MTS Fundamental Video Extensometer - Manual (Page 19)

Principle of Markers Tracking
Fundamental Video Extensometer 19
Seven Markers
A seven-markers test makes it possible to perform a tensile test on sample with a
banded structure. The configuration allows you to measure the longitudinal strain
(by interpolation of the partial strains) in a material section where the transverse
strain is measured. Volume variation during the test is deduced with the
assumption of transverse isotropy.
The markers must be placed as indicated on the figure below:
Starting with the central marker, add two other markers on both sides at equal
distance from the central marker and the border of specimen, and then add the
last four markers along the specimen.
The four extreme markers positioned horizontally and vertically must form a
square.
If the four markers do not form a square it can cause a problem of
repeatability between specimens of the same materials and less accuracy
on the measurement.
It is very important that the four markers form a square because they define the
representative volume element which correctly defines the material behavior.
Width 1