Development of Coupled Thermal, Mechanical, and Material Transport Models of the Friction Stir Welding Process

搅拌摩擦焊接过程的热、机械和材料传输耦合模型的开发

• 批准号: 9978611
• 负责人: Anthony Reynolds
• 金额: $ 33.96万
• 依托单位: University of South Carolina at Columbia
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-10-15 至 2003-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9978611&HistoricalAwards=false
• 关键词: Development; Coupled; Thermal; Mechanical; Material

Optimization of and broadening of applications for the friction stir welding (FSW) process will be greatly accelerated by the development of flexible and accurate process models which can be used to predict the effects of varying FSW process parameters on porosity, mechanical properties of the weld, and, ultimately, final weld microstructure. The intent of the research effort described herein is to take a large step down the path toward development of such models. A hierarchical approach is proposed in which first, a fluid mechanics based model describing the thermal history of material in the weld and the material transport in the weld is used to enhance the understanding of the physics of friction stir welding. Next, using the knowledge and experience obtained from development of the CFD model, a solid mechanics model will be developed. Both models will be developed in combination with a comprehensive, experimental characterization of the friction stir welding process. At every step of the model development, the experimental program will verify assumptions and results and conversely, modeling results will suggest critical experiments to be performed. Initial modeling attempts will be as simple as is consonant with accurately capturing the physical phenomena. As understanding of the process increases, so will the complexity, the fidelity, and utility of the models which follow. The ultimate goal is to create a solid mechanics based model which provides a complete description of the thermal, stress/strain, time history of all the material in a friction stir weld. Experimental tasks to be undertaken include: (1) Temperature measurement during the friction stir welding process. A digital IR camera will measure surface temperatures while embedded thermocouples measure subsurface temperatures. (2) Measurement of energy input to the weld by the friction stir-welding machine (via conversion of electrical energy to mechanical). (3) Determination of material transport in the weld by mapping the movement of marker materials via destructive post weld examination. (4) Post-weld microstructural evaluation. (5) Mechanical testing of weldments and fractographic examination. Each of these experimental tasks will either help to establish proper boundary conditions for the proposed models or will aid in verification of the models or both. Details of the experimental program may be amended as needed to fully support the model development. Critical tasks for the modeling efforts include: (1) Determination of an appropriate model geometry that captures the essence of the physical process without unduly complicating the analysis. (2) Deriving appropriate thermal and mechanical boundary conditions from experimental data that are compatible with the chosen model geometry. (3) Selection of an appropriate material constitutive law for characterizing the behavior of the material in the weld zone. (4) Incorporating the constitutive law into computational fluid/therma/solid analysis packages chosen for the model.If all of the pieces outlined above come together, the result will be a predictive model which can be used to guide friction stir welding process parameter optimization and give guidance in the development of process modifications which can broaden the application of FSW.

通过开发灵活而准确的工艺模型，可以预测不同的搅拌摩擦焊工艺参数对气孔、焊缝力学性能以及最终焊缝组织的影响，将极大地促进搅拌摩擦焊工艺的优化和应用的扩大。这里描述的研究工作的目的是在开发这种模型的道路上迈出一大步。提出了一种分层的方法，首先采用基于流体力学的模型来描述焊缝中材料的热历史和焊缝中的材料传输，以增强对搅拌摩擦焊物理过程的理解。接下来，利用开发CFD模型所获得的知识和经验，将开发出固体力学模型。这两个模型将与搅拌摩擦焊接过程的全面、实验特征相结合开发。在模型开发的每一步，实验程序将验证假设和结果，反之，建模结果将建议执行关键实验。初始建模尝试将与准确捕捉物理现象一样简单。随着对这一过程的理解的增加，随后的模型的复杂性、保真度和实用性也会增加。最终目标是创建一个基于固体力学的模型，该模型提供搅拌摩擦焊中所有材料的热、应力/应变和时间历史的完整描述。将开展的实验工作包括：(1)搅拌摩擦焊接过程中的温度测量。数码红外相机将测量表面温度，而嵌入式热电偶将测量地下温度。(2)通过搅拌摩擦焊机测量输入到焊缝的能量(通过将电能转换为机械)。(3)通过破坏性焊后检查绘制标记材料的运动图，确定材料在焊缝中的传输。(4)焊后组织评价。(5)焊件力学性能试验和断口检验。这些实验任务中的每一项都将有助于为所提议的模型建立适当的边界条件，或者将有助于模型的验证，或者两者兼而有之。实验计划的细节可以根据需要进行修改，以完全支持模型的开发。建模工作的关键任务包括：(1)确定适当的模型几何形状，在不过度复杂化分析的情况下捕捉物理过程的本质。(2)从实验数据中推导出与所选模型几何形状相容的适当的热和力学边界条件。(3)选择合适的材料本构关系来表征材料在焊缝区的行为。(4)将本构关系引入到计算流体/热/固体分析程序包中，将上述各部分综合起来，得到一个预测模型，该模型可用于指导搅拌摩擦焊工艺参数优化，并指导工艺改进，从而扩大搅拌摩擦焊的应用范围。