Thin-walled Structural Elements Research Articles

Detecting Cracks in Intelligent Carbon-Based TRC Elements Through Wetting Events

Textile reinforced concrete (TRC) technology enables to construct sustainable and environmentally friendly thin-walled structural elements with self-sensory capabilities. The self-sensory concept is based on using high-strength and electrically conductive yarns that are simultaneously used as the main reinforcement system and as the sensory agent. By connecting the two ends of the yarns to either direct current (DC) or alternating current (AC) electrical circuits, it is possible to measure changes in the electrical readings and to further correlate them to the structural health. Studies in the literature validated the concept by using carbon yarns as hybrid monitoring agents. Most of them provided integrated assessments of global structural health but lacked the capability to pinpoint individual cracks. The current study offers a new identification procedure to locate cracks and to estimate their severity by combining two advanced monitoring procedures, that is by adopting the Time Domain Reflectometer (TDR) analysis; and by conceptually using the smart water leakage detection method. Both methods take advantage that a pair of carbon yarns can be positioned parallel to each other and connected to the DAQ system. In case of TDR method, one yarn functions as the signal transmitter and the other as insulation. In case of water leakage detection method, the electrical linkage between the two yarns changes the electrical characterization of the electrical circuit and enables the monitoring capabilities. The proposed study argues that a new identification procedure that benefits from each method can be developed and yields to smart identification procedure that has the capability to locate the crack and estimate its severity. The study will demonstrate the feasibility of the new procedure by experimental study. Results from this study will take a significant step toward developing reliable smart carbon-based TRC structures.

Minimization of the weight of the blade of the aerial installation by an adaptive hybrid optimization method

In various fields of engineering practice, such as turbine building, power engineering, elements of thin-walled structures are widely used, which operate under increased loads when interacting with air or water. These include blades of impellers of radial-axial and rotary-blade hydraulic turbines, blades of wind power plants. Designing highly efficient machines and structures with the required level of reliability requires determining their optimal characteristics. The article proposes an adaptive method for finding the minimum of an arbitrary smooth multivariable function. The method was used to solve the benchmark optimization problem of a function in the form of a valley. The essence of the proposed algorithm lies in the sequential approach to the bottom of the valley and the subsequent movement in the direction of decreasing the objective function. Comparison of the results of calculating the minimum point of the function is performed using both non-gradient and gradient methods, namely: Powell, Hook-Jeeves, the steepest descent method and the developed method. It was found that the effectiveness of the proposed method is greater than the usual search algorithms, but it is not without its drawbacks. The method is proposed that represents a number of hybrid methods, which form a hybrid coalition Proposed hybrid algorithm does not provide a satisfactory result in the "single" search. The search algorithm reaches a point where all the values of the function at the surrounding points are greater than the values at the obtained point, and the algorithm cannot overcome the barrier. To solve the problem, it is necessary to take the obtained point as a new starting point and repeat the algorithm for finding the minimum of the function, that is, use the multistart method. The proposed method was used to solve the problem of optimizing the blade of an air installation, which was reduced to the problem of unconditional optimization using the method of penalty functions, but the goal function had a significantly valley structure. The optimal values of section thicknesses were obtained, which made it possible to build a blade with improved characteristics.

Acoustic-Emission Method of Determining Residual Life of Thin-Walled Structural Elements Under the Action of Force Loads and Corrosive Environments

Acoustic-Emission Method of Determining Residual Life of Thin-Walled Structural Elements Under the Action of Force Loads and Corrosive Environments

Specific Features of the Contact Interaction and Wear of Thin-Walled Structural Elements

We consider contact problems for thin-walled structural elements and their wear. We propose a unified method for solving the problems based on the reduction to Volterra integral equations. This enables us to detect singularities of solutions depending on the hypotheses characterizing the process of deformation of thin-walled elements. We present the solutions and analyze the problems of wear of the plates by a rigid punch and a hot punch with regard for the friction heating and changes in the thickness of the plate in the process of wear.

Predicting the buckling behaviour of thin-walled structural elements using machine learning methods

The design process of thin-walled structural members is highly complex due to the possible occurrence of multiple instabilities. This research therefore aimed to develop machine learning algorithms to predict the buckling behaviour of thin-walled channel elements subjected to axial compression or bending. Feed-forward multi-layer Artificial Neural Networks (ANNs) were trained, in which the input variables comprised the cross-sectional dimensions and thickness, the presence/location of intermediate stiffeners, and the element length. The output data consisted of the elastic critical buckling load or moment, while also providing an immediate modal decomposition of the buckled shape into the traditionally defined ‘pure’ buckling mode categories (i.e. local, distortional and global buckling). The sample output for training was prepared using a combination of the Finite Strip Method (FSM) and the Equivalent Nodal Force Method (ENFM). The ANN models were subjected to a K-fold cross-validation technique and the hyperparameters were tuned using a grid search technique. The results indicated that the trained algorithms were capable of predicting the elastic critical buckling loads and carrying out the modal decomposition of the critical buckled shapes with an average accuracy (R2-value) of 98%. The influence of the various channel parameters on the output was assessed using the SHapley Additive exPlanations (SHAP) method.

Some exact solutions of the nonlinear evolutionary equation for the spreading of a plastic layer on a plane

The problem of free spreading of a plastic layer between parallel approaching planes of tool bodies [1] is considered, which simulates the technological process of stamping thin-walled structural elements. To describe the specified flow of a thin plastic layer, A. Ilyushin proposed an effective two-dimensional mathematical model averaged over the layer thickness, to which the original three-dimensional problem of the flow of an ideally plastic body leads. The transition to a two-dimensional problem was carried out on the basis of special hypotheses proposed as a result of the analysis of the well-known Prandtl solution in the problem of upsetting a flat, in a vertical section, layer of plastic material [2]. On the contact surfaces, the condition of complete slippage of the material is assumed, and the shear stresses reach a maximum value equal to the shear yield strength of the layer material. Within the framework of this model, A. A. Ilyushin formulated a boundary value problem in a region with a moving boundary with respect to three unknown functions - contact pressure and two flow velocity components.

Mechanics of Thin-Walled Structural Elements with Boundary Front Surfaces Having Fixed Areas

Mechanics of Thin-Walled Structural Elements with Boundary Front Surfaces Having Fixed Areas

Elastic properties and strength criterion of reinforced composite

Woven composite materials are increasingly being used in various fields of modern technology. Unlike composites reinforced with straight fibers, they have a higher shear stress loading strength and improved impact strength characteristics. Woven composites have good technological properties. Blanks with carbon or glass fabrics are well laid out on tooling in the manufacture of thin-walled structural elements of complex shapes. The technological advantages of woven composite materials have determined the economic feasibility of their widespread use in the aviation industry and the automotive industry. The paper presents a numerical method for identifying the elastic and strength characteristics of woven carbon fiber based on the results of a micromechanical analysis of a representative volume based on the known properties of the matrix and fibers. Numerical experiments on uniaxial tension in the x, y, and z axes directions have been carried out. Modeled shift in three coordinate planes. The strength characteristics of the representative volume of the composite under conditions of tension and compression in three directions, shifts in three planes, and three biaxial tensions are determined.

Моделювання впливу кільцевого включення на концентрацію напружень навколо видовженого еліптичного отвору у сферичній оболонці

Shell structures are widely used in various branches of technology and industry due to a combination of a high strength and a relatively light weight. In the majority of cases, actual structures have openings for manufacturing or design reasons, thus leading to a sharp increase in local stresses and, as a result, to a decrease in the strength and reliability of the structure as a whole. That is why reducing stress concentration in thin-walled structural elements is an important and topical problem in deformable body mechanics. This paper presents the results of a computer simulation and finite-element analysis of the stress and strain field of a thin-walled spherical shell with an elongated elliptical opening and an annular inclusion that surrounds the opening at a certain distance therefrom. The effect of the geometrical and mechanical parameters of the inclusion and its distance from the opening contour on the concentration of the stress and strain field parameters of the shell is studied. The stress and strain intensity distribution in the local stress concentration zones is obtained. It is shown that a rigid annular inclusion located at a certain distance from an opening allows one to reduce the stress concentration factor by nearly 27 percent with a proportional decrease in strain intensity in the vicinity of the opening. The elliptical opening elongation degree greatly affects the concentration of the stress and strain field parameters. If an opening is reinforced with a rigid annular inclusion immediately along its contour, the stress intensity in its vicinity increases, while the strain intensity decreases. The numerical calculations conducted show that surrounding an opening with a rigid annular inclusion located remotely therefrom reduces both the stress and the strain intensity in the vicinity of the opening. If an opening is reinforced immediately along its contour, a decrease in the maximum strain intensity is somewhat greater in comparison with the case where the rigid annual inclusion surrounding the opening is located at some distance therefrom. The use of specially selected and located reinforcements of elongated elliptical openings in spherical shells allows one to control the stress and strain intensity distribution and magnitude in the zones of local concentration of their stress and strain field parameters.

Comparison of Structural Analysis of Thin-Walled Structures Accomplished by Isogeometric Analysis and the Finite Element Method.

Isogeometric analysis (IGA) represents a relatively new method of problem-solving in engineering practice. A huge advantage of this method over the finite element method (FEM), is the reduction of the simulation execution time. Non-uniform rational B-splines (NURBS) allow the use of higher-order basis functions, thus increasing the accuracy of the solution. This paper deals with the comparison of structural analysis of thin-walled structural elements using isogeometric analysis and the finite element method. The investigated objects are modelled using a single patch in MATLAB. The basic functions are created from NURBS, which were previously used in the creation of an accurate geometric model. The paper contains a comparison of the results obtained by the above-mentioned methods. All computations are performed in the elastic domain.

CREEP AND SHRINKAGE OF REINFORCED CONCRETE THIN-WALLED CYLINDRICAL PANELS

One of the main tasks that is solved at the design stage of a reinforced concrete structure and its elements is the analysis of the stress-strain state, as well as the determination of the service life of the structure. The article is devoted to modeling the nonlinear creep of reinforced concrete structural elements taking into account damage and shrinkage of concrete. The high priority of the research topic is substantiated, the goals and objectives of the research are formulated. A combination of a plastic model with fracture mechanics is proposed to simulate the behavior of concrete in accordance with its characteristics, including not only stress and deformation, but also the change in its characteristics over time. The obtained equations of state correspond to the incremental creep law, taking into account the damage and shrinkage. The finite element method is used to solve a boundary value problem. For the purpose of numerical modeling of thin-walled structures, it is proposed to use special shell elements. The mathematical formulation of the problem of creep of reinforced concrete structural elements taking into account creep deformations and volumetric deformations of concrete shrinkage is presented. The problems of creep of thin-walled structural elements were solved using the developed proprietary software. Deformations of a reinforced concrete cylindrical panel are analyzed. Analysis of the results allows us to judge the effectiveness of the proposed model as a whole. The equation of state reflects the properties of the material and takes into account damage, allows you to reliably assess the strength, rigidity and durability of thin-walled reinforced concrete structures. Conclusions are presented regarding the adequacy of the analysis of the reliability and durability of reinforced concrete structures using the proposed model.

NUMERICAL SOLUTION OF THE DYNAMIC PROBLEM OF AXISYMMETRIC VIBRATIONS OF REINFORCED SHELLS

The reliability of the results obtained in the work is determined by the rigor and correctness of the statements of the initial problems; theoretical substantiation of the finite-difference schemes used; controlled accuracy of numerical calculations; conducting test calculations; compliance of the established regularities with the general properties of oscillations of thin-walled structural elements. The correctness of the formulation of the problems is achieved by using the well-known equations of the theory of shells and rods of the Tymoshenko type, which are approximations of the original equations of the three-dimensional theory of elasticity. When deriving the equations, the equations of oscillations of the multilayer shell in the smooth region and the equations of oscillations of reinforcing ribbed elements (transverse ribs) were obtained. It is not difficult to show that the indicated equations by the classification of equations in partial derivatives are equations of the hyperbolic type, which are an approximation of the oscillating equations of three-dimensional elastic bodies and sufficiently correctly reproduce wave processes in non-homogeneous shell structures, taking into account spatial gaps. Numerical algorithms for approximate solutions of the original equations are based on the use of the integro-interpolation method of constructing difference schemes. When constructing difference schemes, kinematic quantities refer to difference points with integer indices, and the values of deformations and moment forces refer to difference points with half-integer indices. This approximation of the initial kinematic and static values allows the fulfillment of the law of conservation of the total mechanical energy of the elastic structure at the difference level. The numerical algorithm is based on the use of separate finite-difference relations in the smooth domain and on the lines of spatial discontinuities with the second order of accuracy in spatial and temporal coordinates.

Review of research solid mechanics laboratory for 2020–2022

The article presents an overview of the research of the Laboratory of Solid Mechanics IMech UFRS RAS for 2020-2022. All studies were published as articles (there are two exceptions in the list of references, registered in the Register of Computer Programs) in well-known domestic and (or) foreign scientific journals on mechanics. During the three years under consideration, a number of new problems of aerohydroelasticity were solved and important results were obtained on the dynamic behavior of thin-walled structural elements interacting with external and internal continuous media. In particular, the linear bending of a cantilever rod loaded with all-round pressure and longitudinal force is considered in static and dynamic formulations. The areas of attraction of the deflection to the upper and lower equilibrium positions of a two-support pipe during its spatial bending-rotational vibrations are determined. The interaction of forced and parametric vibrations of the pipeline has been studied. The influence of the internal and external added masses of continuous media on the frequency of natural vibrations of a pipe moving with acceleration in the transverse direction is studied. The eigenfrequencies of bending vibrations of a micro- and nanometer-sized rod clamped at the ends are calculated. From the solution of the inverse problem for the changed values of natural frequencies, the coordinate and magnitude of the added mass are found. Linear oscillations of micro- and nanostrings are also considered when the pressure in a gaseous medium changes, taking into account surface effects. Using a model of molecular dynamics with a reduced number of degrees of freedom, the eigenfrequencies of bending vibrations of carbon nanotubes (CNTs) of different diameters are calculated under conditions of a plane-deformed state. In addition, part of the work was devoted to the study of the phenomenon of the ascent of an underwater gas pipeline and the determination of its buoyancy parameters. The scientific articles presented in this review are arranged in chronological order. For all articles, their summary is given and the main conclusions are formulated.

Diagnostics of thin-walled structures of complex geometry and structure

The main stages of the birth of thin-walled structures, changes in their relative thickness and mass of a unit area are given; ways of creating perfect thin-walled structures are indicated. The problems arising during the operation of thin-walled structures of complex geometry, as well as approaches and methods of their calculation are noted. To ensure trouble-free operation of a thin-walled structure with a thin-layer coating, under load and exposed to physical fields and environments, it is necessary to correctly diagnose the condition of structural elements. The spline variant of the finite element method in two-dimensional (SV FEM-2) and three-dimensional (SV FEM-3) productions is noted, as well as the synthesis of these variants - SV FEM-2 + SV FEM-3. The combination of the idea of parametrization of the entire domain and approximation of the desired variables within the element by Hermitian cubic splines makes it possible to obtain high-precision consistent finite elements. The developed variants of the finite element method make it possible to evaluate the stress-strain state of structures of complex geometry, including the calculation of multilayer, thin-walled structures with coating and local defects, as well as to take into account specific surface properties other than those of the main array. Studies of stress concentration near local depressions are considered. Two-dimensional experimental and theoretical methods are noted for evaluating the stiffness properties and adhesion of thin-walled, thin-layer and composite structural elements of complex structure, which, along with a distributed complex structure, may have distributed defects. The developments were used in solving specific tasks of a number of enterprises.

COMPUTER SIMULATION IN THE PROBLEMS OF STABILITY OF THIN-WALLED RODS OF AN OPEN PROFILE WITH SHAPE IMPERFECTIONS

The presented numerical methodology is based on the finite element method (FEM) and computational procedures of the NASTRAN software package. It allows to investigate the influence of geometric imperfections in the shape of thin-walled rods of open profile on the critical values of the load, the shape of the stability loss and the stress-strain state. It has been developed an algorithm for computer modeling of initial imperfections in the shape of thin-walled rods, which is implemented in the NASTRAN software package using a neutral NASTRAN PC file and a specially developed program written in FORTRAN language and adapted to this software package. Geometric imperfections of the rods can be represented as their form of loss of stability or the form of deformation from the action of the load with the possibility of varying the maximum value of the imperfections amplitude. Computational procedures for solving the Lanczos stability problem and the geometrically nonlinear static problem by the Newton-Rafson method can be used to model imperfections. The program developed by the authors allows to form new nodal coordinates of a finite-element model of rods and to visualize geometric imperfections in a given scale. The article provides a step-by-step description of finite-element construction models of thin-walled rod of open profile with an ideal surface and taking into account the imperfection of the form, which is presented as the first form of loss of rod stability from longitudinal load applied with eccentricity. With the help of the FEMAP NASTRAN preprocessor is forming the geometry of the middle surface of an ideal rod, and setting the mechanical characteristics of the material, boundary conditions and load. The middle surface of the rod is fed as a set of flat quadrangular finite elements with six degrees of freedom in the node. In the article, a linear calculation of the stability by the Lanzosch method is performed to obtain the form of rod geometric imperfection. Setting the maximum amplitude of imperfections was performed using the program developed by the authors. Using the Newton-Rafson method, the geometrically nonlinear problem of rod statics with a given shape imperfection is solved, the critical value of the longitudinal load is determined, and the corresponding form of the rod stability loss is obtained. The presented numerical technique and the developed algorithm of computer modeling of shape imperfections allow to investigate in nonlinear formulation the stability of open profile thin-walled rods taking into account geometric imperfections of different amplitude as different forms of rod deformation, including the form of stability loss, to assess the impact of imperfections on the critical value of the load, the form of stability loss and stress-strain state. The presented algorithm and numerical technique can be used to study the stability of such thin-walled structural elements as shells, plates and others.

Stress-strain state of reinforced thin-walled structural elements

The most common structures designed for the installation of technological equipment in workshops are beam platforms mounted from rolled steel and sheet elements. The values of strains and stresses of ribbed plates obtained in accordance with the linear theory, significantly differ from the values obtained in terms of physical and geometrical nonlinearities. A joint consideration of the double nonlinearity significantly clarifies the mathematical model of the reinforced flexible plates and shells, which provides a complete idea of the stress-strain state of the structure. The paper presents a calculation algorithm for the flexible plates reinforced by a stiffening plates and hollow shells based on the Lagrange function method. The stress-strain state of a plate symmetrically reinforced by a stiffening plate is investigated under the uniform loading conditions.

Experimental Investigation on Bending Behavior of Textile Reinforced Concrete (TRC) Plates at High Temperatures

Textile Reinforced Concrete (TRC) can be used as independent structural elements due to its high loading capacity and proper to product light weight and thin walled structural elements. In thisstudy, the bending behavior of TRC plates that reinforced with dry carbon fiber textile and exposed to high temperatures was experimentally studied under 4-points bending loading. Theexamined parameters were; (a) number of textile fiber reinforcements layers 1, 2 and 3 layers; (b) level of high temperatures 20°C, 200°C, 300°C, and 400°C. Firstly, the mechanical properties of the cementitious matrix and the tensile properties of TRC coupons at each predefined temperature were evaluated. The results showed that the ultimate tensile stress of the TRC coupons did not affect up to 200°C, however, a significant reduction observed at 300°C and 400°C by 19% and 24%respectively. Regarding the compressive strength and flexural strength of the cementitious matrix, the degradation was not severe until 200°C, while it became critical at 400 °C (23% and22% respectively). The result of the bending of TRC plates showed that doubling and tripling textile fiber reinforcements layers improved the flexural loading. In general, increasing the level of temperatures resulted in decrease in the flexural capacity of TRC plates. The highest decrease recorded for the specimen reinforced with 1-layer of carbon fiber textile subjected to 400 °C and was 33%.

Analysis of steel tank shell deformation and its impact on further utilisation

Recent research in thin-walled structures and steel structures has demonstrated that, in addition to internal forces and membrane stresses of shells, initial deformation and imperfection components should also be considered when calculating design cases. This paper presents a numerical analysis of a steel water tank with an initial deformation of the shell, which is used in an industrial plant for technological purposes. The steel water tank is a typical type of thin-walled structure for which initial deformation may be important. In the numerical example, a round symmetrical steel tank 2.70 m high is analysed under two states: with an undeformed shell and a deformed shell. The complicated interaction between the initial deformation and the vertical and horizontal stresses is analysed in detail. While the initial deformation of the shell may sometimes reduce stresses, in most cases, it substantially increases the overall stresses of the analysed steel water tank shell, up to 820% (for stresses in the horizontal direction) and up to 3554% (for stresses in the vertical direction). This means that initial large deformation and imperfections effects may play an important role not only in the design of industrial structures like silos and tanks but also for very specific slim, thin-walled structural elements.

Influence of adhesive bond line thickness on joint strength of composite aircraft structures

Methods for assessing the effect of the thickness of the adhesive layer in the adhesive joint of thin-walled composite structural elements on the strength of the entire joint are considered; a critical analysis of existing theoretical methods for predicting the strength of adhesive joints is given. The contradiction between the theoretical estimates of the effect of the adhesive thickness on the strength and the results of experiments and practical experience in the use of adhesive joints of composite panels is established. It is revealed that the most effective methods for predicting the load-bearing capacity of adhesive joints are energy models of fracture mechanics based on the intensity of the release of fracture energy and the formation of a pre-fracture zone in the adhesive layer. Assuming the determining role of changes in the size and shape of the initial fracture zone depending on the thickness of the adhesive layer, the results of the prediction of the strength of the adhesive joint are compared with experimental data.

Experimental investigation and analytical modelling of shear strength of thin walled textile-reinforced UHPC beams

The combination of two high performance materials, ultra-high performance concrete and carbon reinforcement, allows for the construction of efficient, durable thin-walled structural elements. In order to investigate the shear behaviour of such elements a test series on thin-webbed textile reinforced T-beams was planned and carried out at the Institute of Structural Engineering at TU Wien. In the experiments the efficiency of carbon textile reinforcement grids with different impregnation materials used as shear reinforcement was analysed. Furthermore, the shear span to effective depth ratio as well as the effect of prestressing on the shear carrying capacity was investigated. This article describes the experimental programme and shows the test results. The evaluation of the results indicates a higher shear performance of beams with lower-tex sand coated, acrylonitrile-styrene-acrylate copolymers impregnated textile fabrics than with Heavy-Tow grids with an epoxy resin impregnation. For the case of prestressing the carbon fibre reinforced polymer an additional increase of the shear carrying capacity of the thin-walled carbon textile reinforced structures was verified.