金属材料断裂准则研究进展

介绍了金属材料断裂准则的研究进展,包括传统强度理论、现代断裂力学理论及常用断裂准则,并对各种准则的特点进行了简要分析。     

金属韧性断裂准则的数值模拟和试验研究

对不同外形的45钢试件进行了拉伸、压缩和扭转等材料试验,对工程中常用的5个韧性断裂准则的适用范围进行了对比研究,并采用Gurson-Tvergaard(GT)多孔材料本构模型对试验过程进行了数值模拟.指出目前使用的断裂准则都不可能对材料在多种变形条件下给出一个固定临界值.根据金属成形工艺特点,综合考虑拉伸型和剪切型2种不同韧性断裂机制,提出一个统一的韧性断裂准则形式.试验和数值计算结果证明了该准则的有效性和普适性,进而利用单向拉伸和扭转试验确定的材料常数合理地预测压缩过程中的韧性断裂现象.     

球形非金属夹杂物与焊缝金属的断裂

对四种不同强度级别的焊缝金属的延性断口和脆性断口上的夹杂物进行了系统的观察与分析，探讨了球形非金属夹杂物对焊缝金属断裂性能的影响。焊缝金属的延性断裂性能与所含夹杂物的数量存在直接关系，而焊缝金属的解理断裂中相当大一部分由尺寸相对较大的、与基体结合强度较高的Ｔｉ型夹杂物所引发。     

新氢压缩机活塞杆断裂分析

用金相显微镜和电子探针对新氢压缩机活塞杆断口进行了分析。结果表明，基材热处理不当以及金属夹杂物的存在引起活塞杆内部缺陷和大量腐蚀气体是造成新氢压缩机活塞杆断裂的主要原因，活塞杆断裂是多源的应力腐蚀疲劳断裂。     

二次应力存在时的J积分和断裂准则

本文对二次应力存在时的修正Ｊ积分参量进行了较全面的介绍和总结，用有限元法对各修正Ｊ积分的守恒性及其相互关系进行了比较和讨论，结果表明Ｊ′积分是适用于二次应力存在的具有明确物理意义的最普遍有效断裂参量，并建立了相应的Ｊ积分断裂准则     

石材爆破的断裂控制原理及措施

首先论述了石材爆破的定向断裂控制基本原理和实施方法，然后介绍了石材爆破的破坏性断裂类型及预防措施。     

基于GISSMO断裂准则的6016铝合金断裂行为研究

目的 研究零部件在成形与碰撞过程中,6016铝合金在不同应力状态下的断裂行为。方法 通过准静态拉伸实验,获得了6016铝合金的基本力学性能。利用Nakajima成形极限实验,获得了6016铝合金材料的断裂成形极限曲线。设计了7种涵盖成形及碰撞过程中应力状态的断裂极限测试试样,采用数字图像相关技术(DIC)记录了试样在变形过程中的全场应变。利用实验-有限元反求方法标定了6016铝合金的GISSMO断裂准则的参数,并用帽形件三点弯曲实验验证了模型的合理性。结果 相比于传统断裂成形极限图的预测结果,基于GISSMO断裂准则的仿真结果与实验具有更好的一致性。结论 所建立的GISSMO模型可以用于预测6016铝合金在复杂应力状态下的断裂行为。     

自动扶手电梯传动轴断裂分析

采用一系列金属物理测试手段对自动扶手电梯传动轴的断裂失效进行了分析，该轴使用态为未经热处理的热轧棒材，加之ＡＢ两轴的轴线偏离主两轴之间的倒角Ｒ不规范，最终导致断裂，提出了改进意见－合理地选材和精心地机加工。     

热轧带肋钢筋断裂分析

为进一步提高产品质量,针对螺纹钢出现的裂纹和断裂事故进行了系统的生产工序分析.采用光谱分析仪分析了断裂钢筋的化学组成,利用光学显微镜、电子能谱仪分析断裂钢筋组织结构和断裂钢筋中非金属夹杂物的类型、数量、大小、组成及分布,并讨论了目前生产工艺中非金属夹杂物的来源.研究表明,钢筋中非金属夹杂物的产生是钢筋裂纹和断裂的根源,夹杂物主要是由炼钢脱氧和耐火材料腐蚀的铝硅酸盐组成.     

金属接骨板断裂分析

对断裂的金属接骨板进行了化学成分、金相组织、硬度、断口的宏观和微观形貌检验和分析,结果表明,该接骨板断裂源处有氧化铝非金属夹杂物聚集,非金属夹杂物周围组织存在变形带,裂源产生在非金属夹杂物边部应力集中部位,最终导致金属接骨板断裂.     

A continuous damage fracture model to predict formability of sheet metal

A continuous damage fracture model, which consists of a fracture criterion and a continuum damage constitutive law was proposed in this paper to calculate formability of sheet metal. In this model, an extension of the McClintock void growth model was selected as the fracture criterion to be incorporated with a coupled damage‐plasticity Gurson‐type constitutive law. Also, by introducing a Lode angle dependent parameter to define the loading asymmetry condition, the shear effect was phenomenologically taken into account. The proposed fracture model was implemented in user defined material subroutines in ABAQUS. The model was calibrated and correlated by the uniaxial tension, shear and notched specimens tests. Application of the fracture criterion for the Limit dome height tests was discussed and the simulation results were compared with the experimental data.     

Creep rupture and fatigue properties of transient liquid phase bonded joints of Ni base single crystal superalloy

Abstract

Creep rupture and fatigue properties of transient liquid phase (TLP) bonded joints of Ni base single crystal superalloy, CMSX-2, were investigated using MBF-80 insert metal. CMSX-2 was bonded at 1523 K for 1.8 ks in vacuum, which was determined as the optimum bonding condition. The (100) orientation of a bonded specimen was aligned perpendicular to the joint interface. The creep rupture strength and rupture lives of all joints were almost identical to those of the base metal. Elongation and reduction area values of joints were comparable to those of base metal, while creep rupture at high temperature was worsened. The low cycle fatigue properties of all joints were also the same as those of base metal. SEM observation of the fracture surfaces of joints after creep rupture tests revealed that the fracture surfaces were classified into three regions, and that the elongation and reduction of area values decreased sharply with increase in the area fraction of interfacial fracture surface.     

Creep rupture behaviour of low alloy ferritic steel weldments

To establish differences in rupture lives and ductilities between parent metal, weld metal and weldjoint, a commercial heat of lCrMoV cast steel welded with 21/4Cr1M0 steel electrodes was creep tested over a range of stresses at 550°C using constant load creep testing units. The results indicate that, while there is no significant variation in rupture lives, ductility in the weldjoint showed a decreasing trend over longer periods of testing. In weldjoint specimens that comprised parent metal, heat affected zone (HAZ) and weld metal, fracture occurred in the weld metal quite near to the fusion boundary over the entire range of stresses. The rupture ductility in the weldjoint was found to be lower than in parent or weld metal.

Scanning electron microscopy (SEM) revealed the fracture surfaces of parent and weld metal to be heavily dimpled, the dimples originating mostly around carbide precipitates, whereas the fracture surfaces of the weldjoint were found to be somewhat faceted.

The results of the present work suggest that weldments made with 2114CrlMo steel deposits possess comparable creep lives to the parent metal of 1CrMoV steel, and the weld metal in the weldjoint near the fusion boundary exhibits a tendency to embrittle over longer periods of testing.     

Modeling and simulation of the effect of fiber breakage on creep behavior of fiber-reinforced metal matrix composites

A theoretical model and computer simulation methodology was developed to predict the effect of fiber fracture on creep behavior of continuous fiber-reinforced metal matrix composites. Initially, a single fiber model was developed based upon the fiber statistical characteristics and a shear-lag analysis to establish the computation simulation route. Then, the methodology was extended to predict the creep behavior of a multiple fiber composite. A failure criterion was also incorporated in the model to predict the rupture life of the composite. A parametric study was also conducted to investigate the effects of properties of the constituents on the longitudinal creep behavior of the SCS-6/Ti composite.     

Failure criteria for linear elastic materials with U-notches

This paper provides a simple, albeit accurate, criterion for prediction of the rupture loads of brittle, or quasi-brittle, U-notched samples, where linear elastic fracture mechanics is not applicable because blunted notches do not exhibit stress singularities. Good agreement is found between numerical predictions and experimental results. The results of fracture tests from 18 different ceramic materials and a polymer (at − 60°C) are summarized and are used as a reference for checking the fracture criterion. Seven fracture criteria are reviewed and it is shown that all can be recast into the proposed criterion.     

Fracture analysis of V‐notched rubbers: An experimental and theoretical study

In this study, the rupture load in rubbers weakened by sharp V‐notch is investigated under mode I loading. To this end, first, mode I fracture tests are performed on V‐notched samples made of styrene‐butadiene rubbers and the corresponding rupture loads are obtained. Then, the effective stretch (ES) criterion, which was recently developed by the present authors for rupture assessment of cracked rubber parts, is extended and used for the V‐notched rubbers. It is shown that similar to cracked rubbers, the state of stress near the notch tip is also nearly uniaxial. By employing the ES criterion, the critical displacements corresponding to the rupture in the tested samples are calculated. Finally, the predictions of the criterion are compared with the corresponding experimental values, and good consistency is shown to exist.     

Multiparametric sufficient criterion of quasi-brittle fracture for complicated stress state

Behaviour of an atomic structure in the vicinity of the crack tip is simulated. Buckling and postbuckling deformation of three- and four-atomic cells at generalized tension is studied. A discrete-integral fracture criterion is proposed for normal rupture cracks when stress fields have a singular component, vectors of fields of stresses and deformations being collinear. When formulating the proposed criterion, we used the new rank of solutions, which differ from solutions applied in formulating the classical sufficient fracture criterion, in conformity with Novozhilov’s hybrid model. The proposed criterion permits limiting passage to necessary criterion when energetic characteristics of postbuckling deformation of cells can be neglected within the limit. Values of critical loads obtained in conformity with the sufficient criterion essentially differ from those obtained in conformity with the necessary criterion.     

LIFE PREDICTION OF 316 STAINLESS STEEL UNDER CREEP-FATIGUE LOADING

Life prediction for creep-fatigue loading conditions should be related to creep damage mechanisms. In order to examine the effect of the creep damage mode on rupture life under creep-fatigue loading, a “combined creep-fatigue loading test” was carried out on 316 stainless steel. In this method, creep loading and fatigue loading are repeated alternately. The fracture criteria under combined loading closely depend on the creep fracture modes of the static creep test. A new life prediction method which uses this new fracture criterion is proposed. The criteria are changed when the creep damage mode varies. In order to verify the adequacy of this method, fatigue tests with a tensile strain-hold wave form were carried out. It is clear that rupture life in such fatigue tests is dependent on the chosen fracture criteria.     

Cleavag Fracture Criterion of Low Alloy Steal and Weld Metal in Notched Specimens

The cleavage fracture criterion of low alloy steel and weld metal in notched specimens is investigated in detail based on a great number of experimental data. It has been found that the most cleavage fractures initiate at a distance shorter (left side) than that of the peak stress location below a notch root, and the cleavage fracture in notched specimens must satisfy a dual criterion, i.e., a critical plastic strain (ε_p ≥ ε_pc) for initiating a crack nucleus, and a critical tensile stress (σ_yy ≥ σ_f) for its propagation. According to the dual criterion model, the great number of experimental data of 4PB (four-point bending) tests for the low alloy steel and weld metal and their statistical distribution are explained. The effects of temperature , the local fracture stress σ_f and the critical plastic strain ε_pc on the locations of cleavage initiation sites and the controlling steps of cleavage fracture process are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the benefits of a stress criterion for the simulation of cup drawing process

Experimental and numerical cup drawing process has been investigated on 0.65 mm zinc sheets. The cup exhibits anisotropic earrings due to the material microstructure. The material formability is studied through elliptical bulge tests in the rolling, diagonal and transverse direction. High anisotropy of the formability is observed. The numerical simulation of cup drawing is then made and demonstrates the correct fitting with experimental results. A stress formability criterion developed by Jansen et al. [14] is then implemented into a finite element method software and applied to predict the material rupture observed for some process conditions. The risk zone of the cup is subjected to some strain path changes according to the simulation whereas the strain value does not explain the rupture according to the experimental formability measured by the bulge tests. It has been shown that the rupture is due to some critical stresses, which are reached in the risk zone of the cup. The use of the stress criterion and its non-dependence on the strain path change allows the fracture prediction. Finally, the numerical fracture propagation by the “kill element method”, as briefly discussed by Bouchard et al. [4], is used and shows a good similarity with the experience.