关键词： Creep   Vertebral body   Material properties   Geometry   Microstructure  

摘要： Creep, the time dependent deformation of a structure under load, is an important viscoelastic property of bone and may play a role in the development of permanent deformity of the vertebrae in vivo leading to clinically observable spinal fractures. To date, creep properties and their relationship to geometric, microstructural, and material properties have not been described in isolated human vertebral bodies. In this study, a range of image-based measures of vertebral bone geometry, bone mass, microarchitecture and mineralization were examined in multiple regression models in an effort to understand their contribution to creep behavior. Several variables, such as measures of mineralization heterogeneity, average bone density, and connectivity density persistently appeared as significant effects in multiple regression models (adjusted r(2): 0.17-0.56). Although further work is needed to identify additional tissue properties to fully describe the portion of variability not explained by these models, these data are expected to help understand mechanisms underlying creep and improve prediction of vertebral deformities that eventually progress to a clinically observable fracture. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Polycrystalline material   Crystal plasticity   Constitutive behavior   Dislocation density   Microscale damage   Thermo-mechanical processes  

摘要： Thermo-mechanical experiments at different elevated temperatures are carried out for tensile and shear-dominant specimens extracted from warming forming materials of 7075 aluminum alloy and 22MnB5 boron steel, respectively. A specimen-embedded furnace jointed by temp-control system to perform the high temperature shear experiments. Driven by microscale anisotropic plastic flow, damage is embedded in each slip system and damage evolution is controlled by the preferential dislocation slip. Combined with microscale damage and dislocation density based constitutive model, an advanced crystal plasticity method is proposed to perform predictions of mechanical behavior of face-center-cubic materials at various temperatures. Reasonable agreement is obtained between experimental and numerical results for different specimens, temperature conditions and materials. This approach simultaneously captures the strain hardening rate, damage softening, non-linear post-necking and fracture strain. Microstructural effects on ductile fracture are tracked and investigated including dislocation density and crystallographic orientation. The results show that local dislocation density rise is associated with damage initiation. Different fracture morphologies and necking paths are caused by distinct initial misorientation distributions in comparison with experimental observation of 7075 aluminum alloy. Local misorientations are investigated and critical misorientation ranges are computed for promoting void growth in zigzag and straight fracture morphologies. Schmid factor is computed as not necessary variable to trigger void growth.

关键词： Mg-Si-Sn-Bi材料   退火   化合物分解   Seebeck系数   热电行为  

摘要： 利用单质粉末冷压成型及高真空500℃-2 h烧结制备了Mg-Si-Sn-Bi材料,随后对制备材料在真空下600℃退火处理,并对制备材料的组成和热电性能进行研究。结果表明,500℃烧结材料仅仅由Mg_2Sn和Mg_2Si两相混合物构成。材料600℃退火,部分化合物分解,Sn和Si首先以单质形式存在;随后Si融入剩余的Mg_2Sn结构中,形成Mg_2(Sn,Si)固溶体;Sn以金属纳米尺寸状态存在;分解的Mg与真空石英玻璃管内残留的氧反应生成MgO相。而且,退火时间延长,Mg_2(Sn,Si)固溶体和纳米尺寸的金属Sn含量增多。材料中Mg_2(Sn,Si)固溶体含量越多,Seebeck系数绝对值越大;材料中纳米尺寸的金属Sn含量越多,电阻率越小。含有纳米尺寸金属Sn的Mg-Si-Sn-Bi材料因Seebeck系数绝对值大和电阻率小,具有较大的功率因子。

关键词： Al2O3-Al-C材料   铝纤维   高温机械性能   显微结构  

摘要： 分别以板状刚玉、α-Al_2O_3微粉、金属铝(铝纤维和铝粉)、石墨为原料,以酚醛树脂为结合剂,制得Al_2O_3-Al-C材料。借助XRD和SEM分析了试样的物相组成和显微结构,研究了铝纤维加入量对材料抗热震性、高温抗折强度的影响,结果表明:用铝纤维代替铝粉可提高材料的高温抗折强度和抗热震稳定性。保持金属铝的总加入量为6%,当铝纤维加量由0%增加到1%时,1400℃的高温抗折强度由26.5 MPa提高到34.7 MPa,热震后的残余强度保持率由62%增加到69%。高温时铝纤维转变为非氧化物晶须编织体或纤维束,与基质紧密结合,起桥接和强化作用,可改善材料的抗热震性并显著提高其高温抗折强度。

关键词： CaCO3 nanoplatelets (CCNPs)   cement-based materials   pore structure   chloride ion permeability   compressive strength  

摘要： Nanomaterials have been widely used in cement-based materials. Graphene has excellent properties for improving the durability of cement-based materials. Given its high production budget, it has limited its wide potential for application in the field of engineering. Hence, it is very meaningful to obtain low cost nanoplatelets from natural materials that can replace graphene nanoplatelets (GNPs) The purpose of this paper is to improve the resistance to chloride ion penetration by optimizing the pore structure of cement-based materials, and another point is to reduce investment costs. The results illustrated that low cost CaCO3 nanoplatelets (CCNPs) were successfully obtained under alkali treatment of seashell powder, and the chloride ion permeability of cement-based materials significantly decreased by 15.7% compared to that of the control samples when CCNPs were incorporated. Furthermore, the compressive strength of cement pastes at the age of 28 days increased by 37.9% than that of the plain sample. Improvement of performance of cement-based materials can be partly attributed to the refinement of the pore structure. In addition, AFM was employed to characterize the nanoplatelet thickness of CCNPs and the pore structures of the cement-based composites were analyzed by MIP, respectively. CCNPs composite cement best performance could lay the foundation for further study of the durability of cement-based materials and the application of decontaminated seashells.

关键词： Joining   Glass-ceramic   SiC   Irradiation  

摘要： The aim of this work was to investigate and discuss the microstructure and interface reaction of a calcia-alumina based glass-ceramic (CA) with SiC. CA has been used for several years as a glass-ceramic for pressure-less joining of SiC based components. In the present work, the crystalline phases in the CA glass-ceramic and at the CA/SiC interface were investigated and the absence of any detectable amorphous phase was assessed. In order to provide a better understanding of the effect of irradiation on the joining material and on the joints, Si ion irradiation was performed both on bulk CA and CA joined SiC. CA glass-ceramic and CA joined SiC were both irradiated with 5.1 MeV Si2+ ions to 3.3 x 10(20) ions/m(2) at temperatures of 400 and 800 degrees C at DuET facility, Kyoto University. This corresponds to a damage level of 5 dpa for SiC averaged over the damage range. This paper presents the results of a microstructural analysis of the irradiated samples as well as an evaluation of the dimensional stability of the CA glass-ceramic and its irradiation temperature and/or damage dependence. (c) 2018 Elsevier B.V. All rights reserved.

关键词： 铝硅比   原位合成   莫来石   显微结构  

摘要： 选用铝矾土作为铝源,煤矸石为硅源,氟化铝和五氧化二钒为添加剂,通过固相反应原位制备了主晶相为莫来石相的晶体。利用X射线衍射仪和扫描电子显微镜以及相应的EDS等手段对莫来石进行了表征分析,并考察了在不同铝硅比的条件下对所制试样的显气孔率、吸水率、体积密度、抗折强度以及显微结构的变化特征。结果表明:当铝矾土与煤矸石的铝硅摩尔比为3.05∶2时,显气孔率为23.6%、吸水率为10.55%、体积密度为2.3 g/cm^3、抗折强度为114 MPa,试样的综合性能最优。

关键词： 共沉淀法   LiNi0.5Co0.2Mn0.3O2正极材料   制备工艺   微结构   电化学性能  

摘要： 为研究制备工艺对LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2正极材料微结构及电化学性能的影响,采用共沉淀法,在搅拌速度分别为500、600、700、800 r/min下合成前驱体,再经850℃焙烧制得LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2正极材料。采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)等表征了样品的微结构;以CV阻抗测试、恒流充放电等技术测试了样品的电化学性能。结果表明,所有样品均为单一的六方晶系相,没有其他杂相。前驱体的搅拌速度为500、600、700、800 r/min时制备的LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2正极材料的首次充电比容量分别为167.4、185.8、169.4、149.6 m Ah/g,首次放电比容量分别为147.9、165.6、141.9、122.6 m Ah/g,首次库仑效率分别为88.3%、89.12%、83.6%、82.0%。可见,前驱体的搅拌速度为600 r/min、焙烧温度为850℃时所制备的LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2正极材料具有较好的电化学性能。

关键词： Fe3Si   第一性原理   微结构   X射线散射理论   消光规律  

摘要： 基于第一性原理的密度泛函理论,对Fe_3Si的微结构及其铁磁性能进行研究,结果表明:Fe_3Si为面心立方有序DO3(cF16)结构,Fe_3Si具有典型金属能带特征,穿过Fermi能级的能带最主要是Fe的3d态电子的贡献,其次是来自Si的3p态电子的贡献.但结合键是金属键和共价键所组成的混合键,Fe_3Si的铁磁性主要来自Fe的3d态电子的自旋.基于X射线散射理论,结合Fe_3Si微结构研究Fe_3Si的消光规律:当衍射面指数nh、nk、nl奇偶混合时,衍射峰消失,系统出现消光.当衍射面指数nh、nk、nl全为奇数或偶数时,产生衍射.根据Fe_3Si晶体布拉格衍射限制条件H^2+K^2+L^2≤53,其最高的衍射指数为640.对进一步研究DO_3结构的晶体具有现实指导意义.