PSI - Issue 56

Radim Halamaa et al. / Procedia Structural Integrity 56 (2024) 111–119 Halama et al / Structural Integrity Procedia 00 (2023) 000 – 000

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Fig. 2. Identification of the border between the gauge part and the curved part during the DIC measurement evaluation.

The circle equation can be used to find the border between the gauge part and the curved part of the specimen: = 0 +√ 2 − ( − 0 ) 2 (1) where is the radius of curvature ( R = 40 mm in our study), and 0 , 0 are the optimized values (least squares). The plane − of the reference coordinate system should contain the specimen axis. 4) Based on knowledge of the parameters describing the curved part DIC points by equation (1), assign the cross sectional characteristics to them. The stress amplitude is calculated as a nominal stress amplitude. 5) Find the mid-life cycle and calculate the amplitude of the response variable (strain). It is noticed that each DIC point has a different quantity of strain amplitude. It is advisable to take into account the occurrence of multi-axial strain by calculating the equivalent strain value for each evaluated point, e.g. according to the von Mises hypothesis: = √ 3 2 √[( 1 − 2 ) 2 +( 3 − 1 ) 2 +( 2 − 3 ) 2 ] (2) where 1 , 2 , 3 are principal strains. It is recommended to measure the strain field on both curved parts of the specimen and calculate the averaged strain amplitude. 3. Experiments The AlSi10Mg is an aluminium alloy, which does not show a strain rate sensitivity. Based on the fact, two proportional loading cases and one nonproportional loading case were considered with a harmonic signal of strain. This helps to get more accurate evaluation of stress and strain amplitudes. In this contribution, the three fatigue tests will be described in detail, the rest of fatigue tests used in the conventional way of cyclic stress-strain curve determination will be described in a separate scientific paper. 3.1. Specimens manufacturing The thin-walled tubular specimen was designed in accordance with the ASTM E2207 standard as shown in Figure 3. The outer diameter of the tubular specimen is 14 mm, while the inner diameter is 11.5 mm. The gauge part length was selected as 28 mm.