单道次三维变截面辊弯成形装备运动学研究

为了开发三维变截面辊弯成形装备的控制算法,分析了三维变截面辊弯成形的基本原理和运动形式,给出了单道次三维变截面成形装备的机构简图,基于D-H方法建立了该机构的正运动学方程,并结合成形轨迹曲线求解了各关节的位置逆解方程.然后,对某型轿车的B柱加强板零件进行了数字实例仿真,获得了相应的各关节的位置曲线,仿真结果表明,本文所提出的运动学分析方法有效、可行,为后续三维变截面成形装备的控制系统开发提供理论依据.

浅析三维变截面钢主塔施工质量控制

结合柳州市双拥大桥钢主塔施工的质量控制经验,简单阐述施工的节段定位及环缝焊接的控制方式。

三维变截面A形钢箱主塔安装测量定位技术

本文介绍了柳州双拥大桥三维变截面A形钢箱主塔安装定位技术,主塔定位使用三维坐标法测量,最大限度的通过坐标修正设置预偏量和误差反量来解决节段定位中遇到的较大偏差、变形,通过精度验算确定方法的可行性.

变截面三维编织复合材料的净形制备及弯曲性能

介绍变截面三维编织预型件的减纱净形制备工艺,通过实验观察与理论建模相结合的方法,分析减纱对预型件细观结构的影响,对比整列减纱、行单元减纱与切削复合材料在变截面区域的弯曲性能。结果表明表面与内部减纱单元是减纱时的基本单位,保证编织规律不变是减纱工艺的基本原则;表面或内部单元减掉后分别会形成两组特殊的纱线轨迹,其中一组纱线的长度与编织角大小较不减纱时增大,而另一组纱线只改变编织角的方向;行单元减纱与整列减纱复合材料的弯曲性能均明显优于切削试件,且行单元减纱试件的弯曲性能比整列减纱试件略高。

减纱工艺对变截面三维编织复合材料弯曲性能的影响

减纱工艺可以实现变截面三维编织复合材料的净形制备,通过对不同减纱方案制备的单次减纱试件和具有不同减纱截面间距的两次减纱试件进行三点弯曲实验,研究了减纱工艺参数对变截面三维编织复合材料弯曲性能和破坏形态的影响。结果表明,行单元减纱试件的弯曲性能略高于整列减纱试件而显著优于切削试件,纱线断裂是减纱试件的主要失效机制,切削试件则以基体和界面损伤为主。两减纱截面间隔1-3个花节时,试件主要在第2个减纱截面附近发生破坏,而间隔4或5个花节时,弯曲破坏集中在两减纱截面的中间区域。随着减纱截面间距由1花节递增至4花节,试件的弯曲性能逐渐提高,而间距为5花节的试件则与间距4花节试件的弯曲性能基本相同。

变截面三维编织预型件的净形制备工艺与细观结构

介绍变截面三维编织预型件的减纱与添纱净形制备工艺,以行单元减纱预型件为代表,观察截面缩减区域的外观形态,并建立表面与内部减纱单元的几何模型,最后讨论了减纱对纱线交织规律的影响。结果表明,保证减纱或添纱后纱线的编织规律不变是净形编织工艺应遵循的原则,预型件在减纱区域呈现平滑的梯形过渡,表面与内部减纱单元中纱线的编织角增大,长度增加,且减纱截面处的纱线交织点位于减纱前两相邻交织点的中心。

减纱工艺对三维编织矩形截面预制件的细观结构的影响

对通过减纱工艺形成的变截面三维编织预制件的细观结构进行了研究,并采用拓扑方法进行理论分析,得到了减纱后通过减纱截面的纱线运动走向和变化规律,从而为更精确的制定异型三维编织预制件的编织工艺打下了基础.

用于三维编织可控增减纱的携纱器设计

为减少三维编织过程中的人工参与,提高三维编织的自动化程度进而提高编织效率,通过介绍三维变截面预制件现有的行列单元增减纱工艺和整行、整列增减纱工艺以及自身可实现增减纱的携纱器设备,比较现有变截面编织工艺和设备的优缺点,在此基础上提出了一种可利用液氮的物理特性并结合刀片的剪切作用通过无线控制来实现自动增减纱的新型携纱器。详述了这种新型携纱器各功能模块的作用,并结合设计图描述了其增减纱的工作过程,举例说明了利用这种新型携纱器进行的编织工艺,认为利用这种新型携纱器,再结合编织工艺可大幅提高变截面编织的灵活性,具有较好的应用前景。

变截面三维编织复合材料减纱工艺与弯曲性能

探讨了变截面三维编织预制件减纱净成型原理,结合图像观测与拓扑分析方法表征减纱区域细观结构,对比减纱变截面与切削变截面复合材料截面缩减区域及相应等截面复合材料的弯曲力学性能,并分析两种变截面试件在破坏模式上的异同。结果表明:减纱应遵循的原则是保证具有连续可编织性,减纱预制件在截面缩减区域呈现平滑的梯形过渡,其弯曲模量与强度显著高于切削变截面试件而略低于等截面试件,且表现为以纱线断裂为主、包括基体开裂和纤维抽拔等模式的复合型破坏。

Cross-sectional distortion behaviors of thin-walled rectangular tube in rotary-draw bending process

The cross-sectional distortion usually appears during rotary-draw bending process of thin-walled rectangular tube with small bending radius.To study the cross-sectional distortion of the tube,a three-dimensional finite-element model of the process was developed based on ABAQUS/Explicit code and its reliability was validated by experiment.Then,the cross-sectional distortion behaviors of the tube were investigated.The results show that a zone of larger circumferential stress appears on the tube when bending angle reaches 30°.And in the larger circumferential stress zone,the sagging phenomenon is produced obviously.The maximum cross-sectional distortion is located in the larger circumferential stress zone and the angle between the plane of maximum cross-sectional distortion and the bending reference plane is about 50°.The position of the maximum cross-sectional distortion keeps almost unchanged with the variation of the clearances between dies and tube.

The development of real time data driving multi-axis linkage and synergic movement control system of 3D variable cross-section roll forming machine

The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential synergic movement of the ganged roller group is used to complete the metal sheet forming according to the shape of the complicated and variable forming part data. The control system should meet the demands of quick response to the test requirements of the product part. A new kind of real time data driving multi-axis linkage and synergic movement control strategy of 3D roll forming is put forward in the paper. In the new control strategy, the forming data are automatically generated according to the shape of the parts, and the multi-axis linkage movement together with cooperative motion among the six stands of the 3D roll forming machine is driven by the real-time information, and the control nodes are also driven by the forming data. The new control strategy is applied to a 48 axis 3D roll forming machine developed by our research center, and the control servo period is less than 10ms. A forming experiment of variable cross section part is carried out, and the forming preci- sion is better than ＋ 0.5mm by the control strategy. The result of the experiment proves that the control strategy has significant potentiality for the development of 3D roll forming production line with large scale, multi-axis ganged and svner^ic movement

Tensile Characteristics Evaluation of Corroded Reinforcing Bars Extracted from Actual Structures

The analysis used simple finite elements is performed to simulate the tensile behavior of corroded reinforcing bars extracted from three actual concrete structures. The cross-sectional area of the elements is set to have the actual distribution measured by 3D laser scanner system. The variable factor in the analysis is the length of the elements. The analysis results show that the length of the elements has a major influence on the deformation capacity after yielding. The calculated stress-strain curves, obtained using the elements with a length that is 2 times the bar diameter, are in good agreement with the tensile test results. The calculated stress-strain curves are modeled using a bi-linear model to facilitate the FEA （finite element analysis） of an overall concrete structure. From the analysis results, both the tensile and yield strengths decrease in proportion to the reduction of the minimum cross-sectional area of corroded bars. The ultimate strain has a remarkable decrement as the reduction of the minimum cross-sectional area. Formulas for determining these values are proposed as a function of the decrement ratio of the minimum cross-sectional area of a corroded bar.

灵活触变挤压A356铝合金的数值模拟

提出了一种新型的三维变截面复杂零件的近净成形方法——灵活触变挤压。运用有限元模拟软件DEFORM-3D对其成形过程进行了数值模拟,得到了成形过程中坯料的流动速度场、等效应变场和挤压杆的压力-行程曲线,分析了坯料在成形过程中的流动规律、应变分布状况和挤压力随挤压行程的变化情况。模拟结果表明,采用灵活触变挤压成形三维变截面复杂零件是可行的。灵活触变挤压与普通挤压相比,在零件成形质量方面具有明显的优势。