高压水射流调控焊接残余应力机理与模型研究

As a new surface strengthening technology with the merits of green and economy, high pressure water jet peening is expected to eliminate the tensile residual stresses on the surface of welded joint for nuclear reactor pressure vessels and improve its resistance to stress corrosion cracking. The aim of this project is to conduct a research on the controlling mechanism and model of welding residual stresses by high pressure water jet peening. The main contents of this project are as follows: (1) The pressure distribution law of high pressure water jet peening with big diameter nozzle and large flow capacity is studied. A theoretical equation describing the pressure load distribution is proposed, and a theoretical model to describe pressure load of high pressure water jet peening is established. (2) According to the model of pressure load, the fatigue response characteristics under multiaxial cyclic are investigated, and the evolution of mechanical response under tensile and compression cyclic load is clarified, and the constitutive model of cycle induced by high pressure water jet is established. (3) Based on the cyclic constitutive model, a numerical prediction method of reducing welding residual stresses by high pressure water jet is established. The relaxation and controlling mechanism of welding residual stress is revealed. Then, a mathematical controlling model of residual stress is established, which is related to the peening process inducing compressive stress. Finally, the precise prediction and control of residual stress reduction by high pressure water jet is realized. This project is expected to provide new ideas for the development of post-weld stress relief technology in equipment manufacturing field and provide scientific support for the design of long-term safe and reliable operation for nuclear power pressure vessels.

高压水射流喷丸作为一种绿色经济的新型表面强化技术，可望实现核反应堆压力容器焊接接头表面残余拉应力的消除，提高抗应力腐蚀开裂能力。本项目围绕高压水射流喷丸调控焊接残余应力的机理与模型展开研究，主要研究内容包括：（1）研究大口径高流量高压水射流喷丸压力载荷分布规律，提出准确描述水射流压力载荷分布的理论方程，建立压力载荷理论模型。（2）依据压力载荷模型，探究材料多轴循环疲劳响应特性，建立高压水射流作用下的循环本构模型，澄清拉压及压压循环载荷下力学响应机理。（3）基于循环本构模型，发展高压水射流消减焊接残余应力的数值预测方法，揭示焊接残余应力释放与调控机理，建立与可致压应力喷丸工艺相关的残余应力调控模型，实现高压水射流消减焊接残余应力的精确预测与调控。本项目有望为装备制造领域中焊后消应力技术的发展提供新的思路，为核电压力容器长周期安全可靠运行设计提供科学支持。

焊接残余拉应力是引起压力容器应力腐蚀开裂的主要原因之一，高压水射流喷丸是一种具有低成本、低噪声、安全、绿色环的表面强化消应力处理方法。本项目提出采用高压水射流喷丸消减焊接接头处残余应力，综合运用试验测试、理论分析、数值模拟等手段，对高压水射流调控焊接残余应力机理及模型进行了系统研究。分析了高压水射流流场特性及作用在材料表面的压力载荷分布规律，探究了不同高压水射流喷丸工艺对压力分布的影响，构建了高压水射流喷丸压力载荷分布与水射流处理工艺的定量关系，提出了高压水射流压力载荷理论方程，设计了水射流压力测试装置，验证了压力载荷模型的正确性。建立了水射流喷丸移动载荷模型和焊接残余应力预测模型，编写了用户材料及移动载荷子程序，实现对高压水射流喷丸处理前后残余应力分布的预测。阐明了残余应力释放率与喷丸参数的定量关系，明确了可致焊接接头表面压应力的水射流工艺，实现高压水射流消减焊接残余应力的精确预测与调控。虽然适当的高压水射流工艺参数可是焊接接头表面产生残余压应力，但单纯通过改变高压水射流残余应力难以使焊接接头获得最大残余压应力的同时又具有良好的处理效果，且对于不同的焊接接头材料，高压水射流参数一旦使用不当对材料表面会产生损伤，影响结构寿命。对此，发明了一种具有高强化效应高处理效果的空化射流同轴复合喷嘴结构，并研发了便携式强化处理装置，并通过试验对该喷嘴处理的焊接试样进行残余应力、疲劳测试，证实了喷嘴强化的可行性及高效性。对比分析了空化射流与超声冲击对2205双相不锈钢十字焊接接头表面完整性及疲劳性能的影响，发现空化射流和超声冲击对焊接接头的强化机理不同，空化射流对焊接接头疲劳寿命的提升效果要优于超声冲击。此项目为进一步发展高压水射流喷丸消应力技术提供了科学支持。