Inflation-extension behaviour of 3D printed elastomer tubes and their constitutive description

It is known that arteries in situ are axially prestretched. This can be proved during an autopsy when a cylindrical segment of an artery is removed from a body. The segment retracts to ex situ length, and the ratio of in situ length to ex situ length defines the amount of prestretching. Ex vivo inflation-extension experiments showed that axial prestretching is advantageous from a mechanical point of view because it minimizes the longitudinal movement of an artery during pressure pulse transmission. Furthermore, calculations suggested that axial prestretching decreases variation of axial stress and makes the radial distension of arteries easier. Recently, it has been shown theoretically that axial prestretching of a nonlinear tube increases the volume, which it is able to accommodate during pressurization. The present study complements previous results with the experimental observation of this fact. Tango Plus tubes, made with the help of 3D printing PolyJet technology, were cyclically pressurized. Axial prestretching was induced by hanging weights on the vertically oriented tubes. The results showed that the internal volume of the tubes increased with the elevated axial prestretch. The recorded mechanical responses were utilized in the regression analysis to identify the material parameters of the tubes. It was found that the hyperelastic Ogden model is suitable for describing the mechanical behaviour of the Tango Plus material. Our study demonstrates that 3D printing can be used to produce tubes, which, for example, may serve as a substitute for biological tissues in laboratory experiments. Simultaneously, this study yields the constitutive parameters of the digital material identified at multiaxial stress conditions. Such parameters are necessary, for instance, in the finite element analyses of parts undergoing loading conditions which result in multiaxial stress states.