In this work, cetyl trimethyl ammonium bromide (CTAB), silane coupling agent (KH570) and polyethylene glycol (PEG) were used to modify the surface property of molybdenum disulphide (MoS 2 ). MoS 2 /nitrile rubber (NBR) composites were directly prepared by mechanical blending. Meanwhile, the effects of loading content of MoS 2 , the kinds of modifiers on the mechanical and tribological properties of the composites were evaluated. The dispersion of fillers in rubber matrix and the worn surface of the composites were analysed by SEM. Results showed that the properties of MoS 2 /NBR composites prepared by CTAB modified MoS 2 were superior to that of KH570 or PEG modified MoS 2 and unmodified MoS 2 because of strong opposite charges attraction between cetyl trimethyl ammonium cation and MoS 2 surface. When adding 10 phr CTAB modified MoS 2 in rubber matrix, the dispersion of filler was optimum, and the coefficient of friction of composite was the lowest in the prepared composites.

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Failure mechanisms for a solid propellant were discussed, and the stip-yield and the inherent flaw models were applied to them. Then, failure assessment diagram methods were investigated by means of modified two models. Fracture toughness tests using CCT(center-cracked tension) specimens made of a solid propellant were conducted to generate the failure assessment diagrams. The failure assessment diagram of the inherent flaw model was normalized in order to compare with that of the modified strip-yield model. From the comparison of two failure assessment diagrams, it was found that the failure assessment diagram of the modified inherent flaw model more conservatively assesses the failure than that of the modified strip-yield model.

An experiment of rapid pressurization-induced crack propagation of solid propellant was conducted by using a windowed test chamber. A pre-cracked specimen of solid propellant is installed in the chamber, and highly compressed nitrogen gas in an accumulator pressurizes the chamber until the chamber pressure reaches set-up pressure to make the chamber depressurization. Pressure-time trace was obtained from the experimental result, and pressurization rate was defined from the trace. In this study, three pressurization rates (64.34, 73.86 and 85.44 MPa/s) are considered, and propagation lengths are measured. Also, a progression of the crack propagation recorded by a high-speed digital camera is presented.

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