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Analytical Methods
Published in Colin R. Gagg, Forensic Engineering, 2020
Magnetic particle inspection: a technique only applicable to ferromagnetic materials. The component is painted with a white paint and then placed in a strong magnetic field. The attachment of strong horseshoe permanent magnets is often sufficient. Any cracks in the component produce local magnetic poles and when ‘ink’ consisting of iron, or iron oxide, particles in paraffin is sprayed on to the component the particles settle at these poles and highlight the crack. Once again it is only applicable to surface cracks in ferromagnetic materials, but is very quick and cost-effective. A similar technique is that of ultraviolet (UV) examination of fluorescent inks. Advantages: quick and relatively uncomplicated, providing immediate indication of defects. Will reveal both surface and near-surface defects, being the most serious stress concentrators. Can be adapted for both site and laboratory use, with no elaborate sample pre-cleaning requirement.Disadvantages: restricted to ferromagnetic materials – usually iron and steel. Cannot be used on austenitic stainless steel. Requires an electrical supply. Spurious, or non-relevant indications possible; thus interpretation is a skilled task.
Improved detection of surface defects at sample edges using high-frequency eddy current amplitude and phase measurements
Published in Nondestructive Testing and Evaluation, 2022
Amanda To, Zhichao Li, Steve Dixon
Many safety-critical components in the aerospace or power generation industries are made from titanium alloys, which have lightweight, high strength and excellent corrosion resistance [1,2]. But they suffer from fatigue of manufacturing defects that can lead to the generation of surface-breaking cracks [3]. Techniques used for surface crack detection include penetrant testing (PT), magnetic particle inspection (MPI) and magnetic flux leakage (MFL) [4]. Unfortunately, the PT method needs critical surface cleaning and is only sensitive to defects open to the surface, while MPI and MFL methods are restricted to ferromagnetic materials. Whilst there are reports of using ultrasound to detect small surface-breaking defects [5], it is rarely in practice used in industry but is obviously a dominant method used in inspecting samples for volumetric defects.
Time Multiplexing of Currents for Magnetic Particle Inspection
Published in Research in Nondestructive Evaluation, 2022
Magnetic particle inspection (MPI) is a nondestructive testing (NDT) method that can be used for surface or subsurface defects detection in ferromagnetic materials. MPI is based on the magnetic flux leakage method and a follow-up visual inspection.