Which type of crack can be detected by magnetic particle inspection with circular or longitudinal magnetization?

The correct choice for this question is based on the principles of magnetic particle inspection, which relies on the behavior of magnetic fields and particles. When using magnetic particle inspection, the method involves magnetizing the test material and applying ferromagnetic particles.

Circular and longitudinal magnetization helps reveal different types of flaws in materials. Specifically, cracks that are at a 45-degree angle to the magnetic field can interrupt the magnetic lines of force, causing magnetic leakage fields that attract the particles. This results in a clear indication of the presence of a crack because the magnetic particles will cluster at the site of the disruption caused by the crack.

In contrast, vertical, horizontal, or parallel cracks relative to the magnetic field may not produce the same effect when using these types of magnetization. Vertical cracks would align with the magnetic field and may not register a significant disturbance or attract particles effectively, while horizontal cracks will generally also align poorly with the lines of force when using circular or longitudinal magnetization. Hence, the distinctive nature of 45-degree cracks interacting with the magnetic field is what makes them detectable using the mentioned inspection methods.