Dynamic indentation system

Abstract

The dynamic indentation system cyclically indents a test material for the purpose of determining mechanical properties that cannot be measured directly, such as in-plane wall stress in intact hearts. A probe or an end surface thereof cyclically indents the test material while the indentation stress acting on the face of the probe and the position of the probe are measured. The indentations can be servo-controlled for added stability. The transverse stiffness of the material is calculated as the slope of the relation between the indentation stress and indentation strain during each indentation cycle. The transverse stiffness is then used as an estimate of wall stress, and the relation between the transverse stiffness and in-plane strain can be used as a direct estimate of material properties. The dynamic indentation system is suitable for estimating in-plane wall stress and material properties from different parts of a test material. Since the vibrations are high in frequency, any gross movement of the test material or of the probe during the period of one oscillation is very small and does not influence the transverse stiffness. The dynamic indentation system allows, for example, estimation of wall stress throughout the course of a single cardiac contraction.

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