Study on the Equivalent Full Charge Conversion Coefficient of the Barrel Life Based on the Thermal-chemical Erosion Model

doi:10.12382/bgxb.2022.0949

Abstract

Abstract:

To explain the paradox between the experimental and theoretical results of equivalent full charge (EFC) conversion coefficient, which can be used to convert the number of firing under various firing conditions to the number of EFC firing, a computational method of that coefficient is investigated on the basis of the thermo-chemical erosion model of the barrel. Supposing that the thickness and composition of the white layer on the inner wall of barrel change periodically after several firings, the relationship among the thermo-chemical erosion volume at the beginning of the rifling and the erosivity of the propellant and the transient temperature field of the inner layer of the barrel is established with the help of the mass diffusion law. During the firing process, the gas temperature in the space behind the projectile and the forced convection coefficient at the innerwall surface of barrel are provided by the classical interior ballistic theory. Hereafter, the model to calculate the transient temperature of the barrel can be developed. In addition, the effect of gas with relative high temperature during the after-effect period is also considered. Eventually, focusing on the firing rate, the charge mass and the charge temperature which have an essential effect on the interior ballistic process, erosion volumes under different firing rates, charge numbers and charge temperatures are calculated. Accordingly, the EFC conversion coefficients under various firing conditions are obtained. It is found that a more severe erosion of the barrel is often related to a faster firing rate, a more charge mass and a higher charge temperature.The EFC coefficient of the supercharge is up to 2.131. The reasonability of the proposed model is verified by using the practical firing data of a 155mm barrel.

Key words: barrel life, equivalent full charge conversion coefficient, thermo-chemical erosion, transient temperature field

CLC Number:

TJ301

LI Yanze, QIAN Linfang, FU Jiawei, CHEN Longmiao. Study on the Equivalent Full Charge Conversion Coefficient of the Barrel Life Based on the Thermal-chemical Erosion Model[J]. Acta Armamentarii, 2024, 45(5): 1426-1435.

Figures/Tables 12

Fig.1 Schematic diagram of barrel erosion model

Fig.2 Calculation flow of barrel erosion volume

Table 1 Material parameters of a 155mm artillery[27]

装药常温/ K	ρ_b/ (kg·m^-3)	c_b/(J·kg^-1K^-1)		λ_b/(W·m^-1K^-1)
装药常温/ K	ρ_b/ (kg·m^-3)	C₀	C₁	C₀	C₁
294	7850	474.71	0.2	43.6	-0.0097

Table 2 Propellant compositions of different charge numbers in vol.%[11,14]

装药号	CO/%	CO₂/%	H₂/%	N₂/%	H₂O/%
强装药	28.70	4.29	15.90	29.10	21.90
0、1装药	28.69	5.76	12.16	27.62	25.20
2~6装药	42.80	9.96	10.30	12.60	23.70

Table 3 Values of k1- k 7 [11]

k₁	k₂	k₃	k₄	k₅	k₆	k₇
114	0.0207	1.0	-0.33	2.4	-3.6	-0.5

Fig.3 Change if temperature and convection coefficient in the space behind the projectile with time

Fig.4 Distribution of transient temperature in the surface layer of barrel

Fig.5 Distribution of transient temperature on the barrel’s inner surface (10 rounds/min)

Fig.6 Conversion coefficient vs. accumulated number of shots fired

Fig.7 Temperature and erosion volume for different charge numbers (charge temperature: 294K)

Table 4 EFC conversion coefficients for different charge numbers (charge temperature: 294K)

装药号	基于烧蚀量	GJB	实验值
强装药	2.131	1.286	2.057~2.422
0	1.000	1.000	1.000
1	0.313	0.531
2	0.261	0.533	0.222
3	0.067	0.328
4	0.011	0.193
5	6.8E-4	0.103
6	1.0E-5	0.046

Table 5 EFC conversion coefficient for different charge temperatures (charge number: 0)

温度/℃	21	-44	55
EFC折算系数	1.0000	0.9386	1.1122

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