运用连续损伤理论对结构损伤分析和寿命预测的研究

【作者】 孙立德；

【导师】 冯刚；

【作者基本信息】 大连理工大学 ， 机械设计及理论， 2004， 硕士

【摘要】 金属结构的损伤分析和疲劳寿命预测是工程界研究的重要课题。金属结构的疲劳失效主要由两部分组成：疲劳裂纹形成期和裂纹扩展期。Paris方程能预测裂纹扩展期的疲劳寿命，但裂纹形成期的寿命无法用其进行计算。 本文旨在建立一个基于连续损伤力学理论的疲劳损伤分析模型，应用该模型分析金属结构的损伤，不仅能预测疲劳裂纹扩展期的寿命，还能预测裂纹形成期的寿命，解决工程中的实际问题。 理论知识和实践调研相结合，配合试验数据的研究方法。 通过实践调研，了解工程实际需要，获得基本数据；本文简要回顾了过去几十年该研究领域国内外的研究工作和成果，包括理论方面的研究和创新，以及各种试验方法和手段；扼要阐述了连续损伤力学理论的基本知识框架和理论体系。结合实验，对疲劳失效的原理进行剖析，详细论述疲劳失效的全过程，即微裂纹的萌生和增长，宏裂纹的形成和稳定扩展，最后失稳扩展导致疲劳断裂。对金属结构进行载荷分析和应力计算，分析疲劳裂纹的出现位置。 定义了一个新的损伤变量，并推导了损伤累积模型和寿命计算模型，模型表达式简洁，物理含义明确，能很好体现金属结构疲劳损伤的全过程。 简要介绍了经典的疲劳累积损伤理论和几个典型的损伤变量定义式。结合金属结构的特点，运用连续损伤力学理论，用结构的有效承载面积定义一个新的损伤变量，推导了疲劳累积损伤计算模型和疲劳寿命计算模型，在此基础上得出了疲劳累积损伤计算方程和相对应的疲劳寿命计算方程。在直角坐标系中绘制关系曲线，运用该模型分析了金属结构的损伤情况，预测疲劳寿命。 结合具体实验数据，用损伤计算方程和疲劳计算方程计算结构的损伤程度和剩余寿命，获得了满意的损伤值和疲劳寿命值。和实验数据进行比较，结果误差在允许范围内，说明文中提出的模型和计算方程是可行的，能够解决实际工程问题，实现了研究的最初设想和目的。并分析了研究成果的不足，展望了金属结构的累积损伤分析和疲劳寿命预测领域将来的发展前景。更多还原

【Abstract】 The damage analysis and fatigue life prediction of metal structures is an important research domain in the engineering field. The fatigue failure process consists of two stages: fatigue crack initiation and crack propagation. The life of the second stage can be calculated by Paris formula, but Paris formula is no use to predict the life of the first stage.The main purpose of this paper is to develop a fatigue and damage analysis model based on continuum damage mechanics. This model is applied to study damage evolution. Using the model the life of crack initiation can be predicted as well as the life of the crack propagation.The following three factors are well combined with each other in this paper: theory knowledge, investigation and experiment.Through investigation the real needs and the basic data have been mastered. In this paper, the research work and accomplishment in this domain in the past several decades has been reviewed in brief which includes research and innovation in theory and the main kinds of approaches in experiment. The basic knowledge frame and theory system of continuum damage mechanics has been introduced mainly. Combining with the experiment, the mechanism of fatigue failure has been analyzed in details and the whole process of fatigue failure has been illustrated. The loading analysis and stress calculation on the metal structures has been carried out, and the locations of fatigue cracks have been pointed out.A new damage variable has been defined while a damage accumulation model and a fatigue life model have been developed. The whole process of fatigue damage accumulation in the metal structure has been well illuminated by the expressions of these two models.The main classic fatigue cumulative damage theories and the representative definitions of damage variable have been introduced briefly. Considering the characteristic of the metal structure and using continuum damage mechanics, a new damage variable has been defined related to the effective loading area. Further more, a fatigue damage accumulation model and a fatigue life calculation model have been acquired and the relationship curves have been described in coordinates. The damage state and fatigue life can be confirmed instantaneously.The experimental results have shown that a damage variable based on the effective loading area decrease can be used to measure cumulative damage and provide a good estimate of the fatigue damage process, as well as to predict the fatigue life. Thus, the original assumption and purpose are realized.The disadvantage of this model has been illuminated and the development prospect of cumulative damage analysis and fatigue life prediction of metal structures has been suggested.更多还原