Axial Stress Distribution Research Articles

Mechanical Characteristics of Fully Grouted and Antiseismic Bolts considering Transverse Deformation in Underground Caverns

The load transfer control equations under bolt-surrounding rock interaction are established on the basis of classical beam theory and the trilinear shear slip model. The axial stress and transverse shear force distributions of the anchorage body are obtained by solving the equations. The equivalent forces obtained by the transverse force and axial shear stress of the bolts are applied to rock mass elements to simulate the support effect. A new dynamic algorithm for bolts is proposed in considering of the axial and transverse deformation of the anchorage body. The rationality of the algorithm is verified by comparing with laboratory pullout and shear tests of bolts. A dynamic time-history case study of underground caverns is conducted using this algorithm. Results indicate that (1) the algorithm may reflect the stress and deformation characteristics of bolts during an earthquake; (2) for the antiseismic support effect of the surrounding rock at fault, the bolt algorithm in this study is more valid than the algorithm that considered only the axial deformation of bolts; (3) in the support force of the bolt to the surrounding rock, transverse force is the key to limit fault dislocation and reduce the dynamic damage of the rock at fault.

Experimental analysis of axial stress distribution in nanostructured core fused silica fibers

We experimentally studied axial stress distribution in recently developed optical all-solid fibers with nanostructured cores. In this type of fiber, the core is composed of thousands of low and high refractive index glass rods with individual diameters of a few hundred nanometers. A distribution of nanorods determines the effective distribution of the refractive index in the core. A structure of nanorods may introduce unrevealed axial stress distribution after fiber drawing, which may induce change of the expected refractive index value. We studied stress in a custom made nanostructured silica fiber with parabolic refractive index distribution in the core and compared it with the reference SMF-28 fiber. For nanostructured fibers we proved that the axial stress is purely thermal with negligible contribution of mechanical stress. This results in the presence of tensile stress in the fiber core, which is in contrary to a standard telecom fiber, where a compressive stress in the core exists. We showed that measured axial stress has negligible impact on refractive index distribution of nanostructured fibers, thus it does not affect its performance.

Investigation on the interaction mechanism and failure behavior between bolt and rock-like mass

The matching relationship between bolt diameter and borehole diameter determines the bolt supporting effect in the mining roadway. In this paper, the failure modes of the anchorage body under different diameter matching were studied by the pullout test. When the anchorage agent was pulled out completely with bolt, the anchoring effect was ideal. Whereas, when the bolt was pulled out smoothly with only a thin layer of anchorage agent, the anchoring effect was relatively worse. Through multiple pullout tests, the suitable diameter matching difference can be defined with a range of 6–11 mm. Based on the interface sliding failure mode between anchorage agent and rock-like mass, a mechanical model of diameter matching was established. Both equations of tensile force and interfacial shear stress along with the anchorage direction in perfectly elastic state were derived. FLAC 3D was applied to analyze the distribution of interfacial shear stress and axial stress under different diameter matching between the bolt and the borehole. As a result, a 4–11 mm diameter difference shows the best anchoring effect. According to both experimental and simulation results, the optimal diameter matching difference is 6–11 mm.

Axial and radial thermal responses of energy pile under six storey residential building

The axial and radial thermal responses of a cast-in-place energy pile, 10 m long and 0.6 m in diameter, installed in unsaturated sand under a six storey building are examined during a heating–cooling cycle. The instrumentation in the pile was configured to compare radial and axial thermal responses at the same elevations and to evaluate the temperature and axial thermal stress distribution across the cross-sectional area of the pile. The magnitudes of the axial thermal strains were more constrained than the radial thermal strains at all depths, leading to the development of axial and radial thermal stresses of up to –4.5 and –0.015 MPa, respectively, for a change in average pile temperature of 24.1 °C. The magnitudes of the radial thermal stresses with changes in pile temperature were significantly lower than the axial thermal stresses at all depths of the pile, indicating that the radial thermal expansion had negligible effects on the development of axial thermal strains and stresses. The temperature distribution over the cross section of the pile showed low variations at all depths, indicating that it would be justified to consider a uniform temperature distribution at least in piles of similar dimensions and with even heat exchanger layouts.

Axial compression tests of grouted connections in jacket and monopile offshore wind turbine structures

Grouted connections (GCs) are widely used in offshore wind turbines to transfer multiple loads from their upper structures to their foundations. Among these loads, axial loads and bending moments dominate in most structural forms. As reported in this paper, a total of seven GC specimens were tested under ultimate axial compression. Two specimens, A-Pre and A-Pos, respectively representing the pre-installed and post-installed pile construction technique in jacket foundations, were directly tested under axial loading. Meanwhile, the other five specimens (RA-1 to RA-5), representing the GCs in monopile foundations, were compressed after 2 million cycles of fatigue bending moments (except RA-5). All seven specimens failed because their steel tubes buckled. However, in Specimen A-Pos, before the steel tube buckled, the grout material broke and slippage occurred, while the axial capacity increased even after the slippage. For the five monopile GC specimens, the failure mode of steel tube buckling indicated that the GCs still had competent axial capacities even after being subjected to fatigue bending moments. It is possible that fabrication quality, rather than fatigue loading histories, dominated the residual capacity in these tests. Moreover, three-dimensional (3D) finite element (FE) models of these GCs were also constructed. The simulation of ultimate axial capacities, failure modes, and stress distributions were basically consistent with the experimental results.

STRESSES IN ANVILS OF VARIOUS CONSTRUCTION OF CONTINUOUS CASTING AND DEFORMATION PLANT AT PRODUCTION OF SHEETS FROM STEEL FOR WELDED PIPES

A comparative assessment of strenuous state of the anvils with and without channels has been carried out for the installation of combined continuous casting and deformation process in the production of steel sheets for welded pipes. The conditions of operation and loading of the anvils of combined continuous casting and deformation process are described. The design of anvil with channels for water cooling and the nature of its loading are given. Using the algorithm for solving problems in the elasticity theory by finite element method, the laws governing the distribution of axial stresses in anvils from the slab reduction force are determined. Effect of the channels for anvils cooling with water on the magnitude and nature of stresses distribution in them from the stress of the slab reduction was estimated. The calculation results of temperature fields and axial and equivalent thermoelastic stresses in anvils with channels are presented for the production process of steel sheets for welded pipes in a combined continuous casting and deformation unit. The article considers regularities of total stresses distribution in anvils with channels. To assess the effect of anvils structure on their stress state, regularities of distribution of thermoelastic and total stresses in strands without channels have been determined. The graph of dependence of thermoelastic stresses in the anvil on temperature of its contact surface is given. Recommendations for choosing the material of the fighters are given. The advantages and disadvantages of the anvils with channels for the unit for combined continuous casting and deformation are described. The parameters of such a pilot installation are presented. The authors also describe the results of an experimental study of the parameters of a combined process at the manufacture installation for continuous casting and deformation of JSC Ural Pipe Plant.

A three-phase model of the single-fiber composite fragmentation test to evaluate viscoelasticity, stress distribution and interface fracture toughness

ABSTRACTA three-phase model of the single-fiber composite fragmentation test is proposed to evaluate viscoelasticity, stress distributions and interface fracture toughness. Based on the three-parameter standard linear solid model, a unit cell is established under periodic boundary conditions to study viscoelasticity considering the interface effect. Under the thermal residual stress and the tensile load, a three-dimensional (3D) theoretical cylinder model is utilized to predict the stress distributions in radial, hoop and axial directions for fiber, interface and matrix. The results are in good agreements with finite element method (FEM) results. Especially, we discuss the effects of the fiber shape on the mechanical behavior. Classic shear-lag theories are compared to modify the axial stress distributions. For the fragmentation test, two basic failure modes are studied in the proposed model. Based on accurate stress distributions, the energy-balance scheme takes into account all strain energies, the failure consumption, the friction consumption and the applied load work to calculate interface fracture energy release rate, results of which is consistent with other models. Furthermore, we study the effects of friction coefficients and radial debonded locations. Using the softening and failure model of the interface, the debonding process is simulated for zero-thickness and thick interfaces, respectively.

On the axial distribution of plaque stress: Influence of stenosis severity, lipid core stiffness, lipid core length and fibrous cap stiffness

Numerical simulations of blood flow through a partially-blocked axisymmetric artery are performed to investigate the stress distributions in the plaque. We show that the combined effect of stenosis severity and the stiffness of the lipid core can drastically change the axial stress distribution, strongly affecting the potential sites of plaque rupture. The core stiffness is also an important factor when assessing plaque vulnerability, where a mild stenosis with a lipid-filled core presents higher stress levels than a severe stenosis with a calcified plaque. A shorter lipid core gives rise to an increase in the stress levels. However, the fibrous cap stiffness does not influence the stress distributions for the range of values considered in this work. Based on these mechanical analyses, we identify potential sites of rupture in the axial direction for each case: the midpoints of the upstream and downstream regions of the stenosis (for severe, lipid-filled plaques), the ends of the lipid core (for short cores), and the middle of the stenosis (for mild stenoses with positive remodelling of the arterial wall).

Load and Stress Distribution of Thread Pair and Analysis of Influence Factors

Analyzing the axial load(axial force) distribution and the stress distribution of the root of the thread is helpful for accurately predicting the thread failure and optimizing the design of the structure of the nut and the bolt. The existing research mainly analyzes the axial load distribution and stress distribution of the thread by using the two-dimensional(2D) finite element model(FEM), and they have no theoretical support. In this paper, a three-dimensional(3D) finite element model was established, and a theoretical model of the stress calculation of the root of the thread was established. The theoretical calculation results of this paper were compared with the results of the 3D finite element model analysis. The results show that the two are in good agreement with each other, which verifies the consistency between the theoretical model and the 3D finite element model. Then, the stress of the root of the bolt and nut is investigated under the action of axial force. And the factors, such as Young’s modulus E, axial total load F, friction coefficient μ, radial thickness H, engaging threads number N, thread defect which affect the load distribution are systematically studied.

Experimental and numerical investigation of the effects of the pre-heating in the modification of residual stresses in the repair welding process

In this paper, the application of pre-heating process on the reduction of residual stress in the repair welding of steel pipes is investigated. In this purpose, a thermo-elastic-plastic molding of the repair welding process is developed using finite element method. In order to verify this modeling method, experimental data of repair welds of a carbon steel pipe, measured by deep hole drilling method, were utilized. The verified results indicated that the developed computational method can be beneficially used as an effective tool to predict the residual stress of the pipes undergo the repair welding. The verified finite element model was utilized in the repair welding of carbon steel and stainless steel pipes to consider the effects of preheating. It was observed that by increasing the preheating temperature in the repair welded pipes, longitudinal residual stress on the inner and outer surfaces of the both carbon and stainless steel pipes decreased about 35–50%, respectively, although the compressive residual stresses on the outer surface have small variations. Moreover, by increasing the preheating temperature, tensile hoop residual stresses on the outer surface of both the stainless steel and the carbon steel pipes decreased, but only a small variation was observed on the compressive hoop residual stress. In general, there are no significant effects on the magnitude and distribution of hoop stresses on the inner surface of the repaired stainless steel pipe. Also, high preheating temperature, leads to a wider distribution of axial residual stresses in repair welded pipes.

Modeling the effects of interfacial properties on the temperature dependent tensile strength of fiber reinforced polymer composites

In this study, the stress distribution of fiber axial stress and interfacial shear stress in fiber reinforced polymer (FRP) composites at different temperatures was derived as a function of fiber axial position. The maximum shear stress criterion was extended to be temperature dependent. Based on the extended criterion, the temperature dependent fiber debonding length of FRP composites was predicted, which is indirectly verified by other scholar's experimental study. Then, by introducing the maximum fiber axial stress transferred from the matrix to fiber by their interface including the effect of partial interfacial debonding, we modified the law of mixtures, and finally established the temperature dependent tensile strength model for FRP composites. The model considers the combined effects of temperature, constituents' properties, interfacial properties and residual thermal stress. Reasonable agreement is obtained between the model predictions and available temperature dependent tensile strength of FRP composites. Additionally, the influencing factors analysis for FRP composites is performed in detail. This work provides some important insights on the strength control mechanisms of FRP composites at different temperatures, which are beneficial to the material evaluation, strengthening, and optimization.

Experimental Investigation of Steel Plate Shear Walls under Shear‐Compression Interaction

Four scaled one‐storey single‐bay steel plate shear wall (SPSW) specimens with unstiffened panels were tested to determine their behaviour under cyclic loadings. The shear walls had moment‐resisting beam‐to‐column connections. Four different vertical loads, i.e., 300 kN, 600 kN, 900 kN, and 1200 kN, representing the gravity load of the upper storeys were applied at the top of the boundary columns through a force distribution beam. A horizontal cyclic load was then applied at the top of the specimens. The specimen behaviour, envelope curves, axial stress distribution of the infill steel plate, and shear capacity were analyzed. The axial stress distribution and envelope curves were compared with the values predicted using an analytical model available in the literature.

ИССЛЕДОВАНИЕ ПОВЕДЕНИЯ ЦИЛИНДРИЧЕСКИХ ТЕЛ В УСЛОВИЯХ СОВМЕСТНОГО РАСТЯЖЕНИЯ И КРУЧЕНИЯ ПРИ НЕПРОПОРЦИОНАЛЬНОМ НАГРУЖЕНИИ

The work is devoted to studying the behavior of cylindrical bodies of structural steels in the conditions of joint tension and torsion under complex loading. The study is aimed at studying and subsequent modernization of the method of increasing the fatigue life of cylindrical products. It consists in creating the product favorable axial compressive residual stresses in the near-surface area due to the successive elastoplastic deformation, first by tension, and then, during fixation of the longitudinal deformation obtained by tension, by torsion. A mathematical model of elastoplastic deformation by joint tension and torsion of a homogeneous cylindrical body, which allows to calculate the distribution of residual stresses created in the body, is constructed. To check the adequacy of the obtained solution and determine the required material parameters of the model, tests were performed on cylindrical samples of steel 15Cr2MnMoV. The necessary studies were carried out at the Center for Experimental Mechanics of Perm National Research Polytechnic University using the Instron 8850 universal two-axis servo-hydraulic test system, which allows for loading by joint tension and torsion. According to the results of the experiments, graphs of the longitudinal force and torque versus the twist angle were obtained with the deformation sequences studied. By comparing the experimental and calculated dependencies, the adequacy of the developed model was confirmed and the range of deformation modes was established, in which it reflects the behavior of the material with an accuracy acceptable for practice. Instead of the existing method of deformation, which includes a single torsion of a product in a state of tension, a new method is considered, consisting in reversional (alternating) torsion of a cylindrical body in a state of tension. Deformation by sequential tension and reversional torsion allows to provide a favorable (from the standpoint of increasing fatigue life) distribution of residual axial stresses over the cross section of the body with minimum values of residual shear stresses.

Gimbaled Tiltrotor Conversion Flight Loads Prediction Using Three-Dimensional Structural Analysis

This paper presents a method for modeling gimbaled rotor aeromechanics in Experimental 3D structural dynamics solver, which is a next-generation three-dimensional finite-element-based rotor structural dynamics solver. The rotor is modeled using a single blade with a free flap hinge at the hub, the motion of which is suppressed at integer multiples of the blade passage frequency by introducing harmonics of the joint rotation angle as additional trim variables, efficiently simulating gimbal kinematics. Rotor frequencies are examined for a three-bladed gimbaled rotor model and are found to combine the modes of both free flap hinge and fixed flap hinge (cantilevered) one-bladed models, similar to a teetering rotor, justifying the gimbal modeling methodology. Gimbal flapping is examined for a proprotor in edgewise flight: successful suppression of steady and 3/rev flapping indicates the gimbal model accurately represents the rotor kinematics. Air loads and blade loads are examined with and without with the gimbal model, revealing an increase in 3/rev sectional normal aerodynamic force on the blade but a decrease in the 3/rev flap and lag bending moment when the gimbal is added. Three-dimensional axial stress distribution at the blade root is examined, revealing only minor differences with and without the gimbal model, primarily in the flex beam.

Effect of stiffeners on the eccentric compression behaviour of square concrete-filled steel tubular columns

Concrete-filled steel tubular (CFST) structures are extensively used in engineering applications in China owing to their high strength and section modulus, ease of construction, and good seismic performance. However, the steel tubes of CFST members are prone to outward buckling under compression loads. Welding longitudinal stiffeners on these steel tubes is one of the most efficient approaches used for delaying the local buckling and improving the mechanical performance of CFST members. This study attempted to investigate the eccentric compression behaviour of concrete-filled stiffened steel tubular members with square sections by experimental studies and finite element analysis (FEA). First, 12 CFST columns with different slenderness ratios and loading eccentricities were subjected to compression loads and tested. It was found that the use of stiffeners increased the ultimate strength and improved the stability of the columns. Subsequently, the behaviour of the stiffened CFST columns was investigated by performing a three-dimensional FEA. The accuracy of the FEA model was verified based on the test results. The working mechanisms of the stiffened CFST members were analysed in detail in terms of the failure modes, load versus deformation responses, deformation of the steel tubes, interaction between the steel tube and core concrete, as well as axial stress distribution of the core concrete. A parametric study was conducted to further evaluate the stiffening schemes that affected the ultimate strength and ductility of the CFST members. Finally, design recommendations on the type of eccentrically-loaded stiffened CFST columns were provided.

Behavior of Geogrid Reinforced and Unreinforced Non-connected Pile Raft Foundation

Presence of reinforcement elements such as geogrid in the cushion layer of the non-connected pile raft foundation changes the load transition mechanism and the portion of piles and raft from the total load. In this paper, experimental studies have been conducted on a non-connected pile raft foundation located in a sandy soil. The effect of parameters such as piles spacing, the thickness of cushion, position, length and number of geogrid layers on the behavior of load settlement, the portion of piles and raft from the total load, and distribution of axial and frictional stress along the pile and position of neutral axis were studied. The results showed that in unreinforced cases, with an optimum cushion thickness and piles spacing, the lowest settlement is observed. The use of geogrid in the cushion layer increases the bearing capacity and the portion of the piles from the total load and led to a move up in the neutral axis to the top of the piles. The optimum position and length of the first and second geogrid layers have also been studied.

Numerical Investigation on Residual Stresses of the Safe-End/Nozzle Dissimilar Metal Welded Joint in CAP1400 Nuclear Power Plants

The residual stress evolution in a safe-end/nozzle dissimilar metal welded joint of CAP1400 nuclear power plants was investigated in the manufacturing process by finite element simulation. A finite element model, including cladding, buttering, post-weld heat treatment (PWHT) and dissimilar metal multi-pass welding, is developed based on SYSWELD software to investigate the evolution of residual stress in the aforementioned manufacturing process. The results reveal a large tensile axial residual stress, which exists at the weld zone on the inner surface, leads to a high sensitivity to stress corrosion cracking (SCC). PWHT process before dissimilar metal multi-pass welding process has a great influence on the magnitude and distribution of final axial residual stress. The risk of SCC on the inner surface of the pipe will increase if PWHT process is not taken into account. Therefore, such crucial thermal manufacturing process such as cladding, buttering and post-weld heat treatment, besides the multi-pass welding process, should be considered in the numerical model in order to accurately predict the distribution and the magnitude of the residual stress.

Analysis on Stress Field of Asymmetrical Cold Ring Rolling for High-speed Rail Bearing Inner Ring

In this paper, the finite element model of asymmetric cold ring rolling for high-speed rail bearing inner ring is built by using ABAQUS software and the inner stress field of the ring metal during the whole cold ring rolling process is researched and analyzed, which reveals. The distribution of radial, axial, circumferential and equivalent stress at the bite rolling stage, the stable rolling stage and the fine rolling stage in the asymmetric cold rolling forming process for high-speed rail bearing inner ring were analyzed respectively. The stress in each direction of the ring was found to increase first and then decrease with each stage of cold rolling going. Finally, it tends to be stable. The stress on the contact area between the ring blank and the drive roll and the mandrel is obviously greater than that on the core of ring, and the stress in the core is more uniform.

Synergistic effects of fiber/matrix interface wear and fibers fracture on matrix multiple cracking in fiber-reinforced ceramic-matrix composites

ABSTRACTIn this paper, the synergistic effects of fiber/matrix interface wear and fibers fracture on matrix multiple cracking in fiber-reinforced ceramic-matrix composites (CMCs) are investigated using the critical matrix strain energy (CMSE) criterion. The shear-lag model combined with the fiber/matrix interface wear model, fibers fracture model and the fiber/matrix interface fracture mechanics debonding criterion is adopted to analyze the fiber and matrix axial stress distribution inside of the damaged composite. The relationships between the matrix multiple cracking, fatigue peak stress, applied cyclic number, fiber/matrix interface wear and debonding and fibers failure are established. The effects of fiber volume fraction, fiber/matrix interface shear stress, fiber/matrix interface debonded energy, cycle number, fatigue peak stress and fibers strength on matrix multiple cracking evolution are discussed. Comparisons of matrix multiple cracking with/without cyclic fatigue loading are analyzed. The experimental multiple matrix cracking of unidirectional SiC/CAS, SiC/CAS-II, SiC/Borosilicate and mini-SiC/SiC composites with/without cyclic fatigue loading are predicted.

Assessing the Difference in Measuring Bolt Stress: A Comparison of Two Optical Fiber Sensing Techniques

Monitoring the load level of the rock bolts is of great importance for assessing risk. Based on the mechanical transmission mechanism of grouting bolts, the bolt pull-out test was carried out in lab. The performance of the bolt under pull-out loading was measured using the pulse-pre-pump Brillouin optical time domain analysis (PPP-BOTDA) and fiber Bragg grating (FBG) sensing technologies. The distribution characteristic of axial stress along the bolt was analysed in combination with the measurements obtained by the two sensing technologies. The relative standard deviation for repeatability errors in the determination and the setting time of resin grout was investigated. The results show that the distribution of axial stress is nonuniform along the anchorage section. The maximum value of axial stress on the bolt is closed to the pull-out side. The relative standard deviation for repeatability errors obtained by PPP-BOTDA is less than that obtained by FBG. The comparison of the measurements obtained by the two methods indicates that when the drawing force is greater than 20 kN and the axial stress is more than 10 kN, the two methods have better consistency. In the field application, it is necessary to estimate the deformation of matrix, leaving at least 500 minutes for resin bond to work.