Veli Çelik

An elasto-viscoplastic analysis of direct extrusion of a double base solid propellant

In this study, three-dimensional modelling of extrusion forming of a double base solid rocket propellant is performed on Ansys(R) finite element analysis program. Considering the contact effects and the time dependent viscous and plastic behaviour, the solid propellant is assumed to obey the large deformation elasto-viscoplastic material response during direct extrusion process. The deformed shape, hydrostatic pressure, contact stress, equivalent stress, total strain values are determined from the simulation in order to get insight into the mechanical extremity that the propellant has undergone during processing. Hydrostatic pressure and contact stress distributions have been found to be important parameters due to safety reasons of the nitro-glycerine content in the bulk of the propellant.

Sliding Friction and Wear Behavior of Pack-Boronized AISI 1050, 4140, and 8620 Steels

This paper describes the dry sliding friction and wear performance of boronized AISI 1050, 4140, and 8620 steels with the Fe 2 B phase coating on the surface. The studies were carried out using a pin-on-disc arrangement. The disc material was made of carburized AISI 1020 steel. For the normalized (untreated) steels, two basic wear regimes were observed; namely, oxidative and severe metallic wear. In the oxidative regime, a low wear rate of 1E-5 mm 3 /Nm was found. The worn surfaces of the pins and discs were smooth and covered with patchy oxides. In severe wear, the wear rate was very high (1 E-3 mm 3 /Nm). The worn specimens were characterized by rough surfaces, plastic deformation, and metallic wear debris. Boronizing changed the wear mechanisms of steels. The test results showed that the boronized steels underwent oxidative fatigue wear with very low wear rate of 2 E-6 mm 3 /Nm. In addition, boronized steels exhibited lower friction coefficient than normalized steels at a sliding speed of 2 m/s.