An investigation of the stress relaxation spectrum of the aortic valve

Traditionally, the viscoelastic behaviour of the aortic valve cusp materials has been investigated through low speed uniaxial tensile testing. Although stress relaxation and creep analysis can be derived from such testing, these tests tend to miss the fundamental relaxation time (time constant) and distort the relaxation spectrums. A high speed hydraulic tensile system connected to a high speed data acquisition system was utilized to acquire the initial (1/100 sec.) relaxation of the aortic valve. Using feedback and set point control of a large hydraulic actuator, testing strain rates of the order 400%/s were achievable. The data was then processed through a non-linear adaptive algorithm to fit a least square decaying exponential curve and produce relaxation spectra. Preliminary result illustrate two distinct clusterings of the relaxation spectra, indicative of two regions of relaxation (fast initial and slow infinite)