PSI - Issue 42

Teresa Morgado et al. / Procedia Structural Integrity 42 (2022) 1545–1551 Morgado et al. / Structural Integrity Procedia 00 (2019) 000 – 000

1548

4

= ×( +120) (√ ) 1/6 × ( 1− 2 )

(9) Where is stress ratio. Factor is given by the following equation: = 0.226 + × 10 −4 , where factor b is 1.43 for a surface defect, 1.56 for an internal defect and 1.41 for a subsurface defect. 3. Material and Experimental Procedure The specimens used in this work were obtained from four pieces of 6060 aluminium alloys extruded: the Billet (BIL) used as raw material in the extrusion process; the hollow rectangular cross-section extruded piece in 6060 T4 namely (RO); the hollow circular cross-section in 6060 T1 namely (CO); and the piece (RM) of approximately rectangular cross-section, solid with rounded corners in 6060 T1 aluminium alloy. The preparation of samples for the hardness test and the manufacturing defects study was performed according to the ASTM E3 - 11(2017). The authors had special care to obtain the sample from different zones of the cross-section contemplating the hot spot zones and nominal zones. Two test specimens geometries with specifications according to ASTM E8/E8M - 21 (2021) were designed for the fatigue tests. In fig. 1 is presented the two geometries of the specimens used.

a)

b)

Fig. 1. Fatigue teste specimens’ specifications: a) aluminium 6060 T4; b) aluminium 6060 T1

3.1. Vickers micro hardness tests The Vickers microhardness tests were conducted following the ASTM standard E384-17 (2017). For these tests, a load of 0.1 kgf was applied for 10 seconds, and the length between indentations was 0.5 mm, ensuring a minimum distance of 2.5 times greater than the Vickers diagonal. The Minitab software was used to confirm that the results followed a normal distribution as requested by the ASTM 384-17 standard. Probability plots were made using the Anderson-Darling test, in which the p-value must be equal to or higher than the confidence value α= 0.05. 3.2. Manufacturing defects analysis To analyse the manufacturing defects, pictures were taken along the specimens with the inverted optical microscope, Leica DMI 5000 M, with five motorized objectives. After that, the software Image J and the threshold function were used to evidence the defects in the pictures obtained. A total of 2330 images were analysed. The manufacturing defects were measured and counted, and were got the defect areas. The defect analysis procedure sequence is presented in Fig. 2.