【作者】 曾志；

【导师】 王立君；

【作者基本信息】 天津大学 ， 材料加工工程， 2009， 博士

【摘要】 铝合金焊接结构广泛应用于船舶、航空航天等工程领域。由于其热膨胀系数大、弹性模量小,在焊接过程中不可避免地产生较大的残余应力与变形。因此,对铝合金焊接结构的焊后残余应力与变形进行研究,具有重要的理论意义和现实价值。本文采用部分与整体的方法,分别采用热弹塑性有限元法和固有应变法对5A06铝合金加筋圈体和筒形结构的焊接残余应力与变形进行了数值分析。在红外实时测温的基础上,对熔化极惰性气体保护电弧焊(MIG)角焊缝间断焊的温度场进行了研究。此外,间断焊过程中存在已焊焊缝的预热作用和后续焊缝的再加热作用。根据MIG焊熔池热流密度的分布及间断焊热循环的特点,提出了结合电弧热流双高斯分布和过热熔滴双椭球形分布的复合型热源分布模式,并采用优化设计的方法确定了间断焊过程中瞬态的热源形状参数。经实验验证,该热源模型可有效地对角焊缝间断焊温度场进行数值模拟。采用间接耦合法深入研究了间断焊过程中的动态焊接应力场的演变及分布规律,对铝合金加筋圈体结构的焊接过程进行了数值分析。加筋结构的角变形是由焊件厚度方向的温度梯度和焊缝的横向收缩两方面决定的,且焊接顺序和焊缝长度对焊接残余应力与变形也有很大的影响。基于角焊缝间断焊热弹塑性分析,并综合考虑了焊接工艺及焊件尺寸对多层多道V型坡口对接焊缝的影响,采用固有应变法对5A06铝合金筒形结构的焊接变形进行了数值计算。结果表明,筒体结构出现了波浪变形,无筋板支撑部分下塌较严重,并对可能发生的失稳变形进行了预先估计和分析。通过加强板焊接前后结构压下载荷的测定实验验证,表明了固有应变法在复杂焊接结构的数值模拟中具有很高的效率并能保证一定的精度。最后,为保证铝合金加筋筒形结构的尺寸精度,对既定加工工序作了一定改进,在间断角焊后对其进行整体退火消应处理,利用有限元方法定量分析了退火温度、保温时间和冷却速度等因素对消应效果的影响,制定了相应的退火规范。研究结果对此类筋板加强结构的焊接生产及热处理工艺的制定具有重要的工艺技术指导作用。更多还原

【Abstract】 The aluminum alloy welding structure has been widely applied in many fields, such as ship engineering, aerospace engineering and so on. Since its large thermal expansion coefficient and small elastic modulus, great welding residual stress and deformation are difficult to avoid in the engineering. Thus, it is important to investigate the welding deformation and residual stress of aluminum alloy welding structure, which would has significant theory meaning and engineering value. The welding residual stress and deformation of 5A06 aluminum alloy reinforced circle and cylinder structure were analyzed by the thermal-elastic-plastic finite element method and inherent strain method respectively in this paper.Based on the infrared thermal imaging results, the temperature distribution of fillet welds during MIG discontinuous welding was researched. There are preheating effect from the welded seam and reheating effect from the sequent weld in the discontinuous welding. According to the distribution of heat flux density in the MIG welding pool and the character of discontinuous welding thermal cycle, a combined heat source model was developed which combining the double Gaussian heat distribution of arc and the double ellipsoidal distribution of over thermal droplet.Subsequently the transient parameters of double ellipsoidal heat source were confirmed with optimization design method. It is found that the combined heat source model produce more accurate numerical simulation result during the discontinuous welding.The transient distribution of welding stress was analyzed by indirect coupling method on the basis of the temperature field in the discontinuous welding, and the welding process of 5A06 aluminum alloy reinforced circle structure was simulated numerically. The angle deformation of the reinforced structure is decided by the temperature gradient of the structure thickness and the weld transverse contraction. The welding sequence and the weld length also have great effects on the welding residual stress and deformation.Based upon the thermal-elastic-plastic analysis of the discontinuous welding, the welding residual stress and deformation of 5A06 aluminum alloy reinforced cylinder structure was researched by inherent strain method, which also considering the effects of welding technology and weldment’s size on the multi-passes V-type butt weld. The cylinder structure represented wave propagation, great stay was appeared where without reinforce plate, and it predicted the possible buckling deformation. Compared to the experimental results of the welding depression load and strain, the inherent strain method has high efficiency and can ensure definite precision in the numerical simulation of the complex welding structure. In the final, in order to ensure the structure’s machining accuracy, the whole structure was annealinged after the discontinuous welding. The effects of annealing temperature, holding time, and cooling rate on the stress elimination were analyzed by finite element method, which constituting the corresponding annealing criterion and improving the manufacturing procedure. The research result could direct the welding production of the reinforced welding structure.更多还原