Neural network applications in determining the fatigue crack opening load

Healing technology for metallic materials is an important subject in terms of long-term reliability and durability of structural members, a healing technology to heal fatigue crack by applying heat treatment at annealing temperature level has been discovered. In this study, the influences of plasticity-induced crack closure on healing were evaluated by obtaining the crack opening load during the pre-crack introduction and evaluating the fatigue crack propagation characteristics before and after the healing heat treatment, using compact tension specimens made of carbon steel with different test conditions. As a result, the specimen with high crack opening load showed high healing effect and were able to heal up to 95% of the pre-crack length. This suggested that the residual compressive stress due to the plasticity-induced crack closure accelerates the solid-state diffusion bonding during the crack healing process and this leads to the improvement of the healing effect.

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Automated real-time measurements of fatigue crack length and crack opening load using unloading elastic compliance method

International Journal of Fatigue ◽

10.1016/s0142-1123(96)00022-9 ◽

1997 ◽

Vol 19 (2) ◽

pp. 169-176 ◽

Cited By ~ 4

Author(s):

C Oh

Keyword(s):

Fatigue Crack ◽

Crack Length ◽

Real Time ◽

Crack Opening ◽

Elastic Compliance ◽

Crack Opening Load ◽

Opening Load

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Modeling of Plane Strain Fatigue Crack Closure

Journal of Engineering Materials and Technology ◽

10.1115/1.2903380 ◽

1991 ◽

Vol 113 (1) ◽

pp. 31-40 ◽

Cited By ~ 63

Author(s):

Huseyin Sehitoglu ◽

Wei Sun

Keyword(s):

Fatigue Crack ◽

Crack Growth ◽

Plane Strain ◽

Crack Closure ◽

Plane Stress ◽

Crack Opening ◽

Crack Tip ◽

Crack Advance ◽

Crack Opening Load ◽

Opening Load

Mechanisms and models proposed for plane strain fatigue crack closure are evaluated. A mechanism based on out-of-plane plastic strain component, εzp, in plane strain is shown not to be adequate in explaining closure over a wide range of applied load levels. In the second model, partial relief of compressive stresses in front of the crack tip upon crack advance is forwarded as responsible for crack closure in plane strain. It is argued that this model would hold only if the crack advanced into a compressive stress zone which is highly improbable. A third model based on compressive strain accumulation in the x-direction, εxp, (transverse or crack growth direction) is studied. Material ahead of the crack tip contracts in the transverse direction and this mechanism provides residual material for crack surfaces as the crack advances. Stress-strain history and material displacements as crack advances are presented for plane strain conditions that lend further support to the third model. The results are obtained with a specialized finite element analysis with provisions for crack advance and crack closure. The crack opening load corresponding to relief of compressive residual stresses behind the crack tip is determined for plane stress and plane strain cases under R= − 1, 0 and 0.3 loading. The load at which stresses ahead of the crack tip become tensile, Pt, is also determined for plane stress and plane strain conditions and is found to exceed the crack opening load in all cases. The relevance of this parameter on fatigue crack growth behavior is discussed.

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