N.S. Brar

PENETRATION OF GROUT AND CONCRETE TARGETS WITH OGIVE-NOSE STEEL PROJECTILES

Abstract We conducted depth of penetration experiments into grout and concrete targets with ogive-nose steel projectiles. Powder guns launched 0.064 kg, 12.9 mm diameter projectiles into grout targets with unconfined compressive strengths of 13.5 M Pa (2.0 ksi) and 21.6 MPa (3.1 ksi). For the concrete targets, powder guns launched projectiles with length-to-diameter ratios of 10; a 0.48 kg, 20.3 mm diameter rod, and a 1.60 kg, 30.5 mm diameter rod. Concrete targets had unconfined compressive strength of 62.8 M Pa (9.1 ksi) for the 0.48 kg rods and unconfined compressive strength of 51.0 MPa (7.4 ksi) for the 1.60 kg rods. For these experiments, penetration depth increased as striking velocity increased until nose erosion became excessive. Thus, we determined experimentally the striking velocities corresponding to maximum penetration depths. Predictions from a previously published model are in good agreement with data until nose erosion becomes excessive.

Impact‐induced failure waves in glass bars and plates

Glass bars and plates were subjected to impact loading. Failure waves were observed to propagate behind the compression waves. Material traversed by the failure wave suffers total loss of tensile strength and substantial drop in shear strength. Failure wave propagation velocities exceed the maximum crack propagation speed, but are not constant. In bars, failure wave speed range from 2.3 to 5.2 mm/μs, increasing with increasing impact velocity; in plates, the wave speed is about 2 mm/μs. The failure is ‘‘explosive’’ in nature, leading to radial expansion in bars and an increase in mean stress in plates.

Penetration of 7075-T651 aluminum targets with ogival-nose rods

Abstract We developed analytical models that predicted forces and penetration depths for long, rigid rods with ogival noses and rate-independent, strain-hardening targets. To verify our models, we conducted terminal-ballistic experiments with 7.1 mm diameter, 0.025 kg, 3.0 caliber-radius-head, ogival-nose rods and 152 mm diameter, 7075-T651 aluminum cylindrical targets. The model predicted penetration depths in good agreement with the data for impact velocities between 370 and 1260 m s−1.

Dynamic high‐pressure properties of AlN ceramic as determined by flyer plate impact

The dynamic properties of hot‐pressed aluminum nitride ceramics were determined in a series of plate impact experiments using longitudinal and transverse in‐material manganin gauges. The Hugoniot curve for hot pressed specimens was determined in the range of 0–190 kbar with a value of 94±2 kbar for the Hugoniot elastic limit (HEL). Using both gauge orientations, the stress deviator in the specimens was determined as the difference between longitudinal and transverse stresses. It was found that the stress deviator remains relatively constant above the HEL, and is about 10% higher than the value at the HEL point. The inferred Hugoniot converges to the extrapolation of the hydrostat. Since the convergence is not due to loss of strength, it may be due to a phase change in the AlN from low‐pressure (wurtzite) structure to high‐pressure (rocksalt) structure.

On the influence of the loss of shear strength on the ballistic performance of brittle solids

Abstract The shear strength of solids correlates with penetration resistance in ballistic experiments. The present study was conducted in order to demonstrate the relation between the loss of shear strength of shock loaded brittle solids and ballistic penetration resistance. Soda lime glass and alumina were chosen as the test materials because their properties under planar shock wave experiments were recently measured. Ballistic experiments using the thick backing configuration demonstrated a correlation between loss of shear strength at high shock pressures and decreased ballistic performance.

Stone impact damage to automotive paint finishes: Measurement of temperature rise due to impact

Abstract Cold rolled steel panels, coated with automobile paint were impact tested by shooting a 2 g granite projectile at the panels at velocities from 47 to 78 m s −1 . The temperature rise in the coating, due to impact, was measured using an array of high speed infrared detectors. The peak measured temperature increases were as high as 200°C, high enough to put the coating past its glass transition temperature, resulting in drastic changes to the coating mechanical properties and hence its resistance to damage.

APPLYING STEINBERG'S MODEL TO THE HUGONIOT ELASTIC LIMIT OF POROUS BORON CARBIDE SPECIMENS

Plate‐impact experiments were performed on boron carbide specimens, having different porosities, in order to measure their Hugoniot elastic limit (HEL) values. The measurements were performed with commercial manganin gauges embedded at the back surface of the specimen and backed by a thick Plexiglas disk. The measured values show an almost linear decrease in the HEL values between 194 kbar (For the fully dense material) to 96 kbar for a specimen with 16.3% porosity. These values were compared with a theoretical model [suggested by D. Steinberg (LLL report LLL‐UCID‐16946, 1975)] which accounts for the dependence of the HEL on porosity, and the agreement is shown to be good.

SHEAR STRENGTH OF TITANIUM DIBORIDE UNDER SHOCK LOADING MEASURED BY TRANSVERSE MANGANIN GAUGES

The shear strength of hot pressed TiB2 was measured under shock compression to about 3 times the HEL (75 kbar) by using transverse manganin gauges. The shear strength is taken as one-half the difference between the longitudinal (shock) and transverse stress. The shock stress was computed by impedance matching with the copper impactor. The strength of TiB2 at a shock level of 240 kbar increases to twice its initial value at the HEL. This pressure hardening may explain the superior ballistic performance of this material. These results are compared with similar data on other ceramics.

Flow stress and material model study at high strain rate and low temperature

The flow stress of M200 maraging steel, C1008 steel, and 6061‐T6 aluminum at low temperatures to 123 K and at a strain rate of about 103 s−1 is measured using split Hopkinson bar (SHB). Liquid nitrogen is used to cool the specimen to the desired temperature. The flow stress of M200 increased to 1.93 GPa at 123 K, an increase of 22 percent compared to 1.58 GPa at room temperature. In the case of 6061‐T6 aluminum the flow stress remains at about 390 MPa at temperatures in the range 293 to 123 K. For C1008 steel, the flow stress increased to 860 MPa at 123 K from its room temperature value of 610 MPa. The failure strain for C1008 steel at 123 K was 0.02, compared to 0.2 at room temperature, suggesting a ductile to brittle transition. The Johnson‐Cook material model constant ‘‘m’’, which accounts for temperature effect, is 0.5 for C1008 at temperatures in the range 123 K to 950 K.

Effect of phase change on shock wave attenuation in GeO2

Stress-wave profiles in vitreous GeO2 induced by planar and spherical projectile impact were measured using piezoresistance gauges in the 4 to 18 GPa shock pressure range. The planar experiments demonstrate the response of vitreous GeO2. This response can be divided into three regimes: (1) An elastic shock regime with ramp 4 GPa Hugoniot elastic limit (HEL) precursor. Shock propagation velocity decreases from an initial longitudinal elastic wave speed of 3.5 to 2.8 km/s at 4 GPa. (2) A transition wave regime where the ramp wave is superimposed on the precursor with an additional amplitude of 0 to 2 GPa followed by a sharp increase in shock pressure achieving peak loading pressures of 8 to 14 GPa. Above 4 GPa the ramp wave velocity decreases to a value below 2.5 km/s (the speed of the bulk wave, at the HEL). (3) A shock wave achieving the final shock state forms when peak pressure is >6 GPa specified by linear shock-particle velocity relation D=0.917+1.71 u (km/s) over the 6-40 GPa range for an initial density of 3.655 g/cm(3). The Hugoniots of GeO2 and SiO2, both initially vitreous, are found to be virtually coincident if pressure in SiO2 is calculated by multiplying the GeO2 pressure by the ratio of the initial densities of vitreous GeO2 to fused SiO2. The volume axes are translated by aligning the specific volumes for onset and completion of the four- to six-fold coordination phase change. Although only limited spherical impactor spherically diverging shock experiments were conducted, our present results demonstrate (1) The supported elastic shock in fused SiO2 decays less rapidly than a linear elastic wave when elastic wave stress amplitude is higher than 4 GPa. A supported elastic precursor in vitreous GeO2 decays faster with radius than a linear elastic wave; (2) in GeO2 (vitreous) unsupported shock waves decay with peak pressure in a phase transition range (4-15 GPa) with propagation radius (r) as proportional tor(-3.35).