Meso-scale Computational Investigation of Shock-Wave Attenuation by Trailing Release Wave in Different Grades of Polyurea

Over the past several years, considerable research efforts have been made toward investigating polyurea, a segmented thermoplastic elastomer, and particularly its shock-mitigation capacity, i.e., an ability to attenuate and disperse shock-waves. These research efforts have clearly established that the shock-mitigation capacity of polyurea is closely related to its chemistry, processing route, and the resulting microstructure. Polyurea typically possesses a nano-segregated microstructure consisting of (high glass transition temperature, T _g) hydrogen-bonded discrete hard domains and a (low T _g) contiguous soft matrix. While the effect of polyurea microstructure on its shock-mitigation capacity is well-established, it is not presently clear what microstructure-dependent phenomena and processes control its shock-mitigation capacity. To help identify these phenomena and processes, meso-scale simulations of the formation of nano-segregated microstructure and its interaction with a leading shock-wave and a trailing release-wave is analyzed in the present work. The results obtained revealed that shock-induced hard-domain densification makes an important contribution to the superior shock-mitigation capacity of polyurea, and that the extent of densification is a sensitive function of the polyurea soft-segment molecular weight. In particular, the ability of release-waves to capture and neutralize shock-waves has been found to depend strongly on the extent of shock-induced hard-domain densification and, thus, on the polyurea soft-segment molecular weight.     

Shock-Wave Consolidation of Rapidly Solidified Superalloy Powders

JOM - The feasibility of consolidating rapidly solidified MAR M-200 powders by explosive means is demonstrated. MAR M-200 powders produced by the rapid solidification rate (RSR) technique and...     

In Situ X-ray Tomography and 3D X-ray Diffraction Measurements of Cemented Granular Materials

JOM - In situ x-ray tomography and three-dimensional (3D) x-ray diffraction analysis have been combined to investigate the mechanical behavior of noncemented and lightly cemented quartz...     

声发射波在不同复合材料容器表面的衰减特性

分析了声发射波在不同复合材料容器表面的衰减特性。通过在复合材料容器表面进行衰减测试,探讨了材料组织方向、容器内的介质、容器受载历史等因素对声发射信号幅值衰减特性的影响。结果表明,以上因素影响了声发射波的衰减特性,结论为声发射检测的后续研究提供数据支持。     

Molecular-Level Analysis of Shock-Wave Physics and Derivation of the Hugoniot Relations for Fused Silica

Equilibrium and non-equilibrium molecular-dynamics simulations are employed in this study to investigate various aspects of shock waves in fused silica (a pure SiO₂ amorphous material used in transparent-armor applications). Equilibrium molecular-dynamics simulations are used first to validate that the initial (unshocked) fused silica possesses the appropriate mass density and microstructure (as characterized by its partial Si-Si, Si-O, and O-O radial distribution functions). Next, non-equilibrium molecular-dynamics simulations are employed, within a continuously contracting computational-cell scheme, to generate planar longitudinal (uniaxial motion) shocks of different strengths. By examining and quantifying the dynamics of shock-wave motion, the respective shock-Hugoniot relations (i.e., functional relations between various material-state variables in the material states produced by the shocks of different strengths) are determined. This methodology suggested that irreversible non-equilibrium deformation/damage processes play an important role in the mechanical response of fused silica to shock loading and that the ??equilibrium?? procedures for Hugoniot determination based on the equation of state and the Rankine-Hugoniot equation may not be fully justified. Finally, the non-equilibrium molecular-dynamics simulations were used to identify the main microstructure modifying/altering processes accompanying the shock-wave motion through fused silica.     

Effect of Shock-Wave Deformation on Acoustic and Elastic Properties of Titanium Nickelide in Phase Transformations

Metal Science and Heat Treatment -     

17Cr2Ni2Mo钢粒状组织和粒状贝氏体的断裂特性

研究了１７Ｃｒ２Ｎｉ２Ｍｏ钢粒状组织和粒状贝氏体经低温和高温回火后的断裂特性。结果表明；粒状组织和粒状贝氏体经低温回火后，由于Ｍ－Ａ岛的分布，尺寸及应变诱发相变的影响而具有良好的强韧性，特别是其断裂韧性Ｊ１ｃ值较板条马氏体几乎高了一倍；而经高温回火后，由于Ｍ－Ａ岛分解出来的碳化物的偏聚，呈现出准解理特征，其断裂韧性远低于回火索氏体。     

Fe-Cu颗粒膜结构及巨磁电阻效应研究

通过磁控溅射方法在室温衬底上制备了Fe23Cu77(at．％)颗粒膜，利用XRD、TEM、VSM及四探针方法对Fe23Cu77颗粒膜的结构、性能进行了研究。结果表明：室温时，尺寸约为1nm～10nm的Fe颗粒非均匀分布在Cu基体中，颗粒膜中存在着明显的织构。VSM测量表明室温颗粒膜呈超顺磁性，其磁化曲线符合朗之万函数。随退火温度提高，颗粒膜的巨磁电阻(GMR)值单调下降，在室温最大，其值约为-1.2％。其原因可归结于颗粒膜在室温下就达到了最佳的表面积与体积比，从而增强了自旋相关散射和GMR效应。通过最小非线性二乘方法拟合GMR-(M／Ms)曲线表明，低场时GMR与(M／Ms)呈平方率关系，而在高场时则偏离平方率关系。     

Formation of Mesoferrite and Granular Bainite in Low-Carbon Low-Alloy Steel

Special features in the formation of mesoferrite and granular bainite in low-carbon low-alloy steels are considered. A diagram of isothermal decomposition of austenite in steel 20Kh2NAch is plotted and the range of existence of mesoferrite is determined. Morphological differences between the granular intermediate structure formed in the isothermal decomposition of supercooled austenite in the intermediate temperature range and the granular bainite formed in the decomposition of austenite in continuous cooling are determined. The role of mesoferrite in the formation of these structures is considered.     

液压泵压力脉动分析及衰减措施

液压泵压力脉动影响系统工作性能，除改进液压泵设计之外，可在泵源装置中采用球腔式压力脉动衰减装置。     

12CrNi3钢粒状贝氏体的组织与性能

通过光学显微镜、电子显微镜研究了12CrNi3钢在不同的热处理条件下获得不同数量的粒状贝氏体,并测定其力学性能,得到粒状贝氏体含量与力学性能关系曲线,同时观察了其断口形貌特征。结果表明:在12CrNi3钢中,当粒状贝氏体含量占混合组织(马氏体 粒状贝氏体)含量30%以下时,合金的力学性能与单一板条马氏体的力学性能相比差别不大;合金中粒状贝氏体数量越多,其强度降低、塑性增加、冲击韧度增加;由断口分析知,不论是马氏体组织还是粒状贝氏体,或者是二者的混合组织,其断裂都表现为韧性断裂。     

球墨铸铁与灰口铸铁的超声衰减鉴别

为了找到快速准确鉴别球墨铸铁件与灰口铸铁件的现场检测方法，采用不同频率的超声波对不同厚度的球墨铸铁和灰口铸铁试样进行了超声衰减测试，发现灰口铸铁件超声衰减明显，而球墨铸铁件超声衰减微乎其微。分析认为在通常采用的波长范围内，产生超声衰减的主要原因是灰口铸铁中石墨晶体的构造以及石墨组织的形状、大小和分布。利用这一原理可以十分方便地鉴别球墨铸铁件和灰口铸铁件。     

珠光体共析转变对碳化物粒状倾向的影响

采用热模拟技术研究GCr15轴承钢经不同温度共析转变,得到不同片层间距珠光体组织对接下来的保温过程中碳化物粒状倾向的影响。结果表明:通过降低共析转变温度得到了细小的珠光体组织,随着珠光体球团直径和片层间距的减小,经过相同保温处理后试样显微硬度减小,碳化物呈粒状倾向增大,在500℃共析转变后得到碳化物片层熔断的退化状态珠光体,碳化物的粒状倾向最大。     

添加石墨量及粒度对铁基材料性能的影响

通过粉末烧结方法分别将100目、200目石墨与铸铁屑按照不同的质量比例（1％、2％、3％、4％）经混合、压块、烧结等程序得到铁基石墨复合材料，并测出不同成分试样的硬度、耐磨性。研究结果表明：随着石墨粒度的细化，铁基石墨复合材料的硬度提高，抗压强度降低，偶件的磨损增大；随石墨添加量增加，材料硬度和抗压强度降低、磨损量增大，材料磨擦系数降低，偶件的磨损量降低。     

Ti衬底层对FePt颗粒膜的微结构和磁特性的影响

在室温下,应用对靶直流磁控溅射设备在普通玻璃基片上制备了FePt(30nm)/Ti(tnm)颗粒膜样品,随后,在真空中进行了原位退火.详细研究了Ti衬底层对FePt颗粒膜的微结构和磁特性的影响.X射线衍射图谱表明样品形成了较有序的L10织构,Ti和FePt形成了三元FePtTi合金.当Ti层厚度t=5 nm、退火温度Ta=500℃时,样品具有高度有序的L10织构、小的颗粒尺寸和优异的磁特性.矫顽力超过了6.7 kOe,饱和磁化强度为620emu/cc.并且具有较小的开关场分布.结果表明FePt/Ti颗粒膜系统可作为超高密度磁记录介质的候选者.     

Ti衬底层对FePt颗粒膜的微结构和磁特性的影响

在室温下,应用对靶直流磁控溅射设备在普通玻璃基片上制备了FePt(30nm)/Ti(tnm)颗粒膜样品,随后,在真空中进行了原位退火.详细研究了Ti衬底层对FePt颗粒膜的微结构和磁特性的影响.X射线衍射图谱表明样品形成了较有序的L10织构,Ti和FePt形成了三元FePtTi合金.当Ti层厚度t=5 nm、退火温度Ta=500℃时,样品具有高度有序的L10织构、小的颗粒尺寸和优异的磁特性.矫顽力超过了6.7 kOe,饱和磁化强度为620emu/cc.并且具有较小的开关场分布.结果表明FePt/Ti颗粒膜系统可作为超高密度磁记录介质的候选者.     

含锆原料及其在耐火材料中的应用

近十多年来,含锆耐火材料得到了迅速发展,天然的含锆矿物原料和人工提取或合成的锆的氧化物和复合氧化物原料被广泛地应用于耐火材料中,并取得了良好效果。     

反射衰减诊断激光光束的应用分析

介绍了普通光学元件反射诊断激光光束的应用,提出了利用平面平晶的平面反射进行光能衰减,详细论述了采用该方法进行光能衰减的可行性,分析了平面平晶反射衰减中反射光S偏振态和P偏振态能量的差异,对激光束诊断的影响和解决方法,结合半导体绿激光器的光束诊断进行了应用分析。实验证明,该方法结构简单、调整方便、误差小,利用普通平面平晶反射衰减即可满足激光强度的匹配要求,实现了待测激光束无失真取样,达到很好的测试效果。     

Integrating Materials and Life Sciences Toward the Engineering of Biomimetic Materials

Research in the field of biological and biomimetic materials constitutes a case study of how traditional research boundaries are becoming increasingly obsolete. Positioned at the intersection of life and physical sciences, it is becoming more and more evident that future development in this area will require extensive interaction between materials and life scientists. To highlight this cross-talking, we provide a brief overview of the field, intended to illustrate how these disciplines can be integrated. We start with a short historical perspective, emphasizing the role of biologists in initiating early studies in the field. In the second part of the paper, a summary of important biochemical concepts and techniques relevant to biological materials is presented, with the goal of guiding nonspecialists towards the relevant techniques and knowledge required to investigate potential model systems. In the third part, we describe two case studies that emphasize the critical role of biosynthesis in understanding structure–function–property relationships in biological materials. We conclude with some remarks related to our own perception of how integration of materials and life sciences will lead to future developments in the field.