A Four Point Bending Experiment
ARMY ARMAMENT RESEARCH AND DEVELOPMENT CENTER WATERVLIET NY LARGE CALIBER WEAPON SYSTEMS LAB
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This report presents data obtained in a four point bend experiment on a 105 mm M68 rotary forged gun tube. The four point bending was accomplished using a standard hydraulic straightening press fitted with a two point loading device designed and fabricated by the Benet Weapons Laboratory Engineering Support Branch. Strains were measured at several points on the surface in a circumferential plane using standard foil type resistance gages and standard strain readout equipment. Deflections at mid-span were measured with a rotary ten turn potentiometer. Load strain and load deflection curves are presented and compared with theory. The agreement is quite good. The difference between theory and experiment probably can be attributed to the larger diameter of the tube nearer the breech end which could contribute to greater stiffness. Maximum strains were less than 1.4 percent and are quite low compared to those expected in three point bending. The experiment shows a good possibility of using four point bending to eliminate the need for hot straightening.