Particle motion and the modelling of strain response in magnetic fabrics

Abstract

SUMMARY Quantitative correlations between the magnetic fabric (magnetic susceptibility or remanent magnetic anisotropies), single mineral anisotropy , and preferred mineral orientation is investigated using computer modelling. The influences of various initial fabric patterns and imposed strain on the magnetic fabric are simulated using multiparticle systems represented by their magnetic anisotropy tensor. Each single mineral is numerically reoriented under coaxial deformation conditions using the strain response models of March and Jeffery/Gay. The calculated strain In (e,) versus magnetic fabric M, = In [k,/(k,,, . kinr . k,,,)1’3] curves show the following characteristics: (1) for initial randomly oriented distributions a log-linear correlation exists for strain magnitudes below 200 per cent. (2) For higher strains the curves asymptotically approach the M, value defined by the particle anisotropy. (3) The slope a of the correlation lines is a function of the particle anisotropy, the ellipsoid shape, and the strain response model. (4) Due to the prolate shape of particles, the maximum susceptibility axes are more sensitive to strain for initially anisotropic fabrics than the minimum axes. (5) The relationship between magnetic fabric and strain in multiparticle systems with known initial preferred orientations and single particle anisotropy shows a similar behaviour. Depending on the pattern and orientation of the initial fabric, the maximum axes show either a log-linear correlation to strain with a characteristic slope a or a kinked curve, with two almost linear parts.