Overview
IEC 61631:2001 specifies a standardized test method for the mechanical strength of cores made of magnetic oxides. The method is designed for consistent measurement of bending strength of common core forms - notably E-cores, ETD-cores and I-cores - and can be adapted for other types (e.g., U-cores) by agreement between parties. The procedure emphasizes controlled test arrangements and reporting so results can be used for material development, quality checking and comparative evaluation.
Key Topics
- Scope and applicability: Test method suitable for most E, ETD and I core types; other geometries may use derived methods agreed by parties.
- Apparatus requirements:
- Loading wedge and supports made of hardened steel with hardness between 40 HRC and 60 HRC.
- Loading wedge and roller bars have a 2 mm radius.
- Testing machine capable of constant loading-rate and peak-load recording; force accuracy per EN 10002-2, Grade 1 (1%).
- Humidity measurement per ISO 4677-1 or ISO 4677-2, accuracy ±2% RH.
- Specimen preparation & quantity:
- Test cores selected as agreed by parties; machining of surfaces permitted but must be reported because surface finish affects strength.
- Minimum five specimens for development/QA; minimum 30 for statistical evaluation (e.g., Weibull parameters).
- Test conditions & procedure:
- Ambient temperature: 15 °C to 35 °C, with ≤3 °C variation during a series.
- Relative humidity: 45% to 85%, with ≤10% variation during a series.
- Preload: 5 N to 25 N to accommodate non-parallel faces.
- Loading rate: 5 mm/min to 20 mm/min until fracture.
- Record peak load at fracture and retain fractured fragments for fractographic examination.
Applications
This standard is primarily used for:
- Material development and characterization of ferrite and magnetic oxide cores.
- Incoming inspection and quality control of core batches.
- Comparative assessments between suppliers or production processes.
Practical benefits include reproducible bending strength data, clearer identification of strength-limiting defects (pores, large grains, surface damage), and standardized reporting that aids decision-making in component design and production control.
Related Standards
- IEC 61246:1994 - dimensions for magnetic oxide E-cores and associated parts.
- EN 10002-2:1992 - verification of force measuring systems for tensile testing machines (accuracy requirements).
- ISO 4677-1/2 - methods for determining relative humidity during conditioning and testing.
Note: IEC 61631 emphasizes careful reporting of test-piece surface condition, handling precautions and test setup since mechanical strength results can be strongly influenced by microstructure, surface finish and environmental conditions.