Theoretical Analysis Of Stresses Research Articles

Theoretical and Experimental Analysis of Inter-Layer Stresses in Filament-Wound Cylindrical Composite Structures.

This paper analyses the issues relative to the modelling of tubular (cylindrical) composite structures. This paper aims to describe the design of a multi-layer structure of filament-wound composite pipes where, after loading, the hoop-stress distribution would be as uniform as possible. That would allow the mass of the composite to decrease while maintaining the proper mechanical strength. This publication presents the development of a calculation model dedicated to mono- and multi-layered tubular composite structures. The equations describing the stress pattern were based on the Lamé Problem, whereas to describe the modelled structures, an anisotropy coefficient was introduced and interlayer pressures values were determined. To verify the calculations, experimental studies were performed. The test specimens were fabricated by winding fibre bundles around a steel core (as rings with an internal diameter of 113 mm and a height of 30 mm). For the test, the method of pressing a conical ring into a split ring, which acts on the internal surface of the tested cylindrical sample, was selected. The operation of the test rig (test stand) was simulated using the Finite Element Method (FEM). Measurements with strain gauges were conducted during the experiments.

A theoretical analysis of longitudinal temporomandibular joint compressive stresses and mandibular growth.

To determine if temporomandibular joint (TMJ) compressive stresses during incisor biting (1) differed between growing children over time, and (2) were correlated with Frankfort Horizontal-mandibular plane angle (FHMPA, °) and ramus length (Condylion-Gonion (Co-Go), mm). Three-dimensional anatomical geometries, FHMPA and Co-Go, were measured longitudinally from lateral and posteroanterior cephalographs1 of children aged 6 (T1), 12 (T2), and 18 (T3) years. Geometries were used in numerical models to estimate subject-specific TMJ eminence shape and forces for incisor bite-forces of 3, 5, and 8 Newtons at T1, T2, and T3, respectively. TMJ compressive stresses were estimated via two steps: First, TMJ force divided by age-dependent mandibular condylar dimensions, and second, modified by loading surfaces' congruency. Analysis of variance and Tukey honest significant difference post-hoc tests, plus repeated measures and mixed effects model analyses were used to evaluate differences in variables between facial groups. Regression analyses tested for correlation between age-dependent compressive stresses, FHMPA, and Co-Go. Sixty-five of 842 potential subjects had T1-T3 cephalographs and were grouped by FHMPA at T3. Dolichofacial (FHMPA ≥ 27°, n = 36) compared to meso-brachyfacial (FHMPA< 27°, n = 29) subjects had significantly larger FHMPA at T1-T3, shorter Co-Go at T2 and T3 (all P < .01), and larger increases in TMJ compressive stresses with age (P < .0001). Higher compressive stresses were correlated with larger FHMPA (all R2 ≥ 0.41) and shorter Co-Go (all R2 ≥ 0.49). Estimated TMJ compressive stress increases from ages 6 to 18 years were significantly larger in dolichofacial compared to meso-brachyfacial subjects and correlated to FHMPA and Co-Go.

Finite element simulation of drilling operation and theoretical analysis of drill stresses with the deform-3D

In this study, it was aimed to improve the cutting performance of the cutting tool (drill) used in drilling which is of great importance in the industry. The study includes experimental determination of thrust force and torque occurred during drilling, and analysis of the effects of these cutting loads on cutting tool with the Deform-3D program based on finite element method (FEM). For this purpose, various drilling experiments with uncoated and TiAlN/TiN coated solid carbide drills were conducted on full solid and pre-drilled AISI 1050 samples using different cutting parameters (cutting speeds of 60, 75, 90, 108 m/min and feed rates of 0.15, 0.20, 0.25 mm/rev). Kistler 9272 type dynamometer was used to measure the thrust force and torque occurring during the drilling experiments. The stress effects of the experimentally measured thrust force and torque on the drill were analysed. In order to improve the performance of the drill, the drilling operation was simulated and the relationships between cutting parameters and stresses were investigated using the Deform3D program. The results obtained from the study will provide significant contributions to improving the cutting performance of the drill and to the selection of optimum cutting parameters. The stress analysis approach applied in the study can also be applied to other metal cutting operations such as turning and milling, and evaluations can be made regarding the design of cutting tools.

Theoretical Analysis of Bending Stresses to Design a Sprocket for Transportation Part of a Chinese Cabbage Collector

Force calculation, stress, and fatigue analysis are major issues in machine design to ensure the life expectancy of sprocket-gear power transmission systems. Therefore, this study aims to conduct a theoretical analysis of bending stresses to select the size and component materials for the power transmission part of a Chinese cabbage collector that is under development. The three-dimensional models of a 14T sprocket gear for two steel materials, SCr420H and SM45C, were generated, employing commercial software. The bending stresses, deformations, and fatigue damages of the designed sprocket were determined by varying the face width and pressure angle of the sprocket teeth. The Lewis and American Gear Manufacturer Association (AGMA) equations were used to calculate the bending stresses. The calculated bending-stress values were compared with the stress values obtained from finite-element analysis (FEA). The maximum stress values on the gear teeth were 650.07, 826.23, and 840.77 MPa for a 20° pressure angle by using the Lewis, AGMA, and FEA methods, respectively. The simulated maximum stress value was higher than the yield strength of the SM45C steel and lower than the yield strength of the SCr420H steel. In addition, the maximum face width showed the minimum bending stress and fatigue damage for the selected material. Hence, considering the safety factor, the steel material SCr420H was selected with a 4.5-mm face width for designing the power transmission part of the Chinese cabbage collector. The analysis of bending stresses presented in this research can guide the design of a sprocket for the efficient transfer of Chinese cabbages using the proposed Chinese cabbage collector.

Theoretical analysis and mathematical modeling of deformation and stresses of the grooving tool

Machining operations involving complex multivariate parameters are defined by many machining parameters. Correct selection of these parameters is crucial for an efficient and economical cutting operation. The grooving operation required in many cases is one of the most problematic methods in all metal cutting operations, especially in terms of chip control. This paper covers theoretical analysis and mathematical modeling of deformation and stresses of the grooving tool. Cutting forces affecting the service life of the grooving tool were measured by various cutting experiments. Deformation and stresses of grooving tool caused by cutting forces were analyzed by finite element method using Ansys software. In modeling with artificial neural networks (ANN), grooving insert width, cutting speed, feed rate, radial force and primary cutting force are inputs in the model and deformation and stresses of the grooving tool are outputs. An algorithm, which is a Matlab script file, was developed to determine the optimal combination of neural network parameters such as the normalization method, number of hidden neurons, transfer function and training algorithm. The best-fitting set determined by the algorithm developed for the model was achieved with the Levenberg–Marquardt backpropagation algorithm, logistic sigmoid transfer function, nine hidden neurons and normalization method with a scaling factor. The MSE, R2, MAPE values of the ANN model are 2.0327 × 10−6, 0.999992 and 0.379227, respectively. Performance results have shown that the proposed approach can also be used for ANN modeling of machining parameters in other cutting operations other than grooving.

Analytical investigation of thermal and mechanical load effects on stress distribution in adhesive layer of double-lap metal-composite bonded joints

Significant thermal stresses are induced in the adhesive layers of a metal-composite bonded joint owing to the large temperature change associated with the difference in the coefficients of thermal expansions of metals and composite adherends. In this study, a theoretical analysis of shear and peel stresses in adhesive layers of a double-lap metal-composite bonded joint is carried out to evaluate the effects of thermal and mechanical loads on the stress distribution in the adhesive layer. The effects of temperature change and adhesive thickness on the shear and peel stresses in the adhesive layer of the bonded joint, with and without external forces, are examined based on the theoretical analysis. The results calculated for the condition involving a mechanical load application to the bonded joint and a decrease in temperature indicate that the absolute value of the shear and peel stresses peak at both ends of the adhesive layer, and that the absolute value of the peak stresses increases in the case of a thinner adhesive layer. When mechanical and thermal loads are simultaneously applied to a double-lap joint, shear and peel stresses synergistically increase at one end of the adhesive layer and decrease with an offset at the other end.

Beaded fiber composites—Stiffness and strength modeling

We present a theoretical analysis of the elastic stresses in a composite reinforced with beaded fibers by extending the classic Cox shear lag theory. The motivation for reinforcing a composite with beaded fibers is to improve both strength and toughness, two often conflicting properties. It is found that owing to their geometry beads intermittently placed on a fiber enhance fiber anchoring in the matrix, and can potentially dissipate energy by deforming the matrix during failure. The composite stiffness is shown to improve compared to a composite with beadless fibers, particularly when the beads are large and stiffer than the surrounding matrix. The stress profiles in the fiber, bead, matrix and along their respective interfaces incur periodic perturbations induced by the beads, modeled by Hill equation. For given elastic constants and bead geometry, these profiles reveal the weakest link loci in the structure, and consequently determine the composite strength and failure mode. A finite element analysis is presented that confirms our results. The bead-fiber and bead-matrix interfaces may be tuned by choice of materials and coatings to achieve desired mechanical properties.

Analysis of Residual Stress in the Rotational Autofrettage of Thick-Walled Disks

Autofrettage is a means of generating compressive residual stresses at the inner side of a thick-walled cylinder or hollow disk by causing nonhomogeneous plastic deformation of the material at the inner side. The presence of residual compressive stresses at the inner region of the cylinder/disk enhance the pressure withstanding capacity, fatigue life and the resistance to stress corrosion cracking of the component. Despite the hydraulic and swage autofrettage are the widely practiced processes in industries, there are certain disadvantages associated with these processes. In view of this, in the recent years, researchers have proposed new methods of achieving autofrettage. Rotational autofrettage is such a recently proposed autofrettage method for achieving the beneficial compressive residual stresses in the cylinders. In the present work, the rotational autofrettage is studied for a thick-walled hollow circular disk. A theoretical analysis of the residual stresses produced in the disk after unloading are obtained assuming plane stress condition, Tresca yield criterion and its associated flow rule. The analysis takes into account the effect of strain hardening during plastic deformation. Further, the effect of residual stresses in the typical SS304 and aluminum disk is studied by subjecting them into three different types of loads viz., internal pressure, radial temperature difference, and rotational speed individually. A three-dimensional (3D) finite element method (FEM) validation of the theoretical stresses during rotational autofrettage of a disk is also presented.

Analytical investigation of thermomechanical stresses in graded interphase between the fiber and the matrix

ABSTRACTIn this article, the thermomechanical stresses in the graded interphase between the fiber and the matrix in fiber-reinforced composites are investigated. First, the general theoretical analysis of two-dimensional steady-state mechanical and thermal stresses in a graded cylinder along the radial direction with the Power Law and Exponential Law distribution of the material properties is developed. Then the theoretical solution is applied to investigate the mechanical stresses and the thermal stresses of the fiber-matrix interphase, and the effects of material graded constant on the mechanical stresses and thermal stresses are discussed. Finally, the stress transfer mechanisms in the graded interphase are investigated which indicates that the total stresses in the fiber-matrix interphase increased with the increasing of the interphase thickness if the material graded constant varied with the radius in Power Law, but decreased in Exponential Law.

(Invited) Dense Gas Separation Membranes - Current Status and Future Challenges

The application areas of oxygen transport membranes (OTM) and the potential benefits they can provide will be described. The importance of close thermal integration with the process to which the oxygen is supplied will be elucidated by balance-of-plant studies and techno-economical evaluations in two different applications; biomass gasifiers and cement production. The status of the technology will be presented with emphasis on results from several national and EU-funded membrane development projects. There are still several challenges to overcome before use of the technology will be wide spread. One is the required upscale of the technology another one is ensuring the required reliability and durability of the membranes. Recently developed methods for characterizing the mechanical properties of OTM materials and components at operating conditions and a theoretical analysis of stresses encountered during operation will be presented and based on these strategies to ensure fail-safe design/operation. An OTM material should ideally have high ionic and electronic conductivity as well as good chemical stability under both oxidizing and reducing conditions. Further, the mechanical properties (strength, toughness, creep rate) must match the requirements of the application. Candidate materials involve a broad class of Fe-, Co- and Ti-based perovskites. Recent results on selected materials from this broad class of materials will be presented. Challenges with reaching both the required transport properties and the required mechanical reliability with such single phase perovskites has spurred renewed interest in dual phase membranes where a good ionic conductor (typically based on zirconia or ceria) is combined with a second phase providing electronic (or mixed) conductivity. Our most recent results on such dual phase membranes will be presented involving both zirconia and ceria based systems. On both tubular and planar LSF/CGO membranes high oxygen fluxes >10 Nml min-1 cm-2 (850°C) have been demonstrated between air on one side of the membrane and a strongly reducing “syngas” mixture (CO/H2/H2O/CO2) on the other side. The tubular membranes were prepared by dip coating on an extruded low cost MgO support and the planar ones by phase inversion tape casting providing a highly oriented pore structure in the support layer. The processes limiting the flux in these systems were investigated in some detail by conductivity relaxation. Whereas the addition of CGO to LSF has the expected effect of increasing the ionic transport in the bulk it also had a more surprising effect of enhancing the surface exchange rate. Possible explanations for this will be presented. Finally, selected results on zirconia based composite membranes optimized for high pO2 applications will be presented including ZnO-ZrO2 and (MnCO)3O4 -ZrO2 membranes. For the latter system (MnCo2O4/(Y2O3)0.01(Sc2O3)0.10(ZrO2)0.89) fluxes around 1 Nml min-1 cm-2 at 850°C have recently been demonstrated between air and a nitrogen purge (pO2~10-3 atm.) using a ~10 μm thick supported membrane.

Experimental–theoretical analysis of local stresses in box girders of trapezoidal cross section

The paper discusses the effect of local stresses on the carrying capacity of box girders of trapezoidal cross-section. The mathematical model used for identifying the stress–strain state of the local stress is formed based on the principle of decomposing the cross-sectional elements. It was confirmed that trapezoidal box girder has more favourable stress state in comparison with the traditional rectangular box girder under the same conditions of global carrying capacity and mass (cross-sectional area). Relevant parameters of the local stress of the trapezoidal box girder carrier were identified. Behaviour of box girders regarding the local stress is primarily dependent on the width and thickness of the plate which is exposed to the direct loading effect. The criteria to be followed when designing box girders were defined. The study was conducted on two diametrically opposite positions of the same girder, while experimental results were verified on the basis of their consistency with the theoretical and numerical values.

Effect of shear deformation on interfacial stress analysis in plated beams under arbitrary loading

Strengthening reinforced concrete (RC) and other materials beams by bonding a steel or fiber reinforced polymer (FRP) has become a popular method due to its rapid, simple and other advantages. However, debonding along the FRP-RC beam interface can lead to premature failure of the structures. The interfacial stresses play a significant role in understanding this premature debonding failure of such repaired structures. In this paper, an improved theoretical analysis of the interfacial stresses is presented for a simply supported plated beam subjected to arbitrary loading. The solution is based on the deformation compatibility approach where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. Indeed, the distribution of shear stress through the thickness of adherends is obtained by solving the equilibrium equations of stresses. The shear stresses, thus obtained, are shape parabolic through thickness of the adherend. The effect of shear deformation on the variation of interface stresses along the reinforcing plate is illustrated by a numerical example to demonstrate the advantages of the current solution. The solution is general in nature and may be applied to the analysis of others composite structures.

The measurement of powder flow properties with a mechanically stirred aerated bed

This paper re-examines a set of experimental data published by Bruni et al. (2007a, 2007b) [Bruni, G., Barletta, D., Poletto, M., Lettieri, P., 2007a. A rheological model for the flowability of aerated fine powders. Chem. Eng. Sci. 62, 397–407; Bruni, G., Lettieri, P., Newton, D., Barletta, D., 2007b. An investigation of the effect of the interparticle forces on the fluidization behaviour of fine powders linked with rheological studies. Chem. Eng. Sci. 62, 387–396] carried out on a mechanically stirred fluid-bed rheometer (msFBR), which was developed to study the rheology of aerated and fluidized powders. The use of aeration below fluidization allowed to carry out experiments with powders at very low consolidation levels. Two mathematical models, based on the Janssen approach to evaluate stresses in powder containers, were developed in order to relate the torque measurements in the Fluidized Bed Rheometer to the flow properties of the powders measured with standard powder flow testers. Results indicate that the models were able to satisfactorily predict the torque measured by the msFBR. The larger complexity of the Walker (1966) [Walker, D.M., 1966. An approximate theory for pressures and arching in hoppers, Chem. Eng. Sci. 21, 975–997] and Walters (1973) [Walters, J.K., 1973. A theoretical analysis of stresses in silos with vertical walls, Chem. Eng. Sci. 28, 13–21] stress analysis adopted in one of the two models did not introduce significant improvements in the evaluation of the stress distribution to justify its use. A procedure for the inverse application of the model was developed and applied to estimate the powder flow properties starting from msFBR data. The application of this procedure provided good results in terms of effective angle of internal friction and is promising for the ability of the system to explore powder flow at very low consolidation states.

Theoretical analysis of tensile stresses and displacement in orthotropic circular column under diametrical compression

This paper shows the solution for an orthotropic disk under the plane strain condition obtained with complex stress functions. These stress functions were induced by Lekhnitskii and expanded by one of the authors. Regarding diametrical compression test, the finite element method poses difficulties in representing the concentrated force because the specimens must be divided into finite elements during calculation. On the other hand, the method shown in this study can exactly represent this force. Some numerical results are shown and compared with those obtained under the plane stress condition for both stress and displacement. This comparison shows that the differences between the tensile stresses occurred under the plane strain condition and also that the differences under a plane stress condition increase as the orthotropy ratio increases for some cases.

Theoretical Analysis of Temperature and Shrinkage Stresses of Box-Girder Section

The objective of this study is to analyze the temperature and shrinkage stresses of the mid-span cross-section of a 20 meters box girder to find the reasons which cause the longitudinal cracks in the web and bottom of box girder. According to the results of damage inspeation, there are many longitudinal cracks in the web and bottom slab of box girders, especially the web of the edger beam, the crack is very clear. Ansys ver.10 software is used to analyze two dimensional finite element model of a typical cross section of a real bridge to calculate the temperature stresses caused by temperature difference between inside and out side of the box and the shrinkage stresses based on moisture diffusion. The results of analysis show that the outer surface of the web and bottom slab of the fabricated box girder will produce tensile stress at the effect of negative temperature difference. If the concrete reaches a certain age, the tensile stress does not cause creaks in the cross-section. The shrinkage stress changes with the moisture gradient in the box section. It will reach the maximum in 15 days and then decreases with the growth of the age. Shrinkage stress may cause cracking of the concrete surface because of the tensile strength is low in the early age.

An improved closed-form solution to interfacial stresses in rc beams strengthened with a composite plate

The strengthening of concrete structures in situ with externally bonded fiber-reinforced plastic (FRP) composite sheets is increasingly being used for the repair and rehabilitation of existing structures. However, debonding along the FRP-concrete interface can lead to premature failure of the structures. The interfacial stresses have played a significant role in understanding this premature debonding failure of such repaired structures. In this paper, an improved theoretical analysis of the interfacial stresses is presented for a simply supported concrete beam bonded with a FRP plate. The shear strains of the adherends have been included in the present theoretical analysis by assuming a parabolic distribution of shear stress across their thickness. Contrary to some existing studies, the assumption that both adherends have the same curvature is not used in the present investigation. The results of this numerical study are beneficial for understanding the mechanical behavior of material interfaces and for the design of hybrid FRP-reinforced concrete structures.

Anisotropy of tensile stresses and cracking in nonbasal plane AlxGa1−xN/GaN heterostructures

Al x Ga 1 − x N films grown on nonpolar m {11¯00} and {112¯2} semipolar orientations of freestanding GaN substrates were investigated over a range of stress states (x≤0.17). Cracking on the (0001) plane was observed beyond a critical thickness in the {11¯00} oriented films, while no cracking was observed for {112¯2} films. Theoretical analysis of tensile stresses in AlxGa1−xN for the relevant planes revealed that anisotropy of in-plane biaxial stress for the nonpolar {11¯00} planes results in the highest normal stresses on the c-planes, consistent with experimental observations. Shear stresses are significant in the semipolar case, suggesting that misfit dislocation formation provides an alternative mechanism for stress relief.

Theoretical Analysis of Stresses in a Lithium Ion Cell

A mathematical model to simulate the generation of mechanical stress during the discharge process in a dual porous insertion electrode cell sandwich comprised of lithium cobalt oxide and carbon is presented. The model attributes stress buildup within intercalation electrodes to two different aspects: changes in the lattice volume due to intercalation and phase transformation during the charge/discharge process. The model is used to predict the influence of cell design parameters such as thickness, porosity, and particle size of the electrodes on the magnitude of stress generation. The model developed in this study can be used to understand the mechanical degradation in a porous electrode during an intercalation/deintercalation process, and the use of this model results in an improved design for battery electrodes that are mechanically durable over an extended period of operation.

Analysis of Effectiveness and Stress Development during Convective and Microwave Drying

The aim of the article is to study the effectiveness of convective and microwave drying with respect to drying time and stress generation in clay-like dried bodies. The theoretical analysis of stresses was confined to the constant drying rate period because clay shrinks and the stresses are generated mainly in this period. The theoretical prediction of stress development was validated using an acoustic emission method by monitoring the micro- and macrocracks formation caused by the stresses. Apart from the stress analysis, the combined convective-microwave drying was examined experimentally during whole process in order to show that the volumetric heat supply due to microwave heating enhances convective drying and, apart from this, such a combined drying process develops less stress in dried material. The theoretical and experimental studies were performed on a kaolin sample in the form of a thin plate.

Theoretical and experimental analysis of stresses and fractures in clay like materials during drying

Theoretical and experimental analysis of stresses and fractures in clay like materials during drying