ABSTRACT
Evaluation of stress distribution beneath plain rigid wheels on soil simulants is useful in analyzing the wheel-soil interaction of planetary rovers. Single wheels moving on a soil simulant are used in the prediction of wheel performance. In this paper, a cast iron small wheel of 160 mm in diameter, 32 mm width and a weight of 52.189 N, and a cast iron large wheel of 210 mm in diameter, 50 mm width and a weight of 67.444 N were studied. The lunar soil simulant on which the wheels moved upon was anorthosite based and called TRI-1. The normal and shear stresses beneath the wheels were determined. An analytical approach was used and the Reece model, Bekker model, Wong-Reece model and Iagnemma model were considered in estimating the normal stresses. The shear stresses were calculated using the Janosi and Hanamoto model. Determining the maximum angle was common for all three models (Reece, Bekker and Wong-Reece), whereas for the Iagnemma model, maximum angle was the average of the entry angle and exit angle. The geotechnical and mechanical properties of the TRI-1 soil simulant were obtained from the experiments in this study. The entry and exit angle for the two wheels were calculated for various models. The Wong-Reece equations were found to register the maximum shear stress (26.3394 kPa) for the small wheel and the Reece model was conservative for the large wheel (34.9298 kPa). The range of stresses corresponded to various soil conditions (loose and dense); the maximum normal stress for the small wheel was 32.1221 kPa (Wong and Reece models) and for the large wheel was 39.0156 kPa (Reece model), within the dense conditions.
