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Vliv rohové singularity na tvar únavové trhliny
Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk ; Seitl, Stanislav
Due to the existence of vertex singularity at the point where the crack intersects the free surface, stress distribution around the crack tip and the type of the singularity is changed. In the interior of the specimen the classical singular behaviour of the crack is dominant and can be described using generally known analytic equations. Contrary to this, at the free surface or in the boundary layer close to the free surface the vertex singularity is significant. The influence of vertex singularity on crack behaviour and crack shape for a three-dimensional structure is described in this paper. To estimate the influence of the free surface on fatigue crack growth rate the model of a general singular stress concentrator was applied. The estimated fatigue crack shape can help to provide a more reliable estimation of the fatigue life of the structures considered.
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INFLUENCE OF MATERIAL PARAMETERS ON POLZNOM USED FOR MODIFICATION PARIS LAW
Seitl, Stanislav
In this paper sensitivity analysis of the effect of material properties (particularly a yield stress and hardening exponent) on the polynomial function used at modification of the Paris-Erdogan law was performed. The modification, which is based on the two-parameter fracture mechanics, describes fatigue crack propagation using a size of the plastic zone. The stress field around a crack tip is described by two parameters – stress intensity factor K and T-stress. Dependency of the plastic zone size and the parameters K, T is then formulated by using the polynomial function, which is found out in the contribution. The finite element method together with the method of modified boundary layer for the numerical simulations was used. The results should lead to safer transmission of the data from laboratory specimens to real structures and their components.
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