An equivalent linear model for magnetostatic nondestructive evaluation

Numerical models capable of modeling magnetic flux leakage (MFL) methods of nondestructive testing are of significant interest to industry. The nonlinear nature of the MFL problem necessitates the use of an iterative model, thereby resulting in excessive computational effort. This paper describes an approach for developing an equivalent linear model (ELM) where the ferromagnetic region is appropriately partitioned into different domains with each domain being assigned a constant permeability value depending on the magnetization level and the flaw size. The nonlinear behavior of the multi-layered object is then modeled using a linear MFL model. The strategy results in significant computational savings without a substantial loss in accuracy. Results supporting the validity of the approach have been obtained using a 3D magnetostatic finite element (FE) model.