PSI - Issue 28

C.D.S. Souto et al. / Procedia Structural Integrity 28 (2020) 139–145

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Carlos D.S. Souto et al. / Structural Integrity Procedia 00 (2020) 000–000

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In this setup, depicted in Figure 1a and shown in Figure 1b, two rails are tested at the same time. This is made possible due to the hinged (pin-joint) connection of the loading device to the load cell, depicted in Figure 1c, allowing for an even load distribution between the two rails, as well as a constant load during testing. The rails are clamped at both ends and, for optimal results, a mid-span support was also included. Fatigue testing is done through load control while strain information is gathered through a strain gauge placed at the profile’s web, near the web-flange corner. Since the real-life cyclic loads due to the passage of a shuttle are impractical to replicate in a laboratory, these loads were reproduced by placing the loading device at the flange of the mid-span of the rail, exerting an up-and-down motion. The loading device was also developed in such a way that it allows for di ff erent load actuators (the part that actually contacts the rail and transfers the load). It also allows to place the actuator at each side of the rail’s flange, in order to test upward or downward loading scenarios. During the development of the experimental setup, it became clear that the load actuator must have a smooth contact area, with no sharp edges, otherwise, material cracks can appear in the rail due to the contact of these sharp edges with the profile’s flange, also creating deep indentations. Using an actuator with a smooth contact area, depicted in Figure 1d, cracks appear in the web-flange corner of the rail, which is to be expected since, due to the profile’s geometry, large stresses are concentrated in that region. Figure 2a shows a downward loading test, where the actuator is placed on top of the rail’s flange. Figure 2b shows an upward loading test, where the actuator is placed on the bottom of the rail’s flange. In an upward loading test, an additional plate is placed in between the cylindrical part and the rail’s flange (Figure 1e), distributing the load over the flange, avoiding local indentations and flange cracking. Both loading cases generate fatigue cracks in the rail’s web-flange corner, as expected (Figure 2c).

(a) Downward testing.

(b) Upward testing.

(c) Generated fatigue crack on a specimen.

Fig. 2: Experimental fatigue testing setup in use.