bird model is established.The perching sequences of the wild eagle are recaptured and regenerated with the proposed 3D bird model.A quasi-steady aerodynamic model is applied in the aerodynamic predictions,a four-step Adams-Bashforth method is used to calculate the ordinary differential equations,thus a BFGS based optimization method is established to predict the perching motions.

Reverse-transformation austenite structure control with micro/nanometer size

To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure,the influences of cold deformation and annealing parameters on the microstructure evolution and mechanical properties of 316 L austenitic stainless steel were investigated.The samples were first cold-rolled,and then samples deformed to different extents were annealed at different temperatures.The microstructure evolutions were analyzed by optical microscopy,scanning electron microscopy(SEM),magnetic measurements,and X-ray diffraction(XRD):the mechanical properties are also determined by tensile tests.The results showed that the fraction of stain-induced martensite was approximately 72% in the 90% cold-rolled steel.The micro/nanometric microstructure was obtained after reversion annealing at 820–870°C for 60 s.Nearly 100% reversed austenite was obtained in samples annealed at 850°C,where grains with a diameter ≤ 500 nm accounted for 30% and those with a diameter > 0.5 μm accounted for 70%.The micro/nanometer-grain steel exhibited not only a high strength level(approximately 959 MPa) but also a desirable elongation of approximately 45%.

Construction and evaluation of co-electrospun poly (butylene succinate)/gelatin materials as potential vascular grafts

In this study,a series of poly(butylene succinate)(PBSU)/gelatin composites were prepared by electrospinning.The morphology,physicochemical analysis,biomechanical properties,biocompatibility,and biodegradability of the materials were evaluated.The results showed that the ultimate tensile stress of the vascular PBSU/gelatin grafts at(95/5),(90/10),(85/15),and(80/20)was(4.17±0.54)MPa,(3.81±0.44)MPa,2.94±0.69 MPa and 2.11±0.72 MPa respectively,and the burst pressure was(282.7±22.3)kPa,(295.3±3.9)kPa,(306.8±13.9)kPa and(307.6±9.0)kPa respectively,which met the requirements of tissue-engineered blood vessels.Furthermore,the addition of gelatin improved the hydrophilicity and degradation properties of PBSU,thus enhancing cell adhesion and promoting the inward growth of vascular smooth muscle cells.In summary,the research in this paper provides a useful reference for the preparation and optimization of vascular scaffolds.

Microstructure evolution of Al-4Cu-Mg alloy during semi-solid treatment

The microstructure of a cold-deformed Al-4Cu-Mg alloy during semi-solid treatment was investigated, which shows that grain detachment and grain spheroidization processes during the semi-solid treatment are very important to control the fabricated semi-solid microstructures. For the two different processes, the driving force comes from the external heat source and the reduction in total interfacial area, respectively. The evolution models of microstructure morphology in the two processes were presented based on microstructure observations. It can be found that these models are useful to provide a reasonable estimated critical time of the evolution of microstructure during the semi-solid treatment.

高精度推动式管线测长系统研究与实现

为加快我国钢铁工业转型升级,推进管线测长设备国产化,研发适合国内自动化生产线的管线测长产品,在对测长原理和系统组成分析的基础上,提出了推动式管线测长系统的设计方案;根据影响测量精度的关键因素分析误差产生原因及误差的性质特点,并探讨减小误差的方法;生产现场的实验证明,测长系统的精度可以满足国家标准要求。

Texture and Microstructure Evolution During Tensile Testing of TWIP Steels with Diverse Stacking Fault Energy

Texture and microstructure evolution in two kinds of the twinning induced plasticity(TWIP)steels(Fe-MnSi-Al and Fe-Mn-C)with diverse stacking fault energies during tensile testing were investigated by interrupted testing.The strain-hardening rate curves of the two steels were quite similar,but the texture characterization curves(maximum of pole density measured by X-ray difraction)were varied.According to the curvature of max pole density curves,the evolution of the texture and the microstructure can be divided into three stages:low strain stage,medium stage and high stage.In low strain stage the diference of the microstructure came from the intensity of dislocation,which was much smaller in Fe-Mn-Si-Al.The main diference of the microstructure in medium and high strain stages originated from the numbers of activated twin systems.There were more than one twin systems activated in Fe-Mn-C,while only a single twin system activated in Fe-Mn-Si-Al.Texture showed various diferences in the whole tensile process because it was afected by their micromechanism,such as concentration of the dislocation and the activation of twin systems.Texture in low strain stage was connected with annealing twin;the evolution ofthe texture was mainly induced by deformation twin generation.More than one activated twin systems in medium and high stages may counteract each other in the view of concentration of the grain orientations.