What is the role of a magnetic yoke in MPI?

The magnetic yoke plays a crucial role in Magnetic Particle Inspection (MPI) by creating a magnetic field across the testing material. This is essential for MPI because the inspection process relies on magnetism to detect surface and near-surface discontinuities in ferromagnetic materials. When the yoke is applied to the test piece, it generates magnetic flux lines within the material, allowing for the attraction of magnetic particles that are used to identify any flaws.

By establishing a controlled magnetic field, the yoke ensures that the magnetic particles can respond to the presence of defects, as they will accumulate at the discontinuities, forming an indication that can be visually assessed. This ability to create and manipulate the magnetic field is the foundation of the MPI technique, making the yoke an indispensable tool in the process.

The other options—amplifying sound waves, generating heat, and enhancing visibility—do not relate to the fundamental purpose of the magnetic yoke. Sound waves are associated with ultrasonic testing, heat generation is not a required component of MPI, and while visibility of indications is important, the definitive role of the yoke pertains specifically to magnetic field generation.