Vibration and wave propagation analysis of twisted micro-beam using strain gradient theory

In this research, vibration and wave propagation analysis of a twisted micro- beam on Pasternak foundation is investigated. The strain-displacement relations （kine-matic equations） are calculated by the displacement fields of the twisted micro-beam. The strain gradient theory （SGT） is used to implement the size dependent effect at micro-scale. Finally, using an energy method and Hamilton＇s principle, the governing equations of motion for the twisted micro-beam are derived. Natural frequencies and the wave prop- agation speed of the twisted micro-beam are calculated with an analytical method. Also, the natural frequency, the phase speed, the cut-off frequency, and the wave number of the twisted micro-beam are obtained by considering three material length scale parameters, the rate of twist angle, the thickness, the length of twisted micro-beam, and the elastic medium. The results of this work indicate that the phase speed in a twisted micro-beam increases with an increase in the rate of twist angle. Moreover, the wave number is in- versely related with the thickness of micro-beam. Meanwhile, it is directly related to the wave propagation frequency. Increasing the rate of twist angle causes the increase in the natural frequency especially with higher thickness. The effect of the twist angle rate on the group velocity is observed at a lower wave propagation frequency.

Effect of strain-gradients of surface micro-beams on frequency-shift of a quartz crystal resonator under thickness-shear vibrations

With introduction of the first-order strain-gradient of surface micro-beams into the energy density function,we developed a two-dimensional dynamic model for a compound quartz crystal resonator（QCR） system,consisting of a QCR and surface micro-beam arrays.The frequency shift that was induced by micro-beams with consideration of strain-gradients is discussed in detail and some useful results are obtained,which have important significance in resonator design and applications.

Carrier fringe method of moire interferometry for tiny strain measurements in micro-field

In this paper, we demonstrate a new optical method for tiny strain measurements based on the principle of carrier fringes of moire interferometry. A cross-line grating with frequency of 1200 lp/mm is replicated on the specimen surface, and the strain can be deduced from the changes in carrier fringes before and after the deformation of an object. Four coherent laser beams are used to obtain the carrier fringe patterns of field U and V. Both theoretical analysis and numerical simulation indicate that the ideal accuracy of strain can be controlled within a range of ±1με. Case study of a plane extension experiment shows that the measurement accuracy of strain can be controlled within the range of ±10με. The average strain values of every row of field U and every column of field V can be obtained by using this method, and approximated strain of every pixel in the whole-field can be further acquired, and thus it is possible to measure tiny strains occurred in a micro-field. The technology in this paper can provide comprehensive information for analyzing related mechanical content in the field of MEMS.

Axial Micro-Strain Sensor Based on FM-FBG via Dual-Mode ML-FMF in Sensor Networks

An in-fiber axial micro-strain sensor based on a Few Mode Fiber Bragg Grating (FM-FBG) is proposed and experimentally characterized. This FM-FBG is in inscribed in a multi-layer few-mode fiber (ML-FMF), and could acquire the change of the axial strain along fibers, which depends on the transmission dips. On account of the distinct dual-mode property, a good stability of this sensor is realized. The two transmission dips could have the different sensing behaviors. Both the propagation characteristics and operation principle of such a sensor are demonstrated in detail. High sensitivity of the FM-FBG, ~4 pm/με and ~4.5 pm/με within the range of 0 με - 1456 με, is experimentally achieved. FM-FBGs could be easily scattered along one fiber. So this sensor may have a great potential of being used in sensor networks.

Necking of anisotropic micro-films with strain-gradient effects

Necking of stubby micro-films of aluminum is investigated numerically by considering tension of a specimen with an initial imperfection used to onset localisation. Plastic anisotropy is represented by two different yield criteria and strain-gradient effects are accounted for using the visco-plastic finite strain model. Furthermore, the model is extended to isotropic anisotropic hardening （evolving anisotropy）. For isotropic hardening plastic anisotropy affects the predicted overall nominal stress level, while the peak stress remains at an overall logarithmic strain corresponding to the hardening exponent. This holds true for both local and nonlocal materials. Anisotropic hardening delays the point of maximum overall nominal stress.

Evaluation of micro-behavior of strain field in Chinese mainland with the GPS time se-ries

Based on the time series of GPS station coordinate in the international Earth reference frame （ITRF）, we evaluate annual micro-behavior of strain field in Chinese mainland with the triangle method. The results show that the annual micro-behavior of strain field is divided into two parts by the north-south earthquake belt in the research region. The prevailing direction of compressive principal strain field is nearly consistent in the western region. From west to east, the direction varies from NS to NE. It is in accordance with the direction of the modem compressive principal strain field. This suggests that geologic deformation in western region was mainly caused by that India tectonic plate pushes the research region northward and the Siberia plate pushes it southward relatively. It is an inheritance of new tectonic motion. The prevailing direction of the compressive principal strain field does not exist in the eastern region .The annual biggest shear strain is different greatly in every grid-cell. The values varies from 4.13×10^-8 to 7.0×10^-10. By and large the annual biggest shear strain in the western region is bigger than that in the eastern region. And so is the variation between any two consecutive biggest annual shear strains in the same grid-cell. The annual surface dilatation show that in most grid-cells of the research region the surface dilatation is in compressibility, and the variation between any two consecutive annual surface dilatation in the same grid-cell is small.

3种方法单独及联合诊断甲状腺微小结节的价值比较

目的 比较二维高频超声、声脉冲辐射力成像(ARFI)-声触诊组织定量(VTQ)技术及应变弹性成像3种方法单独及联合诊断甲状腺微小结节良恶性的价值。方法 回顾性分析2021年6月—2023年6月在陕西省宝鸡市人民医院就诊的99例(107个甲状腺微小实性结节)结节直径≤10.0 mm患者的临床资料,均采用二维高频超声、ARF-VTQ技术及应变弹性成像进行检查,获得超声资料评分及数据,以穿刺活检和手术病理结果为诊断“金标准”,比较3种超声检查方法单独及联合应用对甲状腺微小结节的诊断效能。结果 62例患者(共68个结节)选择FNAB,37例患者(共39个结节)选择手术。107个甲状腺微小结节中,诊断为恶性微小结节45个,良性微小结节62个。恶性微小结节与良性微小结节相比,结节内回声(等回声和高回声、极低回声和低回声)、边界、微钙化、纵横比>1及血供情况和供血动脉阻力指数(RI)比较,差异均有统计学意义(P<0.05)。二维高频超声诊断甲状腺微小结节C-TIRADS积分临界值≥2分(C-TIRADS 4b)时,诊断灵敏度为73.33%,特异度为79.03%,曲线下面积[AUC(95%CI)]为0.762(95%CI:0.670~0.839);ARFI-VTQ技术中,107个甲状腺微小结节SWV测值为0.52~7.55 m/s,平均(2.62±0.61)m/s,其中24个实性结节多次出现×.××m/s,最后测值以7.55 m/s记录。恶性微小结节SWV均值为(5.24±2.23) m/s,高于良性微小结节的(2.11±0.70) m/s,差异有统计学意义(t=10.258,P<0.05);当SWV临界值为3.19 m/s时,诊断灵敏度为77.78%,特异度为80.65%,AUC(95%CI)为0.792(95%CI:0.703~0.865);应变弹性成像检查中,当评分临界值≥3分时,诊断的灵敏度为75.56%,特异度为77.42%,AUC(95%CI)为0.765(95%CI:0.673~0.841)。三者联合应用诊断的阳性微小结节为44个,阴性微小结节63个,诊断灵敏度为93.33%,特异度为96.77%,AUC(95%CI)为0.951(95%CI:0.891~0.983)。三者联合诊断效能与二维高频超声检查、ARFI-VTQ、应变弹性成像单独检测比较,差异均有统计学意义(Z=4.861、4.393、4.842,P<0.05)。结论 二维高频超声联合ARFI-VTQ技术及应变弹性成像可提高甲状腺微小结节良恶性的诊断准确性。

微纳级GaN基VCSEL中周期反射结构与电子阻挡层的设置作用分析

氮化镓(GaN)基微纳米结构生长技术的成熟为微纳级GaN基垂直腔面发射激光器(VCSEL)的制备提供了新的途径。本文设计了基于GaN基轴向异质结微纳米柱的微纳级VCSEL结构,采用Al_(0.8)Ga_(0.2)N/In_(0.2)Ga_(0.8)N应变补偿结构作为上下分布式布拉格反射镜(DBR),其中Al_(0.8)Ga_(0.2)N层的Al组分远高于传统结构中的电子阻挡层(EBL),能够更好地起到电子阻挡的作用。本文使用商用软件PICS3D构建了电子阻挡层处于不同位置的VCSEL数理模型,并进行数值模拟计算,探索和分析物理机理,解释了不同位置EBL对空穴注入效率的影响。结果表明,采用Al_(0.8)Ga_(0.2)N与In_(0.2)Ga_(0.8)N组成的应变补偿DBR可以更好地提高空穴注入效率,优化器件光电性能。

具有初始损伤的混凝土动态轴拉力学性能仿真研究

基于瓦拉文公式与蒙特卡罗方法并采用Matlab语言构建了随机骨料数值模型,在损伤断裂理论基础上通过Python编程语言于砂浆界面、骨料与砂浆界面和骨料界面嵌入黏聚力单元,建立了二级配混凝土黏聚力模型用于描述混凝土中裂纹萌生、扩展、演化和贯通全过程.以建立的细观模型为基础,对不同孔隙率以及不同微裂纹密度混凝土试件进行了不同应变速率下的动态拉伸加载,研究了混凝土动态轴拉力学性能.结果表明:混凝土轴拉峰值应力与孔隙率呈明显非线性关系,下降曲线为对数函数趋势,孔隙率增加后其对混凝土轴拉峰值应力削弱程度降低,具有初始孔隙的混凝土动态抗拉强度随应变速率的增加而提高.具有初始微裂纹混凝土随着微裂纹密度的增加其峰值应力下降,且动态轴拉强度同样具有速率效应.

氧化镁膨胀剂在超长墙体结构裂缝控制中的应用研究

氧化镁膨胀剂的微膨胀性能可较好地补偿混凝土早期温降收缩,在超长墙体结构中具有良好的裂缝控制效果。实体结构监测数据表明,300~400 mm厚墙体结构在木模板带模养护条件下,内部温度在15~24 h到达温峰值,到达温峰值后前3 d的降温速率在5.0~9.3℃/d,在2~5 d内产生早期温降收缩裂缝;超长墙体结构的连续直墙长度越长,裂缝数量越多;在工程实体结构相比普通混凝土,采用氧化镁膨胀剂配制的补偿收缩混凝土30 d内的温度修正后微应变增长了80με~134με,综合微应变值增长了100με~185με。

补偿收缩混凝土在某箱体式污水处理厂中的应用

为提高箱体式污水处理厂主体结构混凝土的抗裂防渗性能,实现箱体式污水处理厂超长超大钢筋混凝土结构的无缝施工,本文采用“氧化镁膨胀剂配制的补偿收缩混凝土+膨胀加强带”组合技术,并在徐州市某箱体式污水处理厂工程箱体中应用。结果表明:在木模板带模养护条件下,外墙大体积混凝土内部到达温峰值后前3 d的平均降温速率超过了5 ℃/24 h,降温速率较快,若拆模过早则会进一步增大降温速率,温降收缩过大会导致竖向墙体结构早期产生有害裂缝;基础筏板和外墙混凝土内部温度修正后微应变最大值范围分别为84~107 με和37~65 με,30 d内缓慢降至8~34 με和-53~-88 με,氧化镁类补偿收缩混凝土能较好补偿早期温降收缩,筏板混凝土在30 d龄期内一直处于微膨胀状态,外墙混凝土收缩量相对较小,各实体结构均具有良好的抗裂防渗性能。

微尺度3D打印柔性传感器创新实验设计与实践

介绍了一种利用微尺度3D打印柔性应变传感器的实验设计及实践,旨在培养学生的创新意识和实践能力,提高教学质量和水平。该实验借助微尺度3D打印技术,实现了传感器微型化和高精度制备,有效地提升了传感器的灵敏度和稳定性。在实践过程中,学生需要独立进行实验设计、制备和测试,注重实验数据的统计和分析,培养了学生的创新思维和实践操作能力。

3D打印柔性微网格的应变传感性能研究

本工作通过直书写式三维(3D)打印工艺将碳黑/聚二甲基硅氧烷(CB/PDMS)复合材料精准成型为不同结构类型的柔性微网格。利用光学显微镜表征了复合材料的成型质量和结构差异,通过流变性和电导率测试确定了打印浆料的配比。通过打印速度和挤出气压等制造工艺参数的优化,实现了600μm线宽的稳定成型。系统研究了结构类型对力学和传感性能的影响规律,优化后的简单立方微网格结构的应变灵敏度可达10.33,响应时间为370 ms。验证了柔性微网格在可穿戴器件领域的应用,展现出了优异的实时动态监测的能力。本文为柔性多功能器件的快速、低成本制造提供了新思路,在柔性电子等领域具有广阔的应用前景。

应变式直剪仪与微型十字板剪切仪测定土壤抗剪强度的对比分析

[目的]分析两种仪器(应变式直剪仪与微型十字板剪切仪)测得的土壤抗剪强度指标(土壤黏聚力值c、内摩擦角φ、土壤剪切力τ)特征,并建立直剪仪测得的c和φ与十字版仪测得的τ之间的函数关系,以期深化对土壤抗剪强度的认识,提高土壤抗剪强度指标测定效率。[方法]选取黄土高原3种典型质地类型土壤(杨凌黏黄土、安塞黄绵土、定边沙黄土),每种土壤设5个含水量梯度(12%,16%,20%,24%,28%),分别用上述两种仪器测定不同处理下土壤抗剪强度指标c,φ和τ,探究了3指标对土壤质地、土壤含水量的响应特征以及3指标间的函数关系。[结果](1)试验条件下,c值在16.88~27.12 kPa范围,φ值在5.03°~21.30°范围,τ值在1.76~7.72 kPa范围变化;(2)不同土壤类型下,c和τ均随含水量的增大呈现先增大后减小趋势,而φ随含水量增大呈现逐渐降低趋势;(3)总体来看,安塞黄绵土的τ,c,φ值略高于定边沙黄土,但它们均显著大于杨凌黏黄土。(4)3种土壤类型下,微型十字板剪切仪所测定的τ值与直剪仪测定的c值均具有较强的线性相关关系(R 2>0.90);而φ值与τ值间并无显著相关关系。如不考虑土壤类型差异,τ与c之间仍有较强的相关性,关系式为c=1.59τ+14.10(R 2=0.51,p<0.01)。[结论]应变式直剪仪测得的黏聚力c值和微型十字版仪测得的土壤剪切力τ值对土壤质地、含水量的响应相似,且二者有显著的相关关系,在一定条件下可以用快速便捷的微型十字版仪测得的τ值估算原本需用直剪仪测的c值。研究结果可为野外极端条件下提高土壤抗剪强度测定效率方面提供参考。

选区激光熔化的微流道换热器芯体传热板成型工艺

为解决传统工艺存在的截面形状受限、污染环境等问题,研究采用选区激光熔化技术制备高通量微流道换热器芯体传热板.分析传热板的几何形状、316L不锈钢粉末的材料特性及主要成型工艺参数,采用Altair Inspire软件的Print3D模块对成型过程进行仿真模拟,研究温度场、Mises应力和塑性应变的分布及变化规律.结果表明:熔化成型区温度随着激光的射入和远离发生剧烈变化;由于激光能量在制件内的累积效应,使得后成型区域的温度明显大于先成型区域.Mises应力和塑性应变与换热板的结构和温度场有密切关系,流道位置结构复杂,Mises应力和塑性应变较大;温度越高的区域金属粉末熔化越充分,Mises应力和塑性应变的值越小.

Improving Tribological Performance of Gray Cast Iron by Laser Peening in Dynamic Strain Aging Temperature Regime

A high and stable brake disc friction coefficient is needed for automobile safety, while the coefficient degrades due to elevated temperature during the braking process. There is no better solution except changes in material composition and shape design optimization. In the dynamic strain aging（DSA） temperature regime of gray cast iron, micro-dimples with different dimple depth over diameter and surface area density are fabricated on the material surface by laser peening（LP） which is an LST method. Friction behavior and wear mechanism are investigated to evaluate the effects of surface texturing on the tribological performance of specimens under dry conditions. Through LP impacts assisted by DSA, the friction coefficients of the LPed specimens increase noticeably both at room temperature and elevated temperature in comparison to untreated specimens. Moreover, the coefficient of specimen with dimple depth over diameter of 0.03 and surface area density of 30% is up to 0.351 at room temperature, which dramatically rises up to 1.33 times that of untextured specimen and the value is still up to 0.3305 at 400℃ with an increasing ratio of 35% compared to that of untreated specimen. The surface of textured specimen shows better wear resistance compared to untreated specimen. Wear mechanism includes adhesive wear, abrasive wear and oxidation wear. It is demonstrated that LP assisted by DSA can substantially improve wear resistance, raise the friction coefficient as well as its stability of gray cast iron under elevated temperatures. Heat fade and premature wear can be effectively relieved by this surface modification method.

Measurement of residual stress in a multi-layer semiconductor heterostructure by micro-Raman spectroscopy

Si-based multilayer structures are widely used in current microelectronics. During their preparation, some inhomogeneous residual stress is induced, resulting in competition between interface mismatching and surface energy and even leading to structure failure. This work presents a methodological study on the measurement of residual stress in a multi-layer semiconductor heterostructure. Scanning electron microscopy（SEM）, micro-Raman spectroscopy（MRS）, and transmission electron microscopy（TEM） were applied to measure the geometric parameters of the multilayer structure. The relationship between the Raman spectrum and the stress/strain on the [100] and [110] crystal orientations was determined to enable surface and crosssection residual stress analyses, respectively. Based on the Raman mapping results, the distribution of residual stress along the depth of the multi-layer heterostructure was successfully obtained.

Deformable micro-continua in which quantum mysteries reside

Deformable micro-continua of highly localized nature are found to exactly exhibit all quantum effects commonly known for quantum entities at microscopic scale.At every instant,the spatial configuration of each such micro-continuum is prescribed by four spatial distributions of the mass,the velocity,the internal stress,and the intrinsic angular momentum.The deformability features of such micro-continua in response to all configuration changes are identified with a constitutive equation that specifies how the internal stress responds to the mass density field.It is shown that these microcontinua are endowed with the following unique response features:(i)the coupled system of the nonlinear field equations governing their dynamic responses to any given force and torque fields is exactly reducible to a linear dynamic equation governing a complex field variable;(ii)this fundamental dynamic equation and this complex field variable are just the Schrodinger equation and the complex wave function in quantum theory;and,accordingly,(iii)the latter two and all quantum effects known for quantum entities are in a natural and unified manner incorporated as the inherent response features of the micro-continua discovered,thus following objective and deterministic response patterns for quantum entities,in which the physical origins and meanings of the wave function and the Schrodinger equation become self-evident and,in particular,any probabilistic indeterminacy becomes irrelevant.

NEW STRAIN GRADIENT THEORY AND ANALYSIS

A new strain gradient theory which is based on energy nonlocal model is proposed in this paper, and the theory is applied to investigate the size effects in thin metallic wire torsion, ultra-thin beam bending and micro-indentation of polycrystalline copper. First, an energy nonlocal model is suggested. Second, based on the model, a new strain gradient theory is derived. Third, the new theory is applied to analyze three representative experiments.

A study on relation between acoustic emission and characteristic displacement field on the sample with multi en echelon structures——The theoretic and experimental explorations of strain gap

Based on the phenomena that the deformation gap was observed before the great Tangshang earthquake, this paper discusses the strain gap according to test and theory. The (strain) patterns were recorded photographically by real-time holographic interferometry and shadow optical method of caustics, as soon as the loading process started. In the meantime, the AE (acoustic emission) signals were recorded by a micro crack information storage-analysis sys-tem. According to damage theory and location of micro fracture, we have studied the stain gap and gained: a) It is necessary that strain gap appears under the condition of linear elasticity theory, and its situation is relatively stable, corresponding to stress concentration. b) Micro fractures, which appear initially at area of high stress, occur rarely at the strain gap, and their locations are finally in the zone between the stress concentration area and the strain gap, which indicate the clusters or groups. However, the major macro fracture (final rupture) started from the shadow areas, and then grew quickly towards the strain gaps, which resulted in failure of sample.