Tensile Stress Distribution Research Articles

Estimation of vertical bending stress in rails using train-mounted vertical track deflection measurement systems

This paper presents a new methodology for the estimation of bending stresses over long sections of rails from the vertical track deflections measured using train-mounted instrumentation. The basis of this method is to apply mathematical correlations between the rail deflections and stresses to interpret the deflection measurements. A new finite element modeling method was developed to investigate mathematical correlations between the rail deflections and stresses for different ranges of track modulus. The stochastic nature of the track modulus, as one of the dominant factors influencing rail deflections and stresses, was simulated. The rail responses to applied loads were then calculated and compared for scenarios of constant and variable track modulus values. The study resulted in a detailed framework that can be employed to estimate rail bending stresses from train-mounted vertical track deflection measurements. This framework allows the estimation of the probability distributions of maximum tensile and compressive bending stresses in the rail head and base, which are necessary for calculating the rail reliability under applied loading.

Wet swelling effect on crack performance of facing concrete for rockfill dams

The swelling of aged concrete is a significant issue in the operation of dams such as concrete-faced rockfill dams (CFRDs). Swelling of concrete is one cause of tensile stress, which is typically related to water movement in concrete pores, especially around the water surface. In this study, the change in the interior relative humidity and deformation in aged concrete specimens around the surface of the water were measured. The experimental results revealed that the swelling of the concrete above the water surface was correlated with an increase in interior relative humidity due to water diffusion, while the swelling of the concrete submerged in the water developed in early and late stages and was dominated by capillary absorption and diffusion. A new theoretical swelling model was developed to predict the deformation development, and the theoretical predictions were validated by the experimental data. The swelling model was applied in a finite-element analysis of a CFRD to obtain more realistic stress distributions. The analysis indicated that the wet swelling of concrete had a significant impact on the increase in tensile stress distribution in the concrete slab around the water surface.

Tensile stress distribution in maxillary central incisors restored with cast-made and prefabricated dental posts.

Abstract: Aim: To analyze and compare the tensile stress distribution in endodontically treated teeth restored with cast-made (Ni-Cr and gold) and prefabricated (titanium and glass fibre) dental posts. Methodology: Four three-dimensional finite element (FE) models of a maxillary central incisor restored with Ni-Cr cast-made (Model Ni-Cr), gold cast-made (Model GO), prefabricated titanium (Model TI) and prefabricated glass fibre (Model FP) posts were constructed. An oblique loading of 100N was applied to each three-dimensional model. Tensile stress distribution within the root dentine and at the post and surrounding structure interfaces were analysed. Results: In all the FE models studied, a higher magnitude of tensile stresses was observed on the palatal aspect of the cervical dentin as compared to the labial aspect and progressively decreases from the outer to the inner part of the root. The gold cast-made and glass fibre post models showed significantly less tensile stress concentration in the post-core component than the other experimental models. The maximum tensile stress was seen on the palatal aspect of the Ni-Cr compared to other posts. The higher magnitude interfacial tensile stress concentration was observed in a pulpless tooth restored with a Ni-Cr cast-made post, followed by titanium and gold cast-made posts, respectively. However, the minimum interfacial tensile stress was noticed in a pulpless tooth restored with a glass fibre post. Conclusion: Glass fibre posts tend to transfer tensile stress more homogenously within the tooth and at interfaces than the other types of investigated posts.

Degree of external restraint of wall segments in semi‐massive reinforced concrete tanks: Part I rectangular segments

This paper presents graphs and formulas serving to define the distribution of the restraint degree of wall segments in rectangular reinforced concrete tanks. The most frequent cases occurring in engineering practice are analyzed, that is, wall segments erected during the first concreting stage and those restrained along three edges. For the latter ones, this paper defines the influence of vertical stiffness in construction joints (depending on the reinforcement degree) on the distribution of the restraint degree. This paper shows a substantial impact of the temperature profile (i.e., imposed strain resulting from the development of hydration heat) on the area where cracks occur first, and on the value and distribution of tensile stresses. A practical aspect of the analysis performed is the possibility of defining the restraint degree for cases and assumptions not included in EN 1992–3.

Location of atypical femoral fracture can be determined by tensile stress distribution influenced by femoral bowing and neck-shaft angle: a CT-based nonlinear finite element analysis model for the assessment of femoral shaft loading stress

IntroductionLoading stress due to individual variations in femoral morphology is thought to be strongly associated with the pathogenesis of atypical femoral fracture (AFF). In Japan, studies on AFF regarding pathogenesis in the mid-shaft are well-documented and a key factor in the injury is thought to be femoral shaft bowing deformity. Thus, we developed a CT-based finite element analysis (CT/FEA) model to assess distribution of loading stress in the femoral shaft. Patients and MethodsA multicenter prospective study was performed at 12 hospitals in Japan from August 2015 to February 2017. We assembled three study groups—the mid-shaft AFF group (n=12), the subtrochanteric AFF group (n=10), and the control group (n=11)—and analyzed femoral morphology and loading stress in the femoral shaft by nonlinear CT/FEA. ResultsFemoral bowing in the mid-shaft AFF group was significantly greater (lateral bowing, p<0.0001; anterior bowing, p<0.01). Femoral neck-shaft angle in the subtrochanteric AFF group was significantly smaller (p<0.001). On CT/FEA, both the mid-shaft and subtrochanteric AFF group showed maximum tensile stress located adjacent to the fracture site. Quantitatively, there was a correlation between femoral bowing and the ratio of tensile stress, which was calculated between the mid-shaft and subtrochanteric region (lateral bowing, r=0.6373, p<0.0001; anterior bowing, r=−0.5825, p<0.001). ConclusionsCT/FEA demonstrated that tensile stress by loading stress can cause AFF. The location of AFF injury could be determined by individual stress distribution influenced by femoral bowing and neck-shaft angle.

Experimental and Numerical Investigation of the Center-Cracked Horseshoe Disk Method for Determining the Mode I Fracture Toughness of Rock-Like Material

This paper presents a new procedure for determining the fracture toughness of rock-like specimens using the diametric compression test with the center-cracked horseshoe disk (CCHD) method. Using finite element analysis, a dimensionless stress intensity factor was obtained and a formula was rendered for determining mode I fracture toughness. To evaluate the accuracy of the measurement results produced by the CCHD method, fracture toughness experiments were conducted on the same rock-like material using the notched Brazilian disk (NBD) method. The CCHD tests were simulated using a two-dimensional particle flow code for validation of the experimental results, and a great agreement between the pattern of crack initiation and propagation between the experimental and numerical simulations was observed. Lower values of fracture toughness were obtained from CCHD experiments than NBD tests due to purely tensile stress distribution at the tip of the existing notch in CCHD method.

Bond behaviour of GFRP reinforcement in alkali activated cement concrete

Bond plays a key role in the performance of reinforced concrete structures. Glass fiber reinforced polymer (GFRP) reinforcing bar and alkali activated cement (AAC) concrete are promising alternative construction materials for steel bars and Ordinary Portland Cement (OPC) concretes respectively. In this study, the bond behaviour between GFRP bars, and AAC and OPC concretes is investigated by using beam-end test specimens. Sand-coated GFRP bars with 12.7mm and 15.9mm diameters and embedment lengths of six and nine times the bar diameter were used. The free end and the loaded end bond slip relationships, the failure mode and the average bond stress were used to analyse each of the specimens. Additionally, the distribution of tensile and bond stress along the embedment length was investigated by installing strain gauges along the embedment length. The results of the study indicate that the tensile and bond stress distribution along the embedment length are nonlinear, and the nonlinearity changes with the load. Finite element analysis was also performed to further study the bond stress distribution along the embedment length of the bar. From the finite element analysis, it was found that the bond stress distribution depends on the embedment length of the specimens; approaching uniform distribution as the embedment length decreases.

Mechanism study on the low cycle fatigue behavior of group studs shear connectors in steel-concrete composite bridges

Clustering the stud shear connectors with a narrow spacing to form group studs is useful for the concrete slab prefabrication in steel-concrete composite bridges. But the existing test and analysis results have shown that arranging studs in group tends to be unfavorable to the stud static and fatigue performance. The current fatigue design of the group studs may still experience an overestimation or an underestimation problem since the fatigue mechanism study on group studs is rare. Therefore, a parametric push-out analysis was carried out for explaining the fatigue behavior of group studs, particularly the low cycle fatigue aspect with the fatigue life lower than 2millioncycles. There were 12 static and cyclic push-out models in the analysis. Meanwhile, a series of static push-out tests were also introduced to verify the analysis works. According to the static analysis results, the unequal stud shear forces in the group studs, which were indicated by the analyzed static failure mode, resulted in the reductions of stud shear stiffness and strength. According to the low cycle cyclic analysis results, the fatigue damage initiated at the bottom point of the stud root section in the push load direction, which can be called the fatigue critical point. The low cycle fatigue life reduction of group studs, which was evaluated by the analysis results and the introduced multi-axial fatigue damage criterion, can be explained by the uneven cyclic tensile strain and stress distributions on every individual fatigue critical point in the group studs.

A simplified model for equilibrium and transient swelling of thermo-responsive gels.

A simplified model is developed for the elastic response of thermo-responsive gels subjected to swelling under an arbitrary deformation with finite strains. The constitutive equations involve five adjustable parameters that are determined by fitting observations in equilibrium water uptake tests and T-jump transient tests on thin gel disks. Two scenarios for water release under heating are revealed by means of numerical simulation. When the final temperature in a T-jump test is below the volume-phase transition temperature, deswelling is characterized by smooth distribution of water molecules and small tensile stresses. When the final temperature exceeds the critical temperature, a gel disk is split into three regions (central part with a high concentration of water molecules and two domains near the boundaries with low water content) separated by sharp interfaces, whose propagation is accompanied by development of large (comparable with the elastic modulus) tensile stresses.

Bond of spliced GFRP reinforcement bars in alkali activated cement concrete

Abstract Glass Fibre Reinforced Polymer (GFRP) bars and Alkali Activated Cement (AAC) concrete are promising materials for replacing steel bars and ordinary Portland cement concrete. These materials can provide a solution to the associated corrosion and environmental issues. However, no design recommendations are available on splicing of GFRP bars in AAC concrete. This may be mainly due to insufficient data that would guide such recommendations. In this paper, the results of testing beams with spliced bars are presented mainly from consideration of the bond property between the spliced GFRP bars and the AAC concrete. The effects of splice length, compressive strength of concrete, and stirrup confinement on the bond behaviour are investigated. Ultimate moment capacity, failure modes, cracking pattern, and strain values in the bars have been determined and used in the analysis. A three-dimensional finite element model (FEM) was then developed. The FEM results show that the model accurately reproduces the experimental behaviour of splice tests with regard to load-deflection curves and failure modes. The reported results and numerical analysis are intended for understanding distribution of tensile and bond stresses in GFRP reinforced AAC concrete. These distributions were observed to be dependent on the applied load.

Structural Limitations of Energy Storage Systems Based on the Virial Theorem

Based on the virial theorem, the structural limitations are compared among superconducting magnetic energy storage (SMES), flywheels, and capacitors. The conventional SMES coils such as toroidal field coils (TFCs) and solenoids and the capacitor generate the compressive stresses. Due to this, the ratio of the stored energy to the required mass of the structure (U/M ratio) is lower than that of the flywheel. The flywheel almost achieves the uniform tensile stress distribution to support the centrifugal force and enables the enhancement of the U/M ratio. Based on the development status, the superconducting coils and the conventional flywheels composed of steel metals achieve almost 12 kJ/kg of the U/M ratio. Especially, using carbon fiber reinforced plastic, the flywheel can increase the U/M ratio to 90 kJ/kg. The force-balanced coils (FBCs) are helically wound hybrid coils of TFCs and a solenoid and become one of the feasible options for the SMES coils. The FBCs remove the compressive stresses by balancing the electromagnetic forces and have a potential for the improvement of the U/M ratio of SMES coils by the effect of the uniform tensile stress distribution. The theoretical limitation of the U/M ratio is more than twice of that in the flywheel case for the same structural materials.

Development and Application of a New Tensile Stress Model for Expansive Soils

Cracks initiate and propagate when tensile stress, caused by an increase in suction, becomes greater than tensile strength in expansive soils. It is important to understand the variation of tensile stress with suction for properly tackling the problems associated with cracks. In this paper, a new practical model is presented for predicting tensile stress from suction, and is verified using finite element analysis. The parametric study shows that drying time and diffusion coefficient control the distribution of tensile stress with depth and the depth to zero tensile stress, while elastic modulus, the difference between final surface suction and initial suction, and suction compression index control the magnitude of tensile stress. The new model can be used to predict the suction where the crack initiates using the soil water characteristic curve (SWCC), to estimate the depth of crack for a specific region, and to estimate the required drying time for a specific crack depth. The new model widens the general application of the SWCC approach in unsaturated soils and can be a useful tool to analyze the interaction between foundation or pavement subgrade and local climatic conditions.

Bond behaviour of GFRP reinforced geopolymer cement concrete

Bond plays a key role in the performance of reinforced concrete structures. Glass fibre reinforced polymer (GFRP) reinforcing bar and Geopolymer cement (GPC) concrete are promising alternative construction materials for steel bars and Ordinary Portland Cement (OPC) concrete respectively. In this study, the bond behaviour between these two materials is investigated by using beam-end specimen tests. The bond behaviour of 15.9 mm diameter sand-coated GFRP bar was investigated. An embedment length of six and nine times the bar diameter were used. The free end and the loaded end bond-slip-relationships, the bond failure mode and the average bond stress were used to analyse each of the specimens. Additionally, the distribution of tensile and bond stress along the embedment length was investigated by installing strain gauges along the embedment length in some of the specimens. Test results indicate that a significant difference exists between the free end and loaded end bond-slip curves, which is due to the lower elastic modulus of the GFRP bars. Furthermore, it was found that the tensile and bond stress distribution along the embedment length is nonlinear and the nonlinearity changes with the load.

An Analytical Study of Failure of Transversely Isotropic Rock Discs Subjected to Various Diametrical Loading Configurations

The indirect (Brazilian) tensile strength test is commonly used in rock engineering and rock mechanics. Most of the research on how to interpret Brazilian test is only valid for isotropic rock. The load may be applied to disc shaped samples through flat platens or curved jaws and the different load configurations give rise to subtle but important differences to stress distributions throughout samples during testing and at the onset of failure. To reliably obtain the tensile strength accurate stress distributions, especially at the location of the initial crack, must be determined. However, most real rocks exhibit a certain type of anisotropy known as transverse isotropy due to the presence of preferred directions of grains, beddings, microcracks or pores. This study focuses on the failure modes when transverse isotropy is present. Previous studies for transverse isotropy indicate that the exact location of the initial crack is at the disc centre. These studies, however, ignore the effect of the load contact configuration on the stress distribution. This paper overcomes this limitation and applies Amadei's analytical solution to assess the effects of the load contact area on the stress distribution. The stress distribution is coupled with a transverse isotropy failure criterion in a mechanically consistent way to find the exact location of initial crack. It is shown that the location of the initial crack depends on the transverse isotropy orientation and load configuration.

CONTINUOUS CASTING AND DEFORMATION INSTALLATION FOR THE PRODUCTION OF STEEL PLATES FOR WELDED PIPES. Report 1

The shortcomings of modern technology of thick-plate rolling, leading to the problems in production of welded pipes, are described. Advantages of thin slab casting technology are indicated, in which casting and reduction of a billet with a liquid phase are combined. The design of the combined continuous casting and deformation installation is described and the technology of steel plate production for welded pipes is provided. The main task of the article was to determine the stress-strain state of metal during formation of a strip from the ingot steel coat with a liquid phase by the coat with a liquid phase narrow walls bending. Computational experiment based on the solution of continuum mechanics task by means of the finite element method was used as a method of investigation. For calculations, a grid of finite elements was taken for a quarter of the model and a coat narrow wall with a facet length of0.5 mm. The elastic-plastic contact task is solved considering large displacements and deformations, and a stress-strain state during formation of a strip in a zone of bending of a coat with liquid phase narrow walls is determined. The calculation was carried out in a flat setting (flat deformed state). The initial data for the solution of the task using advanced ANSYS software are presented. The task statement and the boundary conditions are described. Dependences for calculation of the modulus of elasticity and plastic deformation resistance on temperature, strain degree and strain rate are presented. Epures of displacements, stresses and deformations of metal in the bending zone of a coat with a liquid phase narrow wall are presented. The regularities of distribution of tensile stresses along the outer surface and along the thickness of a coat narrow wall with a liquid phase are described as well as the ways of reducing tensile stresses on the side surfaces of a coat with a liquid phase.

Residual stress of 800 MPa high strength steel welded T section: Experimental study

An experimental study is presented to investigate the residual stress in 800MPa high strength steel welded T sections using the sectioning method. A total of four different sections with 7mm thickness steel plates are tested to quantify the magnitude and distribution of both compressive and tensile residual stress. The effect of the width-thickness ratio of web and flange on the distribution of the residual stress is established. The results show the residual stress in all sections is in self-equilibrium. The maximum tensile residual stress locates in the central portion of flange, while the minimum tensile residual stress distributes on both ends of web and flame cutting edges of flange. The maximum tensile residual stress, ranging from 0.43fy to 0.68fy, has no obvious relations with the width-thickness ratio of plate. The constant compressive residual stress distributes in the central portion of projecting flange and web. The maximum compressive residual stress, ranging from 0.09fy to 0.46fy, decreases as the width-thickness ratio of plate increases, while the area of stress distribution zone increases as the width-thickness ratio of plate increases. A simplified model is suggested for analysis and design based on the magnitude and distribution of residual stress.

The influence of connecting pile cap-column in the mechanisms of break in the two pile caps

Abstract The paper analyzes the two pile caps with partially embedded socket and subject a center load. Three models were experimentally tested, varying the type of conformation of the column and walls of the socket, with a smooth, the other rough, and a monolithic two pile cap, used for reference. The roughening of the column-socket interface was examined with the aim of verifying the difference of the distribution of compressive and tensile stresses in the strut an tie model used for design. The experimental test to show that the two pile caps with conformation rough of the column and walls of the socket, support more load in comparison with two pile caps with smooth of the column and walls of the socket. Both however underperformed the monolithic two pile cap, with values of 66% and 36% respectively.

Parametric study of the distribution of the tensile stresses in pavilion structures constituted by four sectors of barrel shells

A semi-analytical approach is followed in order to obtain an approximate solution for an analytical model describing the static behaviour of pavilion shells. With the aim to parametrically investigate the distribution of the linear elastic tensile stresses, a linear elastic isotropic behaviour of the material is considered. Inside the pavilion shell, a family of arches and a family of straight beams can be recognized. This assumption justifies the separation of the variables which is at the basis of the proposed semi-analytical approach. The sensitivity of the behaviour of the shells to the values of the mechanical and geometrical parameters characterizing the system is investigated. Comparisons with results obtained by finite element models are performed to confirm both the validity of the semi-analytical approach and the provided results. Since only a linear elastic isotropic material has been taken into account, the results do not claim to describe the behaviour of masonry pavilion vaults.

Developing the method of constructing mathematical models of soil condition under the action of a wedge

Studies of the technique of construction of mathematical models on the condition of soil under the action of wedge are presented. Based on hypothesis about separation of the layer of soil by a wedge through its bending, we constructed a mathematical model of determining normal and tangential stresses in soil under the action of wedge. Using mathematical dependencies, we obtained patterns of the distribution of maximum tensile and compression stresses, dependent on the depth of motion of wedge at different angles of crushing the soil. It was found that crushing of soil, which is determined by the size of lumps and chunks, formed under the action of the soil­cultivating working bodies, has a direct dependence on the covered path to reaching limiting stresses in soil. The increase in the distance of the passage of working bodies until the start of the process of cleaving the soil layer contributes to formation of lumps and chunks of larger size. The studies revealed that the wedge, depending on the angle of crushing, strength indices of soil and depth of cultivation, may create in it stresses, necessary for the cleaving, at the initial moment of motion after covering the distance equal to 10 mm and longer. Stresses in soil grow with an increase in the angle of crushing and depth of cultivation. To substantiate parameters of a chisel blade, in particular geometric profile of the rack, we used the method of the calculus of variations. Substantiation of the point of a chisel blade was carried out in two stages. At the first stage we substantiated the profile of chisel of the point taking into account the provision of necessary deepening into soil at minimum energy consumption, at the second stage – the profile of the point with minimum energy consumption by the results of studies, connected with substantiation of the chisel. Analysis of traction resistance of chisel working bodies established that the improvement in the profile of the point ensures reduction in traction resistance of a chisel working body. The data analysis of experiment demonstrated that the coefficient of structuredness of soil after its treatment by standard and experimental points has practically identical value; the improvement of profiles of the points of chisel organs does not lead to worsening the quality of soil treatment. The data analysis on determining traction resistance of chisel working bodies showed that, compared to the standard one, the experimental working body has lower traction resistance. Thus, experimental studies confirm reliability of results of theoretical studies on the substantiation of the profile of the chisel of a chisel working body from the point of view of reduction in their energy consumption while providing for the quality of crushing the soil.

Investigation of Dog-Bone Geometry for Simple Tensile Test of Pseudoelastic Shape Memory Alloys

In the present work, simple tensile test of shape memory alloys (SMAs) is studied by considering stress concentration caused by the grippers. In order to simulate SMA behaviors, finite element method is employed to obtain prestress distribution along the specimen due to fastening the grippers prior to the application of tension. Then, Brinson’s 1-D constitutive model is used to study transformations during the tensile loading–unloading. It is found that the prestress leads to a non-uniform distribution of uniaxial stress as well as martensite volume fraction throughout a wire. Therefore, the so-called dog-bone geometry is suggested and optimum dimensions are proposed to obtain a uniform tensile stress distribution when testing an SMA specimen. This way, a nearly simultaneous transformation can be achieved along the whole specimen. The optimum dimensions are shown to be different from those reported by ASTM for tensile testing of SMAs. In fact, the optimum dimensions depend on material parameters of the test specimen.