MS Thesis Presentation by Nitin R Patel
Wednesday, October 20, 2004
(Dr. Min Zhou, Chair)
"Intermediate Strain Rate Behavior of Two Structural Energetic Materials"
TA new class of materials, known as multi-functional energetic structural materials
(MESMs), has been developed. These materials possess both strength and energetic
functionalities, serving as candidates for many exciting applications. One
of such applications is ballistic missiles, where these materials serve as
part of structural casing as well as explosive payload.
In this study, the dynamic compressive behavior of two types of MESMs is investigated in the intermediate strain rate regime. The first type is a thermite mixture of Al and Fe2O3 particles suspended in an epoxy matrix. The second type is a shock compacted Ni-Al intermetallic compound. Compression experiments on a split Hopkinson pressure bar (SHPB) apparatus are carried out at strain rates on the order of 103s-1. In addition, a novel method for investigating the dynamic hardness of Al + Fe2O3 + Epoxy materials is developed. In this method, high-speed digital photography allows time-resolved measurements of the indentation diameter to be obtained throughout the indentation process.
Experiments show that the NiAl intermetallic compound exhibits a rather ductile behavior and the deformation of Al + Fe2O3 + Epoxy mixtures is dominated by the polymer phase and significantly modulated by the powder phase. The powders act as reinforcement for the polymer matrix, strengthening the material with increasing volume fraction.
To quantify the constitutive behavior of the 100% epoxy and the Al + Fe2O3 + Epoxy materials, experimentally obtained stress-strain curves are fitted to the Hasan-Boyce model. This model uses a distribution of activation energies to characterize the energy barrier of localized shear transformations. The parameters used in this model for the Al + Fe2O3 + Epoxy mixtures reflect the presence of the powders within the polymer matrix. Good fits are achieved for pure epoxy as well as mixtures containing powders.