• Silva, David

Abstract

This study proposes the application of low-field magnetic analysis (LFMA) as an alternative non-destructive testing method based on magnetic flux density for the detection of mechanical ductile damage in sheet metal under uniaxial stress. Ductile damage is related to the development of micro-voids and pores due to large plastic strains. The samples were strained to different levels of strains up to 21% and measured with LFMA after unloading. Our approach is based on the assumption that as the plastic strain in steel increases, more damage is accumulated in the microstructure and therefore the magnetic properties are modified. Numerical simulation using finite element method, as well as experimental measurements such as tensile test, hardness, X-ray diffraction and electrical resistivity, were also applied to validate the proposed method in the detection of damage in tensile sample. It was found that the magnetic flux density indeed varies proportionally to the strain (72.3-63.4 mT (0-12.4% damage) for H = 243.2 Oe). These results demonstrate that the LFMA can be used to evaluate mechanical damages caused by plastic strain changes induced on steel. Furthermore, the LFMA presents accurate results for low magnetic fields with high sensitivity and reliability.

Topics

• density
• impedance spectroscopy
• microstructure
• pore
• polymer
• resistivity
• x-ray diffraction
• simulation
• steel
• hardness
• void