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.

Mechanical Behavior and Failure Mechanism of 2.5D(Shallow Bend-joint, Deep Straight-joint) and 3D Orthogonal UHWMPE Fiber/Epoxy Composites by Vacuum-assistant-resin-infused

Ultra-high molecular weight polyethylene（UHMWPE） fiber/epoxy composites were fabricated by a vacuum assisted resin infused（VARI） processing technology. The curing condition of composites was at a cure temperature of 80 ℃ for 3h in a drying oven. The characteristics of 2.5D（shallow bend-joint and deep straight-joint） structure and 3D orthogonal structure were compared. The failure behavior, flexural strength, and microstructures of both composites were investigated. It was found that the flexural property was closely related to undulation angle θ. The flexural strength of 3D orthogonal structure composite was superior to the other two structures composites with the same weave parameters and resin.

Shape design of the reinforcement for bending load-carrying capacity of under-matched butt joint under four-point bending load

To improve the bending load-carrying capacity （ BLCC） of under-matched butt joint under four-point bending load in the elastic stage, the shape design of the reinforcement is studied based on the theoretics of mechanics of materials. The concept, criterion, realization condition and design proposal of equal bending load-carrying capacity （EBLCC） are put forward. The theoretical analysis results have been verified by the finite element method. The simulation results are coincident basically with the ones of theoretical analysis. The research results show that the shape design of the reinforcement of EBLCC can improve BLCC of under-matched butt joint and the unilateral-side type reinforcement can replace double-side symmetry

The effect of number of joints on bending properties of laminated lumber made from poplar (Populus nigra)

Connection plays an important role in structural components and end jointing is one of the most common connections in structural applications. This study was designed to investigate some mechanical properties （MOE and MOR） of solid wood samples manufactured from poplar （Populus nigra）, joined together through end jointing. As well, we studied combinations of lumber manufactured from 10-mm veneer, using a polyvinyl acetate adhesive. The results show that non-jointed lumber （control samples） have better bending properties （MOE and MOR） than jointed specimens and lumber made from laminated layers. On the whole, side-by- side joints have a negative effect on the MOR and MOE of laminated products, which is more pronounced in the MOR. By increasing the number of joints, the properties of combination of three-ply, i.e., bending strength and modulus of elasticity, decreased.

Bending moment resistance of dowel corner joints in case-type furniture under diagonal compression load

We investigated bending moment resistance under diagonal compression load of comer doweled joints with plywood members. Joint members were made of ll-ply hardwood plywood of 19 mm thickness. Dowels were fabricated of Beech and Hornbeam species. Their diameters （6, 8 and 10 mm） and depths of penetration （9, 13 and 17 ram） in joint members were chosen variables in our experiment. By increasing the connector＇s diameter from 6 to 8 mm, the bending moment resistance under diagonal compressive load was increased, while it decreased when the diameter was increased from 8 to 10 mm. The bending moment re- sistance under diagonal compressive load was increased by increasing the dowel＇s depth of penetration. Joints made with dowels of Beech had higher resistance than dowels of Hornbeam. Highest resisting moment （45.18 N.m） was recorded for joints assembled with 8 mm Beech dowels penetrating 17 mm into joint members Lowest resisting moment （13.35 N.m） was recorded for joints assembled with 6 mm Hornbeam dowels and penetrating 9 mm into joint members.

Structural Analysis of Platforms with the Effect of Joint Flexibility

A modified space beam element is presented in this paper to consider the local joint flexibility of T, Y tubular joints subjected to axial forces and in-plane bending moments for analysis of platforms. Two numerical examples are shown to verify the efficiency and validity of the method presented here.

型钢-UHPC轻型组合桥面板及其抗弯性能研究

正交异性钢桥面是目前800m以上国内外特大跨径钢桥的唯一选择,主因是自重轻、强度高、架设方便。但其存在疲劳开裂风险大、运维成本高的缺点。随着高性能材料UHPC的研发和应用,为构建自重轻、病害少、经济性好的桥面新结构提供了可能性。经过多年研究,作者提出一种新型桥面板结构——型钢-UHPC轻型组合桥面结构,将型钢、钢板条与UHPC组合,桥面板的形成无任何板件焊接,因而具有高抗疲劳性,且与传统钢桥面相比,自重持平、造价减半,可作为除“正交异性钢桥面”外的“第二种”大跨径钢桥的桥面结构方案。该文研究这种轻型组合桥面板预制板及横向接缝的抗弯性能,制作4个条带模型(包括2个预制板试件和2个接缝试件),开展三点弯曲的横向接缝负弯矩试验和预制板正弯矩试验,并对试验结果进行分析;基于“条带法”建立预制板试件极限承载力计算模型,提出接缝试件的UHPC开裂名义拉应力计算方法;基于某斜拉桥应用实例,进行整体计算和局部计算,验证新型组合桥面结构在实桥上应用的可行性。研究结果表明:(1)型钢与UHPC间在极限状态前相对滑移非常小,具有良好的协同受力性能;(2)预制板试件的正弯矩极限承载力以型钢屈服控制,而接缝试件负弯矩极限承载力以UHPC开裂和加密钢筋断裂控制;(3)接缝试件的“T形”接缝、加密钢筋、燕尾形的企口、交错式切割型钢钢条等构造设计对接缝整体抗弯拉性能有很好的提高效果;(4)预制板试件极限承载力计算模型所得计算值与试验值吻合良好,该模型搭配名义拉应力计算方法,可帮助工程实际问题的设计与应用;(5)试验结果与实桥的有限元计算值相比,新型桥面结构均有1.3倍以上的安全系数,新型组合桥面应用于实桥具有可行性。

Preparation of FRC/Steel by Lap-joint and Its Mechanical Properties

The Lap-joint configuration and the vacuum assisted forming method were put forward to meet the demands of the compression bending strength and the strong connection between the steel and FRC.The bending mechanic tests of the Lap-joint bending specimens carried out, the fabricate processing stability, limit carrying capacity and failure modes were analyzed. The experimental results show that the fabricate processing of the Lap-joint is stable; the bending stiffness is 19.5 N/mm, and the limit bending moment reaches 318 N？m. The main failure modes are the failure of core material at junction of sandwich plate and steel, and the bending failure in the position of the inner and outer surface.

大直径盾构隧道新型纵缝接头抗弯性能试验研究

纵缝接头是盾构隧道受力性能的薄弱部位,管片接头的形式直接影响盾构隧道的力学性能。目前国内的盾构隧道纵缝接头使用的连接件多为螺栓,新型纵缝接头使用了一种新的连接件—滑入式连接件,此种接头在大直径盾构隧道中的受力性能有待研究。本文以新型纵缝接头为研究对象,针对两种不同型号的滑入式连接件,采用模型试验的方法探究了大直径盾构隧道新型纵缝接头的受力性能,通过理论分析计算了新型纵缝接头的极限承载力,并比较分析了传统螺栓纵缝接头和新型纵缝接头的受力性能。结果表明:新型接头衬砌管片的薄弱部位在连接件周围的混凝土区域;滑入式连接件的型号直接影响新型纵缝接头的受力性能,两种接头中连接件尺寸较大的接头转角刚度相较于连接件尺寸较小的接头转角刚度增加了7.2~169.5%,极限承载能力增加了69.9%;新型纵缝接头比螺栓接头有更高的转角刚度,受力性能更好,适用于大直径盾构隧道。

Regression Formulations for the Stress at Hot Spot of Multiplanar Tubular DT Joints

Stress concentration analysis of multiplanar tubular DT joints plays an important role in the fatigue design of offshore platforms. A semi-analytic method for stress analysis under the condition of any loads is briefly introduced in the paper. Nineteen multiplanar tubular DT joints with one of two braces of the same dimension subjected to axial loads and out- of- plane bending moments are computed for parametric stress analysis by using the present method. The influence of geometrical parameters on the stresses of multiplanar tubular DT joints is discussed and compared with corresponding uniplanar T joints. The regression formulae for the stress at hot spot of multiplanar DT joints are found by modification of SCF of corresponding uniplanar T joints. The parametric formulae for the maximum stress by superposition. Finally, the influences of stiffening effect and load-interaction effect on the maximum stress of DT joints are discussed.

工字形钢梁-矩形钢管柱单向螺栓节点抗弯承载力理论计算方法

针对工字形纯钢梁和钢-混凝土组合梁分别与矩形钢管柱和矩形钢管混凝土柱采用单向螺栓(也称单边拧紧螺栓)连接形成的4种节点形式,对其在弯矩作用下的受力机理及破坏模式进行分析,讨论导致节点失效的因素。总结节点在弯矩作用下的9种失效模式,包括:单向螺栓拉断、端板受弯屈服、矩形钢管柱壁翼板受拉屈服、矩形钢管柱壁翼板受压屈服、矩形钢管柱壁腹板受压屈曲、混凝土楼板局部压溃、钢筋屈服、矩形钢管柱内混凝土局部压溃、矩形钢管柱壁腹板受压屈服,进而基于破坏模式给出节点各组件承载力的计算公式。对4种节点在不同破坏模式下的正弯矩承载力和负弯矩承载力进行分析,给出节点承载力计算公式。将节点抗弯承载力的理论计算结果与试验结果进行对比,验证理论计算方法的可靠性。

GB/T 2653—2008标准的修改建议

弯曲试验是测定焊接接头塑性变形能力的试验方法。简要介绍了金属材料焊缝弯曲试验的相关国内外标准,对比分析了现行标准GB/T 2653—2008与ISO 5173:2023的差异,建议尽量结合我国实际情况,增强不同标准间的协调性,使新修订的标准更清晰且更易操作。

焊接工艺参数对旋转摩擦焊铝-铜接头弯曲性能的影响

对1070纯铝和T2纯铜进行了旋转摩擦焊接。研究了摩擦焊工艺参数对铝-铜接头弯曲性能的影响。采用电子探针显微分析仪检测了铝-铜接头界面的微观形貌和元素分布。结果表明:较短时间(2 s)摩擦焊制备的铝-铜接头(1号试样)弯曲试验时断裂于铝-铜界面,为脆性断裂,随着摩擦时间的增加,铝-铜接头弯曲试验时断裂于铝侧,为韧性断裂;以2~5 s的摩擦时间制备的铝-铜接头界面均未发现有明显的金属间化合物,但发生了成分变化;较短时间摩擦焊制备的1号试样成分变化区宽约1.6μm,较长时间(5 s)摩擦焊制备的4号试样成分变化区宽约2.7μm;较宽的成分变化区能提高铝-铜接头界面的结合强度,从而提高铝-铜接头的弯曲性能,较窄的成分变化区是弯曲试验过程中铝-铜接头界面断裂的主要原因。

装配工艺参数对止口螺栓连接结构力学特性的影响分析

以航空发动机转子系统中止口螺栓连接结构为研究对象,基于单螺栓连接结构分析弯曲刚度的非线性特征,利用ANSYS实体单元建模方法分析连接结构的弯曲刚度,重点讨论了有无止口连接、预紧力、螺栓直径、止口过盈量等装配工艺参数对连接结构弯曲刚度的影响规律,并分析了止口连接结构对转子系统固有特性的影响.研究结果表明:止口连接结构的弯曲刚度呈现分段特性;增大预紧力、螺栓直径以及止口过盈量能提高连接结构弯曲刚度;有无止口连接结构的转子系统前三阶固有频率的相对误差小于2%,止口连接结构能够降低转子系统的最大振动幅值.

Continuous Damage Monitoring of a Thin Composite Structural with Mismatched Stiffener in a Combined Joint Using Fiber Bragg Grating under Tension and Three-Point Loading

A joint combining riveting and bonding is considered in terms of structural performance if the composite structure has a mismatched stiffener. The transfer loading is correlated with high performance aerospace joints to increase delamination resistance in the out-of-plane direction. However, combined joints (rivet/bonded) will create a bearing area that induces another potential damage source aside from secondary bending moment on the edge of the stiffener. Another problem is that the structure is difficult to be inspected by using conventional methods because of limited accessibility. The use of embedded fiber Bragg grating (FBG) technology in the structure as a strain sensor can potentially solve the problem in structures that have a stiffness mismatch. The FBG can be used to detect and characterize delamination before it reaches a critical stage. The model used to represent this problem is a thin composite stiffened skin under two load cases: tension and three-point bending. Finite element modeling using a traction versus separation theory is performed to determine the critical area on the specimen for placement of the FBG before manufacturing and testing. Experiments were presented to determine the distribution of load in a combined joint under both loading cases using ideal loads to create a secondary bending moment and bearing loads in the stiffness-mismatched structure. In this research, the FBG successfully detected and characterized the delamination caused in both loading cases. In addition, FBG can predict the delamination growth quantitatively. A spectrum graph of the FBG results can be used to replace the conventional mechanical graph in composite structural health monitoring in real applications.

7075–O铝合金搅拌摩擦焊接头微观组织与力学性能

时效硬化态7075铝合金搅拌摩擦焊接头塑性较低,给进一步变形加工带来困难。本文采用3 mm厚的7075–O铝合金板进行搅拌摩擦对接焊,研究焊接速度对接头组织和强塑性的影响,为获得高塑性的搅拌摩擦接头提供解决方案。结果表明,7075–O铝合金接头焊核区为细小的等轴晶粒,随焊接速度的增加,焊核区平均晶粒尺寸呈先减小后缓慢增加的趋势,当焊接速度为40 mm/min时,焊核区晶粒尺寸最小,约为1.96μm。不同焊接速度下接头横截面显微硬度呈“凸”形分布,接头区域发生明显硬化,其中焊核区硬度最高,约为145HV。7075–O铝合金搅拌摩擦焊工艺窗口较宽,焊接速度在20~80 mm/min范围内接头强度均高于母材强度,焊接件伸长率达母材的82%,采用7075–O铝合金不仅能够克服时效硬化态7075铝合金搅拌摩擦焊接头的软化问题,而且能够获得更高的伸长率。接头弯曲试验结果表明,7075–O铝合金搅拌摩擦焊接头能够承受更大的弯曲角度,极限弯曲角达105°,具备更加出色的塑性变形能力。

平面内弯矩作用下T形圆管相贯节点热点应力分布

本文针对平面内弯矩作用下的T形圆管相贯节点焊缝处热点应力分布开展研究.利用径向拉伸法建立了T形圆管相贯节点的有限元网格模型,对热点应力分析结果的可靠性进行了网格密度分析和试验对比分析,提出了满足计算精度要求的基本密度网格.通过无量纲几何参数分析归纳了热点应力沿相贯线的环向分布规律及几何参数影响规律,发现了冠点波峰分裂现象及分裂过程中波峰曲线的三种变化形态,在此基础上提出了采用以π为周期的系数来修正冠点曲线形状的波形修正方法及分布曲线参数公式.与伦敦大学学院(University College London,UCL)两位学者的公式和试验数据进行对比分析,结果表明本文公式具有更简洁的表达形式和更高的精度.

带UHPC接缝的桥面板力学性能试验研究

为掌握带UHPC接缝的桥面板受弯状态下的力学特点,进一步探究UHPC接缝的合理宽度及在接缝宽度相同情况下,不同接缝截面形式、钢筋搭接形式对带UHPC接缝的桥面板抗弯性能影响,设计制作了一块现浇整体板和3块不同湿接缝构造的UHPC预制桥面板,并分别进行四点弯曲试验评估接缝处抗弯性能,对荷载-跨中位移曲线、荷载-主裂缝宽度曲线、混凝土荷载-拉应变曲线、混凝土荷载-压应变曲线、荷载-受拉钢筋应变曲线、极限抗弯承载能力、裂缝发展状况展开相关研究。结果表明:由于UHPC优异的力学性能,4组试验板的荷载-跨中挠度曲线基本相近,带UHPC接缝的桥面板极限承载力优于整体板;接缝宽度、钢筋连接方式相同的情况下,漏斗形或楔形接缝截面形式不会影响预制桥面板的极限承载力,彼此刚度差异不大;在保证桥面板整体性和承载力的前提下,预制桥面板UHPC湿接缝可减小为15 cm宽;UHPC接缝连接的整体性良好,不会影响现浇接缝区段及连接界面的抗拉性能,带UHPC接缝的预制拼装桥面板的初始裂缝和主裂缝均位于普通混凝土区域,UHPC的高弹性模量使得接缝区域局部刚度提高,相较于接缝周围混凝土区域,接缝处的受压区混凝土压应变与受拉区钢筋的拉应变都较小,接缝区域未出现裂缝,UHPC湿接缝与混凝土预制板界面处的裂缝扩展速度缓慢。

大跨度装配式单层网壳十字形半刚性螺栓连接节点抗弯性能研究

装配式连接节点是大跨度装配式单层空间网壳结构体系的关键。提出一种适用于大跨度单层网壳结构的十字形板装配式节点。该节点由圆钢管、十字形钢板、角钢、矩形连接盖板、圆盖板和高强螺栓组成,其中圆钢管、盖板、十字形钢板在工厂焊接,现场将十字形板和角钢、矩形盖板用高强螺栓连接。该节点通过设置角钢、矩形连接盖板和十字形钢板螺栓连接,在节点受到弯曲荷载时,角钢和矩形连接盖板可以首先承受弯曲荷载,从而减少节点内侧的十字形钢板塑性损伤,并且提高节点的抗弯性能。利用有限元模拟方法,构建新型连接节点有限元模型,分析了十字形钢板和角钢厚度等变量如何影响节点在平面内外的抗弯性能。通过对各组成部分尺寸的参数化研究,得到了这些因素对所提出的连接节点平面内外抗弯性能的影响规律。研究结果表明,采用角钢与矩形盖板相连接形成的十字形节点,在抗弯刚度和承载力方面表现出了优异的性能。通过调节十字形板厚度、螺栓个数、角钢和盖板厚度可调控节点的初始抗弯刚度和抗弯承载力。基于刚性节点设计方法,对该半刚性节点进行尺寸理论设计,结果表明该方法可以保证节点弯矩设计值基本达到圆钢管的屈服弯矩,满足设计要求,提高节点安全。

槽型套管加强方钢管X形节点平面内受弯性能试验

槽型套管适用于在役钢管结构的节点局部加强,可有效提高节点承载力和刚度。为研究槽型套管对方钢管节点平面内受弯性能的加强效果,对5组支主管宽度比β为0.58、0.7和1.0的试件进行平面内受弯试验。试验表明槽型套管加强可以有效提升节点受弯性能,β=0.58和β=0.7时槽型套管加强节点的受弯承载力分别提高37%和163%;加强节点的刚度略低于等宽节点,但其延性更优;支主管宽度比和槽型套管厚度是影响加强节点平面内受弯性能的主要参数。槽型套管加强可有效保护节点主管,使试件失效模式由主管或焊缝破坏转移为支管破坏。进一步机理分析表明,加强套管可与主管管壁形成共同承载体,通过局部增厚作用提高节点承载力和刚度。据此对比分析了该类加强节点受弯承载力计算公式的适用性,可供设计参考。