Hysteresis (B-H Curve)

Hysteresis is the lag of magnetization (B) behind the magnetizing force (H) in ferromagnetic materials, producing the characteristic B-H loop whose width is governed by coercive force and whose intercept is residual magnetism.

Definition

The B-H loop shows how a ferromagnetic material magnetizes and demagnetizes. Soft magnetic materials have narrow loops (easy to demagnetize); hard materials have wide loops (retain residual magnetism). Hysteresis dictates whether residual or continuous MT technique is preferred.

Related terms

• Residual Magnetism — Residual magnetism is the magnetization remaining in a ferromagnetic part after the magnetizing current is removed, dependent on the material's magnetic hysteresis behavior and coercive force.
• Demagnetization — Demagnetization is the process of reducing the residual magnetic field in a part after magnetic particle testing, performed by passing the part through a decaying AC field or by AC current with reducing amplitude.
• Magnetic Permeability — Magnetic permeability (μ) is a material property describing how easily it can be magnetized, equal to the ratio of magnetic flux density (B) to magnetizing force (H), and is a primary factor in MT current selection.

More physics terms

Back-Wall Echo · Beam Spread · Near-Field · Far-Field · Dead Zone · Shear Wave · Longitudinal Wave · Surface Wave · Lamb Wave · Mode Conversion

Where this comes up in practice

Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.

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