含缓冲层高强钢焊接接头疲劳扩展模型及机理研究

Research shows: aiming at mechanical state of welded structure, incorporation of a competent buffer layer between weld metal and parent metal can obviously increase its mechanical properties. Whereas that the fatigue resistant mechanism and life prediction of high-strength steel welded joint with a buffer layer is very complicated, and that buffer layer and its thickness are very sensitive to mechanical state and parent-metal properties, we plan to carry out the research. The main researches are as following: (1) The reasons for fatigue weak region of welded joints and its relation to component and microstructure will be analyzed to create the rules for selecting buffer layer and its thickness, which will consider element diffusion, phase transformation and heat conduction mechanism. (2) The effect laws of stress amplitude on drift of fatigue crack growth curve, and the crack-length-related release mechanism of residual stresses, are going to be researched in the project. Based on the fatigue test date of welded joints and Paris model, the project will propose a new fatigue crack growth model which takes into account the effects of stress amplitude and residual stresses. (3) By studying the variation law of overload-related fracture and plastic deformation zones, the project will quantitative describe the effect laws of overload-induced fracture and plastic deformation on fatigue crack growth rate and fracture mechanism. And the mechanism of effect of overload on prolonging life of welded joints will be studied.

研究表明：针对焊接构件的力学状态，在焊接材料和母材之间引入特定缓冲层可有效提高其力学性能。鉴于含缓冲层高强钢接头抗疲劳机理和寿命预测研究的复杂性，以及缓冲层材料和厚度对力学状态和母材性质的“敏感性”，拟开展本研究。主要包括：(1) 通过分析常规接头疲劳“薄弱区”产生原因及与成分和组织的映射关系，并结合焊接过程元素扩散、组织相变和热传导机理，建立缓冲层材料和厚度的选择依据，阐明缓冲层对改善接头疲劳性能的作用机理。(2) 通过对“应力幅对疲劳裂纹扩展曲线“漂移”的影响规律”和 “裂纹长度相关的残余应力释放机理”的研究，利用接头疲劳实验数据并借鉴Paris模型，建立适用于接头非均质区、考虑应力幅影响和残余应力参量的疲劳裂纹扩展模型。(3) 通过对超载条件相关的断裂区和塑性变形区变化规律的研究，定量描述超载诱导的断裂及塑性变形对疲劳裂纹扩展速率及模式的影响规律，澄清超载对接头延寿的作用机理。

本项目通过在高强度焊接材料和高强度母材之间引入具有特定属性的缓冲层来提高焊接接头的力学性能，重点研究了缓冲层材料和厚度对焊接接头抗疲劳性能和断裂机理的影响规律以及接头非均质区疲劳寿命预测模型。主要包括：(1) 通过分析常规焊接接头疲劳薄弱区域产生原因及与成分和组织的关系，建立了缓冲层材料选择和厚度优化的科学依据，分析了缓冲层对改善接头抗疲劳性能的作用机理。(2) 通过“应力幅对疲劳裂纹扩展曲线漂移的影响”和“疲劳过程中的残余应力释放机理”的研究，利用焊接接头疲劳裂纹扩展实验数据并借鉴Paris模型，建立了物理意义明确、适用于接头非均质区的疲劳裂纹扩展速率预测模型。(3) 通过不同实验条件、单次拉伸超载后裂尖断裂区和塑性变形的对比研究，分析了超载条件对疲劳裂纹扩展速率及断裂模式的影响。本研究体现了机械、力学和材料多学科的交叉，从不同角度研究高强钢焊接接头的疲劳断裂机理，对促进高强度焊接结构钢设备关键零部件的寿命设计方法及制造水平、发展“安全、可靠、长寿命”的高强度焊接结构钢设备提供科学支持。培养博士研究生1名，硕士研究生3名。