PSI - Issue 57

C2 - Confidential

Hayder Y Ahmad et al. / Procedia Structural Integrity 57 (2024) 478–486 Ahmad et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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2. Real case study The research in this paper is a real case study of two cylinders assembled inside each other with radial interference fit of 0.203mm, fixed with bolts. Figure 1 shows a schematic section of the inner and outer cylinder.

Outer cylinder Mg alloy

Inner cylinder Iron

Fig. 1. Schematic section showing the inner and outer cylinder

The assembled two cylinders are exposed to two thermal cycling loads (+120°C to -50°C). Therefore, due to the large difference in the coefficients of thermal expansion of the two materials, the maximum hoop stress that results between the two cylinders will be at -50°C. In spite of the low number of the cycling loads, a crack initiated on the surface of the outer cylinder (Mg alloy) in an area far away from the bolt fixing hole. Within 24 hours, the crack had developed and propagated across the full length of the cylinder, passing through one of the fixing bolt counter-bores as shown in Figure 2.

Fig. 2. Location of longitudinal crack

However, upon closer examination, the crack was found to actually consist of two separate cracks that were aligned with the fixing bolt counter bore, one running around the fillet radius at the corner of the counter bore and the second running directly from the fixing hole. Figure 3 shows the two cracks did not join up but were separated by a small ligament of material that was unbroken. Figure 4 shows the crack from inside the outer Mg cylinder.

Fig. 3. Cracks running into fixing bolt

Fig. 4. Position of cracks viewed from the bore