Publications

To address known shortcomings of classical metal plasticity for describing material behavior under shock loading, a model which incorporates a distribution in the deviatoric stress state is developed. This distribution will translate in stress space under loading, and growth of the distribution can be included in the model as well. This proposed model is capable of duplicating the key features of a set of reshock and release experiments on 6061-T6 aluminum, many of which are not captured by classical plasticity. The model is relatively simple, is only moderately more computationally intensive, and requires few additional material parameters.

In the current study we are developing an experimental fracture material property test method specific to dynamic fragmentation. This test method allows the study of fracture fragmentation in a reproducible laboratory environment under well-controlled loading conditions. Motion and fragmentation of the specimen are diagnosed using framing camera, VISAR and soft recovery methods. Fragmentation properties of several steels, nitinol, tungsten alloy, copper, aluminum, and titanium have been obtained to date. The values for fragmentation toughness, and failure threshold will be reported, as well as effects in these values as the material strain-rate is varied through changes in wall thickness and impact conditions.

Sandia National Laboratories has developed a unique method for a hyper-velocity launch (HVL), the three-stage gun. The three-stage gun is a modified two-stage light-gas gun, consisting of a piston used in the first stage, an impactor in the second stage, and a flyer plate in the third stage. The impactor is made up of different material layers that are increasing in shock impedance. The graded or pillowed layers allow the flyer to be launched at velocities up to 16 km/s without the formation of a single shock wave in the flyer plate and without it melting. Under certain experimental conditions the flyer velocity cannot be measured by standard means, X-rays and VISAR. Also, there is a need to know the flyer velocity prior to a launch in order to calibrate instruments and determine the appropriate shot configuration. The objective of HVL{_}CTH is to produce an accurate forecast of the flyer plate velocity under different launch conditions. CTH is a Eulerian shock physics computational analysis package developed at Sandia National Laboratories. Using CTH requires knowledge of its syntax and capabilities. HVL{_}CTH allows the user to easily interface with CTH, through the use of Fortran programs and batch files, in order to simulate the three-stage launch of a flyer plate. The program, HVL{_}CTH, requires little to no knowledge of the CTH program and greatly reduces the time needed to calculate the flyer velocity. Users of HVL{_}CTH are assumed to have no experience with CTH. The results from HVL{_}CTH were compared to results of X-ray and VISAR measurements obtained from HVL experiments. The comparisons show that HVL{_}CTH was within 1-2% of the X-Ray and VISAR results most of the time.