Process and application of shock compression by nanosecond pulses of frequency-doubled Nd:YAG laser
Process and application of shock compression by nanosecond pulses of frequency-doubled Nd:YAG laser
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倍频Nd:YAG激光器纳秒脉冲冲击压缩过程及应用
DOI：
10.1117/12.377033
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发表时间：
2000
影响因子：
6.7
通讯作者：
Tatsuki Ogisu
中科院分区：
文献类型：
--
作者：
Y. Sano;M. Kimura;N. Mukai;Masaki Yoda;M. Obata;Tatsuki Ogisu
提出了一种激光诱导冲击压缩新工艺，在材料表面引入残余压应力，可有效防止金属材料的应力腐蚀开裂，提高材料的疲劳强度。所开发的过程是独特的和有益的。它不需要对表面进行预处理，而传统工艺需要所谓的牺牲层来保护表面免受损害。新工艺可以自由地应用于水浸组件，因为它使用了一种频率加倍的Nd:YAG激光器的可穿透水的绿光。所开发的工艺有可能在制造和维护技术中开辟新的高功率激光应用。激光诱导的冲击压缩过程（LSP）可以将残余应力场从拉伸改善到压缩。为了了解激光辐照的物理特性和优化工艺，以激光诱导等离子体压力为外载荷，采用有限元程序对激光辐照脉冲产生的冲击波的传播和材料的动态响应进行了时效弹塑性计算。分析表明，激波通过后，材料仍存在永久应变和残余压应力，其振幅超过材料的屈服强度。设计、制造并测试了该系统在轻水堆核心部件上的适用性。该系统进入目标部件，并沿着焊接线向热影响区（HAZ）远程照射激光脉冲。使用全尺寸模拟设施进行了各种功能测试，可以模拟反应堆容器中的远程维护工作。结果表明，该系统能够远程接近目标焊缝，并成功引入残余压应力。在对操作人员进行充分培训之后，该系统被应用于现有核电站的堆芯罩。
The authors have developed a new process of laser-induced shock compression to introduce a residual compressive stress on material surface, which is effective for prevention of stress corrosion cracking (SCC) and enhancement of fatigue strength of metal materials. The process developed is unique and beneficial. It requires no pre-conditioning for the surface, whereas the conventional process requires that the so-called sacrificial layer is made to protect the surface from damage. The new process can be freely applied to water- immersed components, since it uses water-penetrable green light of a frequency-doubled Nd:YAG laser. The process developed has the potential to open up new high-power laser applications in manufacturing and maintenance technologies. The laser-induced shock compression process (LSP) can be used to improve a residual stress field from tensile to compressive. In order to understand the physics and optimize the process, the propagation of a shock wave generated by the impulse of laser irradiation and the dynamic response of the material were analyzed by time-dependent elasto-plastic calculations with a finite element program using laser-induced plasma pressure as an external load. The analysis shows that a permanent strain and a residual compressive stress remain after the passage of the shock wave with amplitude exceeding the yield strength of the material. A practical system materializing the LSP was designed, manufactured, and tested to confirm the applicability to core components of light water reactors (LWRs). The system accesses the target component and remotely irradiates laser pulses to the heat affected zone (HAZ) along weld lines. Various functional tests were conducted using a full-scale mockup facility, in which remote maintenance work in a reactor vessel could be simulated. The results showed that the system remotely accessed the target weld lines and successfully introduced a residual compressive stress. After sufficient training for operational personnel, the system was applied to the core shroud of an existing nuclear power plant.