铜、钛元素对镍基耐蚀合金高温氧化行为的影响

采用增重法测出了含铜和钛元素的镍基耐蚀合金在800℃空气中的高温氧化动力学曲线,并用扫描电镜及能谱仪对氧化膜的形貌和成分进行了分析,研究了铜和钛元素对合金高温氧化行为的影响。结果表明:随着铜元素含量的增多,合金的抗高温氧化能力逐渐变弱;在合金中加入一定量的钛元素可以使合金表面的氧化膜更加致密,增强合金的抗高温氧化能力。     

镍基单晶涡轮叶片榫头疲劳裂纹扩展寿命研究

设计航空发动机涡轮叶片榫头/榫槽接触模拟试验件,基于涡轮叶片的实际工况,进行了榫头/榫槽接触疲劳试验。基于Paris公式提出了榫头接触疲劳裂纹扩展寿命模型,并采用晶体滑移有限元程序对涡轮榫头/榫槽接触进行了有限元模拟。有限元分析得到的疲劳裂纹扩展寿命与试验结果相符,表明提出的疲劳裂纹扩展寿命模型可用于指导分析榫头寿命。     

9%Ni钢用国产镍基焊丝的焊接试验研究

针对镍基焊丝的热裂纹敏感性试验,研制出FISCO热裂纹试验装置,利用该装置对研制的ERNiCrMo-3镍基焊丝进行焊接热裂纹敏感性试验,结果表明,研制焊丝的热裂纹敏感性与进口焊丝相当,均具有较低的热裂纹敏感性。采用研制焊丝焊接9%Ni钢的工艺试验结果表明,焊接接头各项力学性能优良,焊缝组织为纯奥氏体组织,析出相很少,可以满足大型LNG储罐的设计要求。     

石墨加入量对激光熔覆原位合成TiC/镍基涂层裂纹敏感性的影响

为降低激光熔覆原位合成TiC/镍基涂层的裂纹敏感性,利用光学显微镜、扫描电镜、X射线衍射仪等研究了石墨加入量对涂层裂纹敏感性的影响.结果表明:通过降低混合粉末中石墨加入量从而减少涂层的碳含量,可以改善涂层组织,降低涂层的裂纹敏感性;当加入的石墨粉与钛粉的质量比为1:5时,可获得无裂纹涂层.     

碳钢法兰密封面堆焊镍基合金耐蚀层的试验研究

通过对各种焊接工艺条件分析和焊接工艺评定,确定耐蚀堆焊工艺,并得到质量较好的法兰密封面堆焊层。堆焊方案采用钨极氩弧焊,在ASTMA350-LF2碳钢基体上多层堆焊镍基合金ERNicrMo-3（Inconel625）耐蚀层。堆焊层金属与基体结合良好,组织细密,具有较好耐蚀性,并有效地指导了实际生产,保证重点建设工程的顺利实施。     

含硫镍基高温自润滑合金摩擦对偶的选择

在２０℃、３００℃和６００℃的大气环境下,用销－盘式高温摩擦试验机考察了一种含硫镍基高温纂 有合金与１Ｃｒ１８Ｎｉ９Ｔｉ、Ｗ１８Ｃｒ４Ｖ、ＴＺｍ、ＧＨ４１６９和ＨａｌｓｔｅｌｌｏｙＣ－２７６合金及自身配副的摩擦磨损行为。试验结果表明,Ａ－６Ｇ合金无论与自身不审与其它材料配副,在温和就是上都具有摩擦系数低,自身及对偶磨损均小的特性,表现出良好的对偶匹配性。尤其,与Ｗ１８Ｃｒ４Ｖ和ＴＺＭ合金配副,具有     

低热裂纹敏感性纯镍铸铁焊条的研究

研究了纯镍铸铁焊条冷焊时，稀土金属镧、铈、镨、钇及钕对焊缝热裂纹敏感性的影响规律，并分析了铈对焊接接头力学性能和加工性能的影响。结果表明：稀土镧、铈、钇和镨能在一定范围内提高焊缝临界变形速度υBL，改善纯镍铸铁焊缝抗热裂性。适量的铈能提高接头力学性能，稀土钕会增加焊缝热裂纹敏感性。在此基础上，研制了具有较低热裂纹敏感性、良好的加工性能，能满足高强度灰口铸铁力学性能要求的纯镍铸铁冷焊焊条。     

含石墨镍基复合材料的摩擦学性能研究

用粉末冶金制备石墨wt．％含量为0，3，6,9的镍基白润滑合金，研究不同石墨含量对材料摩擦学性能的影响。     

SiC纳米粒子增强锌铝基耐蚀涂层的制备及性能研究

为解决锌铝基耐蚀涂层在高速、强摩擦等特殊服役条件下的使用问题，探索性地添加SiC纳米粒子对锌铝基耐蚀涂层进行改性，以提高涂层的硬度和强度。研究了SiC纳米粒子及其添加量对涂层硬度、附着强度、耐冲击性能和耐腐蚀性能的影响，并对涂层的微观组织和成分进行了分析。结果表明，添加SiC纳米粒子可显著提高锌铝基耐蚀涂层的硬度，且没有对涂层的附着强度、耐冲击性能和耐腐蚀性能带来负面影响。SiC纳米粒子在涂层中的均匀分散是保障涂层综合性能优异的必要条件。     

光折变液晶材料的研究进展

介绍了液晶材料光折变效应的基本概念及基本机理及特性,根据光折变液晶材料的发展,分别对掺杂染料的液晶、聚合物分散液晶、掺杂铁电材料液晶等几种液晶材料的光折变效应的各个发展过程及其存在的问题和研究现状作了较为详细的阐述,并展望了其今后的实际应用及发展方向。     

Characterisation of crack tip stresses in elastic-perfectly plastic material under mode-I loading

Asymptotic crack tip stress fields are developed for a stationary plane strain crack in incompressible elastic-perfectly plastic material under mode-I loading. Detailed investigations have revealed that in between the two extreme conditions of crack tip constraint, that is, between the fully plastic Prandtl [1] field and the uniform stress field the most general elastic-plastic crack tip fields can be completely described by the 5-sector stress solution proposed in this article. The 3-sector stress field proposed by Li and Hancock [2] and the 4-sector field proposed by Zhu and Chao [3] are subsets of the general elastic-plastic field proposed in this work. This study has revealed that cases arise where the severe loss of crack tip constraint can lead to compressive yielding of crack flank. This particular situation leads to 5-sector stress field. Detailed studies have revealed that, in the most general case of elastic-plastic crack tip fields, the T_π parameter proposed by Zhu and Chao [3] cannot be used as a constraint parameter to represent a unique state of stress at the crack tip. A new constraint-indexing parameter T_CS-2 is proposed, which along with T_p is capable of representing the entire elastic-plastic crack tip stress fields over all angles around a crack tip. Excellent agreement is obtained between the proposed asymptotic crack tip stress field and the full-field finite element results for constraint levels ranging from high to low. It is demonstrated that the proposed constraint parameters are adequate to represent the crack tip constraint arising due to specimen geometry and loading conditions as well as the additional constraint that arises due to weld strength mismatch.     

Constitutive modelling of the anisotropic creep behaviour of nickel-base single crystal superalloys

This paper focuses on the modelling of primary, secondary and tertiary creep of nickel-base single crystal superalloys at high temperatures. In particular, we propose an extension of the Cailletaud single crystal plasticity model [Méric L, Poubanne P, Cailletaud G. Single crystal modeling for structural calculations: part I—model presentation. Transactions of the ASME 1991;133:162-170] to include tertiary creep. This is achieved by introducing an additional evolution equation for a scalar damage variable per slip system. In addition, a methodology for the calibration of the material parameters of the model to fit the results from experiments has been implemented. The parameter identification rests upon a two-membered evolution strategy. The comparison with uniaxial and multiaxial test data shows a good agreement between model and experiment. The structural simulations have been performed by means of a special element technology which enables efficient and accurate finite element computations.     

Evaluation method of multiaxial low cycle fatigue life for cubic single crystal material

The coupling effect of normal stress and shear stress on orthotropic materials happens when applied loading deflects from the directions of the principal axes of the material coordinate system. By taking account of the coupling effects, formulas of equivalent stress and strain for cubic single crystal materials are cited. Using the equivalent strain and equivalent stress for such material and a variable k, which is introduced to express the effect of asymmetrical cyclic loading on fatigue life, a low cycle fatigue (LCF) life prediction model for such material in multiaxial stress starts is proposed. On the basis of the yield criterion and constitutive model of cubic single crystal materials, a subroutine to calculate the thermo elastic-plastic stress-strain of the material on an ANSYS platform was developed. The cyclic stress-strain of DD3 notched specimens under asymmetrical loading at 680°C was analyzed. Low cycle fatigue test data of the single crystal nickel-based superalloy are used to fit the different parameters of the power law with multiple linear regression analysis. The equivalent stress and strain for a cubic single crystal material as failure parameters have the largest correlation coefficient. A power law exists between k and the failure cycle. The model was validated with LCF test data of CMSX-2 and DD3 single crystal nickel-based superalloys. All the test data fall into the factor of 2.5 for CMSX-2 hollow cylinder specimens and 2.0 scatter band for DD3 notched specimens, respectively.     

The singular stress field and stress intensity factors of a crack terminating at a bimaterial interface

For the fracture evaluation of inclined cracks terminating at the dissimilar material interface, not only the singularities, but also the detailed stress field and its stress intensity factors are necessary. However, though there are many researches reported on the singularity analysis, the stress field and its stress intensity factors are still not clear. This paper has deduced theoretically the singular stress and displacement fields near the tip of a crack terminating at the interface between bonded dissimilar materials, for both cases of real and oscillatory singularities. From the deduced singular stress field, the stress intensity factors are defined for such a crack, and the corresponding numerical extrapolation methods are also proposed. Through the numerical examinations, it is found that the theoretical stress distributions agree well with the numerical results obtained by the finite element method. Moreover, the proposed extrapolation method shows a good linearity, thus it can be used as an efficient way to determine the characteristics of the stress and displacement fields near the tip of a crack terminating at interface.     

Pipe crack identification based on finite element method of second generation wavelets

In this paper, a new method is presented to identify crack location and size, which is based on stress intensity factor suitable for pipe structure and finite element method of second generation wavelets (SGW-FEM). Pipe structure is dispersed into a series of nested thin-walled pipes. By making use of stress intensity factor of the thin-walled pipe, a new calculation method of crack equivalent stiffness is proposed to solve the stress intensity factor of the pipe structure. On this basis, finite element method of second generation wavelets is used to establish the dynamic model of cracked pipe. Then we combine forward problem with inverse problem in order to establish quantitative identification method of the crack based on frequency change, which provides a non-destructive testing technology with vibration for the pipe structure. The efficiency of the proposed method is verified by experiments.     

Nondestructive testing and crack evaluation of ferromagnetic material by using the linearly integrated hall sensor array

Magnetic flux leakage testing (MFLT), which measures the distribution of a magnetic field on a magnetized specimen by using a magnetic sensor such as a Hall sensor, is an effective nondestructive testing (NDT) method for detecting surface cracks on magnetized ferromagnetic materials. A scan-type magnetic camera, based on the principle of MFLT, uses an inclined Hall sensor array on a printed circuit board (PCB) to detect small cracks at high speed. However, the wave forms appear in a direction perpendicular to the scan because the sensors are bonded at different gradients and heights on the PCB despite careful soldering. In this paper, we propose linearly integrated Hall sensors (LIHaS) on a wafer to minimize these waves and to improve the probability of crack detection. A billet specimen is used to determine the effectiveness of the LIHaS in multiple crack detection. This paper was recommended for publication in revised form by Associate Editor Joo Ho Choi Prof. Jinyi Lee was born in Korea in 1968. He received the bachelor degree in mechanical design from Chonbuk University, Jeonju, Korea, in 1992. Also he received the master and Ph.D degree in mechanical and aeronautics & space engineering from Tohoku university, Sendai, Japan, in 1995 and 1998, respectively. He was a Researcher from 1998 to 2000 with the Tohoku university, Iwate university, Iwate Techno-Foundation and Saitama university, Japan. From 2000 to 2003, he worked for Lacomm Co., Ltd. and Gloria Techniques, Korea, as a researcher. In 2003, he was a lecturer with the Chosun university, Gwangju, Korea. Since 2005, he has been an Assistance Professor, Chosun university. His research interests are in application of magneto-optical film, laser and CCD line scan sensor, and development of magnetic camera. He is the author or coauthor of fifteen patents and over 50 scientific papers. Jiseong Hwang was born in Republic of Korea in 1979. He received the B.S and M.S degree in control and instrumentation engineering in 2005 and 2006, respectively, from the Chosun University, Gwangju, korea, where he is currently working toward the Ph.D. degree. His research interests are NDT and Evaluation, Magnetic camera. Jongwoo Jun was born in Korea in 1974. He received the bachelor degree in electronics engineering from Inje University, Kimhae, Korea, in 1999. He received the master degree in electronics engineering from Changwon University, Changwon, Korea, in 2005. Also he is currently working toward the Ph.D. degree in information & communication engineering from Chosun University, Gwangju, Korea. He worked for Lacomm Co., Ltd. and Gloria Techniques from 1999 to 2005, Korea, as a researcher. His research interests are development of magnetic camera, NDT and evaluation. Dr. Seho Choi was born in Korea in 1964. He received bachelor degree in the department of electrical and electronic engineering from Kyungpook National University, Daegu, Korea, in 1987. And he received master degree in the department of elec trical and electronic engineering from Korea Advanced Institute of Science and Technology in 1989. He received Ph.D. degree in the department of electrical and electronic engineering from the University of Sheffield in the U.K. in 2001. He had been worked for Agency for Defense Development as a Researcher from 1989 to 1992, Korea. Since 1993, he has been worked for POSCO Research Lab. as a principal researcher. His main research activities are developing Surface Defect Inspection System for hot and cold rolled steel strip, hot wire rod, and hot slab. He is also interested in developing Internal Defect Detection System for steel products by using Ultra-sonic and magnetic camera techniques. His major is image processing to detect tiny defect in high background noise image. He published many scientific papers as the author or coauthor.     

整体式离合器壳体破裂故障分析与改进

对整体式离合器壳体进行有限元分析,为了考虑其它零件对分析对象的刚度影响以及更好的处理受力边界,模型中加入了发动机机体、变速箱等零件。通过有限元分析,得到离合器壳体的应力分布,找出了该结构薄弱环节,经过与损坏的实物对比发现:有限元分析得到的离合器壳体薄弱部位与实际破裂位置吻合。在有限元分析结果的基础上进行了改进设计,改进方案提高了离合器壳体的结构强度,消除了故障现象。为解决壳体破裂问题提供了重要的依据,也为进一步研究动力总成的载荷传递和变形情况提供了参考。     

Finite element analysis of coating adhesion failure in pre-existing crack field

Abstract

The influence of a pre-existing crack field on coating adhesion failure in a steel surface coated with a 2 μm thick titanium nitride (TiN) coating was investigated by finite element method modelling and simulation. The stress and strain fields were determined in contact conditions with a spherical diamond tip sliding over the coated surface at a loading of 8 N. One crack in or at the coating increased the maximum tensile stresses with six times from 82 to 540 MPa when the crack was vertical through the coating or L shaped and with nine times when the crack was horizontal at the coating/substrate interface. A simulated multicrack pattern relaxed the tensile stresses compared to single cracks. The results indicate that a cracked coated surface needs to have about five to nine times higher adhesive and cohesive bonds to resist the same loading without crack growth compared to a crack free surface. For optimal coated surface design, the strength of the adhesive bonds between the coating and the substrate in the vertical direction needs to be 50% higher than the cohesive bonds within the coating and the substrate in the horizontal direction. The first crack is prone to start at the top of the coating and grows vertically down to coating/substrate interface, and there it stops due to the bigger cohesion within the steel material. After this, there are two effects influencing that the crack will grow in the lateral direction. One is that steel cohesion is normally bigger than the coating/interface adhesion, and the second is that there are higher tensile stresses in the horizontal than in the vertical cracks. Several vertical cracks can stop the horizontal crack growth due to stress relaxation.     

单晶蓝宝石的延性研磨加工

为实现单晶蓝宝石的延性研磨加工,采用纳米压痕和划痕法测试并分析了单晶蓝宝石(0001)面的微纳力学特性,建立了单颗圆锥状磨粒的压入模型并计算了延性研磨加工的受力临界条件,分析了金刚石磨粒嵌入合成锡研磨盘表面的效果.对单晶蓝宝石进行了延性研磨加工试验,采用NT9800白光干涉仪、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等方法分析了单晶蓝宝石的延性研磨表面特征.试验结果表明:采用纳米压痕和划痕法可以为单晶蓝宝石的延性研磨加工提供工艺参数,单晶蓝宝石的延性堆积的极限深度为100 nm,金刚石磨粒的嵌入及在适当载荷下可以实现蓝宝石的延性研磨加工,实验条件下的最佳载荷为21 kPa,延性研磨后单晶蓝宝石表面划痕深度的分布情况较好,分散性小,研磨后的表面发生了位错滑移变形.