Evaluation of micro-damage by acoustic methods

Abstract Several methods for the determination of integral damage in sheet metal are reviewed and investigated at the example of the ferritic steel DC04. A novel method to determine damage in cylindrical rings is proposed. Such a method is useful for the measurement of damage in components manufactured by sheet-bulk forming. In sheet-bulk-forming or precision forging sheets with a thickness in the range of 1-5 mm are processed by making use of an intended three-dimensional material flow to form toothed components such as gears. Damage leads to the modification of physical properties, such as Young’s modulus and the related resonance frequency. Young’s moduli were determined by various methods such as tensile tests and the frequency of natural oscillations of rectangular samples as well as cylindrical rings. Additionally, the change in the propagation velocity of ultrasonic waves in rectangular bars was examined as a damage criterion and reference measurements of damage by electron microscopy were carried out. The damage values obtained by electron microscopy are consistent with the results of the other investigated methods.