The influence of projectile geometry on adiabatic shear and target failure
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An examination has been c a r r i e d out of the ability of projectiles of three different geometries to perforate plates of an age hardened aluminum alloy. It was found that fiat-ended projectiles perforate the target with greater ease than projectiles with more rounded ends. The results are discussed in t e r m s of the ability of a particular projectile geometry to promote adiabatic shear during penetration and the mode of fracture when projectile breakout occurs. T H E perforation (complete penetration) of metal t a r gets by projectile is known to be influenced by a large number of variables which have been extensively discussed in the literature. ~,z More recently it has been found that the formation of bands of intense shear in which adiabatic heating o c c u r s can reduce the energy required for penetration, s,4 It is known, in a general form, that material properties have a significant influence in determining whether a material will be susceptible to adiabatic shear. Some materials (such as titanium 5 and aluminum alloy type 20144) are prone to adiabatic shear whereas it has not been detected in others (such as type 1200 aluminum4'6). Another important p a r a m e t e r is the shape of the impacting projectile since this is known to affect the energy for target perforation. 6 For materials not susceptible to adiabatic shear this is due to the projectile shape affecting the deformation pattern and the extent of the petal tube. 6 For materials susceptible to adiabatic shear the degree to which adiabatic shear occurs can also be influenced by the deformation pattern a s s o ciated with the penetrating projectile. If the deformation is sufficiently concentrated, r i s e s in temperature due to heat generation from plastic deformation can cause thermal softening and so promote adiabatic shear which can lead to catastrophic failure. The purpose of this Investigation was to determine the influence of projectile geometry on the formation of adiabatic shear bands and how such shear bands affect the penetration c h a r a c t e r i s t i c s of the material. EXPERIMENTAL 1.1) Target Material The target material used was 10 mm thick type 2014 aluminum alloy in the T6 condition, a material which shows a strong tendency to form adiabatic shear bands when penetrated by projectiles, s 1.2) Penetration Experiments The projectiles were in the form of hardened steel rods 7 mm diam and 70 mm long. The steel used was type 4340. Three prdjecttle geometries were used; flat ended, hemispherical ended, a n d ogival. To obviate the frictional drag between the rod and the walls of the hole A. L. W1NGROVE is Research Scientist, Australian Defence Scientific Service Department of Supply, Defence Standards Laboratories, Alexandria, New South Wales, Australia. Manuscript submitted April 20, 1972. METALLURGICAL TRANSACTIONS
after perforation, the shanks of the projectiles were r e duced to 6 mm diam, for a distance of 2.5 cm commencing from a point approximately one projectile diameter from the front end. The projectiles were fired fr
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