Ústav stavební mechaniky
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- ItemFatigue behavior of high strength steels under various levels of corrosion(Elsevier, 2024-02-01) Malíková, Lucie; Benešová, Anna; Al Khazali, Mohammad Sami; Seitl, StanislavPropagation of a short fatigue crack directly from a corrosion pit is investigated within this work. A corroded rectangular specimen subjected to remote tensile cyclic loading is modelled via finite element method. Propagation of the angled crack is then controlled by both loading modes (I + II). A parametric study is performed to estimate the directions of further crack propagation for various geometrical configurations. Corrosion pit size is varied to simulate various levels of corrosion, and the analysis is carried out for a range of crack lengths and different initial crack inclination angles. Assumptions of linear elastic fracture mechanics are accepted, and classical maximum tangential stress criterion is applied to calculate the angles of crack deflection. Results obtained are discussed and are prepared to mutual comparison with observations of decrease of fracture mechanical/fatigue properties on real specimens subjected to relevant experiments.
- ItemDual discrete and continuous meso-scale modelling of concrete(Vysoká škola báňská - Technická univerzita Ostrava, 2024-01-04) Mašek, Jan; Miarka, PetrThe present paper is devoted to the development of a software equipment that allows to model composite materials by both discrete and continuous modelling approaches. The aim is to create a geometrical and topological representation of a discrete lattice particle model as well as its 1:1 twin counterpart as modelled by a continuum FEM model. Both representations capture the heterogeneous composite structure at the meso-level. The presented results illustrate the ongoing initial phase of the efforts of the team in advanced modelling of damage propagation within concrete.
- ItemThe generalized Kelvin chain-based model for an orthotropic viscoelastic material(SPRINGER, 2024-03-01) Trcala, Miroslav; Suchomelová, Pavlína; Bošanský, Michal; Hokeš, Filip; Němec, IvanWe propose a constitutive material model to describe the rheological (viscoelastic) mechanical response of timber. The viscoelastic model is based on the generalized Kelvin chain applied to the orthotropic material and is compared to the simple approach given by standards. The contribution of this study consists of the algorithmization of the viscoelastic material model of the material applied to the orthotropic constitutive law and implementation into the FEM solver. In the next step, the fitting of the input parameters of the Kelvin chain is described, and at least a material model benchmark and comparison to the approach given by standards were done. The standardized approach is based on the reduction of the material rigidity at the end of the loading period using a creep coefficient, whereas the loading history state variables are not considered when establishing the result for a specific time step. The paper presents the benefits of the rheological model. It also demonstrates the fitting algorithm based on particle swarm optimization and the least squares method, which are essential for the use of the generalized Kelvin chain model. The material model based on the orthotropic generalized Kelvin chain was implemented into the FEM solver for the shell elements. This material model was validated on the presented benchmark tasks, and the influence of the time step size on the accuracy of model results was analyzed.
- ItemAdvances in low cycle fatigue probabilistic modeling(ELSEVIER, 2024-08-07) Canteli, Alfonso Fernández; Castillo, Enrique; DÍAZ-SALAMANCA, Diego; Muňiz-Calvente, Miguel; Seitl, StanislavNew advances in the probabilistic S-N model proposed by Castillo and Canteli are presented. The requirements for a S-N model derivation to be valid are emphasized, in particular, that of the compatibility between the statistical distributions of lifetime and stress reference variable. The definition of the generalized reference variable (GRV) in the S-N field, as GRV = psi & sdot;sigma M, where psi is a non-dimensional factor derived from the sigma - epsilon law of the material, allows the former model to be applied to LCF data. The new model ensures the incontrovertible and unitary definition of the scatter band in the S-N field and the justification of an asymptotic lower limit of the lifetime, N0. As a result, the stress- and strain-based approaches can be envisaged as a unique probabilistic psi sigma M -N approach applicable in the three conventional, i.e., LCF, HCF and VHCF domains. An extension as the psi sigma M -R -N model that includes the stress ratio effect is presented. The utility of the model is confirmed with the assessment of LCF data from different external experimental campaigns.
- ItemOptimisation of fine RCA content in mortar mixture based on the long-term fracture and fatigue tests(Elsevier, 2025-05-06) Miarka, Petr; Šimonová, Hana; Kucharczyková, Barbara; Seitl, Stanislav; Poletanovic, Bojan; Merta, IldikoThis paper presents the results of an experimental study with a focus placed on the long-term mechanical-, fracture- and fatigue analysis of mortar, in which natural aggregates (NA) were partially substituted with fine recycled concrete aggregates (RCA). Long-term tests were done at 28, 145 and 255 days under natural aging conditions. Fracture and fatigue experimental analysis took place for tensile mode I, which was enriched by fracture tests performed under a combination of tensile and shear load – mixed-mode I/II loading conditions. In total, four mixtures (reference and three with fine RCA) were tested to examine the influence of the aggregate replacement on the fracture and fatigue properties of the material. The experimental results showed that 25% of replacement seems to be an optimum dosage of fine RCA, which improves both the fracture and fatigue properties of tested mixtures.