Testing solid propellants

Monographs on rockets and rocket propellants by the National Aeronautics and Space Administration (NASA), Lewis Research Center, Cleveland. These iaclude the foUowiag Solid Propellant Selection and Characteri tion, Report SP-8064,1971 Solid Rocket Motor Peformance, Report SP-8039,1971 Solid Rocket Motor Igniters, Report SP-8051,1971 Solid Rocket Motor Metal Cases, Report SP-8025, 1970, and Captive Eire Testing of Solid Rocket Motors, Report SP-8041,1971. 

Fig 9 Effect of Aging (70°) and Average Humidity During Processing/Testing Upon thp Mechanical Properties of PBAA (83% Solids) Propellant... 

Cachia, G. P. und Withebread, E. G. The Initiation of Explosives by Shock, Proc. Roy. Soc. A 246, 268-273 (1958). Card-Gap Test for Shock Sensitivity of Liquid Monopropellant, Test Nr. 1, Recommended by the JANAF Panel on Liquid Monopropellant Test Methods, March 1960 Amster, A. B., Noonan, E. C. und Bryan, G. J. Solid Propellant Detonability, ARS-Journal 30, 960-964 (1960)... 

Lupoglazoff, N., and E. Vuillot. 1996. Parietal vortex shedding as a cause of instability for long solid propellant motors — numerical simulations and comparisons with firing tests. AIAA Paper No. 96-0761. 

Niioka, T., Mitani, T and Ishii, S Observation of the Combustion Surface by Extinction Tests of Spinning Solid Propellant Rocket Motors, Proceedings of the 11th International Symposium on Space Technology and Science, Tokyo, 1975, pp. 77-82. 

N.J. Blay I Dunstan, "Compatibility and Stability Testing of Explosives and Solid Propellants , US NTIS, AD Rep 1970,... 

A specific requirement of solid propellant binder polymers is the small tolerance allowed in the reproducibility of the product properties. As a result, some polymers that cannot be specified easily must be adjusted lot by lot in accordance with qualification tests. This is illustrated graphically by the data of Figure 1, where different lots of a carboxy-terminated polybutadiene procured to the same specification are compared with the different equivalents of the BITA (butylene imine adduct of trimesic... 

Solid Propellant Mechanical Properties Testing, Failure Criteria, and Aging... 

Figure 9. Typical stress-strain curve for solid propellants at 0.77 in./min. and 80°F. E is the slope of the tangent to the initial portion of the curve. A variety of curve shapes are possible depending on specific formulations and test conditions...

Although the uniaxial test has traditionally received the most attention, such tests alone may be insufficient to characterize adequately the mechanical capability of solid propellants. This is especially true for ultimate property determinations where a change in load application from one axis to several at once may strongly affect the relative ranking of propellants according to their breaking strains. Since the conditions usually encountered in solid rocket motors lead to the development of multiaxial stress fields, tests which attempt to simulate these stress fields may be expected to represent more closely the true capability of the material. 

Figure 16 illustrates several test specimens which have been used (46) in the multiaxial characterization of solid propellants. The arrows indicate the direction of load application. The strip tension or strip biaxial test has been used extensively in failure studies. It can be seen that the propellant is constrained by the long bonded edge so that lateral contraction is prevented and tension is produced in two axes simultaneously. The sample is free to contract normal to these axes. The ratio of the two principal tensile stresses may be varied from 0 to 0.5 by varying the bonded length of incompressible materials. 

A variety of dynamic tests, testers, and specimen configurations have been used to measure solid propellant response to cyclic loading. Table II summarizes many of the techniques and characteristics. In most instances the loading is applied in a regular sinusoidal manner, although other nonsinusoidal time functions may be considered in some tests. 

Sample shape and size are of considerable importance when selecting dynamic test methods for solid propellants. Preparation must take account of surface conditions and precise dimensions. Usually cast specimens retain a polymer-rich surface layer and should be avoided. Additionally, the sample dimensions should be large compared with the size of the largest solid particle inclusion in the propellant. 

While mechanical testing of all types provides a general description of the bulk properties of solid propellants, it is difficult to make generalizations or even extrapolations which may be used in a predictive fashion. When the content or type of solid filler is changed, or curative ratios are altered, there is no simple corresponding material property change which can be defined based on mechanical testing experience. If filler content... 

The uniaxial failure envelope developed by Smith (95) is one of the most useful devices for the simple failure characterization of many viscoelastic materials. This envelope normally consists of a log-log plot of temperature-reduced failure stress vs. the strain at break. Figure 22 is a schematic of the Smith failure envelope. Such curves may be generated by plotting the rupture stress and strain values from tests conducted over a range of temperatures and strain rates. The rupture locus moves counterclockwise around the envelope as the temperature is lowered or the strain rate is increased. Constant strain, constant strain rate, and constant load tests on amorphous unfilled polymers (96) have shown the general path independence of the failure envelope. Studies by Smith (97) and Fishman (29) have shown a path dependence of the rupture envelope, however, for solid propellants. 

In a recent attempt to bring an engineering approach to multiaxial failure in solid propellants, Siron and Duerr (92) tested two composite double-base formulations under nine distinct states of stress. The tests included triaxial poker chip, biaxial strip, uniaxial extension, shear, diametral compression, uniaxial compression, and pressurized uniaxial extension at several temperatures and strain rates. The data were reduced in terms of an empirically defined constraint parameter which ranged from —1.0 (hydrostatic compression) to +1.0 (hydrostatic tension). The parameter () is defined in terms of principal stresses and indicates the tensile or compressive nature of the stress field at any point in a structure —i.e.,... 

Bills (7) has applied an adaptation of this law to solid propellants and propellant-liner bonds for discrete, constantly imposed stress levels considering U to be the time at the ith stress level and tfi the mean time to failure at the ith stress level. A probability distribution function P was included to account for the statistical distribution of failures. For cyclic stress tests the time is the number of cycles divided by the frequency, and the ith loading is the amplitude. The empirical relationship... 

A prediction of useful life for solid propellant rockets is quite important, from the standpoint of operational readiness and economic considerations. The premature removal and replacement of deployed systems, based on inaccurate storage life estimates, can be costly. A specific missile system and propellant combination could become obsolete while long term storage data are being compiled. Accelerated aging tests are normally used to give qualitative indications of storability, but the deficiencies of these tests are obvious and are discussed later. 

Many of the tests described earlier have been applied in surveillance studies of solid propellants. Both response and failure characteristics may be followed as a function of time during storage at various conditions. Physicochemical analysis of specimens before and after exposure to... 

Tests made on explosives for "sensitivity by impact or friction, although in reality only ignition tests, should correlate well with the hazard of detonating the material. On the other hand, the same tests on a cohesive solid propellant would indicate only its ignitability under that particular stimulus and would not correlate prior experience in the explosives industry. 

Class B Explosive Under the U.S. Department of Transportation (DOT) safety regulations, as per 49 CFR 173.88, Class B explosives are defined as those explosives which in general function by rapid combustion rather than detonation and include some explosive devices such as special fireworks, flash powders, some pyrotechnic signal devices and liquid or solid propellant explosives which include some smokeless powders. The regulations provide specific descriptions of and tests for Class B explosives. 

Art of Combustion of Solid Propellants, US Naval Ord Test Station, China Lake, Calf... 

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