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

482

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Table 2. List of the Materials properties of the two cylinders MATERIAL Young’s Modulus 'E' (GPa) 0.2% proof stress MPa UTs MPa

Elongation %

CTE 1/°C

Density (Kg/m 3 ) 8150.0 1820.0

ν

Iron

230.0 44.0

340 185

700 240

5.2 2.0

9.50E-06 2.450E-05

0.30 0.30

Mg alloy

Using equations 1 to 4, the hoop stress on the outer Mg cylinder is calculated to be 160MPa at -50°C. This stress level is below the yield strength (185MPa) of the magnesium alloy with a safety margin of 1.15. Therefore, the interference fit of the two cylinders was designed to be safe when experiencing the thermal load besides the interference fit. However, the stress level with the number of thermal cycles (only two cycles) are not adequate for the crack initiation. 4. Materials Examination The investigation of the materials used in this research are detailed in this section. A microstructure specimen from the material taken from the casting cracked cylinder was used to produce optical and SEM images showing the grain structure, which confirms that the grain structure shows no unexpected features and is acceptable; see Figure 5.

Neodymium (rare earth) rich phase concentrated at grain boundaries

Average grain size typically 40-70 micron depending on section size and amount of chilling

Zirconium rich phase

Figure 5: Microstructure specimen from material taken from failed generator cylinder casting - Optical x 200

The chemical composition of the melt is compliant which is listed in Table 3:

Table 3. Chemical composition of the Magnesium Alloy in wt.-% Element Ag RE Zr Zn Si

Cu

Mn

Fe

Ni

Mg

Min %

2.0

2.0

0.4

-

-

-

-

-

-

Balance

Max %

2.0

3.0

1.0

0.2

0.01

0.03

0.03

0.01

0.005

Melt %

2.15

2.36

0.58

0.01

0.006

0.004

0.01

<0.001

0.001

Figure 6 shows an example of the EDX images illustrating the elements of the alloy.