Mechanical reliability of ferrite cores in inductive components

It is a widespread practice to glue mated soft ferrite core halves in the manufacture of inductive components. However, thermally-induced stresses can initiate fracture of the ferrite core in such an inductive component, e.g., a transformer in a switchmode power supply. Therefore, it is essential for designers to know the magnitude of these stresses compared with the strength of the ferrite material. These thermally-induced stresses can originate from and/or be enhanced by: the conditions for gluing of the mated core halves; thermal cycling tests; and trends to a higher power throughput, leading to a higher working temperature (100-1250 degrees C). The magnitude of thermal stresses has been studied for some relevant cases. Absolute stress levels as well as the location of the most critically stressed parts have been identified. In addition, methods for testing the strength of a core half have been analyzed. These analyses are used for a discussion of the relevance of various testing methods to assess the mechanical reliability of ferrite cores in inductive components. The simulations show that mechanical stresses induced by temperature cycling tests of glued ferrite core halves can be very well predicted