8NVD48A—27柴油机曲轴的断裂力学分析和实验研究

根据断裂力学原理，采用三维力学模型实验和新兴的焦散线法，对８ＮＶＤ４８Ａ－２Ｕ型柴油机曲轴的三维应力状态、断裂力学参数进行了分析和实验研究，以预报曲轴安全可靠性和寿命，为船舶检验周期提供理论和实验依据。并提出曲轴表面裂纹几何因子的表达方法和曲轴裂纹扩展速率的表达式，对Ｐａｒｉｓ经验公式进行修正。     

应用三维有限元法分析烧瓦对曲轴的影响

针对连杆轴瓦烧损情况,研究烧瓦对曲轴的影响。采用三维有限元技术计算曲轴的温度场。研究结果表明,由烧瓦所引起的曲轴故障表现为轴颈表面的微裂纹或裂纹。轻微烧瓦使轴颈处于回火状态,轴颈材料由于具有回火脆性而使冲击韧性显著下降,冷却后较高的残余热应力导致裂纹的产生。剧烈烧瓦使轴颈部分处于淬火状态,恶劣的淬火条件使曲轴冷却后产生很大的热应力,淬火热应力超过材料的屈服极限和破断抗力,导致曲轴产生变形甚至开裂。     

基于ABAQUS的发动机曲轴模态试验分析

以柴油机发动机曲轴为研究对象,运用CATIA建立发动机曲轴三维几何模型,并运用ABAQUS有限元分析软件对发动机曲轴进行了自由模态分析。再对曲轴的细节特征和约束进行了简化,求出了曲轴自由约束条件下前七阶模态的固有频率和振型。运用实验对比分析方法,通过模态实验可获得曲轴各阶的模态频率和振型,为动力分析提供技术参数,同时也为进一步发动机高速运转时曲轴振动中危险各区域提供了理论依据。     

内燃机曲轴振动特性的三维模拟--基于二次Timoshenko梁单元

本文在有限元法的基础上，采用基于一阶剪切变形理论的三节点、二次Timoshen-ko梁单元模拟内燃机曲轴结构，对一直列式四缸发动机曲轴进行了自由振动特性分析，并与相关研究和实验数据进行了比较；随后，进一步模拟此曲轴的三维动态振动特性，计算并分析了其动态振动响应的结果。     

具有裂纹的曲轴-轴承系统动力学与摩擦学耦合分析

以实测示功图为计算依据,以4缸柴油机的曲轴-轴承系统为研究对象,应用动力学仿真软件ADAMS耦合分析了具有裂纹的曲轴-轴承系统动力学行为和摩擦学特性,提出了"等效直径法"建立具有不同深度裂纹的弹性曲轴有限元模型.由于裂纹的扩展是曲轴动力学响应的慢变参数,从启裂到曲轴断裂采用线性插值法,分别建立具有不同深度裂纹的曲轴-轴承系统动力学和摩擦学耦合分析ADAMS模型并求解.结果表明,裂纹对其附近的曲轴轴承的动力学和摩擦学性能影响较大,随着裂纹深度的增加,裂纹附近的主轴承反力、最大油膜压力峰值和最小油膜厚度均减小,但曲轴轴颈中心径向振动响应振幅增加.     

柴油机曲轴静动特性的三维有限元分析

采用有限单元法，对4190柴油机曲轴进行了符合实际情况的三维建模，研究了整体曲轴的变形和应力状态，校核了曲轴在交变载荷下的疲劳强度，探讨了目前曲轴应力有限元计算中广泛采用的单拐力学模型的可靠性，并对曲轴进行了模态分析，为柴油机改进设计提供了有价值的理论依据。     

通过测量曲轴飞轮系统扭振模态特性诊断曲轴裂纹

本文提出了扭振特性对局部结构裂纹变化敏感度的概念和数学定义,推导了模态特性、频响特性对曲轴局部结构参数的敏感度公式。通过理论分析和模态测试比较了多个振动特征量对曲轴裂纹的感应能力,推荐扭振模态阻尼(阻尼衰减因子)、频响函数模态峰、自谱模态峰为裂纹故障最佳评判量,并对曲轴模拟裂纹进行了诊断。     

内燃机曲轴裂纹故障的动态监测方法研究

采用振动分析法研究了诊断曲轴裂纹的途径。根据曲轴内拐角处裂纹的特点，结合断裂力学中的理论——可以从应变能密度方程出发计算得出因裂纹而引起的局部柔度变化，提出了一种推演含有斜向裂纹矩形截面梁单元刚度矩阵的新方法。应用此裂纹梁单元，采用有限元法模拟，可以计算出含有裂纹的单缸发动机曲轴的非线性振动响应。通过分析计算结果，得出了一些有益于诊断曲轴裂纹的结论。     

基于三维有限元分析的曲轴圆角优化设计

内燃机曲轴轴颈的过渡圆角处是应力高度集中部位，易形成疲劳裂纹源，因此设计者对该部位的几何形状尺寸特别留意。本文的研究对象，是一台由四气缸母型机变形后的三气缸发动机曲轴圆角设计。四气缸母型机的曲轴圆角采用带有沉割槽加滚压的复合工艺加工，由于设备条件的限制，三缸机的试制产品无法实施上述工艺。根据曲轴生产厂家的设备条件和技术能力，拟采用曲轴圆弧过渡。作者以三维有限元应力分析为基础，在不降低曲轴轴颈承压面的前提下，采用优化过渡圆角半径，取得了令人满意的效果。     

曲轴疲劳裂纹扩展可靠性分析的工程方法

以DF4B型机车柴油机球墨铸铁曲轴为研究对象 ,计算了在试验谱下的应力分布 ,提出了一种计算疲劳裂纹扩展可靠寿命的工程方法 ,并对曲轴裂纹扩展可靠寿命进行了计算 ,进而对柴油机曲轴的检修期提出了合理建议。     

4012型柴油机曲轴热处理淬裂失效分析研究

对4012型柴油机曲轴淬裂失效进行了分析研究,在对曲轴断口进行全面的理化检测分析后发现,材料中一定数量的TIN组织出现以及碳元素含量的偏高对曲轴淬裂有直接的影响。原材料中TIN组织的数量和形态,在国标《合金结构钢》GB3077并没有限制规定,我们希望通过此文,给有关机械生产制造厂家以参考借鉴。     

Fracture investigations on piping system having large through-wall circumferential crack

In level-3 Leak-Before-Break (LBB) analysis, stability of a postulated through-wall circumferential crack is demonstrated by simplified fracture mechanics calculations. Detailed experimental studies, conducted by the authors, have revealed that the conventional assessment procedure used to demonstrate LBB is too conservative. There is a large factor of safety due to system indeterminacy. It was observed that the critical load of a cracked piping system (with even a large through-wall circumferential crack of about 120°) is of the order of 75–90% of the collapse load of the uncracked piping system. Reduction in load carrying capacity is even less for a piping system having an off-centre crack. This article discusses the above-mentioned aspects in detail. Detailed 3-D elastic-plastic finite element analyses of some of these tests were performed. The suitability of these numerical results to predict crack initiation load in light of the experimental data is discussed.     

Different fracture performance of all-steel and all-aluminium cylinders with axial cracks

The linear elastic and the nonlinear elasto-plastic fracture mechanics analysis on all-metal (all-steel and all-aluminum) cylinder with different axially oriented cracks were carried out using the three-dimensional finite element method and the experimental method. The crack mouth opening displacement CMOD and the crack driving forces (K_I for elastic deformation state and J_I for elasto-plastic deformation state) of the all-steel cylinder and the all-aluminum cylinder containing axial deep cracks, were obtained. Through analysis of the calculated CMOD and crack driving forces for the all-steel cylinder and the all-aluminum cylinder with cracks, whose sizes are often met, respectively, in the engineering applications, the fracture behaviors of the two kinds of all-metal cylinders are compared. The CMOD for the two kinds of all-metal cylinders with external axial cracks were measured by an experimental method and good agreements between the calculated CMOD and tested CMOD were reached. Some CMOD and crack driving force expressions about the crack sizes, internal pressure and location along the crack front are obtained.     

A fracture mechanics based fatigue-creep-environment crack growth model for high temperature

This paper deals with the development of a fatigue crack growth model for high temperature complex loading and application to turbine disc conditions. The proposed model is based on an extensive experimental study performed on Astroloy at 650°C, which comprises fatigue with or without hold times, special tests with holds at intermediate loads, fast-slow or slow-fast triangular waves, sequence tests, etc.

The crack growth model is built up in the framework of classical linear elastic fracture mechanics. Its structure is quite simple and is supported by previously developed fatigue crack growth models and a companion study made at École des Mines de Paris (EMP) for the oxidation processes on Astrology.     

Wide plate tests and critical crack lengths at general yield

A proposal related to experimental fracture mechanics suggested by Professor W. Soete, Gent University, Belgium, is investigated in the present paper. The concept of two critical crack lengths of general yield is proposed, and their physical meaning and engineering application are presented. Based on the experiment and analysis, an engineering method for the assessment of defects in pressure vessels is suggested.     

Modelling crack growth for creep and fatigue loading

Estimates of creep crack growth in engineering components under steady load conditions are usually based on the application of fracture mechanics concepts. In particular the creep parameter C* has become widely used together with creep crack growth data obtained from laboratory tests. There are now a number of practical methods to utilise experimental data. For high temperature components, which are subjected to cyclic (fatigue) as well as creep loading, the estimation of the fracture mechanics parameters becomes much more difficult, and consequently the extent to which the growth of pre-existing cracks grow by creep and fatigue is difficult to quantify. In this paper the response of Type 316L stainless steel is examined. This material progressively strain hardens under reversed cyclic loading, and the creep behaviour also changes. Using uniaxial fatigue and creep results, fracture parameter maps are developed to establish the appropriate regimes for creep-fatigue crack growth. Using the maps a model is developed which can predict the combined effect of fatigue and creep on crack growth. The implications of the model are discussed in relation to the limitations of obtaining results from laboratory tests at short times, and the assessment of practical engineering components.     

Stress intensity factors for a pipe-plate welded joint

A major component of any linear elastic fracture mechanics model for fatigue crack growth is the calculation of the crack tip stress intensity factor. This is particularly difficult for welded joints due to the complex geometry. While some data are available for cracks in welded T-plate joints, there is relatively little data available for larger cracks in more complex tubular joints. Such cracks are of significant interest since the most practical application of fracture mechanics models is the prediction of remaining life for cracks discovered in service.

A pipe-plate joint has been developed as a simplified model of tubular joint geometries for fatigue studies. Two such specimens have been tested in air, with detailed monitoring of crack growth behaviour using potential drop techniques. These data were used to obtain crack growth rate data from which estimates of stress intensity factors were made. Separately, finite element analyses for various discrete crack configurations were performed. The results of these analyses are presented and discussed, with particular emphasis on the accuracy of the results and the implications for fracture mechanics modelling.     

The net-section stress associated with the extension of a part-through full-circumference crack in a pipe

Earlier workers have used a simple net-section stress approach, based on collapse-type analyses, to predict the size and shape of a part-through circumferential crack that will cause failure of a pipe fabricated from a ductile material: stainless steel. The equations of equilibrium are applied, assuming that the cracked section behaves like a plastic hinge, with a region of uniform tensile stress, σ*, acting above the neutral axis and a region of uniform compressive stress, — σ*, acting below the neutral axis; σ* is the average of the yield and ultimate stresses. Both experimental and fracture mechanics calculations have hither to shown that crack extension occurs at net-section stresses that are approximately the same as that used in the collapse analysis, when the crack is of the through-wall type, thus providing partial vindication of the net-section stress approach. The present paper extends this work and a fracture mechanics analysis shows that the net-section stress associated with the extension of a part-through full-circumference crack can be appreciably higher than that for a through-wall crack. The paper therefore provides further support for the usefulness of the simple net-section stress approach for predicting the failure of a stainless steel pipe containing a circumferential crack, since its predictions should be conservative in this situation.     

Two-dimensional finite element analysis of stably growing cracks in inhomogeneous materials

The finite element method was applied to a generation phase analysis for stable crack growth in inhomogeneous materials. Experimental data on stable crack growth in bimaterial CT specimens, which were made of a weldment of the A533B Class 1 steel and HT80 steel, were numerically simulated using the node-release technique to obtain the variations of the fracture mechanics parameters such as the J-integral, T^*-integral, -integral and CTOA with crack extension. New evaluation schemes for the integral fracture mechanics parameters were proposed as being valid for integral paths passing a fusion line of dissimilar materials. It was examined whether the simple formulae of the J-integral for a monolithic CT specimen can be applied to a bimaterial CT specimen or not. The effect of inhomogeneity on the fracture mechanics parameter is discussed in terms of the Q-factor.