Tunable topological interface states and resonance states of surface waves based on the shape memory alloy

Topological interface state(TIS)of elastic wave has attracted significant research interest due to its potential prospects in strengthening acoustic energy and enhancing the signal accuracy of damage identification and quantification.However,previous implementations on the interface modes of surface waves are limited to the non-adjustable frequency band and unalterable mode width.Here,we demonstrate the tunable TIS and topological resonance state(TRS)of Rayleigh wave by using a shape memory alloy(SMA)stubbed semi-infinite one-dimensional(1D)solid phononic crystals(PnCs),which simultaneously possesses the adjustable mode width.The mechanism of tunability stems from the phase transformation of the SMA between the martensite at low temperature and the austenite at high temperature.The tunable TIS of Rayleigh wave is realized by combining two bandgap-opened PnCs with different Zak phases.The TRS with adjustable mode width is achieved in the heterostructures by adding PnCs with Dirac point to the middle of two bandgap-opened PnCs with different Zak phases,which exhibits the extraordinary robustness in contrast to the ordinary Fabry–Perot resonance state.This research provides new possibilities for the highly adjustable Rayleigh wave manipulation and find promising applications such as tunable energy harvesters,wide-mode filters,and high-sensitivity Rayleigh wave detectors.

Improving comprehensive properties of Cu-11.9Al-2.5Mn shape memory alloy by adding multi-layer graphene carried by Cu_(51)Zr_(14)inoculant particles

In order to improve the comprehensive properties of the Cu-11.9Al-2.5Mn shape memory alloy(SMA),multilayer graphene(MLG)carried by Cu_(51)Zr_(14)inoculant particles was incorporated and dispersed into this alloy through preparing the preform of the cold-pressed MLG-Cu_(51)Zr_(14)composite powders.In the resultant novel MLG/Cu-Al-Mn composites,MLG in fragmented or flocculent form has a good bonding with the Cu-Al-Mn matrix.MLG can prevent the coarsening of grains of the Cu-Al-Mn SMA and cause thermal mismatch dislocations near the MLG/Cu-Al-Mn interfaces.The damping and mechanical properties of the MLG/Cu-Al-Mn composites are significantly improved.When the content of MLG reaches 0.2 wt.%,the highest room temperature damping of 0.0558,tensile strength of 801.5 MPa,elongation of 10.8%,and hardness of HV 308 can be obtained.On the basis of in-depth observation of microstructures,combined with the theory of internal friction and strengthening and toughening theories of metals,the relevant mechanisms are discussed.

Comparison of Cu−Al−Ni−Mn−Zr shape memory alloy prepared by selective laser melting and conventional powder metallurgy

This work aimed to investigate and critically analyze the differences in microstructural features and thermal stability of Cu−11.3Al−3.2Ni−3.0Mn−0.5Zr shape memory alloy processed by selective laser melting(SLM)and conventional powder metallurgy.PM specimens were produced by sintering 106−180μm pre-alloyed powders under an argon atmosphere at 1060°C without secondary operations.SLM specimens were consolidated through melting 32−106μm pre-alloyed powders on a Cu−10Sn substrate.Mechanical properties were measured through Vickers hardness testing.Differential scanning calorimetry was conducted to assess the martensitic transformation temperatures.X-ray diffraction patterns were collected to identify the metallurgical phases.Optical and scanning electron microscopy was used to analyze the microstructural features.b′1 martensite was found,irrespective of the processing route,although coarser martensitic variants were present in PM-specimens.In conventional powder metallurgy samples,intergranular eutectoid constituents and stabilized austenite also formed at room temperature.PM-specimens showed similar average hardness values to the SLM-specimens,albeit with high standard deviation linked to the porosity.The specimens processed by SLM showed reversible martensitic transformation(T0=171°C).PM-processed specimens did not show shape memory effects.

Ingredient Losses during Melting Binary Ni-Ti Shape Memory Alloys

Losses of the alloying elements during vacuum induction melting of the binary NiTi alloys were evaluated by visual observation and chemical analysis of the NiTi melted specimens and the scalp formed on the internal surface of the crucible. The results indicated that the major sources of the losses were （a） evaporation of the metals, （b） formation of the NiTi scalp and （c） the sprinkling drops splashed out of the melt due to the exothermic reactions occurring between Ni and Ti to form the NiTi parent phase. Quantitative evaluations were made for the metallic losses by holding the molten alloy for 0.5, 3, 5, 10 and 15 min at around 100℃ above the melting point inside the crucible.Chemical analysis showed that there existed an optimum holding time of 3 min during which the alloying elements were only dropped to a predictable limit. Microstructure, chemical composition, shape memory and mechanical properties of the cast metal ingots were determined to indicate the appropriate achievements with the specified 3 min optimum holding time.

The Richtmyer–Meshkov instability of a 'V' shaped air/helium interface subjected to a weak shock

The Richtmyer-Meshkov instability ofa ‘V＇ shaped air/helium gaseous interface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a ‘V＇ shaped interface with accurate initial conditions. Five kinds of ‘V＇ shaped interfaces with different vertex angles are formed to highlight the effects of initial conditions on the flow characteristics. The results show that a spike is generated after the shock impact, and grows constantly with time. As the vertex angle increases, vortices generated on the interface become less noticeable, and the spike develops less pronouncedly. The linear growth rate of interface width after compression phase is estimated by a linear model and a revised linear model, and the latter is proven to be more effective for the interface with high initial amplitudes. The linear growth rate of interface width is, for the first time in a heavy/light interface configuration, found to be a non-monotonous function of the initial perturbation amplitude-wavelength ratio.

Melting Intercalation Method to Prepare Lauric Acid/Organophilic Montmorillonite Shape-stabilized Phase Change Material

A kind of novel shape-stabilized phase change material （SSPCM） was prepared by using a melting intercalation technique. This kind of SSPCM was made of lauric acid （LA） as a phase change material and organophilic montmorillonite （OMMT） as a support material. And the thermal properties and morphology of the SSPCM were characterized by X-ray diffraction （XRD）, transmission electron microscope （TEM）, scanning electronic microscope （SEM）, scanning calorimeter （DSC）, and differential thermal cravimetry （TG）. The DSC result shows that the phase change temperature of the SSPCM is close to that of LA, and its latent heat is equivalent to that of the calculated value based on the mass ratio of LA measured by TG. The XRD, SEM and TEM results demonstrate that the LA intercalates into the silicate layers of the OMMT, thus forming a typically intercalted hybrid, which can restrict the molecular chain of the LA within the structure of OMMT at high temperature. And consequently SSPCM can keep its solid state during its solid-liquid phase change processing.

MELTING AND CRYSTALLIZATION BEHAVIOR OFAN AROMATIC POLY (AZOMETHINE ETHER) WITH NON-LINEARLY SHAPED MOLECULAR CONFORMATIONS

The melting and crystallization behavior have been investigated for an aromatic poly (azomethine ether)with non-linearly shaped molecular conformations. This polymer was found to undergo multiple melting processes and its phase transition behavior was influenced sensitively by the thermal history of sample. A significant difference between the polymer chain aggregation abilities of samples cooled from the different states was observed. The possible molecular morphology and aggregation models for describing the structures of this polymer were proposed and discussed. The crystallization behavior of the samples cooled from the partially isotropic state and the influence of cooling rate on it have also been examined with DSC.

Numerical simulations of stress wave propagation and attenuation at arc-shaped interface inlayered SiC/Al composite

The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceramic to A1 alloy, the tensile stress decreases and the attenuation coefficient of the stress wave increases with increasing central angle of the concave interface between SiC and A1. But for the convex interface, the tensile stress increases and attenuation coefficient decreases with increasing central angle. As the stress wave propagates from A1 alloy to SiC ceramic, the atten- uation coefficient of stress wave decreases with increasing the central angle of the concave interface. For the convex interface, the attenuation coefficient increases with increasing central angle.

不同成形方式对WE43镁合金组织和力学性能的影响

采用激光选区熔化成形(SLM)、铸造及挤压方式制备了WE43镁合金试样,通过维氏硬度计、密度测试计、光学显微镜、扫描电镜以及拉伸试验机等设备分析了不同制备方式下WE43镁合金的宏微观组织和力学性能变化规律;设计了基于指数函数的模型对不同成形方式的WE43应力–应变曲线进行统一拟合,为WE43材料未来增材、减材以及等材工艺复合制造复杂零件打下基础。结果表明,SLM成形WE43有明显的各向异性,铸态和挤压态不明显。SLM成形WE43镁合金的强度最高,抗拉强度达到313 MPa,是铸态的183%;挤压态WE43镁合金塑性最好,伸长率达到10.2%,是铸态的232%;此外,SLM态镁合金密度只有1.731 g/cm^(3),仅为挤压态的85.7%和铸态的95.2%。在断裂特性上,SLM态和挤压态为韧性断裂,而铸造态为脆性断裂。在内部存在20μm左右孔洞形缺陷的情况下,SLM成形镁合金依然具有最高的强度,主要原因是SLM成形WE43镁合金平均晶粒尺寸仅为2.6μm,基体内存在大量的稀土相沉淀以及纳米级亚稳相。由此可知,通过进一步的后处理方法焊合SLM态镁合金内部孔洞形缺陷后,材料力学性能可以大幅提高。

熔压温度对光纤面板抗弯强度的影响

光纤面板在微光夜视、空间探测、核诊断、医学诊疗等领域有着广泛的应用,在使用过程中对强度有一定要求,目前缺少相关研究,本文研究了熔压温度对光纤面板x、y、z三个方向抗弯强度的影响,采用三点弯曲法测试光纤面板的抗弯强度。结果表明:熔压温度为660℃时,二次复丝之间熔合不充分,存在间隙,光纤面板抗弯强度较低,x、y、z方向抗弯强度分别为107、93、114 MPa;熔压温度为670℃时,二次复丝之间间隙消除,但依然存在界面,抗弯强度有所提升,x、y、z方向抗弯强度分别为110、109、125 MPa;熔压温度为680℃时,二次复丝充分熔合,此时光纤面板抗弯强度在x、z方向满足复合材料混合定律,分别为123、127 MPa,y方向芯玻璃作为增强相对皮玻璃起到增强作用,抗弯强度为113 MPa。本文研究对提高光纤面板强度以满足装管和使用需求具有重要意义。

First-principles thermodynamics of metal-oxide surfaces andinterfaces:A case study review

An important step for achieving the knowledge-based design freedom on nano-and interfacial materials is attained by elucidating the related surface and interface thermodynamics from the first principles so as to allow engineering the microstructures for desired properties through smartly designing fabrication processing parameters.This is demonstrated for SnO2 nano-particle surfaces and also a technologically important Ag-SnO2 interface fabricated by in-situ internal oxidation.Based on defect thermodynamics,we first modeled and calculated the equilibrium surface and interface structures,and as well corresponding properties,as a function of the ambient temperature and oxygen partial pressure.A series of first principles energetics calculations were then performed to construct the equilibrium surface and interface phase diagrams,to describe the environment dependence of the microstructures and properties of the surfaces and interfaces during fabrication and service conditions.The use and potential application of these phase diagrams as a process design tool were suggested and discussed.

选区激光熔化成形NiTi合金工艺参数对表面粗糙度的影响规律

目的针对选区激光熔化(SLM)制备NiTi形状记忆合金表面粗糙度难以满足实际应用要求,通过优化工艺参数(激光功率、扫描速度、扫描间距)以有效地降低表面粗糙度以及研究各工艺参数对表面粗糙度的影响规律。方法采用L16正交阵列的田口模型设计选区激光熔化制备NiTi样品的工艺参数,通过对表面粗糙度信噪比值进行统计方法分析以及样品表面形貌的表征,研究不同工艺参数对表面粗糙度的影响程度以及影响机理,最终优化出制备低表面粗糙度的工艺参数组合。结果在激光功率为20 W和30 W时,NiTi粉末不能够充分熔化造成熔道不连续,使得样品表面起伏增大,粗糙度值最大到7.8μm;增大激光功率到40W和50W时,粉末充分熔化,样品表面形貌明显改善;在相同功率下,扫描速度从200mm/s增加到500mm/s时,样品的粗糙度值也随之增大。结论工艺参数对表面粗糙度影响的重要性顺序依次为激光功率、扫描速度、扫描间距;最终优化出的工艺参数组合为激光功率50W、扫描速度200mm/s、扫描间距0.07mm,并在该工艺参数下制备的样品表面粗糙度值为1.38μm,与模型预测的值1.43μm接近,相差仅为9.97%。

输电线路单导线覆冰形状对直流大电流融冰时间的影响

直流大电流融冰是输电线路冰灾防御的有效手段。根据实际运行条件下输电线路单导线覆冰形状在导线各处不一的情况,计算分析单导线圆形覆冰和翼形覆冰的直流大电流融冰时间。计算结果表明,翼形冰融冰时间仅为圆形冰融冰时间的10%左右。在重庆大学雪峰山能源装备安全国家野外观测研究站对LGJ—300/50和LGJ—400/35两种型号单导线进行直流大电流融冰实验。实验结果表明:LGJ—300/50导线翼形冰融冰时间为圆形冰融冰时间的10.6%,LGJ—400/35导线翼形冰融冰时间为圆形冰融冰时间的8.3%。基于此,该文提出抑制导线形成圆形冰促使其生长为翼形冰可降低直流大电流融冰时间,减少融冰能量消耗。

石漠化山区露石岩面流对岩-土界面土壤氮磷淋溶与输入作用的研究

基岩出露的石漠化区露石岩面在承接降水(含穿透雨)后易形成岩面流,并携带岩面有机或无机物质输送至岩周土壤中,对岩-土界面土壤养分变化具有重要影响。为探明岩面流对岩-土界面土壤氮磷的淋溶与输入影响,选取基岩明显出露的休耕地(1年岩面流作用)、退耕灌草地(5年岩面流作用)和坡耕地(无/少岩面流作用)3种样地,并分别选择外凸、平直和内凹3种特殊的岩面形状,研究了距岩面不同水平距离及土层的岩-土界面及非岩-土界面土壤的全氮和全磷变化特征。结果表明:岩面流对0~10 cm表层岩-土界面土壤氮磷产生输入或淋溶作用,对10~20 cm层岩-土界面土壤氮磷作用不明显。不同岩面形状形成的岩面流对岩-土界面土壤氮磷的淋溶与输入作用强度依次为:内凹型>平直型>外凸型。其中,在1年岩面流作用的休耕地中,内凹型岩面形成的岩面流对岩-土界面土壤氮素的影响主要表现为淋溶,而平直型和外凸型岩面表现为输入作用;不同形状岩面流对岩-土界面土壤磷素的影响均表现为淋溶。然而,在植被生长较好的退耕灌草地中,5年岩面流作用下不同形状岩面流对岩-土界面土壤氮磷的影响主要表现为输入。研究结果可为深入认识出露岩石对喀斯特生态系统土壤特性的影响提供科学依据。

坩埚底角形状对提拉法生长同成分铌酸锂晶体的影响

铌酸锂晶体集压电、非线性、电光、光折变等效应于一身,同时其物理化学性质稳定,在集成光学领域极具应用潜力。然而,大尺寸铌酸锂晶体生长的热场设计难度大,其中坩埚形状作为热场设计的重要因素,对晶体生长的影响显著。坩埚直径和高度受制于装料量和晶体直径等硬性约束,因此通常通过改变坩埚局部的形状以改善热场。针对坩埚底角形状对大尺寸同成分铌酸锂晶体生长的影响,本研究使用两种底角形状的坩埚进行了四英寸同成分铌酸锂晶体生长实验。通过数值模拟,分析了坩埚底角形状对固液界面附近晶体内和熔体内轴向温度梯度的影响,以及对固液界面下方熔体内温度分布的影响,进而结合晶体生长结果分析了坩埚底角形状对晶体生长的影响。研究表明:坩埚底角形状的变化会引起坩埚侧壁上温差的变化和熔体内温度梯度的变化,并改变熔体自然对流的强弱;与底部斜角坩埚相比,使用底部弧角坩埚时,固液界面附近晶体内和熔体内的轴向温度梯度较大,固液界面下方熔体内的轴向温度梯度较大,自然对流更强。这一研究结果有助于解决晶体生长脊展宽和胞状界面生长等问题。

寒旱环境灌木根系增强春融期边坡稳定性影响

春融期边坡极易发生热融滑塌现象,为研究植被根系与边坡冻融界面呈不同夹角α条件下边坡的潜在滑移面破坏形式、位移特征以及稳定性影响。结果表明:随融化深度的增加,春融期素土及根-土复合体边坡的等效塑性应变贯通带越明显,易沿着冻融界面发生平面状滑塌;相比于素土边坡,春融期(3月份)根-土复合体边坡最大位移量减小约69.65%,春融期(4月份)根-土复合体边坡最大位移量减小约71.88%,且根-土复合体边坡位移的减少量随着α角的增大而呈增大趋势,表现出根系伸入冻融界面处时具有较强的固土能力;当根系与冻融界面夹角α由45°增大至90°时,根-土复合体边坡的安全系数呈增长趋势,且根系与边坡冻融界面垂直时,根系具有相对最大限度地增强春融期边坡固土护坡作用,可有效提高春融期边坡的稳定性。研究成果为探讨冻融界面处植物根系对春融期边坡稳定性具有理论研究价值和实际指导意义。

基于Python的托卡马克等离子体位形编辑器设计与实现

等离子体位形控制是等离子体实验控制的重要组成部分,设计满足放电要求的等离子体平衡位形是等离子体控制系统的重要功能之一。根据位形计算原理、中国聚变工程实验堆等离子体控制系统用户界面集成原理及用户界面需求,采用开源的Python语言及PyQt库,设计开发位形编辑器,用于等离子体期望位形设计和优化;并提供期望位形输入数据,供其集成使用。对主要模块进行复用,开发可独立运行的位形编辑器,能够灵活适用于不同的托卡马克装置。测试结果显示,该编辑器能满足单机运行的需求,同时消除了必须登录等离子体控制系统才可进行位形设计工作的弊端。

基于形函数的非一致网格接触修形新方法

针对接触压力分布不均导致机械零部件过早失效的问题,提出了一种非一致网格接触修形新方法。基于单元形函数和“虚拟节点”建立了非一致网格接触节点之间的力学关系,推导得到了节点修形量与接触压力之间的数学方程,提出了一种通过最小化最大接触压力求解修形量的极小极大模型,并根据其数学特点将该模型转换为线性规划模型,提高了修形量计算的效率和全局收敛性。通过三个弹性接触修形实例,验证了该方法对一般弹性接触修形问题的适用性和有效性。

碲锌镉晶体生长温度梯度与界面形状稳定性关系的研究

碲锌镉晶体被广泛用作红外探测器碲镉汞薄膜的外延衬底和制造室温核辐射探测器。在晶体生长过程中,界面形状与热量传输状态密切相关。本文结合数值模拟技术控制碲锌镉晶体生长过程中温度场分布,设计了垂直布里奇曼法和垂直温度梯度凝固法微凸固液界面的晶体生长程序,并根据实际晶体生长实验,分析了晶体生长方法差异与碲锌镉晶体单晶率之间的关系。通过光致发光谱进行成分测试获得了碲锌镉晶体等径段纵截面中Zn值分布谱图,以研究固液界面温度场分布与晶体Zn值宏观偏析之间的关系。结果表明,在晶体生长过程中固液界面两侧温场梯度分布对界面的形状选择和稳定性有重要影响,更大的固相侧温度梯度有助于实现稳定的凸界面晶体生长,从而提高晶体成晶率。

应用Proofman-LMTIA技术双重检测当归和东当归

通过梯型熔解温度核酸等温扩增技术(Ladder-shape melting temperature nucleic acid isothermal amplification,LMTIA)与校对酶介导探针(Proofreading enzyme-mediated probe cleavage,Proofman)联合的方法对当归和东当归进行双重检测。以ddH2O为阴性模板,当归和东当归基因组DNA为阳性模板,测定当归和东当归引物的最适温度、灵敏度及稳定性,并进行了真实样品检测。结果表明,应用Proofman-LMTIA双重检测当归和东当归,引物测定的最适温度为62℃,当归引物灵敏度低至10 pg/μL,东当归引物灵敏度低至1 pg/μL,具有良好的稳定性。7份市售当归样品经检测均为当归。该研究可为当归和东当归的鉴别提供一种新的检测方法。