基于缺口应力的超声冲击处理焊接钢节点疲劳寿命提高机理及预测方法研究

Cracks are easily to occur at the welded joint of steel structures under fatigue loading. They can cause great economic lost and threat the safety of the entire structure. Ultrasonic peening treatment can enhance significantly the fatigue life of the welded joints, but its mechanism has not been understood very well, and also, there is a lack of accurate fatigue life prediction method for the ultrasonic peened welded joints. This project aims to propose a new notch stress model of the weld toe via the combination of experimental tests and finite element analyses. The proposed model will build a direct connection between the fatigue life of the ultrasonic peened welded joint and the changes of the weld toe local geometry, local residual stress distribution and refinement of the local micro-structural grains, and thus, reveal the mechanism of the fatigue life enhancement using ultrasonic peening treatment. Subsequently, the effective notch stress of the ultrasonic peened joints will be calculated using finite element analyses, Finally, the fatigue design curve will be regressed combing the effective notch stress and the fatigue test data. This project will provide an accurate fatigue life prediction method for the ultrasonic peened welded joints based on the effective notch stress. The proposed prediction method will help design engineers predicting quickly and efficiently the fatigue life of ultrasonic peened welded joints, and thus, promote the application of ultrasonic peening treatment in engineering practice to ensure the safety of the entire structure.

焊接钢结构在疲劳荷载作用下焊接部位易出现裂纹，会造成极大的经济损失并威胁到结构的整体安全。超声冲击处理能够显著的提高焊接节点的疲劳寿命，然而目前其提高焊接节点疲劳寿命的机理尚未彻底明确，且缺乏能够准确预测超声冲击处理焊接节点疲劳寿命的方法。本项目拟通过试验测试和有限元分析结合的方法，建立新的焊趾部位缺口应力模型，将超声冲击处理造成的焊趾局部几何形状变化、局部应力场变化和局部晶粒细化与焊接节点的疲劳寿命建立直接联系，从而揭示超声冲击处理提高焊接节点疲劳寿命的深层机理。随后使用有限元分析计算所研究焊接节点的有效缺口应力，最终结合这些焊接节点的疲劳寿命测试数据，拟合相应的疲劳寿命预测曲线。本项目的研究成果将提供一种基于有效缺口应力的超声冲击处理焊接节点疲劳寿命准确预测方法，方便工程设计人员快速准确的对该类焊接节点进行疲劳设计，推动超声冲击处理工艺在工程中的广泛应用，从而保障焊接钢结构的整体安全。

焊接钢结构在疲劳荷载作用下焊接部位易出现裂纹，会造成极大的经济损失并威胁到结构的整体安全。超声冲击处理能够显著的提高焊接节点的疲劳寿命，然而目前其提高焊接节点疲劳寿命的机理尚未彻底明确，且缺乏能够准确预测超声冲击处理焊接节点疲劳寿命的方法。本项目对超声冲击处理焊接节点疲劳寿命提高机理和预测方法进行了研究。对对焊接头和十字接头的进行了疲劳测试，研究发现超声冲击处理能够有效的提高焊接接头的疲劳寿命，同时发现预疲劳焊接接头相比于无预疲劳焊接接头经超声冲击处理后疲劳寿命显著降低，表明预疲劳荷载会降低超声冲击处理疲劳寿命提高效果。基于疲劳测试结果，提出了一种两参数折减曲线用于预测具有预疲劳荷载的焊接接头疲劳寿命。此外，通过比较冲击处理前后焊趾部位的残余应力状态、缺口尺寸变化和冲击部位的微观结构，本项目对超声冲击处理焊接接头疲劳寿命提高机理进行了详细的研究。研究结果表面经超声冲击处理后，焊趾冲击部位的残余应力状态发生了变化，由残余拉应力变为残余压应力；冲击后焊趾部位出现明显的光滑缺口，有效的降低了焊趾部位的应力集中；焊趾冲击部位出现致密塑性层，有效的延迟了裂纹萌生和扩展。由于我国存在较多的焊接钢结构疲劳延寿需求，预期本项目的研究成果能够应用于服役钢结构的疲劳延寿。