Shuichi Arikawa

Measurement of discontinuous displacement/strain using mesh-based digital image correlation

In this study, a method for evaluating discontinuous displacement and strain distributions using digital image correlation (DIC) is proposed. A finite element mesh-based DIC method is used for measuring displacements while taking into account displacement and strain discontinuities. Smoothed displacements are thus obtained, and strains are computed from the measured displacements using the finite element mesh again. Discontinuous strains can be obtained by the proposed method using a split finite element mesh. The effectiveness of this method is validated by applying it to measure the displacement and strain in a triaxially woven fabric composite containing numerous free boundaries, to measure displacements around a crack and the displacement and strain around the interface between dissimilar materials. Results show that the discontinuous displacement and strain distributions can be measured by the proposed method. The proposed method is expected to be applicable for the experimental evaluations of various structures and members, including displacement and strain discontinuities such as free boundaries, cracks, and interfaces.

Observation of Thermal Strain on Electronic Packages Using Digital Image Correlation

In this study, the thermal expansion of bi-metal specimen is measured by digital image correlation (DIC). A measurement system is developed for the evaluation of complex thermal strain distribution on electronic packages. A heating chamber is designed for applying the thermal load and DIC provides the full-field thermal deformation distribution of the bi-metal specimen due to temperature changes. The in-plane strain distribution measured by DIC is influenced by the out-of-plane displacement. By measuring the thermal expansion of the materials having known thermal expansion coefficient at same time, the effect of the out-of-plane displacement on the in-plane strain measurement is corrected. Experimental Results show that the thermal strain of the bi-metal specimen can be obtained by the measurement system including the out-of-plane displacement correction.

Evaluating Thermal Stresses and Strains from Measured Displacements Using an Experimental-Numerical Hybrid Method

An experimental-numerical hybrid method is proposed for obtaining reliable and accurate strains induced by temperature change. Strains obtained from measured displacement distributions are suffered from the measurement errors. Therefore, the measured displacements are used as the input data for determining boundary condition of a finite element model. Nodal forces at all nodes in the finite element model are identified from the measured displacements by the proposed method. Simultaneously, the reliable displacements and the strains are obtained. Effectiveness is validated by applying the proposed method to the displacement fields in dissimilar materials under thermal load obtained by digital image correlation. Results show that the nodal forces for a local finite element model obtained by the proposed method. It is expected that the proposed method can be powerful tool for stress analysis of electronic devices under thermal load.

Bi-Directional Displacement Measurement by Speckle Interferometry Immune to Random Vibration

A bi-directional in-plane displacement measurement by speckle interferometry using an optimum image extraction under environmental disturbances as random vibrations is investigated. A compact speckle interferometer which has 4 laser beams for bi-directional sensitivity is constructed on a tripod. The polarizations of laser beams of each sensitive direction are arranged orthogonal and diffuse reflected laser beams from an aluminum target can be separated by a polarizing beam splitter in front of digital cameras. The bi-directional in-plane displacement measurement is made possible by a simultaneous capturing of the speckle images for each sensitive direction. An in-plane rotation of the target is measured by the proposed method in a presence of the random vibration. A lot of images are captured at the initial and the rotated state. Then, optimum images which can make interference fringes are extracted. A phase analysis by random phase-stepping method using extracted images is performed. As a result, the analyzed phase difference maps show a good agreement with the given rotation angle. Therefore, it is validated that the bi-directional displacement measurement by speckle interferometry under environmental disturbance is possible.

Micro-Polarizer Array Based Instantaneous Phase-Stepping Interferometry for Observing Dynamic Phenomena

We propose a method for determining phase distribution of interference fringes utilizing a CCD camera equipped with a micro-polarizer array. An optical setup of polarization interferometry using a Mach-Zehnder Interferometer with two polarizers is constructed to analyze the distribution of the thickness change of the transparent sample. Light emerging from the interferometer is recorded using a CCD camera that has a micro-polarizer array on a CCD plane. This micro-retarder array has four different principal directions. The four images separated from the image recorded by the CCD camera are reconstructed using gray level interpolation. Subsequently, the distributions of the Stokes parameters that represent the state of polarization are calculated from the four images. The phase distribution of the interference fringe pattern produced by the Mach-Zehnder interferometer is then obtained from these Stokes parameters. This method is applicable to dynamic phenomena because multiple exposures are unnecessary for sufficient data acquisition for phase analysis of fringes.

Photoelastic Determination of Boundary Condition for Finite Element Analysis

An experimental-numerical hybrid method for determining stress components in photoelasticity is proposed in this study. Boundary conditions for a local finite element model, that is, tractions along boundaries are inversely determined from photoelastic fringes. The tractions can be obtained by the method of linear least-squares from both principal stress difference and principal direction. On the other hand, the tractions can also be determined only from the principal stress difference if nonlinear least-squares is used. After determining the boundary conditions for the local finite element model, the stresses can be obtained by finite element direct analysis. The effectiveness of the proposed method is validated by analyzing the stresses in a perforated plate under tension. Results show that the boundary conditions of the local finite element model can be determined from the photoelastic fringes and then the individual stresses can be obtained by the proposed method.

Investigation of Electronic Speckle Pattern Interferometry with Line Laser Scanning for Large Area Deformation Measurement

For measuring small deformations in large structures by electronic speckle pattern interferometry (ESPI), the increase of laser power is required for providing the sufficient laser power per area. However, high-power lasers lead increasing the risk of exposure to laser, the size of the equipment and the cost. In this study, ESPI with line laser scanning is investigated for large area deformation measurements without increasing the laser power. A dual-beam interferometer for a horizontal displacement measurement which can illuminate horizontal line lasers and can scanning for vertical direction is constructed. A static in-plane deformation of an aluminum sheet specimen is measured. Speckle images for each vertical position are captured at the initial and the deformed state. Analyzed phase maps for each line show mismatch of the phases. Additionally, a method for integrating the mismatched line phase maps are investigated.

Thermal Strain Measurement Using Digital Image Correlation with Systematic Error Elimination

This research aims to develop a method for measuring small strains at minute area on an electronic packaging using digital image correlation. To this end, the systematic error in the measured displacement is corrected by using the relation between measured displacement and actual displacement. This relation is obtained by measuring rigid rotation and in-plane translation. The strain distribution with high spatial resolution can be obtained from the displacement distribution because the systematic error that affects the resolution of the strain is eliminated. This error elimination method is applied to the thermal strain measurement of a bimaterial which is composed of copper and steel. Results show that high spatial resolution strain distributions at minute area can be obtained by using this method.

Elimination of Periodical Error for Bi-directional Displacement in Digital Image Correlation Method

A technique for eliminating the periodical systematic error in bi-directional displacements by a digital image correlation method is investigated. The technique is based on a periodical error elimination method for single directional displacements which has been developed by the authors. In this technique, rotated and multiple translated images for the horizontal and the vertical directions are captured before a deformation. Translation amounts are determined from the rotation and the translated images. After the deformation, a single image is captured. The periodical error is eliminated using a calculation based on the translation amounts and the measured multiple displacements from the single deformed state image with the initial translated images. The elimination is applied to a thermal deformation measurement. As a result, periodical errors for bi-directional displacements can be eliminated. Therefore, it is expected that accurate in-plane displacements and strain components can be obtained using the proposed technique.

In Situ SEM Deformation Behavior Observation at CFRP Fiber-Matrix Interface

This paper studies deformation of CFRP at microscopic area and observing technique. Tensile test is carried out for CFRP specimen and digital image correlation (DIC) method is used to observe deformation of microscopic area, especially around its fiber interface. CFRP specimen is loaded by tensile testing machine for investigating deformation around vertical section of fiber. Diameter of carbon fiber used which is mainly interested in the specimen is micro scale, therefore scanning electron microscope (SEM) is used to gain high magnification and resolution pictures as they deforms. To achieve this in situ experiment, testing machine which can be used in SEM is developed. The essential to achieve DIC is selection of random pattern used to follow up change of the area, which greatly influences accuracy of result. Colloidal silica and the other particles are utilized for random pattern with adjustment of concentration. The pattern must be seen clearly and small enough compared to fiber vertical section. Through this research, examination of deformation observation at microscopic area and consideration of starting and fracturing procedure of CFRP are performed.