Comprehensive Erosion Model for the 120-MM M256/M829A2 Gun System

Distinct erosion patterns and mechanisms are emerging as our gun erosion database increases for in-service and out-of-service 120-mm M256 tubes with M829A2 rounds. Variability exists for M256 guns with MS29A2 rounds depending on round count, round type, round-conditioning temperature, and their orde...

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Bibliographic Details
Main Authors: Sopok, S, Vottis, P, O'Hara, P, Pflegl, G, Rickard, C
Format: Report
Language:English
Subjects:
120-MM M256 CANNON
COMPUTER APPLICATIONS
COMPUTER PROGRAMS
DEGRADATION
EROSION
GUN BARRELS
GUN EROSION MODELING
Guns
INTERIOR BALLISTICS
M829A2 AMMUNITION
MATHEMATICAL MODELS
SOFTWARE
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Summary:Distinct erosion patterns and mechanisms are emerging as our gun erosion database increases for in-service and out-of-service 120-mm M256 tubes with M829A2 rounds. Variability exists for M256 guns with MS29A2 rounds depending on round count, round type, round-conditioning temperature, and their order. Our M256/M829A2 gun system erosion model - with its interior ballistics, thermochemistry, and boundary layer components - is constantly being guided and refined by the erosion and materials analysis data from fired gun tubes. A recent refinement includes improvement of the gun steel subsurface exposure model due to high quality, difficult to obtain data from in-service M256 tubes. Other recent refinements to the boundary layer heat transfer model are based on thermal data from M256 tubes. These refinements include the improvement/incorporation of case gas cooling effects, turbulent gas mixing/heating effects, and a very minor contribution from forcing cone-induced vena contracta cooling effects. These latter refinements are calibrated away from crack walls by positional thermal wall repacking depth, thermal wall transformation depth, and thermocouple data. A comprehensive gun erosion model and multiple single-shot erosion condemnation predictions are described for the l20-mm M256 gun with its M829A2 round for hot-conditioned rounds only, ambient-conditioned rounds only, cold-conditioned rounds only, and an equal distribution of hot/ambient/cold-conditioned rounds. The gun erosion mechanism consists of heat checking the inert chromium plate, subsequent interfacial degradation of the subsurface gun steel substrate at the chromium crack bases, then chromium platelet spalling, and subsequent bare gun steel gas wash. This gun erosion model correctly calculates and predicts that the worst eroded region is at 1.2 to 2.4 meters from the rear face of the tube. The excessive muzzle wear is by a different, purely mechanical gas wash-free mechanism. Presented at Joint Configuration Board Meeting, 11-13 May 98.