PSI - Issue 48

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Gomes et al/ Structural Integrity Procedia 00 (2023) 000–000

* Corresponding author. E-mail address: vgomes@inegi.up.pt

V.M.G. Gomes et al. / Procedia Structural Integrity 48 (2023) 142–148

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1.1. UIC Parabolic Leaf Springs

UIC parabolic leaf springs are made of chromium-vanadium alloyed steel. These springs are quenched and tempered, giving them high mechanical strength and hence a higher fatigue strength (Gomes et.al., 2022). Figure 1 illustrates the parabolic leaf spring geometry normalized by UIC for application in two-axle freight wagons. This type of leaf spring is constituted by 5 leaf springs, 4 of which constituted the main leaf spring. The fifth leaf spring is called an auxiliary spring and serves to increase suspension stiffness for high loads. As can be seen in Figure 1, the leaf spring is constituted by leaves of constant width, but with varying curvature and thickness.

Point 1

Point 2

Fig. 1. Geometry of UIC parabolic leaf springs applied in freight wagons. Presentation of spots considering for the analysis.

1.2. Manufacturing Processes

Regardless of the type of leaf spring, the production process consists essentially in the steps shown in Figure 2. Initially, steel and flat leaves are produced, then flat leaves need to acquire the required geometry for the design. Some hot-forming processes are carried out at this stage such as: tapering, cutting, cavities, eyes and C shapes. The last procedure consists of shaping the spring curvature. In certain situations, the quenching process is carried out together with the camber formation of the leaf. Subsequently, the spring leaf is subjected to tempering (Yamada, 2007 and UIC, 2017).

Fig. 2. Summary of different production phases of parabolic leaf springs.

In spite of the quenching and tempering processes provide to their high strength, the structural integrity of leaf springs has a fundamental role in vehicle safety, becoming fatigue, one of the concerning phenomena in the mechanical design phase. One way to increase fatigue resistance is by introducing an initial compressive stress state on the free surface and sub-surface regions by shot peening. One of the efficient and widely used in the leaf spring industry is shot peening (Kaiser, 1987 and Mueller, 2019). Shot peening is a mechanical process in which small spheres are blasted against the surface to be treated. The spring-back effect after the plastic deformation generates compressive residual stresses that are beneficial to increase the fatigue life. One interesting feature of the shot peening process is that the residual stress profile generated by this process is independent of the previous residual stress state Lawerenz, 1995, Ammar et al . 2017, Huang et al ., 2022). The fatigue resistance is still improved by considering the shot peening