Advanced modelling of sports footwear

A need to reduce the number of design iterations, coupled with a requirement to reduce the weight of the new generation of TPU running shoes has lead to the use of finite element analysis (FE) within the athletic shoe industry. The collaborators in this research, adidas, were already using the technology, but only on individual parts, and on a reverse engineered basis. This thesis presents a thorough review into the materials used in athletic footwear, their application within running shoes and the methods of testing non-linear, highly deformable polymers and polymer foams. The fundamentals of the FE process are examined, along with a discussion of the current testing methods for shoes. The novelty in this work comes mainly from the comprehensive, logical progression through the modelling process as applied to this new area. Sample materials were tested, revealing new test methods. These were then analysed and converted for use in ABAQUS v6.5 which was the FE software used. The modelling of the sample materials, their tests, then shoe parts and midsole assemblies are discussed at length. At each stage the required complexities were added to the model, and these are detailed. This includes the import, conversion and repair of highly complex geometry, meshing techniques for this geometry, methods of building models of shoe assemblies and all relevant issues that arose from these processes. In addition, a shoe with an internal mechanism was modelled to assist in the design process. The effect of damage to shoe materials was also studied. Physical tests were carried out to verify all the FE models, and the results are presented. In addition, shoes taken from the end of the production line with the uppers attached were tested in order to compare the change in performance between the component parts and a finished product. The results of the modelling showed that was possible to construct and run full shoe assembliesw ithin a reasonablet ime. Fair prediction of the physical responseo f the assemblies was seen using material data taken directly from the sample data, but a method of correcting the initial error in the material test is presented which gives very good force/deflection results in TPU parts. A method of adjusting the entire assembly's material models is then presented, which improves the initial verification. In addition to force/deflection readings, digital image processing was used to monitor the structural response of the shoe during loading, and a set of structural metrics is put forward. The results of these indicated that while the shoe models were representing the cushioning response well, the shape of the shoe was not replicated, suggesting that the model in its present state would be unsuitable for use in some forms of test. Suggestions for improvement are made. Comparison of the structural metrics between shoe assemblies and production shoes suggests the possibility of a quantifiable metric for what would be considered a `good' shoe. The repercussions of this are discussed in the conclusions