锆合金氧化膜的内应力计算

锆合金氧化膜中的内应力是锆合金腐蚀动力学中的重要影响因素,目前没有统一的方法得到氧化膜中内应力的大小,且数值差异较大。在传统的实验和理论方法的基础上,建立ZrO₂/Zr合金双层氧化弯曲几何模型,计算不同腐蚀状态下氧化膜中的内应力大小,得到内应力变化规律并分析其影响因素,为锆合金氧化膜内应力研究提供了一种较为可靠的方法。      

高燃耗陶瓷燃料颗粒的参数化建模及强度分析

弥散燃料芯体中的陶瓷燃料颗粒在辐照条件下会形成裂变气孔,燃料颗粒内部气孔间的相互干涉作用及气孔内压的增长致使局部拉应力超过材料强度极限,进而导致燃料颗粒开裂。本文考虑高燃耗燃料颗粒内气孔尺寸和位置分布的非均匀性,实现了颗粒内部的细观结构参数化建模。运用有限元方法计算并分析了气孔尺寸、基体约束压应力、温度和气孔分布方式对颗粒内部最大拉应力的影响,研究了颗粒内开裂危险区的分布规律。结果表明,陶瓷燃料颗粒最大拉应力随气孔尺寸和温度的增加而增大,随基体约束压应力的增加而减小;燃料相的断裂强度减小,开裂危险区面积增大;燃料颗粒从内部多处开裂破坏,而表层处开裂的概率更大。本文为弥散燃料失效研究及优化设计提供了分析方法及数值参考。     

A signal-processing tool for non-destructive testing of inaccessible pipes

The design of Non-Destructive-Testing systems for fault detection in long and not accessible pipelines is an actual task in the industrial and civil environment. At this purpose, the diagnosis based on the propagation of guided ultrasonic waves along the pipes offers an attractive solution for the fault identification and classification. The authors studied this problem by means of suitable Artificial Neural Network models. Numerical techniques have been used to simulate the guided wave propagation in the pipes. In particular, the finite element method has been used to model different kinds of pipes and faults, and to obtain several returning echoes containing the faults information. Torsional wave modes have been used as excitation waves. The obtained signals have been processed in order to reduce the data dimensionality, and to extract suitable features. The features selected from the signals can be further processed in order to limit the size of the Neural Network models without loss of information. At this purpose, the principal component analysis has been investigated. Finally, the selected features have been used as input for the neural network models. In this paper, traditional feed-forward, multi-layer perceptron networks have been used to obtain the information on size and location of localized notches.     

Stress and Defect Characteristics in Oxide Films and Corrosion Resistance of Zr-1Nb Alloy

Two approaches to testing corrosion in autoclave with different time intervals for heating and cooling were carried out to investigate the corrosion resistance of Zr-1Nb alloy in the 0.01 mol/L LiOH aqueous solution at 360 °C/18.6 MPa, the stress, and defect density in the oxide film. The stress and defect density in oxide film were measured by a curl method and the Ion Migration Method (IMM), respectively. Results showed that the stress level and defect density in the oxide film in the shorter interval corrosion tests were lower than that in the longer interval corrosion tests at the initial stage of corrosion with the weight gain less than 34.37 mg/dm2. The corrosion resistance in the subsequent stages of corrosion was better in the shorter interval corrosion tests. It indicates that at the initial stage of corrosion the weight gain shows no obvious difference between the two approaches of corrosion tests in autoclave under different time intervals for heating and cooling. However, the stress level and defect density in the oxide film exhibit noticeable differences, which leads to two distinct microstructural evolution rates of the oxide film. The distinct microstructural evolution rates cause different corrosion resistance in the subsequent corrosion stages.     

Eddy current flaw characterization in tubes by neural networks and finite element modeling

For quantitative flaw characterization in steam generator tubes, inversion of eddy current testing (ECT) signals in an automated fashion is strongly desired. In this paper, we report our effort to develop a systematic approach for flaw characterization in tubes by the novel combination of neural networks and finite element modeling.Specifically, the finite element model that can predict ECT signals from axisymmetric flaws in tubes was developed, and its accuracy was verified experimentally. Using this model, an abundant synthetic database with 400 ECT signals generated from 200 axisymmetric machined grooves in four types has been constructed with two test frequencies per flaw.For the automated inversion of ECT signals, a total of 22 features have been extracted from each flaw. Then, a set of 10 features has been selected for flaw classification, while the other set of 10 features for flaw sizing. For the determination of the flaw type and the flaw size parameters, we have proposed an intelligent flaw characterization system that adopts two different paradigms of neural networks: probabilistic neural networks for flaw classification and back propagation neural networks for flaw sizing.The performance of this system has been investigated using the synthetic ECT signals in the database. The excellent performance presented here, even though it has been obtained from synthetic flaws representing machined grooves in tubes, demonstrates the high potential of this system to serve as a robust tool for practical flaw characterization in tubes.     

钛表面辉光无氢渗碳动力学与耐蚀性能研究

利用电子背散射衍射(EBSD)取向成像技术,对TA16和TA17管板组装焊缝的显微组织、晶界特征、晶体学取向进行表征研究.结果表明:TA16管母材为细小等轴α晶粒,大部分为大角度晶界,且其织构类型为纤维织构.TA17板母材呈典型的轧制态,且由α相和少量晶间分布的β相两相组成,大部分为小角度晶界,为基面织构.热影响区晶粒呈梯度长大分布,管侧的小角度晶界高于板侧.熔区为粗大的α’马氏体相交织成的网篮状组织,大部分为大角度晶界,织构比较漫散.     

锆合金氧化膜在真空退火过程中的氧扩散行为

针对已预腐蚀生成一定厚度氧化膜的Zr-Sn-Nb合金,研究了其在不同温度下进行真空热处理过程中的氧扩散动力学及亚稳相演变行为。结果表明,真空退火后氧化膜变薄,氧在氧化锆基体中的扩散增强,并计算了特定合金中氧的扩散系数。退火后微观化学分析表明亚稳相层厚度增加。固溶氧锆基体(Zr(O))层也明显增厚。针对该现象,讨论了对应氧扩散及亚稳相形成过程：该扩散极为可能是由ZrO₂和(Zr(O))之间存在的氧含量梯度以及锆基体的高氧溶解度造成,受抑制的氧化速率将促进亚稳相的生长。在实际水腐蚀情况下,氧化及氧化膜向基体溶解过程应该是共存的。当氧化速率受限时,氧化膜向基体溶解作用将增强,有利于形成较厚的亚稳层。     

Preparation and tensile behavior of SiCf/SiC mini composites containing different types and thicknesses of interphase

SiC fiber-reinforced SiC matrix (SiC_f/SiC) composites are promising materials for high-temperature structural applications. In this study, KD-II SiC fiber bundles with a C/Si ratio of approximately 1.25 and an oxygen amount of 2.53%, were used as reinforcement. PyC interphase, PyC-SiC co-deposition interphase I and II, with different thicknesses, and SiC matrix were deposited into the SiC fiber bundles by using chemical vapor infiltration (CVI) to form SiC_f/SiC mini composites. When the thickness of the interphase is approximately 1000 nm, the ultimate tensile stress and strain of SiC_f/SiC mini composites with PyC-SiC co-deposition interphase I can reach 1120.0 MPa and 0.72%, respectively, which are significantly higher than those of SiC_f/SiC mini composites with a PyC interphase (740.0 MPa, 0.87%) and PyC-SiC co-deposition interphase II (645.0 MPa, 0.54%). The effect of thicknesses and types of interphase on tensile fracture behavior of mini composites and then the fracture mechanism are discussed in detail.     

Effect of iodine partial pressure on the iodine stress corrosion cracking behaviors of Zr–Sn–Nb alloy using the ring tensile test

In order to evaluate the effect of iodine partial pressure on the iodine stress corrosion cracking (I-SCC) behaviors of a Zr–Sn–Nb alloy, ring tensile tests were conducted at 350 °C and in atmosphere without iodine and with iodine partial pressure of 10², 10³, and 10⁴ Pa, respectively. Results show that the maximum load, fracture displacement, tensile strength, and fracture energy of the Zr–Sn–Nb specimens decrease monotonically with the increase of iodine partial pressure. The fracture morphology of specimen with 10² Pa iodine exhibits two different fracture regions. One is the mixture form of ductile and brittle fracture, and the other is only ductile fracture. For the specimen with 10³ Pa, stair-shaped fracture surface is formed as a result of the alternative propagation of transgranular cracks and intergranular cracks. The critical iodine partial pressure of the Zr–Sn–Nb alloys is lower than 10² Pa under the present conditions.