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What we can learn from hr-ebsd about crack closure effects during fatigue crack propagation

Thursday (27.09.2018)
09:45 - 10:00 S1/01 - A1
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Crack closure is an issue controversially discussed in view of fatigue crack growth. Crack closure can lead to a deceleration of crack grow rates, a mechanism not included in the commonly used K-concept. Three common reasons for premature contact of crack edges are roughness induced crack closure, environmental assisted crack closure as well as plasticity induced crack closure. The origin of plasticity induced crack closure is a material transport to the plastic wake of the fatigue crack by the emission of dislocations at the crack tip during crack growth. Quantitative measurement of lattice rotations, strains and stresses near closed crack tips can help to evaluate the impact of plasticity induced crack closure compared to the other two options. Thus, coarse-grained annealed Fe3wt%Si is the material of choice due to its low Young’s modulus and relatively high strength. This allows a high strain and therefore good stress resolution, necessary because the forces in the residual plastic zone leading to crack closure may be low. The distribution of the whole strain tensor in the crack tip region was meassured by HR-EBSD using the software tool Crosscourt. Although experimental results indicate a residual plastic zone near the crack edges by the existence of counter-rotating residual lattice rotations on both sides of the crack, the stress fields show that plasticity induced crack closure is more complex than simple simulations and analytical solutions assume.

Marc Laub
Saarland University
Additional Authors:
  • Matthias Thielen
    Saarland University
  • Florian Schäfer
    Saarland University
  • Dr. Michael Marx
    Saarland University
  • Prof. Dr. Christian Motz
    Saarland University