乌梢蛇腹部表皮的纳米力学性能研究

用纳米硬度仪研究了不同载荷条件下乌梢蛇腹部表皮的弹性模量、压入硬度等纳米力学性能.结果表明:在法向载荷小于10 mN的范围内,腹部表皮的弹性模量和压入硬度均随载荷的增加而减小,弹性模量的数值范围在300～830 MPa,且为载荷的幂函数;压入硬度的数值范围在37～62 MPa,与载荷成线性关系.腹部表皮的接触刚度随载荷的增加而增加,其数值范围在3.5×103 N/m～5.7×103N/m,为载荷的幂函数.研究结果对深入研究蛇类腹部表皮的摩擦特性及蛇皮的仿生制造提供了基础资料.     

用侧向力显微镜对力/电/热耦合作用下金表面力学行为的研究

对微构件力/电/热等多域场下力学行为的研究有着重要的意义,利用原子力显微镜采用纳米压痕法对样品金在力-电-热耦合作用下的表面力学性能进行了研究,实验表明在压痕过程中,无论在无电场作用下还是有电场作用下,压痕周围的金属由于挤压形成了凸起,从扫描得到的形貌图中可以明显的看出,压痕周围的亮区为材料被挤出的区域.此外,在外加直流电场作用下,随电流的增大,硬度值有增大的趋势,而残余压痕和弹性模量都呈现减小的趋势.     

用测向力显微镜对力／电／热耦合作用下金表面力学行为的研究

对微构件力／电／热等多域场下力学行为的研究有着重要的意义，利用原子力显微镜采用纳米压痕法对样品金在力-电-热耦合作用下的表面力学性能进行了研究，实验表明在压痕过程中，无论在无电场作用下还是有电场作用下，压痕周围的金属由于挤压形成了凸起，从扫描得到的形貌图中可以明显的看出，压痕周围的亮区为材料被挤出的区域．此外，在外加直流电场作用下，随电流的增大，硬度值有增大的趋势，而残余压痕和弹性模量都呈现减小的趋势．     

薄膜热膨胀系数测试技术研究

热膨胀系数是薄膜的重要热学性能参数,也是薄膜热应力和残余应力计算分析过程中的关键数据.文章基于热诱导弯曲原理,分别采用单基片法和双基片法对氮化钛(TiN)和铝(Al)薄膜的热膨胀系数进行测试,并着重对双基片法的测试误差和适用性进行了分析.研究结果表明,薄膜在不同材质基底上弹性模量的差异是影响双基片法薄膜热膨胀系数测试精度的重要因素.当不同材质基片上薄膜弹性模量差异较小时,双基片法测得的热膨胀系数与单基片法所获结果基本一致;而当不同材质基片上薄膜弹性模量相差较大时,双基片法将不再适用.此外,文章结合薄膜的形貌、结构和残余应力表征测试,对TiN和Al薄膜热膨胀系数与其块体材料的差异进行了分析,结果显示残余压应力会导致薄膜热膨胀系数增大,而残余拉应力则具有相反的效果.     

Ti 和 TiN 薄膜的制备以及残余应力的测试方法研究

基底曲率半径法是一种测量薄膜残余应力的常用方法,其中的光杠杆法应用最为广泛.文章在SUS304基底上使用电弧离子镀法制备了不同厚度的钛(Ti)和氮化钛(TiN)薄膜,研究了薄膜的形貌、密度以及物相,基于光杠杆原理分别从正面(正测法)和反面(背测法)对两种薄膜样品镀膜前后基底的曲率半径进行了测量,采用Stoney公式计算薄膜残余应力.通过对比正测法和反测法的测试结果,结合薄膜形貌、密度以及晶体结构表征分析,对背测法的测试误差和适用范围进行了分析.研究结果表明,背测法测得的应力值低于正测法的测量结果,薄膜残余应力水平越高,背测法的测量结果与正测法越接近:当薄膜残余应力水平较高(>1 GPa)时,背测法结果可以如实反映薄膜的应力水平;但当薄膜应力水平较低(<1 GPa)时,背测法结果存在较大误差.     

基于Abaqus的足部有限元分析

通过Engauge软件从CT图像上提取出成年男子足部轮廓数据,根据得到的数据运用SolidWorks建立足部模型,然后利用Abaqus进行应力分析.分析人体站立及承受碾压力时足部受力情况,结果表明:该成年男子站立时最大应力及变形均在跖骨,应力为0.919 MPa,变形为1.19mm;足部承受100 N碾压力时,跖骨的最大应力为2.635 MPa,碾压力为1 000 N时,跖骨的最大应力已达到23.572 MPa.人体足部受到碾压时,跖骨极易出现损伤.     

压头速度对Ni3Al纳米压痕过程影响的数值仿真

用分子动力学仿真分析金刚石压头速度（5~30 m/s）对Ni3Al纳米压痕分子动力学结果的影响.采用中心对称参数（Center Symmetry Parameter,CSP）分析相同压入深度时各模型基体内部位错的萌生和生长情况.结果表明压头压入速度对纳米压痕过程有显著影响：压头压入速度越大,最大加载力和相应的硬度也越大;压入速度对基体内部位错萌生和生长的发生时间有显著影响,但其对位错运动的总体趋势不能产生明显影响.     

纳米压痕仿真软件系统的开发

随着纳米技术的发展,人们越来越关注材料在纳米级条件下的力学性质。以分子动力学方法为基础。开发了纳米压痕仿真软件包（NIMS1.0）。软件包括前处理、求解、后处理等三个模块。可以仿真纳米压痕全过程。能够方便地获得和跟踪试样的多种重要参数。显示二维、三维仿真结果,输出载荷-压痕曲线并计算纳米硬度值。通过仿真,可以对实验中无法观察到的现象进行研究并探索其机理。将仿真结果与实验结果相比较,验证了仿真的可靠性。软件本身具有良好的可扩展性和可移植性。作为纳米压痕技术的重要辅助与补充。该软件为纳米科学研究提供了又一有力手段。     

微力微位移天平测试方法

介绍了一种简单有效的微力、微位移天平测试方法,通过对薄型硅悬臂梁进行力—挠度特性测试进而提取材料杨氏模量的方法是简便、可行的。还介绍了用于测量薄膜应力的悬臂梁挠曲法,对于硅上热生长1.1μm SiO_2的结构,测得SiO_2膜内的压应力为200～230MPa.微力微位移天平测试方法操作方便,仪器成本低,具有较高精度。     

带三维结构的惯性MEMS器件的微细铣削加工

将微细铣削技术应用到了带三维微结构的惯性MEMS器件的加工中.该类惯性MEMS器件由高弹性合金制作,特征尺寸在10μm～200μm,加工精度要求在±1 μm,而且对加工残余应力有较高要求.利用自行研制的三轴联动微小型精密铣床,在研究了微径铣刀的悬伸量、径向切深、每齿进给量等切削参数对切削力影响的基础上,提出了最佳切削参数,成功实现了该器件的加工,并采用微桥法对其弹性模量和残余应力进行了测量.     

Measurement of Young’s modulus and residual stress of thin SiC layers for MEMS high temperature applications

Silicon carbide (SiC) is a promising material for applications in harsh environments. Standard silicon (Si) microelectromechanical systems (MEMS) are limited in operating temperature to temperatures below 130°C for electronic devices and below 600°C for mechanical devices. Due to its large bandgap SiC enables MEMS with significantly higher operating temperatures. Furthermore, SiC exhibits high chemical stability and thermal conductivity. Young’s modulus and residual stress are important mechanical properties for the design of sophisticated SiC-based MEMS devices. In particular, residual stresses are strongly dependent on the deposition conditions. Literature values for Young’s modulus range from 100 to?400?GPa, and residual stresses range from 98 to?486?MPa. In this paper we present our work on investigating Young’s modulus and residual stress of SiC films deposited on single crystal bulk silicon using bulge testing. This method is based on measurement of pressure-dependent membrane deflection. Polycrystalline as well as single crystal cubic silicon carbide samples are studied. For the samples tested, average Young’s modulus and residual stress measured are 417?GPa and 89?MPa for polycrystalline samples. For single crystal samples, the according values are 388?GPa and 217?MPa. These results compare well with literature values.     

Microbridge testing on symmetrical trilayer films

In this paper, we extended the microbridge testing method to characterize the mechanical properties of symmetrical trilayer thin films. Theoretically, we analyzed the deformation of a trilayer microbridge sample with a deformable boundary condition and derived load-deflection formulas in closed-form. The slope of a load-deflection curve under small deformation gives the relationship between the bending stiffness and the residual force of a trilayer microbridge. Taking this relationship, we were able to assess simultaneously the Young's modulus of two kinds of materials composing the symmetrical trilayer film and the thickness-averaged residual stress of the film. Experimentally, we fabricated symmetrical trilayer microbridge samples of SiO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2/ on 4-inch p-type (100) silicon wafers and conducted the microbridge tests with a load and displacement sensing nanoindenter system equipped with a microwedge indenter. The experimental results verified the proposed microbridge testing method. The thickness-averaged residual stress of the 1.1-/spl mu/m trilayer thin films was determined to be 8.8 MPa, while the Young's modulus of the 0.3-/spl mu/m silicon oxide layers and the Young's modulus of the 0.5-/spl mu/m silicon nitride layer were evaluated to be 31 GPa and 294 GPa, respectively.     

Characterization of Young's modulus and residual stress gradient of MetalMUMPs electroplated nickel film

Metal multi-user MEMS processes (MetalMUMPs) offered by MEMSCAP provide a 20 μm thick electroplated nickel film suitable for constructing micro RF tunable capacitors, RF inductors, relays, switches, etc. Currently the Young's modulus and the residual stress gradient of the MetalMUMPs nickel film have not been characterized. In this paper the resonance method is used to characterize the Young's modulus of the MetalMUMPs nickel film. The characterization results show that the nickel film has a Young's modulus of 155–164 GPa with an average of 159 GPa. A stress gradient induced free beam mechanism is proposed in this paper to characterize the residual stress gradient in the MetalMUMPs nickel film. Characterization results show that the residual stress in the electroplated nickel film has a gradient across the film thickness of −5.49 MPa/μm to −4.30 MPa/μm with the average of −4.72 MPa/μm. The residual stress change from the bottom surface to the top surface of the nickel film is −97.7 MPa. The Young's modulus and residual stress gradient of the MetalMUMPs nickel film obtained in this paper provide MetalMUMPs users an important reference for designing, optimizing and analyzing suspended nickel structures. The stress gradient induced free beam mechanism proposed in this paper provides a method of characterizing negative residual stress gradient in thin films without using trenches or through-wafer holes.     

Ultra-light Mg–Li alloy by design to achieve unprecedented high stiffness using the CALPHAD approach

Over decades, Mg–Li alloys have been widely used in aerospace industries owing to their low density (<1.65 g/cm³), medium strength (UTS: 130–200 MPa; YS: 100–170 MPa), and exceptional ductility (elongation: 5–30%). However, their stiffness is so poor (Young's Modulus: 45–47 GPa) that cannot meet many engineering design requirements such as space exploration and Lunar/Mars landing. Therefore, increasing modulus without degrading the strength and ductility of Mg–Li alloy has been a tough problem to be solved for many years. In this study, we have successfully made a significant breakthrough in improving the performance of Mg–Li alloys by inventing a new composition and a new processing route using CALPHAD for ultra-light Mg–Li alloys (density∼1.57 g/cm³), achieving high-strength (UTS: 335 MPa and YS: 290 MPa) and high-modulus (62.5 GPa). The origin of modulus improvement has been discovered by using a combination of SEM, TEM, XCT, nanoindentation, and neutron scattering experiments. Thermodynamically, it was found the high strength and modulus are attributed to the enhanced Mg–Mg bonding in the matrix and the increased elastic interaction forces from the lattice mismatch between the solute atoms and the solvent Mg. Meanwhile, the solution strengthening by lithium and precipitation hardening is discovered by inhibiting dislocation motion. Interestingly, age softening in Al–Li has been found to be a result of phase transformation from high-modulus particles into low ones using TEM, SANS, and nanoindentation tests.     

Mechanical characterization of post-buckled micro-bridge beams by micro-tensile testing

A micro-tensile testing system has been developed to measure the mechanical properties of post-buckled silicon dioxide micro-bridge beams. A kind of vernier-groove carrier is presented to improve alignment precision and repeatability of the measurement, and the stiffness coefficient of the tensile system is calibrated in situ in order to obtain the deformation of the tensile beams. Through analyzing a series of stress states in the beam over film preparation, post-buckling and unfolding of the beam, the initial residual stress in the film is obtained from the original load–displacement curves. The residual stress of 354 MPa is consistent with that calculated from the theory of finite deflection of buckled beams. Young’s modulus and tensile fracture strength are also obtained from the load–displacement curves. The measured modulus and strength are 64.6 ± 3 GPa and 332–489 MPa respectively. The measured properties of the thermal silicon dioxide film are reasonably coherent with other reports.     

Nano-microscale moulding of some metal plates with high strength Ni–W alloy moulds

High strength nanocrystalline and amorphous Ni-14–24 at. % W alloys with their tensile strengths of about 3 GPa have been prepared by electrodeposition. Nano-microscale Ni–W alloy mould inserts, consisting of line and space structures with the line-widths of 700 and 300 nm and the height of 200 nm, were fabricated. High compression stress moulding of some metal plates of pure-Al, SUS-316L stainless steel and Zr₆₉Cu₁₆Ni₅Al₁₀ bulk metallic glass with the Ni–W alloy inserts was carried out at room temperature. In the case of the pure-Al under moulding stress of about 350 MPa, full moulding was achieved with the depths of about 200 nm approximately equal to the height of the inserts. Repeat moulding of 200 cycles did not cause any noticeable change or degradation of the Ni–W alloy inserts. In the case of the SUS-316L stainless steel under the moulding stress of about 1 GPa, however, the nano-microscale moulding was not achieved. This may be due to the high strain hardening ability of the SUS-316L stainless steel during plastic deformation. In the case of the Zr₆₉Cu₁₆Ni₅Al₁₀ bulk metallic glass with a high yielding stress of about 1.5 GPa and no strain hardening ability, full moulding was almost achieved successfully under the high moulding stress of about 2 GPa.     

Characterization of Deformation Behaviors and Elastic Moduli of Multilayered Films in Piezoelectric Inkjet Head

A bulge testing system was developed to mechanically characterize the deformation behaviors and elastic moduli of multilayered films, mainly composed of polycrystalline silicon (polysilicon) and lead zirconate titanate (PZT), used in a multilayer actuator of a piezoelectric inkjet head. In the tests, commercial inkjet heads including a few tens of multilayer actuators were directly pressurized by air, and the corresponding deflections were measured via full-field optical measurement techniques. An analytic solution derived from a thin-plate theory and finite-element analysis were used to describe pressure-deflection behaviors of films, and the results were compared with the experimental data to evaluate the elastic modulus of individual film. The results showed that the elastic moduli of polysilicon and PZT films are ~110 and ~49 GPa, respectively. These values were consistent with the nanoindentation results. For polysilicon films, about 30% reduction in elastic modulus, compared with that calculated from single-crystal elastic constants, was observed, and this was most likely attributed to the presence of microdefects like voids and microcracks at grain boundaries between columnar grains.     

Size effect on mechanical properties of TiO2 capped nanotubes investigated using in situ transmission electron microscopy

In situ transmission electron microscopy nanoindentation tests are used to measure the compressive fracture and mechanical properties of individual titanium oxide (TiO₂) capped nanotubes. The average critical loads ranged from 3.6 to 9.6 μN. Individual TiO₂ capped nanotubes with lengths of 8–10 μm were found to have Young’s modulus values of ~2.2–9.4 GPa and work energy values of ~3.1–6.6 × 10^?13 J. The results indicate that the Young’s modulus and tensile strength depend on capped nanotube length.     

Mechanical properties of thin films from the load deflection oflong clamped plates

A plane-strain load-deflection model for long plates clamped to a rigid support is developed. The analytical model describes the nonlinear deflection of plates with compressive or tensile residual stress and finite flexural rigidity under uniform load. It allows for the extraction of the residual stress and plane-strain modulus of single-layered thin films. Properties of compressively and weakly prestressed materials are extracted with an accuracy achieved previously only with tensile samples. Two approximations of the exact model are derived. The first reduces the plates to membranes by neglecting their flexural rigidity. Considerable errors result from this simplification. The second approximation provides an exact expression for the linear plate response. Using the model, mechanical properties were extracted from two plasma-enhanced chemical-vapor deposition (PECVD) silicon nitride films with weakly tensile and compressive prestress, respectively. Measured residual stresses are 1.3±3.8 and -63±12.4 MPa, respectively. Corresponding plane-strain moduli are 134.4±3.9 and 142±2.6 GPa, respectively     

Micro-tribological properties of heat treated hard disk evaluated by force modulation method

As evaluation of the durability of lubricant and heat cure treated perpendicular hard disks was carried out. With regard to the heat treated perpendicular hard disks, their micro-tribological properties such as hardness, storage modulus, loss modulus, and tan δ have been evaluated by scanning probe microscopy (SPM). In the quasistatic nanoindentation hardness test, it can be observed that nanoindentation hardness in the valleys is higher than that on the hill, and the hardness of the hard disk was increased after it was heat treated. Corresponding to the results of quasistatic nanoindentation in a dynamic nanoindentation test, storage modulus and loss modulus were increased after the heat treatment. Moreover, tan δ also has increased as viewing of viscoelastic properties. On the other hand, for microwear properties, the wear depth of the heat-treated disk and its wear volume were decreased by heat treatment, corresponding to the result of quasistatic nanoindentation.