FEM MODELING OF STRESS INTENSITY FACTORS FOR FATIGUE-CRACK GROWTH AT ULTRASONIC FREQUENCIES

The inverse iteration FEM is used to determine the stress intensity fa ctor of a single edge notched specimen as used in ultrasonic resonance testing of fatigue crack growth. The stress intensity factor is deter mined as a function of velocity or amplitude at the specimen ends. Res onance frequency and tension-compression ratio R are calculated for di fferent crack lengths. It is shown that the R-value increases from R = -1 to R = -0.90 when the relative crack length (a/W) increases from 0 .067 to 0,4. The stress intensity factor for high frequency resonance loading is compared with the stress intensity amplitude for two static loading conditions. Significant differences are found in comparison w ith static concentric loading and similarities with static uniform dis placement loading.