There are some Polyurethane compression test specimens (According to ASTM-D575 standard - 12mm thickness) in 3 hardness 55, 65 and 75 ShoreA. The test results are reported in the form of time-force-displacement and now I'm trying to plot true stress-strain curve of compression behavior of these specimens. If the strain will be calculated using "delta l / l" formula (engineering strain), the strain range will be 0-100% that is physically sensible but using the strain integration (integral of "dl/l") (true strain), the strain is from 0 to near 300% (the specimens compressed about 11.8 mm). Now, my question is that, this range for true strain is correct? and what does physically means?
Thanks in advance, best regards.