残余应力—疲劳载荷耦合作用下高强钢接头寿命预测及缓冲层延寿机理研究

Based on the requirement for long life and reliable operation of high-strength-steel welded equipments, fatigue crack propagation and life prediction model under coupling action of residual stress (considering re-distribution mechanism) and constant amplitude fatigue load (considering load-amplitude influence) will be studied for high-strength low-alloy welded joints together with the mechanics of prolonging the life resulting from buffer layer. The main researches are as following: (1) Element- and microstructure- distribution in the welding-interface region and adjacent regions will be analyzed to propose the selection mechanism of buffer layer taking in account element diffusion, heat conduction mechanism and phase transformation. Also, the effect of buffer layer on fatigue resistance and crack growth will be studied basing on the above mentioned research. (2) The effects of stress amplitude, fatigue numbers and ‘fatigue’ crack length on residual stress redistribution will be analyzed to study residual-stress influence on fatigue life and crack growth rate of welded joint.（3）The effect of load amplitude on drift of fatigue crack propagation curve will be studied. Based on the redistribution mechanism of residual stress and Paris model suited for homogeneous materials, this project will propose a fatigue crack growth and life prediction model taking into account load-amplitude variation and residual-stress redistribution.

面向高强度焊接结构钢设备长寿命可靠运行的需求，针对残余应力（考虑重分布机制）—常幅疲劳载荷（考虑载荷幅值效应）耦合作用下高强钢焊接接头的疲劳裂纹扩展和寿命预测模型以及缓冲层延寿机理开展研究。主要包括：（1）通过焊接界面两侧区域元素和组织分布的观测与分析，结合焊接过程中元素扩散原理、热传导机理及组织演化规律，建立缓冲层及厚度的选择机制，阐述缓冲层对接头疲劳抗力及裂纹扩展影响的作用机理；（2）通过应力幅值、疲劳周次、“疲劳”裂纹长度相关的残余应力重分布机制研究，定量阐述残余应力对接头这种非均质试样疲劳寿命及裂纹扩展速率的影响规律并建立映射关系；（3）通过对“载荷幅值相关的裂纹扩展速率曲线‘漂移’规律”的定量描述，结合残余应力重分布机制，借鉴适用于均质试样的Paris模型，建立适用于焊接接头、包含载荷幅值效应及残余应力重分布参量、物理意义明确的疲劳裂纹扩展及寿命预测模型。

本项目针对残余应力—常幅疲劳载荷耦合作用下高强钢焊接接头的疲劳寿命预测模型，以及材料准脆性断裂开展研究。主要研究成果包括：（1）通过焊接界面两侧区域元素和组织分布的观测与分析，结合焊接过程中元素扩散原理、热传导机理及组织演化规律，建立了缓冲层及厚度的选择机制，阐述了缓冲层对接头疲劳抗力及裂纹扩展影响的作用机理；（2）定量阐述了残余应力对接头这种非均质试样疲劳寿命及裂纹扩展速率的影响规律并建立映射关系；（3）借鉴适用于均质试样的Paris模型，建立了适用于焊接接头、物理意义明确的疲劳裂纹扩展及寿命预测模型；（4）构建了考虑材料微观结构的非线弹性断裂力学模型。本研究 体现了机械、力学和材料多学科的交叉，对促进结构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”的高强结构设备提供科学支持。培养博士研究生3名，硕士研究生9名。