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Valeri G.,University of South Carolina | Koohbor B.,University of South Carolina | Kidane A.,University of South Carolina | Sutton M.A.,University of South Carolina | Schreier H.,Correlated Solutions, Inc.
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2017

Recent results from a DIC-based experimental analysis conducted to identify the tensile response of materials at high temperature are presented. Full-field deformation response of stainless steel specimen subjected to quasi-static tension at temperatures between 300 and 900 °C is examined using 3D digital image correlation. Band-pass filters along with a blue light source are used in the experimental setup, with images acquired using regular CCD cameras. A portable induction heating device equipped with water-cooled copper coils is used to heat the specimen. The use of this equipment allows for rapid heating of the designated area of interest in a specimen to the desired temperature with fairly uniform temperature distribution. Using the load history and measured full-field strain data as input, a VFM-based approach is implemented to identify the constitutive parameters governing the plastic deformation of the material at high temperatures. © The Society for Experimental Mechanics, Inc. 2017.

Ke X.-D.,Correlated Solutions, Inc. | Schreier H.W.,Correlated Solutions, Inc. | Sutton M.A.,University of South Carolina | Wang Y.Q.,University of South Carolina
Experimental Mechanics | Year: 2011

Increasing interest in the use of digital image correlation (DIC) for full-field surface shape and deformation measurements has led to an on-going need for both the development of theoretical formulae capable of providing quantitative confidence margins and controlled experiments for validation of the theoretical predictions. In the enclosed work, a series of stereo vision experiments are performed in a manner that provides sufficient information for direct comparison with theoretical predictions using formulae developed in Part I. Specifically, experiments are performed to obtain appropriate optimal estimates and the uncertainty margins for the image locations/displacements, 3-D locations/displacements and strains when using the method of subset-based digital image correlation for image matching. The uncertainty of locating the 3-D space points using subset-based pattern matching is estimated by using theoretical formulae developed in Part I and the experimentally defined confidence margins for image locations. Finally, the uncertainty in strains is predicted using formulae that involves both the variance and covariance of intermediate variables during the strain calculation process. Results from both theoretical predictions and the experimental work show the feasibility and accuracy of the predictive formulae for estimating the uncertainty in the stereo-based deformation measurements. © 2011 Society for Experimental Mechanics.

Wang Y.-Q.,University of South Carolina | Sutton M.A.,University of South Carolina | Ke X.-D.,Correlated Solutions, Inc. | Schreier H.W.,Correlated Solutions, Inc. | And 2 more authors.
Experimental Mechanics | Year: 2011

Using the basic equations for stereo-vision with established procedures for camera calibration, the error propagation equations for determining both bias and variability in a general 3D position are provided. The results use recent theoretical developments that quantified the bias and variance in image plane positions introduced during image plane correspondence identification for a common 3D point (e.g., pattern matching during measurement process) as a basis for preliminary application of the developments for estimation of 3D position bias and variability. Extensive numerical simulations and theoretical analyses have been performed for selected stereo system configurations amenable to closed-form solution. Results clearly demonstrate that the general formulae provide a robust framework for quantifying the effect of various stereo-vision parameters and image-plane matching procedures on both the bias and variance in an estimated 3D object position. © 2011 Society for Experimental Mechanics.

Makeev A.,University of Texas at Arlington | He Y.,University of Texas at Arlington | Schreier H.,Correlated Solutions, Inc.
Strain | Year: 2013

This work presents a thorough description of a short-beam shear (SBS) test method coupled with digital image correlation (DIC) for the measurement of shear stress-strain curves of polymer matrix composites. The method provides a time- and cost-effective alternative to established methods, and the authors hope this work can serve as a starting point for discussions on the developments of new standards for the characterisation of shear stress-strain curves for composites. The experimental set-up, including several modifications to the American Society of Testing and Materials current standard configuration, is described. Implementation of the DIC technique to obtain accurate surface strain in the SBS specimens is also presented. Accuracy of beam theory-based shear stress calculation is assessed using a non-linear finite element model (FEM). A simple means to improve the accuracy of the closed-form shear stress approximation is provided. Glass/epoxy and carbon/epoxy composite material systems are used to demonstrate the developed method. Strain surveys are conducted to compare the experimentally generated and FEM-computed strain fields and verify the accuracy of the shear stress-strain curves. Shear stress-strain response generated from SBS tests is also compared with V-notched beam test results for further verification. © 2013 Wiley Publishing Ltd.

Khatibi G.,University of Vienna | Lederer M.,University of Vienna | Byrne E.,Correlated Solutions, Inc. | Kotas A.B.,University of Vienna | And 2 more authors.
Journal of Electronic Materials | Year: 2013

The stress-strain response of miniaturized Sn-Ag-Cu (SAC) lead-free solder joints in the thickness range of 80 μm to about 1.1 mm was studied. A high-resolution three-dimensional (3D) digital image correlation system was used for in situ measurement of displacement and strain fields in the solder joints during tensile testing. These measurements showed that the localization of plastic strain and stress buildup occurs mainly at the interface of the solder. With increasing solder gap thickness the size of the plastically deformed zone in the solder increases, resulting in transformation of a brittle interfacial fracture to a ductile fracture within the bulk of the solder. The experimental deformation plots of solder joints and strain-rate-dependent tensile tests on bulk solder material were used to establish a new constitutive material model for the solder. This strain-rate- and pressure-dependent material model was implemented in ABAQUS through the user subroutine CREEP. In agreement with the experiments, the finite-element method simulation revealed a pronounced thickness effect leading to higher tensile strength of thinner solder joints. © 2012 TMS.

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2015

ABSTRACT:A cooperative small business and university research and development program is proposed to begin development of a robust, non-contacting, digital image correlation based, full-field strain measurement system for high temperature applications. The Phase I studies will demonstrate that a robust high temperature digital image correlation system (HTDICS) can be developed that is capable of acquiring full field deformation measurements (a) over a range of temperatures from room temperature to 1800F and higher, (b) over the same range of temperatures while subjected to different loading rates, including high levels of broadband acoustic loading and (c) at near real-time or at real time rates for immediate visualization of the deformation fields and potentially control of portions of the experiment.BENEFIT:Development of an HTDICS capable of acquiring full-field measurements at high temperature in quasi-real time will provide unprecedented ability for investigators to monitor progressive damage accumulation. This will improve understanding of the evolution processes prevalent in modern material systems subjected to aggressive environmental conditions, resulting in a more efficient (e.g. cost effective) life cycle testing environment without service interruptions. Furthermore, if HTDICS measurements can be acquired in real time, then it offers the potential for real-time control of experiments so that the environment can be altered in response to material changes in a manner that would increase understanding of the damage progression processes. Of course, the ability to acquire real time deformation measurements has broader implications regarding the ability to perform experiments with feedback control based on direct measurements of material response, a possibility that has hitherto been unattainable. Finally, when a structure (e.g. hypersonic vehicle/structure) is subjected to higher rate excitation/loading, then the ability to obtain near real time measurements provides investigators with the ability to modify the excitation so that structural failure does not occur.

Agency: Department of Defense | Branch: Army | Program: SBIR | Phase: Phase I | Award Amount: 119.26K | Year: 2010

The availability of ultra-high speed imaging equipment capable of frame rates up to 1 GHz has opened the potential for measurement of full-field three-dimensional deformation data during highly dynamic events by employing the digital image correlation method. However, due to the characteristics of ultra-high speed cameras as well as experimental conditions during ballistic events, the application of digital image correlation is not straightforward. We propose to develop novel image correlation algorithms and data pre- and post-processing technologies that address these issues and utilize the image data from ultra-high speed sensors to its optimal potential. Furthermore, we propose to develop an improved ultra-high speed image sensor that can provide greatly reduced bias in practical applications as well as enhanced light sensitivity. These developments will ultimately result in a full-field deformation measurement system capable of acquiring data at rates of 1 GHz with an accuracy comparable to current quasi-static stereo image correlation systems.

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 750.00K | Year: 2010

A user-friendly software package for rapid fatigue evaluation of specific scalable flaw geometries, as well as stable tearing after crack length reaches a specified size, is being developed. The package will employ modified CRACK3D code and use VCCT with 10-noded tetrahedral elements to determine fatigue crack tip parameters (e.g. dK1, dK2, etc.) for fatigue cracks undergoing (a) mixed mode, in-phase fatigue conditions and/or (b) out-of-phase fatigue conditions, performing research that compares experimental evidence to computational predictions. To simplify the computational overhead, a computational model database with multiple selected flaw geometries and specimen configurations (e.g., corner crack from hole in tension) will be developed and a graphical user interface developed to efficiently convert model data into CRACK3D format for rapid analysis capability of scaled geometric configurations. BENEFIT: Automated scaling of models in the database will increase productivity of aerospace engineering personnel by simplifying the process of (a) building a FE model with cracks in several sizes and configures, (b) automating extraction of information necessary for decision making and (c) extending the concepts not only to uniaxial fatigue but to mixed mode fatigue conditions and even out-of-phase fatigue so that such conditions can be evaluated when necessary. It is expected that initial commercialization will be focused on the USAF and other DoD agencies requiring the use of the specific specimen geometries developed during Phase Additional commercialization will focus on specific structural areas where fatigue crack growth simulations are required on a consistent basis and the need is highest (e.g., tier 1 suppliers). Since the modules developed during this phase will reduce the cost of man power required for conducting crack growth simulations and minimize the requirement on engineer’s knowledge for correct use of the our simulation tool, expansion into these areas is consistent with the capabilities of the Phase II software.

Agency: Department of Defense | Branch: Army | Program: SBIR | Phase: Phase II | Award Amount: 729.05K | Year: 2012

We propose to develop and implement a full-field, non-contacting deformation and strain measurement system capable of operating at frequencies above 1 MHz with unprecedented accuracy. The system will incorporate two ultra-high speed cameras in order to obtain three-dimensional shape and deformation data using the digital image correlation method. To obtain optimal accuracy at high rates, we propose to implement optimized digital image processing algorithms to mitigate artifacts caused by the ultra high speed imaging sensor as well as the experimental conditions encountered during blast testing. The developed error mitigation algorithms will be incorporated into the proven digital image correlation software Vic-3D, and the system will be validated through extensive experiments. At the conclusion of the project, a fully functional prototype system will be delivered.

Apparatuses and methods related to measuring motion or deformations of vibrating objects are provided. A plurality of images of an object are acquired in synchronization with a plurality of determined times of interest during oscillation of the object. The plurality of images are compared to obtain one or more quantities of interest of the object based at least in part on the plurality of images.

Loading Correlated Solutions, Inc. collaborators
Loading Correlated Solutions, Inc. collaborators