连铸钢板坯凝固壳横截面变形与内部裂纹的关系

对实际观察到的连铸钢板坯拉出结晶器时的横截面形状与最终形成的内部裂纹进行了理论分析 ,找到了凝固壳横截面形状变化与内部裂纹的形成及种类之间的因果关系及规律性 ,为预防连铸钢板坯内部裂纹提供了理论依据。同时对YB/T 4 0 0 3- 1991标准中的有关问题进行了讨论 。

考虑横截面变形的合成桥面桁梁的扭转计算方法

为了分析横向联结系刚度比较弱的合成桥面桁梁在扭转荷载作用下的响应,文章根据等效前后变形相等的原则将空间上离散的桁梁转化为空间上连续分布的薄壁箱梁。在乌曼斯基闭口截面薄壁杆件扭转理论的基础上,考虑横截面的剪切变形,推导变形响应公式,并以杨泗港长江大桥的加劲梁作为实例,采用ANSYS建立精细的板—梁混合单元有限元模型进行求解。与解析法的计算结果进行了对比,解析法具有较好的计算精度,求解效率高。

基于贝叶斯网络的盾构隧道横截面变形预测方法

盾构隧道横截面变形是影响隧道安全运营的重要因素,目前尚缺乏合理考虑多源不确定性的横截面变形预测方法,同时也忽视了钢筋锈蚀对其变形的影响。首先,根据钢筋腐蚀影响建立了管片刚度退化模型;然后,采用均质圆环法建立了基于贝叶斯网络的隧道管片横截面变形预测模型;最后,利用监测数据及马尔科夫链蒙特卡罗模拟方法对模型进行更新和验证。研究结果表明,经过贝叶斯网络模型更新后,模型预测的结果与监测值更为接近,其中2013年的模型后验预测结果与实测值完全一致,2015年的模型预测值与实测值的误差仅为1.6%。而贝叶斯网络更新前,2013年及2015年的预测误差分别为21.1%及21.9%,可见当融入从实测数据得到的信息时,贝叶斯网络的预测结果与实际监测数据更为符合,提高了模型预测精度。

环形件螺旋成形截面形状尺寸分析与优化

为了研究环形件毛坯在螺旋成形时横截面的变形规律,结合某工厂的实际生产工艺,建立了环形件毛坯螺旋成形的三维弹塑性非线性有限元模型。基于该模型得到的仿真结果与现场测量结果基本一致,通过对仿真结果分析得到了成形过程中环形件毛坯横截面形状尺寸变化规律。分析表明：横截面会由矩形变为近似等腰梯形（内缘宽度增加,外缘宽度减小,长度减小）;内、外缘宽度变化量与宽长比呈线性函数关系,长度变化量与宽长比呈二次函数关系。在此基础上优化了环形件毛坯横截面的尺寸参数。结果表明,优化后的工艺大大改善了环形件毛坯横截面的成形质量。

不同地质条件下盾构隧道受力变形特性研究

针对天津滨海地区盾构隧道衬砌结构,采用大型有限元软件ABAQUS建立三维地层-结构模型,考虑隧道管片材料非线性特征,利用混凝土材料的塑性损伤本构模型,研究地层和隧道结构相互作用后隧道管片结构内力分布与变形特征,以及隧道管片受拉和受压损伤情况。最后,研究不同地质条件和超载作用对隧道管片结构的影响。数值分析结果表明:隧道管环横截面变形表现为水平向外扩张、竖向压缩的特点,呈现'横鸭蛋'形状;隧道管环拱顶轴压力最小,拱腰轴压力最大;管片外侧受拉时最大弯矩位于拱腰,内侧受拉时最大弯矩位于拱顶;受拉和受压损伤分布均集中在拱底附近,其中管环受压损伤面积比受拉损伤面积大;地质条件越好,变形随轴线方向变化越均匀,轴力和弯矩、隧道结构竖向位移、横截面收敛变形,以及管环损伤面积与损伤程度越小。研究结果以期为进一步探讨隧道衬砌结构的变形性能与损伤分布提供参考。

管材弯曲成形的国内外研究现状及发展趋势

总结了近年来国内外学者和工程技术人员从理论分析、实验研究、有限元数值模拟方面着手对管材弯曲成形开展的大量研究工作和取得的研究进展 ,包括管材弯曲过程中的起皱和破裂分析、横截面变形以及卸载后的回弹分析和预测等 ,并阐述了管材弯曲成形研究的发展趋势。

Deformation behaviors of 21-6-9 stainless steel tube numerical control bending under different friction conditions

For contact dominated numerical control(NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional(3D) elastic-plastic finite element(FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die-tube reduces the wrinkling wave ratio η and cross section deformation degree ΔD and increases the wall thinning degree Δt. The large friction of mandrel-tube causes large η, Δt and ΔD, and the onset of wrinkling near clamp die. The large friction of pressure die-tube reduces Δt and ΔD, and the friction on this interface has little effect on η. The large friction of bending die-tube reduces η and ΔD, and the friction on this interface has little effect on Δt. The reasonable friction coefficients on wiper die-tube, mandrel-tube, pressure die-tube and bending die-tube of 21-6-9(0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05-0.15, 0.05-0.15, 0.25-0.35 and 0.25-0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.

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.

5S-111GP吸油管生产工艺的改进

5S-111GP变速器吸油管进行弯曲加工产生截面变形的问题，一直采用灌铅限制变形的工艺方法解决，该工艺除需耗费大量氧气、乙炔外，而且效率低，劳动强度大。并且铅有毒，污染大，严重影响工人的身体健康，已不能满足工厂现代化生产的需要。现对吸油管弯曲加工工艺进行了改进，改进后的弯管工艺，不用给管子灌铅，而是采用空管弯曲，然后用模具校正的方法，解决了管子的横截面变形问题。而且生产效率高，耗材小，无污染，取得了较好的综合效益。