Engineering design optimization of heel testing equipment in the experimental validation of safe walking

Experimental test methods for the evaluation of the resistance of heels of ladies' shoes in the case of impact loads are fully defined by International Organization for Standardization (ISO) procedures that indicate all the conditions of experiment. A first Standard (ISO 19553) specifies the test method for determining the strength of the heels in the case of single impact. The result offers a valuation of the liability to fail under the sporadic heavy blows. A second Standard (ISO 19556) details a method for testing the capability of heels of women' shoes to survive to the repetition of small impacts provoked by normal walking. These Standards strictly define the features for two different testing devices (with specific materials, geometries, weights, etc.) and all the experimental procedures to be followed during tests. On the contrary, this paper describes the technical solutions adopted to design one single experimental device able to perform impact testing of heels in both conditions. Joining the accuracy of mechanic movements with the speed of an electronic control system, a new and flexible equipment for the complete characterization of heels respect to (single or fatigue) impacts was developed. Moreover a new level of performances in experimental validation of heel resistance was introduced by the versatility of the user-defined software control programs, able to encode every complex time-depending cycle of impact loads. Dynamic simulations permitted to investigate the impacts on heel in different conditions of testing, optimizing the machine design. The complexity of real stresses on shoes during an ordinary walk and in other common situations (as going up and downstairs) was considered for a proper dimensioning.