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Numerical Modelling of Fatigue Crack Closure
Oplt, Tomáš ; Růžička, Milan (referee) ; Horníková, Jana (referee) ; Hutař, Pavel (advisor)
This Ph.D. thesis was written under the supervision of Assoc. prof. Pavel Hutař, Ph.D., and Assoc. prof. Luboš Náhlík, Ph.D. The thesis is focused on the effect of plasticity induced crack closure, its characteristic and ways of numerical modelling. Premature fatigue crack closure has a significant effect on the fatigue crack propagation rate and therefore on the residual lifetime of a structure. A three-dimensional numerical model allows a detailed look at the stress and strain distribution along the crack front, and particularly it allows a local description of parameters along the crack front which governs the fatigue crack propagation rate. In the first part of the thesis, the study is focused on the influence of a singular stress field at the vicinity of the free surface on the crack front curvature without crack closure being involved. In the second part, a numerical model in 2D of plasticity induced crack closure was created and verified by experimental results. In the final part, a 3D numerical model is used to describe the influence of the crack closure on its fatigue propagation rate and explains typical crack front curvature. The suggested technique allows quantitative accuracy improvement of numerical simulation of the fatigue crack propagation and therefore, more reliable estimation of the residual lifetime of the cracked structure.
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Numerical Modelling of Fatigue Crack Closure
Oplt, Tomáš ; Růžička, Milan (referee) ; Horníková, Jana (referee) ; Hutař, Pavel (advisor)
This Ph.D. thesis was written under the supervision of Assoc. prof. Pavel Hutař, Ph.D., and Assoc. prof. Luboš Náhlík, Ph.D. The thesis is focused on the effect of plasticity induced crack closure, its characteristic and ways of numerical modelling. Premature fatigue crack closure has a significant effect on the fatigue crack propagation rate and therefore on the residual lifetime of a structure. A three-dimensional numerical model allows a detailed look at the stress and strain distribution along the crack front, and particularly it allows a local description of parameters along the crack front which governs the fatigue crack propagation rate. In the first part of the thesis, the study is focused on the influence of a singular stress field at the vicinity of the free surface on the crack front curvature without crack closure being involved. In the second part, a numerical model in 2D of plasticity induced crack closure was created and verified by experimental results. In the final part, a 3D numerical model is used to describe the influence of the crack closure on its fatigue propagation rate and explains typical crack front curvature. The suggested technique allows quantitative accuracy improvement of numerical simulation of the fatigue crack propagation and therefore, more reliable estimation of the residual lifetime of the cracked structure.
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The influence of T-stress on proporcional factor
Hutař, Pavel
Relation between crack opening displacement and J integral is of a great importance in fracture mechanics.The basic aim of this paper is to describe an influence of T-stress on proporcional factor. This factor is occured on the J integral and CTOD estimation equations. Specimens with different values of T-stress (compact tension,three point bend and single edge cracked tension) are analysed by finite element method, the factor is calculated as function of corresponding crack length. The influence of different material constants on proporcional factor are analysed by modified boundary layer model. Results are discussed from the point of view of two-parameter fracture mechanics.
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THE INFLUENCE OF T-STRESS FOR RELATIONSHIP BETWEEN CTOD AND J
Hutař, Pavel ; Knésl, Zdeněk
Relations between crack opening displacement (CTOD) and other fracture mechanics parameters are of a great importance in fracture mechanics. The basic aim of this paper is to describe an influence of T-stress on the plastic eta factors, plastic rotation factor and proporcional factor, i.e. the factors correlating J-integral and CTOD. Specimens with different values of T-stress (compact tension,three point bend and single edge cracked tension) are analysed by finite element method, the factors are calculated as functions of corresponding crack length and results obtained are discussed from the point of view of two-parameter fracture mechanics.
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The influence of T-stress on the characteristics of a fatigue crack
Hutař, Pavel
The influence of the T-stress values on the propagation of fatigue cracks is analyzed. The parameters of the plastic zone are studied at two levels of applied stress, i.e. loading and unloading. The CTOD parameter and rp (plastic zone size) in the crack grow direction are discussed as a driving parameter of a fatigue crack propagation rate. The three ways of determination of propagation rate of a fatigue cracks are compared. Recommendations for applications of these methods are discussed.
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