Hole-drilling method using grating rosette and Moire interferometry

The hole-drilling method is one of the most wellknown methods for measuring residual stresses. To identify unknown plane stresses in a specimen, a circular hole is first drilled in the infinite plate under plane stress, then the strains resulting from the hole drilling is measured. The strains may be acquired from interpreting the Moire signature around the hole. In crossed grating Moire interferometry, the horizontal and vertical displacement fields （u and v） can be obtained to determinate two strain fields and one shearing strain field. In this paper, by means of Moire interferometry and three directions grating （grating rosette） developed by the authors, three displacement fields （u, v and s） are obtained to acquire three strain fields. As a practical application, the hole-drilling method is adopted to measure the relief strains for aluminum and fiber reinforced composite. It is a step by step method; in each step a single laminate or equivalent depth is drilled to find some relationships between the drilling depth and the residual strains relieved in the fiber reinforced composite materials.

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.

HIGH TEMPERATURE MOIRE INTERFEROMETRY TECHNOLOGY

In order to investigate the survivable specimen gratings, the crossed-line300 lines/mm gratings were chemically etched directly into the surface of the specimens.In order to obtain high diffraction efficiency and to minimize the shear lag, the etcheddepth of the gratings was one fourth the wave length of coherent light. The influence ofthe uneven window on the high temperature moire interferometry was preliminarily analyzed. The quartz and inconel 718 specimens were tested up to 1200℃ and 900℃. Thecrack tip deformation singular field as well as load-induced and thermal expansion displacement fields were measured by means of high temperature moire interferometry.

THE APPLICATION OF MOIRE INTERFEROMETRY IN THE MEASUREMENT OF DISPLACEMENT FIELD AND STRAIN FIELD AT NOTCH-TIP AND CRACK-TIP

This paper presents the application of Moire interferometry in measuring the displacement and strain field at notch-tip and crack-tip before and after crack propagation.The experiment is carried out using a three point bending beam with a notch.The N_x and N_y fringe patterns representing displacement field,and the ΔN_x/Δx and ΔN_y/Δy fringe patterns representing the strain field are obtained.The sensitivity of the meas- ured displacement is 0.417μm per fringe order.The displacement and strain distribution along the section x=0 have been worked out according to N_x and N_y fringe patterns.

MEASURING DISPLACEMENT FIELDS OF CURVED SURFACE BY MOIRE INTERFEROMETRY OF PARTIAL COHERENT LIGHT

This paper presents a method to measure the in-plane displacement fields of curved surface by moire interferometry of partial coherent light.The method has the following advantages:simple optical system,no requirement on vibration isolation,high sensitivity,large measuring range,high contrast of inter ference fringes and availability to in-situ structural testing.The present paper also gives theoretical analysis of the method and the formulas of light intensity and displacement field,and introduces a replication technique to form a high frequency reflectance grating on the curved surface.The experiments achieved the measurement of the surface displacement field of a cylindrical shell—the simultaneous circumferential,axial and 45° displacement fields.The torsional test data for surface displacement of a circular bar agree well with the theoretical result.

STUDY OF TRANSFORMATION PLASTICITY IN TETRAGONAL ZIRCONIA POLYCRYSTALS BY MOIRE INTERFEROMETRY

Transformation plasticity in ceria-stabilized tetragonal zirconia poly- crystals due to the stress-induced tetragonal-to-monoclinic martensitic transforma- tion under tension and bending is studied by moire interferometry. The whole fringe patterns including u fields and v fields are acquired. According to these patterns, the distributions of transformation plasticity in transformation zones are obtained, and the phenomenon of plastic flow localization for transformation is revealed. The above work provides a significant experimental foundation for establishing transformation constitutive relations

Residual Stress Measurement for Ion-implanted NiTi Alloy by Using Moiré Interferometry and Hole-drilling Combined Method

Residual stresses in ion-implanted NiTi alloy are measured by a combined method ofMoir6 interferometry and hole-drilling. Oxygen ions are implanted into the NiTi alloy under a voltage of 30 kV by a dose of 1.0×10^17ions/cm^2 for one hour. Subsequently, in order to avoid dimensional error, a hole is drilled exactly in the center of the sample. The distribution of residual stresses around the hole is measured. It is indicated that the method which combines the Moire interferometry with hole-drilling is able to be used to measure residual stresses produced by ion implantation.

2D PHASE SHIFTING AND LOGICAL MOIRE USED IN FRINGES ANALYSIS

Phase Shifting And Logical Moire (PSALM) is a kind of computer image processing method which can be used in phase measurement and to obtain the shape, deformation and strain distribution of an object.This paper presents the structure and working procedure of a 2D phase measurement PSALM2D program and its application. When analyzing moire interferometric fringes,we can obtain 2D distribution of displacement and strain.When it is used in reflection moire we can measure the slope of a specimen.Satisfactory visualization and quantitative results are given by PSALM2D.

STUDY ON FRACTURE BEHAVIOR OF FERROELECTRIC CERAMICS UNDER COMBINED ELECTROMECHANICAL LOADING BY USING A MOIR(?) INTERFEROMETRY TECHNIQUE

This paper discusses an in situ observation of fracture behavior around a crack tip in ferroelectric ceramics under combined electromechanical loading by use of a moiré interferometry technique.The deformation field induced by the electric field and the stress concentration near the crack tip in three-points bending experiments was measured.By analysis of the moiré images it is found that under a constant mechanical load,the electric field almost has no effect on the crack extension in the case that the directions of the poling,electric field and crack extension are perpendicular to each other.When the poling direction is parallel to the crack extension direction and perpendicular to the electric field,the strain decreases faster than that calculated by FEM with and without electrical loading as one goes away from the crack tip.In addition,as the electric field intensity increases,the strain near the crack tip increases,and the strain concentration becomes more significant.

STUDY OF THERMAL DEFORMATION OF MICROELECTRONICS PACKAGING PRODUCT BY INTERFEROMETRIC TECHNIQUE

In this paper, the out-of-plane deformation of silicon surface of Direct Chip Attachment (DCA) assembly, under thermal loading, was measured in real-time by Twyman/Green interferometry. The contour maps of the out-of-plane displacement fields of silicon surface under thermal loading and cycling of various temperature were obtained, Experimental results show that the relation between the out-of-plane displacement and temperature is nonlinear and varies with temperature cycling, due to nonlinear mechanical behavior of the materials used in electronic packaging. A comparison of the aut-of-plane displacement Gelds of silicon surface measured by T/G interferometry in real-time and replicating technique of high temperature specimen grating of moire interferometry was made.

干摩擦面上接触应力分布的混合分析法((英文))

A hybrid method is established by combining photoelastic experiment and finite element analysis. The method is used to evaluate contact stress distribution on dry friction interfaces, such as the contact interfaces between shrouds of fan blades and turbine blades. The photoelastic stress frozen experiment method is used to decide the displacement boundary conditions of numerical calculation. Higher accuracy and efficiency of solving problems are improved by the method. Technical difficulty and high cost of experiment are also avoided by the method. Good agreement of the stress distribution by using the hybrid method and experiment is obtained. \{

SIMULTANEOUS RECORDING OF FRINGE PATTERNS WITH ONE CAMERA

A novel method to separate and simultaneously record the Moiréinterferometry fringe patterns of three deformation fields with only one CCD camera is developed;details of its operation principle,key points and error analysis are presented.With this technique,the deformation in U,V and W fields can be measured simultaneously,so dynamic test with comprehensive information can be performed.The advantage of this technique over other similar techniques lies in its simplicity,easy implementation and low cost.An application of this technique is given to show its feasibility.Technical problems that may be caused with this technique are also analyzed.

Experimental Investigation of the Dynamic Deformation of LY12 Aluminum Plate Heated by Strong Electrical Current

The moire interferometry method was used with holographic gratings for high temperature and high speed photography to measure the dynamic deformation of LY12 aluminum plate with a central hole under tensile loading condition and heated by a strong current. Transient fullfield fringe patterns were acquired during the heating process. Transient temperature of the specimen was simultaneously recorded by a temperature measurement system. The experimental results show that dynamic moire fringe patterns can be measured during high heating rate conditions using high speed photography.

Thermal Deformation Measurement and Stress Analysis of PQFP Assembly during Power Cycling

The three dimensional displacements fields in a surface mounted plastic quad flat pack (PQFP) assembly are measured during power cycling using a combination of holographic interferometry and high sensitivity moire interferometry. Detailed in plane and out of plane whole field displacement data of the top and bottom ends of the gull wing leads and their distributions along the edge of PQFP are provided. The maximum deformations of the gull wing leads occur at the four corners of the PQFP. The experimental results are used as displacement boundary condition in a linear elastic analysis of the thermal stresses of the corner lead and its solder joint using a 3 D finite element method (FEM). The highest stresses occur in the area connecting the lead and the solder joint. The results should be useful in the evaluation of thermal fatigue damage of surface mount assemblies.

RECENT PROGRESS IN RESIDUAL STRESS MEASUREMENT TECHNIQUES

Residual stress measurement is of critical significance to in-service security and the reliability of engineering components, and has been an active area of scientific interest. This paper offers a review o[ several prominent mechanical release methods for residual stress measurement and recent developments, focusing on the hole-drilling method combined with advanced optical sensing. Some promising trends for mechanical release methods are also analyzed.