Artem S. Semenov

Fatigue Damage Accumulation under the Complex Varying Loading

Fatigue analysis of steel parts of structures, which are subjected to complex irregular loading programs caused by wind, thermal, wave loads, earthquakes and combined imposed actions, requires in some cases using special methods of stress-strain evaluation. The model of the low cycle fatigue nonlinear damage accumulation is developed with taking into account the history of the deformation process. The damage is defined on the base of considering the quasi-static accumulation of maximal strain (stress) and hysteresis loops. The identification of material constants of the model is discussed. Application of the damage model for fatigue analysis of the antennas, pipelines, basements and fasteners units is considered and a comparison with experiments is given.

About the causes of cyclical instability at computations of large elasto-plastic strains

Response of various elasto-plastic models is compared at large strains under cyclic loading. In contrast to the small strain case, the cyclic instability is observed at large strains for some elasto-plastic material models with a kinematic hardening. The cyclic instability manifests itself as changing of shape, size or location of the hysteresis loop during cycling. Causes of the cyclic instability are analyzed. Conditions ensuring the cyclic stability of elasto-plastic models are proposed.

Experimental Investigation and Finite Element Simulation of Fracture Process of Polymer Composite Material with Short Carbon Fibers

This work is devoted to the research of mechanical and strength properties of polymer composite material with short carbon fibers produced by injection molding technology. The material is PEEK90HMF20 with 20 % of carbon fibers mass fraction and based on polyether ether ketone (PEEK) polymer matrix. Mechanical and strength properties were researched on samples that had been cut from molded plates. A set of tension tests was performed and stress-strain diagrams of samples with different orientation in relation to the global direction of injection were obtained. Two-step homogenization procedure and pseudo-grains failure model were used to describe composite material behavior. The material model parameters were calibrated with experimental data by means of reverse-engineering procedure. Finite element simulation of tension tests was performed to check the quality of built model from the point of view of its ability to predict failure.

Finite Element Modeling of Steel Pipeline Reconstruction Using Fiberglass Composite Material

A stress state of the partially damaged underground steel pipeline after reconstruction by means of the fiberglass composite material is considered. The strength properties of the composite are determined experimentally. The effective elastic moduli of the composite are determined by means of the finite element homogenization. Tsai-Wu failure criterion is used for the composite part of the pipeline. The influence of geometrical parameters and loading conditions on the safety factor of the pipeline is analyzed and discussed.

Fracture Analysis of Reinforced Concrete Bridge Structures with Account of Concrete Cracking under Steel Corrosion

A direct 3D finite element (FE) modeling of fracture processes in reinforced concrete bridge structures is considered with account of the macrocracks initiation and propagation, real geometry of reinforcing elements, discontinuity in the bond-slip behavior, using elastic-plastic-damage constitutive equations for concrete. The comparison of obtained FE results with experimental data is presented and discussed for the pulling ribbed bars out of concrete blocks, the spalling of concrete cover at the automobile bridge and cracking of ballastless deck at the railway bridge.

Thermal fatigue strength of heat-resistant alloys

Results obtained from exposure of nickel-based heat-resistant alloys to thermal fatigue tests carried out for several years are presented. A methodology of carrying out tests in vacuum is used, which makes it possible to observe incipience of microcracks and their propagation rate. Results obtained from a calculation of sample strain conditions are analyzed.

Modification of the multisurface theory of plasticity with one surface: comparison with experimental data

Experimental - theoretical research of the plastic deformation of thin-walled steel and nickel tubular specimens was done. The experimental results and forecasts of the kinematical hardening model and multisurface model with one active surface were compared. A modification of the plasticity theory was gone. The modification takes into account character of a loading path. The constitutive equation gives the possibility to make predictive calculations when either loading or strain path (in whole strains) is known. The research is performed for complex periodic loading paths, containing partial and complete unloading.

Prevention of cyclic instability at the modeling of elasto-plastic deformation at large strains under proportional and non-proportional loading

The cyclic instability phenomenon is investigated at the modeling of large elasto-plastic strains. The instability is observed at large strains for some elasto-plastic material models with a kinematic hardening in contrast to the small strain case. The cyclic instability manifests itself as a changing of shape, sizes or location of the hysteresis loop during cycling. In partial case the cyclic instability leads to the stress ratcheting. Responses of 50 various models of elasto-plastic material have been considered under proportional loading (cyclic simple shear) and non-proportional loading (combined cyclic simple shear and tension-compression). Causes of the cyclic instability are analyzed and conditions ensuring the cyclic stability of elasto-plastic models are proposed.

Strength Assessment for Cooled Gas Turbine Blades

Evaluation of safety margins under static and thermocyclic loading of cooled turbine blades from low-ductile and ductile heat-resistant polycrystalline alloys is examined. Different approaches to the assessment of thermocyclic strength are established to be appropriate for use depending on load paths of different blade elements and ultimate strain of the material. The procedure of evaluating the strain span per cycle at proportional and disproportionate loads is proposed. The procedure was verified on the blades of a power gas turbine plant.

Simulation and Experimental Investigation of Deformation and Fracture of the Masonry

The masonry model, representing an elastic mortar and elastic bricks, is analyzed with aim to evaluate effective elastic moduli and strength properties. By means of the direct finite element simulation and homogenization procedure the analysis of variation influence in the heterogeneous material microstructure characteristics (influence of brick aspect ratio and orientation angle) on the local stress-strain state and mechanical properties of the representative volume element of considered composite has been fulfilled.