Sergey Semenov

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.

Experimental Study and Mathematical Modeling of Bond of Different Types Winding Glass-Plastic Reinforcement with Concrete

The experimental studies of flat and relief glass-plastic reinforcement bond with concrete were conducted. The comparative analysis of obtained experimental data with results of other researchers in field of reinforcement and concrete bond was made. It was identified that composite reinforcement with flat winding has better bond characteristics in comparison with steel reinforcement and other winding types composite reinforcement. The analytical dependencies, allowing to simulate the process of fiber-plastic reinforcement bond with concrete, were obtained. The finite element modeling of deformation process of concrete foundation of transport constructions with fiber-plastic reinforcement were made.

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.

Thermal-Fatigue Analysis of Turbine Discs under Complex Thermo-Mechanical Loading with Account of Plasticity and Creep Effects

During operation of transport and maneuverable gas-turbine units, there are crack formation in turbine disc rims what exerted by thermomechanical cycling loads. For in-depth study of these problems we have to use theories of plasticity and creep which form the basis for determining the complex stress-strain state in the stress concentration zone for disc rims, and a modern failure criterion which can predict lifetime under conditions of simultaneous plastic and creep strain accumulation. There is a finite-element method (FEM) that allows us to evaluate the stress-strain state in a stress concentration zone for a non-elastic material behavior. With plasticity and creep theories, it is possible to determine local strain quiet reliable by FEM.

Long-term strength determination for cooled blades made of monocrystalline superalloys

For the manufacture of blades for modern gas-turbine installations, monocrystalline alloys are used. Traditional methods for the calculation of stressed-deformed state and safety factors for these alloys developed and verified for polycrystalline materials need to be adjusted. This paper deals with methodological principles for an approach to the solving of the problem concerning a finite-element determination of the long-term static strength for cooled monocrystalline blades employed in gas-turbine installations based on the use of two different models (phenomenological and micromechanical) considering the inelastic deformation of monocrystalline superalloys. An analysis has been performed for the distribution of Schmid factors in the spherical triangle for primary and secondary octahedral and cubic slip systems. Calculations are performed using Larson–Miller’s parametric dependences taking into account the crystallographic orientation of the material. A determination procedure for the anisotropy coefficients of long-term strength is described based on data for different orientations. A comparative analysis of the results of finite-element calculations made using phenomenological and micromechanical (crystallographic) creep models for the long-term static strength of cooled monocrystalline blades used in a gas-turbine engine has been performed. It is shown that the location of the most loaded sections of such a blade coincide with the results of calculations according to these models. It has been found that the micromechanical deformation model results in the obtaining of the most conservative estimate for the long-term strength of turbine blades made of monocrystalline alloys. It is shown that the calculations using models for materials with isotropic properties can produce considerable errors in determining the durability of the blades. The possibility is considered for using 1D-, 2D-, and 3D-models for turbine monocrystalline blades in the determination of their durability parameters.

Special Features of Creep and Long-Term Strength of Single-Crystal Refractory Nickel-Base Alloys

Results of experimental studies of creep in a wide range of temperatures and stresses are presented for three modern single-crystal nickel-base alloys. A method for determining the creep characteristics by tests including step increase of the tension is suggested and tested. The effect of transition into plastic condition on the creep parameters, the influence of the chemical composition and loading conditions on the duration of creep stages I, II and III, and the conditions of appearance of crystallographic and not crystallographic modes of fracture are analyzed. Possible simple approximations of the creep curves are considered with allowance for the accumulation of damage and occurrence of unsteady creep stages.

Methods of Computational Determination of Growth Rates of Fatigue, Creep, and Thermal Fatigue Cracks in Poly- and Monocrystalline Blades of Gas Turbine Units

The crack growth kinetics of fatigue, creep, and thermal fatigue cracks in blades of gas turbine units is studied through a direct three-dimensional finite-element stepwise modeling of the crack propagation process. Prediction of crack growth rate involves the use of the criteria based on stress intensity factors (or J-integrals) for fatigue cracks, on C*-integrals for creep cracks, and on a combination of stress intensity factors (or J-integrals) and C*-integrals for thermal fatigue cracks. The authors discuss the methods for determination of fatigue life of polycrystalline blades as well as some special features of calculations of the crack growth kinetics in monocrystalline blades. The paper presents some examples of results of finite-element calculations of the fatigue, creep, and thermal fatigue crack growth processes in rotating blades of gas turbine units.

Development and Investigation of Mechanical Properties of Glass Fiber Reinforced Concrete

Nowadays, new types of concrete reinforcement are finding increasing use in civil engineering applications. The use of fibrous materials as reinforcement for building structures gives opportunity for the manufacturing of concrete elements with reduced thickness, high strength, and high corrosion resistance. This paper includes development and determination of mechanical behavior of concrete reinforced with glass fiber, roving and composite reinforcement.

Modeling of Deformation and Fracture of Concrete Structures with FRP Reinforcement

Carrying capacity and fracture modes of concrete beams reinforced by different types of fiber reinforced plastic (FRP) bars are analyzed experimentally and numerically. The four-point-bending test is used as a typical loading case for this purpose. Synchronous registration of loading level, displacements and strains is performed by using InstronTM servohydraulic machine, LVDT sensors, strain gauges and digital image correlation Vic3DTM system. The experimental data and results of finite element simulations are compared and discussed.