ryan

很多人会选择在情人节表白，情书无意是如今最文艺浪漫的形式之一。贴心的老鬼给大家准备了两种风格的情书参考，一种是柔情风格即常说的小清新，详见《文艺青年们的柔情情书》，一种是激情风格即常说的重口味（如下），请按照男女主性格进行选择。

Publication date: 15 April 2015
Source:Acta Materialia, Volume 88
Author(s): Z. Wu , W.A. Curtin
The competition between dislocation emission and cleavage at a crack tip plays an important role in governing the intrinsic fracture behavior of crystalline materials. This competition is not well understood in magnesium, which has many different combinations of cleavage planes and dislocation slip systems. Here, using both anisotropic linear elastic fracture mechanics theory and atomistic simulations, the emission/cleavage competition in magnesium is evaluated for a comprehensive set of crack orientations and crack tip geometries under mode I crack tip stress intensity loading at T =0K. Both theory and simulation show that cleavage is favored in most crack orientations, including basal plane cracks, tensile twin and basal-prismatic plane interface cracks. Initial slight crack tip blunting does not significantly change the behavior. These results suggest that magnesium has extremely low intrinsic fracture toughness, consistent with observations of many different cleavage-like planes in low-temperature fracture experiments. Based on T =0K properties, obtaining a more-ductile material via crack tip dislocation emission on the pyramidal and basal slip systems would require substantial and moderate reductions of the unstable stacking fault energy ( ∼ 50% and ∼ 20%, respectively) to be achieved at finite temperatures and/or via alloying.

Publication date: 15 April 2015
Source:Acta Materialia, Volume 88
Author(s): Marko Knezevic , Milovan Zecevic , Irene J. Beyerlein , John F. Bingert , Rodney J. McCabe
We investigate the temperature and rate dependence of slip, twinning, and secondary twinning in high-purity hexagonal close packed α-Zr over a wide range of temperatures and strain rates (from 76K to 673K and 0.001s⁻¹ to 4500s⁻¹). To reliably identify the dominant deformation mechanisms for each condition, we employ electron-backscattered diffraction (EBSD), dislocation theory, multi-scale polycrystal constitutive modeling, and a thermally activated dislocation density evolution based hardening law. We demonstrate with direct comparison with measurement that the constitutive model, with a single set of intrinsic material parameters, can predict the underlying texture evolution, primary and secondary slip and twin activity, and twin volume fraction associated with the different loading orientations and applied temperatures and strain rates. We find that the { 1 0 1 ‾ 2 } 〈 1 0 1 ‾ 1 ‾ 〉 twin is the preferred tension twin, either as a primary or secondary twin depending on the sample orientation, over the broad temperature and strain rate range tested. In contrast, we show that the preferred contraction twin, whether { 1 1 2 ‾ 2 ‾ } 〈 1 1 2 ‾ 3 ‾ 〉 or { 1 0 1 ‾ 1 } 〈 1 0 1 ‾ 2 ‾ 〉 , is sensitive to temperature but insensitive to strain rate and whether it is a primary or secondary twin. Based on the concomitant changes in the dominant slip mode predicted by the model and revealed by the texture development, we rationalize that the temperature-induced transition in contraction twinning is due to the increased predominance of basal 〈a〉 slip at high temperatures (>673K). Last, our analysis implies that all twin modes studied are rate insensitive and so the strong influence of strain rate and temperature on twinning is due to the rate-sensitivity of slip.

Publication date: 1 February 2015
Source:Acta Materialia, Volume 84
Author(s): M. Arul Kumar , A.K. Kanjarla , S.R. Niezgoda , R.A. Lebensohn , C.N. Tomé
We present here a numerical study of the distribution of the local stress state associated with deformation twinning in Mg, both inside the twinned domain and in its immediate neighborhood, due to the accommodation of the twinning transformation shear. A full-field elastoviscoplastic formulation based on fast Fourier transformation is modified to include the shear transformation strain associated with deformation twinning. We have performed two types of twinning transformation simulations with: (i) the twin completely embedded inside a single crystal and (ii) the twin front terminating at a grain boundary. We show that: (a) the resulting stress distribution is more strongly determined by the shear transformation than by the intragranular character of the twin or the orientation of the neighboring grain; (b) the resolved shear stress on the twin plane along the twin direction is inhomogeneous along the twin–parent interface; and (c) there are substantial differences in the average values of the shear stress in the twin and in the parent grain that contains the twin. We discuss the effect of these local stresses on twin propagation and growth, and the implications of our findings for the modeling of deformation twinning.

曲名：Piano On The Beach 艺人：Chamras Saewataporn 专辑：Empty Streets 年代：2006 风格：轻音乐，钢琴曲 介绍：《Piano On The Beach》（沙滩上的钢琴）是一张自然与音乐融合的专辑，有着自然生命的灵魂，可以说是来自天堂的声音，彷佛让人呼吸到充满透明感的空气，且满满蕴含着自然的生命力，让你抛却工作中的紧张、压抑情绪，在感受自然的音乐之旅中放松自己、享受生活。

曲名：匆匆那年 艺人：王菲 作词：林夕 专辑：匆匆那年主题曲 年代：2014 介绍：电影《匆匆那年》由“青春片教父”张一白导演，彭于晏、倪妮、郑恺、魏晨、张子萱等主演，陈赫友情主演，根据九夜茴经典小说改编，通过平淡而真实文字，以方茴和陈寻的爱情故事为主线，描述了80后的情感与生活历程。 电影《匆匆那年》同名主题曲由王菲演唱，林夕作词，梁翘柏作曲，这是继《因为爱情》后王菲和张一白导演第二次合作电影主题曲。

作者: lfaitaoyao 版块: 硕博家园

作者: sam_sunny 版块: 分子生物

Graphene is aligned with a layer of hexagonal boron nitride to achieve the valley Hall effect. [Also see Perspective by Lundeberg and Folk] Authors: R. V. Gorbachev, J. C. W. Song, G. L. Yu, A. V. Kretinin, F. Withers, Y. Cao, A. Mishchenko, I. V. Grigorieva, K. S. Novoselov, L. S. Levitov, A. K. Geim

A new microscope allows three-dimensional imaging of living systems at very high resolution in real time. Authors: Bi-Chang Chen, Wesley R. Legant, Kai Wang, Lin Shao, Daniel E. Milkie, Michael W. Davidson, Chris Janetopoulos, Xufeng S. Wu, John A. Hammer, Zhe Liu, Brian P. English, Yuko Mimori-Kiyosue, Daniel P. Romero, Alex T. Ritter, Jennifer Lippincott-Schwartz, Lillian Fritz-Laylin, R. Dyche Mullins, Diana M. Mitchell, Joshua N. Bembenek, Anne-Cecile Reymann, Ralph Böhme, Stephan W. Grill, Jennifer T. Wang, Geraldine Seydoux, U. Serdar Tulu, Daniel P. Kiehart, Eric Betzig

艺人：丢火车乐队 专辑：丢火车 发行时间：2008年06月23日 介绍：丢火车的作品对流行、民谣、英伦、等音乐风格都有所涉及。

作者: shuchangtuzi 版块: 金属

Publication date: 17 November 2014
Source:Materials Science and Engineering: A, Volume 618
Author(s): Changfa Guo , Renlong Xin , Xuan Zheng , Yue Xiao , Changhong Ding , Qing Liu
{10−12}〈10−11〉 twinning plays an important role in plasticity of Mg alloys. Therefore, the reliable identification of twin variant is necessary for understanding the deformation mechanism of Mg alloys. This work aims to investigate the influence of observation plane on the identification of twin variant by twin plane trace and misorientation analysis using the electron backscatter diffraction technique. The twin characteristics in compression of a basal textured AZ31 alloy were examined on two different observation planes. The results indicate that the two geometrically favorable twin variants always have a low angle between their traces on the plane perpendicular to the c-axis, while a high angle range of 79–86° on the plane parallel to the c-axis and compression direction. Such high trace angle in the latter case makes it easy to unambiguously identify the active twin variant. Moreover, the reliability of variant identification is not affected by the number of activated twin variants and their misorientations. Further analysis indicates that the optimum observation plane on rolled and extruded Mg alloys is always the plane parallel to the c-axis and compression direction.

Publication date: December 2014
Source:Acta Materialia, Volume 81
Author(s): A. Luque , M. Ghazisaeidi , W.A. Curtin
Twinning is an important deformation mode in lightweight Mg alloys, but the mechanisms of nucleation and growth of twins and their interactions with solutes remain largely unresolved. Here, a new model for thermally activated, stress-driven growth of twin boundaries is presented and the role of random and segregated solutes in controlling this growth is studied analytically and using direct molecular dynamics simulations. Twin growth occurs by the thermally activated nucleation and expansion of twin dislocation loops on a pre-existing twin boundary. Fluctuations in the local concentration of random solutes lowers the energy barrier for this process and thus facilitates twin growth. Segregation of solutes to the twin boundary strongly increases the energy barrier and suppresses twin growth. In random solid solutions at experimental strain rates, the thermally activated nucleation process is sufficiently fast at low applied stresses so that growth of the twin is controlled by solute strengthening of the nucleated twin loop as it expands across the twin boundary. Annealing of a deformed sample leads to solute segregation and very strong pinning so that further twinning can only be accomplished by nucleation of new twins, consistent with experimental observations. The new mechanism also (i) operates for detwinning and rationalizes complex twin shapes observed in experiments, and (ii) suggests a process for dynamic strain aging commonly observed in Mg alloys at elevated temperatures.

Publication date: 1 January 2015
Source:Acta Materialia, Volume 82
Author(s): S.Q. Zhu , H.G. Yan , X.Z. Liao , S.J. Moody , G. Sha , Y.Z. Wu , S.P. Ringer
We have recently reported that a high strain-rate rolling process is effective for producing strong and ductile Mg alloy sheets. Here we elucidate the fundamental mechanisms that are responsible for plastic deformation in this process via systematic physical thermomechanical plane-strain rolling simulations on a Mg–Zn–Zr alloy. The strain-rate sensitivities of the alloy’s microstructure and flow curves were closely correlated to the onset of deformation twinning and dynamic recrystallization (DRX). Unlike deformation at low strain rates, deformation at the high strain rates applied here induced a high number density of twins, including a predominance of { 1 0 1 ¯ 1 }–{ 1 0 1 ¯ 2 } double twins in coarse grains, and a predominance of { 1 0 1 ¯ 2 } twins in fine DRX grains. We also report a new observation of { 1 0 1 ¯ 2 } nanotwins in ultrafine grains with high density in bulk Mg alloy when processed at high strain rates. We propose that the high propensity for twinning at high strain rates provides nucleation sites for DRX, resulting in a uniform, ultrafine-grained microstructure that exhibits a weakened basal texture and thus excellent mechanical properties.

Publication date: 1 December 2014
Source:Materials Science and Engineering: A, Volume 619
Author(s): Jeong Hun Lee , Taekyung Lee , Seok Weon Song , Sung Hyuk Park , Chong Soo Lee
A remarkable improvement in the tensile yield strength of rolled Mg–3Al–1Zn alloy with pre-existing { 10 1 ¯ 2 } twins was achieved by inducing double twinning through compression deformation. The resulting formation of { 10 1 ¯ 2 }–{ 10 1 ¯ 2 } double twins inside pre-existing { 10 1 ¯ 2 } twin bands effectively suppressed the detwinning of pre-existing twins during subsequent deformation. This in turn led to a change in the dominant deformation mode from detwinning to slip, significantly increasing the yield strength. The mechanisms behind this behavior are considered to be a combination of the redistribution of residual tensile stress within pre-existing twins, refinement of pre-existing twins by double twins, a change in texture due to double twinning and a loss of coherency at twin boundaries.

作者: suzhuoqun 版块: 电脑软件资源

Publication date: 1 December 2014
Source:Scripta Materialia, Volume 92
Author(s): L. Wang , J. Lind , H. Phukan , P. Kenesei , J.-S. Park , R.M. Suter , A.J. Beaudoin , T.R. Bieler
Far-field high-energy X-ray diffraction microscopy (HEDM) was used to study {10 1 ‾ 2}〈 1 ‾ 011〉 twinning in Ti. Twin nucleation within a bulk parent grain is observed at a resolved shear stress (RSS) of 225MPa. During unloading, the RSS on the twin plane reversed sign, providing a driving force for detwinning. Formation of the twin, however, prevented the parent grain from returning to its original stress state even after complete unloading. The twin morphology and surrounding environment were examined using near-field HEDM.

Teamwork at centre of Chinese Academy of Sciences reform.

Nature 513 468 doi: 10.1038/513468a

作者: 525482838 版块: 程序语言

Publication date: 3 November 2014
Source:Materials Science and Engineering: A, Volume 617
Author(s): Huihui Yu , Yunchang Xin , Hua Zhou , Rui Hong , Lingyu Zhao , Qing Liu
Detwinning behavior of a strongly textured magnesium alloy AZ31 at different temperatures was investigated, with a focus on the effect of temperature on twin boundaries (TBs) migration. A hot extruded Mg alloy AZ31 rod was subjected to a 3% pre-compression along the extrusion direction (ED) to generate { 10 1 ¯ 2 } twins. Subsequent tensions along the ED at temperatures of 30°C, 100°C, 150°C, 200°C and 250°C, respectively, were carried out to initiate detwinning. Mechanical behavior and microstructure evolution during detwinning deformation were examined. Our results show that the activation stress for { 10 1 ¯ 2 } TBs migration decreases with the increasing of temperature from 30°C to 250°C. Even at 250°C, detwinning rather than non-basal slips dominates tension along the ED of pre-strained specimens. All strain hardening curves of detwinning deformation at temperatures of 30–250°C contain three stages that often appear in a { 10 1 ¯ 2 } twinning predominant deformation. The length of Stage II is predominantly related to { 10 1 ¯ 2 } twin volume fraction. It is found that the peak hardening rate in Stage II decreases with increased temperature.

Publication date: November 2014
Source:Acta Materialia, Volume 80
Author(s): M.R. Barnett , A. Ghaderi , J. Quinta da Fonseca , J.D. Robson
The resolved shear stress is believed to play an important role in twin formation. The present study tests this idea for an extruded magnesium alloy by examining “tension” twinning in different grain orientations. Electron backscatter diffraction analysis is employed for alloy AZ31 tested in compression along the extrusion axis to strains between 0.008 and 0.015. For heavily twinned grains, it is seen that twinning occurs on 2.3 twin systems per grain on average. The active systems are also most commonly those with, or very near to, the highest Schmid factor. The most active system in multiply twinned grains accounts on average for ∼0.6 of the twinning events. In addition, it is found that the twin habit plane falls within 6° of the K 1 plane. Orientations with the highest Schmid factors (0.45–0.5) for twinning display twin aspect ratios greater by ∼40% and twin number densities greater by ∼10 times than orientations with maximum Schmid factors for twinning of 0.15–0.2. Thus the Schmid factor for twinning is seen to affect nucleation more than thickening in the present material. Viscoplastic crystal plasticity simulations are employed to obtain approximations for the resolved shear stress. Both the twin aspect ratio and number density correlate quite well with this term. The effect of the former can be assumed to be linear and that of the latter follows a power law with exponent ∼13. Increased aspect ratios and number densities are seen at low Schmid factors and this may relate to stress fluctuations, caused most probably in the present material by the stress fields at the tips of blocked twins. Overall, it is evident that the dominance of twinning on high Schmid factor systems is preserved at the low strains examined in the present work, despite the stress fluctuations known to be present.

Baby boom in Africa set to push global population as high as 12 billion by the year 2100, study finds.

Nature News doi: 10.1038/nature.2014.15956

Publication date: December 2014
Source:Acta Materialia, Volume 81
Author(s): Y. Chen , X.Y. Fang , Y. Brechet , C.R. Hutchinson
It is well known that solid-state precipitation forms an important microstructural component of many engineering alloys and is used to help control the bulk mechanical properties. In this contribution, a thermal treatment process is introduced that can induce solid-state precipitation also on the surfaces of engineering alloys, resulting in patterned surfaces. The process requires only thermal treatments and could be integrated into existing thermal or thermomechanical processing schedules for engineering alloys—as a consequence, one of the advantages over existing surface treatment processes is that it is comparatively cheap. Three Al–Si-based alloys are used to demonstrate the key features of the surface precipitation process. Surface area coverage of 30% of Si particles, Si(Ge) core–shell particles, and Mg2Si particles on Al–Si, Al–Si–Ge and AA6061 alloys, respectively, are demonstrated. The kinetics of surface precipitation are studied using in situ hot-stage optical microscopy. The surface precipitation process brings together aspects of surface science and physical metallurgy and represents a fertile field for collaboration between these disciplines and for the investigation of surface precipitation, as a potential future surface treatment. The ability to cheaply pattern the surfaces of engineering alloys with compounds that may themselves exhibit interesting functional properties highlights an opportunity for alloy designers and functional materials researchers to collaborate for the long-term goal of functionalizing structural engineering alloys.

Microstructures that increase metal crystallite size from nanoscale with surface depth are both strong and ductile Author: K. Lu

Publication date: December 2014
Source:Acta Materialia, Volume 81
Author(s): Z. Xu , M. Weyland , J.F. Nie
The coupled distribution of β1 and β′ particles is frequently observed in aged microstructures of Mg–RE (RE represents rare-earth elements) alloys. The crystallography of these coupled β1/β′ particles is characterized using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, and the shear and dilatation strains associated with the migration of the β1/β′ interface are analysed. It is found that the orientation relationship between the β1 and β′ phases, and the irrationally oriented and yet fully coherent interface associated with this orientation relationship, can both be well described by the crystallography of phase transformations. It is also found that there exists a large shear strain for the β1/β′ transformation or the migration of the fully coherent β1/β′ interface. The magnitude and sign of this shear strain are compatible, but opposite to those of the shear strain involved in the α-Mg/β1 transformation. Hence the coupled distribution of β1/β′ particles offers a unique opportunity to almost fully self-accommodate the shear strains involved in the α-Mg/β1 and β1/β′ structural transformations. This is perhaps why the β1 plates with β′ particles attached to their ends are the most commonly observed distribution in aged microstructures of Mg–RE alloys.

Publication date: December 2014
Source:Acta Materialia, Volume 81
Author(s): Yi Wang , Hahn Choo
The influence of changes in crystallographic texture on the Hall–Petch (H–P) relationship for an Mg alloy was investigated. First, the texture variations were facilitated by changing the uniaxial tensile loading orientation with respect to the normal direction of the rolled Mg plate. With a strong plane texture of the as-received material, the initial dominant deformation mechanisms were systematically varied from the basal slip and prismatic slip to extension twinning, as well as combinations thereof. Second, different grain sizes were produced for each loading orientation through isochronal annealing at various temperatures up to 773K while closely monitoring grain size and texture distributions. The experimental results are presented for the grain growth kinetics during annealing, changes in yielding behavior as a function of grain size and initial texture, and H–P relationship as a function of the texture. Moreover, the effects of changes in texture and dominant deformation mechanism on H–P parameters – namely, friction stress, σo , and strength coefficient, kσ – are discussed. Finally, H–P relationships for each individual deformation mode including basal, prismatic and pyramidal slips as well as extension twin are identified.

Publication date: November 2014
Source:Scripta Materialia, Volumes 90–91
Author(s): Q. Sun , X.Y. Zhang , Y. Ren , J. Tu , Q. Liu
A typical { 1 0 1 ¯ 2 } twin tip, which contains straight { 1 0 1 ¯ 2 } twinning planes and basal–prismatic interfaces, is characterized in deformed Mg–3% Al–1% Zn alloy by transmission electron microscopy (TEM) and high-resolution TEM. The existence of basal–prismatic interfaces is responsible for the deviation of the actual { 1 0 1 ¯ 2 } twinning boundary in the vicinity of the twin tip from the theoretical one. The process of twinning dislocation gliding around the twin tip boundary is described.

第一次听Leonard Cohen的歌是《In My Secret Life》，他沧桑磁性的声音让人难以自拔。《我是你的男人：莱昂纳德·科恩传记》前言中写到：“他是那种喜欢独处、腼腆羞涩的男人。不过如果你刨根问底，他也会不失风度地幽默应对。他的回答措辞谨慎，像是一位诗人，或是一个政客，精确、隐晦、富有韵律、避重就轻；他爱放烟雾弹，说话时显得诡秘，一如他唱歌，仿佛是在吐露隐秘。”

作者: zhanxu5555 版块: 外语学习