Session V1: ME.3 Inelastic Deformation, Fracture, and Spall X

Damage in Low Alloy Steel Produced by Sweeping, Interacting Detonation Waves

Detonation waves that sweep along the surface of a metal plate induce reduced pressure and enhanced shear, relative to the same detonation at normal incidence. Detonation waves at intermediate obliquity impress intermediate combined stress states. Release waves from the free surfaces may enter into play and contribute to the damage. Initiation of explosive at discrete points produces strong pressure, density, and velocity gradients in the gaseous explosive products where the waves collide that are impressed in an adjacent metal, causing similar stress gradients within the metal that often cause intense damage. In this work, we investigate damage generated in AISI 4130 steel by the combined effects of oblique drive and interacting detonation waves. The experimental data consists of multipoint velocimetry points probing the free surface in regions loaded by interacting detonation waves and regions between the interactions. Metallography on recovered plate records the plastic flow and damage correlated with the velocimetry data. Calculations provide further insight into the loading conditions created by the sweeping, interacting detonation waves. Spall is indicated in most regions, but not some, and the alpha-epsilon stress-induced phase transformation appears in most regions, but not all. Correlations of the observed physical effects with incident wave obliquity and transverse position relative to the wave interactions are discussed.   

A Consistent Approach To Stochastic Seeding of Simulations of Fragmenting Ductile Metals

For failure by brittle fracture the well-known weakest-link arguments have led to widespread use of a two-parameter Weibull distribution. The probability of failure by a ductile damage mechanism at small plastic strains is exceedingly small. This results in a threshold for deformation induced damage and attendant failure that should be manifest in the statistical description. A three-parameter Weibull distribution with a lower cut-off satisfies this constraint. The three-parameters are determined systematically from experiments. The Weibull modulus is estimated by examining the results of scaled experiments. The values of the most-likely failure strain were inferred from simulations of quasi-static tests. The lower cut-off failure strain was estimated from the tensile test data. This approach was applied to different microstructures of AISI 4340 steel achieved through various heat treatments to determine the three parameters and constitutive response for each heat treatment. Exploding pipe simulations were run to determine fragment distributions for two explosives and each heat treatment. These simulated distributions were then compared to high fidelity experimental data for distributions of the same heat treatments and explosives simulated.   

2169 Steel Waveform Experiments

In support of efforts to develop multiscale models of materials, we performed eight gas gun impact experiments on 2169 steel (21\% Cr, 6\% Ni, 9\% Mn). These experiments provided shock, reshock and release velocimetry data, with initial shock stresses ranging from 10 to 50 GPa (particle velocities from 0.25 to 1.05 km/s). Both windowed and free-surface measurements were used, with samples 1 to 5 mm thick. The study focused on dynamic strength determination via the release/reshock paths. Reshock tests with explosively welded impactors produced clean results. The free-surface samples, which were steps on a single piece of steel, showed lower wavespeeds for thin (1 mm) samples than for thicker (2 or 4 mm) samples. A configuration used for the last three shots allowed release information to be determined from these free surface samples as well. The sample strength appears to increase with stress from $\sim$1 GPa to $\sim$3 GPa over this range, consistent with other recent work but about 40\% above the Steinberg model. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.   

Dynamic Crack Tip Opening Displacement (DCTOD) as governing parameters for material fragmentation

Fragmentation in metals can be approached either by Mott statistical or by Energy-based fragmentation theory. Recently, Grady showed that the two theories can be reconciled showing that the material parameter that drives tendency to fragmentation and fragment size is the dynamic fracture toughness. Experimental data do not completely agree with these conclusions. In this paper, the dynamic CTOD -- crack tip opening displacement -- is proposed as fracture parameter which can account for plastic deformation occurring prior fracture. Here, an experimental procedure for determining the DCTOD is presented. Two sample geometries, namely 1/2'' compact tension C(T) and circumferential crack bar tension CCB(T), have been investigated for their use with tensile Hopkinson bar testing equipment. The respective calibration functions in the dynamic range were determined via FEA. DCTOD was measured using both high speed video recording with digital image correlation (DIC) technique and clip gauge at the crack mouth. The proposed procedure has been used to investigate dynamic fracture resistance of 316L stainless steel and high purity copper (99.98{\%}) and to correlate with available fragmentation data..