Determination of Feature Line Equation for Self-adapting Incremental Press Bending

The basie idea and method about determination of the feature line equations and how to apply them to the numerical control of the press bending of panei skins were introduced. Research indicates that it is feasible to realize the self adapting incremental press bending by adopting the feature line equation. The feature line equation, which is based on the database of the status of practical processes, can be adjusted in time, and the forming precision can be improved. It is important to correctly select and reasonably predict the feature line equations to enhance the accuracy of the incremental press bending based on the feature line database and algorithm. The determination of the feature line equation settles necessary data foundation for further research on the database of self-adapting incremental press bending, and it supplies a new clue for the development of self-adapting incremental press bending.

Prediction of stiffener buckling in press bend forming of integral panels

In order to predict the buckling of stiffeners in the press bend forming of the integral panel,a method for solving the critical buckling load of the stiffeners in press bend forming process was proposed based on energy method,elastic-plastic mechanics and numerical analysis.Bend to buckle experiments were carried out on the designed press bend dies.It is found that the predicted results based on the proposed method agree well with the experimental results.With the proposed method,the buckling of the stiffeners in press bend forming of the aluminum alloy integral panels with high-stiffener can be predicted reasonably.

THEORY OF ELASTICITY OF AN ANISOTROPIC BODY FOR THE BENDING OF BEAMS

A theory of elasticity for the bending of orthogonal anisotropic beams was developed in this paper by analogy with the special case, which can be obtained by applying the theory of elasticity for bending of transversely isotropic plates to the problems of two dimensions. The authors also presented a method to solve the problems of bending of orthogonal anisotropic beams and a new theory of the deep-beam whose ratio of depth to length is larger. It is pointed out that Reissner's theory which takes into account the effect of transverse shear deformation is not suitable for the components of stress in our case.

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.

FEM equivalent model for press bend forming of aircraft integral panel

An original plastic equivalent model was proposed to solve the problem of excessive FEM simulation time when designing the press bend forming path and optimizing the process parameters of press bend forming of the integrally stiffened aircraft panels. Based on the in-depth analysis of the mechanics of the bending and springback of the detailed model and the equivalent model of the integral panels,the plastic equivalent model of the virtual material with special initial yield stress and hardening coefficients was constructed. FEM results indicate that the objective of getting the similar contour with the same press bend forming path is achieved with the error less than 6%,and the efficiency of FEM simulation is improved by more than 80%. The plastic equivalent model is valuable and essential for the further research on the press bend forming process of large scale complicated integral panels.

Strength performance of mortise and loose-tenon furniture joints under uniaxial bending moment

We determined the effects of adhesive type and loose tenon dimensions （length and thickness） on bending strength of T-shaped mor- tise and loose-tenon joints. Polyvinyl acetate （PVAc） and two-component polyurethane （PU） adhesives were used to construct joint specimens. The bending moment capacity of joints increased significantly with increased length and thickness of the loose tenon. Bending moment capacity of joints constructed with PU adhesive was approximately 13% higher than for joints constructed with PVAc adhesive. We developed a predictive equation as a function of adhesive type and loose tenon dimensions to estimate the strength of the joints constructed of oriental beech （Fagus orientalis L.） under uniaxial bending load.

Effect of equal channel angular extrusion on Al-6063 bending fatigue characteristics

The purpose of this investigation was to refine the grains of annealed 6063 aluminum alloy and to improve its yield stress and ul- timate strength. This was accomplished via the equal channel angular extrusion （ECAE） process at a temperature of 200℃ using route A, with a constant ram speed of 30 mm/min through a die angle of 90° between the die channels for as many as 6 passes. The experiments were conducted on an Avery universal testing machine. The results showed that the grain diameter decreased from 45 μm to 2.8 μm after 6 extru- sion passes. The results also indicated that the major improvement in fatigue resistance occurred after the first pass. The subsequent passes improved the fatigue life but at a considerably lower rate. A maximum increase of 1100% in the case of low applied stresses and an ap- proximately 2200% increase in fatigue resistance in the case of high applied stresses were observed after 5 passes. The improvement of fa- tigue resistance is presumed to be due to （1） a reduction in the size and the number of Si crystals with increasing number of ECAE passes, （2） the aggregation of Cu during the ECAE process, （3） the formation and growth of CuA12 grains, and （4） grain refinement of the A1--6063 alloy during the ECAE process.

P-FEMOL ANALYSIS OF PLATE BENDING PROBLEMS

In this paper, the p- version of the finite element method of lines (FEMOL) for the analysis of the Mindlin-Reissner plate bending problems is presented and a class of p-FEMOL elements with polynomial degrees as high as nine is developed. Numerical examples given in this paper show tremendous performance of the present method: namely, rapid convergence rate, high accuracy for both displacements and stress resultants, removal of shear-locking trouble, capability of dealing with difficult problems such as the boundary layer behavior near a free edge and stress concentration around a hole.

熔压温度对光纤面板抗弯强度的影响

光纤面板在微光夜视、空间探测、核诊断、医学诊疗等领域有着广泛的应用,在使用过程中对强度有一定要求,目前缺少相关研究,本文研究了熔压温度对光纤面板x、y、z三个方向抗弯强度的影响,采用三点弯曲法测试光纤面板的抗弯强度。结果表明:熔压温度为660℃时,二次复丝之间熔合不充分,存在间隙,光纤面板抗弯强度较低,x、y、z方向抗弯强度分别为107、93、114 MPa;熔压温度为670℃时,二次复丝之间间隙消除,但依然存在界面,抗弯强度有所提升,x、y、z方向抗弯强度分别为110、109、125 MPa;熔压温度为680℃时,二次复丝充分熔合,此时光纤面板抗弯强度在x、z方向满足复合材料混合定律,分别为123、127 MPa,y方向芯玻璃作为增强相对皮玻璃起到增强作用,抗弯强度为113 MPa。本文研究对提高光纤面板强度以满足装管和使用需求具有重要意义。

轻质高强异形管件充液压制成形技术

目的针对轻质高强异形管状构件的迫切需求,研发了充液压制成形技术,以在低载荷下成形出具有高强度、大尺寸、小圆角等特征的异形空心薄壁管状构件。方法给出了充液压制成形的力学原理,建立了成形过程压制力计算模型与临界支撑内压理论模型,分析了充液压制成形过程失稳屈曲/起皱规律、圆角充填机理与壁厚分布规律。结果当管材充液压制过程所需的支撑内压为内高压成形压力的1/10~1/20时,就可以避免管坯发生失稳屈曲与起皱,同时使压制力大幅降低。在弯曲与压缩应力复合作用下对管坯进行圆角充填,充液压制成形得到的管件壁厚减薄非常小。结论利用小吨位合模压力机在超低压条件下可以充液压制成形出具有小圆角与均匀壁厚的轻质高强异形管件,解决了传统内高压成形压力高、易发生开裂等难题。

热压法制备多孔氮化硅陶瓷

以CaF_(2)作为α-Si_(3)N_(4)粉末的烧结助剂,同时充当多孔氮化硅陶瓷的造孔剂,采用热压烧结工艺在较低温度下制备多孔氮化硅陶瓷。研究烧结助剂的含量对多孔氮化硅陶瓷显气孔率、抗弯强度的影响,分析材料的组分并观察断口结构。结果表明:在温度1450℃,压力0.55T的条件下,当CaF_(2)添加量为6.0wt%时,多孔陶瓷的性能较为优异,其孔隙率为38.8%,α-Si_(3)N_(4)→β-Si_(3)N_(4)的相变程度为38.5%,抗弯强度为137.1 MPa。

单组份环保型环氧树脂压浆料制备及性能研究

以E-51环氧树脂、甲基异丁基酮和间苯二甲胺为原料研制了单组份环氧树脂胶结料,并制备了单组份环保型环氧树脂压浆料,分别考察了单组份环氧树脂胶结料掺量对压浆料可操作时间、抗压强度、抗折强度、黏结耐久性的影响,养护条件对单组份环氧树脂压浆料力学性能的影响,不同锚固长度下单组份环氧树脂压浆料的黏结力。研究表明:当单组份环氧树脂胶结料掺量为10%、单组份环氧树脂压浆料锚固长度为2.5 m,温度33~42℃,相对湿度55%~90%养护14 d时,预应力钢绞线与单组份环氧树脂压浆料粘结体系的极限抗张拉拔力达到1839 kN,高于设计要求的1723 kN。

播量对缩行带状滴灌燕麦抗倒伏能力和产量的影响

为明确缩行带状滴灌下播量对燕麦抗倒伏能力和产量的影响,于2022—2023年以抗倒伏品种“坝莜1号”和易倒伏品种“燕科2号”为试验材料,分别设90 kg hm^(-2)(S1)、120 kg hm^(-2)(S2)、150 kg hm^(-2)(S3)、180 kg hm^(-2)(S4)和210 kg hm^(-2)(S5)5个播量,研究其对燕麦茎秆基部理化特性、抗倒伏能力、产量及构成因素的影响。结果表明,燕麦株高和重心高度随播量增加呈先升高后降低趋势,“坝莜1号”在S3处理下最高,较其他处理株分别增加了2.63%~13.36%和1.49%~12.30%;“燕科2号”在S2处理下最高,较其他处理分别增加了2.52%~15.20%、4.67%~21.21%。两燕麦茎秆基部第二节间长随播量增加而增加,S1较其他处理降低了10.86%~96.39%,第二节间粗、干重、充实度及抗折力随播量增加而减小,S1较其他处理分别增加了1.76%~32.81%、9.08%~125.89%、26.88%~292.64%、6.48%~129.70%。随着播量的增加,燕麦茎秆基部纤维素、可溶性糖、C/N、钾、硅含量逐渐降低,氮含量相反。与其他处理相比较,S1处理各化学组分含量分别增加了5.81%~74.10%、1.62%~24.34%、4.78%~55.41%、1.90%~107.78%、2.00%~17.37%,氮含量降低了2.95%~22.66%。倒伏率和倒伏级别在不同年份和品种间表现不同:2022年坝莜1号和燕科2号分别在S4~S5和S3~S5播量下发生倒伏,2023年两燕麦均发生倒伏,且倒伏率和倒伏分级随播量增加而增加。穗粒数和千粒重随播量增加而降低,但籽粒产量呈先升高后降低趋势,“坝莜1号”和“燕科2号”分别在150 kg hm^(-2)和120 kg hm^(-2)下籽粒产量最高。相关性分析表明,燕麦茎秆基部节间形态特征和化学组分含量显著影响茎秆基部抗折力,从而影响田间倒伏率和级别,可作为评价燕麦抗倒伏能力的关键指标。综合考虑抗倒伏能力与籽粒产量,坝莜1号最佳播量为150 kg hm^(-2),燕科2号最佳播量为120 kg hm^(-2)。

锈蚀箍筋约束混凝土压弯构件恢复力模型优化

箍筋锈蚀后受其约束的钢筋混凝土构件承载能力、强度、刚度都降低,塑性、延性变差,影响了构件的抗震性能。研究基于恢复力模型,考虑到箍筋锈蚀后约束混凝土应力-应变关系的改变,建立锈蚀箍筋约束混凝土压弯构件的退化三线型恢复力模型,并进行有限元分析。结果表明,按照构建的恢复力模型计算得到的骨架曲线、滞回曲线与试验结果较为接近,由此得出该模型有效。

热压工艺参数对TA2/CF/PEEK层板弯曲性能的影响

以TA2箔、碳纤维和PEEK材料体系为基础,探索钛箔-碳纤维布-PEEK薄片直接复合的热压法制备工艺。在对初始材料进行超声清洗除油、砂纸打磨等预处理后,手工铺层并放入自行设计的热压模具,基于不同温度(370和390℃)、压力(0.8、1.6和2.5 MPa)与保压时间(20和40 min)的热压法制备了TA2/CF/PEEK层板。利用三点弯曲实验方法探究了热压工艺参数对层板弯曲性能的影响。结果表明,较佳的热压工艺为:成形温度390℃、热压压力1.6 MPa、保压时间40 min且每侧铺设两片树脂薄膜。在此工艺下制备的TA2/CF/PEEK层板弯曲强度为681.68 MPa,弯曲模量为69.5 GPa。

SiCp粒径级配对55%SiCp/6061Al复合材料组织和性能的影响

采用真空热压法制备了55%SiCp/6061Al(55%为体积分数)复合材料,研究SiCp粒径级配对复合材料SiCp分布均匀度、致密度和抗弯强度的影响.研究结果表明:粒径级配复合材料组织致密、SiCp分布均匀且SiCp与6061Al合金基体界面结合强度高.双粒径(60+25)μm、质量比4∶1复合材料热处理后抗弯强度由395 MPa提高为548 MPa;三粒径级配为(120+60+25)μm、质量比为1∶1∶1的复合材料热处理前抗弯强度最高,为397 MPa;双粒径级配(106+25)μm、质量比4∶1的复合材料致密度>99.0%、均匀度>90.00%、热处理后抗弯强度>400MPa,具有优异的综合性能.

端板支承式多肋预制底板承载力试验研究

端板支承式多肋叠合板是一种主肋在端部收齐,端部主筋弯起,再焊以抗剪角钢部件后设计的新型叠合板,主要应用于现代物流仓储等承载力大、对空间要求较高的场景.为研究多肋预制底板在施工过程中的受力及破坏特征,设计了多肋预制底板的简支均布静载试验来分析预制底板的承载力、支座受力特征等.试验表明,随着荷载的增加,多肋混凝土预制底板的抗弯强度呈下降趋势,达到最大承载力时,支座位置出现断裂,此时角钢达到屈服应变;且该多肋混凝土预制底板的破坏特征与适筋梁破坏形式类似,构件的破坏过程均可分为3个阶段.最后,通过有限元模拟软件ABAQUS对角钢的变形状态以及在加载的4个阶段对不同部位的纵筋应变进行分析,将试验结果与ABAQUS模拟结果进行对比研究,得出有限元软件可较好模拟并呈现多肋混凝土预制底板破坏形态的结果,这一结果可为后续叠合板的研究提供一定的依据.

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。

V弯试验设备的自动化改造及效率提升

V弯试验是评估镀锌板性能的重要方法,但传统设备依靠人工操作,效率低且存在安全隐患。因此,文章提出一种V弯试验设备的自动化改造方案,通过集成机械手、优化夹具设计、升级控制系统等,实现装夹、弯曲、压平等全流程自动化。结果显示,改造后的设备单件效率提升30%~50%,角度重复精度改善64%~66%,在提质增效方面效果显著。

新赛道 新商机 新希望——变化中的网版与新赛道网版(十一)

现代的电子元器件组装技术,随着电子元器件的小型化、微型化,以及器件间距、开孔尺寸越来越小,模版厚度越来越薄。为了增加焊锡膏释放率,一般采用电铸钢版或加纳米涂层的激光钢版,同时还要选择印刷精度较高、全自动化智能化的锡膏印刷机(网版印刷机)。