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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and roll fixtures. For the 1045 steel the principal applications are: gears, pins, rams, shafts, rolls, sockets, axles, spindles, worms, bolts, ratchets, light gears, studs, crankshafts, guide rods, connecting rods, torsion bars and hydraulic clamps. These two materials have been investigated under different mechanical tests. The 4140 steel has been subjected to Charpy impact tests to investigate the microstructural properties of this steel, Chaouch et al. (2018); the effect of quenching and tempering heat treatments on the mechanical properties of AISI 4140 steel, Meysami et al. (2010). The effect of austempered AISI 4140 steel with dissolved hydrogen on its fatigue crack behavior, Nagarajan et al. (2017). Concerning the 1045steel: the effect of heat treatment on hardness and microstructure on this steel, Ibrahim and Sayuti (2015); the parameters involved and the mechanical properties modification of the 1045 steel, cutting at very high speeds, Ye et al. (2012). The enhancement on fatigue strength of 1045 steel by tempering treatment and shot peening, Yazdani et al ((2007). Some investigations have been carried out to access the fatigue behavior of these two popular car steels: the improvement of fatigue strength of 4140 steel by dynamic strain aging and dynamic precipitation during warm laser shock peening, Ye et al. (2011). The enhancement on fatigue endurance of 4140 steel by an ion nitriding process, Celik and Karadeniz (1995); the fatigue strength improvement of 1045 steel coated with Colmonoy 88 alloy deposited by HVOF thermal spray, Puchi-Cabrera et. al (2010); or the corrosion-fatigue behavior of 1045 steel coated with electroless nickel-phosphorus, Pertuz et. al. (1999). Nevertheless, no ultrasonic fatigue endurance has been reported, in the best knowledge of the authors, for the 4140 steel, neither the 1045 steel. This work is oriented to investigate the fatigue endurance of these two car steels, under ultrasonic fatigue tests. 2. Testing material and experimental set up. The two car steels were machined as received, in order to obtain the profile fitting the resonance condition under this modality of fatigue tests. Figure 1 (a) shows the process of machining of one specimen, and Figure 1 (b) the dimensions obtained for the two tested materials, fitting the resonance condition.

(a)

(b)

Fig. 1. (a) Machining process of testing specimens, (b) Dimensions (mm), of hourglass shape specimens for ultrasonic fatigue.

In order to fit the resonance condition for the two tested materials, modal numerical simulation were performed to obtain the natural frequency of oscilation in the longitudinal direction of specimens, which must be close (± 300 Hz), to the excitation frequency of ultrasonic machine (20 KHz). Figure 2 shows the result of numerical simulation for the two tested materials. The numerical simulation is obtained introducing three principal mechanical properties in the simulation program: density, Young’s Modulus and Poisson ratio. Since these three mechanical properties are close for the two tested steels, the simulation of Figure 2 is valid for the two tested materials. In Table 1 and Table 2 a listed the chemical composition in weight and principal mechanical properties for the 4140T and 4045 steels, respectively. All tests were carried out at room temperature (20° C), without control of environmental humidity (50 – 65%), and with zero mean stress (R = -1).