Abstract
To ensure long life reliability of the machine parts made of thin sheet metals, ultrasonic plain bending fatigue test method for thin sheet metals was developed. One end of the sheet specimen is fixed at a loop point of the bar oscillating at a frequency of 20kHz and the other end is set free. As a result, when a frequency of the first characteristic bending mode vibration of the specimen is also 20kHz, a resonance occurs in the specimen due to the forced vibration at the fixed end. This is a similar situation to the plain bending fatigue and the maximum cyclic stresses of tension-compression result near at the fixed end of the specimen. To calculate stress, deflections both at the free end and at the fix end of the specimen oscillating at a frequency of 20kHz have to be measured. A laser displacement sensor and a gap sensor based on variation of the capacitance were used to measure these deflections. Thus, long life fatigue strengths of thin sheet metals can be obtained in a very short period of time. Stainless steel, phosphorous bronze, commercially pure aluminum and maraging steel were used as the test materials and fatigue properties of those sheet metals of around 0.2mm thick were obtained up to the giga-cycle regime. From the results, it is confirmed that this method can be used practically to obtain very high cycle fatigue properties of sheet metals in a very short time.
