Numerical calculation and experimental research on crack arrest by detour effect and joule heating of high pulsed current in remanufacturing

The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is developed. According to finite element theory, the finite element（FE） model of the cracked rectangular specimen is established firstly. Then, based on electro-thermo-structure coupled theory, the distributions of current density, temperature field, and stress field are calculated for the instant of energizing. Furthermore, the simulation results are verified by some corresponding experiments performed on high pulsed current discharge device of type HCPD-I. Morphology and microstructure around the crack tip before and after electro pulsing treatment are observed by optical microscope（OM） and scanning electron microscope（SEM）, and then the diameters of fusion zone and heat affected zone（HAZ） are measured in order to contrast with numerical calculation results. Element distribution, nano-indentation hardness and residual stress in the vicinity of the crack tip are surveyed by energy dispersive spectrometer（EDS）, scanning probe microscopy（SPM） and X-ray stress gauge, respectively. The results show that the obvious partition and refined grain around the crack tip can be observed due to the violent temperature change. The contents of carbon and oxygen in fusion zone and HAZ are higher than those in matrix, and however the hardness around the crack tip decreases. Large residual compressive stress is induced in the vicinity of the crack tip and it has the same order of magnitude for measured results and numerical calculation results that is 100 MPa. The relational curves between discharge energies and diameters of the fusion zone and HAZ are obtained by experiments. The difference of diameter of fusion zone between measured and calculated results is less than 18.3%. Numerical calculation is very useful to define the experimental parameters. An effective method to prevent further extensi     

Testing of a scanning adiabatic calorimeter with Joule effect heating of the sample

We evaluated a scanning adiabatic resistive calorimeter (SARC) developed to measure the specific enthalpy of viscous and gel-type materials. The sample is heated employing the Joule effect. The cell is constituted by a cylindrical jacket and two pistons, and the sample is contained inside the jacket between the two pistons. The upper piston can slide to allow for thermal expansion and to keep the pressure constant. The pistons also function as electrodes for the sample. While the sample is heated through the Joule effect, the electrodes and the jacket are independently heated to the same temperature of the sample using automatic control. This minimizes the heat transport between the sample and its surroundings. The energy to the sample is supplied by applying to the electrodes an ac voltage in the kilohertz range, establishing a current in the sample and inducing electric dissipation. This energy can be measured with enough exactitude to determine the heat capacity. This apparatus also allows for the quantification of the thermal conductivity by reproducing the evolution of the temperature as heat is introduced only to one of the pistons. To this end, the system was modeled using finite element calculations. This dual capability proved to be very valuable for correction in the determination of the specific enthalpy. The performance of the SARC was evaluated by comparing the heat capacity results to those obtained by differential scanning calorimetry measurements using a commercial apparatus. The analyzed samples were zeolite, bauxite, hematite, bentonite, rice flour, corn flour, and potato starch.     

涡流热成像裂纹检测中的形状大小影响分析

涡流热成像无损检测技术可以对金属表面裂纹进行快速、准确的检测,但是不同的线圈、试件以及裂纹大小对检测效果影响很大。通过建立感应加热二维模型,选取裂纹处与非缺陷处温差作为特征量,对不同组成部分形状大小对涡流热成像检测的影响规律进行了数值模拟;对比分析了不同裂纹深度下温差随体积深度比的变化规律,采用数据拟合方法研究了相似裂纹检测规律,并提取出试件形状以及线圈形状对检测效果的影响曲线;最后进行了涡流热成像试验验证。结果表明:当裂纹深度较大时,体积深度比影响规律可分为上升阶段、平稳阶段和下降阶段;相似裂纹间温差变化符合二次变化规律;涡流热成像技术可有效检测超大或超厚试件表面裂纹;减小线圈提离、曲率和线径的大小有助于增强检测效果。实际检测过程中,可据此针对不同被检试件采用不同线圈,提高检测能力。     

Corrosion effects on fatigue crack propagation of stainless steel and its heat affected zone in pH buffer solutions

A corrosion fatigue crack propagation test for 430 stainless steel and its heat affected zone was conducted in pH buffer solutions, and the results were compared with model predictions. The bare corrosion effect on fatigue crack propagation, particularly in corrosive environments was evaluated by means of a modified Forman equation. As shown in the results, the average corrosion rate determined from the ratio of corrosion induced crack length to the entire crack length under a cycle load was 0.11 and 0.37 for the base metal and heat affected zone, respectively, with a load ratio of 0.5, frequency of 0.5, and a pH 10.0 environment. The modeling and experimental processes demonstrate a step towards a methodology enabling the corrosion effects on fatigue crack propagation behavior to be determined.     

Analysis of short and long crack behavior and single overload effect by crack opening stress

The study analyzed the behaviors of short and long crack as well as the effect of single tensile overload on the crack behaviors by using fatigue crack opening behavior. Crack opening stress is measured by an elastic compliance method which may precisely and continuously provide many data using strain gages during experiment. The unusual growth behaviors of short crack and crack after the single tensile overload applied, was explained by the variations of crack opening stress. In addition, fatigue crack growth rate was expressed as a linear form for short crack as for long crack by using effective stress intensity factor range as fracture mechanical parameter, which is based on crack closure concept. And investigation is performed with respect to the relation between plastic zone size formed at the crack tip and crack retardation, crack length and the number of cycles promoted or retarded, and the overload effect on the fatigue life.     

样本容量和分布类型对疲劳寿命分布的推断影响分析

应用蒙特卡罗数值仿真方法,就样本容量及分布类型的选取对产品疲劳寿命概率分布函数推断的影响进行了研究,给出不同样本容量及分布函数类型下,各分布函数通过拟合优度检验被接受作为产品疲劳寿命概率分布函数的概率.还探讨了选取非真实分布函数作为产品疲劳寿命概率分布函数对累积失效概率的影响,并将对应给定百分位点下,由非真实分布函数求得的累积失效概率与真实累积失效概率进行了对比分析.所得结论对产品的设计和安全性评估均有参考价值.     

Analysis of the hydrodynamic torque effects on large size butterfly valves and comparing results with AWWA C504 standard recommendations

Butterfly valves are widely used in various industries such as water distribution, sewage, oil and gas plants. The hydrodynamic torque applied on the butterfly valve disk is one of the most important factors which should be considered in their design and application. Although several methods have been used to calculate the total torque on these valves, most of them are based on hydrostatic analysis and ignore the hydrodynamic effect which has a major role to determine the torque of the large-size valves. For finding the dynamic-valvetorque, some empirical formulas and methods have been proposed; for example in AWWA C504 standard, a relationship for calculating the dynamic torque has been given and its variation versus disk angle has been stated. However, the use of these empirical relationships is restricted due to the conditions defined in the standards. In this paper, the dynamic-valve-torque has been calculated for a large butterfly valve under different conditions and also at the different opening angles of the valve disk. For this purpose a computational fluid dynamics (CFD) method has been used. The results have been compared with those given in the AWWA C504 standard recommendations. Moreover, the effects of the disk shape and its deformation, surface roughness, upstream/downstream pressure variation and disk-offset value have been studied.     

Analysis of friction and surface roughness effects on edge crack evolution of thin strip during cold rolling

Experimental investigation and mechanical analysis have been carried out to study the edge crack formation during cold strip rolling using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The effects of friction and surface roughness on edge crack initiation and growth rate have been discussed. Friction leads to an increase in fracture loads and decreasing the friction coefficient is effective in preventing the microcracks. Surface roughness variation along the strip width contributes to stress distribution and inhibits crack nucleation. The findings reveal that the behaviour of crack evolution is influenced by fracture surface roughness as well as rolling friction.     

The identification and study of the critical state of a transverse crack in a zone with a lap based on artificial neural networks

A method for the identification of the geometry of a transverse crack in a layer with a lap with subsequent estimation of the critical state of its structure is proposed. The solution of the problem proceeds in two steps, which form the general method. The determination of a crack in a layer is performed with the use of artificial neural networks, which use the data of an ultrasonic study. To determine an internal crack, the problem of the pulse excitation of a wave field in a considered object was studied. Using a piezotransducer on a free coating surface, the results of an action are obtained. The input vectors for the artificial neural network are considered to be a regularly digitized echo signal. Based on the generated database of input vectors, the optimal training algorithm and the structure of the network were determined. After reconstruction of the geometry of a crack, the critical state is estimated with the use of integral equations, which were obtained from the solution of the corresponding linear problem of elasticity theory. In this problem, the coating medium is replaced by special boundary conditions on the upper surface of the layer. When using a generalized Fourier transform in the equilibrium equations in displacements, the problem is reduced to a singular first-order integral equation, whose solutions were derived by the small parameter and collocation methods. The stress-intensity coefficients were obtained and analyzed directly near the tops of the crack for various coating materials and geometric parameters of the crack.     

Analysis of thermal diffusivity of Ti thin film by thermoreflectance and periodic heating technique

Thermal diffusivity of Ti thin film with several hundred nanometers thickness has been measured by means of thermoreflectance (TR) technique and periodic heating using front heating and front detection configuration. Ti thin films were prepared on Si substrates by dc sputtering method. Then thin Mo layers as reflection layers were coated on Ti thin films. Surface of the Mo layer is irradiated by sinusoidally intensity modulated heating laser. Temperature response at the heated area is measured by a probe laser beam with constant intensity, as a TR signal. Phase lag between the phase of TR signal and that of heating laser beam was obtained from 100 kHz to 2.6 MHz. To analyze thermal diffusivity of Ti thin films using the phase lag data, we developed a three-layer analytical model such as Mo coating (100 nm)∕thin film∕semi-infinite substrate. The calculated phase lag using analytical model is in good agreement with the experimental data for the whole frequency range. The thermal diffusivity of two Ti thin films is determined to be 5 × 10(-6) m(2)∕s, which is 53% of the bulk one.     

飞机紧固件孔周裂纹检测远场涡流传感器设计及优化

飞机多层金属紧固结构作为飞机重要承力部件在连续受地-空-地循环载荷作用,使铆钉、高锁螺栓等紧固件孔周产生应力集中从而萌生疲劳裂纹。传统无损检测方法难以在在役情况下进行检测,而远场涡流检测技术在原理上突破集肤效应限制,对深层隐藏缺陷检测具有巨大优势。设计研发了与传统平面远场涡流传感器结构不同的新型平面远场涡流传感器,采取激励线圈与检测线圈同轴放置,大幅缩小了传感器尺寸,检测线圈位于激励线圈内部,且在检测线圈与激励线圈之间设计有磁场分流结构。通过有限元仿真对激励线圈尺寸、磁场分流结构材料及其组成方式进行系统的分析,得出最优的传感器设计方案。试验结果表明,设计研发的新型远场涡流传感器可以检测埋深4 mm、尺寸为(长×宽×深) 2×0. 2×4 mm的紧固件孔周裂纹,且随着缺陷长度的增大,信号幅值也随之增大。     

矩形薄板通透开裂缝对固有频率和模态的影响分析

针对四边固支矩形板薄受到通透开裂影响,引起模态中固有频率和模态振型变化的问题,对两种开裂位置中不同开裂长度进行了研究。首先,应用ANSYS软件建立有限元模型;然后,对开裂裂缝平行于薄板短边且位于板中心(对称开裂)和不位于板中心(不对称开裂)的各25种裂缝长度进行了仿真计算,获得了薄板的固有频率和模态振型。分析结果表明,裂缝的长度和位置影响矩形薄板的固有频率和振型;开裂的缝长和开裂中心位于节线上或者附近是产生模态交叉的两个重要因素,可为板结构开裂的检测提供依据。     

用流式细胞仪研究秋茄叶柄薄壁细胞大小及叶绿素含量与海水盐度的关系

采用快速离析方法和流式细胞仪研究了红树植物秋茄成熟叶柄薄壁细胞的大小和叶绿素含量与海水盐度之间的关系。结果表明 ,海水盐度为 0 .8%～ 2 .0 %时 ,随着盐度的升高 ,叶柄薄壁细胞大小和单位体积叶绿素含量的变化趋势与叶肉细胞一致。海水盐度为 0 .8%～ 1.0 %时 ,随着盐度升高 ,向有利于提高光合作用强度的方向发展 ;海水盐度在 1.0 %～ 2 .0 %之间时 ,随着盐度的升高 ,向加强生理干旱适应性方向发展。海水盐度高于2 .0 %时 ,叶柄薄壁细胞的大小和单位体积薄壁组织叶绿素含量随盐度的变化趋势与叶肉细胞不同 ,原因尚待进一步研究。实验结果表明 ,借助快速离析方法 ,使用流式细胞仪研究器官细胞相关特性是可行的 ,为从形态学角度研究红树植物耐盐机理提供了可能 ,扩大了流式细胞仪的应用领域     

Analysis and compensation of ADCP current direction error caused by ambient magnetic field

Internal magnetic compasses of acoustic Doppler current profilers (ADCPs) are easily disturbed by significant amount of hard/soft iron in some moorings or ships, causing the significant current direction error. In this paper, with the consideration of the roll and pitch of ADCPs mounted on moorings or ships, we deduce and derive the quantitative relationship between the magnetic deviation and its induced current direction error. According to the relationship and the characteristic model of the magnetic deviation, the compensated coefficients are calibrated on the spot and applied to compensate the subsequent current observation. Compared with the current direction without the magnetic deviation affection, the measured current direction accuracy evaluated by the root mean square error improves remarkably. From the experimental result, the approach is proved to be effective for correcting the fixed-point current direction measurement of ADCPs, which are affected by the magnetic deviation and in the small tilt condition.     

振幅矢量叠加法分析X射线波带片加工误差对效率的影响

使用振幅矢量叠加法,通过叠加X射线波带片每一对环带对焦点的贡献,计算和分析了随机环带位置误差、宽度误差、扩散和粗糙度对波带片的效率的影响。用Strehl 比来量化和衡量与理想波带片有偏差的波带片的性能,对两个波带片实例分别用Strehl 极限确定了能容许的4种误差的最大值。计算了Ni软X射线波带片的随机环带位置误差及宽度误差对主焦点效率的影响;计算了SiO₂/Ni硬X射线溅射切片波带片的两种材料的相互扩散和粗糙度对衍射效率的影响。结果表明:4种误差越大,主焦点效率越小,对Ni软X射线波带片,随机环带位置误差均方根和宽度误差均方根小于最外环宽度的20%左右时,对SiO₂/Ni硬X射线溅射切片波带片,扩散区宽度和粗糙度均方根分别小于最外环宽度的90%和60%左右时,得到的Strehl 比在Strehl 极限之上。     

Theoretical analysis of the effects of linear birefringence upon optical glass current transformers with different optical designs

The effects of linear birefringence (LB) upon bulk glass optical current transformers (BGOCTs) with different optical path designs, such as the orthoconjugate reflection (OCR)-typed, the direct reflection (DR)-typed and the roof-prism reflection (RPR)-typed BGOCT designs, are theoretically analyzed and compared with that of the BGOCT with a single-loop optical path in this paper. The results show that the return-back dual-loop current sensing designs with conventional signal processing scheme of “−/+” cannot eliminate the harmful effects of the LB thoroughly, if suitable signal processing schemes, which can separate the LB from Faraday effect, are not used.     

Vortex flowmeter with enhanced accuracy and reliability by means of sensor fusion and self-validation

Due to the complementary qualities of the principles of vortex frequency estimation and vortex time of flight estimation they are ideally suited for an effective sensor fusion within flow measurement. A flow meter which combines the results of the two individual systems in an intelligent manner was built and beside theoretical considerations the performance of the fused system is demonstrated by a variety of measurements. In comparison with conventional vortex meters which only use the vortex frequency to estimate the flow rate, the measuring range can be extended by a factor of 8–10 and the accuracy of the system as well as the robustness to disturbances like a second fluid phase or depositions on the bluff body are strongly increased.     

Particle concentration and size effects on the erosion-corrosion of pure metals in aqueous slurries

In previous studies of erosion-corrosion, several different theories have been developed to produce a model which represents the relationship between particle erosion and chemical corrosion. Regimes in the models define how the two mechanisms behave relative to one another, whether it is erosion dominated, corrosion dominated. This paper investigates the effect of particle and target material on the erosion-corrosion mechanisms. The performance of Fe as the target material will be modelled when considering particle concentration and size. A comparison is made between the erosion-corrosion mechanisms of Fe, Ni, Al and Cu under different conditions of particle size and concentration. By producing several maps, the regimes and wastage rates predicted as functions of velocity and applied potential will be discussed.