Nonlinear stress relaxation of trabecular bone

The viscoelastic behavior of bovine trabecular bone is investigated by means of relaxation tests carried out either in compression or in bending configurations. The experimental curves show that the stress relaxation process has two distinct stages: a long-term process depending only on the time variable, and a short-term process whose magnitude is affected from elastic stresses. An analytical expression describing the normalized relaxation curves is proposed, and the relevant characteristic times are identified by fitting the experimental data. The characteristic times are found to be material properties not depending on the particular loading configuration.