Having been cooled to room temperature, the
fixed specimen was tested to failure again. The ratio of tensile
strength of the healed specimen to that of the virgin one gave
healing efficiency. The tests were repeated for several times to
study the multiple healing ability. Each batch included six specimens
to yield average value. It is worth noting that tensile test is
inherently designed to characterize bulk continuum deformation
leading up to failure, but gives little information about failure itself.
The ultimate stress and strain values might be misleading as the
material necks prior to failure (which is not applicable for the
polyurethane studied in this work). Crack propagation test focusing
on characterizing the regime of material response is the most
relevant to self-healing functionality. Employment of suitable
specimen geometry is critical for evaluation of self-healing materials