Abstract:

An automated measurement system for complex shear compliance, J[sup *]=J[sup ']-iJ[sup ''], shear modulus, G[sup *]=G[sup ']+iG[sup ''], and shear wave velocity and attenuation from 2 to 10 000 Hz at temperatures from -25 to 150 (degrees)C [E. R. Fitzgerald, Proc. Am. Chem. Soc. 60, 573--578 (1989); U. S. Patent 5,081,870 (1992)] has been used to determine these viscoelastic parameters for blubber and skin of several marine mammals. Excised samples from two stranded harbor seals, for which rescue efforts failed, were measured at 20 (degrees)C from 2 to 1000 Hz, at short intervals, from 1.9 to 12 h after death. Values of the elastic (J[sup ']) and viscous (J[sup '']) compliance components decreased with time after death, and showed sharp, ``life-to-death'' slope transitions at 4 to 6 h after death, as found in prior animal tissue measurements [Fitzgerald et al., J. Acoust. Soc. Am. 29, 61--64 (1957); E. R. Fitzgerald, Biorheology 12, 397--408 (1975)]. These measurements are compared with those previously reported for pilot whale and dolphin blubber [E. R. Fitzgerald and J. W. Fitzgerald, Mater. Sci. Eng. C 2, 209--214 (1995); Proc. Third Int. Conf. Intel. Mater. SPIE 2779, 83--88 (1996)]. [This work was supported, in part, by the Advanced Research Projects Agency and the Office of Naval Research.]