高分子材料的极限断裂强度和破坏性能的研究——Ⅳ.等速拉伸下屈服强度动力学模型理论

本文从高聚物结构多重性和形变不均一性出发,结合应力集中区的形变具有受迫高弹性和高弹性的动力学本质及分子运动松弛特征,将等速拉伸下的应力-应变关系式与应力集中链及断链动力学方程联系起来,推导出等速拉伸屈服状态方程,并讨论了屈服破坏机理。     

关于岩土材料屈服破坏准则的若干问题研究

岩土材料的屈服破坏准则问题是岩士工程中最基础也是最为重要的问题,前人对此已开展了大量的研究工作并取得了丰富的研究成果,但由于岩土材料力学性质的复杂性,目前仍存在一些问题尚存在诸多争议,例如如何反映岩土材料不同于金属的特殊力学性质,如何建立岩土材料的能量屈服准则,如何描述破坏,仍有待进一步研究。本文首先论述了这一问题的提出,明确相关概念,之后分析了屈服破坏准则的概念和条件,进而论述了岩土破坏准则的几个基本问题,以期能够引起更多的人对该问题的关注。     

测定材料屈服强度的应变计法试验研究

对应变计测量屈服强度的可能性做了讨论，选择适合弹塑性区测试的应变片，进行与引伸计的对比试验以考察测试结果的异同试验表明两种方法测试同一试样所得值之差最大为７ＭＰａ，测试相同状态不同试样所得平均值之差不到７ＭＰａ，由于差别很小，故应变计法可用于屈服强度的工程测试，且与引伸计法具有相同的测量精确度。     

变形镁合金的强度大于铝

英国镁电子公司制造出一种变形镁合金，据称其强度在100℃以上比铝还要好。被称作E1ektron 675的合金，其强度在100℃以上比铝2000和7000系列合金的强度高。在200℃时的屈服强度达290MPa，极限抗拉强度380MPa。这比2024系铝的强度高出100％，比7075铝的强度高出200％。这些特性相当于钛，但比钛轻一半多，而且加工起来比钛容易。     

面内异性材料的应力和应变状态分析

迄今有关材料应力和应变状态的分析多限于面内同性材料。然而,绝大多数板树为面内异性,因此对所有板材的塑性变形问题一味在面内同性之条件下研究未免就有不妥之处。本文在面内异性的前提下,对板料的应力和应变状态进行了分析,并且初步探讨了用液压胀形试验求得应力应变曲线的一些问题。     

超细晶/纳米晶反Hall-Petch变形机制最新研究进展

晶粒细化是提高晶体材料力学性能的一种有效强化方式,Hall-Petch关系表明晶体材料的屈服强度和硬度随晶粒尺寸降低而增强.随着超细晶材料和纳米材料的深入研究,实验发现了反Hall-Petch现象,即随着晶粒尺寸的减小,材料性能下降.综述了反Hall-Petch现象中屈服强度、显微硬度及模拟现状,并指出了超细晶和纳米晶细化晶粒的研究方向.     

粉末粒度对蒙乃尔合金多孔材料压缩性能的影响

烧结蒙乃尔合金多孔材料是重要的金属过滤材料之一,凭借其优良的耐高温抗腐蚀及良好的抗冲击、可焊接等优势广泛应用于化工、核工业、石化等诸多领域.随着蒙乃尔过滤材料应用领域的拓展及使用环境越来越苛刻,其力学性能的研究显得尤为重要.采用粉末冶金法制备(O)20mm×25mm柱状压缩试件,利用MTS810对这些试件进行力学性能测试,采用准静态单一轴向的加载方式对试样进行压缩性能的测试,并详细分析了相同孔隙度下粒度对镍合金多孔材料压缩性能的影响,结果表明,镍合金多孔材料的压缩应力-应变曲线有塑性材料的特征;对于同一孔隙度的试样,弹性模量和屈服强度都随着粒度的减小而增加,当粒度<75μm时,屈服强度和弹性模量增加得很快.     

电场时效对LY12铝合金微变形行为的影响

研究了电场时效处理中电场强度对LY12铝合金的微屈服强度和微变形行为的影响，也研究了直流电场时效和脉冲电场时效对合金微变形行为的影响。结果表明，适当的电场时效可以使合金的微屈服强度明显提高，优选出最佳的电场时效工艺参数是：E=2kV／cm，190C／10h。     

Energy Version of the Theory of Creep of Materials with Different Resistance to Tension and Compression

We propose an energy version of the theory of creep for initially isotropic materials containing parallel plane microcracks and deduce constitutive equations of creep and the kinetic equation of accumulation of damage. We consider basic experiments aimed at the determination of material constants according to the proposed theory. The theoretical results are compared with the experimental data obtained for a light alloy with different resistance to tension and compression.     

Deformation instability and strength of structural alloys under conditions of stress concentrations and cryogenic temperatures

The investigation results for the effect of stress concentration on the mechanical behavior of titanium alloy 3M and aluminum alloy AMg5 within the temperature range of 293 to 4.2 K Under conditions of deep cooling, its character is shown to change considerably due to a manifestation of the effect of low-temperature jumplike deformation. __________ Translated from Problemy Prochnosti, No. 2, pp. 153–156, March–April, 2007.     

Further Development in Thermodynamic Approach for Thermoviscoelastic Materials

In this paper we derive linear and nonlinear theories ofthermoviscoelasticity for thermorheologically simple materials. Thisderivation is based on two theories: the Thermodynamic of IrreversibleTheory and the Generalized Viscoelastic Standard Theory. These twotheories, along with other assumptions, lead to three-dimensionalthermoviscoelastic models. The derivation we give here is an extensionof Schapery's models. We will soon state the relations expressing thebalance of energy, i.e., the specific heat capacity and the heatconduction equation.     

二氧化锡颗粒增强银基复合材料的电阻率

根据复合材料的传导理论ｇ－ＭｅＯ系金属基复合材料电阻率的计算模型，并与Ａｇ－Ｓ的实验结果进行了对比。结果分析表明，颗粒增强金属基复合材料的电阻率不仅与基体和颗粒材料的电阻率及颗粒的体积分数有关，还与颗粒粒度及在基体中的分布状态有关。     

遗态材料的研究理念和研究进展

介绍了遗态材料的研究理念和国内外的研究进展.针对遗态材料在植物模板的选取、熔融浸渍体的种类以及不同的制备工艺路线进行了详细论述,并分析了遗态材料作为结构功能一体化材料的应用性能及影响因素,最后总结了遗态材料存在的不足及发展方向.     

材料抗冲蚀性的研究进展

综述了材料内在因素和环境因素变化对冲蚀的影响,韧性材料的耐冲蚀性能优于脆性材料,脆性材料仅在10^0冲蚀角以下才表现出较好的耐冲蚀性;冲蚀下的脆性材料和塑性材料的区分不仅与材料的韧脆性有关,还与冲击粒子的动能有关。当粒子质量发生变化时,材料的冲蚀机理随之变化;影响材料耐冲蚀磨损的重要内在因素是弹性模量而不是硬度;各种冲蚀机理都有一定的适应性和局限性。     

Supramolecular Energy Materials

Self-assembly is a bioinspired strategy to craft materials for renewable and clean energy technologies. In plants, the alignment and assembly of the light-harvesting protein machinery in the green leaf optimize the ability to efficiently convert light from the sun to form chemical bonds. In artificial systems, strategies based on self-assembly using noncovalent interactions offer the possibility to mimic this functional correlation among molecules to optimize photocatalysis, photovoltaics, and energy storage. One of the long-term objectives of the field described here as supramolecular energy materials is to learn how to design soft materials containing light-harvesting assemblies and catalysts to generate fuels and useful chemicals. Supramolecular energy materials also hold great potential in the design of systems for photovoltaics in which intermolecular interactions in self-assembled structures, for example, in electron donor and acceptor phases, maximize charge transport and avoid exciton recombination. Possible pathways to integrate organic and inorganic structures by templating strategies and electrodeposition to create materials relevant to energy challenges including photoconductors and supercapacitors are also described. The final topic discussed is the synthesis of hybrid perovskites in which organic molecules are used to modify both structure and functions, which may include chemical stability, photovoltaics, and light emission.     

Solar Energy Materials

Solar energy materials have properties tailored to meet requirements set by the spectral distribution, angle of incidence, and intensity of the electromagnetic radiation prevailing in our natural surroundings. Specifically, the optimization can be performed with regard to solar irradiation, thermal emission, atmospheric absorption, visible light, and photosynthetic efficiency. Materials for thermal and electrical conversion of solar energy in man‐made collectors, as well as for energy‐efficient passive design in architecture, are typical examples. This paper reviews solar energy materials with emphasis on the thermal applications of a variety of types. Electrical applications are given a more cursory exposition, the reason being that a systems perspective—rather that a materials perspective—is most fruitful in this case.     

塑性加工法制备各向异性稀土永磁材料的研究进展

塑性加工是一种可制备各向异性材料并可实现近终形成形的方法,已有一系列尝试将其应用于制备高性能各向异性稀土永磁材料的研究报导.介绍了用于制备各向异性磁体或磁粉的塑性加工方法,包括热压、模压、轧制、正挤压、反挤压、等径角挤压等,和用各种塑性加工方法提高永磁材料性能的基本原理、效果,以及工业化应用进展.