Issue34

G. M. Domínguez Almaraz et alii, Frattura ed Integrità Strutturale, 34 (2015) 498-506; DOI: 10.3221/IGF-ESIS.34.55 504 Figure 10 : Bi-dimensional numerical model to evaluate J and K under plane strain, different crack lengths and applying loads. a) b) Figure 11 : Numerical results for the J integral and the stress intensity factor K, for three applying loads and different crack lengths. C ONCLUSIONS he following conclusions can be drawn from this research work:  Ultrasonic fatigue endurance on polymeric material ABS was obtained under controlled temperature.  Experimental tests were carried out under mechanical domain, since thermal domain was minimized by three factors: low loading, low dimensions of testing specimen and immersion in a cooling liquid.  Ultrasonic fatigue life of ABS polymer is close to one millions of cycles when the applied load is close to 7 MPa; it increases to one thousand millions of cycles when the applied load decreases to 2.25 MPa, no matter the cooling liquid used (water or oil).  Under ultrasonic fatigue testing with low applying load and predominant mechanical domain, the yield stress increase (aging) is low and it is developed during the first 100 seconds of ultrasonic testing; for the long testing time, an asymptotical tendency is observed. This behavior is not modified using water or oil as cooling liquid.  The patters of crack initiation and propagation of this polymer were quite different for specimens immersed in water and in oil: for the first ones, crack initiates at one corner of prismatic specimen associated with appreciable plastic deformation; then, crack propagates contouring the protuberance and extending to lateral sides with low plastic deformation. For specimens immersed in oil, crack initiates at the top of the protuberance with apparently less plastic deformation; then, it propagates along the principal axis of the elliptical bubble, extending to lateral sides where plastic deformation is very low. T