Analysis Of Bolts Research Articles

Bearing Capacity Characteristic Analysis of Anti-floating Bolts in Unsaturated Soil Based on Mindlin Solution

AbstractBased on Mindlin solution and the theory of unsaturated soil mechanics, the theoretical solutions of shear stress and axial force distribution in the elastic stage of full-length binding-type anti-floating bolts were derived, and the bearing capacity characteristics of such bolts and the influencing factors were analyzed. In this paper, the design parameters of anti-floating anchor in a negative two-floor basement of a commercial square are substituted into the formula derived in this paper. The results show that, in unsaturated soil, the shear stress and axial force of the full-length bonded anti-floating anchor are distributed along the total length of the anchor, but neutral points appear in both of them, which is mainly due to the reduction of the axial force and shear stress of the anti-floating anchor caused by the matric suction. The formula derived in this paper is used to analyze the factors affecting the bearing capacity of anti-floating anchor bolt in unsaturated soil. The results show that: the greater the elastic modulus of soil mass, the greater the peak value of shear stress curve, the closer the peak value is to the head of anchor bolt, and the greater the axial force decline rate. With the increase of anchor solid diameter D, the peak value of shear stress decreases, the peak value moves backward, the neutral point moves forward, the negative shear stress value increases, the decline rate of axial force distribution curve decreases, but the negative axial force increases. With the increase of the additional shear stress τ0, the peak value of the shear stress curve decreases, the peak value moves to the hole of the anchor rod, the neutral point moves to the hole, the negative shear stress increases, the decline rate of the axial force distribution curve increases, and the negative axial force increases.

Fracture failure analysis of high-strength bolts in power plant steel structures

The high-strength bolts of a power plant steel structure fractured and failed in many places. To find the cause of the failure, this paper analyzed the failure reasons of fractured bolts through macroscopic inspection, chemical composition analysis, mechanical performance test, metallographic inspection, and fracture microscopic analysis. The results show that the main cause of bolt fracture is that improper heat treatment leads to a carburized layer on the surface of the bolt, which makes the surface of the bolt sensitive to hydrogen. At the same time, there is a certain amount of hydrogen in the material matrix, which leads to hydrogen accumulation and cracks in the bolt at the stress concentration. Eventually, the cracks propagate and lead to fracture failure.

Tensile mechanical properties and damage analysis of layered woven GFRP composite bolts

Composite bolts have become one of the research focuses in screw threads joints due to their lightweight, high-strength, and wave transmission properties. We elucidate the differences in tensile properties, damage processes, and tensile failure forms between two types of layered woven GFRP composite bolts through tests and numerical simulations. It was found that the tensile strength of layered plain woven bolts is 40% higher than layered twill woven bolts. The failure forms of both types of bolts are related to their layered woven structure. The fracture surface of plain bolts is planar, while the fracture surface of twill bolts is apex shaped. Subsequently, a refined thread stretching model was established to study the effect of loading speed on the tensile property of screw threads. It was found that the tensile strength of plain woven screw threads and twill woven screw threads at a loading speed of 1 mm/min was 11% and 6% higher than that at 3 mm/min, respectively. The results show that the bolts and screw threads with layered plain woven have stronger tensile strength than those with layered twill woven, and a decrease in loading speed within a certain range can improve the tensile strength of the screw threads.

The Forming Analysis of SCM440 Alloy Steel Hexagon Head Flange Bolts

The Forming Analysis of SCM440 Alloy Steel Hexagon Head Flange Bolts

Crack propagation analysis and fatigue life assessment of high-strength bolts based on fracture mechanics

To investigate the effect of initial cracks on the fatigue performance of high-strength bolts for high-speed train brake discs, the fatigue crack propagation behavior of high-strength bolts under the coupling action of preload and dynamic fatigue load was investigated experimentally and numerically based on the theory of linear elastic fracture mechanics. Firstly, fatigue tests of high-strength bolts with initial crack defects were carried out, and then a three-dimensional accurate numerical model with the hexahedral mesh for a bolt-nut was established by MATLAB, and the fatigue crack propagation behaviors were investigated using ABAQUS-FRANC3D interactive technology. In this paper, the effects of the initial crack state, the bolt preload, the axial excitation load, and the friction coefficient of the screw pair on crack propagation life were emphatically studied, and the simulated crack propagation trajectory and crack propagation life agreed well with the experimental results. The findings indicated that 0°-oriented cracks beginning at the maximum principal stress were predicted to have the shortest fatigue life. The crack propagation life was sensitive to the initial crack size, the coefficient of initial crack geometry, and the bolt preload, but not to the friction coefficient of the screw pair. Furthermore, when evaluating the effect of fatigue load on crack propagation, the load ratio, the mean load, and the load range should all be considered.

Failure Analysis of High-Strength Bolts in Spherical Joint Assembly under In-Plane Quasi-Static Loading

Failure Analysis of High-Strength Bolts in Spherical Joint Assembly under In-Plane Quasi-Static Loading

Fatigue life analysis of high-strength bolts based on machine learning method and SHapley Additive exPlanations (SHAP) approach

Fatigue failure of high-strength bolts is one of the causes of collapse of steel structures. In this paper, six different machine learning models were used to analyze and predict the fatigue life of high-strength bolts, and the relationship between fatigue life of the bolts and the influencing factors was analyzed by SHAP method. During this process, a data set of fatigue life of high-strength bolts was presented, and 30 percent of the data was randomly selected as the test set. Geometric dimensions and stress states of bolts were as input features, and fatigue life was output label. After training the model, the errors of bolt fatigue life prediction of six machine learning models were compared. Finally, the most adverse factors affecting the fatigue life of the bolts are analyzed. It was found that XGBoost has the best performance on prediction of fatigue life of high-strength bolts, R2 reaches 0.881 and 0.788 in training set and test set, respectively. At the same time, the prediction result of the model is also better than that of the traditional fracture mechanics method. In addition, according to the analysis of SHAP value, the stress amplitude (SA) applied on the bolt has the greatest impact on the fatigue life. Larger SA value will accelerate the expansion of fatigue crack, thus increasing the degree of fatigue damage of the bolt. At the same time, the combination of MAXS (maximum stress applied on high-strength bolts) and SA is the most unfavorable factor to affect the fatigue life of the bolt. Increasing both factors can greatly reduce the fatigue life of the bolt. Finally, the current mainstream steel structure design codes have sufficient safety reserves, and M39 bolt has the best fatigue performance.

Analysis and prediction of wind turbine bolts based on GPR method

Analysis and prediction of wind turbine bolts based on GPR method

Shear Strength Analysis of Anti-Rust Bolts with a Spiral Oil-Guiding Slot and Oil-Bearing Hole: Simulation and Experiment

This paper studies the shear strength of an anti-rust bolt with a spiral oil-guiding slot and oil-bearing hole by conducting a simulation and experiment. A finite element model with the bolt and the clamp tool is developed for simulating the shearing of the bolt in progressive failure analyses. An indirect method is proposed to generate a spiral entity that can produce excellent spiral elements. A clamp tool is designed for the shear experiment of the bolt. Moreover, a substitute calculation method is presented for the shear strength analysis of the special bolt, and the effect of using the oil-guiding slot on shear strengths is considered by reducing the bolt’s radius. The study results show the following: The results of the simulation are in good agreement with the experimental results. One side of the bolt with the oil-bearing hole is first cut off, and the deviation between the result obtained by using the substitute calculation and the experiment’s result is 7.97%.

Stress Characteristic Analysis of Pump-Turbine Head Cover Bolts during Load Rejection Based on Measurement and Simulation

It is not uncommon for pump-turbine units in pumped storage power plants to experience load rejections due to the sudden disconnection of the generator from the power grid. Load rejection can suddenly increase the rotating speed of the pump-turbine and cause strong pressure fluctuations in the flow passage of the pump-turbine unit. During load rejection, the strong pressure fluctuations caused by the water hammer effect can cause strong structural vibrations, high stresses and even damage to the turbine runner, head cover, stay ring, bottom ring, head cover bolts and bottom ring bolts. In order to study, in detail, the flow-induced stress characteristics of the prototype pump-turbine unit, and the pressure variations during load rejection in a high-head pumped storage power plant were measured first. Then the measured data were used to set up computational fluid dynamics (CFD) simulations in the entire flow passage of the prototype pump-turbine and to calibrate the simulation results. The calculated pressure distributions in the flow passage during load rejection were exported and mapped on the finite element model of the stationary structures of the pump-turbine unit so that the flow-induced stresses on the head cover, stay ring, bottom ring, head cover bolts and bottom ring bolts can be calculated. The results of the analysis show that the maximum stresses in the head cover bolts and bottom ring bolts are located on the rounded corner of the bolt near the stay ring and that the stresses in the bolts vary with time during load rejection. The maximum stresses of the head cover bolts are higher than the maximum stresses of the bottom ring bolts, and the maximum stresses of the bolts are above two-thirds of the yield strength of the bolt material. It is recommended to use larger nominal diameter bolts to avoid damage to the connecting bolts of the pump-turbine unit.

Failure case analysis of fastening bolts for trolley rail of quay crane

This paper presents a premature failure analysis of bolts used for trolley rail fastening system of quay crane. The investigation included experimental and numerical analysis. Failure bolt inspection revealed the failure site was at the combination of thread run out and under-head-to-shank transition. Failure bolt chemical composition analysis shows no material and manufacturing defect. Fracture surfaces morphology of the failure bolts reveals premature fatigue fracture process. Structural health monitoring (SHM) and field test indicated the main failure cause are high strength impact due to trolley passing through rail gap because of worn rail pad and unreasonable design of rail clip. Numerical simulations have been conducted. The installation simulation of rail fastening system shows eccentricity loading condition of bolt due to incline of rail clip. Combined with field test of rail gap region vertical acceleration, the trolley rail system has been simulated via finite element analysis to illustrate the mechanism of bolt failure. Worn rail pad at rail gap region produced high level of impact load due to trolley passage. The influence of worn level of rail pad on bolt stress has been investigated. A modified design of rail clip is presented. The comparison of the original and modified rail fastening system as well as the elastic and rigid rail fastening system had been conducted.

Failure Analysis of Alloy Boron Steel Bolts in Steel Structure Assembly

Failure Analysis of Alloy Boron Steel Bolts in Steel Structure Assembly

Eccentric Shear Failure Mode and Mechanical Simulation Analysis of Web Bolts of Steel Box Girder Bridge

Eccentric Shear Failure Mode and Mechanical Simulation Analysis of Web Bolts of Steel Box Girder Bridge

Mechanical Properties and Fracture Analysis of High Strength Bolts in Nuclear Power Plant

A high-strength bolt of a steel structure of a nuclear power plant failed and fell off. In order to determine the cause of the bolt’s fracture, a series of tests such as macro inspection, physical and chemical performance test, and microscopic analysis of the fracture were carried out on the failed bolt. The results show that the cause of bolt fracture is hydrogen embrittlement. Hydrogen infiltrated into the bolt during the phosphating process and the corrosion process during use, and then hydrogen continued to accumulate eventually causing hydrogen embrittlement fracture. Dehydrogenation treatment should be performed immediately after the phosphorylation treatment, and the anti-corrosion method of the bolt should be optimized, which is an effective measure to prevent the hydrogen embrittlement of high strength bolts.

Failure analysis of gas turbine torque tube bolts

The cracking of torque tube bolts of a 130 MW gas turbine is investigated in the current work. Visual inspections along with microstructural and finite element analyses were performed for determining the cracking mechanisms. It was observed that the fracture surface was intergranular in appearance indicating crack growth along the grain boundaries. Furthermore, finite element results indicated that crack growth direction was relatively in accordance to the simulated stress distribution in the bolt. Microstructural analysis was performed and a continuous M23C6 carbide layer was observed along the grain boundaries. Although it was not clear what mechanism was responsible for the cracking, one potential mechanism of the cracking could be stress corrosion cracking (SCC). Remedial actions are proposed to minimize future occurrences of cracking.

Failure analysis of boron steel 27MnCrB5-2 structural bolts during tightening of railcar wheel-axle

Herein, a premature failure analysis of structural tempered high-strength boron steel 27MnCrB5–2 bolts (0.0006 wt B), used for railcar wheel-axle assembly, is presented. Fractographic analysis revealed a moderate ductile fracture. The applied torque produced elongation of the bolt until final fracture. A scarce presence of precipitates was observed, mainly of Ti(C,N), TiC, and inclusions such as Al2O3 and MnS. The mechanical properties of the boron steel 27MnCrB5–2 bolts were 1112 and 1170 MPa for the yield strength of 0.2% (σ0.2%) and ultimate tensile strength (UTS), respectively. However, the calculated Von Mises equivalent stress (916 MPa) was lower than σ0.2% and UTS values. It was found that during tightening, the washers are crushed and, therefore, their coefficient of friction decreases, which causes a considerable increase in the applied torque and the equivalent stress. The engineering failure analysis showed that a decrease in the friction coefficient of the washer from 0.16 to 0.07 causes the failure of boron-steel 27MnCrB5–2 bolts during tightening of railcar wheel-axle.

Discussion on Supervision and Inspection Method of High Temperature Bolt of Steam Turbine

Based on the failure analysis of high-temperature bolts in a thermal power plant, this paper proposed that the fracture mechanism of high-temperature bolts is mainly creep fracture. According to the bolt replacement and rejection criteria, the effectiveness of the current bolt supervision and inspection method was analyzed. It was proposed that the power station should strengthen the creep deformation measurement at the thread of the high-temperature bolt part, not just the screw part.

Failure analysis of fractured motor bolts in high-speed train due to cardan shaft misalignment

Motor of high-speed train is normally connected with suspending devices through bolts. This paper presents an investigation of six motor connecting bolts, based on GB/T 3077 standard and strength grade of 8.8, which fractured at the thread close to the contact surface of motor and suspending device before the designed service life. The investigation includes macro examination, chemical compositions analysis, tensile tests, hardness tests, metallographic examinations were used to analyze the cause of fracture. The results revealed that the strength and material of bolts met the standard, no metallurgical defect was found in examination, and the bolts fractured were due to alternating load. According to the spectrum of acceleration signal measured by the sensor mounted on the motor housing and subsequent inspection of the cardan shaft and rotor of motor, revealed the alternating load is caused by misaligned cardan shaft. Further dynamic analysis shows that the rotation of misaligned cardan shaft resulted in huge unbalance force. To confirm the findings, finite element analysis on the bolts subjected to pre-tensile load reveals that the materials at the bottom surface of the first thread suffered high alternating stress and reaches the fatigue limit. From the above findings, this paper proposes an innovative strategy to avoid similar accidents of high-speed train suspending devices.

Failure analysis and countermeasures of the SCM435 high-tension bolt of three-step injection mold

PurposeThe objective of this study was to perform damage analysis of SCM435 high-tension bolts connecting upper and lower parts of a three-stage injection molding machine.Design/methodology/approachDamage material used in this study was a SCM435 high-strength bolt connecting upper and lower molds of a three-stage injection mold. Causes of damage were determined by macroscopic observation. Microstructure observation was done using a metallic microscope, scanning electron microscope (SEM, S-2400, HiTachi, Japan), energy dispersive X-ray spectroscopy (EDS, Kevex Ltd., Sigma) and Vickers hardness tester (HV-114, Mitutoyo). Fatigue limit of the damaged material was evaluated using equivalent crack length.FindingsBolts were fractured by cyclic bending stress in the observation of ratchet marks and beach marks. The damaged specimen showed an acicular microstructure. Impurity was observed. Chromium carbide was observed near the crack origin. Both shape parameters of the Vickers hardness were similar. However, the scale parameter of the damaged specimen was about smaller than that of the as-received specimen. Much degradation occurred in the damaged specimen. Bolts should undergo accurate heat treatment to prevent the formation of chromium carbide. They must prevent the action of dynamic stresses. Bolts need accurate tightening and accuracy of heat treatment. Screws require compression residual stress due to peening.Originality/valueThis study conducted failure analysis of damaged SCM435 bolts connecting upper and lower parts of the three-stage injection mold. Fatigue limit of the damaged material was evaluated using equivalent crack length. In order to control this fracture, accurate tightening of bolts, accuracy of heat treatment and screws are required for compression residual stress due to peening.

Fracture analysis of 600 MW steam turbine valve bolts based on ultrasonic technology for coarse grains detection

Failure analysis of valve high temperature 20Cr1Mo1VTiB bolts used in a 600 MW steam turbine has been carried out. The valve bolts fractured with evidence of coarse grains. Chemical analysis, micro-structural characterization, fractography, mechanical properties measurement and ultrasonic detection were used for the analysis. The microstructure is frame structured bainite, coarse grains with serious directional were found. Which lead to the inferior impact toughness. It was concluded that all these factors produced brittle failure. In the meantime, the ultrasonic technology was be found which could efficiently to detect coarse grains of 20Cr1Mo1VTiB bolt. It is recommended to first guarantee the microstructure and mechanical properties of material. Secondly, use ultrasonic technology could detect coarse grains phenomenon of bolt. Finally, it is necessary to use the ultrasonic technology and metallographic examination technology to detect the coarse grains of all in-service 20Cr1Mo1VNbTiB or 20Cr1Mo1VTiB bolts, in order to avoid the same type of bolts fracture accident.