PSI - Issue 83

Sze Pei Tan et al. / Procedia Structural Integrity 83 (2026) 28–40

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3.2. Fatigue life testing Fatigue is a progressive and localized change to the structure when it is subjected to cyclic loading. Fatigue life testing is performed to evaluate the life expectancy for the material when it is under fatigue loading. It may also determine when the structure might fail due to crack or fractured. A dozen specimens are produced by DMLS using AlSi10Mg material where half of them are peak hardened to T6. Fig. 4 (c) depicts the fatigue specimen that was made with a continues radius of 50 mm and minimum diameter of 6 mm. The specimens are printed vertically, parallel to the Z axis. All the specimens are grinded and polished to remove the rough surface and scratches that might lead to pre-mature surface crack. In line with the ASTM E466 standard, fatigue life tests were performed using stress control. The testing was completed with the help of an Instron 8801 servo-hydraulic machine depicted in Fig. 4 (d). The machine is equipped with 100 kN load cells for uniaxial fatigue testing and the test is run at room temperature. The loading is selected from UTS where, for highest load is at 90% of the UTS and decreased to 80% of UTS. It is repeated until all six specimens for as-built and another six specimens for heat treated. The test frequency is set to 20 Hz, and a stress ratio R = 0.1 is used. The stress ratio is a ratio between maximum stress applied during experiments to the minimum stress The stress ratio is also used during fatigue crack propagation testing and surface crack growth testing. The subsequent subsection will be discussing fatigue crack growth testing.

Fig. 4. Material characterization test.

3.3. Fatigue crack propagation testing Fatigue crack propagation testing is carried out to observe the behaviour of the material when it is subjected to cyclic loading with respect to SIF, K . The fatigue crack propagation testing is performed using the as-built material using the universal testing machine Instron 100 kN. Fig. 5 (a) shows the test used a compact tension (CT) specimen with specific geometry. The thickness of the specimen is 12.5 mm with knife edges tip designed for mounting the crack opening displacement (COD) sensor for crack measurement. The COD comprises of two metallic arms instrumented with strain gauges. The COD measures the crack length according to the number of cycles. In this study, the fatigue crack propagation is performed to attain the material constant of C and n for computational