Basic Characteristics of a New Flexible Pneumatic Bending Joint

Several typical flexible pneumatic actuators （FPA） and different mechanical models describing their behaviors have been proposed, however, it is difficult to balance compliance and load capacity in conventional designs, and these models still have limitations in predicting behavior of FPAs. A new flexible pneumatic bending joint （FPBJ） with special anisotropic rigidity structure is proposed. The FPBJ is developed as an improvement with regard to existing types of FPA, and its principal characteristic is derived from the special anisotropic rigidity structure. With this structure, the load capacity in the direction perpendicular to bending plane is strengthened. The structure of the new FPBJ is explained and a mathematical model is derived based on Euler-Bernoulli beam model and Hook’s law. To obtain optimum design and usage, some key structure parameters and input-output characteristics are simulated. The simulation results reveal that the relationship between the structure parameters and FPBJ’s bending angle is nonlinear. At last, according to the simulation results, the FPBJ is manufactured with optional parameters and tested. The experimental results show that the joint’s statics characteristics are reflected by the mathematical model accurately when the FPBJ is deflated. The maximum relative error between simulation and experimental results is less than 6%. However, the model still has limitations. When the joint is inflated, the maximum relative error reaches 20%. This paper proposes a new flexible pneumatic bending joint which has sufficient load capacity and compliance, and the mathematical model provides theoretical guidance for the FPBJ’s structure design.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅲ)-CALCULATION FOR C-SHAPED BELLOWS

This is one of the applications of Part (Ⅰ), in which the angular stiffness, the lateral stiffness and the corresponding stress distributions of C_shaped bellows were calculated. The bellows was divided into protruding sections and concave sections for the use of the general solution (Ⅰ), but the continuity of the stress resultants and the deformations at each joint of the sections were entirely satisfied. The present results were compared with those of the other theories and experiments, and are also tested by the numerically integral method. It is shown that the governing equation and the general solution (Ⅰ) are very effective.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅳ)-CALCULATION FOR U-SHAPED BELLOWS

This is one of the applications of Part (Ⅰ),in which the angular stiffness, and the corresponding stress distributions of U_shaped bellows were discussed. The bellows was divided into protruding sections, concave sections and ring plates for the calculation that the general solution (Ⅰ) with its reduced form to ring plates were used respectively, but the continuity of the surface stresses and the meridian rotations at each joint of the sections were entirely satisfied. The present results were compared with those of the slender ring shell solution proposed earlier by the authors, the standards of the Expansion Joint Manufacturers Association (EJMA), the experiment and the finite element method. It is shown that the governing equation and the general solution (Ⅰ) are very effective.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅰ)-GOVERNING EQUATION AND GENERAL SOLUTION

The overall bending of circular ring shells subjected to bending moments and lateral forces is discussed. The derivation of the equations was based upon the theory of flexible shells generalized by E.L. Axelrad and the assumption of the moderately slender ratio less than 1/3 (i.e., ratio between curvature radius of the meridian and distance from the meridional curvature center to the axis of revolution). The present general solution is an analytical one convergent in the whole domain of the shell and with the necessary integral constants for the boundary value problems. It can be used to calculate the stresses and displacements of the related bellows. The whole work is arranged into four parts: (Ⅰ) Governing equation and general solution; (Ⅱ) Calculation for Omega_shaped bellows; (Ⅲ) Calculation for C_shaped bellows; (Ⅳ) Calculation for U_shaped bellows. This paper is the first part.

Precision and Flexible Bending Control Strategy Based on Analytical Models and Data Models

Forming of various customized bending parts,small batches,as well as numerous types of materials is a new challenges for Industry 4.0,the current control strategies can not meet the precision and flexibility requirement,expected control strategy of bending processes need to not only resist unknown interferences of process condition and models,but also produce various new parts automatically and efficiently.In this paper,a precision and flexible bending control strategy based on analytical models and data models is proposed to build adaptive bending systems.New analytical prediction models for loading and unloading are established and suitable for various materials,a sequential identification strategy is proposed to search nominal properties using the four sub-optimization models.A data-based feedback model is established to prevent over-bending and eliminate online deviation.Above models are merged into a precision and flexible control strategy.The system firstly uses sub-optimization models to search the nominal point which is near to target point,secondly the system further uses feedback model to eliminate residual error between the nominal point and target point.Compared with four kinds sheet metals,the allowable ranges for variables are determined for a good convergence.The target bending angles were set to 20°,40°,and 60°.Forty parts were tracked for each kind material,the adaptive bending system converged after one iteration,and exhibited better performances.

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.

The development of studying flexible pipe bend reinforced by Kevlar fibers

The flexible pipe bend can not only reduce the structural vibration and fluid noise in pipeline, but also realize the flexible connection of a horizontal line and a vertical line and compensate the displacement of three dimensions produced by the shock or vibration of pipeline in the special situations. Up to now, little attention has been paid to study the flexible pipe bend applied in the pipeline of medium or high pressure, because no appropriate framework materials can be used to reinforce it which must endure the burst pressure higher than 10 MPa. The investigation shows that it is possible to produce the flexible pipe bend of medium or high pressure if such fibers with high performance as Kevlar fibers are used to be its reinforced materials. However, its structural designing theory, manufacturing technology and measuring techniques aren't yet perfect and systematic, which leads to the instability of the performance of products. Furthermore, few references about its research can be seen. Therefore, it is necessary to systematically and thoroughly develop the structural designing theory, manufacture technology and measuring techniques of flexible pipe bend.

Helical Wire Stress Analysis of Unbonded Flexible Riser Under Irregular Response

A helical wire is a critical component of an unbounded flexible riser prone to fatigue failure. The helical wire has been the focus of much research work in recent years because of the complex multilayer construction of the flexible riser. The present study establishes an analytical model for the axisymmetric and bending analyses of an unbonded flexible riser. The interlayer contact under axisymmetric loads in this model is modeled by setting radial dummy springs between adjacent layers. The contact pressure is constant during the bending response and applied to determine the slipping friction force per unit helical wire. The model tracks the axial stress around the angular position at each time step to calculate the axial force gradient, then compares the axial force gradient with the slipping friction force to judge the helical wire slipping region, which would be applied to determine the bending stiffness for the next time step. The proposed model is verified against the experimental data in the literature. The bending moment-curvature relationship under irregular response is also qualitatively discussed. The stress at the critical point of the helical wire is investigated based on the model by considering the local flexure. The results indicate that the present model can well simulate the bending stiffness variation during irregular response, which has significant effect on the stress of helical wire.

AN EXACT METHOD OF BENDING OF ELASTIC THIN PLATES WITH ARBITRARY SHAPE

This paper presents a new method exactly to solve the bending of elastic thinplates with arbitrary shape. First the analytic solution of differential equation ofelastic thin plate is derived in polar coordinate, then the analytic solution is substituted into the boundary conditions of elastic thin plate with arbitrary shape. The boundaryequations are expanded along the boundary by the use of Fourier series, all unknown coefficients can be decided. The results are exact.

Articulated Lifting System Modeling Based on Dynamics of Flexible Multi-Body Systems

In lifting sub-system of deep-sea mining system, spherical joint is used to connect lifting pipes to replace fixed joint. Based on Dynamics of Flexible Multi-body systems, the mechanics model of articulated lifting system is established. Under the four-grade and six-grade oceanic condition, dynamic responses of lifting system are simulated and experiment verified. The simulation results are consistent with experimental ones. The maximum moment of flexion is 322 kN-m on the first pipe under six-grade sea condition. It is seen that the articulated connection can reduce the moment of flexion. The bending deformation of pipe center is researched, and the maximum is 0. 000479 m on the first pipe. Deformation has a little effect on the motion of system. It is feasible to analyze articulated lifting system by applying the theory of flexible multi-body dynamics. The articulated lifting system is obviously better than the fixed one.

Subsurface damage and bending strength analysis for ultra-thin and flexible silicon chips

Subsurface damage(SSD) is an unavoidable problem in the precision mechanical grinding for preparing ultra-thin and flexible silicon chips. At present, there are relatively few studies on the relationship between SSD and the bending strength of ultra-thin chips under different grinding parameters. In this study, SSD including amorphization and dislocation is observed using a transmission electron microscope. Theoretical predictions of the SSD depth induced by different processing parameters are in good agreement with experimental data. The main reasons for SSD depth increase include the increase of grit size, the acceleration of feed rate, and the slowdown of wheel rotation speed. Three-point bending test is adopted to measure the bending strength of ultra-thin chips processed by different grinding conditions. The results show that increasing wheel rotation speed and decreasing grit size and feed rate will improve the bending strength of chips, due to the reduction of SSD depth. Wet etching and chemical mechanical polishing(CMP) are applied respectively to remove the SSD induced by grinding, and both contribute to providing a higher bending strength, but in comparison, CMP works better due to a smooth surface profile. This research aims to provide some guidance for optimizing the grinding process and fabricating ultra-thin chips with higher bending strength.

NUMERICAL SIMULATION FOR LASER BENDING OF SHEET METAL

The new flexible forming technique of sheet metal laser bending process is numerically simulated by using finite element method of large elastic plastic deformation. The temperature fields and stress strain distribution in deformation area are calculated, forming process is described and relationship between bend angle and width of sheet is discussed. It is shown that the calculated values are in good accordance with the experiments.

增强型气动柔性驱动器形变与驱动特性实验

为解决现阶段柔性驱动器负载能力低、变形范围小等问题,设计并制作一种三自由度气动柔性驱动器,分析其变形机制并通过实验研究增强肌肉对驱动器伸长量、弯曲方向及弯曲角度、驱动力的影响。实验结果表明:通过控制驱动器人工肌肉内腔气压,驱动器可以产生轴向伸长和空间0°~360°任一方向弯曲变形;增强肌肉通压对驱动器变形量和驱动力有增幅作用,0.4 MPa气压下驱动器无增强肌肉时伸长率为49%,弯曲角度为68°,轴向驱动力为278 N;有增强肌肉时驱动器伸长率为54%,弯曲角度为77.5°,轴向驱动力为300 N。

柔性玻璃的化学强化及其力学性能研究

具有高弯曲强度的柔性玻璃是柔性电子显示的重要组成部分,但柔性玻璃本质是脆性材料,因此其力学性能仍然不能满足使用要求。化学强化是提高柔性玻璃弯曲半径、抗划伤性等力学性能的有效途径,本文采用一步化学强化法,将90μm超薄高铝柔性玻璃在纯硝酸钾熔盐中进行强化,研究离子交换工艺对样品表面应力、维氏硬度及弯曲半径的影响规律。结果表明:在380℃进行1 h的离子交换后,样品的表面压应力达834.1 MPa,应力层深度为15.91μm,此时玻璃具有最佳的弯曲性能和耐划伤性;经化学强化后,90μm柔性玻璃的最小弯曲半径可由(29.8±0.73)mm降低至(6.94±0.99)mm;随着继续升高交换温度和延长时间,柔性玻璃的力学性能会有所降低。

中低速磁浮圆曲线钢箱梁桥车致振动响应研究

随着圆曲线钢箱梁桥在城市交通中的应用愈发广泛,为探究其在中低速磁浮车辆运行作用下的振动响应特性,基于多体动力学和有限元方法建立车辆-轨道-钢箱梁刚柔耦合动力学模型,采用动态电磁阻尼力影响的二维磁轨关系,并考虑轨道关键部件的参振作用,分析圆曲线段钢箱梁的振动特性,探讨钢箱梁板厚、车辆速度及车体质量对钢箱梁振动响应的影响。结果表明:受曲率影响,钢箱梁在发生弯曲的同时亦会伴生扭转,产生弯扭耦合振动;钢箱梁的振动主要由10~20 Hz的钢箱梁整体弯曲振动、30~40 Hz的钢箱梁扭转振动以及50~70 Hz的轨道局部振动引起;计算得到的钢箱梁跨中横向及垂向最大挠度分别为1.26 mm、3.88 mm,均满足相关标准要求,钢箱梁具有足够的支撑刚度;各工况下的垂向加速度均未超过5.0 m/s^(2)的限值,且最高达到2.2 m/s^(2);在板厚10 mm以及超员载荷工况下,横向加速度大多超过1.4 m/s^(2)的限值,且最高达到4.0 m/s^(2);车辆速度的减小和车体质量的增加均会放大弯扭耦合作用影响,而板厚的增加则能够有效降低弯扭耦合作用影响,当板厚由10 mm增至40 mm时,一阶横弯及扭转频率对应振幅分别减小94.3%、98.7%。

风力机叶片预弯状态颤振效应分析

风力机叶片预弯设计大多采用静气弹分析方法,忽略了叶片气动力、惯性力和弹性力三者相互作用而引发的气弹耦合失稳问题,而预弯对百米量级超长柔性叶片的颤振性能影响尤为显著。为对比分析不同预弯尺寸对叶片颤振临界状态的影响,基于主梁刚度等效原则进行叶片气弹模型设计,通过风洞试验发现了15 MW两种预弯叶片颤振区间及其临界风速的差异;进一步基于修正的叶素动量理论和几何精确梁理论(Blade Element Momentum Theory-Geometrically Exact Beam Theory,BEM-GEBT)耦合计算方法对4种预弯叶片进行分析,对比了不同预弯尺寸叶片的颤振临界风速、气动力分布和位移频谱特性,并揭示了颤振耦合模态机理。研究表明:BEM-GEBT耦合计算方法结果与风洞试验结果吻合较好;随着预弯尺寸的增大,挥舞-摆振耦合颤振临界风速提高,颤振区间范围基本一致;不同预弯尺寸叶片升力系数和俯仰力矩系数发散速率与位移发散速率呈正相关,平均风压曲线在预弯3~4 m范围内出现显著变化,挥舞-摆振耦合效应大于挥舞-扭转耦合效应,其颤振耦合频率由一阶挥舞频率主导。

聚乙烯醇-乙烯/SiO 2复合柔性驱动膜的制备及其性能

针对当前柔性智能驱动材料在开发过程中存在的响应性差、制备工艺复杂、成本高、刺激源污染大等问题,采用分层喷涂法制得具有非对称结构的聚乙烯醇-乙烯共聚物(PVA-co-PE)/SiO 2双层复合柔性驱动膜,并对其表面形貌、亲疏水性、力学性能、驱动性能等进行表征与测试分析。结果表明:纳米纤维直径越小,越有利于SiO 2粉体在纳米纤维表面的附着,复合驱动膜的亲水性随着纳米纤维直径的增加呈现逐渐下降的趋势,同时纤维直径的增加可大幅提升复合驱动膜的拉伸应力;另外,随着纳米纤维直径从180 nm增加至390 nm,复合驱动膜的形变角度逐渐变小,且当复合驱动膜中纳米纤维直径为180 nm,SiO 2粉体粒径为15 nm时,制备的复合驱动膜具有最佳的驱动性能,在0.7 s左右即可达到180°的最大弯曲角度。基于该PVA-co-PE/SiO 2复合驱动膜快速的刺激响应性、大尺度的弯曲形变能力,其在智能操控、人工肌肉以及智能服装领域中具有较好的应用前景。

有机--无机共添加增强柔性钙钛矿太阳能电池机械弯曲及环境稳定性能

近年来,钙钛矿太阳能电池发展迅速,其光电转换效率(Power Conversion Efficiency,PCE)已经提高到26.1%,但是柔性钙钛矿太阳能电池(Flexible Perovskite Solar Cells,F-PSCs)的机械弯曲和环境稳定性仍然是其商业化的主要障碍。本研究通过添加琼脂糖(Agarose,AG)以改善薄膜的质量和结晶性能,系统探究了AG对钙钛矿的作用机理,组装成的F-PSCs的PCE和机械弯曲及环境稳定性能。研究发现当AG添加浓度达到最优值3 mmol/L时,薄膜表面变得更为致密平滑,钙钛矿结晶度和吸光度增加。此时器件的陷阱态密度降到最低,电荷传输电阻低至2191Ω,光电性能达到最佳,PCE由15.17%提升至17.30%。进一步引入TiO2纳米颗粒(0.75 mmol/L),与AG(3 mmol/L)共同作用,可以提供刚性骨架结构,增强钙钛矿层的机械性能和环境稳定性。循环弯曲1500次(半径为3 mm)后,AG/TiO2共添加器件可保持初始PCE的84.73%,远高于空白器件的9.32%;在空气中放置49 d后,该器件仍可保持初始PCE的83.27%,优于空白器件的62.21%。该研究成果为制备高效且稳定的F-PSCs提供了可能性。

柔性构件对液舱晃荡行为的影响

液舱晃荡可能引起强烈的砰击载荷,对舱壁结构安全产生威胁。传统的制荡方法是在舱内内置各种刚性构件,因此提出在舱底内置一竖向柔性构件的方法进行有效制荡。基于有限元法(FEM)和流体体积法(VOF)建立流体-挡板-液舱流固耦合(FSI)晃荡数值计算模型。在多种激励工况下,针对不同抗弯刚度的柔性构件,利用晃荡过程柔性构件的变形能与晃荡液体的动能相互转化以及构件对运动自由液面的约束作用,研究柔性构件的制荡效果。结果表明:在合适的抗弯刚度下,柔性构件既约束自由液面运动,又大量吸收晃荡流体的动能而转化为变形能,从而达到更佳的制荡效果。