Structural Integrity of Components with Deep Compressive Residual Stresses

激光喷丸(LP)是一种相对较新的表面处理技术，在减缓原本限制寿命的表面裂纹方面具有巨大的潜力。利用激光产生等离子体冲击波，就有可能在金属部件内部产生深层的压应力。这些压缩应力对提高部件的疲劳寿命有显著影响。令人不快的是，由于商业对开发这些技术的兴趣很大，对这些过程及其影响缺乏基本的了解。因此，优化是临时的且耗时的，喷丸可能会导致意外的应力分布，特别是对于复杂和薄的几何形状，并且当前的寿命策略仅基于大型测试矩阵。由于激光冲击波产生的应力可能很深，平衡张力可能是亚表面的，也可能是横向产生的。令人惊讶的是，薄样品以及孔和网周围的3D分布是未知的，这些孔和网可能在延长寿命方面获得最大的优势。特别关注的领域涉及：-需要优化喷丸工艺条件以确保最佳残余应力，-缺乏对几何效应的了解，对于深加工而言，几何效应在压应力和拉伸热点位置方面都比喷丸工艺复杂得多--在室温和高温下疲劳时残余应力的稳定性--缺乏工艺优化建模工具--需要有效的寿命方法。此外，在英国，几乎所有的开发工作都集中在Ti-6Al-4V上。由于缺乏其他材料的数据库，阻碍了其他工程部门采用这一进程。在“热点”地区，LP的性价比最高。典型的位置包括紧固孔、腹板、叶片前缘、叶片根部固定等。因此，在本项目中，我们将重点关注薄片和厚片以及孔周围。我们将首先研究激光喷丸参数、材料性能和样品几何形状(曼彻斯特/MIC)之间的关系。这些数据将用于开发工艺预测模型(牛津大学)，以便对工艺进行优化，并为钛、铝和钢经济地引入最有利的应力场。然后使用典型的薄片和带有应力集中器的样品的通用试件几何形状，我们将检查这些应力的演变以及在室温(Al)(空中客车/曼彻斯特)和高温(Ti6246)(曼彻斯特/斯旺西/劳斯莱斯)下的裂纹扩展，从而评估结构完整性影响(斯旺西)。

Laser peening (LP) is a relatively new surface treatment technique with tremendous potential for the mitigation of otherwise life-limiting surface cracking. Using a laser to create a plasma shock wave it is possible to introduce compressive stresses deep into metallic components. These compressive stresses can have a significant effect in increasing the fatigue life of components.Paradoxically, because of the pace of commercial interest in exploiting these techniques, a basic fundamental understanding of the processes and their effects is lacking. As a result optimisation is ad-hoc and time consuming, peening can lead to unexpected stress distributions especially for complex and thin geometries, and current lifing strategies are based solely upon large test matrices. Because the stresses introduced by the laser shock wave can be very deep, the balancing tension may be sub-surface or may arise laterally. Surprisingly the 3D distributions are unknown for thin samples and around holes and webs where greatest advantages in life prolongation are likely to be obtained. Areas of particular concern relate to:- The need to optimise peening processing conditions to ensure optimal residual stress , - The lack of understanding of geometry effects which are much more complex for deep processes than for shot peening, both in terms of compressive stress and location of tensile hot spots- The stability of the residual stresses under fatigue at room and elevated temp- The lack of a process optimisation modelling tool, - The need for a validated lifing approach. In addition, in the UK nearly all the development work has been focused on Ti-6Al-4V. The lack of a database for other materials is hindering the take up of the process by other engineering sectors. LP is most cost-effective at 'hot spot' locations. Typical locations include fastener holes, webs, the leading edges of blades, blade root fixings, etc. For this reason, within this project we will focus on thin sections vs thick as well as around holes.We will first investigate the relationship between the laser peening parameters, materials properties and sample geometry (Manchester/MIC). This data will be used to develop predictive models of the process (Oxford) so that the process can be optimised and the most advantageous stress fields introduced economically for Ti, Al and steel. Then using generic test-piece geometries typical of thin sections and samples with stress concentrators, we will examine the evolution of these stresses as well as crack growth under fatigue at room (Al) (Airbus/Manchester) and elevated temperature (Ti6246) (Manchester/Swansea/Rolls-Royce) and thereby evaluate the structural integrity implications (Swansea).