Distance between two marks on a tensile test sample
Jorge Garcia
5 Posts
I need to measure the distance between two moving marks on a silicone rubber specimen while the specimen is being pulled apart until it breaks.
To picture what I need to do, imagine two objects 3 m apart. They both start travelling in the same direction at the same time, but the one in front is travelling at a much greater speed and the difference in speed changes with time. The task for Tracker is to measure the distance between the two moviing objects.
I've managed to get Tracker to track each mark individually, but not at the same time (otherwise I could have taken the difference between the x or y values of each mark). The online manual for tracker suggests that I can set up a "tape" and attach each end of the tape to each object/marker.
But I have not been able to get tracker to attach both ends of the tape to separate moving targets and autotrack the distance between the two moving targets
Has anyone tried to do something similar with Tracker? Do you have any hints? Do you know of any video tutorials showing how to do this?
Solved (sort of): Distance between two marks on a tensile test sample -
Jorge Garcia
5 Posts
Basically I did what the Tracker help file says - (under the Tape Measure)
Attached a Marker to each end of a Tape Measure and used Auto Tracker to track first one Marker and then the second Marker
I had not realised that this had to be done sequentially for each marker and that the values of the tape measure would be updated after the second auto track
The values of length on the tape measure are automatically updated after the second Auto Track and the table of the tracked tape measurements can be cut and pasted into excel for further processing (A plot of stress vs strain).
I have not figured out whether auto tracker can auto track the two ends of the tape simultaneously, in the meantime, I'll make this work.
Re: Distance between two marks on a tensile test sample -
Lester Frederick
1 Posts
Thanks for sharing your experience with Tracker! It's good to know that the automatic updates after tracking both ends of the tape measure are working for you. I totally get the frustration with the need for sequential tracking, especially if you're trying to save time. If Tracker doesn't support simultaneous tracking of both ends, your workaround of tracking them separately and then combining the data in Excel sounds like a solid plan. Just make sure the markers are as clear and consistent as possible to get the most accurate measurements. Good luck with your stress vs. strain plots--hope everything goes smoothly!
