CONCEPTUAL PROBLEMS WITH FATIGUE CRACK CLOSURE AND PLASTICITY: INFLUENCE OF CYCLIC SOFTENING

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Plasticity-induced crack closure (PICC) should be proportional to the amount of plastic deformation near the crack tip. This suggests that softer materials have larger PICC than harder materials, which is often a way of explanation of the observed crack growth rates at low R. However, experimental data showed that at high load ratio R = 0.8 (presumption of no crack closure), the crack growth rates were higher in a high-strength steel limited cyclic hardening), denoted as "hard steel", compared to a steel with pronounced cyclic softening (denoted "soft steel"). At low load ratio R = 0.1 in the Paris regime, it was the opposite: the "hard steel" exhibited slower crack propagation. This means that the crack closure effect was much larger in the harder material. Such behaviour cannot be explained based on classical ideas about crack closure.

Plasticity-induced crack closure (PICC) should be proportional to the amount of plastic deformation near the crack tip. This suggests that softer materials have larger PICC than harder materials, which is often a way of explanation of the observed crack growth rates at low R. However, experimental data showed that at high load ratio R = 0.8 (presumption of no crack closure), the crack growth rates were higher in a high-strength steel limited cyclic hardening), denoted as "hard steel", compared to a steel with pronounced cyclic softening (denoted "soft steel"). At low load ratio R = 0.1 in the Paris regime, it was the opposite: the "hard steel" exhibited slower crack propagation. This means that the crack closure effect was much larger in the harder material. Such behaviour cannot be explained based on classical ideas about crack closure.

Plasticity-induced crack closure, cyclic hardening, cyclic softening, finite element method

11.04.2022

University of Zagreb

Zagreb

978-953-7738-83-9

Sixth IJFatigue & FFEMS Joint Workshop Characterisation of Crack/Notch Tip Fields under Static, Dynamic or Cyclic loading - Book of Abstracts

32–32

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