Title: Investigation of static and dynamic coefficient of friction

An investigation was initiated to determine the coefficient of static friction between explosives and the surfaces to which the explosive are held during machining and gaging. An attempt was made to duplicate as nearly as possible the conditions found in the fabrication of explosive assemblies, so that the measured coefficients will be useful in calculating safe loads.

A new test technique has been developed for adhesive metal/metal friction at high sliding rates and plastic stress levels. The test specimen consists of a thick walled metal tube and a tapered metal rod. The rod is pulled through the tube at rates up to /approximately/10/sup 4/mm/sec. The tubes plasticity can be varied by changing the tapered rod. Finite element simulations were used. Both the quasistatic code JAC and the dynamic wave propagation code PRONTO were used. Tests were performed using annealed OFHC copper tubes and cold worked 316 stainless steel rods. Two tests were performed at 1.67 mm/sec: onemore » unlubricated, and one using MoS/sub 2/ lubrication resulted in approximately a factor of two reduction of load. The third test was unlubricated at 7.44 /times/ 10/sup 3/mm/sec. This test yielded a maximum load one half that found in the unlubricated static test, indicating a rate dependence of the plastic friction coefficent. The finite element model was compared with experiment. Results suggest that the unlubricated, static test yields a value ..mu.. = 0.4 while both the lubricated, static test, and the unlubricated, dynamic test result in ..mu.. = 0.2. This is consistent with those of previous workers and with features observed on the wear surfaces using scanning electron microscopy.« less

Dynamic elastic modulus (resonance frequency) and internal friction measurements have been carried out on SAP-ISML with the double purpose (i) of making an attempt to clarify the mechanisms (of internal friction) in this material and (ii) of reaching more informations on the general structural properties of the material itself. Measurements have been carried out between 20 and 500 deg C, in the kilocycle frequency range, employing a Bordoni type apparatus. Frorn the point of view of the general properties of SAPISML, the measurements effected confirm that SAP in the cold worked state is a material which inherently maintains the propertiesmore » of cold worked materials despite any subsequent annealing treatment. (auth)« less

This report describes the results of a program designed to evaluate the breakaway friction and dynamic friction/wear characteristics of materials having potential for use as load bearing components in a high-performance high-temperature heavy duty diesel engine. Ten candidate materials were selected, six of which were evaluated under all possible material combinations as both stationary as well as moving breakaway specimens. The remaining materials were evaluated either in the static mode against themselves and all other materials, or against themselves only. Experiments were performed at five temperatures up to 650 C (1200 F) and unit pressures of 700 kPa (100 lb/sqmore » in.), 3500 kPa (500 lb/sq in.), and 7000 kPa (1000 lb/sq in.). Experimental results indicate that under dynamic conditions, four of the ten materials exhibited good to excellent friction/wear characteristics in various material combinations. These materials were: titanium carbide, silicon nitride, silicon carbide (reaction sintered), and Refel (SiC).« less