| 基于当量初始缺陷尺寸(EIFS)的TC4钛合金损伤容限特性研究 | |
| 李华 | |
| Subtype | 硕士 |
| Thesis Advisor | 雷家峰 ; 刘羽寅 |
| 2012 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 北京 |
| Degree Discipline | 材料工程 |
| Keyword | 损伤容限 原始疲劳质量 当量初始缺陷尺寸 裂纹扩展 寿命预测 Damage Tolerance Ifq Eifs Crack Growth Life Prediction |
| Abstract | " 本文针对TC4钛合金（Ti-6Al-4V）双态和片层两种典型显微组织，研究了两种组织的原始疲劳质量、近门槛区疲劳裂纹扩展行为以及基于当量初始缺陷尺寸（EIFS）的疲劳寿命预测，研究目的是为航空钛合金结构设计及选材提供参考。 采用紧固孔试样，通过在疲劳载荷中添加标识载荷的方法，获得了疲劳裂纹长度（a）随循环周次（N）变化的裂纹扩展数据，在此基础上对双态组织和片层组织的原始疲劳质量（IFQ）做了评定，并对其进行了符合性检查。结果显示，两种组织的IFQ都满足原始疲劳质量控制要求；与双态组织相比，片层组织的IFQ较差，这是因为片层组织的疲劳裂纹萌生抗力较差。 采用恒Kmax方法测试了两种组织的疲劳裂纹扩展速率以及疲劳裂纹扩展门槛值。结果显示，与双态组织相比，片层组织具有较低的疲劳裂纹扩展速率和更高的门槛值。这不仅与裂纹闭合有关，还与片层组织较高的本征裂纹扩展抗力（曲折的疲劳裂纹扩展路径）有关。片层组织近门槛区裂纹闭合程度较高主要与近门槛区Ⅰ型裂纹扩展机制断口高度差较大有关。 采用疲劳裂纹扩展门槛值和疲劳极限建立了双态组织高周疲劳试样的EIFS，并应用EIFS和疲劳裂纹扩展速率对高周疲劳寿命进行了预测。预测结果与实验值符合较好，说明基于EIFS的裂纹扩展分析方法能够对高周疲劳寿命做出较准确预测。 采用一种应力水平的紧固孔疲劳寿命和疲劳裂纹扩展速率，分别反推建立了两种组织紧固孔的EIFS， 基于EIFS对其他应力水平的紧固孔疲劳寿命做了预测。结果发现，应力水平较高时，实验值与预测值符合较好，而在应力水平较低时，实验值与预测值偏差较大。说明相同初始损伤状态在不同应力水平时对结构疲劳寿命的影响不同。 " |
| Other Abstract | " In this paper, IFQ(initial fatigue quality), fatigue crack growth behavior and fatigue life prediction based on EIFS(equivalent initial flaw size) was investigated, in terms of TC4 titanium alloy with bimodal and lamellar structure, for the purpose of providing reference on structural design and material selection. Fatigue crack growth a-N data of fastener holes of TC4 titanium alloy with bimodal and lamellar structure was obtained from fracture surfaces by marker load technique. Based on fatigue crack growth a-N data, the general distribution of EIFS was established to describe IFQ of fastener holes. The results show that the IFQs of fastener holes of TC4 titanium alloy with both structures are of a high level and the results of coincidence check meet the requirement well. Compared with lamellar structure, bimodal structure exhibits much higher IFQ, for lamellar structure with lower fatigue crack initiation resistance. Fatigue crack growth rate and threshold were tested by constant Kmax method. It shows fatigue crack growth rate of lamellar structure is lower than that of bimodal structure, and lamellar structure exhibits a higher fatigue crack growth threshold compared with bimodal structure. The lower fatigue crack growth rate and higher fatigue crack growth threshold of lamellar structure is partly attributed to crack closure effect, however, intrinsic fatigue crack growth resistance also plays a significant role while crack closure is absent. The crack closure extent is much higher in near threshold region, for the serious toughness caused by stageⅠfatigue crack propagation related to single slip model. EIFS of TC4 titanium alloy with bimodal structure was established using fatigue crack growth threshold and fatigue limit. The life prediction of HCF was conducted based on the EIFS and fatigue crack growth rate. The results of fatigue life prediction are coincident with experimental data well. Fatigue life prediction of fastener holes of TC4 titanium alloy with both structures was conducted based on EIFS established from back-extrapolation method. The results of fatigue life prediction are consistent with experimental data in higher stress level, whereas prediction results are longer than experimental data in lower stress level. The results reveal that the initial damage condition of real component plays a significant role in fatigue life, especially in lower stress level. " |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/64547 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 李华. 基于当量初始缺陷尺寸(EIFS)的TC4钛合金损伤容限特性研究[D]. 北京. 中国科学院金属研究所,2012. |
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