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Digital image correlation is an excellent strain measurement technology (especiallyuseful for high temperature creep tests). The below are two images taken using adigital image correlation technique on a piece of prestressing steel. The top imageillustrates time zero with an applied stress of zero. The second photo below showsthe specimen at a test time of 100 seconds. That image shows the bar maintainingan applied stress of 1950 MPa (a stress much below ultimate). The speckle paintedpattern shown on the steel in the images allows a 'software' to track the movementof the bar as it deforms (strains) between different pictures. The software tracks tinypatches. Think of them like a box as shown below. The software will tell the userhow much this patch moves between the images. In this example the software wouldindicate that Patch A moved75 pixels, where Patch B moved 115 Pixels.

Assuming the pixel movement of both patches above as provided from the digitalimage correlation software, calculate both the engineering and true strain in thepiece of steel.Assuming the original diameter of the steel bar was 4.4 mm, calculate the new(а).(b).diameter of the bar at stress of 1950 MPa.

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