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Elizabeth Jones

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University of Illinois at Urbana-Champaign

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15 Aug 2013 Screenshot Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones digital image correla..., experimental mechanic..., noncontact, optical, fullfield strains, fullfield displacemen... 155 16
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13 May 2014 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones

Hi Alberto,

I am not familiar with the PIVMat Toolbox, so I am not sure what the best way is to reformat the data from my DIC code for use with the PIVMat Toolbox. However, from your description, it looks like you need the x- and y-coordinates of the control points and the u- and v- components of the displacements. (I assume you want the displacement components when you say velocity components?) The grid coordinates are found in the .mat file “grid_data”, and the displacement components are found in the .mat file “disp_raw_data” (for the raw correlation data) and “disp_smooth_data” (for the smoothed displacement field, if you have run “compute_data_GUI”). Does this provide the information you need?

Cheers,
Elizabeth

05 May 2014 Fast and Robust Curve Intersections Computes intersection points of two curves. Author: Douglas Schwarz

18 Apr 2014 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones

Hi Deborah,

Poisson's ratio is the negative of the ratio of the axial strain to the transverse strain when a specimen is undergoing uniaxial tension or uniaxial compression. If the direction of force is, for example, in the y-direction, then Poisson's ratio = -e_yy / e_xx. Assuming you don't have plastic deformation, using the large strains (E_yy and E_xx) will give the same result.

To access the small and large strains, load "DU_data" into your workspace. All of the strain matrices are in the structures "large_strain" and "small_strain".

Cheers,
Elizabeth

02 Jan 2014 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones

Hi Stephen,

You have the choice to run the code in serial mode or in parallel mode. The benefit to running the code in parallel mode is the reduced computation time, but it does require the Parallel Computing Toolbox. If you do not have the Parallel Computing Toolbox, you may run the code in serial mode. You'll get the same results, but it will take longer to process large batches of images.

Thanks,
Elizabeth

04 Dec 2013 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones

Hi Marcraven,

Thanks for your interest in my DIC code. There are two principle displacement data files. The first, disp_raw_data.mat, is generated when you run “correlate_images_GUI”, and is a calculation of the displacements before any smoothing has been done. These displacements are in terms of pixels. The second, disp_smooth_data.mat, is generated when you run “compute_data_GUI.” These displacements are scaled and smoothed according to the parameters you set in “compute_data_GUI.”

To work with the raw displacements, type “load disp_raw_data” in the command window. Two variables, dispx_raw and dispy_raw, should now be in your workspace. These matrices are the horizontal (x) and vertical (y) displacements respectively. The rows of the matrices represent the control points from your correlation, and the columns represent the images that you correlated. For example, the x-displacements for image 5 would be the entire column 5 of dispx_raw.

Similarly, to work with the scaled and smoothed displacements, type “load disp_smooth_data” into the command window, and the two variables dispx_smooth and dispy_smooth will be in your workspace.

Please let me know if you have further questions.

Sincerely,
Elizabeth

Comments and Ratings on Elizabeth's Files View all
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14 May 2014 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones Alberto

Yes, thank you very much Elizabeth! More or less I've managed to get what I wanted.

Best,

Alberto.

13 May 2014 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones Jones, Elizabeth

Hi Alberto,

I am not familiar with the PIVMat Toolbox, so I am not sure what the best way is to reformat the data from my DIC code for use with the PIVMat Toolbox. However, from your description, it looks like you need the x- and y-coordinates of the control points and the u- and v- components of the displacements. (I assume you want the displacement components when you say velocity components?) The grid coordinates are found in the .mat file “grid_data”, and the displacement components are found in the .mat file “disp_raw_data” (for the raw correlation data) and “disp_smooth_data” (for the smoothed displacement field, if you have run “compute_data_GUI”). Does this provide the information you need?

Cheers,
Elizabeth

07 May 2014 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones Alberto

Hi Elizabeth!

I am using your code so as to then post process the vector field with PIVMat Toolbox to reconstruct the height of the surface, but the latter (in particular, the function 'plotvec.m') requires an specific format for the .mat files to work. It includes the x and y coordinates, the x and y velocity components, etc. :

For vector fields, the PIVMat structure F contains the following fields:
x,y vectors containing the X and Y coordinates
vx,vy (vz) matrices of the x, y (and z) components of the velocity
ysign string, upward or downward Y axis
namevx, unitvx, namex, unitx... strings
name name of the VEC/VC7 file from which originates V
setname name of the parent directory (called 'SET' in DaVis)
Attributes Additional informations from DaVis (see getattribute)
choice An array of 6 integers, giving the 1st, 2nd, 3rd, 4th choice vectors, the number of filled/processed vectors and the number of missing vectors.
history Remind from which command V has been obtained

Do you know if there is a simple way to get this format from the files your code provide? If not, could you tell me in which files I can find the information I need?

Thank you in advance.

Best regards,

Alberto.

22 Apr 2014 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones Deborah

Thank you very much Elizabeth!

18 Apr 2014 Improved Digital Image Correlation (DIC) Calculate full-field displacements and strains from a set of images with a random speckle pattern. Author: Elizabeth Jones Jones, Elizabeth

Hi Deborah,

Poisson's ratio is the negative of the ratio of the axial strain to the transverse strain when a specimen is undergoing uniaxial tension or uniaxial compression. If the direction of force is, for example, in the y-direction, then Poisson's ratio = -e_yy / e_xx. Assuming you don't have plastic deformation, using the large strains (E_yy and E_xx) will give the same result.

To access the small and large strains, load "DU_data" into your workspace. All of the strain matrices are in the structures "large_strain" and "small_strain".

Cheers,
Elizabeth

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