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In recent years, dynamic indentation tests have been shown to be useful bothin identification of mechanical properties of biological tissues (such asarticular cartilage) and assessing their viability. We consider frictionlessflat-ended and spherical sinusoidally-driven indentation tests utilizingdisplacement-controlled loading protocol. Articular cartilage tissue is modeledas a viscoelastic material with a time-independent Poisson's ratio. We studythe dynamic indentation stiffness with the aim of formulating criteria forevaluation the quality of articular cartilage in order to be able todiscriminate its degenerative state. In particular, evaluating the dynamicindentation stiffness at the turning point of the flat-ended indentation test,we introduce the so-called incomplete storage modulus. Considering the timedifference between the time moments when the dynamic stiffness vanishes(contact force reaches its maximum) and the dynamic stiffness becomes infinite(indenter displacement reaches its maximum), we introduce the so-calledincomplete loss angle. Analogous quantities can be introduced in the sphericalsinusoidally-driven indentation test, however, to account for the thicknesseffect, a special approach is required. We apply an asymptotic modelingapproach for analyzing and interpreting the results of the dynamic sphericalindentation test in terms of the geometrical parameter of the indenter andviscoelastic characteristics of the material. Some implications tonon-destructive indentation diagnostics of cartilage degeneration arediscussed.

european journal of mechanics - a/solids

Accounting for the thickness effect in dynamic spherical indentation of  a viscoelastic layer: Application to non-destructive testing of articular  cartilage