scholarly journals Real-Time GPU-Based Digital Image Correlation Sensor for Marker-Free Strain-Controlled Fatigue Testing

2019 ◽  
Vol 9 (10) ◽  
pp. 2025 ◽  
Author(s):  
Andreas Blug ◽  
David Joel Regina ◽  
Stefan Eckmann ◽  
Melanie Senn ◽  
Alexander Bertz ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Real Time ◽  
Digital Image ◽  
Graphics Processing Units ◽  
Fatigue Testing ◽  
Sampling Rate ◽  
Surface Preparation ◽  
Image Correlation ◽  
Marker Free ◽  
Path Dependent

Digital image correlation (DIC) is a highly accurate image-based deformation measurement method achieving a repeatability in the range of   σ =   10−5 relative to the field-of-view. The method is well accepted in material testing for non-contact strain measurement. However, the correlation makes it computationally slow on conventional, CPU-based computers. Recently, there have been DIC implementations based on graphics processing units (GPU) for strain-field evaluations with numerous templates per image at rather low image rates, but there are no real-time implementations for fast strain measurements with sampling rates above 1 kHz. In this article, a GPU-based 2D-DIC system is described achieving a strain sampling rate of 1.2 kHz with a latency of less than 2 milliseconds. In addition, the system uses the incidental, characteristic microstructure of the specimen surface for marker-free correlation, without need for any surface preparation—even on polished hourglass specimen. The system generates an elongation signal for standard PID-controllers of testing machines so that it directly replaces mechanical extensometers. Strain-controlled LCF measurements of steel, aluminum, and nickel-based superalloys at temperatures of up to 1000 °C are reported and the performance is compared to other path-dependent and path-independent DIC systems. According to our knowledge, this is one of the first GPU-based image processing systems for real-time closed-loop applications.

scholarly journals Significance of Parallel Computing on the Performance of Digital Image Correlation Algorithms in MATLAB

Designs ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 15
Author(s):  
Andreas Thoma ◽  
Abhijith Moni ◽  
Sridhar Ravi
Keyword(s):  
Digital Image Correlation ◽  
Real Time ◽  
Digital Image ◽  
Correct Choice ◽  
Image Correlation ◽  
Particle Swarm Algorithm ◽  
Processing Unit ◽  
Time Analysis ◽  
The Real ◽  
Real Time Analysis

Digital Image Correlation (DIC) is a powerful tool used to evaluate displacements and deformations in a non-intrusive manner. By comparing two images, one from the undeformed reference states of the sample and the other from the deformed target state, the relative displacement between the two states is determined. DIC is well-known and often used for post-processing analysis of in-plane displacements and deformation of the specimen. Increasing the analysis speed to enable real-time DIC analysis will be beneficial and expand the scope of this method. Here we tested several combinations of the most common DIC methods in combination with different parallelization approaches in MATLAB and evaluated their performance to determine whether the real-time analysis is possible with these methods. The effects of computing with different hardware settings were also analyzed and discussed. We found that implementation problems can reduce the efficiency of a theoretically superior algorithm, such that it becomes practically slower than a sub-optimal algorithm. The Newton–Raphson algorithm in combination with a modified particle swarm algorithm in parallel image computation was found to be most effective. This is contrary to theory, suggesting that the inverse-compositional Gauss–Newton algorithm is superior. As expected, the brute force search algorithm is the least efficient method. We also found that the correct choice of parallelization tasks is critical in attaining improvements in computing speed. A poorly chosen parallelization approach with high parallel overhead leads to inferior performance. Finally, irrespective of the computing mode, the correct choice of combinations of integer-pixel and sub-pixel search algorithms is critical for efficient analysis. The real-time analysis using DIC will be difficult on computers with standard computing capabilities, even if parallelization is implemented, so the suggested solution would be to use graphics processing unit (GPU) acceleration.

SIF determination with digital image correlation

2015 ◽  
Vol 6 (6) ◽  
pp. 668-676 ◽  
Author(s):  
Paulo J Tavares ◽  
Tiago Ramos ◽  
Daniel Braga ◽  
Mario A P Vaz ◽  
Pedro Miguel Guimarães Pires Moreira
Keyword(s):  
Experimental Data ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Fatigue Testing ◽  
Image Correlation ◽  
Image Method ◽  
Mode Ii ◽  
Pure Mode ◽  
Great Success ◽  
Content Type

Purpose – Hybrid methods, wherefore numerical and experimental data are used to calculate a critical parameter, have been used for several years with great success in Experimental Mechanics and, in particular, in fracture mechanics. The purpose of this paper is to report on the comparison of the strain field from numerical modelling forecasts against the experimental data obtained with the digital image correlation method under Mode II loading in fatigue testing. The numerical dual boundary element method has been established in the past as a very reliable method near singular regions where stresses tend to grow abruptly. The results obtained from the strain data near the crack tip were used in Williams expansion and agree fairly well with both the numerical results and the analytical solution proposed for pure Mode II testing. Design/methodology/approach – The work presented in this note is experimental. The proposed methodology is of an hybrid experimental/numerical nature in that a numerical stress intensity factor calculation hinges upon a stress field obtained with an image method. Findings – The obtained results are an important step towards the development of a practical tool for crack behaviour prediction in fatigue dominated events. Research limitations/implications – The results also stress the necessity of improving the experimental techniques to a point where the methods can be applied in real-life solicitations outside of laboratory premises. Originality/value – Although several research teams around the globe are presently working in this field, the present research topic is original and the proposed methodology has been presented initially by the research team years ago.

A new surface preparation method for microscopic digital image correlation applications

2019 ◽  
Vol 12 ◽  
pp. 377-382
Author(s):  
Edgar Peretzki ◽  
Martin Stockmann ◽  
Thomas Lehmann ◽  
Jörn Ihlemann
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Preparation Method ◽  
Surface Preparation ◽  
Image Correlation
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