Interpretation of the generalized parameter of the probability of failure through the plastic stress intensity factor

The main purpose of this work is to statistically analyze the fracture toughness of compact specimens made of S55C steel in terms of elastic and plastic stress intensity factors. The fracture toughness tests results at three-point bending were used for a comparative statistical analysis of the fracture parameters. Five type of specimen configuration with various thicknesses were tested at a constant ratio between crack length and specimen width. The critical loads were obtained as a tests result for various combinations of crack length and specimen thickness. In addition, uniaxial tensile tests were carried out to determine the main mechanical properties of the material. Obtained material properties were used in numerical calculations. Numerical calculations were carried out to determine the elastic and plastic stress intensity factors. Three-dimensional finite element analysis was performed on the basis of the experimental data on curvilinear crack front positions in tested specimens. The crack tip stress-strain fields were obtained for each of the tested samples as a result of numerical calculations. These fields were used to calculate the values of the plastic intensity factors along the curvilinear crack fronts. A statistical analysis of the fracture toughness of compact specimens made of S55C steel was carried out based on the obtained critical values of elastic and plastic stress intensity factors. The advantages of using the plastic stress intensity factor as a generalized parameter for the fracture probability are demonstrated. In addition, the sensitivity of the plastic stress intensity factor to constraint effects avoids the introduction of additional parameters into the statistical models.

ANALYSIS OF DYNAMIC STRESS INTENSITY FACTORS FOR CRACKED STIFFENED PLATES BASED ON EXTENDED FE METHOD

The dynamic stress intensity factors (DSIFs) for cracked stiffened plates considering the actual boundary conditions in ship structures are analyzed by the extended finite element method (XFEM). The sensitivity of numerical results with respect to mesh size and time step is discussed. Some other influential parameters including stiffener height, crack location and crack length are also analyzed. The numerical results show that the convergence is affected by mesh size and time step. By using XFEM, singular elements are not needed at the crack front and moderately refined meshes can achieve good accuracy. The height of the stiffener and crack location significantly effect DSIFs, while the crack length slightly influences the DSIFs.