Three-dimensional Deformation Measurement Research Articles

Global and local characteristics of an autogenous single pass electron beam weld in thick gage UNS S41500 steel

Electron beam welding of UNS S41500, a low carbon martensitic stainless steel utilized in hydroelectric turbine manufacturing, was investigated by applying a single pass autogenous process to penetrate a section thickness of 72mm without preheating. In the as-welded and post-weld heat treated conditions, the evolution in microhardness and microstructure across the weldments, as well as the global and local tensile properties, were evaluated. In the as-welded condition, assessment of the microhardness and the associated microstructure across the welds led to the identification of six regions, including the fusion zone, four heat affected zones and the base metal; each of these regions consisted of different phase constituents, such as tempered martensite, untempered martensite, delta ferrite and retained austenite. Post-weld heat treatment, undertaken to temper the untempered martensite in the as-welded microstructure, was effective in homogenizing the hardness across the weldment. The mechanical response of the welds, determined through tensile testing at room temperature with an automated non-contact three-dimensional deformation measurement system, indicated that the global tensile properties in the as-welded and post-weld heat treated conditions met the acceptance criteria in the ASME Section IX standard. Also, evaluation of the local tensile properties in the fusion and heat affected zones of the as-welded samples allowed a more comprehensive understanding of the strength and ductility associated with the different microstructures in the “composite” nature of the weldment. Fractographic analysis demonstrated dimpled features on the tensile fracture surfaces and failure was associated with debonding between the martensitic matrix and the secondary phases (such as delta ferrite and retained austenite) that resulted in the formation, growth and coalescence of voids into a macroscale crack.

Synchronous measurement of three-dimensional deformations by multicamera digital speckle patterns interferometry

We present a spatial phase-shift digital speckle patterns interferometry (SPS-DSPI) system with the capability of measuring three-dimensional (3-D) deformations under a dynamic loading condition simultaneously using multiple cameras. The Fourier transform method is utilized to calculate the phase difference. The consistency of different cameras is achieved using digital image correlation (DIC) technology. Calibration and calculation programs are compiled to make sure each subset on the measuring surface is uniform. SPS-DSPI and DIC techniques are combined to provide a direct measurement of the 3-D deformation of the entire surface area simultaneously. The theory, application result, and validation experiment are presented.

Single-camera stereo-digital image correlation with a four-mirror adapter: optimized design and validation

A low-cost, easy-to-implement but practical single-camera stereo-digital image correlation (DIC) system using a four-mirror adapter is established for accurate shape and three-dimensional (3D) deformation measurements. The mirrors assisted pseudo-stereo imaging system can convert a single camera into two virtual cameras, which view a specimen from different angles and record the surface images of the test object onto two halves of the camera sensor. To enable deformation measurement in non-laboratory conditions or extreme high temperature environments, an active imaging optical design, combining an actively illuminated monochromatic source with a coupled band-pass optical filter, is compactly integrated to the pseudo-stereo DIC system. The optical design, basic principles and implementation procedures of the established system for 3D profile and deformation measurements are described in detail. The effectiveness and accuracy of the established system are verified by measuring the profile of a regular cylinder surface and displacements of a translated planar plate. As an application example, the established system is used to determine the tensile strains and Poisson׳s ratio of a composite solid propellant specimen during stress relaxation test. Since the established single-camera stereo-DIC system only needs a single camera and presents strong robustness against variations in ambient light or the thermal radiation of a hot object, it demonstrates great potential in determining transient deformation in non-laboratory or high-temperature environments with the aid of a single high-speed camera.

Three-dimensional microscopic deformation measurements on cellular solids

The increasing interest in small-scale problems demands novel experimental protocols providing dense sets of 3D deformation data of complex shaped microstructures. Obtaining such information is particularly significant for the study of natural and engineered cellular solids for which experimental data collected at macro scale and describing the global mechanical response provide only limited information on their function/structure relationship. Cellular solids, in fact, due their superior mechanical performances to a unique arrangement of the bulk material properties (i.e. anisotropy and heterogeneity) and cell structural features (i.e. pores shape, size and distribution) at the micro- and nano-scales.To address the need for full-field experimental data down to the cell level, this paper proposes a single-camera stereo-Digital Image Correlation (DIC) system that makes use of a wedge prism in series to a telecentric lens for performing surface shape and deformation measurements on microstructures in three dimensions. Although the system possesses a limited measurement volume (FOV~2.8×4.3mm2, error-free DOF ~1mm), large surface areas of cellular samples can be accurately covered by employing a sequential image capturing scheme followed by an optimization-based mosaicing procedure. The basic principles of the proposed method together with the results of the benchmarking of its metrological performances and error analysis are here reported and discussed in detail. Finally, the potential utility of this method is illustrated with micro-resolution three-dimensional measurements on a 3D printed honeycomb and on a block sample of a Luffa sponge under compression.

Prediction of time-dependent swelling of flexible polymer substrates using hygro-mechanical finite element simulations.

The prediction of hygroscopic swelling of flexible polymer substrates is crucial in various fields from smart structures to flexible electronics. In this study, the prediction method for time-dependent hygroscopic deformation is presented by employing the finite element method (FEM). In order to precisely consider the strain gradients inside the substrate, moisture distribution depending on time is quantitatively investigated by a moisture absorption analysis and sequentially combined with a mechanical deformation analysis. The essential hygroscopic properties including the saturated moisture content, moisture diffusivity, and the coefficient of moisture expansion are precisely measured. Through the application of these hygroscopic properties to a hygro-mechanical analysis model, the moisture distribution and the hygroscopic deformation are quantitatively simulated with time. For the verification of this model, the simulation results of bilayer structures are compared with the experimental results, which are measured using a three-dimensional deformation measurement system. The presented model demonstrates that the global and local hygroscopic deformations are accurately predicted by this approach, showing above 90% averaged accuracy at each time step. These results can be obtained by precisely measured hygroscopic properties and the consideration of the effect of non-uniform distribution on the hygroscopic deformation.

A novel technique for measuring 3D deformation of adhesively bonded single lap joint

An easy-to-implement yet practical single-camera microscopic stereo-digital image correlation (stereo-DIC) technique is proposed for surface three-dimensional (3D) deformation measurement of singe lap joint (SLJ) samples subjected to mechanical loads. The basic principles, optical configurations and implementation procedures of the proposed technique are described in detail. Compared with existing single-camera 2D-DIC technique, which has been regularly used for in-plane deformation measurement of a SLJ specimen, the proposed technique offers the special merit of simultaneously determining all the three displacement components by simply adding two additional optical elements to existing single-camera 2D-DIC systems. The accuracy and effectiveness of the proposed technique is demonstrated by measuring the 3D deformation of a SLJ specimen subjected to quasi-static tensile loads.

Measurement of three-dimensional surface deformation by Cosmo-SkyMed X-band radar interferometry: Application to the March 2011 Kamoamoa fissure eruption, Kīlauea Volcano, Hawai'i

Abstract Three-dimensional (3D) surface deformation is retrieved for the March 6–10, 2011 (UTC dates), Kamoamoa fissure eruption along the East Rift Zone of Kīlauea Volcano, Hawai'i, through the integration of multi-temporal synthetic aperture radar (SAR) interferometry (InSAR) and multiple-aperture interferometry (MAI) measurements from the COSMO-SkyMed X-band SAR. The measurement accuracies of 1) the individual and multi-stacked MAI interferograms and 2) the 3D deformation, which is measured from COSMO-SkyMed data, are assessed using continuous GPS stations. The root-mean-square (RMS) errors of individual MAI interferograms for descending and ascending data are 2.97 ± 0.6 cm and 3.20 ± 0.62 cm, respectively. The MAI interferograms stacked from multi-temporal observations can produce better results by emphasizing surface deformation signals, with the RMS errors of 1.06 and 1.24 cm for descending and ascending data, respectively. The empirical equations for measurement uncertainties are determined with respect to interferometric coherence for individual and stacked MAI interferograms. An assessment of the 3D components of deformation was performed as well, and RMS errors of 0.75, 0.83, and 0.68 cm were estimated in the east, north, and up directions. A performance test of magma source model parameter estimations was carried out by using the InSAR and 3D measurements. From the 3D deformation field, we found that the magma chamber source at the Kīlauea caldera should be modeled by the spheroid source rather than the simple point source. The performance comparison between the InSAR and 3D modeled results showed that the 3D deformation field allows for precise model parameter estimation.

3D deformation measurement based on colorful electronic speckle pattern interferometry

In this paper, we proposed a transient three-dimensional deformation and profile measurement method based on colorful electronic speckle pattern interferometry (ESPI) and wavelet transform. The method employs a color CCD to capture the speckle pattern from three deformation directions (vertical in-plane, horizontal in-plane and out-of-plane) by taking three different colorful lasers as light sources, respectively. The colorful speckle pattern is separated into three images according to different colors. Each separated speckle interferogram is processed with wavelet transform algorithm to demodulate the deformation phase in the corresponding direction and then to get the 3D deformation of the tested object. It can also measure the profile of an object with the out-of-plane speckle pattern. Computer simulation and experimental results are presented to verify that the system can achieve 3D transient deformation and shape measurement using a plate and a cylindrical object as the samples.

On the Extraction of Elastic–Plastic Constitutive Properties From Three-Dimensional Deformation Measurements

In this article, a coupled experimental and numerical method is utilized for characterizing the elastic–plastic constitutive properties of ductile materials. Three-dimensional digital image correlation (DIC) is used to measure the full field deformation on two mutually orthogonal surfaces of a uniaxial tensile test specimen. The material’s constitutive model, whose parameters are unknown a priori, is determined through an optimization process that compares these experimental measurements with finite element simulations in which the constitutive model is implemented. The optimization procedure utilizes the robust dataset of locally observed deformation measurements from DIC in addition to the standard measurements of boundary load and displacement data. When the difference between the experiment and simulations is reduced sufficiently, a set of parameters is found for the material model that is suitable to large strain levels. This method of material characterization is applied to a tensile specimen fabricated from a sheet of 15-5 PH stainless steel. This method proves to be a powerful tool for calibration of material models. The final parameters produce a simulation that tracks the local experimental displacement field to within a couple percent of error. Simultaneously, the percent error in the simulation for the load carried by the specimen throughout the test is less than 1%. Additionally, half of the parameters for Hill’s yield criterion, describing anisotropy of the normal stresses, are found from a single tensile test. This method will find even greater utility in calibrating more complex material models by greatly reducing the experimental effort required to identify the appropriate model parameters.

Accurate three-dimensional shape and deformation measurement at microscale using digital image correlation.

Based on stereomicroscope and three-dimensional (3D) digital image correlation (DIC) method, a non-contact measurement technique is presented to measure the 3D shape and deformation data on miniature specimens and the corresponding microscopic measurement system is developed. A pair of cameras is mounted on a binocular stereo light microscope to acquire pairing micrographs from two different optical paths of a specimen surface spraying with speckle pattern. Considering complex optical paths and high magnification, an accurate equivalent relative calibration method, combining a priori warping functions, is proposed to correct image distortions and optimize the intrinsic and extrinsic parameters of stereomicroscope. Then, a fast one-dimensional synchronous stereo matching method, based on the DIC method and image rectification technique, is proposed to search for discontinuous corresponding points in the pairing micrographs. Finally, the 3D shape is reconstructed from the corresponding points, while the temporal micrographs acquired before and after deformation are employed to determine the full-field deformation. The effectiveness and accuracy of the presented microscale measurement technique are verified by a series of experiments.

Application of the digital phase-shifting method in 3D deformation measurement at micro-scale by SEM

There have been many approaches for three-dimensional (3D) deformation measurement at the macro-scale, but these methods are mostly not applicable to 3D deformation measurement at the micro-scale due to the low resolution. With the broad application of the scanning electron microscope (SEM) at micro-scale measurement, in-situ deformation measurement under SEM has been made feasible. The 3D deformation measurement method based on digital phase shifting and the SEM system is proposed in this paper. In the proposed method, two SEM images of a specimen grating at different tilting angles are required to solve the in-plane and out-of-plane displacement. The digital generated reference grating is superimposed with the SEM images of a the specimen grating at different tilting angles to form the digital moiré. Using the digital phase-shifting method, the phase information of the grating at different tilting angles can be acquired. With the derived relationship between the phase of the grating at different tilting angles and the in-plane and out-of-plane displacement, 3D displacement can be obtained. To verify the feasibility and assess the accuracy, a numerical experiment is conducted to reverse the given in-plane and out-of-plane deformation. The proposed method is used to measure the out-of-plane deformation of aluminum film on a soft substrate. The successful results indicate that this method is feasible and has the potential to be applied in 3D deformation measurement at micro-scale.

Diffraction-Assisted Image Correlation for Three-Dimensional Surface Profiling

The recently developed Diffraction-Assisted Image Correlation (DAIC) method (Xia et al. Exp Mech 53(5):755–765, 2013) provides a simple and accurate means for three-dimensional (3D) full-field deformation measurement. In the DAIC method, a test specimen is viewed through a transmission diffraction grating, resulting in multiple diffracted views of the same specimen that encode 3D geometric information. Here, we extend the original DAIC method to permit quantitative measurement of 3D surface profiles. We show, through a pinhole projection model, that the 3D shape of an object surface can be reconstructed by simply performing two-dimensional digital image correlation (2D-DIC) analysis between the negative and positive first-order diffracted views. Test results on a Barbie doll’s face and a set of well-defined cylindrical, conical and step surfaces are presented to illustrate the implementation and performance of the proposed surface profiling method.

Development of three-dimensional welding deformation measurement based on stereo imaging technique

Due to the rapid improvement of digital cameras, especially the pixel resolution, digital image correlation (DIC) has been introduced to measure the deformation and strain of structures. Using digital cameras for the DIC technique is an easy and fast method for obtaining structural information, represented as all the pixel points in a photo. Because a wide range of structural deformation can be obtained with high accuracy, this method has the potential to be very useful. Currently, DIC can execute a measurement with high accuracy only when the out-of-plane displacement is small. When the out-of-plane displacement is large, the deformation causes the measurement error. Therefore, a stereo imaging method using two digital cameras is proposed in this study. The proposed method can measure not only in-plane deformation but also out-of-plane deformation with high accuracy without calibration of the errors caused by the out-of-plane displacement. In this paper, the measurement accuracy of the proposed method for in-plane deformation and out-of-plane deformation is discussed through the application of a bead-on-plate welding test. The proposed method can measure transverse shrinkage and angular distortion with high accuracy. In contrast to the vernier caliper and laser distance metre measurement methods, which can measure only a few points at a time, the proposed method using two digital cameras can measure the full field in a short time. These results confirm that the proposed method is more advantageous than other methods.

Diffraction Assisted Image Correlation: A Novel Method for Measuring Three-Dimensional Deformation using Two-Dimensional Digital Image Correlation

Digital Image Correlation (DIC) provides a full-field non-contact optical method for accurate deformation measurement of materials, devices and structures. The measurement of three-dimensional (3D) deformation using DIC in general requires imaging with two cameras and a 3D-DIC code. In the present work, a new experimental technique, namely, Diffraction Assisted Image Correlation (DAIC) for 3D displacement measurement using a single camera and 2D-DIC algorithm is presented. A transmission diffraction grating is placed between the specimen and the camera, resulting in multiple images which are then used to obtain apparent in-plane displacements using 2D-DIC. The true in-plane and out-of-plane displacements of the specimen are obtained from the apparent in-plane displacements and the diffraction angle of the grating. The validity and accuracy of the DAIC method are demonstrated through 3D displacement measurement of a small thin membrane. This technique provides new avenues for performing 3D deformation measurements at small length scales and/or dynamic loading conditions.

Development of a Robust Stereo-PIV System for 3-D Soil Deformation Measurement

Abstract This paper presents a robust stereo-particle image velocimetry (Stereo-PIV) system developed for three-dimensional (3-D) soil deformation measurement in geotechnical engineering. Also known as digital image correlation, PIV is a popular image processing technique to measure two-dimensional (2-D) fluid velocity in fluid dynamics. The Stereo-PIV technique extends 2-D deformation measurement to 3-D based on a binocular vision model, where two cameras with a well posed geometrical setting, are utilized to image the same object. Although commercial Stereo-PIV systems are available in the market, the applications of this technique are still limited by their high cost and special hardware requirements. This study presents a robust Stereo-PIV system, which utilizes two standard complementary metal–oxide–semiconductor (CMOS) cameras and two open software packages to apply this technique to geotechnical engineering testing. In order to apply this technique, three steps have to be performed: the first step is the calibration for the system to get the parameters of the two cameras with respect to the region of interest (ROI); the second step is to obtain a series of paired images of the ROI during deformation and calculate the corresponding 2-D displacement fields from these images; and the last step is to construct a 3-D displacement field based on the camera parameters calculated in the first step and the corresponding 2-D displacement vector pairs from the second step. The developed system is applied in a model test to measure 3-D sand deformation around a laterally loaded pile. The results demonstrate that the system can obtain a reasonable result and can be readily adjusted for more advanced 3-D deformation measurement in geotechnical engineering research.

Application of the speckle technique for three-dimensional deformation measurement

In order to obtain more comprehensive three-dimensional (3-D) deformation data, improve the flexibility and precision of 3-D deformation measurement, and describe the real-time displacement of various points in the measurement scope, we researched speckle methods in this field. First, we expounded basic theories of speckle technique and elaborated on several important aspects of 3-D measurement, including camera calibration, images matching, and 3-D coordinate and displacement calculation. Then, we established the relevant mathematical models and developed a corresponding measurement and analysis software, XJTUDIC. Aided with the appropriate hardware devices, this software recorded and analyzed the whole process of tensile deformation. When compared with the results of the simulation analysis using ANSYS, this method achieved a relative error within ±0.75%, demonstrating the reliability, feasibility, and advantage of this method and its corresponding applied software and hardware.

数字散斑相关法和电子散斑干涉术相结合的三维变形测量方法

数字散斑相关法和电子散斑干涉术相结合的三维变形测量方法

1324 電子スペックル干渉計測法による変形前後二枚のスペックルパターンを用いた三次元変形計測法の開発(OS-10 計測技術(3))

1324 電子スペックル干渉計測法による変形前後二枚のスペックルパターンを用いた三次元変形計測法の開発(OS-10 計測技術(3))

Linear friction welding of a near-β titanium alloy

The linear friction welding (LFW) behaviour of near-β titanium alloy Ti–5Al–5V–5Mo–3Cr (Ti-5553) was investigated by varying the processing conditions of frequency and axial pressure. The examined mechanical properties of the welded material included microhardness and tensile properties. The maximum strains experienced by the material during LFW for each set of welding parameters were estimated based on the process parameters and then evaluated using Aramis, a three-dimensional optical deformation measurement system. The LFWed Ti-5553 was examined with electron backscatter diffraction techniques to relate the texture and phase changes to the thermomechanical conditions. Characterisation of the welds included analysis of the microstructural features of the weld region and the thermomechanically affected zone in relation to the parent material.

Determination of Global and Local Tensile Behaviours of Laser Welded Ti-6Al-4V Alloy

In this study, the global and local tensile behaviours of laser welded 5.1-mm thick Ti-6Al-4V alloy were obtained at various welding speeds and defocusing distances using a digital image correlation (DIC) technique with a full field three-dimensional deformation measurement system. The local tensile properties including elastic modulus, yield stress, and maximum plastic strain were determined at various locations by assuming an iso-stress condition. It was found that the elastic modulus and yield stress were maximum in the fusion zone (FZ) and minimum in the heat-affected zone (HAZ). Porosity and underfill defects were the main reasons for the failures in the FZ and/or the HAZ. Maximum plastic strain at fracture was observed at the failure location in most cases.