טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSchneebaum Yaron
SubjectTheoretical and Experimental Investigation of Barrel Steel
Erosion Mechanics in Hot Reactive Flows
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Alon Gany


Abstract

This research work presents the experimental results and the proposed model for the process of metal erosion by reactive hot gas flows in gun tubes. The erosion mechanism with implication to tube wear combines aerodynamics, thermodynamics, chemical (surface) reactions and metallurgical (physical) processes.

The R&D effort to achieve higher performance in guns/cannons means higher muzzle velocity for given projectiles. This leads to the use of hot energetic propellants with novel ignition methods. Normally, the composition of the propellant combustion product gases changes with a rise in temperature. This affects the gas-wall interaction mainly in the boundary layer. The main effects: heat transfer, mass transfer, chemical and physical processes, act simultaneously in the erosion/wear phenomenon.

The experimental test results were obtained from a uniquely designed vented combustor simulating gun system. This enabled us to measure the erosion effects of different propellants on several gun steels.

The research  used a variety of existing propellants, including types, which are still under development for future propelling charges.

The propellant combustion gases flow through a tube fitted with rings (nozzles). These rings consist of different gun tube steels. In this way, we achieved a net effect of chemical and thermal interaction between the combustion products and the steel, without nosing parts. This yields the upper value of the chemical and thermal effect, occurring during a ballistic cycle in the gun.

The test results were compared with the theoretical model. The model was then calibrated in order to predict wear/erosion in gun/cannon tubes.

The analysis of the gun tube steel rings cross sections reveals three reaction zones:

A.     A white layer zone - approximately 2 micrometers thick.

B.     A thermally affected zone - approximately 200 micrometers thick.

C.     A bulk material zone.

The process of heat and mass transfer from the flow core through the boundary layer to the wall exposes the wall to reactive hot gas, in which the dominant ingredients are carbon-monoxide and carbon-dioxide. These two components are the main carbon and oxygen sources found in the white layer and in the termal zone of the analyzed rings.

The oxygen observed in the samples is mainly concentrated in a thin sublayer of the white layer, up to 6000 Angstrom deep in exstreme cases. The carbon is highly concentrated  in the white layer and throughout the thermal layer.

A broad database as well as better insight of the erosion phenomena under extreme conditions of pressures and temperatures has been the outcome of the work.