Aspects of the Tribology of the Plastic Bonded Explosive LX‐04

The coefficient of friction, {mu}, of the plastic bonded explosive (PBX) LX-04 was measured on stainless steel, aluminum, Teflon and the explosive itself as a function of temperature between ambient and 135 C at a rotational speed of 0.0025 rad/sec{sup -1}. An optical profilometer was used to analyze the mean surface roughness, R{sub a}, of the various materials. LX-04 is a composite of the explosive 1,3,5,7-tetranitroazacyclooctane (HMX) and Viton A in an 85/15 weight ratio. The average roughness of the pressed explosive surface was R{sub a} = 0.55 {micro}m. The coefficient of friction for LX-04 on stainless steel of R{sub a} = 0.40 {micro}m decreased from 0.38 at ambient to 0.18 at 95 C. Above this temperature {mu} was nearly constant to about 125 C, where the coefficient began to increase again. The opposite behavior was observed with aluminum with R{sub a} = 0.31 {micro}m. The coefficient of friction increased from about 0.3 at ambient to 0.46 at 125 C. At this temperature or above, {mu} tended to increase during the measurement, indicating that the sample may have been sticking to the counter surface. The coefficient of friction against Teflon of R{sub a} = 0.054 {micro}m was nearly constant frommore » ambient to 65 C at 0.43 {+-} 0.02, then decreased to 0.17 at 100 C and remained there up to 135 C. Against LX-04 itself at temperatures between 35 and 95 C the coefficient of friction averaged 0.64, but tended to increase during the measurement, probably due to adhesion of the Viton to itself. Above 95 C the coefficient dropped off and became nearly constant again at 0.16 from 115 up to 135 C. Some preliminary measurements on stainless steel with the mock explosive RM-04-BR, a composite of cyanuric acid and Viton A in the same weight ratio as the actual explosive, were made to evaluate the set up procedures and safety of the operation with live explosive. Both pressed, R{sub a} = 0.37 {micro}m, and machined, R{sub a} = 1.7 {micro}m, surfaces were evaluated for the mock. Results compared reasonably well with the explosive itself on steel, indicating that the binder plays a major role in determining the coefficient of friction for these types of composites.« less