PSI - Issue 18

G.M. Dominguez Almaraz et al. / Procedia Structural Integrity 18 (2019) 594–599 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 3. Numerical higher stress induced of 200 MPa at the neck section of testing specimen with 12.5  m of displacements at the ends.

Since the three mechanical properties of the two tested steels are similar (density, Young’s Modulus and Poisson ratio), the simulation of Figure 3 applies for the two materials. In Figure 4 (a) is presented the fractured specimen and the thermographic image of 4140T steel, showing that the higher temperature attained at the specimen neck section when crack initiates was 180° C; whereas the Figure 4 (b) illustrates the same condition for the 1045 steel, where the higher temperature at crack initiation was 124° C. With 200 MPa of high stress at the neck section of specimen, this represents 48,2% of yield stress for the 4140T steel, but 64.5% of yield stress for the 1045 steel.

(a) (b) Fig. 4. (a) Thermographic higher temperature at crack initiation for 4140T steel, (b) Thermographic higher temperature at crack initiation for 1045 steel. 3. Experimental results Two principal experimental results are obtained with this investigation: ultrasonic fatigue endurance for the two car steels, and the analysis of fracture surfaces related to crack initiation and propagation on these steels, under the described loading modality. In Figure 5 (a) are plotted the ultrasonic fatigue results for the 4140T steel; whereas the Figure 5 (b) presents ultrasonic fatigue results for the 1045 steel. Concerning the fracture surfaces of these steels, in Figures 6 (a) and (b) are shown the corresponding for 4140T steel; whereas the Figures 7 (a) and (b) present the fracture surfaces for 1045 steel. Figure 6 (a) and (b), show two fracture surfaces of the 4140T steel; two principal trends are observed: 1) the crack initiation is associated frequently with the non-metallic inclusions, and 2) The slow propagation crack zone increases as the applied load decreases.