Methods and techniques to characterise Terfenol-D

Characterisation parameters are required in order to provide reliable comparisons of different materials, for quality control in material production and to enable the design of more efficient transducers and control systems. Representation of non-linear, hysteretic behaviour is achieved by modelling either hysteresis loops or resonant response. In each case, by comparing the model predictions with the observed responses, numerical values can be assigned to the parameters that describe the material. Both the hysteresis loops and resonant response methods have a useful role but the latter is inherently more valuable, especially for description of the different contributions to the overall losses under dynamic conditions. A plane wave model of resonant response has the benefit that it can be developed to characterise either materials or devices under working conditions. These characterisation methods and techniques have been applied to different forms of Terfenol-D - random polycrystalline, grain oriented and a laminated sample. The results demonstrate that the resonance modelling can quantify the differences in behaviour between grain-oriented and random polycrystalline samples and that laminations successfully achieve full field penetration at frequencies when a large volume fraction of an unlaminated sample is screened. (C) 1997 Elsevier Science S.A.