PSI - Issue 39

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Hannes Panwitt et al. / Procedia Structural Integrity 39 (2022) 20–33 Author name / Structural Integrity Procedia 00 (2019) 000–000

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HSA ( ε 1 ≥ 4 mm/m)

b1-4: Branches n1: Nodes

Fig. 1. Detection procedure of the crack pattern using the first principal strain distribution by the ACDM-script of Gehri et al. (2020).

3. Extension of the ACDM-script In the following, the extension of the original ACDM-script especially for fatigue crack growth is presented. Therefore, the measurement of the number of cycles N and crack length a is explained. As the crack length is only measurable with the definition of a start and end point, a procedure to evaluate branched cracks is also presented. 3.1. Measurement of the number of cycles In order to evaluate information about the loading cycles within the extended ACDM-script, the number of the current cycle for each picture is additionally exported from the digital image correlation software to the ACDM-script. To use this data, two methods have been developed and implemented into the existing ACDM-script. The first approach uses the crack width calculation provided by the original ACDM-script and is referred to as the crack width method in the following. The second procedure utilizes the threshold value of the principal strain-field from the crack pattern detection and is referred to as the ε1 -method . Due to the detection of the final crack pattern as a whole from the combined HSA (Fig. 2a and b), the information, at which loading cycle the crack tip reaches a certain point on the crack, cannot be obtained during this step. Instead, with both methods the respective loading cycle is calculated after the crack path detection step.