非金属夹杂物与钢的韧性研究

２０年前已经研究过非金属夹杂物对钢性能的影响。本文较为详细地研究试样中含有硫化物和氮化物两种类型的夹杂物对负韧性的影响。根据一系列试样测定了几种断裂参数,用以验算Ｋｒａｆｆｔ和其他学者建立的断裂模型。实验结果得出这样的结论：按照Ｋｒａｆｆｔ公式计算的ＫＩＣ值与通过实验获得的ＫＩＣ植相一致。     

夹杂物和晶粒尺寸对洁净车轮钢室温冲击韧度的影响

对洁净车轮钢在不同温度下进行正火处理,得到不同晶粒尺寸的显微组织,然后对车轮钢进行室温冲击试验,利用扫描电镜对冲击试样断口形貌进行观察,研究了夹杂物和晶粒尺寸对洁净车轮钢室温冲击韧度的影响。结果表明：部分车轮钢冲击试样以夹杂物起裂,夹杂物类型为Ti（C,N）,另一部分冲击试样断口起裂源处则未发现有夹杂物,但尺寸在10μm以下的Ti（C,N）夹杂物对车轮钢的冲击韧度没有明显的影响,而晶粒尺寸对车轮钢的冲击韧度有明显影响;其主要原因是室温下车轮钢冲击断裂的临界事件是微裂纹穿过晶界扩展引发解理断裂,因此晶粒尺寸是决定洁净车轮钢冲击韧度的主要因素。     

夹杂物特征参数对40CrNi2Mo钢塑性的影响

用定量金相、扫描电镜和能谱分析等方法获取了用2种工艺冶炼的40CrNi2Mo钢中夹杂物尺寸特征参数,研究了这些参数对钢塑性的影响。结果表明:由于夹杂物的体积分数和尺寸比较小,夹杂物间距的增大,在塑性断裂时由夹杂物形成的微孔洞很难以内颈缩形式聚合,微孔洞间的局部剪切也不容易扩展。由此判断,真空自耗重熔钢的断面收缩率比电渣重熔钢的高。钢中的夹杂物对其均匀延伸率、形变硬化指数和拉伸强度没有影响。     

平面应变断裂韧度的试验原理与过程控制

阐述了平面应变断裂韧度试验的理论模型和GB/T 4161-2007中平面应变断裂韧度KIC有效性判定依据的构建原理,在此基础上分析了预置裂纹应力强度因子和拉伸速率两个影响试验结果的因素,明确说明增大试样厚度是有效提高试验获得KIC值的方法,并以TC4和TA15两种钛合金材料的平面应变断裂韧度试验数据加以证明。     

非金属夹杂物对纯镍N6焊接接头组织性能的影响

以纯镍N6为主要研究对象,借助光学显微镜(OM)、扫描电镜(SEM)、能谱分析仪(EDS)、X射线衍射仪(XRD)及电解萃取装置等手段分析了非金属夹杂物对纯镍N6焊接接头结构及性能的影响.结果表明:纯镍N6试样断裂与非金属夹杂物尺寸、形貌、数量等因素有直接的关系;非正常断裂试样的断口表现为沿晶断裂,断口上夹杂物主要由Al、Si、Ca、Mg、O、Fe等元素组成;对试样的金相组织与夹杂物进行分析发现非正常断裂试样中夹杂物数量及尺寸均大于正常试样,杂物数量大于50个/mm2且夹杂物尺寸大于10 μm的试样均发生断裂;夹杂物主要为氧化铝类(Al2O3、SiO2)、硅酸盐类、氮化物类(AlN、TiN、Ti(C,N))及复相夹杂物;原位拉伸试验表明,断裂的主要原因是在金属基体中存在的夹杂物诱发裂纹源,在应力的作用下裂纹扩展导致断裂.综合分析表明,纯镍N6焊接接头在生产中的断裂是由脆性夹杂物的存在而引起的.     

钢管压扁断裂原因分析

用带钢制成的钢管在压扁试验中出现断裂。采用扫描电镜、能谱和金相分析等方法,对断裂试样进行了夹杂物、晶粒度、显微组织、断口及氧含量的检验和分析。结果表明,钢中夹杂物多和氧含量偏高是导致压扁断裂的主要原因。     

粉末高温合金中夹杂物特性及其质量控制

研究了粉末高温合金中夹杂物特性及对材料断裂行为的影响 ,研究内容包括 :夹杂物的性质及来源、夹杂物在材料变形过程中的形变特征、夹杂物对材料疲劳断裂行为的影响等 ,同时研究了盘件在生产过程中夹杂物质量控制方法 .     

钢凝固过程元素偏析和夹杂物生成预报模型研究进展

钢中的非金属夹杂物对钢的加工和服役性能有重要影响,夹杂物的准确预测和表征可以为优化控制夹杂物形态和性质提供指导。近年来,由于计算机和数学物理模型的不断发展,钢中夹杂物预测模型也得到了很大发展。本文总结和分析了钢凝固过程中元素偏析、夹杂物生成预报模型和精炼-连铸耦合夹杂物预测模型的最新进展。这些模型均可在一定程度上预测钢中夹杂物的组成和数量,但难以预测夹杂物形成的过程。基于此,本文提出一种基于二步形核理论预测凝固过程中夹杂物析出的新思路。     

使用A法和K法检测帘线钢中非金属夹杂物含量的探讨

非金属夹杂物含量是衡量金属材料质量的一个重要指标,笔者通过对同一炉70级帘线钢盘条中的5个试样,分别利用GB/T 10561-2005中的A法和DIN 50602-1985中的K法进行非金属夹杂物含量测定,得到了两种不同的检测结论。通过探讨发现非金属夹杂物的宽度指标是产生两者检测结果差别的主要原因,建议在GB/T 10561-2005的后期修订过程中,考虑非金属夹杂物宽度指标对评定结果的影响。     

某船体结构焊缝非金属夹杂物对断裂韧度的影响

研究了某船体结构焊缝试样断裂韧度试验中的局部"失稳"现象,研究表明局部"失稳"是由于焊缝中残存的非金属夹杂物的局部断裂引起的.该夹杂物系多道焊层间清理不彻底而残留的氧化物夹杂.氧化物夹杂可使断裂韧度水平降低约三分之二.此类缺陷在实际船体结构上是不能接受的.     

Prediction of ductile fracture initiation using micromechanical analysis

In the paper ductile fracture initiation analysis of low-alloyed ferritic steel has been made by application of two micromechanical models: the Rice–Tracey void growth model and the Gurson–Tvergaard–Needleman (GTN) model. The aim of the study was to analyse transferability of micromechanical parameters determined on specimens without initial crack to pre-cracked specimens. A significant part of the research has been carried out through participation in the round robin project organised by the European Structural Integrity Society (ESIS). Tensile tests have been performed on cylindrical smooth specimens and CT specimens. Critical values of micromechanical parameters determined on smooth specimen for both applied models, have been used for prediction of the crack growth initiation in CT specimen. Modelling of the first phase of ductile fracture––void nucleation––has been carried out using quantitative metallographic analysis of non-metallic inclusion content in tested steel. For determination of critical values of model parameters corresponding to ductile fracture initiation a simple procedure has been applied based on a combination of experimental and numerical results. Evaluated J-integral values corresponding to onset of crack growth, J_i, are in good agreement with experimental result and both models have proved to be suitable for determination of the ductile fracture initiation in tested steel. The effect of FE size at a crack tip on J_i-value has been particularly analysed: it has been established that the calculation with FE size corresponding to the mean free path λ between inclusions in steel gives results that are in accordance with the experimental ones.     

碳纤维三维立体织物中纤维表面改性的均一化研究

采用阳极氧化法对碳纤维三维织物进行了表面处理。通过复合材料的界面强度、抗冲击性能和抗压性能,研究了阳极氧化处理工艺参数对碳纤维三维织物复合材料性能的影响。实验结果表明该方法不仅能对三维织物表层的碳纤维进行表面改性, 而且能深入织物内部, 实现对碳纤维三维织物的均一化处理, 从而使碳纤维三维织物/酚醛复合材料的界面强度均得到大幅度提高, 复合材的整体性能得到改善。      

Examination of the causes of a bucket wheel fracture in a bucket wheel excavator

A bucket wheel excavator failure occurred in a brown-coal mine. The failure was caused by a fractured shaft of the bucket wheel. An attempt to determine the causes of the bucket wheel shaft fracture has been made. To that end, the character of changing loads and their maximum amplitudes has been determined by performing measurements on the excavator. A discreet model of the shaft was built and a numerical simulation of the shaft operation using the FEM method was achieved. An analysis of the materials in the fracture area was also implemented. Macroscopic and microscopic images of the fracture area are provided. The shaft fracture was mainly caused by a non-metallic inclusion located below the surface of the shaft as a result of its being rolled. Moreover, it was discovered that the shaft had not been heat-treated.     

FGH95粉末高温合金裂纹闭合数值模拟

夹杂、温度和远场应力是影响粉末高温合金材料断裂性能的重要因素.本文建立了考虑裂纹面接触的含夹杂裂纹体有限元模型,计算了夹杂、温度和远场应力对裂纹闭合的影响.计算结果分析表明:当夹杂与基体未脱开时,夹杂对裂纹的张开应力几乎没有影响,而裂开的夹杂可显著提高裂纹的张开应力;均匀的温度场能显著降低裂纹的张开应力;远场应力越大,裂纹张开应力越大.     

Plastic zone correction on a Zener–Stroh crack interacting with a circular inclusion in ductile materials

Elastic–plastic stress analysis on a matrix Zener–Stroh crack interacting with a circular inclusion (fibre) in fibre‐reinforced composites has been carried out. The Zener–Stroh crack is initiated near the fibre in the pure matrix. Plastic zone correction is introduced the first time for such a crack–inclusion interaction problem so that the fracture behaviour can be analysed more accurately. To determine the plastic zone sizes, a generalized Irwin model is proposed for the mixed‐mode problem where the Von Mises stress yielding criterion is employed. Different to a Griffith crack, a Zener–Stroh crack propagation always occurs from the sharp tip whose relative position to the inclusion has great effect on the elastic–plastic fracture behaviour of the crack. In our study, the plastic zone size (PZS), crack tip opening displacement (CTOD) and effective stress intensity factor (SIF) are evaluated by solving the formulated singular integral equations. Through the numerical examples, the influence of the inclusion (fibre) shear modulus, crack–inclusion distance and the crack sharp tip position on the fracture behaviour of the crack is discussed. It is found that the shear modulus ratio and the crack–inclusion distance have great effect on the normalized values of PZS and CTOD, but the effects highly depend on the crack sharp tip position.     

Fracture initiation at a sphrerical inclusion in a matrix plastically deformed by shear

The critical strain for fracture initiation of a metallic material with a spherical inclusion has been analysed using EaheIby,s inclusion method forthree types of fracture initiation models including the recovery effect by diffusion of atoms. When the elastic constant of inclusion approaches that of the matrix, the critical strain for fracture initiation becomes large in the case of uniform shear deformation of the matrix. It was found that the critical strain becomes large due to the diffusion of atoms, especially for inclusions of small size and a large elastic constant. The model in which the inclusion is cracked by the localized shear deformation can explain the observed inclusion size dependence of the strain for fracture initiation. The inclusion size dependence of the critical strain for fracture initiation by uniform shear deformation of the matrix is different from that by localized shear deformation. Therefore, it is important to know which mechanism governs the fracture.     

Study of elastic-plastic fracture toughness determination

The elastic-plastic fracture toughness viaJ-integral and crack tip opening displacement (CTOD) has been obtained in two structural steels using several fitting equations representing the resistance curve of the material. The toughness is determined as the values corresponding to the critical stretched zone width (SZW) on theR-curves and with respect to 0.2 mm crack growth. The SZW measurements were performed by scanning electron microscopy. The various toughness values have been compared and the importance of using appropriateR-curves based on physical considerations has been pointed out. TheJ-CTOD relationship during the blunting process has been experimentally investigated from load-displacement records of the fracture test.     

Deformation and fracture of materials near spheroidal inclusions

We have proposed a model of the deformation and fracture of an elastoplastic body with an elastic spheroidal inclusion. The problem has been reduced to the solution of an integro-differential equation, and its numeral solution has been obtained by the method of mechanical quadratures. Using the strain criterion of crack initiation in the neighborhood of an inclusion, we have established the main parameters affecting local fracture. The results of investigations are presented in the form of plots.     

Simulation investigations of the position of Fatigue Fracture Plane in materials with biaxial loads

In the paper three methods of determination of the expected fatigue fracture plane position under random triaxial stress state have been presented. They are: weight function method, variance method and damage cumulation method. The weight function method for biaxial cyclic loadings has been analysed with digital simulation. The fatigue fracture plane position has been determined with mean values of the direction cosines of principal stress axes. Averaging has been done at angle values with use of weights. Eleven various weights have been presented and their usability has been analysed on the basis of experimental results obtained by Rotvel, and Nishihara-Kawamoto. The weights with good agreement of results of simulation tests and experiments have been shown.     

D6AC钢冲击断口形貌的分形研究

本文利用扫描电镜对含Mn$夹杂物和含ZrN夹杂物的D6AC钢的冲击断口形貌进行了观察与分析;利用数字图象法测定了试样的断口分形维数,揭示了冲击断口形貌和冲击韧性与夹杂物含量之间的内在联系,探讨了材料冲击断口形貌与分形维数的关系,拓宽了分形几何学在材料领域的应用范围.