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Elizabeth Jones

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University of Illinois at Urbana-Champaign

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23 Sep 2014 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... 208 18
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5.0 | 7 ratings
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11 Sep 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 Jorge,

Yes, you can get the average values from the plot generated using the "Spatial Average" function. Simply save the plot, close out of the GUI, open the plot, and then use the following code:

ax = gca; %Gets the current axis
objs = get(ax,'children'); %Gets the objects of the current axis
y_data = get(objs,'ydata'); %Gets the y-data from the objects, i.e. the average strain values

The above method is a general method that you can use to get the data from any plot in Matlab. I have considered making an option directly in the GUI to save the data as a .mat file in addition to plotting the data, but as of now, I have not implemented this functionality. However, the method described above will work with little extra effort.

Thank,
Elizabeth

28 Aug 2014 Ternplot Plots ternary phase data on a ternary phase diagram. Author: Carl Sandrock

Great function, thanks for putting this up. It worked right away, without any tweaking, which is not always the case for files on FileExchange but is always much appreciated. One feature that I did not see right away is the ability to set the size and style of the tick mark labels and axis labels, i.e. change from size 10 to size 12, make bold, etc. I had to go and select each tick mark label individually to change its size. Other than that, super program.

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

Comments and Ratings on Elizabeth's Files View all
Updated File Comment by Comments Rating
11 Sep 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 Jorge,

Yes, you can get the average values from the plot generated using the "Spatial Average" function. Simply save the plot, close out of the GUI, open the plot, and then use the following code:

ax = gca; %Gets the current axis
objs = get(ax,'children'); %Gets the objects of the current axis
y_data = get(objs,'ydata'); %Gets the y-data from the objects, i.e. the average strain values

The above method is a general method that you can use to get the data from any plot in Matlab. I have considered making an option directly in the GUI to save the data as a .mat file in addition to plotting the data, but as of now, I have not implemented this functionality. However, the method described above will work with little extra effort.

Thank,
Elizabeth

10 Sep 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 jorge

Hello Elizabeth,

I would like to know if it´s possible to get a list of average values of strain over entire images. i mean, can i get the values of the average strain plotted in spatial Average plots?

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.

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