DETERMINING CRITICAL TIME OF ROCK DYNAMIC FRACTURE BY DYNAMIC MOIRE METHOD

An effective Dynamic Moire method was presented to determine the critical time of crack instable propagation in rock dynamic fracture. Two pieces of grating were installed near the notch of Short Rod specimen to form the Moire fringes, then the COD versus time could be monitored from the movement of the Moire fringes, and finally the critical time could be determined from the velocity of COD. This method was also compared with another one.It could be concluded that the critical time determined by Dynamic Moire method corresponds with that of the Transmitted Wave method at the loading rates from 103 to 104 MPa·m(1/2)·S(-1).

A NEW COPY TECHNIQUE·FOR SPECIMEN GRATING IN MOIRE METHOD

A special X-radiography,used in obtaining the deformed specimen grating in in-plane moire method is introduced.The density of gridline is up to 50 lines / mm.This method is suitable not only for the copy of grating in fiat surface but also for that in curved surface.From unfolding the copy and superposing it with a reference grating,the moire effect arises.By processing this moire fringes with the digital image processing unit, the strain distribution would be obtained.Furthermore,the u-and v-displacement fields could be separated by the optical processing of this copy.The measurment sensitivity and accuracy become better simultaneously because of the fringe multiplication.Thus,this method makes it possible to measure the elastic-plastic strain precisely in any developable curved surfaces,for example, the surface of shaft,rotary-wing,cylindrical shell and cone shell etc.

APPLICATION OF THE DIGITAL MOIRE METHOD IN FRACTURE ANALYSIS OF A CRACKED RUBBER SHEET

This paper deals with the mode I crack problem of a cracked rubber sheet under plane stress condition using the delicate digital moiré technique. Through the four step phaseshifting method of automated fringe analysis, the displacement fields in the Cartesian coordinate system are given. By the coordinate-transform equation, the radial and circular displacement distributions in the polar coordinate system are obtained. The displacement isoline distributions and displacement vector distributions near the crack tip are discussed. The strain isoline distributions near the crack tip are also analyzed in this paper. Finally, the distribution rules for the mechanical fields near the crack tip are discussed with the sector division method.

A NEW METHOD FOR CONSTRUCTING DIGITAL-STRAIN-FIELD-IMAGES FROM MOIRE PATTERNS

A new method for constructing digital-strain-field-image from a moire pattern with the help of digital image processing technique is proposed in this paper. The digital-strain-field-image expresses the strain values directly by its grey levels. The digital-strain-field-image can be obtained by making a differentiation for the digital moire pattern and doing a simple division operation. This image not only gives the visual strain field distribution, but also gives the strain values of every point. This method is simple and applicable and has satisfactory accuracy.

Fabrication of micro-scale gratings for moiré method with a femtosecond laser

Fabrication of micro gratings using a femtosecond laser exposure system is experimentally investigated for the electron moire method. Micro holes and lines are firstly etched for parameter study. Grating profile is theoretically optimized to form high quality moire patterns. For a demonstration, a parallel grating is fabricated on a specimen of quartz glass. The minimum line width and the distance between two adjacent lines are both set to be 1 μm, and the frequency of grating is 500 lines/ram. The experimental results indicate that the quality of gratings is good and the relative error of the gratings pitch is about 1.5%. Based on molte method, scanning electron microscope （SEM） moire patterns are observed clearly, which manifests that gratings fabricated with the femtosecond laser exposure is suitable for micro scale deformation measurement.

Electron Moirémethod

It is very important to measure local deformations for an in-depth understanding of mechanical properties and fracture mechanism of structural and functional materials. In this paper, different types of model grid fabrication methods and many types of electron Moire methods using an electron beam drawing system, a scanning electron microscope or a focus ion beam are reported, together with their applications in the measurement of deformations occurring in various engineerings and materials science research.

Determination of the full-field stress and displacement using photoelasticity and sampling moirémethod in a 3D-printed model

The quantitative characterization of the full-field stress and displacement is significant for analyzing the failure and instability of engineering materials.Various optical measurement techniques such as photoelasticity,moiréand digital image correlation methods have been developed to achieve this goal.However,these methods are difficult to incorporate to determine the stress and displacement fields simultaneously because the tested models must contain particles and grating for displacement measurement;however,these elements will disturb the light passing through the tested models using photoelasticity.In this study,by combining photoelasticity and the sampling moirémethod,we developed a method to determine the stress and displacement fields simultaneously in a three-dimensional(3D)-printed photoelastic model with orthogonal grating.Then,the full-field stress was determined by analyzing 10 photoelastic patterns,and the displacement fields were calculated using the sampling moirémethod.The results indicate that the developed method can simultaneously determine the stress and displacement fields.

Geometrical Moir Methodand Its Application

A geometrical moir method for displaying directly isochromatics and isoclinics of a diametrically pressed circular disk is presented. It is demonstrated that by using two identical or different Wulff nets (or grids) not only the stress fields of a circular disk can be displayed, but the u -and v -displacement fields can also be produced.

Characterization of the arrangement feature of copper interconnects by Moir inversion method

This paper explores the planar arrangement feature of the copper interconnects in a view field of several millimeters by the focused ion-beam （FIB） Moire inversion method quantitatively. The curved FIB Moire patterns indicate that the copper interconnects are a series of curves with continuous variations instead of beelines. The control equation set of the copper interconnects central lines is attained through the Moire inversion method. This work can be extended to inspect the structural defects and provide a reliable support for the interconnects structure fabrication.

EXPERIMENTAL GH SINGULARITY FIELD AROUND GROWING CRACK-TIP

The displacement fields u_x,u_y at growing crack tip of LYI2-M specimens with double edge cracks are measured using moire method.The experimental singularity fields are compared with GH theoretical field [12-14].The size and shape of the experimental GH singularity fields are obtained.The error in both the experimental and theoretical evaluations is controlled within ±10%.The experiments show that there is (In A/r)^(+1)singularity dominant around a growing crack tip.The shape of this dominant region ranges from butterfly wing to oblate and circular.Inside GH-field,there is a 3-D deformed damage zone where no GH sin- gularity exists.

DeformationMeasurementofImpulsedPlateUsingDynamicMoireMethod

In this paper, the car damper is simplified as an impulsed plate, and the dynamic deformations of the impulsed plate are measured using the moire method. The experimental method and procedures, as well as the experimental results are discussed in detail. The good experimental results verify the feasibility of studying the damper damage procedure with the single flash dynamic moire method.

NUMERICAL SIMULATION ON ALUMINIUM SHEET ROLLING

The aluminium sheet rolling is studied by using three dimensional elastic-plastic finite element method (FEM) based on considering both material and geometric non linearity.Three dimensional distribution of the stress and deformation are given on the VAX11 / 780 computer. The spread deformaton of the workpiece is analyzed by means of the moire method.The calculation results are compared with experimental results of the moire and agreement is well.

Experimental analysis of crack tip fields in rubber materials under large deformation

A three-nested-deformation model is proposed to describe crack-tip fields in rubber-like materials with large deformation. The model is inspired by the distribution of the measured in-plane and out-of-plane deformation. The in- plane displacement of crack-tip fields under both Mode 1 and mixed-mode （Mode I-II） fracture conditions is measured by using the digital Moir6 method. The deformation character- istics and experimental sector division mode are investigated by comparing the measured displacement fields under differ- ent fracture modes. The out-of-plane displacement field near the crack tip is measured using the three-dimensional digital speckle correlation method.

Multiphysics coupling in situ measurement method for laser repair of the Inconel 718 alloy structure

As an additive manufacturing technique,the laser-aided direct energy deposition(L-DED)method has been widely used for component repair(also called laser repair).With significant differences from traditional manufacturing techniques,the laser repair process has the characteristics of point-by-point deposition and has a high-temperature gradient in the repair area,resulting in the formation of heterogeneous thermal deformation and residual stress after cooling.High stress may lead to the appearance of cracks in the repair area and may seriously influence the bearing capacity of the repaired parts.Therefore,the characterization of the temperature and deformation fields of the components during laser repair is important for the analysis of the mechanism of damage evolution in the repair area,optimization of the process parameters,and improvement of the mechanical properties of the repaired components.Because of the demand for the simultaneous measurement of the temperature and deformation fields,using a multispectral camera and a self-designed three-peak filter,a temperature-deformation field measurement technique was developed and applied to in situ monitoring during the L-DED manufacturing process.In the actual measurement process,the synchronous measurement of the temperature field of the laser molten pool and the deformation field of the side surface of the repaired component were realized using the images of multiple channels in the multispectral camera.The experimental results verify that a three-peak filter can effectively eliminate the influences of glare and overexposure on the recorded multispectral images.Moreover,the amplitude of the displacement field and the temperature gradient of the repaired component will increase with the increase in laser power,which may affect the final molding of the repaired component.This work extends the function of the multispectral camera to measure the temperature and deformation fields and provides a new measurement method for further optimizing the process parameters of laser repair.

A micro-scale strain rosette for residual stress measurement by SEM Moiré method

In this paper,a new method combining focused ion beam(FIB)and scanning electron microscope(SEM)Moirétechnique for the measurement of residual stress at micro scale is proposed.The FIB is employed to introduce stress relief like the macro ring-core method and fabricate gratings with a frequency of 5000 lines/mm on the measured area of the sample surface.Three groups of gratings in different radial directions are manufactured in order to form a micro-scale strain rosette.After milling ring-core by FIB,the deformation incurred by relief of the stress will be recorded with the strain rosette.The displacement/strain field can be measured using SEM scanning Moiréwith random phase-shifting algorithm.In this study,the Nickel alloy GH4169 sample(which was processed by laser shock peening)is selected as a study object to determine its residual stress.The results showed that the components of the in-plane principal stresses were-359 MPa and-207 MPa,respectively,which show good agreement with the results obtained from the available literature.

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.