Integrative calculation of the weld strength of plastics parts based on an interdiffusion model presented for laser transmission welding

与所考虑的焊接工艺无关，结合强度是焊接部件的机械设计的重要特征值，因为焊缝通常是薄弱点，因此是结构中的潜在失效位置。除了焊接材料的机械性能和热性能外，焊接强度的高低也主要取决于焊接参数。目前，在迭代过程中发现焊接区的设计，其中焊接参数以及焊接区的实际几何形状都根据经验指南进行调整。目前还没有基于物理模型的粘结强度预测，因此，在本项目中，应建立并验证通过激光透射焊接实例计算粘结强度的多尺度模拟。激光透射焊接是热塑性塑料焊接的一种重要方法，因此，所建立的方法可以用激光焊接进行验证。此外，还应核实所制定的一般方法的可转让性。除了输入焊接部件的热量低之外，使用该工艺的主要原因是焊接速度高以及焊缝中的结合强度高。焊缝中的结合强度是局部尺寸，其既依赖于位置又依赖于工艺参数。焊缝中的结合强度可以通过在分子水平上发生的相互扩散过程的模拟来确定。这种模拟应该基于爬行模型。因此，有必要对焊缝局部温度分布进行接近实际的计算。请愿人已经提出了一个适当的概念，应在本研究项目的过程中进一步加以发展。这一概念可用于计算互扩散本身以及由互扩散引起的焊缝结合强度分布。除了焊缝中的结合强度分布外，热致残余应力对焊接件的抗拉强度也有很大的影响。根据热计算，应进行热机械模拟，以确定焊缝中的残余应力分布。该分布取决于焊接参数。通过模拟确定结合强度以及残余应力分布，可以明显改善对焊接部件的结构机械行为的预测。

Independent of the considered welding process the bond strengths is an important characteristic value for the mechanical design of welded parts, because the weld seam often is a weak point and therefore a potential place of failure in a structure. In addition to the mechanical and thermal properties of the welded materials the height of the bond strength is crucially dependent on the welding parameters. Currently the design of the welding zone is found in an iterative process, where both the welding parameters as well as the actual geometry of the welding zone are adjusted following to empirical guidelines. At this time there is no prediction of the resulting bond strengths based on physical models.Therefore in this present project a multi scale simulation for the calculation of the bond strength through the example of laser transmission welding shall be established and validated. The laser transmission welding is an important method for the welding of thermoplastics, so that the established approach can be validated using the laser welding. In addition the transferability of the developed general approach shall be verified. Besides the low heat input into the welded parts the main reason for the use of this process is the high welding speed as well as the high bond strength in the weld. The bond strength in the weld seam is a local size, which is both position-dependent as well as process parameter-dependent. The bond strength in the weld seam can be determined through a simulation of the interdiffusion processes, which take place on a molecular level. This simulation should be based on a reptation model. Therefore a close to reality calculation of the local temperature distribution in the weld seam is necessary. A suitable concept has already been developed by the petitioner, which should be developed further in the course of this research project. This concept can be used to calculate the interdiffusion itself as well as the bond strength distribution in the weld seam caused by the interdiffusion. In addition to the distribution of the bond strength in the weld seam thermal induced residual stresses have a huge impact on the tensile strength of welded parts. Based on the thermally calculations thermo-mechanical simulations for the determination of the residual stress distribution in the weld seam shall be executed. This distribution is dependent on the welding parameters. Through a simulative determination of both the bond strength as well as the residual stress distribution a clearly improved prediction of the structural mechanical behaviour of welded parts is possible.