Magnetic and electric poling effects associated with crack growth in BaTiO3-CoFe2O4 composite

Magnetoelectroelastic composite possesses the dual feature that the application of magnetic field induces electric polarization and electric field induces magnetization. The poling directions introduced magnetically and electrically can be different in addition to those for the applied magnetic and electric field. Their choices can influence the character of crack growth which could be enhanced or retarded. The details of how the directions of poling and applied field would affect crack initiation and growth are discussed in relation to the volume fraction of inclusions for a BaTiO3-CoFe2O4 two phase composite. The multi-functional aspects of magnetoelectroelastic materials are involved since they entail multi-scaling features. Failure criteria that applies to isotropic elastic materials may not hold for composites exhibiting piezomagnetic and piezoelectric properties. For instance, a negative energy release rate has been obtained for cracks in piezoelectric materials. In view of what has been said with reference to the energy release rate approach, it is desirable to use the strain energy density function as a failure criterion, even if it is only for its positive definiteness character. Physically speaking, it is attractive to have a function that could rank the proportion of energy related to volume and shape change. They determine the proportion of the hard and soft phase of the composite and hence the volume fraction of the constituent. Strength and toughness parameters used for ranking isotropic and homogeneous materials will not apply for anisotropic and/or nonhomogeneous materials if these microstructure effects could not be suppressed to a lower scale and represented as an average at the macroscopic scale. Too much emphases cannot be placed on the need to clarify the multi-scaling aspects of piezoelectric and piezomagnetic materials. Their behavior as affected by the presence of crack-like defects should be understood prior to deciding whether the material characterization approach would be suitable. That is whether simplicity could justify at the expense of conceptual rigor. Much of this would depend on scaling the time and size related to loading and material structure interaction. The magnetoelectroelastic crack model selected in the work to follow perhaps will provide an insight into the complexicity of the state of affairs for treating the finer details of material behavior with rigor. The proposed test model shows that crack growth in the magnetoelectroelastic materials can be suppressed by increasing the magnitude of the piezomagnetic constants in relation to those for piezoelectricity. A more rational means of evaluating the resistance of materials against fracture is thus proposed, particularly when anisotropy and inhomogeneity might be present. (C) 2003 Elsevier Science Ltd. All rights reserved.