Structural Integrity of Components with Deep Compressive Residual Stresses

激光强化（LP）是一种相对较新的表面处理技术，具有巨大的潜力，以减轻其他限制寿命的表面裂纹。使用激光产生等离子体冲击波，可以将压应力引入金属部件的深处。这些压应力对提高部件的疲劳寿命有显著的作用。矛盾的是，由于开发这些技术的商业利益的步伐，对这些过程及其影响的基本理解是缺乏的。因此，优化是临时的，耗时的，喷丸可能导致意想不到的应力分布，特别是对于复杂和薄的几何形状，目前的寿命策略完全基于大型测试矩阵。由于激光冲击波所引入的应力可能非常深，平衡张力可能在地下或横向产生。令人惊讶的是，薄样品和孔和网周围的三维分布是未知的，而孔和网在延长寿命方面可能获得最大的优势。特别关注的领域涉及：-需要优化喷丸处理条件以确保最佳残余应力，-缺乏对几何效应的理解，这对于深加工来说比喷丸处理要复杂得多，无论是压缩应力还是拉伸热点的位置-在室温和高温下疲劳下残余应力的稳定性-缺乏工艺优化建模工具，-需要一个经过验证的寿命方法。此外，在英国，几乎所有的发展工作都集中在Ti-6Al-4V上。由于缺乏其他材料的数据库，妨碍了其他工程部门参与这一进程。LP在“热点”地点最具成本效益。典型的位置包括扣件孔、腹板、叶片前缘、叶根固定等。出于这个原因，在这个项目中，我们将重点关注薄截面与厚截面以及孔周围。我们将首先研究激光强化参数、材料性能和样品几何形状之间的关系（曼彻斯特/MIC）。这些数据将用于开发该过程的预测模型（牛津），以便优化该过程，并为Ti， Al和钢引入最经济的应力场。然后，使用典型的薄片和带有应力集中器的样品的通用试样几何形状，我们将检查这些应力的演变以及在室温（Al）（空客/曼彻斯特）和高温（Ti6246）（曼彻斯特/斯旺西/劳斯莱斯）下疲劳的裂纹扩展，从而评估结构完整性的影响（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).