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The shear stresses and pressures in the socket-stump interface were calculated for four transfemoral amputees, using the finite element method. A dynamic explicit model was developed for the simulation of the fitting procedure of the socket and the applying of the loads corresponding to the support phase during the gait, and a constitutive multilayer hyper- elastic model was employed for the soft tissues (skin, fat and muscle) because of their large strains and displacements, and lineal isotropic models for the bone and socket. In order to determine the influence of the friction coefficient on the socket-skin interface, its value was varied from a minimum value of 0.5 to a maximum of 1.0. Then, the zones where the greatest pressures and stresses occurred were identified, where the use of a horizontal strip was proposed with a variation of the friction coefficient from 0.2 to 0.6, in order to ob- serve its effect on the obtained stresses. The strip has a width of 10 cm and is located approx- imately 2.0 cm below the ischial support of all the individuals. It was observed that the pres- sure does not change significantly when varying the friction coefficient. However, the average shear stress tends to rise when increasing the friction coefficient, and after applying the strip the average shear stress reduced up to 25%, while the pressure variation was not significant. Finally, the experimental validation of the behavior of the friction coefficient between the polypropylene and the skin was performed with a sclerometer. This experiment considered factors such as the patient's sweat, the amount of hair and the surface texture of the polypro- pylene coating, and it proved that the surface texture of the coating must be accounted for when measuring the friction coefficient. |
