viscoelastic behaviour Flashcards
What is the difference between creep and stress relaxation?
creep is a phenomenon in viscoelastic materials. Initially there is a rapid deformation stage, where fluid is rapidly pushed out of the cartilage. As the amount of fluid in the cartilage diminishes, the rate of fluid being expelled from the cartilage decreases until equilibrium. at this point the applied load is borne completely by the solid matrix. In relatively thick cartilage this takes about 4-16 hours to reach equilibrium. At equilibrium, the majority of fluid still remains in the articular cartilage.
stress relaxation?
occurs in viscoelastic materials, when the material is kept under a constant deformation. The stress is reduced over time, as the material is kept at a constant strain. The load required to maintain the strain/deformation decreases with time. During initial deformation, interstitial fluid is forced out as surface layers are compacted. Because of the large frictional drag associated with the flow of fluid through the solid matrix, LARGE LOADS are needed to compress the tissue. From point B onwards (during the stress reelaxation phase, the stress required to maintain the deformation is reduced as fluid is no longer being forced out and the fluid within the tissue is redistributed from the least compacted deeper layers to the most compacted surface layers within the AC. Once load is taken away, cartilage will regain its original size and shape.
