论船体结构疲劳强度的检验

船体结构局部因磨损、腐蚀、脱焊、裂纹等缺陷,导致疲劳强度不足,引发重大事故。为此从保障航运生产安全的实际求出发,对船体疲劳强度校核的意义、校核的部位及实用的校核方法给出了详细的说明,并结合计算软件的开发介绍了进行船体疲劳强度校核的计算流程。     

型钢混凝土梁梁连接节点疲劳强度分析

基于疲劳试验进一步分析了H型钢混凝土(SRC)梁梁连接节点的疲劳破坏模式和机理,探讨了表征这种组合节点疲劳强度的参数,对其疲劳强度进行了评估。研究表明:SRC梁梁节点疲劳破坏发生在连接到主梁的次梁截面上,次梁H型钢受拉翼缘的疲劳断裂是这种组合节点疲劳破坏的关键特征;提出了采用次梁H型钢受拉翼缘应力幅和国内外钢结构疲劳设计规范相关的S-N曲线的计算方法来进行对SRC梁梁节点的疲劳强度评估,该方法简单实用且偏于安全。     

港口集装箱轨道吊结构疲劳强度校核分析

经济发展促进港口机械的快速发展,从而引起了研究者对机械结构疲劳程度的评估。港口集装箱轨道吊是港口集装箱装卸作业中的重要设备,在该文作者提出了一种基于有限元仿真的疲劳强度校核。通过建立集装箱轨道吊金属结构的有限元模型,进行有限元分析仿真各结构件的静强度计算,运用许用应力计算模型,确定最小疲劳寿命部位,并采用应力比法对疲劳强度进行校核分析。     

50CrVA扭杆断裂原因分析

对断裂的50CrVA扭杆进行断口宏微观观察、金相组织检查、硬度测试及疲劳强度校核.疲劳强度校核结果说明扭转载荷过大是扭杆疲劳断裂的主要原因.材质分析显示扭杆中含有大尺寸富Zn夹杂物,它促进了疲劳裂纹的萌生,缩短了扭杆的疲劳寿命.     

铝-铝-钢与铝-钛-钢复合板疲劳性能对比研究

针对船体结构对铝-钢复合板的选材与节点设计需求,对铝-铝-钢与铝-钛-钢复合板开展了轴向拉-压疲劳试验,测试了材料的条件疲劳强度与S-N曲线,对比分析了两种铝-钢复合板的疲劳断裂行为与断裂位置。结果表明,在应力比为-1,轴向拉-压载荷条件下,铝-铝-钢复合板的条件疲劳强度为28.8 MPa,铝-钛-钢复合板的条件疲劳强度为55.0 MPa。在疲劳寿命接近的条件下,后者比前者能够承受更大的应力,抵抗疲劳扩展能力更强。铝-铝-钢复合板疲劳断裂主要发生于1060纯铝层,铝-钛-钢复合板疲劳断裂发生于3003铝合金层,疲劳断裂位置与铝-钢接头组成材料的抗拉强度大小密切相关。      

机械设计疲劳极限指标的可靠度提高问题探讨

疲劳抗力指标受试样的微观组织结构、加工方法、实验条件等诸多因素的影响。大多数设计手册中应提供的疲劳强度指标、材质不明，数据单一，增大了设计过程的盲目性。提高手册中疲劳抗力指标的可靠度，是提高机械设计结果准确性的前提。疲劳抗力指标受试样的微观组织结构、加工方法、实验条件等诸多因素的影响。大多数设计手册中提供的疲劳强度指标，材质不明，数据单一，增大了设计过程的盲目性。提高手册中疲劳抗力指标的可靠度，是提高机械设计结果准确性的前提。本文从疲劳破坏的特征出发，分析了传统设计方法，结合提高机械设计疲劳极限指标的影响因素与设计准则，得出了提高机械设计疲劳极限指标的策略。     

船舶工程焊接接头完整性评估与疲劳寿命预测技术综述

介绍了船体结构中含缺陷的焊接接头完整性评估以及疲劳寿命预测方法，对结构完整性评估的K准则、COD准则、J积分准则、SINTAP/FITNET安全性评定方法以及评定流程、国内外标准进行介绍。并对焊接接头的疲劳强度影响因素，如平均应力、残余应力以及接头几何形状应力集中等进行了分析；介绍了焊接接头疲劳寿命预测的常用方法，如基于名义应力的评估方法、基于断裂力学的评估方法、基于损伤力学的评估方法以及其它疲劳评估方法等。此外，还对基于断裂力学法建立的焊接残余应力与疲劳裂纹扩展寿命之间的函数关系进行了介绍，该方法实现了对含残余应力的焊接结构疲劳寿命的精确预测。     

舰船静置爆炸气泡时总纵强度计算方法研究

新型“大气泡能”概念武器在水下爆炸能产生大气泡，对船体总纵强度造成很大影响，有可能使舰体发生纵向折断或倾覆。为研究这种作用，建立了舰船静置爆炸气泡时总纵弯曲强度的理论计算方法。采用静置爆炸气泡的假设，将气泡产生的浮力损失和压力差转化为等效载荷，计算气泡作用后船体的总纵弯矩和剪力并进行强度校核。以某舰艇为例进行计算，结果表明，爆炸气泡作用下船体的剪力和弯矩比静浮状态增大很多，船体发生纵向折断破坏的危险性也随之增大。     

抗冰导管架平台疲劳可靠性优化

疲劳破坏是海洋工程结构的一种主要破坏形式。对于渤海有冰边际油田,需要在满足冰激疲劳要求的同时考虑平台成本。该文建立了抗冰导管架疲劳可靠性优化模型,利用虚拟激励法并结合兼顾整体和局部的混合有限元模型,实现了复杂管节点冰激疲劳的快速高效分析,并利用对数正态格式计算冰激节点疲劳可靠性。渤海JZ20-2NW平台算例分析表明,通过优化设计可以在满足节点疲劳可靠性要求的同时降低结构重量,可以为冰区海洋平台设计提供参考。     

非接触空爆对舰艇结构的破坏作用分析

基于非接触空爆理论，对作用于船体结构的载荷进行了分析，并将船体结构简化为板架模型进行了破坏作用的数值计算，计算结果与实际情况相符。     

Time-domain fatigue assessment of ship side-shell structures

Loads acting on ship side-shell structures are complex and vary randomly over time. The current study proposes a direct calculation procedure for the fatigue assessment of ship side-shell structures. The calculation procedure is characterised by nonlinear time-domain hydrodynamic simulations followed by finite element (FE) analyses. Sensitivity and feasibility analyses of the proposed time-domain procedure were carried out, and the calculated fatigue damages were compared with full-scale measurements made on a container vessel. Fatigue life analyses were carried out by both the spectral method and the time-domain approach. In addition, two approaches for local stress analysis are presented and discussed: an engineering-based definition of the stress concentration factor (SCF) and a proposed local stress factor (LSF) that utilises stress ranges extracted from the stress history. The results from the fatigue analysis using the LSF indicated a shorter fatigue life than the results obtained using the SCF. This difference is observed because the LSF accounts for the effects of wave-induced loads under ship operation conditions in a more realistic manner.     

Quality assurance of welds in ship structures

This paper describes procedures for predicting the growth rate of fatigue cracks in ship structure welds under sea-wave loading as well as the stress corrosion cracking behaviour of steel in marine structures. A computer program which can be applied to assess the residual life-time and to estimate the probability of failure of marine structures under wave action is presented. The main objective of applying this program is the development of an optimal inspection and maintenance policy for marine structures. Moreover, the presented computer program is of value to insurance companies in order to assess the safety level of a marine structure and consequently to estimate their financial risk.     

Structural integrity of copper-nickel to steel using metal inert gas welding

Metal inert gas (MIG) welding may be used as a technique to attach copper-nickel panels to steel substrates to minimize the corrosion and biofouling of offshore structures and ship hulls. A series of plug welds must be located on each panel in order to eliminate bowing when the panels are subjected to compressive loadings. Laboratory tests on MIG plug-welded specimens have shown that the fatigue life of the plug welds is the same as the fatigue life of the copper-nickel cladding without the plug welds. The possible increase in fatigue life attributed to the lack of bowing of the sheets is offset by the stress concentration created by the weld. SEM examination of the failed weld site showed that fracture was predominantly intergranular in the regions adjacent to the weld, while regions remote from the weld exhibited fatigue striations.     

Some considerations of fracture mechanics applications in ships design,construction and operation

The structural performance demands placed on present day high performance ships and some types of shipboard liquid natural gas (LNG) cargo containment systems requires the use of new materials which can perform under higher loadings and severe service environments. Such critical designs must be accomplished while maintaining a high structural reliability and decreased life-cycle costs. For high performance ships these critical designs can be accomplished with damage-tolerant design procedures which provide for redundant load paths and/or crack arrest capabilities. The ship construction and maintenance requirements must also be included in the design because of their effect on the structural life performance of the high performance ship. For shipboard LNG cargo containment systems modified LEFM (linear elastic fracture mechanics) is used in the design phase.The paper discusses the philosophy of a fatigue and fracture control plan for high performance ships and the use of modified LEFM for shipboard LNG cargo containment systems. Current applications of a fatigue and fracture control plan are discussed. The types of shipboard cargo containment systems designed using the modified LNG approach are described.The paper addresses the need for an integrated life time quality assurance program. Such a program is shown to require a synthesis of materials characterization, structural analysis and nondestructive testing. A service performance feedback loop will assist the designers in continually improving the then governing design criteria. In addition, areas requiring further work and possible future applications for fatigue and fracture analysis will be discussed.     

On the behavior of bonded joints in composite material structures

The application of advanced reinforced composite materials in aerospace structures during the remainder of this century is widely predicted. The joining of structural components by adhesive bonding is extremely desirable, because both bolting and riveting result in the cutting of fibers as well as the introduction of stress concentrations, both of which reduce the structural efficiency. R.E. Watson states that, “The next two decades will surely see dramatic advances in structures as compared to those experienced over the last 30 years. Improved titanium alloys and the advanced high strength composites, with more strength per pound than aluminum, will be the principal materials used.” Further he writes, “New bonding techniques will gradually replace riveting in many applications, permitting greater design stresses and more efficient distribution of the materials.”Because in aerospace structures dynamic loads are always present, it is absolutely essential that the fatigue behavior of bonded joints between composite material components be better understood, in order to have available design principles and rationale to take advantage of the desirable characteristics of composite materials.To date the few isolated experimental studies of composite-composite or composite-metal adherend bonded joints have been conducted under static and/or constant amplitude cyclic loading, and no generally accepted cumulative damage theories have evolved.The present research is a systematic, analytical and experimental program of study concentrating on those parameters considered to be the most influential on the static and fatigue life of an adhesive bonded single lap joint. The objectives of the program are to better understand the reasons why certain parameters have such a large influence on the structural integrity of the joint. As a result it is hoped that considerable insight will be gained as to static and fatigue life of more complicated joints such as the doable lap, the scarf, and the stepped lap joints. The analytical as well as the experimental static and fatigue test portions of the program are reported on herein.The following parameters, deemed to be the most important, were selected for study: overlap length, adhesive thickness, orientation of the laminae of the laminated adherends (particularly the lamina immediately adjacent to the adhesive), and the effect on the fatigue life of whether or not the mean value of the fatigue load causes maximum stresses above or below the shear proportional limit of the adhesive material.The determination of stresses in the test specimens is made by an analysis method developed in this program.     

Fatigue life prediction of a stainless steel plate-fin structure using equivalent-homogeneous-solid method

Stainless steel plate-fin heat exchangers are key components in nuclear power stations and hydrogen production systems using High Temperature Gas-cooled Reactors (HTGR). Fatigue is the most failure mode for plate-fin structures because they operate under cyclic high pressures and high temperatures. This paper establishes a life prediction method of fatigue based on equivalent-homogeneous-solid method for a 304 stainless steel plate-fin structure. A finite element analysis (FEA) program of fatigue life has been developed, which has been verified by fatigue experiments. By using this method, both the local stress concentration and the fatigue life for the whole plate-fin structure can be predicted. The results show that the fatigue cracks initiate at the fillet and then propagate to the interface and eventually the base metal of fin. The fatigue fracture in the filler metal shows brittle character, while typical dimple and striation are shown in the base metal.     

Short surface fatigue cracks growth under constant and variable amplitude loading

This paper deals with the fatigue strength of S355NL steel, of a common use within the shipbuilding industry, under uniaxial constant and variable loading. Indeed, ship structures are subjected to variable loading due to various sea states, wind and waves. As a consequence, a better knowledge of fatigue behavior under real loading conditions is needed. This study aims at analyzing the influence of loading conditions (load ratio and variable amplitude loading) on the short crack behavior and last, with a proposed model to assess the fatigue crack life. The tools used to prepare inspections in critical areas only take into account the long crack behavior. The results from the proposed model were compared to the assessments these tools are providing with.     

Three-dimensional calculations of high cycle fatigue life under out-of-phase multiaxial loading

In this study, we investigate the prediction of fatigue life at a high number of cycles (>5 × 10⁴ cycles) for three-dimensional structures. An approach has been developed that includes the results of fatigue tests in a program using the finite element method. Numerical fatigue life calculations using three fatigue criteria were conducted to predict S – N curves. To complete the study and validate this approach, tests were carried out on FGS 700/2 cast iron with different geometrical structures and different fatigue loadings.     

Effect of fatigue loading on the modal properties of composite structures and its utilization for prediction of residual life

The design of composite structures for fatigue loading utilizes S-N curves to predict the fatigue life based on coupon testing. Due to the complex manufacturing process, the initial fabrication inconsistencies may cause the predicted number of cycles to failure to be off by one or two orders of magnitude. An experimental method is developed to predict the residual fatigue life of composite structures and continuously refine the prediction during the service life of these structures. Global effects on modal parameters, natural frequencies and damping ratios are investigated during the fatigue process. The Random Decrement signal processing technique is used. Changes of modal parameters are correlated with the prediction of fatigue failure life for selected graphite/epoxy composite specimens. The nature of the proposed method lends itself to real-time applications, especially, in service structures, as a nondestructive indicator.