【作者】 朱援祥；

【导师】 胡伦骥；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2007， 博士

【摘要】 巨型水电站压力管道取消伸缩节是压力钢衬设计的发展趋势,采用厂坝间一段垫层钢衬来取代伸缩节,垫层钢衬上、下游端分别置于大坝和厂房混凝土中并随之变形。分析垫层钢衬在大坝变形和焊接变形共同作用下的组合应力,选择合理的接头形式,防止裂纹产生和蜗壳被拉动,探求取消伸缩节后焊接对垫层钢衬施工及运行的影响,具有重要的理论价值和工程意义。本文在广泛查阅国内外科技文献资料的基础上,分析了合拢缝接头形式和施工工艺,对大坝在常规荷载和温度荷载作用下的变形、大坝变形和焊接变形对垫层钢衬作用应力、强拘束条件下高强钢的抗裂性、拘束与锤击复合控制焊接变形影响、垫层钢衬合拢缝接头形式五个方面进行了系统深入的研究,包括大型结构实验研究、理论建模与数值仿真。本文的主要研究内容如下:选用先进器件研制了基于计算机控制的工业三坐标测量系统和数字成像收缩非接触测量系统,其测量精度满足巨型结构变形测量的要求。对接接头方式合拢缝焊接过程中各种应力和变形的观测表明:钢衬轴向收缩由预热膨胀造成的收缩和接头横向收缩组成;钢衬轴向收缩几乎全部转化为钢衬和蜗壳进水管的弹性变形,焊接带来的负面影响为钢衬轴向收缩太大,从而形成较大轴向拉应力;垫层钢衬受混凝土约束的情况下,合拢缝焊接拘束度不大。试验表明垫层钢衬用材610F钢裂纹敏感性较低,一般认为在强约束、恶劣环境条件下提高预热温度是提高大厚度焊接结构抗裂性的有效手段,但封闭结构的合拢缝焊接时提高预热温度是不恰当的;研究发现合拢焊时提高预热温度增加钢衬轴向收缩;采用变拘束长度实验研究表明在强拘束、低预热温度下锤击可提高焊缝的抗裂性。锤击使焊缝硬度有所提高,冲击韧性下降,提高预热温度可改善锤击后焊缝韧性和硬度。综合接头性能和钢衬轴向收缩研究成果提出了合拢焊采用双预热温度的设想。研究表明影响合拢缝轴向收缩的因素除工艺参数外,还与接头形式、预热温度和接头间隙有关。大型拘束框实验研究了合拢缝两种接头形式在锤击与拘束条件下收缩变形和拘束应力规律,锤击和拘束对套管式接头的横向收缩影响很小,对对接接头的横向收缩影响很大,拘束时锤击比不锤击更有效减少横向收缩;对接接头的拘束应力比套管式接头大;对接接头安装间隙越大,轴向收缩越大;套管接头安装间隙对轴向收缩无影响。探讨拘束与锤击复合作用减少大厚板横向收缩机理,试验研究表明在多层多道焊接过程中减少横向收缩变形需要较大的拘束应力,锤击既减少横向收缩又降低焊接过程的拘束应力。建立有限元模型计算拘束板和缝隙焊缝的拘束度,得到了结构尺寸与拘束度的关系;研究表明采用拘束板和缝隙焊缝联合拘束方式既控制厚度方向的不均匀收缩变形,又有效控制横向收缩变形量。改变边界冷却条件可改善钢衬轴向收缩。预热温度越高,反变形时钢衬和坡口的受力越大,降低预热温度和改善冷却条件有利于改善焊接时坡口的应力状况。简化巨型钢衬,建立平截面传热有限元模型,模拟厚板在拘束条件下多道焊时动态应力和残余应力大小及分布。模拟结果与实验测量的应力基本一致,验证了非线性有限元数值模拟法研究焊接残余应力和拘束应力的有效性。拘束条件下的应力模拟结果表明:拘束度越大拘束应力越大,最后焊接横向残余应力越大。预热温度越低,焊接残余应力越大,动态应力达到某一定值的时刻越早;模拟发现第一道横向应力动态变化为拉应力不断增加,直到最大值;而最后一道的横向应力的动态变化为在较短时间升到最大值,然后略有下降。采用接触力学理论分析锤击力与弹塑性材料塑性应变场的关系,建立圆柱和球头型锤击有限元模型,确定了锤击参数与消除残余应力的关系。锤击过程有限元模拟结果显示:锤击能量增加,产生的压应力增加,锤击接触区的变形程度增加,消除残余应力的效果明显;锤头尺寸增加,消除应力的有效范围增加,但焊缝的残余应力降低幅值下降。焊缝应力测试结果表明:逐层锤击处理后接头内部残余应力较好地被消除,并在焊缝表面及一定深度范围内构成双向压应力层。采用坝体、厂房及基础岩石所组成的整体模型进行三维有限元分析,计算在常规荷载和温度荷载作用下厂坝间垫层钢衬的位移,结果表明:结构相对位移随年时间的变化有周期性。采取子模型方式建立厂坝间垫层钢衬模型,计算垫层钢衬在各种荷载组合下的应力。研究表明合拢时机冬季要优于夏季,对接接头反变形加分段联合拘束方案最大组合应力最小。尽管套管接头合拢焊缝横向收缩小于对接接头,但采用有限元计算表明,套管接头应力集中系数高达11,而对接应力集中系数一般为2,用应力集中系数可经济地研究对接、套管两种接头形式的疲劳性能差异,研究各种参数对疲劳性能的影响,分析结果和试验结果均证明:对接方式的疲劳寿命远远高于套管式接头,且疲劳寿命对套接间隙较敏感。综合以上研究可以得到,合拢缝的性能和受力状态与焊接工艺和接头形式密切相关,通过采用分段联合拘束控制横向收缩、反变形,在双预热温度条件下辅以逐层锤击的工艺方案,可实现获得刚性拘束条件下无裂纹、小收缩、高质量对接接头形式的合拢焊接接头。利用自身拘束焊接时且有预应力的横行收缩规律需进一步的研究。更多还原

【Abstract】 The trend of penstock design is canceling telescopic joint of penstock in the giant hydropower station. A section of penstock with soft cushion layer is adopted as the replacement of telescopic joint, upper reach tip and lower reach tip of the penstock with soft cushion layer respectively lie in the concrete of the dam and plant, and distorts with the concrete. Stress-strain field of the penstock with soft cushion layer is analyzed under dam displacement and welding deformation. Appropriate joint type is chosen to prevent the appearance of crack and the shift of spiral case. Research was done to discover the effects of welding after canceling telescopic joint upon the construction and running of penstock with soft cushion layer. Therefore, the paper has great importance both in academy and engineering.Based on a great number of references at home and abroad, the paper analyzes various welding procedure and joint type of the closure weld. Further research covers systematically the following aspects, such as dam displacement under routine load and temperature load, stress of penstock with soft cushion layer caused by dam deformation and welding deformation, crack resistance of highly intensive steel under high restraint, deformation controlled by restraint and peen, performance of two kinds of closure welding joints, which includes welding tests, theory models and numerical simulation study. The main work and research content is as follows:Three coordinate measuring system and digital images non-contact measuring system based on computer are developed with advance devices. Their measuring accuracy are satisfied with deformation requirement. Stresses and deformations measurement in the welding of the butt closure joint show that axial contraction of penstock consists of transversal contraction and the contraction because of preheat. Axial contraction of penstock transfers elastic strain of penstock . Negative effect caused by butt joint type is that axial contraction of penstock and axial stress is too large . Although penstock is bond by concrete, restraint intensity of closure weld is low.610F steel has good crack resistance performance by means of many tests. It is general thought that raising the preheat temperature can effectively prevent the appearances of crack in thick closure weld under high restraint and bad environment condition. Research shows that it is unapt to raise the preheat temperature to 100℃in closure weld, raising the preheat temperature is unbeneficial to reducing axial contraction. Peening can prevent the appearance of crack under lower preheat temperature and high restraint condition by flexible restraint length experiment; Peening was proved to affect the performance of the joint by raising the hardness of the weld and depressing the striking-tenacity; Raising the preheating temperature was proved to improve the hardness tenacity of weld after peening. According to performance of the joint and axial contraction, a method of adapting double preheating temperature is suggested.Factors affecting axial contraction are the type of joint, preheat temperature and root opening except for welding procedure parameters. The contraction rule of two joint type has been studied within the big restrain frame, the rules of the transverse contraction and restraint stress of different butt joint root opening and lapped joint root gap in peening and restraint are explored. Research shows that peening and Restraint have little effect on transverse contraction of lapped joint, but have great effect on that of butt joint; when in restraint peening have more effect on reducing transverse contraction than without peening in butt joint; the transverse contraction increases with the increasing of root opening of the butt joint, so the strain-stress is greater; the restraint stress of butt joint is greater than that of lapped joint. It is probed that the mechanism of reducing transverse contraction with the compound effect of restraint and peening . Research shows that reducing transverse contraction need big tension stress in welding process, peening can reduce contraction and tension stress.Finite element models is built up to calculate the restraint intensity of the restraint plate and slit-type weld, and the rule of restraint intensity is known. The method of combining restraint by restraint plate and slit-type weld was suggested. Combining restraint experiment shows that it can control transverse contraction ,and can also control the thick asymmetry contraction. It is analyzed that free and compulsive boundary cooling affects temperature field of penstock, anti-deformation in huge penstock is also studied, and the loading of penstock and root face under anti-deformation are analyzed, and the method of segmented combining restraint controlling the transverse contraction of huge penstock is put forward.With huge penstock simplified, non-liner finite element models and heat source models is set up, the transverse contraction and restraint stress of multi-pass weld is simulated and analyzed under restraint condition. Instantaneous stress and residual stress of multi-pass weld is simulated and analyzed under restraint condition.. The real measurement of the residual stress are basically agreement with the numerical results distribution patterns of using the two-dimensional models comparatively, The validity of using non-liner finite element numerical simulation to investigate the welding residual stress is verified. The stress results under restrain show that the bigger the restraint intensity is, the greater the restrain stress is; the transverse stress is great under restrain. According to the result of the stress simulation, the lower the preheating temperature is ,the greater the residual stress is, and the time that the dynamic stress reaches a fixed value become earlier; the welding residual transverse stress increases with the restraint intensity. Accord to the simulation, the dynamic stress of first pass is constantly increasing until weld totally cooled and the dynamic stress of last pass is raising to maximum in short time, then slightly decline.Relationship between peen force and plastic deformation of elastic-plastic materials is analyzed by contact mechanics. Column and globe finite element models are set up to simulate that peen produces stress and deformation. Relationship between magnitude of residual compressive stress field and peen parameters, and distribution of residual stress after peen is studied. The magnitude of peen indentation is correlated with the magnitude of hammer and energy of peen. Residual stress and transverse contraction affected by peen and restraint is studied. Lager magnitude of peen is, effective field of stress reduced increase ,but value of stress depressed lower. Research shows that residual stress in inner weld can be relieved by way of bead by bead peening .The models that consists of dam/workshop/bedrock is analyzed as three dimension finite element integral models, and displacement of penstock with soft cushion layer among dams is calculated under routine load and temperature load. It shows that relatively displacement changes with annual periodicity. Sub-models is set up to penstock with soft cushion layer, and stress of the penstock with soft cushion layer is calculated under various loads combination. Researches show that closure in winter is better than in summer, and the case of butt joint anti-deformation with segment combining restraint has the least combined stress.In despite of axial contraction of lapped joint is less than butt joint `s, models of stress concentration factor for lapped joint and butt joint is set up and are calculated, lapped joint is 12 and butt joint is 2. Fatigue performance difference between the lapped joint and butt joint is economically analyzed by means of stress concentration factor, and fatigue performance of lapped joint is testly researched after peened/welded and in different clearance of weld. The result of the calculate and experiment shows that the fatigue life of the butt joint is much longer than that of lapped joint; fatigue performance of the lapped joint is sensitive to gap of lap. Peening can improve fatigue performance of joints.In a word , the properties and stress of closure weld is relevant to welding procedure and joint type . By adopting anti-deformation and segmented restraint and peening, type of closure weld joint is butt joint that there is no crack, small contraction and high quality is got in the case of double preheat temperature and high restrain. Transverse contraction with pre-stress is necessary in the future.更多还原