基于累积递增塑性破坏的船体结构低周疲劳强度研究

The fatigue strength of ship's structure has very important significance on the safety and survivability. At present all the research achivements and applications of fatigue strength are basically for high-cycle fatigue of ship hull structures. Along with the increasing in ship dimensions and more use of high-strength steel in recent years, the stress and deformation of ship structures are so high and large, which result in very prominent problem of low-cycle fatigue damage to large-scale ships. This has become the key issues demanding prompt solution in the development of large-scale ships. Analysis shows that most overall fractures of ship hulls tend to be the coupling interaction result of low-cycle fatigue and increasing plasticity. Therefore, the low-cycle fatigue analysis and estimation based on the accumulated incremental plastic damage can more realistically predict the fatigue strength of ship hull structures. Based on the accumulated incremental plastic damage, this project will carry out theretical, numerical and experimental research on the low-cycle fatigue of ship hull structures. The crack tip opening displacement (CTOD) will be applied to the analysis of low-cycle fatigue crack extension, taking the lead in solving the problem in the field. The research findings of the project could more accurately assess the low-cycle fatigue damage of ship hull structures under extreme sea conditions, it is the ddevelopment on the theory of fatigue strength analysis and application. The research work can provide more advanced and reliable theoretic base and analysis method for the prediction of low-cycle fatigue of ship hull structures.

船舶结构的疲劳强度对船舶的安全性和生命力有着十分重要的意义。目前船体结构疲劳强度的研究成果及应用基本都是针对高周疲劳。近年来随着船舶主尺度的不断加大，采用的高强度钢越来越多，船舶结构所受的应力及变形也越来越大，使得大型船舶结构的低周疲劳损伤问题显得十分突出，成为大型化船舶发展中亟待解决的关键性问题。研究分析表明，大多船体结构的总体断裂破坏往往是低周疲劳破坏与递增塑性破坏两种破坏模式耦合作用的结果。因此，基于累积递增塑性破坏的结构低周疲劳分析能够更为符合实际地评估船体结构的低周疲劳断裂。本项目基于累积递增塑性对船体低周疲劳强度全面开展理论、模型及数值分析研究，率先将裂纹尖端张开位移（CTOD）应用于低周疲劳裂纹的扩展分析。研究结果可以更确切地分析评估船体在极值海况下的低周疲劳破坏，是疲劳强度理论分析与应用上的一个发展，为正确预报船体结构的低周疲劳提供更为先进的理论依据及可靠的分析计算方法。

船舶结构的疲劳强度对船舶的安全性和生命力有着十分重要的意义。实际恶劣海洋环境中船体结构承受的交变载荷会在结构中造成两种形式的损伤：一种是低周疲劳的高应力幅引起局部结构应力集中区域裂纹的形成和扩展，导致结构的疲劳断裂破坏；另一种是每次高应力幅循环之后产生不断增长的累积塑性变形损伤，导致结构材料延性丧失而破坏。实际上塑性变形破坏及交变塑性变形破坏（或低周疲劳）并不是相互独立的，它们之间具有耦合作用的关系。因此，在研究船体结构的低周疲劳性能时必须考虑这种耦合的破坏模式。.本项目基于累积递增塑性对船体低周疲劳强度全面开展理论、模型及数值分析研究，率先将裂纹尖端张开位移（CTOD）应用于低周疲劳裂纹的扩展分析。.本项目主要完成了以下研究工作：1）完成循环载荷下船体结构裂纹尖端弹-塑性理论分析和推导，获得船体结构裂纹尖端张开位移(CTOD)计算模型；2）提出循环载荷下以CTOD为参量的船体结构低周疲劳寿命的理论计算模型，完成船体结构低周疲劳寿命计算方法研究；3）建立反映循环载荷下船体结构累积递增塑性破坏和低周疲劳破坏耦合作用关系的理论分析模型；4）完成模型实验，弄清循环载荷下基于累积塑性破坏的、以CTOD作为参量表征的船体结构的低周疲劳寿命的变化规律，验证、比较理论方法的正确性、合理性和有效性，实现循环载荷下船体结构数值仿真技术的计算精度与效能的提升；5）完成循环载荷下的累积塑性破坏和低周疲劳破坏耦合作用关系的有限元数值仿真，以及多种影响因素作用下的参数分析研究。.研究结果可以更确切地分析评估船体在极值海况下的低周疲劳破坏，是疲劳强度理论分析与应用上的一个发展。研究工作为正确预报船体结构的低周疲劳强度提供更为先进的理论依据及可靠的分析计算方法。