Advanced numerical techniques to simulate soil-tool interface problems
In most mine clearing or earth moving equipment such as bulldozers, the working tool is a blade. The blade geometry and operating conditions, such as cutting speed, cutting angle, and cutting depth, have a great effect on overall machine productivity. Most of the published experimental studies confirm these effects. However experimental studies are expensive and their results are highly dependant on the accuracy of measurement devices and the reliability of experimental procedures employed. Numerical techniques have recently shown more promise especially with the current increase in computational power and development of more sophisticated material models. However in order to simulate the soil-tool interface process accurately, careful selection of the appropriate material model for the soil and the interface is required. This should, ideally, be based on a reasonable number of material parameters that have direct physical meaning. In this study a review of the available constitu tive models for soil (particularly sand) and soil-tool interface was carried out. This review study concluded by selecting the so called hypoplastic model as the most appropriate to simulate the sandy soil behavior over a wide range of stresses. Some modifications were carried out on this selected hypoplastic model to optimize it for simulation of the soil-tool interaction process, which is characterized by monotonic loading and high deformation. The modified model was verified numerically and then implemented into the finite element method via an ABAQUS user defined subroutine UMAT. Then the implemented model was verified through analysis of some benchmark problems and results were compared with results from different classical failure criteria. The finite element analysis revealed the high performance of the hypoplastic model in simulating sand behaviour. Finally an analysis of various factors affecting soil-tool interaction was carried out in both two-dimensions and three-dimensions. Results revealed the significant effect of both geometry and operating conditions on blade cutting forces and confirmed the ability of the finite element method to analyze the soil-tool interaction process.