Performance loss of Terfenol-D particle epoxy composites under cyclic magneto-mechanical loading at the matrix glass transition start and finish temperatures

The present paper presents cyclic strain amplitude and longitudinal strain measurements of longitudinally compressed Terfenol-D particle samples subjected to strain cycling. A four way comparison is made of the responses of material processed under high longitudinal magnetic field, material processed under no magnetic field, material strain cycle tested at temperatures near the matrix glass transition finish temperature, and material strain cycle tested at a temperature near the matrix glass transition start temperature. The cyclic strain amplitude of magnetically-aligned material during processing was clearly larger than that of non-magnetically-aligned material. The cyclic strain amplitude of the material was significantly larger when tested at a temperature near the matrix glass transition finish temperature. A useful range of longitudinal applied stress exists where the composite suffers little apparent degradation. Beyond this range the composite exhibits steadily decreasing cyclic strain amplitude with increases in longitudinal compressive stress magnitude. Scanning electron microscopy indicated that the primary mode of initial failure of the material was near-surface circumferential cracking in the Terfenol-D particles.