Nanostructures Integrated Laser Shock Peening (nLSP) Processes and Their Mechanisms for Enhanced Fatigue Performance

该奖项的研究目标是研究一种创新的混合工艺，将激光冲击强化与纳米结构的产生相结合，以最大限度地减少压缩残余应力的松弛和加工硬化。本项目将发现纳米颗粒集成激光冲击强化工艺的基本工艺机制，并了解该工艺如何产生独特的微/纳米结构，从而实现稳定的残余应力和加工硬化。实验和模拟将研究纳米颗粒的类型、尺寸和分布对所得微观结构和残余应力分布的影响。利用透射电镜和x射线衍射研究了不同温度和循环载荷下的残余应力和位错结构的稳定性。将研究位错-钉住机制来解释稳定效果。为了研究提高疲劳寿命的机理，在实际使用条件下，考虑时变残余应力和硬度，建立疲劳寿命模型来预测提高的疲劳寿命。将设计疲劳试验来验证该模型。该工作的成功完成将对激光冲击强化产生压缩残余应力和加工硬化层的问题进行改进。这项工作可以确保将预应力概念集成到组件设计中，以最小的风险提高疲劳寿命，提高可靠性和减轻重量。这种冲击可以转移到大多数承重和结构部件上。该项目将通过以下方式应对材料科学、工程和制造教育方面的挑战：(a)加强普渡大学跨学科和非传统制造的研究和教育，(b)为学生提供多学科研究机会，促进对尖端制造工艺的发现和理解，(c)向本科生和研究生推广，使他们留在科学和工程领域。尤其是代表性不足和少数族裔的学生。

The research objective of this award is to investigate an innovative hybrid process combining laser shock peening with creation of nanostructures to minimize the relaxation of compressive residual stresses and work hardening. This project will discover the fundamental process mechanisms of the nanoparticle integrated laser shock peening process, and understand how this process produces the unique micro/nanostructures, which results in stabilized residual stresses and work hardening. Experiments and simulations will be conducted to investigate the effects of the type, size and distribution of the nanoparticles on the resulting microstructure and residual stress distribution. The stability of residual stress and dislocation structure under different temperatures and cyclic loadings will be studied using transmission electron microscopy and X-ray diffraction. Dislocation-pinning mechanisms will be investigated to explain the stabilizing effects. In order to study the mechanism of fatigue life enhancement, we will build a fatigue life model to predict the improved fatigue life considering the time variant residual stresses and hardness under real service conditions. Fatigue testing experiments will be designed to validate this model.The successful completion of this work will make an improvement to laser shock peening that produces compressive residual stress and a work hardening layer. This work can ensure the benefit of integrating a pre-stressing concept into component design with minimum risk for improved fatigue life, increased reliability and reduced weight. The impact can be transferred to the majority of load-carrying and structural components. This project will meet the challenges of education in materials science, engineering and manufacturing by (a) enhancing interdisciplinary and nontraditional manufacturing for research and education in Purdue University, (b) providing a multidisciplinary research opportunity for students to advance discovery and understanding of cutting edge manufacturing processes and (c) outreach to undergraduate and graduate students to retain them in science and engineering, especially underrepresented and minority students.