Untersuchung der Wirkflächenreibung mit Hilfe des Flachstauchversuchs

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Axial forces and bending moments in the loaded rabbit tibia in vivo

<p>Abstract</p> <p>Background</p> <p>Different animal models are used as fracture models in orthopaedic research prior to implant use in humans, although biomechanical forces can differ to a great extend between species due to variable anatomic conditions, particularly with regard to the gait. The rabbit is an often used fracture model, but biomechanical data are very rare. The objective of the present study was to measure axial forces, bending moments, and bending axis directly in the rabbit tibia <it>in vivo</it>. The following hypothesis was tested: Axial forces and bending moments in the mid-diaphysis of rabbit tibia differ from other experimental animals or indirectly calculated data.</p> <p>Methods</p> <p>A minifixateur system with 4 force sensors was developed and attached to rabbit tibia (<it>n </it>= 4), which were subsequently ostectomised. Axial forces, bending moments and bending angles were calculated telemetrically during weight bearing in motion between 6 and 42 days post operation.</p> <p>Results</p> <p>Highest single values were 201% body weight [% bw] for axial forces and 409% bw cm for bending moments. Whereas there was a continous decrease in axial forces over time after day 10 (<it>P </it>= 0.03 on day 15), a decrease in bending moments was inconsistent (<it>P </it>= 0.03 on day 27). High values for bending moments were frequently, but not consistently, associated with high values for axial forces.</p> <p>Conclusion</p> <p>Axial forces in rabbit tibia exceeded axial forces in sheep, and differed from indirectly calculated data. The rabbit is an appropriate fracture model because axial loads and bending moments in rabbit tibia were more closely to human conditions than in sheep tibia as an animal model.</p

From the experimental determination of stress-strain full fields during a bulge test thanks to 3D-DIC technique to the characterization of anisotropic Mullins effect

International audienceThe bulge test is usually mostly used to analyze equibiaxial tensile stress state at the pole of inflated isotropic membranes. Three-dimensional digital image correlation (3D-DIC) technique allows the determination of three-dimensional surface displacements and strain fields. A method is proposed to calculate from these experimental data the membrane curvature tensor at each surface point of the bulge specimen. Curvature tensor fields are then used to investigate axisymmetry of the test; in the axisymmetric case, membrane stress tensor fields are determined from meridional and circumferential curvatures combined with the measurement of the inflating pressure. Stress strain state is then known at any surface point which enriches greatly experimental data deduced from bulge tests. This method is then used to treat an experimental bulge test on a filled silicone rubber membrane. The results highlight that a global membrane with a very heterogeneous strain history is obtained , from equibiaxial behavior at the center of the membrane until a planar (pure) shear state at the periphery of the bulge. Next, different small tensile specimens are cut from the pre-stretched silicone membrane. Identical cyclic tensile tests are realized on all these specimens. The curves are compared and highlight the difference of the stress-softening according to the place of the cut specimen and according to its orientation with respect to the circumferential or meridional direction