Static and dynamic pore-collapse relations for ductile porous materials are obtained by analysis of the collapse of a hollow sphere of incompressible elastic-plastic material, with appropriate pore radius and over-all porosity. There are three phases of the pore-collapse process: an initial phase, a transitional elastic-plastic phase, and a plastic phase. The change in porosity during the first two phases is quite small. In the plastic phase, the static pore-collapse relation is an exponential law that depends only on the yield strength of the material; the dynamic relation is a nonlinear second-order ordinary differential equation that involves the yield strength and a material constant (with the physical dimension of time) that depends on the yield strength, the density, the initial porosity, and the pore radius. Comparison of the theoretical predictions with finite-difference computer-code calculations for pore collapse of a hollow sphere of compressible material indicates that the effect of elastic compressibility on pore collapse is quite small, so that the pore-collapse relations obtained from the incompressible model should have a wide range of validity. Also, the specific internal energy at the pore boundary has a logarithmic singularity as the pore closes.

No abstract

Abstract. We measured the ballistic performance offive ceramic materials (alumina, silicon carbide, boron carbide, aluminum nitride, and titanium diboride) and Pyrex, when they are backed by thick steel plates. The projectile for all tests was a rightcircular cylinder of tungsten sinter-alloy W2 with length 25.4 mm and diameter 6.35 mm,j%ed at velocitiesfrom 2.35 to 2.65 km/s. For this threat we determined the minimum area1 density of each material that is needed to keep the projectilefrom penetrating the backup steel. For all of the facing materials studied here, this performance measure increases approximately linearly with projectile velocity. However, the rate of increase is significantly lower for aluminum nitride than for the other materials studied. Indeed, aluminum nitride is a poor performer at the lowest velocity tested, but is clearly the best at the highest velocity. Our computer simulations show the significant influence of the backing material on ceramic performance, manifested by a transition region extending two projectile diameters upstreamfrom the material interface. Experiments with multiple material layers show that this inJuence also manifests itself through a significant dependence of ballistic performance on the ordering of the material layers.

We suggest that the relationship between the pressure P in a porous material and the average matrix pressure Pm in the material should be P=Pm/α, where α is the ratio of the specific volumes of the porous material and the matrix material.

Articles you may be interested inA single quartz crystal to measure dynamic elastic moduli at several ultrasonic frequencies Rev.Dynamic yield strengths, compression data under uniaxial shock-wave loading, and sonic velocities at 1 bar are reported for polycrystalline TiB 2 , SiC, Be 4 B, Be 4 B+8 wt% BeO, Be 2 B, AIBw TiBe 1 2' and ZrBelJ. Hugoniot elastic limits were measured as 86, 80, 74, 77, 65, 87, 53, and 71 kbar, respectively. Evidence of phase transitions was seen for the Be 4 B materials at 500 kbar and for SiC at 240 and 960 kbar. H PBX 9404 (HMX) Pressed TNT J PBX 9205 (RDX)