3-D finite element computation and dynamic modal analysis on ultrasonic vibration systems

Stress and modal analyses are performed on an ultrasonic vibration system by means of a 3-dimensional finite element computation and dynamic modal analysis code "Algor" The system consists of an edge-cracked specimen linked elastically with one or two amplifying horns which come into resonant longitudinal vibration at 20kHz.Operating principle of the ultrasonic fatigue machines and experimental procedures for ultrasonic fatigue crack growth studies are briefly presented.     

Determination of stress intensity factors in ultrasonic fatigue loading

The application of displacement and energy approaches to the determination of stress intensity factors in ultrasonic fatigue crack growth (fcg) studies is discussed.The particular advantages as well as the limitations of the two approaches are evaluated.Two types of ultrasonic fatigue loading with different stress ratios are exerted on the specimen respectively: the ultrasonic fatigue loading with a stress ratio R=-1 and the ultrasonic fatigue excitations superposed upon a static mean stress with R>-1 From comparison the conclusion is formed that the energy approach developed in the investigation is more accurate,concise and suitable than commonly adopted approaches and/or formulas proposed.Experimental fcg data on a titanium alloy Ti-6Al-4V and the characteristic mechanism of the ultrasonic fcg are investigated.