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This study focuses on crack propagation rates of AISI 304 stainless-steel specimens made from selected structural components experimentally tested in three-point bending. Components of two productions loaded with constant force with selected stress ratio were submitted to cyclic loading in order to measure crack opening displacement. Experimentally obtained data were evaluated using 3D modelling in finite element modeling software intending to determine fracture mechanical parameters. The tool to describe fatigue behavior was Paris’ law, used to describe crack propagation in intermediate crack growth rate range. Paris–Erdogan equation was evaluated as a fitting of linear part of the graphical plot of crack growth rate with respect to the stress intensity range and material constants were gained from numerical description of the relation. Comparison of fatigue crack behavior in AISI 304 steel components of two productions was studied and evaluated.

This contribution deals with the analysis of fatigue damage in high-performance concrete (HPC) studied by three-point bending test. The concrete sample was tested with frequency of 10 Hz and it was exposed to a total number of load cycles 2×106. The internal structure and damage localization was studied by CT tomography. Found locations of internal damage i.e., cracks, were discussed.

Laser cladding is a relatively new technology how to combine properties of various materials. Thus, bi-material interfaces are presented in real structures and can affect the fatigue crack propagation. A cracked bar subjected to pure tensile loading is numerically simulated in this work in order to analyze the effect of the interphase layer between the cladded metal layer and the steel substrate on crack growth in the surface layer. Particularly, the influence of various Young’s modulus of the interphase on the stable/unstable edge crack propagation is assessed. Moreover, the number of cycles necessary for achievement of the defined critical crack length is calculated and it is summarized that knowledge of elastic properties of the thin interphase is crucial for fracture and fatigue analyses.

Crack propagation under mixed-mode (I + II) conditions has been investigated in a semicircular disc where various levels of mixed-mode can be achieved by means of different geometry configurations. The research has been performed on a novel cementitious material, alkali-activated concrete. Its main advantage is that it is environment-friendly. On the other hand, its fracture mechanical properties, as of yet, have not been described sufficiently. Therefore, a fracture analysis has been performed. The crack deflection under three-point bending conditions has been investigated numerically as well as experimentally. The numerical approach is based on a combination of the common finite element analysis and a multi-parameter form of the maximum tangential stress criterion. This generalized method is suitable especially for materials with specific (elasto-plastic, quasibrittle etc.) fracture behaviour. The over-deterministic method together with the Williams expansion is applied to approximate selected stress tensor components around the crack tip. In this work, the influence of the eccentric crack is also discussed. In the conclusions, several recommendations about using single-parameter/multi-parameter fracture mechanics are stated.

An influence of the bi-material interface between a steel substrate and a thin protective layer applied through laser cladding was investigated. A range of elastic properties and thicknesses of the layer were considered to cover the behaviour of a short crack in the selected materials such as bronze, nickel or cobalt alloys. The special case of the crack terminating directly at the interface was investigated, which is connected to the necessity of application of generalized approaches of linear elastic fracture mechanics. The results contribute to better understanding of fracture response of selected materials and to a more reliable decision on choosing a proper material of the protective layer.

A typical example of an alternative binder to commonly used Portland cement is alkali-activated binders that have high potential as a part of a toolkit for sustainable construction materials. One group of these materials is alkali-activated slag. There is a lack of information about its long-term properties. In addition, its mechanical properties are characterized most often in terms of com-pressive strength; however, it is not sensitive enough to sufficiently cover the changes in micro-structure such as microcracking, and thus, it poses a potential risk for practical utilization. Con-sequently, the present study deals with the determination of long-term mechanical fracture and fatigue parameters of the fine-grained composites based on this interesting binder. The me-chanical fracture parameters are primarily obtained through the direct evaluation of fracture test data via the effective crack model, the work-of-fracture method, the double-K fracture model, and complemented by parameter identification using the inverse analysis. The outcome of cy-clic/fatigue fracture tests is represented by a Wöhler curve. The results presented in this article represent the complex information about material behavior and valuable input parameters for material models used for numerical simulations of crack propagation in this quasi-brittle material.

Příspěvek se zabývá únavovým chováním nerezového nosníku I průřezu s koncentrátorem napětí. Ocelový nosník z IPE 80 je zatížen tříbodovým ohybem a je provedena analýza rychlosti růstu únavové trhliny pro různé tvary jejího čela. V rámci analýzy jsou sledovány hodnoty součinitele intenzity napětí ve vrcholu trhliny pod středem stojiny. Na základě AISI 304 parametrů Parisova vztahu jsou odhadované rychlosti šíření diskontinuity/trhliny v IPE 80. Zatížení a počet cyklů je stanovený pomocí předpokladů únavového chování materiálu a výsledky jsou porovnány s výsledky studií experimentálně provedených laboratorních testů na stejném materiálu., The focus of this contribution is to investigate fatigue behaviour of I cross-section beam. Stainless steel IPE beam with initiate concentrator is loaded in three point bending and the crack growth rate is analysed for various crack front shapes. Stress intensity factor size in the crack tip is being investigated in relation to growth rate of discontinuity. Load number of cycles is predictable basing on hypothesis of fatigue behaviour of material and the results are compared to experimental results of studies performed on compact tension specimen made from the similar material.

From the volumetric point of view, aggregate is the most important ingredient in any kind of concrete. It is impossible to use raw soil instead of aggregate to produce concrete. There are numerous reasons for not using soil for concrete production on Earth, and we should not use lunar soil for concrete production on the Moon for the same reasons. Nevertheless, almost all developed lunar concrete-like composites, such as sulphur or polymeric concretes, are based on raw lunar soil. In the research programme, cement composite based on lunar aggregate simulant was tested. The mechanical fracture properties of the composite were the key point of interest. It was proven that the tested lunar concrete is characterized by stable and uniform properties. The obtained results were compared with the properties of other ordinary cement composites.

Utilization of various steel grades in civil engineering allows designing bridges, bridge elements or simple structures according to their fracture mechanical properties. The service intervals of structures, which are going to be in use for a long time, cannot be calculated only on the basis of tensile and brittle fracture properties but also on the knowledge of the resistance to the fatigue crack growth. This contribution presents a comparison of the fatigue behaviour of two modern steel grades S235 J2, S355 J2 and a steel extracted from an old crane way. The comparison of these steel grades is done by fatigue crack propagation tests (the results of the experimental tests are described using concept of the stress intensity factor range K). The fatigue properties are discussed and recommendations for the use of the steels are stated.