Dai Fulong

Performance of sub-pixel registration algorithms in digital image correlation

Developments in digital image correlation in the last two decades have made it a popular and effective tool for full-field displacement and strain measurements in experimental mechanics. In digital image correlation, the use of the sub-pixel registration algorithm is regarded as the key technique to improve accuracy. Different types of sub-pixel registration algorithms have been developed. However, little quantitative research has been carried out to compare their performances. This paper investigates three types of the most commonly used sub-pixel displacement registration algorithms in terms of the registration accuracy and the computational efficiency using computer-simulated speckle images. A detailed examination of the performances of each algorithm reveals that the iterative spatial domain cross-correlation algorithm (Newton–Raphson method) is more accurate, but much slower than other algorithms, and is recommended for use in these applications.

NANO-MOIRE METHOD*

Nano-moiré method presented in this paper is an experimental technique which allows direct measurement of nanoscopic mechanical parameters, such as displacement, strain and dislocation distribution. The basic idea is the formation of moiré fringes when a HREM (high resolution electron microscopy) image of crystal material is superimposed with a unidirectional grating. Fourier filtering technique is used to increase the contrast of fringes and to multiple the fringes. This method has atom-size sensitivity and spatial resolution, and relatively large range. It provides a new experimental technique with very high sensitivity and spatial resolution for nanomechanics.

The dynamic deformation measurement of the high speed heated LY12 aluminium plate with moire interferometry

Abstract Using the moire interferometry method, the dynamic deformation of a pre-loaded LY12 aluminium tensile specimen under a thermal heating was studied. The dynamic deformation of the specimen under high speed heating procedures was recorded with a film video camera. The experimental results showed that it is feasible to use moire interferometry for measuring dynamic deformations under conditions of fast heating.

Measurement of non-uniform residual stresses by combined Moiré interferometry and hole-drilling method: Theory, experimental method and applications

Hole-drilling method is one of the most convenient methods for engineering residual stress measurement. Combined with moiré interferometry to obtain the relaxed whole-field displacement data, hole-drilling technique can be used to solve non-uniform residual stress problems, both in-depth and in-plane. In this paper, the theory of moiré interferometry and incremental hole-drilling (MIIHD) for non-uniform residual stress measurement is introduced. Three dimensional finite element model is constructed by ABAQUS to obtain the coefficients for the residual stress calculation. An experimental system including real-time measurement, automatic data processing and residual stresses calculation is established. Two applications for non-uniform in-depth residual stress of surface nanocrystalline material and non-uniform in-plane residual stress of friction stir welding are presented. Experimental results show that MIIHD is effective for both non-uniform in-depth and in-plane residual stress measurements.

Study on fracture behavior of ferroelectric ceramics under combined electromechanical loading by using a moiré 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.

600°C creep analysis of metals using the Moiré interferometry method

Abstract Using a holographic grating for the high temperature and Moire interferometry method, this paper offers an experimental study on the residual creep strain of a No. 20 carbon steel specimen with a central hole under a tensile load. The test was carried out at 600°C for 40 h. The residual creep strain distribution of the specimen over the minimum cross-section and the changing trend of the strain-concentration factors with creep were obtained.

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 out-of-plane displacement fields of silicon surface measured by T/G interferometry in real-time and replicating technique of high temperature specimen grating of moire interferometry was made.

Archimedes Spiral Cracks Developed in a Nanofilm/Substrate System

Perfect Archimedes spiral cracks at micrometer scales are found in a colloid film of several hundred nanometers in thickness coated on a glass substrate. To explain the formation of this kind of spiral crack, the relation between the geometrical properties of the Archimedes spiral and the growth kinematics of the spiral cracks are analyzed. Meanwhile, the initiation and propagation of the spiral cracks are speculated upon logically from the specific material system based on sufficient evidence. In addition, we introduce a new cracking phenomenon and provide an insight into the new mechanism for crack propagation in soft material nano films coated on stiff substrates.

Study of failure modes of microelectronic packaging modules by holography quasi projection moire method

In this paper, a novel interferometric method with a wide range of sensitivities, called holography quasi projection moire, is proposed. It combines the features of the variated double projection moire method and the holographic interferometry method. This technique is used to study the failure modes of microelectronic packaging modules.

High resolution, high sensitivity moire method

Based on geometric moire method, moire interferometry and microscopic moire interferometry, a high spatial resolution and high sensitivity geometric microscopic moire method is presented. Geometric micron-moire patterns are produced by the superposition of two high frequency gratings through a microscope system. Compared with other grating-based photo-mechanics methods, microscopic moire method could provide whole-field moire patterns of both high spatial resolution and high sensitivity. The frequency of specimen and reference gratings used in this method can be from 1 line/mm to 10000 lines/mm. Additionally, a 4F optical filter system is used to enhance the contrast of microscopic moire patterns effectively.