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Magnetic particle inspection (MPI) is a nondestructive testing process where a magnetic field is used for detecting surface, and shallow subsurface, discontinuities in ferromagnetic materials. Examples of ferromagnetic materials include iron , nickel , cobalt , and some of their alloys .
This method is unaffected by all non conductive materials such as concrete, wood, plastics, bricks, etc. However any kind of conductive materials within the magnetic field will have an influence on the measurement. Advantages of the pulse induction method: high accuracy; not influenced by moisture and heterogeneities of the concrete [2]
Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnetic tape can with relative ease record and play back audio, visual, and binary computer data.
The range of materials tested during this 36-year period included iron, steel, brass, bronze, wood, stone, and concrete as well as miscellaneous items such as manila, cotton yarn, hemp, and roller skates. In total, 87,062 tests were conducted for the government, while 27,096 were performed for private enterprise. [1] [5]
The magnetic material is normally in the form of tape, with the tape in its blank form being initially demagnetised. When recording, the tape runs at a constant speed. The writing head magnetises the tape with current proportional to the signal. A magnetisation distribution is achieved along the magnetic tape.
Recording onto a metal tape requires special high-flux magnetic heads and high-current amplifiers to drive them. [19] [79] Typical metal tape is characterized by remanence of 3000–3500 G and coercivity of 1100 Oe, thus its bias flux is set at 250% of Type I level.
Coercivity in a ferromagnetic material is the intensity of the applied magnetic field (H field) required to demagnetize that material, after the magnetization of the sample has been driven to saturation by a strong field. This demagnetizing field is applied opposite to the original saturating field.
ISO 16428:2005 Implants for surgery – Test solutions and environmental conditions for static and dynamic corrosion tests on implantable materials and medical devices ISO 16429:2004 Implants for surgery – Measurements of open-circuit potential to assess corrosion behaviour of metallic implantable materials and medical devices over extended ...