No abstract

The paper focuses on the comparison of different methods for calculating stress intensity factors (K ' ) in surface crack problems based on results of numerical analyses of elastic crack-tip fields. The computational accuracy is quantified by means of the so-called 'averaged error estimation technique' which is extended to the evaluation of local errors in the determination of stress intensity factors at characteristic points of the crack front. Numerical data involved in the present study are obtained from boundary-element calculations. Three values of the stress intensity factor, i.e. those defined from nodal tractions, displacements and energy-release rate, are provided. The highest error level is found for the displacement-based data, while the energy-release calculations yield the best accuracy. A considerable increase in the error value is noticed near the intersection of the crack front with a body surface where the conventional assumption on the square-root stress singularity is, in general, not applied. It is shown that the accuracy of stress intensity factor analysis can be improved by eliminating uncertainties associated with the local stress state along the crack front.

A set of polynomial influence functions is derived for some typical cracks in nuclear reactor components. The crack geometries considered are circumferential and axial partelliptical cracks on the inner surface of a cylindrical pressure vessel. Based on the boundary-element method, the influence functions are calculated for a wide range of crack configuration parameters and at numerous kinds of polynomial crack-face loading. Based on the averaged error estimation technique, the efficiency of numerical analyses and the accuracy related solutions are shown to be rather high. The results on stress intensity factors are fitted by parametric formulae making use of the least-square procedure. The derived solutions are employed for crack analyses at pressurized thermal shock loading of a reactor pressure vessel, as well as for the verification of existing regulatory guides

In the present study, Organosandwich structures consisting of a folded polypropylene (PP) honeycomb core and glass-fiber reinforced PP cross-ply face sheets are investigated with the aim of developing a valid method for structural simulation of Organosandwich structures. On the one hand, effective material properties are gained from a mesoscopic model on the basis of a representative volume element (RVE) and compared with data from experimental characterization. The morphology of the folded honeycomb structure was investigated via X-Ray computed tomography and 3d image analysis. On the other hand, the differences between experimental and effective core properties are shown, and the correlation between the mesoscopic honeycomb core structure and the entire sandwich behavior is validated by bending tests and a corresponding finite element model. A comparison shows that results can be achieved with the RVE model as well as with the homogenized core FE model with good agreement with the experimental data.