Ti-Al金属间化合物脆性问题的研究进展

运用从宏观到微观的不同层次理论对Ti-Al金属间化合物室温脆性的研究进展进行了回顾,讨论了Ti-Al金属间化合物室温脆性的形成原因,并重点从电子结构层次阐述了金属间化合物室温脆性的成因,提出了从各个结构层次综合改善室温脆性的具体措施和实现途径.     

Al2O3/ZrO2(Y2O3)共晶复合陶瓷晶体生长机理

基于国外定向凝固氧化物/氧化物共晶复合陶瓷的晶体生长动力学行为的研究成果,阐述其动力学机制,分析动力学因素对微观结构形态的影响,探讨晶体生长热力学、动力学行为与微观结构形态之间的关系,同时结合以燃烧合成、快速凝固技术制备的新型高强韧Al2O3/ZrO2(Y2O3)共晶复合陶瓷,探讨共晶复合陶瓷在快速凝固条件下的晶体生长动力学行为.结合定向凝固与快速凝固两种晶体生长机制,得知过冷度、凝固界面前沿的温度梯度是影响晶体生长方式的重要因素,且受二者决定的凝固速率(即晶体生长速率)则决定材料的最终微观结构与形态.     

几种金属材料织构参数与工艺参数的关系

一、前言 材料的宏观特性是由它的微观结构和性质所决定的。为了提高材料的性能,在进行工艺研究时必须对材料的微观结构、组织状态、晶粒大小及取向分布等进行观察,从而来指导工艺研究。文中介绍了三种不同金属材料的织构与加工工艺参数的关系。     

基于表面改性的非均匀结构硬质合金研究进展

表面改性是使材料表面获得与其基体不同微观组织的处理技术,能够有效调控材料表面的力学性能.因此,将表面改性方法应用于改善硬质合金表面的微观组织,能够有效避免均匀结构硬质合金显微结构-宏观性能的局限性,为制备高性能非均匀结构硬质合金提供技术方案.由于硬质合金表面改性研究的起步较晚且表面改性方法较多,表面改性方法的选取及其改...     

焦炭X射线衍射分析技术的研究进展

利用X射线衍射分析技术对焦炭微观结构进行分析,可以在微观尺度上深入研究焦炭显微结构.介绍了焦炭微晶结构与其宏观性质的关联,煤化度及热解过程对微晶结构的影响等,并说明了研究焦炭结构的意义及其发展前景.     

数值仿真技术在粉末冶金零件制造中的应用及研究进展

数值仿真技术可用于粉末零件制造的工艺设计与优化,为缺陷预测与预防、零部件性能改善提供有效的理论支持和技术指导。基于粉末零件压制和烧结机理的本构模型是进行准确可靠的数值计算的必要条件。本文主要介绍了粉末压制模拟中常用的本构建模方法,如粉末烧结体塑性力学方法、广义塑性力学方法及微观力学方法,和粉末烧结模拟中的微观结构模拟方法,如分子动力学法、相场法、蒙地卡罗法及元胞自动机法等,并对以上各种建模方法的计算原理、适用范围及近些年的应用进展做了简要介绍,最后对数值仿真技术在粉末零件制造中的发展方向进行了展望。     

高性能海洋用钢智慧研发之二——钢铁材料基因与显微组织数字化表征

材料基因的识别及显微结构的数字化表征在科技创新、工业制造以及国家安全建设等方面的作用尤为重要。基因结构数据的高质量提取不但关系到重大工程的服役安全,也关系到材料智慧设计及产品终端质量与成本。如何高质量、高效率地提取和分析材料大数据已成为当前制约新材料智慧研发的关键。综合分析数字化时代下材料研发的特点及今后发展方向,针对材料基因库的构建提出了可视化及数字化表征的方法,建立了材料微观基因结构与宏观力学性能的数字化关联。     

粉未钛合金新工艺

美国马萨诸塞州伯林顿Dynamet技术有限公司研制并申请了新的钛合金宏观和微观材料的近净形产品,除了TiC粒子量与组成基体合金元素粉未混合计算,作为”陶瓷钛”设计的工艺基本是与整体钛合金生产相似的。用冷、热等静压方法将混合物压实。随后,进行挤压或锻造。 Dynamet有限公司在材料进展和工艺杂志中发表的文     

千枚岩岩石微观破裂机理与断裂特征研究

岩石的宏观断裂与其内部微结构和微缺陷紧密相关,建立岩石微观破裂机理和宏观断裂之间更直观的联系是当今断裂力学的难题之一.本文以金沙江上游泥盆系中统中段的绢云母千枚岩与硅质板状千枚岩为研究对象,利用扫描电镜与力学试验等多种测试手段,通过对2种千枚岩岩石断口的微观形貌特征的研究,揭示了千枚岩岩石微观破裂形式、破裂机理与其矿物组成之间的联系.指出绢云母千枚岩岩石以沿晶面擦花的微观破裂形式为主,是典型的微观脆性剪断,而硅质板状千枚岩岩石既有沿晶断裂的拉断破裂,又存在切晶擦花的剪切微破裂形式,是属于拉、剪破裂并存的微观破裂机制.进一步结合岩石断裂的力学特征,分析千枚岩微观破裂与宏观断裂之间的联系.结果显示:千枚岩岩石在外力作用下的断裂形式与其微观破裂形式是可对应的.这一结论为建立起岩石微观破坏机制和宏观断裂特征的桥梁提供了依据,具有一定的理论意义.     

冲击条件下临界空穴扩张比参数V_(GC)的测试研究

1 引言随着断裂力学进一步发展,人们越来越重视对细观断裂机理的研究。可以认为细观断裂力学理论与应用的研究已成为当前断裂力学深入发展的关键,为此国内外很多学者都争相开展这方面的工作。现在不仅理论研究,就是试验研究也已深入到新层次。自郑长卿等提出新的材料韧断特性参数——临界空穴扩张比参数V_(GC)以来,在该方面已进行了较为广泛而深入的研究。多种材料宏观与微观试验结果证实,V_(GC)是一个对应     

Impact Mechanics and High-Energy Absorbing Materials: Review

In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models) and computational methods (finite-element, finite-difference, and mesh-free methods) used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys) are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures.     

带式烧结机台车起拱的力学分析及仿真

针对带式烧结机台车在尾部回程道的起拱问题,对尾部台车的力学关系进行了分析,得出了带式烧结机台车不起拱条件下的力学控制阀值;利用ADAMS软件,建立了450 m2带式烧结机的虚拟样机且进行了动力学仿真,得出了尾部回程道下台车及台车列力值曲线。通过力学阀值进行虚拟控制,达到了无起拱目的,证明了阀值公式的正确性,从力学角度揭示了带式烧结机起拱原因。该研究结果可为今后带式烧结机的工程设计及应用提供理论依据。     

Nanomechanics Modeling and Simulation of Carbon Nanotubes

Carbon nanotubes (CNTs) have been perceived as having a great potential in nanoelectronic and nanomechanical devices. Recent advances of modeling and simulation at the nanoscale have led to a better understanding of the mechanical behaviors of carbon nanotubes. The modeling efforts incorporate atomic features into the continuum or structural mechanics theories, and the numerical simulations feature quantum mechanical approach and classical molecular dynamics. Multiscale and multiphysics modeling and simulation tools have also been developed to effectively bridge the different lengths and time scales, and to link basic scientific research with engineering application. The general approaches of the theoretical and numerical nanomechanics of CNTs are briefly reviewed. This paper is not intended to be a comprehensive review, but to introduce readers (especially those with traditional civil engineering or engineering mechanics backgrounds) to the new, interdisciplinary, or emerging fields in engineering mechanics, in this case the rapidly growing frontier of nanomechanics through the example of carbon nanotubes.     

Mechanisms of Load-Deformation Behavior of Molecular Collagen in Hydroxyapatite-Tropocollagen Molecular System: Steered Molecular Dynamics Study

Bone is a widely studied structure due to its important function in the human body and also for its unique mechanical properties, which depend upon several factors, such as, its hierarchal structure, its constituents, degree of interactions between different constituents, etc. The major constituents of bone are collagen and hydroxyapatite (HAP). In this work, the load-carrying behavior of collagen is evaluated using steered molecular dynamics simulations. It is observed that the mineral HAP influences the load-deformation behavior of collagen. The collagen molecule (tropocollagen) requires more energy to deform when it is in close proximity of HAP. The reasons for a typical load-deformation behavior are also analyzed. It is observed that with stretching of the tropocollagen, first hydrogen bonds between the tropocollagen chains break, as a result of which more water molecules start interacting with chains. HAP significantly alters the interaction between tropocollagen and water. The load-carrying behavior of tropocollagen at different loading rates is also analyzed by pulling collagen at different velocities. These simulations give important information about the molecular mechanics of collagen and are also useful for the development of novel biomimetic artificial implant materials.     

硅钢酸洗系统硅泥去除技术的功能解析与改进

针对硅钢酸洗系统易失稳、可靠性差的状况进行了系统的分析。描述硅垢在酸洗系统中形成的过程及机理,并对硅泥和硅垢如何使得紊流酸洗降效进行了系统的阐述。对在线脱硅的结构功能及工艺原理和碱洗的原理及碱洗的不同模式进行分析。通过对酸洗系统、在线脱硅和碱洗系统的深度解析,并结合硅垢对系统产生失效的机理,首次认清了三者的工艺逻辑关系。对系统中结构不完善的地方进行了有效的改进,从而提高了整个酸系统的可靠性、稳定性,降低了机组运行的成本。     

管材矫直机预紧机架力学模型及有限元分析

根据矫直机工作原理以及无缝钢管的特殊工艺,通过弯矩理论和材料力学理论从理论上计算出了六个辊的矫直力解析解。分析了预紧力规律和预紧理论,从而确定了矫直机机架需要施加的预紧力。创新性的完成了矫直机机架的力学模型的实体有限元化。有限元计算结果显示机构符合设计要求。计算结果有助于同类机构的设计。     

Impact Testing and Analysis of Composites for Aircraft Engine Fan Cases

The fan case in a jet engine is a heavy structure because of its size and because of the requirement that it contain a blade released during engine operation. Composite materials offer the potential for reducing the weight of the case. Efficient design, test, and analysis methods are needed to efficiently evaluate the large number of potential composite materials and design concepts. The type of damage expected in a composite case under blade-out conditions was evaluated using a subscale test in which a glass/epoxy composite half-ring target was impacted with a wedge-shaped titanium projectile. Fiber shearing occurred near points of contact between the projectile and target. Delamination and tearing occurred on a larger scale. These damage modes were reproduced in a simpler test in which flat glass/epoxy composites were impacted with a blunt cylindrical projectile. A surface layer of ceramic eliminated fiber shear fracture but did not reduce delamination. Tests on 3D woven carbon/epoxy composites indicated that transverse reinforcement is effective in reducing delamination. A 91-cm (36 in.) diameter full-ring subcomponent was proposed for larger scale testing of these and other composite concepts. Explicit, transient, finite-element analyses indicated that a full-ring test is needed to simulate complete impact dynamics, but simpler tests using smaller ring sections are adequate when the evaluation of initial impact damage is the primary concern.     

冲击荷载下岩石裂纹扩展研究进展

为了给深部资源开采和大型地下空间工程中围岩体的变形机理及稳定性控制提供理论基础,通过查阅大量关于表征岩石裂纹扩展的裂纹扩展模型、应力强度因子和断裂韧性的国内外文献,总结了前人的研究成果。依据现有研究,提出了动荷载作用下岩石裂纹扩展的几点建议：（1）综合考虑弹性力学、断裂力学和损伤力学建立岩石材料从微观断裂到宏观破坏这一演变过程的理论模型,使理论模型更加适应岩石材料的非线性特征;（2）采用分形、自组织和混沌等非线性理论表征动荷载作用下岩石内部以及表面裂纹的扩展演化特征;（3）采用颗粒离散元和有限差分模拟岩石材料裂纹扩展演化特征。     

Prevalence of penile human papillomavirus DNA in husbands of women with and without cervical neoplasia: a study in Spain and Colombia

Quinidine is an active antimalarial compound extracted from the bark of Cinchona trees. The activity differences among structurally related molecules appears to depend on the absolute stereochemistry of some functional groups, a result that stimulated a detailed conformational analysis of these molecules of biological interest. In the present study, the potential energy surface (PES) for the antimalarial agent quinidine (C20H24O2N2) has been comprehensively investigated using the molecular mechanics (MM) and quantum mechanical semiempirical AM1 and PM3 methods. Six distinct minimum energy conformations were located on the multidimensional PES and also characterized as true minima through harmonic frequency analysis. The relative stabilities and thermodynamic properties are reported. The coexistence of different conformers is discussed for the first time in the literature based on the transition state (TS) structures located on the PES for the quinidine molecule. The theoretical results reported in the present study are in agreement with the experimental proposal, based on NMR data, that there are two conformations existing in solution for the quinidine molecule.     

Quantum Notions of Stress

Existing notions of stress in a quantum mechanical framework are reviewed and discussed in a semitutorial manner suitable for a mechanics audience. Notwithstanding early fundamental work in this area since the 1930s, the increasing availability of computational tools to perform ab initio quantum mechanical calculations with high accuracy and efficacy has renewed interest in this field especially in the context of computational mechanics and materials science. Although some unresolved issues remain, the subject has evolved considerably in the past two decades with various authors offering their own unique viewpoint. In the present paper, we summarize the debate over the “definition” of stress in a quantum mechanical setting and discuss some controversial issues such as the uniqueness of the stress.