PSI - Issue 75

Hayder Y Ahmad et al. / Procedia Structural Integrity 75 (2025) 245–253 Hayder Y Ahmad et al. / Structural Integrity Procedia (2025)

248

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3.1. Material Characterisation A 2024-T4 aluminium alloy plate with nominal dimensions of 440 mm × 215 mm × 12.5 mm was provided for this study in accordance with the EN AW-2024 T4 specification. To ensure conformity with standard requirements, the chemical composition of the alloy was analysed and verified to be within the acceptable limits. The composition results are presented in Table 1. Additionally, three tensile tests were conducted on specimens in the as-received condition, in accordance with ASTM E8, to confirm the mechanical properties of the material. The average values of yield strength, ultimate tensile strength, and elongation are presented in Table 2 along with their corresponding standard deviations (SD). The standard deviation was calculated using the conventional sample formula (Montgomery & Runger, 2014): = √ − 1 1 ∑ ( − ̅) 2 = 1 (1) where x i is each individual measurement, ̅ is the arithmetic mean, and n is the number of tests. Table 1. Chemical composition of the supplied plate

%

Si

Fe

Cu

Mg

Mn

Cr

Zn

Ti

Zr

Al

Standard

0.5

0.5

3.8-4.9

1.2-1.8

0.3-0.9

0.1

0.25

0.15

0.05

Rem

Measured

0.48

0.49

0.44

1,5

0.55

0.09

0.20

0.1

0.06

Rem

Table 2: Typical mechanical property of 2024 T4

0.2% PS (MPa)

UTS (MPa)

Elongation %

Standard*

324

469

20

Average Measured ±SD

310 ± 4.5

465 ± 5.6

19 ± 1.7

*AA; Typical, Aerospace Specification Metals (ASM) To investigate fatigue crack growth behaviour, Compact Tension (CT) specimens were machined in accordance with the ASTM E647 standard, which prescribes the geometry and dimensions necessary for fatigue crack growth testing. The machining process was conducted with precision to ensure compliance with standard specifications, minimising deviations that could influence test results. The detailed dimensions of the CT specimens are presented in Fig 3.

Fig. 3. Shape and dimensions of ASTM E647 standard compact tension (CT) specimens In this study, three distinct surface conditions were evaluated to assess their influence on fatigue performance: untreated 2024-T4 aluminium alloy (baseline), CSP and LSP. Details of the CSP and LSP processes used in this study are presented below, along with their effects on near-surface characteristics relevant to fatigue performance. For each surface condition, three test specimens were prepared and tested. These specimens were used in the fatigue crack growth experiments to ensure consistency and to allow for statistical evaluation of the results. 3.2. Conventional shot peening (CSP) process The CSP treatment was applied to all surfaces (including notches and sides) of three compact tension (CT) specimens to evaluate its influence on fatigue crack initiation and propagation. The specimens were treated for 20 minutes using a Sintokogio STB-OB peening machine, which propelled low-carbon steel shots with an average