Structure prediction, electronic, and mechanical properties of alkali metal MB_(12)(=Be, Mg, Ca, Sr) from first principles

Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB_(12)(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1–2 formula units(f.u.)at 0 GPa. The structure, electronic, and mechanical properties of MB_(12) are obtained from the density functional theory using the plane-wave pseudopotential method within the generalized gradient approximations. The formation enthalpies of MB_(12) regarding to solid metal M and solid alpha-boron suggested the predicted structures can be synthesized except for BeB12. The calculated band structures show MB_(12)(M = Be, Mg, Ca, Sr) are all indirect semiconductors. All the calculated elastic constants of MB_(12) satisfy the the mechanical stable conditions. The mechanical parameters(i.e., bulk modulus,shear modulus, and Young’s modulus) are derived using the Voigt–Reuss–Hill method. The G/B ratios indicated that the MB_(12) should exhibit brittle behavior. In addition, the hardness, Debye temperature, universal anisotropic index, and the percentage of anisotropy in compression and shear are also discussed in detail. We hope our results can inspire further experimental study on these boron-rich alkali-metal compounds.

Investigate the Effect of the Magnetic Field on the Mechanical Properties of Silicone Rubber-Based Anisotropic Magnetorheological Elastomer during Curing Process

In this investigation,a new silicone rubber-based MRE material was prepared to be used as a forming medium in manufacturing thin-walled complexshaped Ni-based tubes through the bulging process.Thus,it is significant to investigate the effect of magnetic field intensity,magnetic field loading time,and angle on the mechanical properties of the prepared MRE material during the curing process.The obtained results showed that increasing the magnetic field intensity during the curing process can improve the orientation of the chain structure in the elastomer matrix effectively.However,its mechanical properties are the best under the corresponding magnetic field intensity of 321 mT.Besides,by extending the magnetic field loading time in the curing process,the orientation of the chain structure was optimized,at the same time,the mechanical properties were also improved,and the best loading time is about 20–25 min.By changing the loading angle of the magnetic field during the curing process,the mechanical properties of the MRE were improved.When the loading angle of the magnetic field is 90°,the elastomer showed the best compression mechanical properties and excellent compression reversibility.Besides,for the anisotropic MRE material,the performance with magnetic compression is always better than that without magnetic compression.

First-principles investigations of structural, mechanical, electronic and optical properties of U_3Si_2-type AlSc_2Si_2 under high pressure

The structural, elastic, electronic and optical properties for U3Si2-type AlSc2Si2 compound under pressure were systematically investigated by using the first-principles calculations. The values of elastic constants and elastic moduli indicate that AlSc2Si2 keeps mechanical stability under high pressure. The mechanical properties of AISc2Si2 are compared with those of Al3Sc. The results indicate that AlSc2Si2 is harder than AI3Sc. Anisotropic constant AU and 3D curved surface of elastic moduli predict that AISc2Si2 is obviously anisotropic under pressure. The electronic structure of AlSc2Si2 exhibits metallic character and the metallicity decreases with the elevated pressure. In addition, optical properties as a function of pressure were calculated and analyzed. The present work provides theoretical support for further experimental work and industrial applications.

Analysis and Research of Ice Loads Acting on Offshore Structures

Usually, the action of sea ice on offshore engineering structures is one of the controlling loads in cold waters engineering structure design. The reasonable selection of environmental condition and the physical mechanical properties of ice in the region are directly related to the structure design, operation and safety. In this paper, the sea ice force acting on the structure, the physical mechanical properties of ice and the selection of parameters in calculation are discussed. Some suggestions are proposed as to the calculation of various kinds of ice loads acting on the structure.

Impacts of multiple laser shock processing on microstructure and mechanical property of high-carbon steel

Multiple laser shock processing （LSP） impacts on microstructures and mechanical properties were investigated through morphological determinations and hardness testing. Microscopic results show that without equal channel angular pressing （ECAP）, the LSP-treated lamellar pearlite was transferred to irregular ferrite matrix and incompletely broken cementite particles. With ECAP, LSP leads to refinements of the equiaxed ferrite grain in ultrafine-grained microduplex structure from 400 to 150 nm, and the completely spheroidized cementite particles from 150 to 100 nm. Consequentially, enhancements of mechanical properties were found in strength, microhardness and elongations of samples consisting of lamellar pearlite and ultrafine-grained microduplex structure. After LSP, a mixture of quasi-cleavage and ductile fracture was formed, different from the typical quasi-cleavage fracture from the original lamellar pearlite and the ductile fracture of the microduplex structure.

First-principles study on mechanical properties of LaMg_3 and LaCuMg_2

Abstract： With the substitution of part Mg in LaMg3 by Cu, the elastic constants CH and C12 increase while C44 decreases, implying an enhanced Poisson effect and smaller resistance to 〈001〉（100） shear. Furthermore, the bulk modulus B increases, while the shear modulus G, elastic modulus E and anisotropie ratio A are reduced. The calculated Debye temperature of LaCuMg2 is lower, implying the weaker interaction between atoms in LaCuMg2. Then, the stress-strain curves in entire range and the ideal strength at critical strain are studied. The present results show that the lowest ideal tensile strength for LaMg3 and LaCuMg2 is in the 〈100〉 direction. The ideal shear strength on the 〈 1 ^-1 0〉（110） slip system of LaMg3 is greater than LaCuMg2. The density of states and charge density distribution are further studied to understand the inherent mechanism of the mechanical properties.

Ab initio study on crystal structure and phase stability of ZrC_(2) under high pressure

The structural stabilities and crystal evolution behaviors of the hyper stoichiometric compound ZrC_(2)(carbon rich;C/Zr> 1.0) are studied under ambient and high pressure conditions using first-principles calculations in combination with the particle-swarm optimization algorithm.Six viable structures of ZrC_(2) in P21/c,Cmmm,Cmc2_(1),P4_(2)/nmc,Immm and P6/mmm symmetries are identified.These structures are dynamically stable as their phonon spectra have no imaginary modes at zero pressure or at the selected high-pressure points.Among them,the P21/c phase represents the ground state structure,whereas P21/c,P4_(2)/nmc,Immm and P6/mmm phases are part of the phase transition series.The phase order and critical pressures of the phase transition are determined to be approximately 300 GPa according to the equation of states and enthalpy.Furthermore,the mechanical and electronic properties are investigated.The P21/c and Cmc2_(1) phases display a semi-metal nature,whereas the P4_(2)/nmc,Immm,P6/mmm and Cmmm phases exhibit a metallic nature.Moreover,the present study reveals considerable information regarding the structural,mechanical and electronic properties of ZrC_(2),thereby providing key insights into its material properties and evaluating its behavior in practical applications.

聚酯纤维泡沫混凝土力学性能及孔结构研究

纤维的掺加可有效地改善泡沫混凝土抗压强度低、脆性特征显著的缺陷,增强其工程适用性。本工作针对聚酯纤维对泡沫混凝土力学性能的改善开展试验研究,选定密度等级为700 kg/m3的泡沫混凝土,考虑不同纤维体积掺量(0.1%、0.2%、0.3%和0.4%)对其抗压强度、抗折强度、劈裂抗拉强度以及延性的影响。结果表明:纤维掺量为0.1%时,材料表现出较优的抗压和劈裂抗拉性能,28 d强度分别增加了86.4%和91.3%;纤维掺量为0.2%时,材料表现出较优的抗折性能,28 d抗折强度提升了39.1%。试样破坏形态和应力-应变曲线表明,聚酯纤维可有效地提升泡沫混凝土的延性。最后,运用图像分析处理法分别获得了五组试件的孔结构参数,从细观孔结构的角度讨论了聚酯纤维对泡沫混凝土抗压强度的影响机理。

低温靶向再生活化剂与废橡胶再生胶性能的构效关系研究

为了实现废橡胶节能减排高品质再生,提出了低温靶向再生活化剂的设计理念,将含有-SH、-OH或-COOH的主再生活化剂(MS)与含有-OH或-COOH的次再生活化剂(有机酸A1)并用,在再生温度25~125℃下开展研究。结果表明:MS/A1具有协同效应,低温靶向再生胶拉伸强度和扯断伸长率分别达15.17MPa、360.65%,门尼黏度为79,达到了《再生橡胶通用规范》(GB/T 13460-2016)全胎胶粉优质品级R-T再生胶的性能要求,再生胶所含18项多环芳烃总含量小于20mg/kg,符合欧盟REACH法规(REACH-2009/48/EC)环保指标的要求。与高温再生工艺相比,低温靶向再生工艺节能20%~60%不等。

竹节结构及力学性能研究现状

竹材优异的柔韧性有利于其塑性加工应用,但在竹材展平或塑性弯曲成型时常常出现开裂现象,尤其在竹节位置,严重影响成品质量。在现行的实验标准中未对竹节处加工进行特别规定,忽略了竹节结构的特殊性及其对竹材整体性能的影响。文章分析了竹节特殊的形态结构、力学性能及其对竹质板材及仿生材料的影响,对比了竹节与节间在结构及力学性能方面的差异,旨在探索更高效的竹材加工方式,提高竹质板材的成品率,为竹质板材的结构设计以及竹材塑性加工提供理论参考。分析显示,竹节与节间在形态结构及力学性能方面均有明显差异,竹节处交错的水平维管束和垂直维管束提高了竹材整体的横向抗拉强度、抗弯强度和抗压强度,增强了竹材纵向承载力和横向稳定性;但对于锯切后的竹条单元,则在一定程度上降低了其顺纹抗压、抗弯和抗拉强度。

Ti_(x)NbMoTaW系高熵合金性能的第一性原理计算

NbMoTaW合金是目前研究极广泛的难熔高熵合金之一,具有高熵合金高强度、高硬度、耐磨损的优异性能,但其韧性塑性较差,极大影响了其在工程中的应用。本研究在NbMoTaW合金中添加不同比例的Ti元素以提高该合金的塑韧性,通过相形成参数计算确定了Ti_(x)NbMoTaW系合金的相结构为固溶体相,运用基于密度泛函理论的第一性原理方法计算合金晶格常数、基态能量、形成能及焓变值,分析了合金结构稳定性。通过计算合金不同Ti含量时弹性常数、弹性模量、B/G、泊松比ν、柯西压C_(12)-C_(44)等参数研究了合金弹性性质的变化规律。最后对电子态密度分析得知,合金体系成键共价性降低,金属键增强,弹性性质和态密度的结果表明添加Ti有助于该合金韧性的提高。此研究可为设计、改善难熔高熵合金性能提供一定设计思路和理论指导。

三维纺织复合材料热-力学性能研究进展

三维纺织复合材料具有优异的力学性能、可设计性强和耐极端环境等优点,在航空航天领域有着广泛应用。为深入了解应用于高温环境中三维纺织复合材料的结构体系和力学行为,本文从三维纺织结构出发,综述了三维纺织复合材料结构类型及其在航空航天领域上的应用;总结了三维纺织复合材料成型工艺和结构特征;分析了三维纺织复合材料热-力学性能的研究进展情况;提出了未来的研究重点和需解决的关键问题,以期为新一代三维纺织复合材料的耐高温/承载设计、制造和应用提供依据。

Sr_(2)ReNbO_(6)双钙钛矿电子结构及性质的第一性原理研究

基于密度泛函理论(DFT),采用Perdew–Burke–Ernzerhof交换关联势的PBEsol–GGA泛函优化Sr_(2)ReNbO_(6)(Re=La,Gd,Lu)双钙钛矿晶体的结构,获得最低能量的稳定结构。以优化的结构为模型,计算Sr_(2)ReNbO_(6)(Re=La,Gd,Lu)晶体的能带结构和态密度(DOS)、复介电函数ε(ω)、折射率n(ω)、反射率R(ω)及消光系数k(ω)等光学特性指标,分析入射光子能量对材料光学特性的影响;计算Sr_(2)ReNbO_(6)(Re=La,Gd,Lu)晶体的弹性常数Cij,并由Cij进一步获得杨氏模量(Y)、体积模量(B)、剪切模量(G)和泊松比(χ)等机械特性指标,分析晶体结构对材料机械特性的影响。结果表明:优化双钙钛矿晶体结构获得的晶格常数与现有的实验值吻合较好;Sr_(2)ReNbO_(6)(Re=La,Gd,Lu)材料的能带结构呈现半导体特性,其中立方结构的Sr_(2)LaNbO_(6)带隙宽度为3.12 eV,且为直接带隙,而单斜结构的Sr_(2)GdNbO_(6)和Sr_(2)LuNbO_(6)为间接带隙,带隙宽度分别为3.25,3.29 eV;Sr_(2)ReNbO_(6)(Re=La,Gd,Lu)的最大反射率R(ω)分别为32.8%,29.3%,33.0%,在紫外区域存在较大的吸收系数;Sr_(2)ReNbO_(6)(Re=La,Gd,Lu)的泊松比χ分别为0.27,0.28,0.27,均位于0.25附近,该系列材料的原子更倾向于以离子键的形式结合,表现出一定的柔韧性。

三维机织间隔织物增强复合材料的研究进展

随着现代科学技术的迅速发展,复合材料在轻质量、高比强度、抗冲击性和耐疲劳等方面的要求越来越高。以机织间隔组织为增强体的复合材料能较好地满足上述要求,成为研究热点之一。概述了机织间隔织物复合材料在空间结构设计、成型工艺、性能测试等方面的研究进展,综述了结构参数对间隔织物夹层性能的影响以及间隔织物复合材料夹层板的填充和成型工艺,总结了间隔织物复合夹芯板的力学性能,包括弯曲、压缩、低速冲击性能,展望了机织间隔织物增强复合材料的发展前景。

Mechanical and corrosion fatigue behaviors of gradient structured 7B50-T7751 aluminum alloy processed via ultrasonic surface rolling

In this work,ultrasonic surface rolling process(USRP)was utilized to produce a gradient structured layer on 7 B50-T7751 aluminum alloy,and the mechanical properties and corrosion fatigue behavior of treated samples were studied.These results reveal that underwent USRP,a 425~m thick gradient structure and a 700~m deep compressive residual stress field are created,aluminum grain size become fine(~67 nm),and the corrosion rate of treated surface reduces by 60.08%owing to the combined effect of compressive residual stress and surface nanocrystallization.The corrosion fatigue strength is enhanced to 117%of that of 7 B50 Al alloys by means of USRP due to the introduced compressive residual stress,which is considered as the major favorable factor in suppressing the initiation and early propagation of corrosion fatigue cracks.Besides,the gradient structure is an important factor in providing a significant synergistic contribution to the improvement of corrosion fatigue performance.

基于原位拉伸的HTPB推进剂多尺度损伤演化分析

作为由填料和基体混合而成的复合材料,端羟基聚丁二烯(HTPB)推进剂的损伤主要涉及颗粒的破碎、基体的断裂以及粘结界面层的脱粘,为进一步探究其在外载作用下结构损伤和力学性能的演变,通过微CT、高速CCD相机,以及全原子分子动力学模拟,实现原位加载下推进剂多尺度损伤分析。结果表明,推进剂典型损伤过程起始于粘结界面层破坏,扩展于脱粘孔隙的增长,演化于孔隙的合并,加速于局部大变形的汇集,终止于基体的断裂;界面结合能和应力集中程度使得大粒径高氯酸铵(AP)颗粒最先脱粘,且孔隙率与应变呈现类指数函数关系;微观界面层牵引⁃分离曲线符合指数型内聚力模型,微观空隙的萌生与扩展破坏了其内聚性,而分子间距则影响了应力的演变。

新型管状增强超弹多孔结构设计制备及减振性能研究

传统的橡胶阻尼材料拥有较好的减振能力,但其力学承载能力不足。针对上述问题,基于仿生梯度设计思想,结合轻质多孔结构的优异力学性能和聚氨酯材料的高阻尼超弹性性能,设计一种具有优异力学承载性能和减振性能的新型管状增强超弹梯度多孔结构,开发出了模压灌注一体化成型工艺,实现了不同规格超弹梯度多孔结构减振器的制备。通过模态分析和频响试验获得结构的固有振动和减振性能,揭示了不同硬度聚氨酯材料、不同拓扑构型增强管等参数对结构减振性能的影响规律。结果发现,相比与其他结构,圆型增强结构在低频段具有较高的基频和较低的共振峰值,表现出结构高刚度高阻尼的优异性能;而在高频段三角型增强结构整体响应更低,减振性能较优异。

Nb掺杂对Mo_(2)FeB_(2)弹性、硬度和电子结构影响的第一性原理计算

Mo_(2)FeB_(2)具有耐高温、耐磨、高强度,是一种良好的硼基金属陶瓷材料,在模具领域有很广阔的应用前景.本文采用第一性原理计算的方法,研究了Nb元素掺杂Mo_(2)FeB_(2)合金的结构稳定性、弹性、硬度和电子结构.结合能和生成焓的计算结果表明,Nb在Mo_(2)FeB_(2)中更容易占据Fe位置,并且在Fe位掺Nb的Mo_(2)FeB_(2)比在Mo位处掺Nb具有更好的力学性能.此外,计算结果还表明,Nb掺杂可以提高Mo_(2)FeB_(2)的剪切模量、杨氏模量、体积模量和硬度,但塑性略有下降,合适的掺杂浓度应为2.5 at.%.电子结构计算结果表明,Nb掺杂Mo_(2)FeB_(2)力学性能的提高可归因于Nb-B共价键的形成.

Clathrate structure of YB_(3)C_(3) for high-performance thermoelectrics with superior mechanical properties

Exploring high-performance thermoelectric materials with improved mechanical properties is important for broadening the application scope and the assembly requirement of stable devices.This work presents an effective strategy to discover hard thermoelectric material by inserting foreign atoms in the rigid covalent framework.We demonstrate this in boron-carbon clathrate VII structure,showing a promising candidate for highly efficient thermoelectric energy conversion,especially with Y atom filled in the cage,with a peak zT of 0.73 at 1,000 K.The ab initio calculations indicate that YB_(3)C_(3) system has low lattice thermal conductivity of 4.5 W/(m·K)at 1,000 K due to the strong rattling of encaged Y atom.The strongly covalent framework provides highly degenerate band structures consisting of heavy and light electron pockets,which can maintain high carrier mobility arising from small effective mass and thus large group velocity.Consequently,high power factor can be achieved in YB_(3)C_(3) for both electron and hole doping.In addition,it exhibits well mechanical properties and a Vickers hardness of 23.7 GPa because of the strong covalent boron-carbon framework.This work provides a novel avenue for the search of high-performance thermoelectric materials with excellent mechanical properties,based on boron-carbon clathrate structure.

真空状态不同爆轰工艺下铜钢复合材料界面组织和性能研究

【目的】对热交换领域、电力领域中铜基复合材料在应用过程中出现的高温变形、界面金属间化合物、产品性能不稳定等难点问题进行研究。【方法】在真空状态中,采用不同爆轰工艺对TU1紫铜和Q345R钢进行爆炸复合试验,并对复合材料的金相组织和力学性能进行测试和分析。【结果】由试验结果可知,随着爆轰速度的增大,界面波纹深度也会随之增加。复合材料(Z向)分离强度的平均值为483 MPa、界面剪切强度的平均值为238 MPa、显微硬度的最大值为196 HV,即距界面位置越远,越趋近于本体材料。当爆轰速度为2200 m/s时,断口处出现铜侧粘连现象。【结论】复合材料的各项性能指标均优于组成该复合材料的本体金属,界面处均呈正弦波状结合形态。从界面向本体金属方向来看,晶粒组织呈现出多样化晶体转变的特征。通过进一步对结合界面进行分析,发现该界面未出现氧化物/氮化物等有害物质。