PSI - Issue 42

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

1550

6

the extrusion pieces can increase or decrease the total area defects comparatively with the billet piece (die-casting aluminium).

Table 1. Results of Vickers´ hardness and manufacturing defects area. Material HV

Total defects area (μm 2 )

BIL (6060)

33.30±0.4 49.94±1.9 35.38±0.1 40.06±0.5

532817.93 327452.81 648142.78 317600.66

RO (6060 T4) CO (6060 T1) RM (6060T1)

In the fatigue tests, the infinite life considered was 10 6 cycles and were obtained the fatigue limit stress, σ w (experimental). The results of microhardness tests and the defect areas made it possible to compare the prevision life models, shown in Table 2. So, it was calculated the fatigue limit with equations (6), (8), (9), and then the relative error. To the RO (6060 T4), the equations (6) (Murakami et al., 1991) and (9) (Schönbauer et al., 2016) present the lowest errors (9.82% and 7.53%, respectively), comparing the prevision models with the experimental results from fatigue tests. On the other hand, the error values to the RM (6060 T1) are too high (superior to 5%) independently of the empirical model. The Ueno et al. (2021) model presents high error values for both pieces. All the empirical models give error values superior to 5%, but this is not accepted.

Table 2. Results of prediction fatigue limit stress considering the empirical models of Murakami, Ueno and Schönbauer.

Empirical Model Murakami et al. (1989)

Empirical Model Ueno et al. (2012)

Empirical Model Schönbauer et al. (2016)

σ w (experimental) [MPa]

Piece (material)

σ w [MPa]

Error [%]

σ w [MPa]

Error [%]

σ w [MPa]

Error [%]

RO (6060 T4) RM (6060 T1)

83.78 100.6

92.01 86.88

9.82

62.01 57.25

25.99 43.09

77.47 73.21

7.53

13.64

27.23

Therefore, new models were developed to predict the fatigue limit stress of extruded 6060 aluminium with T1 and T4 thermal treatment, considering hollow rectangular cross-section (RO) and approximately rectangular cross-section, solid with rounded corners (RM). These new models were based on the models of Murakami and Schönbauer and are presented in table 3. The fatigue limit prediction values obtained with these new models were also compared with the experimental results and presented errors of less than 1%.

Table 3. Predict fatigue limit stress new models for 6060 extruded aluminium alloys. Piece (material) New Model R=0.05 New Model = 0.226 + × 10 −4 ROM (6060T4) ≅ 0.55 ( + 390)/(√ ) 1 6 (equation (10)) = 0.61 × ( + 424.78) (√ ) 1/6 × ( 1 − 2 ) (equation (11)) RM (6060T1) ≅ 1.53 ( + 150)/(√ ) 1/6 (equation (12)) = 1.70 × ( + 163.07) (√ ) 1/6 × ( 1 − 2 ) (equation (13))