A simplified life estimation method for the spherical hull of deep manned submersibles

Creep and fatigue are involved in the loading of deep manned submersible, which is a rather complex variable amplitude pattern. Dwell effects resulting in lower life than pure fatigue are observed in the prior experimental research while no proper prediction methods are available to explain the phenomenon. Recently, the authors proposed a modified crack growth rate model to explain the creep effect under the cyclic loading which is validated for the crack growth of some titanium alloys under cyclic creep loading, however, its application is restricted to the condition where lots of parameters have to be determined based on many experiments and it is not very convenient in the material selection and primary design stage of a component. In this paper, a simplified prediction model for the load pattern of constant amplitude cyclic loading is proposed aiming at one of the most applicable materials for the pressure hull of submersibles, Ti–6Al–4V ELI. The method can be easily used to estimate the life of the pressure hull based on two series of basic mechanical properties of the material and validated by the modified crack growth rate model with parameters determined by large amounts of experimental data.     

随机载荷作用下焊接结构表面裂纹扩展研究

随机载荷作用下焊接结构表面裂纹的扩展问题是工程结构中常见的问题.文中设计了随机载荷作用下焊接结构的疲劳断裂试验,试样由平板以一定的角度焊接而成,配合相应的夹具采用轴向加载,在MTS疲劳试验机上进行试验,采用应变片对裂纹的萌生进行监测,用降载勾线法描绘裂纹的扩展形貌,最后利用试验数据对文献中提到的等效厚度法和等效应力强度因子法进行了验证,结果表明:这两种方法的计算结果都与试验结果比较接近,可以用于计算表面裂纹的疲劳扩展.     

数字化船坞快速搭载的技术应用

传统船坞搭载使用二维平面搭载坐标系，搭载精度数据传输效率低、无法共享。为解决上述问题，构建数字化船坞系统。以数字化船坞三维测控网为基准，以数字化船坞精度管理系统实现船坞搭载数据的无纸化传输、实时共享和统计分析，精度数据真正实现前后生产工序互联互通。实际应用表明，数字化船坞用于多总段连续模拟搭载、总段搭载定位和船坞移船坐墩定位可大幅提高搭载定位精度和作业效率。     

Numerical simulation of fatigue crack propagation under biaxial tensile loadings with phase differences

Fatigue crack propagation under the biaxial tensile loading, which loading directions are normal and parallel to the initial crack position, is highlighted in this study. Most of in-service structures and vessels are subjected to many types of loading. Generally, these loadings have different axial components with different phases. However, the structural integrities of structures and vessels are evaluated according to design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S–N curves approach. An approach that does not use S–N curves has been favored by researchers, with the fracture mechanics approach preferred for evaluating the fatigue life of structures. An advanced fracture mechanics approach was developed based on the Re-tensile Plastic zone Generating (RPG) stress criterion for fatigue crack propagation. In this study, fatigue crack propagation tests under biaxial loading with six different phase and loading conditions are performed and the effect of the phase difference under biaxial loading is evaluated. A numerical simulation method of fatigue crack propagation based on the RPG stress criterion under different biaxial loading phase conditions is presented and compared to measured data.     

Experimental and analytical investigation of fatigue characteristics of 350WT steel under constant and variable amplitude loadings

Fatigue analysis is a complex and uncertain process. Various models have been proposed; however, no universal or all-encompassing model exists.A state-of-the-art literature review of available fatigue crack propagation models, both for constant and variable amplitude loadings, was conducted to identify their advantages and limitations. Emphasis was placed on models that were simple to evaluate and required few (if any) empirical curve-fitting parameters.An experimental fatigue program was conducted, consisting of constant and semi-random (variable) amplitude cyclic loadings on 350WT steel 40J at −40°C. The fatigue models examined in the literature review were then compared to results obtained from the experiments.Findings for the constant amplitude loading (CAL) fatigue baseline data obtained experimentally for 350WT steel are reported and evaluated against the predictions by various models. Results of an experimental investigation into fatigue crack propagation (FCP) response of the steel under variable amplitude loading (VAL), consisting of CAL with random overloads (OL) is also presented. This includes a summary of theoretical models applicable to VAL fatigue crack propagation, and comparison of the experimental results to the models.     

有效应力强度因子幅值计算模型的验证

裂纹闭合效应在金属疲劳中有着十分重要的作用,裂纹闭合概念已经用于解释变幅载荷作用下的裂纹扩展问题,已提出了许多基于裂纹闭合概念的有效应力强度因子计算模型.黄等人在Newman模型的基础上,提出了考虑因素更全面且便于应用的有效应力强度因子幅计算模型以及变幅载荷下工程结构疲劳寿命预测模型.为了验证该模型对不同材料的有效性和适应性,收集了一些相关的试验数据,和该模型的预测结果对比发现该模型的预测结果和试验数据符合得很好.对几种钢、铝合金和钛合金材料在不同应力比下的裂纹扩展速率数据用该模型转换成用有效应力强度因子表示的裂纹扩展速率,结果表明由有效应力强度因子幅表示的扩展速率将不同应力比下较分散的裂纹扩展率数据集中在一个很小的分散带内,同时得到了有参考价值的的一些结论.     

金属疲劳裂纹扩展速率的贝叶斯正则化BP神经网络预测

人工神经网络是进行预报裂纹扩展率的一个重要方法。文章针对不同金属的疲劳裂纹扩展速率分别建立贝叶斯正则化BP(Back Propagation)神经网络,将各材料在不同应力比R下的疲劳裂纹扩展速率试验数据分为两部分,一部分用来进行训练网络,另一部分用来测试训练好的网络,检验其泛化能力。将从文献中获取的4种不同金属材料的疲劳试验数据作为算例,来检验网络的性能。计算结果表明贝叶斯正则化BP神经网络不仅对训练样本有很好的拟合能力,而且对于未训练过的测试样本也有较好的预测能力,即有较强的泛化能力。同时,指出了建立网络时减少门槛值附近的试验样本点,可以提高网络的预测能力。研究结果表明,该方法可以方便地获得不同应力比R下的疲劳裂纹扩展速率,从而达到减少试验次数,充分利用已有数据的目的。并且可以进一步应用于其他金属的疲劳裂纹扩展速率的预报。     

随机载荷作用下的疲劳裂纹扩展

船舶等许多工程结构在服役过程中的受载荷历程是一个随机过程.而变幅载荷下的载荷相互作用对疲劳裂纹扩展寿命将产生显著的影响.因此研究随机载荷作用下的裂纹扩展及定量计算对船舶结构的疲劳寿命预测的可靠性是十分重要的.该文提出了一个基于有效应力强度因子,以应力比和裂纹尖端塑性区尺寸为主要参数的随机载荷作用下疲劳寿命预测模型.该模型用于预测几种载荷谱作用下的裂纹扩展试验,结果表明预测结构和实验结果符合得很好.     

基于累积塑性破坏的船体板低周疲劳裂纹扩展寿命研究

船体板的总体断裂破坏往往是低周疲劳破坏与累积塑性破坏两种破坏模式耦合作用的结果,故在船体板低周疲劳裂纹扩展寿命评估中,其基于累积塑性应变的船体板低周疲劳裂纹扩展寿命分析能够更为符合实际地评估船体板的总体断裂承载能力。船体板低周疲劳裂纹扩展寿命由宏观可检测裂纹扩展到临界裂纹而发生破坏这段区间的寿命。船体在实际航行中受到多次波浪外载作用而使其进入塑性变形不断累积或不断反复的破坏过程,并最终导致低周疲劳裂纹的萌生及扩展而使结构破坏,其破坏形式分别对应于增量塑性变形破坏（或棘轮效应）或交变塑性变形破坏（或低周疲劳）。局部塑性变形的累积会加剧低周疲劳裂纹不断扩展,因而基于累积塑性破坏研究船体板低周疲劳扩展寿命更为合理。文中以船体板单次循环载荷后塑性应变大小为基础,依据累积递增塑性破坏过程及弹塑性理论,计算经过N次变幅循环载荷后船体板累积塑性应变值,结合循环应力—应变曲线获得相应的稳定的迟滞回线,确定裂纹尖端应力应变曲线及确定相关塑性参量并依据选取的断裂判据判定裂纹扩展。建立循环载荷下基于累积递增塑性破坏的船体板低周疲劳裂纹扩展寿命的计算模型考虑应力比对此裂纹扩展寿命计算模型的影响。由该方法计算出的疲劳裂纹扩展寿命将对正确预估船舶结构的低周疲劳强度从而提高船舶安全性有重要意义。     

07MnNiCrMoVDR钢在硫化氢溶液中的腐蚀疲劳裂纹扩展速率数学模型

本文通过试验研究07MnNiCrMoVDR钢在硫化氢水溶液中的腐蚀疲劳裂纹扩展特性,根据试验数据,利用神经网络,以介质浓度、载荷频率、应力比作为输入节点,裂纹扩展速率系数C作为输出节点,训练该网络预测不同条件下的裂纹扩展速率.根据由神经网络所预测的数据找出这三个影响因素在裂纹扩展速率系数C中的关系表达式,从而回归出07MnNiCrMoVDR钢在硫化氢水溶液中的腐蚀疲劳裂纹扩展速率数学模型.     

Multi-scale modeling of fatigue crack propagation applied to random sequence of clustered loading

Fatigue crack propagation in marine structures is obviously governed by mechanics of the considerably different four levels of multi-scale problems. Problems of structural response to environmental loads have length scale of several hundred meters, whereas possible detectable size of cracks from initial defects in a weld is of the order of millimeters. Once a fatigue crack initiates, crack tip plasticity is of the order of several grain sizes, while the resulting fatigue crack growth in each load cycle is of the order of nanometers. In our previous work, the first author and their associates have developed the so-called CP-System, which can treat the first two multi-level problems as an integrated system. Furthermore, we have incorporated the third level of mechanics by using the stress intensity range corresponding to the repeated tensile plastic deformation ahead of the crack tip. In the present paper, we shall discuss a more rational integral equation-based formulation in order to integrate the third and fourth levels of micro-mechanics to the first two levels of continuum mechanics.The method is then applied to fatigue crack propagation under the effects of random sequence of clustered loading. As an example of the random sequence of clustered load, we shall use the so-called “storm model”. In the crack propagation simulation, we have to take into account of the plastic wake on the crack surfaces, whose thicknesses are influenced by the material parameters involved in the crack growth model. These parameters are first identified by the fatigue tests under combined constant and random loading using a CT specimen. Then, fatigue crack growth is investigated by numerical simulation and fatigue tests for various random sequences of clustered loading. The experimental and numerical results agree quite well with each other, and fatigue crack propagation is found to be considerably retarded under random sequence loading, so that the conventional equivalent stress approach may provide rather conservative results to the real seaway loading.     

An experimental study on water entry of horizontal cylinders

Complex hydrodynamics of a circular cylinder entering into water horizontally for low Froude numbers is experimentally studied. A high-speed digital video camera system is used to record the water entry process. The emphasis of this study is to investigate the three-dimensional effect on the water entry of the horizontal cylinders. A new experimental setup is built for this purpose and great effort is put on taking high quality pictures of the free surfaces. In the experiment four length to diameter ratios, two cylinder-water density ratios, and two release heights are investigated. For comparison, experiment with a sphere is also carried out. Quantitative analysis is performed based on the digital video images and the results are presented. The results obtained from this study can be used not only for understanding the physics but also for the purpose of validation of numerical models.     

基于疲劳裂纹扩展率单一曲线模型的疲劳寿命预测

基于疲劳裂纹扩展率单一曲线模型对铝合金D16CzATWH等在不同加载次序下的疲劳裂纹扩展行为进行了预测.通过与已有文献试验数据和NASGRO条带屈服模型的计算结果进行比较,发现本模型的预测结果和试验数据符合得较好,并能解释NASGRO模型不易解决的过载迟滞效应.同时该模型需要的参数相对较少且易于确定,因此该模型有良好的工程适用性.模型中载荷效应指数与过载频率以及过载幅度相关,它的取值对预测结果有显著影响.     

考虑累积塑性的船体裂纹板变幅低周疲劳裂纹扩展行为研究

船舶结构的扩展断裂失效往往是低周疲劳破坏和累积递增塑性耦合作用的结果,疲劳裂纹的扩展就是裂纹尖端前缘材料刚度不断降低、延展性不断耗失而逐渐分离的过程。基于弹塑性断裂力学理论,文章在作者对常幅载荷下提出的考虑累积塑性损伤的低周疲劳裂纹扩展速率预测模型的基础上对具有单个过载峰的拉伸/压缩过载下的扩展行为进行了研究。通过低周疲劳裂纹扩展试验进一步验证了该预测模型能合理评估具有单个过载峰的拉伸/压缩过载下的低周疲劳裂纹扩展行为。     

Prediction of crack growth in 350WT steel subjected to constant amplitude with over- and under-loads using a modified wheeler approach

Previous efforts have suggested that tensile overloading may cause significant crack growth retardation. On the other hand, crack growth acceleration may occur under the influence of compressive underloading. In practice, however, the effects of compressive underloading are often neglected. An experimental/analytical and computational investigation was therefore undertaken to evaluate the effects of both tensile and compressive overloading on the fatigue crack growth behavior in 350WT steel.Simplicity and accuracy in fatigue crack growth prediction is of extreme importance. One of the most commonly used models for crack growth prediction under variable amplitude loading is that of Wheeler. Unfortunately, overload effects involving compression cannot be handled by the model in its current form. Using a computational methodology, an effective plastic zone was established as a mean to incorporate the sequence effects, thus resulting in creation of a modified Wheeler approach. Fatigue life predictions provided by the revised approach/model agree reasonably well with experimental results.     

循环载荷下AH32钢低周疲劳与累积塑性破坏交互作用试验研究

文章对AH32钢在循环载荷下低周疲劳破坏和累积塑性破坏的交互作用进行了试验研究.试验中分析了平均应力、应力幅值及应力比对低周疲劳裂纹扩展寿命和累积塑性应变的影响.试验结果表明,较大的循环载荷下发生两种失效模式,由裂纹扩展导致的低周疲劳失效和较大的塑性应变导致的累积塑性破坏.在试验结果的基础上,文中提出了考虑低周疲劳破坏和累积塑性破坏交互作用的失效模型,模型结果与试验结果较为吻合,说明其具有一定的可行性.     

Towards a holistic digital twin solution for real-time monitoring of aquaculture net cage systems

Digital twins and relevant concepts are being applied in a wide variety of ways, and they are of most use when an actual real-world physical system or process (a physical twin) is changing over time and when measurement data correlated with this change can be captured. In this work, a digital twin model was implemented for real-time monitoring of aquaculture net cage systems, which is notoriously challenging because of several difficult-to-measure properties, such as forces on and deformation of the flexible netting structures, waves and flow field alterations around the cage and complex stiffness behaviour of the mooring elements made by fibre ropes. These properties were set to be adaptable according to the resultant outputs, such as cage responses and mooring loads that were continuously compared with the measurement data obtained from remote monitoring sensors. In this way, real-time sensor data were assimilated into the numerical simulation model for representing the actual net cage system. No dedicated sensors were used for fish monitoring, but the fish behavioural responses to current, wave and cage deformation were modelled according to relevant field observational data. A wireless sensor network has also been tested for the digital twin implementation, which was found to be suitable for practical uses in fish farms.     

具初始裂纹钢桥梁焊接构件疲劳裂纹扩展和疲劳寿命计算

钢桥梁构件因焊接缺陷或者在疲劳应力交互作用下萌生裂纹,钢桥梁构件因存在初始裂纹大大地降低焊接构件的疲劳性能.文中考虑到焊接构件往往会存在初始缺陷,研究了含初始缺陷的桥梁焊接构件的疲劳分析方法.在已有的大量含裂纹构件的疲劳实验工作基础上,结合课题组所做的焊接构件疲劳实验资料,假设初始裂纹焊接构件在疲劳裂纹扩展过程中裂纹形状保持为半椭圆形状;针对桥梁构件实际受力特征,由钢桥梁构件的高周疲劳损伤演化方程入手,考虑初始裂纹条件下裂纹前缘的损伤区的存在及其对裂纹扩展的影响,采用虚拟裂纹扩张方法推导了适用于钢桥梁构件的疲劳裂纹扩展分析的疲劳裂纹扩展率公式,建议了裂纹扩展和疲劳寿命数值计算方法.采用文中的计算方法,研究了已有的钢桥梁结构焊接构件疲劳实验的裂纹扩展过程和疲劳寿命的计算.计算结果表明:裂纹的扩展过程中裂纹的深度和表面半长度之比a/c是一个变化的数值,且在一定的a0/t0条件下,随着a0/c0的增加,循环次数逐渐增大.     

大型砝码加载系统的设计

本文涉及的装置,其目的是利用不同量程的大质量高精度砝码对各种精度电子衡进行称重数值的校验,以便校准电子衡的精度偏差,文章详细叙述了对于大质量、多量程的吊挂式砝码组合卸载机构的设计原理、结构特点、技术创新及市场前景,为评定大量程电子衡的优劣提供了技术实现手段.     

两级交变载荷下船体结构典型节点疲劳试验研究

江海直达船属于浅吃水大型宽船,往复航经江段和海段,其疲劳问题不容忽视。将江段和海段载荷简化为小和大2级交变载荷,选取较为典型的船底纵骨贯穿横舱壁节点,通过对比试验探讨2级交变载荷对该船疲劳寿命的影响。试验结果表明,在试验工况下,变幅载荷中的大载荷是导致裂纹扩展的主要因素,小载荷的参与会降低大载荷作用下裂纹扩展的速率。采用等效应力法对变幅载荷下节点的疲劳寿命进行评估,发现采用Miner准则所得结果偏保守,采用均方根法所得结果偏危险,采用修正的Miner准则所得结果精度较高,推荐采用该方法评估2级交变载荷下船体结构典型节点的疲劳寿命。