Experimental and analytical investigation of the modified wyoming shear-test fixture

The interaction between the isopescu shear-test specimen and the modified Wyoming shear-test fixture was investigated. This involved three areas of study. First, strip strain gages were applied to the specimen contact surfaces to measure strains induced by the fixture. While it has generally been assumed that the fixture induces an asymmetric load into the specimen, the measured strains indicated a nonasymmetric loading. Second, the effect of an out-of-plane moment, externally applied to the fixture, on gage section shear strains was observed. The shear strains observed were small leading to the conclusion that the fixture is very resistant to out-of-plane moments. Finally, the effect of fixture misalignment on the observed shear modulus was determined. The results indicate that the observed shear modulus increased significantly for slight amounts of misalignment. Therefore, experimental techniques should be modified to include a check for misalignment. Beyond this, it is suggested that the fixture design be modified to prevent misalignment and to achieve an asymmetric loading of the specimen.     

Gage-length errors in the resolution of dispersive stress waves

The effect of measuring the time history of a passing dispersive wave with a finite-length gage is to introduce time and amplitude errors between the actual values and the measured values of the wave function. In this paper, mathematical expressions relating the size of these errors to the gage length, properties of the material, and spectral content of the incident wave are derived. These expressions are used to predict the response of a long, resistance strain gage, attached in the longitudinal direction on the lateral surface of a long slender rod of a linear viscoelastic material (Lexan), to a short pulse. The shape of the pulse just before and just after the region of the long gage was measured by means of very short gages. The dispersion and attenuation properties of the material were obtained from the short-gage data. This information and the previously derived mathematical-correction equations were used to predict the response of the long gage. Good agreement was obtained between the predicted and measured values of the response of the long gage. In addition, the correction equations and the response of the long gage were used to predict the incident pulse. Good agreement with the known experimental values was obtained.     

捷联惯性系统初始对准中IMU安装误差及陀螺漂移的估计与补偿

为尽可能消除IMU安装误差和陀螺漂移对系统精度的影响，运用主从惯导传递对准技术，采用扩展状态滤波器和速度／姿态角组合匹配的方法，估计出IMU安装误差和陀螺漂移误差，并对系统进行补偿。仿真结果表明，补偿了安装误差和陀螺漂移后，捷联惯性系统的导航参数精度可提高1个数量级以上。     

Application of carbon-powder-polymer composite as a continuous crack-length sensor

This paper explores the application of carbon-powder-impregnated polymeric composites for measuring crack extensions. The strain sensitivity of the gage material is shown to be very small. In the first series of tests, the gage material is characterized by measuring the change in electrical resistance due to machined slits for various gage lengths. The measured response is compared with the response predicted from a very simple electrical model. On the basis of good correlation and repeatability, the usefulness of such gages to measure crack extensions is assessed by a second series of tests. Further work to improve the gage response by optimizing the shape of the gage and making the gage and the adhesive layer thinner is proposed. The presented concept, with improvements, can result in a reliable, inexpensive crack gage requiring inexpensive instrumentation. Paper was presented at the 1990 SEM Spring Conference on Experimental Mechanics held in Albuquerque, NM on June 3–6.     

Attainable accuracy of strain measurements with thum-sevenson-weiss mechanical-inductive strain gages

This paper determines the accuracy that can be attained with the Thum-Svenson-Weiss mechanical-inductive strain-measuring method. After stating advantages and disadvantages of this measuring method, the strain gage, the electrical parts and the calibration equipment are described. The determination of accuracy is based on the laws of statistics considering all the errors as distributed completely at random. The behavior of the electrical parts, of the mechanical parts, of the strain gage and of the calibration equipment are separately investigated. It is evident from these investigations that the strain measurement with the Thum-Svenson-Weiss mechanical-inductive strain gages is one of the most accurate strain-measuring methods to date.     

Dynamic characteristic analysis of spur gear system considering tooth contact state caused by shaft misalignment

The effect of gear contact state change due to shaft misalignment on meshing stiffness is usually neglected in the traditional stiffness calculation model with misalignment error, the further influence mechanism of shaft misalignment on gear dynamic characteristics is also unclear. To address these shortcomings, a new mesh stiffness calculation model with misaligned gear considering the effects of tooth contact state is proposed by combining the improved loaded tooth contact analysis (LTCA) model. Then the effects of tooth contact state changes aroused by shaft misalignment on the meshing stiffness excitation are investigated. Moreover, a dynamic model of the misaligned gear system with 8 degrees of freedom (DOF) is established, and based on which the dynamic characteristics of the gear system are investigated and verified by experiment. The study results indicate that the proposed model can be used to evaluate the stiffness excitation and dynamic characteristics of the misaligned gear system with the tooth contact state taken into consideration. This study can provide a theoretical method for evaluating and identifying shaft misalignment errors.

     

预测滤波器理论在惯导非线性对准中的应用

讨论了预测滤波器的基本算法，并针对平台惯性导航系统在大方位失准角情况下的非线性对准中，用预测滤波器无法估计陀螺误差的问题，提出了将预测滤波和扩展卡尔曼滤波相结合的算法。通过对大失准角下的静基座和动基座对准的仿真，证明预测滤波和扩展卡尔曼滤波相结合的算法能够提高的平台姿态误差角特别是方位误差角的估计精度。比起扩展卡尔曼滤波算法，该算法还能降低系统的维数，减小计算量。     

载体运动对双轴连续旋转调制式惯导方案误差的影响

引入系统级旋转自补偿技术可以提高惯性导航系统的精度,该技术是指对整个IMU施加旋转运动从而改变元器件的工作方式,使元件误差得到调制,在进行积分时调制后的误差在一个周期内得到抵消.在捷联式惯导系统中,当载体处于动态时,标度因数误差和安装误差与惯性传感器的输出产生耦合,旋转调制对系统的补偿效果将受到影响.改进的途径一是提高元件标度因数稳定性,减小系统安装误差角;二是隔离载体运动,即减小陀螺仪和加速度计的输出值.本文通过对比分析在静态和动态条件下双轴连续旋转调制式惯导的误差方程,解释了载体运动对旋转调制效果的影响机理,并通过数字仿真验证了载体运动对系统补偿效果的影响.分析和仿真发现,在静态和动态条件下旋转调制都可以提高系统的精度,而在静态条件下或者在通过环架结构隔离了载体运动后旋转调制的效果相对于动态下有较为明显的提高.     

Dynamic strain measurement with the interferometric strain gage

The interferometric strain gage has a short gage length, high-frequency response and the capability of measuring large plastic strains. Furthermore, the gage is easily ruled directly onto the specimen, and no mechanical or electrical contact needs to be made during the measurement. These features make the interferometric strain gage particularly suitable for dynamic plastic-strain measurement. In this paper, the details of an experimental setup for generating and measuring dynamic plastic strain are given. The photometric techniques of measuring the fringe motion of the interference patterns are describle as well as the data-reduction procedure. A typical result is presented, and the validity of the method is established.     

Load sharing in bioinspired fibrillar adhesives with backing layer interactions and interfacial misalignment

Bio-inspired fibrillar adhesives rely on the utilization of short-range intermolecular forces harnessed by intimate contact at fibril tips. The combined adhesive strength of multiple fibrils can only be utilized if equal load sharing (ELS) is obtained at detachment. Previous investigations have highlighted that mechanical coupling of fibrils through a compliant backing layer gives rise to load concentration and the nucleation and propagation of interfacial flaws. However, misalignment of the adhesive and contacting surface has not been considered in theoretical treatments of load sharing with backing layer interactions. Alignment imperfections are difficult to avoid for a flat-on-flat interfacial configuration. In this work we demonstrate that interfacial misalignment can significantly alter load sharing and the kinematics of detachment in a model adhesive system. Load sharing regimes dominated by backing layer interactions and misalignment are revealed, the transition between which is controlled by the misalignment angle, fibril separation, and fibril compliance. In the regime dominated by misalignment, backing layer deformation can counteract misalignment giving rise to improved load sharing when compared to an identical fibrillar array with a rigid backing layer. This result challenges the conventional belief that stiffer (and thinner) backing layers consistently reduce load concentration among fibrils. Finally, we obtain analytically the fibril compliance distribution required to harness backing layer interactions to obtain ELS. Through fibril compliance optimization, ELS can be obtained even with misalignment. However, since misalignment is typically not deterministic, it is of greater practical significance that the array optimized for perfect alignment exhibits load sharing superior to that of a homogeneous array subject to misalignment. These results inform the design of fibrillar arrays with graded compliance capable of exhibiting improved load sharing over large areas.     

双轴旋转式SINS自主标定技术

在双轴旋转式SINS中,惯性元件常值漂移误差对系统的影响可以得到调制,但安装误差和标度因数误差对系统的影响无法得到调制,同时这些误差会与旋转角速率耦合,引起速度锯齿波等误差从而降低了系统的各项性能指标。为了减少这种影响,分析了光学陀螺双轴旋转式SINS误差传播特性,利用奇异值分解法对系统的可观测程度进行了分析,经分析,与转动轴相关的安装误差和标度因数误差的可观测度较好,据此设计了系统的自主标定方案及滤波算法,进行了数字仿真和半实物仿真验证试验。试验结果表明,利用设计的自主标定方案,在1 h内能估计出转轴上两个陀螺的标度因数误差及与转轴相关的四个安装误差,估计精度能达到95%以上。导航试验验证表明,利用自主标定的参数,相对于传统标定方法,使系统定位精度提高了20%。     

A simple estimate for the effect of cross sensitivity on evaluated strain-gage measurement

The cross-sensitivity factor of a short-wire strain gage can sometimes be estimated by comparison of its gage factor with that of a long gage of similar construction and material. A plot of the error introduced by the usual neglect of cross sensitivity against the known or estimatedtrue ratio of transverse to longitudinal stress or strain yields a quick estimate for any given cross-sensitivity factorn of the gage, any Poisson's ratio ν of the test piece and any stress or strain ratio. It shows whether in any particular test the influence of cross sensitivity warrants further special attention. If the longitudinal strain exceeds the transverse strain, the error is seen to be always less than 1.3n, but if the transverse strain is larger, the error may be so high as to vitiate the result. In computations from rosette measurements, the diagram shows that the larger principal stress can be determined with an error below 1.3n, as can Tresca's and von Mises's criteria of yield, while the error in the smaller principal stress tends to be large for principal strain ratios above +10 or below ?1.5.     

Development of New Strain Gage for High-Pressure Hydrogen Gas Use

The output changes of two conventional strain gages (Cu–Ni and Ni–Cr) and a newly-selected strain gage for high-pressure hydrogen gas use (Fe–Cr–Al) in 90 MPa hydrogen and nitrogen gases were measured under unloading conditions to find a high-performance strain gage for high-pressure hydrogen gas use. The changes in the outputs of the Cu–Ni and Ni–Cr gages in hydrogen gas were much larger than those in nitrogen gas, and the Fe–Cr–Al gage showed almost the same output changes in both gases. These results imply that the Fe–Cr–Al gage is superior to the others as a strain gage for high-pressure hydrogen gas use. A large amount of hydrogen entered the Cu–Ni and Ni–Cr foils, and the electrical resistances of these foils were significantly changed by hydrogen exposure, whereas almost no hydrogen entered the Fe–Cr–Al foil, and its electrical resistance was not changed. These resistance changes of the foils as a result of hydrogen entry were consistent with the gage output changes in hydrogen gas.     

准静态压缩应力-应变曲线测量方法的探索

本文介绍了用应变片直接测量材料的准静态应力-应变曲线的试验研究。在MTS810材料试验机上分别对93W、G50、砂浆等几种材料进行了准静态压缩试验。由于仪器的系统误差不能由MTSCod规准确的得到材料的真实的弹性变形。为此在试件的中部贴应变片得到材料的弹性变形,塑性变形仍旧由MTSCod规记录,从而得到试样的真实的应变,准确获得准静态压缩应力-应变曲线。试验结果表明:在试件中部贴应变片的方法能够准确得到该材料的杨氏模量;在试件两端垫块的刀口上安置Cod规可得到材料的应力应变曲线。两者的合理组合即可得到准确而完整的准静态压缩应力-应变曲线。试验中还发现准静态实验中试件的断面加工不平,偏心压缩等都会影响E的准确测量。     

惯导平台陀螺安装误差角辨识的制约因素分析及对策

在惯导平台多位置静态测漂方案下,对陀螺安装误差角的辨识结果往往很不理想。本文通过分析陀螺误差角影响惯导平台漂移的机理,发现平台壳体的角速率是制约误差角辨识精度的主要因素。由此,在测漂过程中有针对性地引入了转台相对地面的角,速率。仿真结果显示,转台角速率的引入能使陀螺安装误差角的辨识精度得到明显的提高。     

自动消除载荷偏心影响的引伸计研究

本文基于拉伸圆截面试样圆周上各点的应变分析，提出一种自动消除载荷偏心影响的引伸计。该引伸计结构简单、可靠、使用方便。特别是在测定金属杨氏模量中更为适用。用电测实验对比校核的数据表明，自动消除载荷偏心影响引伸计安装在不同位置上测量的相对误差不超过０．５％。     

Residual stress by blind-hole method with off-center hole

Application of the blind-hole drilling technique to measurement of residual stresses in areas too restricted for drilling guides is now possible by using a set of equations derived to account for off-center drilled holes. Prior technique required the hole to be drilled concentric with the gage center within ±0.001 in (0.0254 mm), thus requiring the use of a precision locating and drilling guide. The equations apply to commercially available 0-, 90- and 225-deg strain-gage rosettes, but can be easily modified or scaled for different arrays. Details of a hand-drilling procedure are presented, along with examples. Potential errors and data interpretation are discussed.     

Transient-velocity gage for structures

A compact gage has been developed to measure transient velocities up to about 600 cm/sec. The design is based on the principle of a highly overdamped seismic oscillator. Frequency response of the gage is flat from 1 to 500 cps. The gage can be used at any inclination and measures the velocity component along one axis only unaffected by crosswise motion.     

Small attachable interferometric strain gages

Laser-based interferometry from two tiny reflective indentations can be used to measure in-plane strain/displacement over a very short gage length (on the order of 100 μm). If the specimen material is not reflective, then some other means of generating the interference patterns must be found. This paper describes two kinds of attachable gages: plated acetate replicas of indentations and reflective foils that are indented after application. In either case, the gage is applied with the techniques used for foil-resistance gages and the gage itself is very small. The manufacturing procedures are described. The results of experiments comparing the strain to that measured with foil-resistance gages are presented. Finally, the small interferometric gage is used to measure strain on one of the metal strips in a foil-resistance gage.