Titanium 64 cold dwell fatigue loading - effect of stress concentrations and fatigue crack growth rates

钛 64 冷驻疲劳载荷 - 应力集中和疲劳裂纹扩展速率的影响

• 批准号: 2879427
• 金额: --
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2879427
• 关键词: Titanium; 64; cold; dwell; fatigue

The phenomenon of cold dwell fatigue can occur under cyclic loading where the maximum tensile load is maintained for a given duration (e.g. 2 minutes). The phenomenon is called "cold" dwell fatigue as it is prevalent at room temperature and remains pronounced at 120C but fades out above 200C. It has been discovered that this loading regime can lead to a large knock-down in fatigue life in certain titanium alloys, such as Ti64, when there is strong crystallographic texture heterogeneity in the material. Cold dwell fatigue was found to be the cause of several relatively recent failures of aero engines, which experienced Ti-64 front fan-hub ruptures. It is therefore a high priority for aircraft manufactures to better understand the risks this phenomenon might pose to other airframe components, which can have different microstructures and loading regimes. In particular, there is an urgent need to understand if dwell fatigue can lead to a fatigue life debit around fasteners which create a local stress concentration but a more complex local stress field, and during growth of cracks. This is because airframes are designed for 'damage tolerance', where a pre-existing crack is assumed to exist and life is calculated on the basis of the crack growth rate. Both of these topics have not been previously sufficiently addressed in the context of a dwell debit. The aim of this project will therefore be to use advanced materials testing and characterization techniques and modelling to understand the sensitivity of Ti64 materials with heterogeneous textures to damage accumulation around stress concentrations and during crack propagation under dwell fatigue loading conditions. This will involve running high fidelity in-situ cyclic loading tests, while employing a digital image correlation technique to measure the plasticity that occurs locally within the microstructure, using model materials that have been sourced with different types of texture heterogeneity. The results of such experiments will be compared to crystal plasticity simulations, using modelling tools being developed in the LightForm research group (https://lightform.org.uk).

在循环载荷下可能会发生冷保压疲劳现象，其中最大拉伸载荷保持给定的持续时间（例如2分钟）。这种现象被称为“冷”停留疲劳，因为它在室温下普遍存在，在120 ℃时仍然明显，但在200 ℃以上逐渐消失。已经发现，当材料中存在强烈的晶体织构不均匀性时，这种加载方式可导致某些钛合金（例如Ti64）的疲劳寿命的大的降低。冷驻留疲劳被认为是最近几次航空发动机故障的原因，这些发动机经历了Ti-64前风扇轮毂破裂。因此，对于飞机制造商来说，更好地了解这种现象可能对其他机身部件造成的风险是一个高度优先事项，这些部件可能具有不同的微观结构和加载机制。特别是，有一个迫切需要了解，如果停留疲劳会导致疲劳寿命借记周围的紧固件，创建一个局部应力集中，但更复杂的局部应力场，并在裂纹的增长。这是因为飞机机体是按“损伤容限”设计的，即假定存在预先存在的裂纹，并根据裂纹扩展速率计算寿命。这两个主题以前在驻留借记的背景下都没有得到充分的解决。因此，本项目的目的是使用先进的材料测试和表征技术和建模，以了解具有异质纹理的Ti64材料在应力集中周围和驻留疲劳载荷条件下裂纹扩展期间对损伤累积的敏感性。这将涉及运行高保真原位循环加载测试，同时采用数字图像相关技术来测量微观结构内局部发生的塑性，使用具有不同类型纹理异质性的模型材料。这些实验的结果将与晶体塑性模拟进行比较，使用LightForm研究小组正在开发的建模工具（https：lightform.org.uk）。