Spall Fracture of Multi-Material Plates Under Explosive Loading Engineering Project Second Progress Report Presentation By James Danyluk

Spall Fracture in Solids Shock waves traveling through a solid material is reflected at changes in material or free surfaces. These reflected shock waves are known as rarefaction waves or relief waves. When a free surface and rarefaction wave interact, a tensile stress can be generated in the solid material. ◦ This can also happen with two rarefaction waves interact. If this tensile stress exceeds the dynamic tensile strength, or spall strength, the material can fracture.

Hydrocode Model ANSYS AUTODYN, an explicit dynamics code, was used to model the system. The Euler Multi-material solver was used. The model was setup with an Explosive, Solid Material and Air layers. The analysis modeled different materials and material combinations ◦ The tensile wave generated in the solid material(s) was examined in each model. The analysis was separated into four sets of iterations ◦ 1D Elastic only material models ◦ 1D Elastic/Plastic material models ◦ 1D Elastic/Plastic/Failure material models ◦ 2D Elastic/Plastic/Failure material models

Hydrocode Model Single Plate Model Two Plate Model Three Plate Model

Single Plate Hydrocode Results Al6061-T6 Plate

Single Plate Hydrocode Results Shock wave in explosiveShock wave in plate Rarefaction wave generated

Two Plate Results Tungsten/Polyethylene CombinationTungsten/304L Steel Combination

Three Plate Results Tungsten/Polyethylene/Tungsten304L/Tungsten/304L

Spall Failure Model Results Tungsten/Aluminum Aluminum/Tungsten

Current Conclusions Stacking materials can dictate how spall failures occur For most cases, the outer solid layer developed spall planes, while the inner layer remained intact. ◦ This method can be used to develop “spall plates”, plates that are intentionally designed to spall off, leaving the desired material (inner layer) intact. When a highly dense material (tungsten) is mated next to a very low density material (aluminum, polyethylene), a rarefaction wave can be generated by the material interface that will cause the tungsten plate to spall. ◦ Other material combinations did produce rarefaction waves, but they were not large enough to overcome the explosive loading and produce a tensile stress in the plate. ◦ In these cases, the spall can happen in both the inner and outer layers, but the amount of spall is highly reduced in the outer layer.

Schedule/Milestones 9/21/10:Submit Proposal 9/28/10:Complete Hand Calculations/Finish Research 10/5/10:Complete 1-D Elastic Hydrocode Model Results 10/12/10: Complete 1-D Elastic/Plastic Hydrocode Model Results 10/19/10:Submit First Progress Report 10/26/10:Complete 1-D Elastic/Plastic/Failure Hydrocode Model Results 11/9/10:Submit Second Progress Report 11/18/10:Complete 2-D Elastic/Plastic/Failure Hydrocode Model Results 11/30/10:Submit Final Draft 12/14/10:Submit Final Report