Computational weld mechanics

提出的研究是为了解决焊接结构的设计问题，即我们不再假设设计是给定的。相反，我们假设给出了在役载荷和没有指定焊接接头的初步设计。分析应预测所有焊缝的最佳位置和尺寸、焊接工艺、焊接工艺、夹具设计和夹具工艺。对于一类重要的焊接结构，其主要失效模式是疲劳。给定一个结构（如大型拖拉机）的零件几何形状的CAD文件，每个零件的材料类型和相关的使用载荷，我们提出以下策略：自动网格化所有零件。然后，用户应用服务中的负载和约束。然后应用相邻部件之间的约束自动执行线性静态（或动态）三维有限元分析。此外，潜在的焊接路径自动识别邻接部分之间。根据每个潜在焊接路径上单位长度的约束力，将计算出试焊尺寸和焊接程序。接下来，结构被重新网格化，以包括用填充金属提出的焊接接头。然后对焊接结构中的焊缝进行热应力分析，计算其瞬态温度、组织演变、残余应力和焊接变形。焊接池的大小和形状将使用Ohji-Sudnik焊接池模型进行计算。微观结构的演变将使用蒙特卡罗算法和计算热力学建模。应力分析将包括单晶热粘塑性分析演变的微观结构。在此基础上，重新进行了带约束的线性或非线性塑性有限元分析。在这些焊缝中，计算了由于使用载荷和焊缝中残余应力引起的三维应力分布，特别是在焊接趾等高风险特征中。根据焊缝的应力分布和在役载荷循环，估算焊缝的疲劳寿命。如果疲劳寿命太长，可以减小焊缝尺寸。如果疲劳寿命太短，则必须对焊缝进行强化或重新设计。这个过程将自动完成。

The proposed research is to solve for the design of welded structures, i.e., we no longer assume the design is given. Instead we assume that we are given in-service loads and a preliminary design with no weld joints specified. The analysis should predict the optimum position and size of all weld joints, weld procedures, weld schedules, fixture design and fixture schedule.  For an important class of welded structures, the primary failure mode is fatigue.  Given CAD files for the geometry of the parts for a structure such as a large tractor, the material type for each part and the associated in-service loads, we propose the following strategy:  Mesh all parts automatically. Then the user applies in-service loads and constraints. Then with constraints between adjacent parts applied automatically perform a linear static (or dynamic) 3D FEM analysis.   Also potential weld paths are identified automatically by adjacency between parts.  From the constraint force per unit length along each potential weld path, a trial weld size and weld procedure will be computed.  Next the structure is remeshed to include the proposed weld joints with filler metal.  Then a thermal stress analysis of the weld joints in the welded structure is done to compute the transient temperatures, microstructure evolution, residual stress and distortion due to welding.  The weld pool size and shape will be computed using an Ohji-Sudnik weld pool model. Microstructure evolution will be modelled using Monte Carlo algorithms and computational thermodynamics. The stress analysis will include single crystal thermo-visco-plastic analysis of the evolving microstructure.  Then either a linear or a non-linear plastic FEM analysis with constraints is redone with the new weld joints.  In these weld joints, the 3D stress distribution due to in-service loads and residual stress in the weld joints and particularly in high risk features such as the weld toe are computed.  From the stress distribution and in-service load cycles, the fatigue life of the weld is estimated. If the fatigue life is too long, the weld size can be reduced. If the fatigue life is too short, the weld must be strengthened or redesigned. This process will be done automatically.