Fatigue Testing beyond Extremes

疲劳是影响几乎所有工业部门的最普遍的故障模式，包括涉及发电厂、风电和潮汐水流发电机的能源行业；运输车辆和飞机；铁路和桥梁等国家基础设施；从发动机叶片到整艘船的军事设备；医疗器械和人体植入物。骨折的经济成本是巨大的，接近GDP的4%，而所有这些机械故障中有50%-90%是由于疲劳造成的。大多数疲劳故障都是意想不到的，可能会导致灾难性的后果。在航空航天和核工业等安全关键部门，对更好地了解金属部件的微观结构和所处的苛刻环境方面的疲劳的要求越来越高。我创造的超小型、超快速疲劳测试技术能够通过解决疲劳裂纹萌生(FCI)和短裂纹扩展(SCG)中的经典大海捞针问题而取得突破。这些早期阶段的疲劳局限在几百微米范围内。然而，它们在低周疲劳(LCF)下的寿命占50%以上，在高周疲劳(HCF)下约占90%，并且对散布的贡献最大。我的微观和细观悬臂梁技术能够在选定的微结构特征中隔离FCI和SCG，允许系统地探索滑移演化、滑移带解离和短裂纹扩展，在材料的精致特征体积的背景下。高达20 kHz的超快测试速率意味着，与传统方法所需的数月或数年相比，可以在数小时内实现长达109个周期甚至更长时间的强大探测。这项建议通过进一步开发最先进的极小和快速疲劳测试技术，希望从根本上改变疲劳分析的技术范围，允许在FCI和SCG级别以及在HCF和LCF制度下系统地探索环境影响。现场超声疲劳试验台将安装在先进的扫描电子显微镜中，能够以~1 nm的分辨率原位观察HCF FCI和SCG的进展。我将应用这些尖端技术来支持钛和镍合金的主要疲劳问题，这些问题对航空发动机工业和质子加速器具有重要的技术意义，特别是：(I)实现对钛合金中关于环境的HCF FCI和SCG的力学理解的突破，并提供基本的HCF FCI和SCG性能；(Ii)对钛合金的阿尔法疲劳和驻留疲劳进行开创性的研究，这是航空发动机工业的主要问题；(Iii)确定强辐照对将用于下一代质子加速器的钛合金的HCF性能的影响；(Iv)全面了解单晶镍高温合金的环境对疲劳的影响，该合金具有伽马相的非均匀分布和元素偏析；。(V)测定镍涡轮叶片表面多功能涂层在大气、温度和预腐蚀处理下的HCF和LCF性能。将建立超声波疲劳测试中心，以满足业界频繁的HCF评估要求。在该项目中，超声波疲劳试验台上开发的新功能将转移到库勒姆的国家实验室，以更新‘热室’中的定制试验台，用于研究支持裂变和聚变创新的活性材料。

Fatigue is the most pervasive failure mode that affects nearly all industrial sectors - including energy industries involving power plants, anemo-electric and tidal stream generators; transport vehicles and aircraft; national infrastructure such railway and bridges; military equipment from a blade in an engine to a whole ship; medical devices and human body implants. The economic cost of fracture has been enormous, approaching 4% of GDP, whereas 50-90% of all these mechanical failures are due to fatigue. Most fatigue failures are unexpected, and can lead to catastrophic consequences. In safety-critical sectors such as the aero-space and nuclear industries, there are ever increasing demands for better understanding of fatigue with respect to the microstructure of metallic components and the demanding environments that they are placed in.The ultra-small, ultra fast fatigue testing techniques I have created are able to make a breakthrough by addressing the classic needle in haystack problem in fatigue crack initiation (FCI) and short crack growth (SCG). Fatigue at these early stages is localized within a few hundred micro-meters. However, they account for more than 50% life in low cycle fatigue (LCF) and approximately 90% in the high cycle fatigue (HCF) regime, and contribute to the largest portion of scatter. My micro- and meso- cantilever techniques are capable of isolating FCI and SCG in selected microstructure features, allowing for the systematic exploration of slip evolution, slip band decohesion and short crack propagation in the context of an exquisitely well characterised volume of material. The ultra-fast testing rate up to 20 kHz means robust exploration can be achieved to 10^9 cycles and beyond, in hours in contrast to months or years demanded by the conventional method. This proposal, through further development of state-of-the-art extremely small and fast fatigue testing techniques, looks to radically change the technical scope of fatigue analysis by allowing environmental effects to be systematically explored at the levels of FCI and SCG and across the HCF and LCF regimes. In-situ ultrasonic fatigue testing rig will be installed in an advanced scanning electron microscope, enabling in-situ observation of the progression of HCF FCI and SCG at the resolution of ~ 1 nm. I will apply these cutting edge techniques to underpinning major fatigue issues in Ti and Ni alloys of technologically importance to the aero-engine industry and proton accelerators, specifically:(i) To achieve a breakthrough in mechanistic understanding of HCF FCI and SCG in titanium alloys with respect to the environments and deliver essential HCF FCI and SCG properties;(ii) To make groundbreaking study of fatigue in Alpha Case and dwelling fatigue in titanium alloys, which are major issues in aero-engine industry; (iii) To determine the effect of the heavy irradiation on HCF performance of Ti-alloys that will be used in the next generation proton accelerators; (iv) To achieve comprehensively understanding of the environmental effect on fatigue in single-crystal nickel superalloys that have the heterogeneous distribution of gamma' phase and element segregation;(v) To determine the HCF and LCF performance of the multi-functional coatings on the surface of a nickel turbo blade in the context of atmosphere, temperature and pre-corrosion treatment.A Ultrasonic Fatigue Testing Centre will be established to satisfy the frequent HCF assessment requests from the industry. The new functions developed on the ultrasonic fatigue testing rig in this project will be transferred to the national lab at Culham to update the bespoke rig in a 'hot cell', for study of active materials in support of fission and fusion innovation.