Rotating Band Pressures and Engraving Forces in 155mm Artillery Shells

Introduction
INOWLEDGE of the mechanical interaction resulting from interference between the rotating band on artillery projectiles and the rifling grooves in the gun tube through which it is forced are of great interest both to interior ballisticians and projectile and gun tube designers. The ballistician's concern stems primarily from a desire to assess the influence of the band pressure on the retardation forces witnessed by the projectile while in t h e gun tube; t h e designers wish to know if t h e mechanical structures will survive the combination of this load with the loads resulting from the high pressures behind the projectile. Several evaluations [1, 2, 3, 4] 2 of the pressures existing between the gun tube and the projectile rotating band have been made for specific shell-tube combinations. N o methods are presently available, however, to describe the engraving forces as a function of these band pressures or of predicting changes in these engraving forces with variations in projectile and band design.
K,
Determination of Rotating Band Pressure
Three instrumented projectiles were hydraulically forced through a 155mm M-2 gun tube. T h e three projectiles used were an M118 illuminating round, a projectile similar to t h e The transformation of the observed strains into band pressureXM549, and a Sandia-designed projectile with a titanium base. was made by a set of strain-influence coefficients determine! The latter projectile is referred to as an ATAM5 round. Strain from finite element computer models of the barrel and projed in1gauges were installed inside t h e projectiles under t h e rotating The axisymmetric SAAS [6] computer code was used for ni> band to measure the hoop strains inside the projectile. I n addipurpose. Assuming a position for the projectile, band presr-'ii'"' strain coefficients were determined for t h e gauge on the barrel' which was directly above t h e center of t h e rotating band, -1"' for the gauges immediately adjacent on either side. I n addr-i"" 1 This work was supported by the U. S. Atomic Energy Commission. 2 to the strain resulting from the band interaction, the hydro'-1'1' Numbers in brackets designate References at end of paper. pressure expands the barrel significantly and a second set ol -11' Contributed by the Materials Division for publication (without TECHNOLOGY. Manuscript received at ASME Headquarters, April 25, 1972. Paper No. 72-Mat-L. 124 . / A P R I L 19 7 3
tion, the hoop strains on the exterior of the gun tube were measured at ten locations 3 along t h e gun tube. For redundancy, gauges were placed 180 deg apart on the barrel at several lm-.v tions. A standard piezoelectric pressure transducer was employed to monitor the hydrostatic pressure in the breech. The translation of the projectile from its initial contact position undetected with a displacement gauge accurate to about O.Ofi in. over t h e first 4 in. of travel. Thereafter, t h e position undetected by a calibrated rod extending out the muzzle. The projectiles used for these tests varied both in the structural stiffness of the round and in the geometrical properties »l the affixed rotating bands. The pertinent values are shown I• • Table 1. Additional projectile definition, details of the experiment and a complete listing of the experimental data appecr in reference [5]. T h e stresses in both t h e barrel and projccliii were low enough that neither undergoes significant plastic deformation, and a linear elastic analysis is appropriate;. 11"' problem then becomes one of determining a consistent value ni band pressure which will result in the observed strains both in the barrel and in the projectile for a particular position of '•*•'•'' projectile. As the primary interest for this study was in deicfmining the forces acting on the projectile early in its travel, ;•"• strain data over only the initial 10 in. of motion will be discussen.
presentation) in the JOURNAL OF ENGINEERING MATERIALS AND
3 The gauges were located 0, 2, 4, 6, 10, 30, 66, 26, and 23F from the commencement of rifling.
W. F. HARTMAN
A n a l y t i c a l Development Division.
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P. P. STIRBIS
A p p l i e d Mechanics Division. M e m . ASME Sandia Laboratories, Sandia C o r p o r a t i o n , A l b u q u e r q u e , N. M e x .