Mechanical properties of orthopaedic soles under cyclic loads and correlation with daily use

Aim of the work was the definition of an experimental procedure enabling to evaluate the mechanical properties of orthopaedic insoles used in daily and sport activities. Customers and manufacturers can be interested in knowing which is the durability of the insoles for a correct substitution of an exhausted sole together with for product liability. A cyclic test was developed for the measure of stiffness and damping properties of different types of insoles under pulsated compression loads applied by means of a servo hydraulic test machine. Accelerated fatigue tests were performed by applying repeated blocks of compression overloads and measuring periodically the mechanical properties of the insoles to estimate the insole durability. Finally, a group of subjects wearing insoles during daily life was involved in the study and two pairs of identical insoles were prepared for each subject: one pair underwent the fatigue test and the other pair was used by the subject in his daily activity (normal or sport) during a given period of time. Final comparison between the mechanical properties of used and tested insoles enabled to define the number of equivalent damage cycles per month of each type of customer.