【作者】 高杰；

【导师】 段梦兰；

【作者基本信息】 中国石油大学(北京) ， 安全科学与工程， 2023， 博士

【摘要】 北极近海油气资源储量丰富,而常规海域近岸自升式平台需要经过改造升级,才能应用于极地海域。而新研发的高原铁路桥梁钢Q690q E可以服役于高寒地区,低温环境下具有优良的防断性能,且工程造价相对较低,若能应用于极地自升式平台建造中,将带来较大效益。本文考虑到极地低温以及风、浪等环境载荷作用,系统的研究了Q690q E高强钢应用于自升式平台的低温断裂韧性及疲劳问题。首先基于理论分析及有限元计算对自升式平台典型结构断裂驱动力展开了研究,进而通过试验与仿真方法研究了Q690q E低温环境下的力学性能,基于以上研究内容,进一步对应用于自升式平台的Q690q E钢选材及断裂失效问题展开了研究;最后针对应用Q690q E钢的桁架桩腿疲劳失效问题进行了计算和分析。具体地,本文开展了以下几方面研究:(1)针对桁架自升式平台典型的KK管接头以及H型结构,确定了裂纹的具体形式,基于断裂力学中的D-M带状屈服理论模型和裂纹尖端扩展位移(CTOD)理论,通过理论和有限元相结合的方式,分别建立了自升式平台典型KK管接头以及H型结构的断裂驱动力计算公式。(2)针对自升式平台高强钢在极地面临低温脆断问题,选取不同厚度的Q690q E钢板母材及焊缝,分别开展了小试件低温夏比冲击试验以及全厚度试件的低温CTOD试验,研究了Q690q E高强钢母材及焊缝的低温断裂韧性,并从宏观和微观两方面阐述了Q690q E高强钢材料在低温环境下断裂特征及韧-脆转变机制。通过对两种防断评价试验数据进行非线性分析,提出了夏比冲击功与CTOD关系改进的模型。(3)针对极地自升式平台高强钢低温选材问题,考虑Q690q E材料的低温本构,对不同厚度Q690q E高强钢CTOD试件的断裂韧性进行了数值仿真,并结合不同厚度高强钢的低温断裂韧性试验结果,建立了典型结构的断裂抗力公式;同时,基于自升式平台不同构件的应力等级,结合自升式平台典型结构的断裂驱动力计算公式,提出了Q690q E高强钢不同结构的低温防断选材方法。基于材料在低温环境下的力学性能参数,采用失效评定图建立了不同温度下的失效评估曲线,并对Q690q E高强钢试件的低温断裂韧性进行了断裂失效评估。(4)针对最易发生疲劳的自升式平台桁架桩腿KK管接头结构,考虑到海洋工程常见的轴向载荷、面内弯曲和面外弯矩载荷,基于不同的几何设计参数,建立了不同工况下的弯曲度几何参数方程,可以有效地评估载荷形式对自升式平台桁架桩腿疲劳寿命的影响,进而通过结构应力法计算了焊缝的等效结构应力,建立了KK管接头的疲劳主S-N曲线,并分析了沿焊缝各节点的疲劳寿命。基于以上研究成果,在材料断裂韧性以及结构疲劳性能方面,对高原铁路桥梁钢Q690q E应用于极地自升式平台设计和建造的可行性、安全性进行了评价,可以满足其在极地海域夏季无冰期时的正常工作要求。更多还原

【Abstract】 Arctic offshore oil and gas reserves are abundant,while conventional offshore jack-up platforms must be upgraded before they can be used in arctic seas.The newly developed plateau railway bridge steel Q690 q E can serve in alpine regions,and has excellent anti-break performance in low temperature environments,and the project cost is relatively low.It will bring greater benefits if it can be applied to constructing arctic jack-up platforms.Considering the arctic low temperature and environmental loads such as wind and waves,the low-temperature fracture toughness and fatigue of Q690 q E high-strength steel applied to jack-up platforms are systematically studied.First,based on theoretical analysis and finite element calculation,the driving force of the typical structural fracture of the jack-up platform was studied,and then the mechanical properties of Q690 q E in low-temperature environment were studied through experiments and simulation methods.The Q690 q E steel material selection and fracture failure of the platform were studied;finally,the fatigue failure of the truss legs using Q690 q E steel was calculated and analyzed.Specifically,this paper carried out research on the following aspects:(1)The specific form of the crack is determined for the typical KK pipe joint and H-shaped structure of the truss jack-up platform.Based on the D-M band yield theory model in fracture mechanics and the crack tip propagation displacement(CTOD)theory,through the theory and combining finite element methods,the formulas for calculating the fracture driving force of typical KK pipe joints and H-shaped structures of jack-up platforms were respectively established.(2)Due to the problem of low-temperature brittle fracture of high-strength steel for jack-up platforms in arctic regions,Q690 q E steel plate base materials and welding consumables of different thicknesses were selected to carry out low-temperature Charpy impact tests on small specimens and low-temperature CTOD tests on full-thickness specimens.,studied the low-temperature fracture toughness of Q690 q E high-strength steel base material and welding consumables,and expounded the fracture characteristics and ductile-brittle transition mechanism of Q690 q E high-strength steel materials in low-temperature environments from both macroscopic and microscopic aspects.Through the nonlinear analysis of the data of two kinds of fracture prevention evaluation tests,an improved model of the relationship between Charpy impact energy and CTOD is proposed.(3)Aiming at the problem of low-temperature material selection of high-strength steel for arctic jack-up platforms,considering the low-temperature constitutive of Q690 q E material,the fracture toughness of CTOD specimens of Q690 q E high-strength steel with different thicknesses was numerically simulated,combined with the low-temperature fracture toughness of high-strength steel with different thicknesses.Based on the test results,the fracture resistance formula of the typical structure was established.At the same time,based on the stress levels of different components of the jack-up platform,combined with the calculation formula of the fracture driving force of the typical structure of the jack-up platform,the low-temperature fracture-proof material selection of Q690 q E high-strength steel material was proposed method.Based on the mechanical property parameters of the material at low temperature,the failure evaluation curves at different temperatures were established by using the failure evaluation diagram,and the fracture failure evaluation of the low temperature fracture toughness of the Q690 q E high-strength steel specimens was conducted.(4)For the KK pipe joint structure of jack-up platform truss legs that is most prone to fatigue,considering the common axial load,in-plane bending and out-of-plane bending loads in marine engineering,based on different Geometric design parameters,established the geometric parameter equation of degree of bending under different working conditions,which can effectively evaluate the influence of load form on the fatigue life of jack-up platform truss legs,and then calculated the equivalent of the weld by structural stress method.Besides,based on the effective structural stress,the main fatigue S-N curve of the KK pipe joint is established.Based on the above research results,in terms of material fracture toughness and structural fatigue performance,the feasibility and safety of plateau railway bridge steel Q690 q E applied to the design and construction of arctic jack-up platforms were evaluated,which can meet the normal working requirements of its use in arctic seas during the ice-free summer period.更多还原