Performance of Soils under Track Loads. Report 3. Track Mobility Number for Coarse-Grained Soils.

摘要

Dimensional analysis was used to produce a listing of 28dimensionless Pi terms from which to develop a comprehensive description of straight-line,level-ground,single-track performance in soil. Five of these terms--P.W,PT/W, M/Wr, z/l,and theta include dependent performance variables:pull (P),towed force (PT),torque (M), sinkage (z),and trim angle (theta),respectively. The remaining 23Pi terms contain only independent variables; 15of these terms are needed to describe track operation in air-dry sand. Among the independent variables included in these 15terms,seven were determined from laboratory model-track tests to have significantly more effect than the rest on track pull at 20percent slip:load,sand penetration resistance gradient,track width,nominal trakc-ground contact length hard-surface road-bogie deflection,horizontal at-rest center of gravity,and spacing between road wheels. A single dimensionless predication term,sand-track mobility number was developed that takes all seven of these independent variables into account. Road-wheel spacing was found to influence track performance significantly only for those values of road-wheel diameter larger than those ordinarily used or recommended for prototype tracked vehicles. Track pull is increased slightly by (1) locating the drive sproket at the rear rather than the front of the track; (2) maintaining high tension in the track belt;and (3) using a decreasing,rather than an increasing,front-to-rear pattern of road-bogie cylinder pressure, i.e. by decreasing the ability of the road bogies to resist deflection from fron to rear of track.