Modeling anisotropic magnetic hysteresis properties with vector stop model by using finite element method

Purpose This paper aims to use a history-dependent vector stop hysteresis model incorporated into a two dimensional finite elements (FE) simulation environment to solve the magnetic field problems in electrical machines. The vector stop hysteresis model is valid for representing the anisotropic magnetization characteristics of electrical steel sheets. Comparisons of the simulated results with measurements show that the model is well appropriate for the simulation of electrical machines with alternating, rotating and harmonic magnetic flux densities. Design/methodology/approach The anisotropy of the permeability of an electrical steel sheet can be represented by integrating anhysteretic surfaces into the elastic element of a vector hysteresis stop model. The parameters of the vector stop hysteresis model were identified by minimizing the errors between the simulated results and measurements. In this paper, a damped Newton method is applied to solve the nonlinear problem, which ensures a robust convergence of the finite elements simulation with vector stop hysteresis model. Findings Analyzing the measurements of the electrical steel sheets sample obtained from a rotational single sheet tester shows the importance to consider the anisotropic and saturation behavior of the material. Comparing the calculated and measured data corroborates the hypothesis that the presented energy-based vector stop hysteresis model is able to represent these magnetic properties appropriately. To ensure a unique way of hysteresis loops during finite elements simulation, the memory of the vector stop hysteresis model from last time step is kept unchanged during the Newton iterations. Originality/value The results of this work demonstrates that the presented vector hysteresis stop model allows simulation of vector hysteresis effects of electrical steel sheets in electrical machines with a limited amount of measurements. The essential properties of the electrical steel sheets, such as phase shifts, the anisotropy of magnetizations and the magnetization characteristics by alternating, rotating, harmonic magnetization types, can be accurately represented.

Analysis of Environmentally Assisted Cracking in S420 Steel by Using the Theory of Critical Distances

The behavior of S420 steel under cathodic polarization in low pH aqueous environment is analyzed following the assumptions of the Theory of Critical Distances. This methodology has been successfully applied in fracture and fatigue analysis, but it has not been employed yet under stress corrosion cracking or hydrogen embrittlement conditions. This work focuses on the problem of environmentally assisted cracking by using the Point Method and the Line Method, both of them belonging to the Theory of Critical Distances. Fracture mechanic tests were carried out, using a slow strain rate machine, at two different solicitation rates (6·10−8 m/s and 6·10−9 m/s). The study is based on an experimental program composed of C(T) specimens with notch radii varying from 0 mm up to 2 mm. Cathodic polarization with a 5 mA/cm2 current has been employed and the aqueous aggressive environment was made using the Pressouyre’s method. The study has been completed with finite elements simulation analysis. The results reveal that the Theory of Critical Distances provides accurate predictions of the environmentally assisted cracking behavior of S420 steel in notched conditions.

Finite elements simulation of improvised explosively formed projectiles

Purpose The purpose of this paper is to investigate the applicability of the LS-DYNA software using a Lagrangian formulation in the jet formation, flight and penetration of improvised explosively formed projectiles (EFPs). Numerical results dealing with different properties of the EFPs have been validated with a significant number of field tests. Design/methodology/approach 2D and 3D Lagrangian models, using different material definition, are developed to reproduce the field-measured characteristics of copper- and steel-made EFPs: projectile size and velocity. After validation, the model has been extended to analyse the penetration features. Two different plasticity models have been used to describe the steel target, Plastic-Kinematic and Johnson–Cook. Findings Despite the difficulty in characterizing a non-industrial artefact, the results show that both Lagrangian models (2D and 3D) are able to simulate the projectile size, velocity and penetration capability with errors less than 10 per cent when using the Johnson–Cook material model for both liner and target. Practical implications These data can be used to test the penetration ability of improvised EFP’s against different targets, i.e. light armoured vehicles. Originality/value There are no references that address the application of the Lagrangian simulation of non-industrial EFPs and its validation with field tests, including penetration assessment.