船体结构低周疲劳寿命直接计算法

发布时间：2018-05-28 02:13

本文选题：应力-应变关系 + 低周疲劳　；参考：《华中科技大学》2015年硕士论文

【摘要】：船舶与海洋工程结构物长期处于风浪流等周期性载荷作用下,应力集中的局部位置容易产生疲劳问题。对于潜艇、深潜器、FPSO等承受周期性的较大载荷作用的结构物,局部的应力值超过材料的屈服应力,必须考虑结构物的低周疲劳(应变疲劳)问题。本文基于疲劳问题的宏观机理,研究结构物在对称循环载荷作用下的低周疲劳寿命计算方法。结构物产生疲劳问题的原因是局部应力集中处不可逆转的塑性应变的累积。因此,首先研究材料的单调应力-应变曲线和循环应力-应变曲线及两者之间的关系,这是计算低周疲劳寿命的基础。本文研究结构危险点应力应变的计算方法,验证Neuber假设的正确性并针对其缺陷提出相应改进方法,即基于弹性分析的Neuber方法。计算结构低周疲劳寿命的曲线主要有两种:应力-寿命曲线、应变-寿命曲线。考虑到应变-寿命曲线的缺陷,提出适用于低周疲劳计算的伪热点应力方法,并给出基于伪热点应力的低周疲劳寿命曲线设计方法。基于伪热点应力的方法可以避开复杂的弹塑性分析,直接通过弹性分析得到结构的低周疲劳寿命。疲劳寿命估算方法主要包括三大内容。结合三大内容中的不同计算方法,给出两种典型的低周疲劳寿命计算方法:弹塑性计算法、弹性计算法。根据疲劳问题的宏观机理提出直接计算法,利用不同的典型算例验证三种方法的正确性,并分析其适用范围及改进思路。
[Abstract]:When ships and offshore structures are subjected to periodic loads such as wind, wave and current for a long time, the local position of stress concentration is easy to cause fatigue problems. For submarine, deep submersible FPSO and other structures subjected to large periodic loads, the local stress value exceeds the yield stress of the material, so the low cycle fatigue (strain fatigue) problem of the structure must be considered. Based on the macroscopic mechanism of fatigue problem, the calculation method of low cycle fatigue life of structures under symmetrical cyclic load is studied in this paper. The fatigue problem of structures is caused by the accumulation of irreversible plastic strain at local stress concentration. Therefore, the monotone stress-strain curve and cyclic stress-strain curve of materials and the relationship between them are studied firstly, which is the basis of calculating low cycle fatigue life. In this paper, the method of calculating the stress and strain of structural danger point is studied, the correctness of Neuber hypothesis is verified, and the corresponding improvement method, that is, the Neuber method based on elastic analysis, is put forward in view of its defects. There are two kinds of curves to calculate the low cycle fatigue life of structures: stress-life curve and strain-life curve. Considering the defects of the strain-life curve, a pseudo hot spot stress method for low cycle fatigue calculation is proposed, and the design method of low cycle fatigue life curve based on pseudo hot spot stress is given. The method based on pseudo-hot stress can avoid the complicated elastoplastic analysis and obtain the low cycle fatigue life of the structure directly through elastic analysis. Fatigue life estimation includes three parts. Combined with different calculation methods in three major contents, two typical methods for calculating low cycle fatigue life are presented: elastic-plastic method and elastic method. According to the macroscopic mechanism of fatigue problem, a direct calculation method is put forward. The correctness of the three methods is verified by using different typical examples, and the scope of application and the way of improvement are analyzed.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U661.4

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