高碾压混凝土重力坝分区材料-结构界面特性与变形协调仿真分析

高碾压混凝土重力坝不同功能部位"结构特性"与"材料性能"的差异产生的变形协调问题直接关系到工程结构的安全运行,现阶段变形协调分析多是对结构变形和受力进行分析,对异种材料变形协调机理认识不足,缺乏理论基础研究。本文基于界面力学理论,考虑混凝土坝分区中常见的两种双材料界面形式与理想界面的连续边界条件,基于奇异性特征值的特征方程,提出了以应力奇异性特征值作为异种材料变形协调的评价指标,并通过有限元分析验证了理论计算的正确性与有效性;进而分析了界面结合角度和异种材料组合对单侧自由界面端与埋入界面折点处应力奇异性的影响,通过非均质有限元数值仿真分析了复合试件破坏模式,研究了抗压强度与应力奇异性特征值的关系;最后通过统计实际混凝土坝工程中不同坝段内的双材料界面的材料参数(弹性模量)与结构参数(界面形式与结合角度),计算奇异性特征值,评价了该工程中界面的变形协调特性,为高混凝土坝分区材料-结构设计与材料选取提供新的思路。     

半轴套管多工位挤压自动化生产线中冲连皮缺陷产生机理及参数优化

针对半轴套管多工位热挤压自动化生产线工艺调试过程中,正挤压工序冲连皮时,管端易出现连皮粘连缺陷的问题,探讨了有可能造成连皮粘连的原因。通过对工艺流程和现场情况进行综合分析,提出了圆柱形坯料周向温度加热不均是关键的影响因素。采用Deform有限元分析软件,模拟了不同加热温差条件下,反挤压和冲连皮时材料变形及材料剪断过程。通过对模拟结果的分析,揭示了连皮粘连机理,并可知,当坯料周向加热温差小于30℃时,连皮可顺利冲下。根据模拟得出的合理温差,进行现场试验,实际情况与模拟结果具有较高的一致性,生产出的产品锻件切口平齐、连皮撕裂带分布均匀,有效地解决了连皮粘连的问题。     

冷喷涂固态颗粒沉积中颗粒间结合形成机制研究进展

就目前主流的冷喷涂颗粒结合形成机理进行了系统总结和评述,为冷喷涂沉积体性能的调控和后续研究提供借鉴。分别就经典的颗粒界面绝热剪切失稳结合机理,颗粒界面应力波释放诱导材料射流形成结合机理,以及高速碰撞诱导颗粒表面氧化膜破碎、新鲜金属接触结合机理的基本概念、原理、特点进行了概括总结。通过大量系统文献的调研,指出现有理论目前存在的相悖和不足之处,并简要分析了现有颗粒间结合形成理论对冷喷涂沉积体质量调控方面的指导意义。最后基于现有研究的不足,对冷喷涂颗粒界面结合机制方面的研究进行了展望。     

New insight into the formation and oxygen barrier mechanism of carbonaceous oxide interlayer in a multicomponent carbide

Early transition metal carbides are considered to be superior candidate materials for oxidizing environments at temperatures exceeding 2000°C. Generally, the remarkable oxidation resistance is largely attributed to a carbonaceous oxide interlayer (eg, Hf–O–C, Zr–O–C, and Ta–O–C), located at the interface between the external oxide layer and internal carbide (eg, HfC, ZrC, and TaC), acting as the primary oxygen barrier. However, the oxygen barrier mechanism of the carbonaceous oxide interlayer remains unclear. Herein, through studying the oxidation behavior of a novel multicomponent carbide Hf_0.5Zr_0.3Ti_0.2C in oxidizing environments up to 2500°C, the oxygen barrier mechanism of the carbonaceous oxide was recently revealed. We found that the oxygen barrier resulted from the slow oxygen diffusion through the inner grains of Hf-Zr–Ti–O due to the presence of carbon formed at the grain boundaries because of the existence of compact external oxide layer, beneath which the Hf–Zr–Ti–O–C interlayer possesses much lower oxygen activity and temperature that allow carbon to exist stably. This as-formed carbon strongly retarded the fast diffusion of oxygen along the grain boundaries of oxides. Additionally, desirable synergisms of the designed multicomponent system, particularly, the outward short-circuit diffusion of Ti, lead to the self-healing of the external oxide layer, evidently enhancing integral protection performance against oxidizing environments.     

Computation and investigation of mode characteristics in nonlinear system with tuned/mistuned contact interface

This study derived a novel computation algorithm for a mechanical system with multiple friction contact interfaces that is well-suited to the investigation of nonlinear mode characteristic of a coupling system. The procedure uses the incremental harmonic balance method to obtain the nonlinear parameters of the contact interface. Thereafter, the computed nonlinear parameters are applied to rebuild the matrices of the coupling system, which can be easily solved to calculate the nonlinear mode characteristics by standard iterative solvers. Lastly, the derived method is applied to a cycle symmetry system, which represents a shaft–disk–blade system subjected to dry friction. Moreover, this study analyzed the effects of the tuned and mistuned contact features on the nonlinear mode characteristics. Numerical results prove that the proposed method is particularly suitable for the study of nonlinear characteristics in such nonlinear systems.     

Study on the interfacial properties of active Ti element/ZrO2 by using first principle calculation

Ti element is an important active element in brazing Zirconia ceramic (ZrO₂) ceramic. Therefore, the interface bonding mechanism of Ti and ZrO₂ was studied by using first principles calculation. Two kinds of interfaces with different termination and stacking sequence were established, and the interfacial bonding mechanism was studied using work of adhesion (W_ad), electronic behavior and interface energy. The results show that in the O-terminated interface, Ti and O form a strong ion-covalent bond at the interface, and the W_ad can reach 13.61 J/m². In the Zr-terminated interface, Ti and Zr form a metal-covalent bond, and the W_ad is 5.56 J/m². At a temperature of 1123K, when the lnP_O2 is larger than e⁻¹⁷, the O-rich interface is more stable in thermodynamics. Therefore, under the experimental condition, the interface tends to form Ti-O compounds when ZrO₂ is brazed using Ag(Ti) filler metal.     

热镀锌带钢表面色差缺陷形成机理及改进措施

为了消除热镀锌板卷的色差缺陷，从热轧、镀锌、冲压工艺对色差缺陷形成机理进行分析。导致热镀锌板卷色差缺陷的主要原因有原料表面粗糙度不均匀、锌层厚度不均、冲压导致锌层开裂。针对这3种不同原因，制定了相应措施在热轧工序冷却装置上进行边部遮蔽；提高沉没辊安装精度、调节镀后冷却段移动风箱上下表面的风量；冲压模具表面强化、润滑等，有效减少了色差缺陷的不合格率。     

基于仿生结构的Al-Ti-Ti2AlNb层状复合材料的组织与力学性能

受生物材料的韧脆复合结构的启发，本文将Al箔、Ti箔和Ti2AlNb箔材堆叠排列，采真空热压烧结技术制备了层级结构的Al-Ti-Ti2AlNb层状复合材料。利用SEM、XRD等技术表征了材料的微观结构，并测试了抗弯与抗压性能。研究发现，本文设计的层状结构复合了Ti、TiAl系列间化合物、Ti2AlNb等多种材料，层级结构明显，界面清晰。抗弯强度与抗压强度分别为1231±71MPa和1341±63MPa，相比同类材料具有显著的优势。分析认为，多层级结构的存在对裂纹的扩展有显著地阻碍作用；相比常规的二元TiAl层状材料，Ti2AlNb层的存在显著提高了力学性能。     

Role of interface on irradiation damage of Cu−diamond composites using classical molecular dynamics simulations

Cu?diamond composites have been proposed as a candidate thermal management material for spacecraft electronics. Nevertheless, irradiation effects on the composites remain poorly understood at present. Here we focus on investigating the influence of Cu?diamond interfaces (CDIs) on energetic displacement cascades using atomistic simulations. Results show that a primary knock-on atom of Cu (PKA-Cu) can induce more significant damage than a PKA-C. Under almost all circumstances, the statistically averaged fraction of surviving interstitials is not only lower than that of vacancies but also no more than 1. Because of the unique nature in the mobility and interactions with CDIs, Cu interstitials exhibit the lowest concentration among all defects in most cases. The high residual rate of displaced defects in diamond makes it relatively difficult to heal. The structural damage is mainly manifested in a short-range disorder of diamond and a long-range disorder of Cu after irradiation. At elevated temperatures, the atomic displacement region may form compact chain-like defects to restrain lattice loosening. Despite the above, CDIs could act as effective sinks to facilitate the recombination and/or annihilation of irradiation-induced defects in all scenarios. This study provides an important insight into the understanding of the microscopic evolution of irradiation defects for the composites.