====    Digital image correlation methods    ====   

	This embodiment of digital image correlation uses digital cameras and an interface card connected to a Windows 7 computer. Proprietary software requires a license embedded in USB stick.  As of Jan. 2016, one is for data acquisition and one is for analysis. It would fail to work if both were plugged in. As of March 1 2016, there is only one USB stick which suffices; no warning was given. 
	Cameras: two 5.0-MP  (3.45 micrometer sensor pixel size), 8-mm, 17-mm, and 35-mm lenses. Longer focal length entails a tighter field of view. Resolution is quoted as up to 1/100,000 field-of-view. For 3D, use two cameras. For 2D use one camera. Cameras plug into an adapter that pugs into the right side of the computer. 
	Specimens must provide contrast via a speckle pattern. The speckles must be large enough to be resolved by the digital camera but small enough that there are many speckles in an image. If the specimen does not have its own contrast pattern, one can spray it with a brief burst of spray paint in the fume hood or use rubber stamp to ink a speckle pattern. 
	Start the computer and provide the password meerc twice. A white screen appears first; give password though it may not be obvious why. Enter the password again after about 45 seconds of loading. A blue Correlated Solutions screen should appear. 

Data acquisition
	Plug the license USB stick into the computer.  Plug in the second power plug for the camera controller. 
	Hit camera icon at lower left. A prompt appears, where to save image data. Provide a location. The physical camera has a lens cap; remove it. Focus the lens by rotating it until the image on the screen appears sharpest. The lens can unscrew as much as 12 mm before it comes off. Do not unscrew it that much. The lens has an aperture control; numbers are inverse to aperture diameter. So a small number corresponds to a large aperture that lets in more light but allows less depth of field. The aperture control has a screw lock so that the user can prevent aperture from changing during focusing. 
	Red areas on the screen image indicate overexposure. Adjust the lens aperture until they disappear but the image is not too dark. There is a slider under the screen image that adjusts shutter speed, which also controls the exposure, hence image brightness. Zoom using a mouse wheel or the right part of track pad (slide finger up or down on track pad). One can zoom using controls on screen: right click on zoom menu to get a choice. 	
	To capture an image, hit the space bar on the computer. Deform the object, then capture another image. When done, quit camera application and remove acquisition USB stick.

Data analysis
	Plug the analysis USB stick into the computer but not the acquisition one.  
	For 2D analysis hit VIC2D icon lower left to launch. 
	Load the images using link, speckle images or star icon that looks like a lumpy four pointed star. Go to your folder, select images for undeformed and deformed object. 
	Calibrate the scale. Hit calibration link at top, select calibrate scale. Use tools, 3rd icon from left, cross. Draw a line on the image corresponding to a distance that you know; hold pressure on track pad, then release button. It is easier to use 2nd icon from left, manually select. Enter the length of the line in mm. Hit OK. It may reply image is only some percent of diagonal. Go ahead anyway. If calibration is not done successfully one can still obtain strain, but displacements are given only in pixels. 
	Select an area of interest (AOI). Use AOI tools, a square, 3rd icon from left. Select area on image; it will turn blue. Release button. Area turns red. It can be resized if needed by moving corner points. 
	Choose averaging area (subset)(default is 21 pixels) and step size (step) (default is 5). A small square in the middle of the area of interest shows the subset size. This square must be on a solid part of the specimen, not a hole, because the analysis begins at the square. If need be, drag the square. 
	If subset is too large, results are blurred, preventing the capture of fine gradients. If subset is too small, results may be noisy or no results at all. Subset should be larger than the smallest speckle. Step 5 means analyze every fifth point.  
	Do analysis. Hit green arrow, top icons. Alternatively, hit Data link, top row, start analysis, hit run. 
Get color map, then close that window. If you try to go back to control window, color map blinks and will not let you. So close it. 
	Choose data tab under project. Double click deformed image. Get picture image at right. 
	Hit left tab, contour. Choose the variable you want to display. Image at right shows a color contour map of that variable. X and Y are coordinates calibrated in distance; U and V are calibrated displacements. It is possible to change the scale. If there are dark spots or regions without color, the algorithm was unable to calculate deformation in those regions, called drop outs. If there are too many of these, it may help to redo the analysis using a larger averaging area or subset. The disadvantage is that sharp gradients of deformation will be blurred. 
	Obtain point-wise results. Under inspector tools on left pane, hit point inspect to obtain value at a point. There is also an icon for extensometer. Draw a line using the left mouse button. The displayed number is the strain in the direction of the line, based on averaging. 
	Obtain graphical results. Hit plot tab, choose inspector, use inspector tools. Inspect line. Use dotted line icon. Draw a line on the image for the abscissa direction for your plot. The line cannot extend beyond the colored area that has been analyzed. The line should turn red when you tap the track pad. 
	If you want to draw another line, delete the first one as follows. Hit skull icon, 2nd from right, click on end point of line to delete it. 
	To draw a graph, hit X icon on right of set, pane on left, inspector tools. A window appears. Set variables you want to plot. 
	Save data. Set check mark only  for deformed image, otherwise the data will contain extra columns of zero deformation for the undeformed image. In data, x_c refers to calibrated abscissa in mm; similarly u_c calibrated displacement; x and u are in pixels. One can save graph as an image or save data. It may be impossible to save data with no reason given. If that happens redo the analysis beginning with a larger subset area. Check the data. If there are meaningless data or zeroes where they should not be, redo the analysis beginning with a larger subset area. 
	Quit data analysis program; it asks whether you want to save project. If you save it, then there is no need to redo calibration or analysis. Click on saved project: see region of interest selected in red. Go to data tab on left to see contour plots or plot more variables.