Analysis of melt flow in thick-walled heated element butt welded thermoplastic joints by FE simulation.

由于管道缠绕技术和挤压技术在管道建设中的进一步发展，可以生产直径超过3,000 mm、壁厚超过100 mm的管道。这些壁厚的半成品的连接导致需要重新评估当前的强度理论。正如研究和损坏案例所表明的那样，薄壁构件的有效关系不能通过相似定律转移到厚壁构件上。厚壁部件的显著更长的流动通道导致更高的流变流动速度和熔体接触时间。这与作为连接过程的结果的熔体的长剪切相结合，可能导致高度有序状态的形成，并因此导致边缘区域中的各向异性材料行为。因此，可以想象，除了熔体的最小流动速率的标准之外，还必须存在与最大时间相关剪切或熔体运动相结合的最大流动速率的标准。研究应用的技术/科学原因是，在安装情况下，在某些情况下，在短期负载下，厚壁部件焊缝上的焊缝断裂发生率增加。科学上的必要性是基于这样的事实，即在连接大壁厚的结构相关的剪切和应变流动速度包括更大的规模范围比已经在科学工作中研究到目前为止。结合更不均匀的冷却条件，这导致了以前不了解的焊接形态和残余应力状态。初步研究表明，厚壁部件中的熔体处于塑性状态的时间比以前假设的要长。目前，在德国DVS 2207-1、英国WIS 4-32-08或美国PPI-TR 33中未考虑这一点。在该项目中，通过建立连接阶段加热行为和熔体流动的数值模型，以及将影响与短期和长期强度联系起来，填补了对该过程理解的空白。这就需要对复杂的依赖关系进行实验阐述，例如对熔体层厚度和流速的依赖关系。该模拟有助于提高对工艺的理解，并使经验最小化。努力在两个申请人的合作下，这一研究思路具有很高的成功前景，并为深入理解厚壁构件的凝固和结晶过程做出了重大贡献，并扩展了对强度机制的理解。此外，通过对焊缝中的热/流变过程进行模拟描述，可以在强度、使用寿命和无残余应力焊缝成形方面实现最佳工艺设计。

Due to the further development of pipe winding technology and extrusion technology in pipeline construction, pipe dimensions of more than 3,000 mm diameter and wall thicknesses of more than 100 mm can be produced. The joining of semi-finished products of these wall thicknesses has led to a need to re-evaluate current strength theories. As investigations and cases of damage have shown, the effective relationships of thin-walled components cannot be transferred to thick-walled components by means of the law of similarity. The significantly longer flow channel of thick-walled components leads to higher rheological flow velocities and melt contact times. This, in conjunction with the long shear of the melt as a result of the joining process, possibly leads to the formation of a high state of order and thus to anisotropic material behavior in the edge regions. It is therefore conceivable that, in addition to the criterion of the minimum flow rate of the melts, there must also be a criterion of the maximum flow rate in conjunction with a maximum time-dependent shear or melt movement. The technical/scientific reason for the research application is the increased occurrence of weld fractures on weld seams in components with large wall thicknesses, in some cases with short-term loading in installation situations. The scientific necessity is based on the fact that the structurally relevant shear and strain flow velocities in the joining of large wall thicknesses encompass much larger scale ranges than have been investigated in scientific work to date. In conjunction with the more inhomogeneous cooling conditions, this leads to weld morphologies and residual stress states that were not previously understood. Preliminary investigations show that the melt in thick-walled components is in the plastic state for longer than previously assumed. Currently, this is not taken into account in German DVS 2207-1, English WIS 4-32-08 or American PPI-TR33. In the project, the gaps in the understanding of the process are to be closed by setting up numerical models for the heating behavior and the melt flow in the joining phase, as well as linking the influences to the short- and long-term strengths. This requires the experimental elaboration of the complex dependencies, e.g. on melt layer thickness and flow velocity. The simulation serves to improve the understanding of the process and to minimize the exp. effort. In the cooperation of the two applicants, this research idea has high prospects of success and makes a significant contribution to the in-depth understanding of the solidification and crystallization processes in thick-walled components and extends the understanding of the strength mechanisms. Furthermore, the simulative description of the thermal/rheological processes in the weld seam enables the optimal process design with regard to strength, service life and residual stress-free weld seam formation.