Footwear and soft ground interaction
The aim of the research reported in this thesis was to improve the understanding of footwear and soft ground interaction and, in particular, its mathematical modelling. The work was undertaken for the Military Footwear Section of the MOD's Defence Clothing and Textiles Agency (DCTA) who funded the research in conjunction with the Engineering and Physical Sciences Research Council (EPSERC). Although research has been carried out on the interaction of footwear on firm surfaces, minimal work has previously been carried out on softer surfaces often encountered in combat situations and little effort has been applied to its mathematical modelling. The research programme included the development of mathematical models using soil mechanics theory, and experimental work using a soft-ground slip-rig. The prototype soft-ground footwear slip-rig that has been developed is a manually operated device based on simple mechanical mechanisms using weights and pulleys. The rig enables the measurement of traction and sinkage for different soil types, sole materials and tread geometry, at various angles of heel contact and applied vertical load. All experimental work has been carried out with the use of scaled up cleats to obtain measurable results. An investigation into three dimensional end effects has determined at what cleat length the problem becomes two dimensional. The experimental results have shown the effects of cleat geometry on total cleat traction for sand, and in particular the geometric characteristics that promote and reduce traction. These results have been analysed using Taguchi's Analysis of Variance technique. Traction distribution experiments have determined the proportion of traction obtained from different cleat areas. Soil mechanics theory, and in particular Coulomb's retaining wall theory, has been applied in the theoretical modelling of footwear and soft ground interaction. A two dimensional total traction model has been developed using MATLAB software and experimental and theoretical results have been compared. The traction versus cleat geometry trends for both the experimental and theoretical results were in good agreement.