Measurement of strain concentration factor of composites plate using moiré interferometry

In this paper, using a 1200 lines/mm replicated grating, the moiré interferometry method was applied to study the strain concentration factor of a carbon fibre composites plate with a central hole. The rules of strain concentration factors were determined under different loads.     

Thermal Properties Measurement of Micro-electromechanical System Sensors by Digital Moire Method

Abstract:  The thermal properties of a micro-electromechanical system sensor were analysed by a novel digital moiré method. A double-layer micro-cantilever sensor (60  μ m long, 10  μ m width and 2  μ m thick) was prepared by focused ion beam milling. A grating with frequency of 5000 lines mm⁻¹ was etched on the cantilever. The sensor was placed into a scanning electron microscope system with a high temperature device. The observation and recording of the thermal deformation of the grating were realised in real-time as the temperature rose from room temperature to 300 °C at intervals of 50 °C. Digital moiré was generated by interference of the deformed grating and a digital virtual grating. The thermal properties including strain distribution of the sensor and the linear expansion coefficient of polysilicon were accurately measured by the phase-shifted moiré patterns.     

APPLICATION OF GRIDS TO PLASTICS FOR THE MOIRE FRINGE METHOD OF STRAIN MEASUREMENT

There has been considerable interest during recent years on the measurement of strain using the moiré fringe method. This report reviews the techniques of applying grids to specimens and gives details of methods used at NEL. Strain measurements on a simple tensile test specimen using the moiré mismatch technique are compared with those obtained with a Linley extenso-meter.     

Application of moiré technique in the stress analysis of cutting tools

Knowledge of the stress field in cutting tools is necessary for their strength evaluation. However, the experimental analysis of stresses in cutting tools during machining poses a number of problems in view of the steep stress gradient present. Photo-elasticity and the 'built-up tool' methods are the common techniques used for this purpose. In the present paper results on the stresses in cutting tools obtained during actual machining through the successful application of the transmitted moiré technique, are presented. In these experiments transparent epoxy tools carrying moiré gratings were used to machine commercial lead alloy at low speeds. The tool rake angle was varied. The effectiveness of moiré method, basically a displacement analysis technique, in providing useful data on tool stresses comparable with the other direct stress analysis techniques such as photo-elasticity is also discussed in the paper.     

Grid emission suppression characteristics of molybdenum grids coated with Hf and Pt films

Hf and Pt were deposited onto molybdenum grids by ion beam-assisted deposition (IBAD). Electron emission characteristics from these coated molybdenum grids contaminated by active electron emission substances (Ba, BaO) of the cathode were measured using the analogous diode method. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed on the surface of molybdenum grids coated with Hf and Pt films. When emission substances were deposited onto the grid surface, the reaction between BaO and Hf formed a BaHfO₃ compound that markedly reduced the accumulation of BaO and accordingly decreased grid emission. The decomposition of BaO on the surface of Pt under high temperature was believed to lead to the formation of Ba and its re-evaporation from the surface, reducing active electron emission substances with a consequent significant reduction in grid emission. According to the comparison of their grid emission suppression mechanisms, it could be concluded that grid emission suppression was mainly the reduction of active electron emission substances on the grid surface, in particular BaO. This could be a worthwhile approach for the development of new grid coating materials.     

Deformation Data from Thermal Marking

Abstract: A novel experimental technique for strain measurement, named thermal moiré, and based on a combination of thermography and moiré concepts, is presented in this paper. The proposed technique essentially involves the temporary imprinting of a thermal pattern onto the surface of the object of interest as a substitute for conventional gratings, to remove the need for physical printing, etching or bonding. In materials with low diffusivity, the thermal pattern can be observed with an infrared camera and analysed using conventional techniques. Work on the development of suitable laboratory apparatus is described, and preliminary experimental results are presented to illustrate the feasibility of the method.     

CFRP网格-聚合物水泥砂浆加固RC梁抗剪承载力计算方法

为揭示碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)网格-聚合物水泥砂浆(Polymer cement mortar,PCM)抗剪加固钢筋混凝土(RC)梁的受剪机制并建立其承载力计算方法,对RC梁进行了四点弯曲试验和有限元模拟,重点分析了CFRP网格对RC加固梁的抗剪贡献,建立了基于改进的桁架拱模型的抗剪承载力计算方法。结果表明：RC梁侧粘贴CFRP网格-PCM加固层不仅可以抑制斜裂缝的发展,而且还提高了抗剪承载力;CFRP网格与钢筋之间具有良好的协同工作性能,其中,横向CFRP网格筋分担了约16%的箍筋应变;回归分析指出纵向CFRP网格筋的应变约为横向CFRP网格筋应变的0.29倍;综合考虑纵向CFRP网格的销栓作用和横向CFRP网格分担的箍筋应变,提出了基于改进桁架-拱模型的承载力计算方法,具有更好的适用性和准确性,能够满足设计要求。     

Micro 3D measurement method using SEM

Three diamensional (3D) measurement method by Scanning Electron Microscope (SEM) has already been proposed by using the principle of shadow moiré. In the method, the image of original grid in shadow moiré image must be clearly removed in fringe analysis process in order to perform high resolution analysis. A new method based on the principle of projection moiré is proposed to solve the trouble concerning the grid. In this paper, the mechanism of producing some shadows of grid on the surface of the object by back scattering electron beam in the new method is discussed. Fringe image as shadow of grid is analyzed by Wavelet transform. The precise 3D measurement is realized by using the phenomenon of shadows of grid. Furthermore, a 3D micro structure on the head of a hard disk is measured. From the comparison of results obtained by Atomic Force Microscope (AFM), it is confirmed that the proposed method has high-resolution power(about 20nm).     

The use of strippable photographic film for moire grating production

Practical details are presented concerning the use of strippable film for the production of moiré gratings. Strippable film is produced primarily for application in graphic arts. The influence of the use of the film on the accuracy of measurement in the direct moiré method is discussed.     

Experimental and Numerical Investigation of Mechanical and Thermal Residual Strains in Adhesively Bonded Joints

Abstract:  This paper describes an investigation of residual and mechanical strains in aluminium/aluminium (Al/Al) and aluminium/carbon fibre-reinforced polymer (Al/CFRP) adhesively bonded double-lap joints. Residual strains were measured inside the adherends by means of neutron diffraction (ND) and modelled using finite element analysis (FEA). In the Al/Al joints the measured residual strains were negligible, showing good agreement with FE predicted results. However, considerable strains developed in the Al/CFRP joint because of differential thermal contraction of the two materials during joint manufacture. Although considerable scatter was seen in the ND results, the measured and predicted trends showed similar behaviour and were of comparable magnitude. The paper also reports measurements of internal strains in an Al/CFRP joint under tensile load using ND and of surface strains using moiré interferometry (MI). In general, good agreement was observed between FE predictions, surface strains measured with MI and internal strains measured with ND for the loaded Al/CFRP joint.     

Quantitative evaluation of high temperature deformation mechanisms: a specific microgrid extensometry technique coupled with EBSD analysis

A microgrid extensometry method has been developed and used to obtain information about intragranular and intergranular creep mechanisms. An oxide grid was deposited on a creep specimen using an electron lithography technique. This oxide grid offers high backscattered electron contrast and can withstand long duration creep tests under vacuum in the 700–850 °C range without degradation. Specific methods were used to measure in-plane displacements at the grid nodes or at the grain boundaries using correlation of grid images taken before and after the creep test. The local strain and grain boundary sliding (GBS) data were then calculated. Combined information about grain boundary crystallography and GBS has been obtained by superimposing the electron backscattered diffraction (EBSD) map on the deformation maps. To illustrate the potential of this set of processes, two examples of application on a nickel-base disc superalloy are presented. The first one concerns the influence of the creep temperature on the local strain and the GBS. The second application quantitatively shows the influence of grain boundary character on GBS of this material.     

TRIAXIAL ANALYSIS OF THE "POKER-CHIP" TEST

Axial compression of thin circular discs made of plasticized epoxy resin was studied. The plane faces were cemented to platens rigid compared with the material of the discs so that the constraint due to cementing created in the discs a three-dimensional state of stress. The internal strain distribution was measured by the moiré method which yielded enough data for an evaluation of this state of stress. The influence of the aspect-ratio of diameter D to thickness t of the disc was investigated.     

An experimental-finite element analysis of the plane stress local torsion

The plane stress local torsion (PSLT) is an attractive method to strengthen the material in the areas of interest. A closed form solution of the problem is complex and an interpretation of the measured raw torque–twist data into the effective stress and strain is not straightforward. These hinder the optimization and control of the technique. In this study, the PSLT test was performed using Ti-IF steel specimens and their torque–twist response and radial distortion were compared with those obtained from an elastic–plastic model of the PSLT developed by the commercial finite element software, ABAQUS. The resultant microstructure in the samples as a result of large local shear strains and the extent of deformation were studied using SEM and a grid distortion technique, respectively. Mechanical property changes after the PSLT processing were characterized in samples of different geometry using a dedicated formulation based on the similarity theory. The micro shear punch tests allowed characterizing the gradient of the reinforcement in the radial direction of the samples.     

纤维网格高延性混凝土加固RC柱抗剪性能试验研究

箍筋配置不当、剪跨比较小和轴压比较大的钢筋混凝土(RC)框架柱在地震作用下通常发生脆性剪切破坏。为提高框架柱的抗剪性能,提出采用碳纤维(CFRP)网格和高延性混凝土(HDC)复合加固RC柱。设计了6个RC柱试件,通过低周反复荷载试验,研究加固方式、纤维网格层数和轴压比对加固柱破坏形态、受剪承载力、延性及耗能能力的影响。结果表明：采用HDC和CFRP网格复合加固,可显著提高柱的抗剪承载力,明显改善其延性、变形性能和耗能能力;提高加固层的网格层数,对抗剪承载力影响较小,但加固柱的延性和变形能力得到较大改善;轴压比增大,复合柱的抗剪承载力稍有提高,但试件的延性、变形能力和耗能能力均降低;增加网格层数对高轴压比加固柱的增强效果和对低轴压比柱基本一致。最后基于桁架-拱模型,提出加固柱的抗剪承载力计算公式,计算结果与试验值吻合较好。     

MEASURING STRAINS UNDER WELDS BY THE MOIRÉ FRINGE TECHNIQUE

A method of measuring strains very close to weld deposits has been developed using moiré fringe technique and mismatch gratings. It is necessary to compromise between accuracy and gauge length, but an accuracy of 100μin/in (-10^-4) can be achieved with a gauge length of 0.2 in (5mm). Strains parallel to the weld deposit can be measured right up to the fusion line, but in the direction normal to the weld deposit the first strain reading is controlled by the gauge length, as defined by the distance between successive fringes.     

FATIGUE CRACK TIP STRAINS IN 7075-T6 ALUMINUM ALLOY

Abstract— The plastic enclave surrounding a fatigue crack in a 7075-T6 aluminum alloy specimen is studied using moiré interferometry. Two distinct plastic zones are identified from inspection of moiré interferometric fringe patterns. The sizes and shapes of the monotonic and the cyclic plastic zones are correlated with previous theoretical and experimental results. Live load strain distributions in the plastic enclave are computed from high sensitivity (0.417 micron per fringe) full-field in-plane displacement contour maps. Comparison with theoretical and experimental strain distributions are included.     

Spherical aberration correction using a liquid-crystal spatial-light modulator in off-axis electron holography

One can correct spherical aberration in a transmission electron microscope by using a newly developed aberration-correction method involving off-axis electron holography. In this method, a liquid-crystal spatial-light modulator (LC SLM) is employed during the holographic reconstruction step to compensate for spherical aberration. Application of this method to high-resolution off-axis electron holograms of fine gold particles is presented. The phase distribution of the corrected object wave is visualized by the Zernike phase-contrast method carried out with the same LC SLM.     

离子束辅助沉积铪膜抑制栅电子发射性能研究

利用离子束辅助沉积（IBAD）方法在Mo栅极表面沉积铪膜,采用模拟二极管方法测量和比较阴极活性物质Ba、BaO蒸发在镀铪和纯钼栅极表面的电子发射性能。实验结果表明,镀铪栅极抑制电子发射性能较好,并初步探讨了离子束辅助沉积铪膜抑制栅电子发射的机理。     

Variation of transverse and shear stiffness properties of wood in a tree

In this work, the application of the unnotched Iosipescu test for the evaluation of the radial variability of longitudinal–radial stiffness parameters of maritime pine wood was investigated. Rectangular specimens with grain at 45° were tested using the Iosipescu fixture. For this configuration both the transverse (Q₂₂) and the shear (Q₆₆) stiffness parameters can be simultaneously identified by the virtual fields method. Displacement fields were measured by the grid method. The strain fields were reconstructed from the raw displacement fields using a polynomial approximation scheme. For the tested wood material, it was found that both parameters decrease from the centre to about the middle radius of the stem and increase afterwards to the outermost positions. Moreover, a relatively good correlation was obtained between the patterns of radial variability of Q₂₂ and Q₆₆.     

Curvature contours of flexed plates by a multiple illumination moiré shearing interferometer

A new moiré method is proposed to map partial slope, partial curvature and twist curvature contours of laterally loaded specularly reflecting plate models. Converging HeNe laser light is diffracted by a lens plane cross grating, different combinations of orders are selectively permitted through the Fourier transform plane and collimated to illuminate the plate model. This technique eliminates the difficulties involved in Fourier filtering in the imaging optics, thereby extending the reflection moiré' interferomelry to general plate structures and loading. The slope contours are obtained still by double exposure.