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Evaluation of notch geometry effect on behaviour of fracture toughness testing specimen
Seitl, Stanislav ; Klusák, Jan ; Keršner, Z. ; Knésl, Zdeněk
The basic fracture properties of cement-based composite are ascertained on the basis of test evaluations of the specimens in suitable test configurations. Three-point bending specimens with a central starting notch are the most frequently used specimen for laboratory testing. Through models of equivalent elastic cracks the critical crack length and effective fracture toughness (or toughness) can be calculated. The influence of the geometry of the starting notch in a three-point bend specimen on the resulting values of critical applied force and fracture toughness is studied in this paper. To this end, a crack initiation at the notch tip is numerically simulated. It is shown that the values of fracture toughness obtained for specimens with larger widths of starting notch can be overestimated.
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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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Influence of the T-stress on Plastic zone shape and size for different form of specimens
Seitl, Stanislav
In framework of two-parameter fracture mechanics the shape and size of the plastic zone at the tip of a crack were studied. Analytical estimate of the size and shape of the plastic zone was made by substituting Mises yield criterion. For three different specimens (namely CCT-center cracked plate tension specimen, CT-compact tension specimen and 3PB-single edge cracked three point bending specimen) the numerical solution is calculated by using ANSYS. Numerical results are presented to show the influences of the T-stress on the plastic zone. Both solutions are compared and the effect of constraint on the plastic zone was discussed
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Assessment of T-stress values using finite element method
Seitl, Stanislav ; Hutař, Pavel ; Knésl, Zdeněk
The common used procedures for calculation values of T-stress are presented by using finite element method in this contribution. Such calculational procedures, that make possible to estimate T-stress by using comparison of analytical and numerical solution stress and strain near crack tip, are presented. The aim of contribution is provide survey these procedures and points to their advantages and disadvantage and in this way we intend to possible users the endeavourer orientation in this realm. Contribution is appended with practical examples of calculation of T-stress values.
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TWO-PARAMETER DESCRIPTION OF CRACKS IN THE VICINITY OF INHOMOGENEITY
Seitl, Stanislav ; Knésl, Zdeněk
In case of two-parameter linear fracture mechanics a study of inhomogeneity influence on behaviour of short cracks is performed. The values of stress intensity factor (KI), T-stress and strain energy density (SED) are shown as a function of material constants of both components. The calculation of numerical values of mechanical parameters is accomplished by using finite element method ANSYS.
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