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A prefabricated concrete column-to-column structure connected by high-strength bolts is proposed. To explore the seismic performance and failure form of the structure, the finite element analysis software is used to simulate the low-cycle repeated load test. The hysteretic curve and skeleton curve of the structure are obtained, and the stiffness degradation law, ductility and energy dissipation capacity of the structure are quantitatively analyzed to evaluate the seismic performance of the structure. The results show that the ductility coefficient of the structure is basically between 2.19 and 4.97, and the ductility coefficient of most specimens is greater than 3.0, indicating that the structure has good ductility and deformation capacity. The equivalent viscous damping coefficients of the specimens are in the range of 0.21–0.29, indicating that the structure has good energy dissipation capacity. In a certain range, increasing the thickness of the end plate has no significant impact on the energy consumption capacity of the structure. The compressive strength of the concrete in the core area is greatly improved under the constraint of the end plate bolts, and end plate bolt connection can well realize the transmission of force and give full play to the performance of materials.

Copyright of Rolling Stock (1002-7602) is the property of Rolling Stock Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rolling Stock (1002-7602) is the property of Rolling Stock Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the effect of corrosion on the tensile properties of high-strength bolts, neutral salt spray accelerated corrosion test and tensile test were carried out. The effects of different corrosion time on the corrosion morphology, mechanical properties of high-strength bolts were compared by mass loss rate, electron microscope and optical microscope observation and theoretical analysis. The power function relationships between the mass loss rate, corrosion weight loss and corrosion time of high-strength bolts were established. It is found that the thicknesses of inner and outer rust layers increase significantly with the corrosion days. In addition, two failure modes of high-strength bolts are found: bolt breaking and the thread of bolt stripped. The critical corrosion time for the failure modes transformation is 180 days (mass loss rate of 7. 8% ). When the corrosion days are less than 180 days, bolt breaking occurs, otherwise the thread of bolt stripped. The quantitative formulas between tensile bearing capacity Fm, tensile strength Rm, relative stiffness E and mass loss rate η are established respectively with the two failure modes, which exhibited piecewise linear decreasing relationships. [ABSTRACT FROM AUTHOR]

In order to study the mechanical property degradation after corrosion, corrosion and mechanical tests were conducted on the M24 high strength bolts, which were treated with and without oil immersion. On the basis of neutral salt spray corrosion test, macro morphology of bolt corrosion products with different corrosion time was observed. It was found that the thickness of rust layer and the surface roughness of bolt increase with corrosion time. The corrosion of oil-free bolt was more serious than that of oil-immersed bolt in the early stage of corrosion, but the surface morphology was basically the same in the later stage of corrosion. Besides, the relationships of the two kinds of bolt between mass loss and corrosion time were stablish. On the basis of static tensile tests, it was found that the stiffness of bolt decreased gradually with the increase of corrosion degree. The stiffness degeneration formula was regressed. In addition, the load-displacement curves of oil-immersed and oil-free bolt were obtained at different corrosion time. With the increase of accelerated corrosion time, the yield strength and ultimate strength were found to have distinct decrease trends, but the elongation and area reduction were hardly influenced.

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bolted spherical joints (BSJs) are integral to large-span space grid structures commonly used in expansive public and industrial buildings. BSJs are susceptible to fatigue damage in high strength bolts due to variable random loads. This study summarized findings from prior fatigue tests, detailing the fatigue failure patterns and S–N curves for grade 10.9 M20, M30 high strength bolts, and grade 9.8 M39 high strength bolts in BSJs. By employing finite element analysis, the study determined the stress concentration factors for these bolts, which were then utilized in fatigue life estimations using the Heywood model and the local strain approach (LSA). Both methods could yield satisfactory predictions, but when it came to the Heywood model, particularly when modifying it in areas of high stress, it demonstrated superior accuracy in predicting the performance of M20, M30, and M39 high strength bolts. Additionally, incorporating initial defect considerations, fatigue life was predicted using the damage tolerance design method (DTDM). Finally, when comparing the fatigue life prediction results obtained from various methods, it became evident that the modified Heywood model outperformed the other methods. This not only provided a superior solution but also demonstrated user-friendliness, thereby establishing itself as the preferred option for predicting the lifespan of high strength bolts in BSJs. • Fatigue test results of M20, M30, and M39 high strength bolts in bolted spherical joints (BSJs) were summarized. • Stress concentration analysis for high strength bolts in BSJs were conducted. • Fatigue life prediction methods for high strength bolts in BSJs were discussed. • A modified Heywood model was recommended for life prediction of high strength bolts in BSJs. [ABSTRACT FROM AUTHOR]

A detailed FE study is presented investigating the factors affecting failure modes of bolt assemblies under tensile force at ambient and elevated temperatures. Axisymmetric FE models incorporating important behavioural aspects including surface interaction and damage modelling were developed. Stripping failure is generally undesirable because it results in premature failure of the bolt, which can deteriorate the rotational capacity of connections and robustness of steel frames. The paper discusses how the thread length in the grip Lt can affect the failure mode of bolt assemblies at elevated temperatures. This paper concludes that at ambient temperature, stripping can occur at certain Lt length dependent upon the nut dimension deviation from the basic profile; this length reduces with temperature. [ABSTRACT FROM AUTHOR]

The slip‐resistant shear connections with preload bolts have traditionally use in the steel structures exposed to cyclic / fatigue loading or in the cases when the bolt slipping or connection deformations should be restricted. Hence, the shear load is transferred through the friction surfaces rather than the contact between bolt surface and hole. The main influencing parameters determine the connection slip resistance are the friction between the contact surfaces and the level of preload in the bolts. This paper presents an experimental study of preloaded bolted connections under cyclic load. Experiment was performed on double lap shear connections using high strength bolts and lock bolts, both M20 of grade 10.9. The steel plates used in experiment are grade S355JRG2. Sandblasting was performed using quartz sand as the abrasive after which the zinc‐silicate coating was applied on plate surfaces. To address the required pretension force in the bolts, the strain gauge method was employed. All strain gauges were calibrated. Six specimens were exposed to cyclic loading after monitoring initial and short‐term losses of pretension forces in the bolts. The main objective of the presented study is to investigate the influence of the cyclic load on the losses of pretension force in high strength bolts and lock bolts. The results of comparative experimental analysis are presented and discussed. [ABSTRACT FROM AUTHOR]

The axial stress of high strength bolts for bridges affects the service life directly, it is necessary to measure it regularly. Based on the theory of acoustic elasticity and combination of longitudinal and shear waves, a new theoretical analysis method is proposed. The stressed and non-stressed areas of bolt are separated, and the derived formula only use the flight time and difference of acoustoelastic coefficients to get axial stress. Further, the preload experiments with high strength bolts of grade 8.8S and 10.9S is designed, the experimental results show that the proposed method is applicable to the axial stress of the bridge bolts with any specifications, material and different screwing depth used in this paper, the effect of elastic deformation on the flight time is eliminated, and the measuring error is within 5%. [ABSTRACT FROM AUTHOR]

The microscopic structures and inclusion in 42CrMoV bolt were investigated by SEM,STEM and software ASPEX. The results show that the matrix structure of 42CrMoV bolt is tempered sorbite,but still retains the original morphology of martensite. Carbides precipitate and arrange orderly in intracrystalline and lath boundaries,and the amount of precipitated carbides in grain boundaries are more than that in intracrystalline. Besides,the micro-hardness HV0.2 is 330 and the grain size(level) of austenitic is 9. The Mn S and aluminate are the main inclusion types in 42CrMoV bolt,and the size of inclusions are mostly less than 5 μm,the level of A,B,C,D and Ds inclusion was basically less than or equal to Level 0.5.

In view of the mechanical characteristics of precast reinforced concrete (RC) shear wall assembled by high strength bolts, the formulae of the anti-sliding capacity of horizontal connection and yield load of connecting steel frame (CSF) were deduced. The local buckling of CSF was analyzed. Based on the results of existing research and the mythology of current design codes, the cracking load, yield load, peak load and shear capacity of the precast walls were calculated. Based on the established calculation model for the horizontal connections, the formula of shear capacity was proposed subsequently. The research results show that the calculated characteristic loads as well as the load bearing capacities are in good agreement with the test results of the proposed assembled shear wall. Relative slippages at the tension end of the connection can be prevented before yield load or peak load. The CSF does not yield at the tension end throughout the test. The critical buckling stress can be significantly increased by improving the quality of the welding between the CSF flange and web. Therefore, the local buckling can be avoided. The shear capacity of horizontal connections is mainly attributed to the slip resistance of high strength bolt connections and the friction between the wall bottom and the CSF web at the compression side. [ABSTRACT FROM AUTHOR]

Failure analysis of a fractured high strength bolt used in a MW Class wind turbine blade connection system was conducted to clarify the failure cause and to determine the prevention method. Applying detailed mechanical characteristics and metallurgical investigations, the bolts failure cause can be attributed to bending fatigue. Evidenced by the nut polished markings, insufficient tightening was considered as the important reason for the bolt failure. The thread microstructure indicated that the fractured bolt thread was rolled rather than machined. However, rolling induced cracks locating on the thread crest and non-uniformly distributed decarburized layer on the bolt thread root existed. Thus, it can be concluded that the bolt failure was caused by the insufficient tightening and improper manufacturing procedure. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The steel truss high-strength bolt application project has outstanding features such as large bolt information, high construction difficulty, large single-node workload and high installation precision. In view of the above characteristics, BIM technology and refine management theory are introduced, and a new method of refine management of steel truss high-strength bolts based on BIM technology is proposed. The high-strength bolts of typical steel truss of Sanmenxia Yellow River and Railway Bridge are applied. Taking the engineering as an example, the parametric modeling method and specific application of steel truss nodes based on Revit and Dynamo are introduced. The results show that in the aspects of material extraction, model deepening, assembly construction and post-operation and maintenance, the application of BIM technology can improve the precision and effectiveness for the refine management of steel truss high-strength bolts. The findings of this study provides a reference for the refine management in steel truss high-strength bolts. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The post-fire mechanical properties of Grade 12.9 bolts were investigated. • The modulus of elasticity did not significantly change after a heating-cooling cycle. • The strength decreased after a heating-cooling cycle with temperatures above 400 °C. • The effect of diameter on the post-fire yield and tensile strengths was negligible. • SEM images showed remarkable changes in microstructure for elevated temperatures. This paper aims to experimentally investigate the post-fire mechanical properties of Grade 12.9 high-strength bolts. To evaluate the effects of elevated temperatures and the bolt diameter on the post-fire mechanical properties, seven different diameters of the Grade 12.9 bolts were heated based on a standard temperature–time diagram with the ranges of 20 to 900 °C. Upon air-cooling and reaching room temperature (a heating and cooling cycle), 105 bolt specimens were subjected to the standard tensile test. The experimental results, including the post-fire stress–strain curve, yield strength, tensile strength, modulus of elasticity, and ductility, were presented. The results indicated that changes in mechanical properties were noticeable for temperatures higher than 400 °C. Although the post-fire modulus of elasticity did not significantly change, the post-fire yield and tensile strengths decreased substantially if the maximum temperature exceeded 400 °C. After heating up to 900 °C and then cooling down and reaching ambient temperature, Grade 12.9 steel bolts showed a 60% reduction in strength. The comparison of the results showed that the effect of diameter on the post-fire yield and tensile strengths of Grade 12.9 bolts was insignificant and could be neglected, but on elastic modulus and ductility, the diameter effect needs to be considered. In addition, the scanning electron microscope (SEM) images indicated that the elevated temperatures remarkably changed the microstructural characteristics of the Grade 12.9 bolts. Finally, based on the test results, the prediction equations of the post-fire mechanical properties of the Grade 12.9 high-strength bolts were proposed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Premature bolt failures of trolley rail fastening systems for quay crane are analyzed. • The combination of thread run out and under-head-to-shank transition results in stress concentration on bolt. • Worn rail pad results in impact load and Unreasonable design of rail clip induces eccentricity load to bolt. • FEM model was used to reproduce the loading condition of the failure bolt. • Safety thickness of rail pad and modified rail clip are suggested. 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. [ABSTRACT FROM AUTHOR]

High strength preloadable bolts are key components influencing strength, stiffness and ductility of beam-to-column joints. In Europe the HV and HR systems are the most commonly used types of pre-loadable bolt assemblies. EN 1993-1-8 provides design rules for bolted connections, without distinguishing the type of high strength preloadable bolt system. However, HV and HR are characterized by both different force-displacement responses and failure modes, which may significantly influence the performance of bolted joints under monotonic and cyclic actions, especially for seismic applications. The rational selection of the most suitable bolt type per specific structural demand may avoid premature reduction of joint strength for higher levels of joint rotation, or provide further rotational capacity. In order to investigate these features, experimental monotonic and both variable and constant amplitude cyclic inelastic tests were carried out on both HV and HR bolt assemblies, varying the shank diameters. The monotonic tests enabled to identify the failure modes and the relevant force-displacement monotonic response and ductility per type of bolt assembly. The variable amplitude cyclic tests allowed quantifying the strength degradation induced by cyclic actions, while the constant amplitude low-cycle fatigue tests enabled to investigate the fatigue capacity at different threshold of plastic strain and to determine the strain-number of cycles (i.e. ε- N ) curves. The influence of the type of bolt assembly on the response of T-stub connections is also discussed on the basis of analytical models. [ABSTRACT FROM AUTHOR]

The upper and lower prefabricated reinforced concrete (RC) wall panels are jointed together using high strength bolts and the connecting steel frame (CSF)，forming a rectangular section precast shear wall. To investigate the basic mechanical performance of the totally prefabricated shear wall and the working mechanism of the bolted connections, monotonic loading tests were carried out on three specimens with different flange thicknesses in the connecting steel frames and different nominal diameters and pretensions of the high strength bolts. Then the loaddisplacement curves and the feature points，the strains in the reinforcing steel bars，the relative slippages between the connecting steel frame and the embedded limbic steel frame (ELSF) set at the precast shear wall panel end，and the strain distribution in the connecting steel frame，were subsequently analyzed. The test results show that the ductility of the totally prefabricated shear wall is relatively good ； the decrease of the diameter and pretension of the bolt results in the increase of the relative slippage in the bolted connection ； the decrease of the flange thickness leads to the increase of the stress in the connecting steel frame ； the normal stress in the compressive zone is far larger than that in the tensile zone, and the demarcation point between them is nearly identical with that of the precast RC wall panel. On the basis of the experimental study, the working mechanism of the horizontal bolted connections was analyzed. The analysis indicates that the friction action and the dowel action are the main load-transferring mechanisms for the tensile connections ； however, the working mechanism of the compressive connections is related to the initial gap in the connections, and the friction action, the dowel action and the extrusion action are the main load-transferring ways in general. [ABSTRACT FROM AUTHOR]

• The influence of high-strength bolt preload loss on structural mechanical properties is carried out by means of experiment, finite element and theoretical calculation. • Increasing the bolt preload only has function on the slip connection strength of the structure, but slight on the ultimate bearing capacity. • The result of numerical model is in good agreement with the experimental data. • One theoretical model is established and verified by the experimental and numerical data. High-strength friction bolts in engineering are affected by corrosion, fatigue and other factors in long-term use, and preload loss is a common phenomenon in engineering. In order to study the influence of the preload loss of high strength bolt group on the basic mechanical properties of structures, a flexural test of steel beams connected by high strength friction bolt group was numerically and experimentally investigated in this study. The variable between each specimen is the preload value of the high-strength bolt group. To this end, the strength of bolt connection, the rotational stiffness of the whole structure and the local joint, the deformation distribution of the structure, slippage curves, cross-section strain and ultimate bearing capacity are evaluated and discussed. In addition, the mechanics of the structure at different sliding stages are theoretically calculated. The research results show that the preload of the high-strength bolt group loss will reduce the connection strength and structure stiffness, but has very limited influence on the ultimate bearing capacity of the structure. [ABSTRACT FROM AUTHOR]

In this study, high strength bolts of 1100MPa and 1300MPa grades were charged with hydrogen to measure the sensitivity of hydrogen embrittlement (HE). Different levels of stress conditions based on various tensile stress and strain rates were applied. The bolts were then examined to see whether cracks were formed on the screw threads. The tensile stress and strain rate condition producing the most number of cracks on the screw thread of the bolt was decided as the most suitable test condition for the measurement of sensitivity of HE. For 1100MPa grade high strength bolts, the most cracks were observed at the tensile stress ratio of 0.85 (load of 80kN) and strain rate of 1.6×10E−5/s, while for 1300MPa grades, the most cracks were observed at tensile stress ratio 0.87 (load of 100kN) and strain rate of 1.6×10E−5/s. No cracks were found on the screw threads of bolt when the strain rate was increased over 8.3×10E−4/s. [ABSTRACT FROM AUTHOR]

Abstract: Aluminum alloy 6061-T6 was used to produce an ultrafine-grained specimen by spring-loaded equal channel angular pressing (ECAP), which was continuously applied to a commercial multi-stage former at a production rate of 30rpm at room temperature to manufacture high strength aluminum bolts. In order to increase the mechanical strength of the manufactured bolt, the bolt-forming process was introduced based on extrusion process in the present work. With the specimens processed by a single pass ECAP, underfilling at the bolt head and surface cracking at the flange of the produced bolts were observed due to the geometry of the ECAPed specimen and friction at the die interface, respectively. To remove these defects, modified route C for the second pass ECAP and aluminum fluoride coating with metal soap for the initial specimen were applied. Finally, the ultrafine-grained aluminum bolts were successfully manufactured in a continuous sequence. Both the ultimate tensile strength (UTS) and elongation to fracture of the manufactured bolts increased compared to the conventionally made bolts. According to the present investigation, an innovative approach utilizing the ECAP to develop high strength bolts without modifying conventional material is demonstrated. [Copyright &y& Elsevier]

• Four bending tests for splice connection are tested and simulated. • Bilinear two-stage bending behavior for connection is discovered. • Classification of the proposed splice connection is analyzed. • A comprehensive parametric study is conducted. • Satisfactory tolerance for lost of bolt-pretension force is found. Splice connection consisting of slip-critical high strength bolt and side plate is a promising connection type for future modular construction. However, recognitions on basic performance for this connection are still limited. To fill this gap, this paper conducted a comprehensive research on basic bending behavior of a simple splice connection proposed by the authors for corner-supported steel modular building. The basic bending behavior of the proposed splice connection was analyzed in details by combined experiments and numerical simulations. It is found that the proposed splice connection can achieve a favorable ductile behavior in bending. Bilinear profile with two stages is clearly observed in the relationship between moment and connection rotation. These two stages have different stiffness but the applied load can keep increasing in the second stage with excessive deformation of the specimen. Such phenomenon reveals adequate reserve of bending resistance for the proposed splice connection under large deformation scenario. Based on method of farthest point, a transition point is defined and determined in the relationship between moment and connection rotation. This transition point represents an important change in the bending behavior, which is valuable for practical design. Numerical simulations are also introduced to supplement the tests. The analyses on stress states of components and variation in bolt pre-tension force properly explains anisotropy in resistance at the transition point for different loading directions. A parametric study is further conducted. Results indicate that the proposed splice connection possesses satisfactory tolerance for loss of bolt pre-tension force in the practical construction. [ABSTRACT FROM AUTHOR]

Most of the past studies on high strength bolted tensile joints have dealt with the local load transferring mechanism of connections, such as split tee joints subjected to only tension, for simplicity. However, in order to apply these joints to bridge structures, the overall behavior of such connections must be made clear considering actual load combinations consisting of axial force, bending moment and shear force. In this study, therefore, the loading tests of connections using this type of joints for box cross-sections are carried out, paying attentions to the effect of the load combinations on the rigidity and strength. Based on the experimental results, the applicability to the connections of bridge structural members is discussed. [Copyright &y& Elsevier]

• A stock-removing machine was used to quantitatively simulate the corrosion process. • The clamping forces are significantly affected by the bolt head corrosion. • The formula for evaluating the clamping force of high strength bolt is proposed. High-strength bolts are widely used for connections in steel structures and the load-bearing capacity of such connections is very important for the safety of steel structures. However, numerous traces of corrosion have been observed around high-strength bolt joints of steel structures on site, which can affect the tightening force of these bolts and therefore reduce the bearing capacity of the bolt joints. In this study, the stock-removing machine was used to quantitatively simulate the corrosion of high strength bolt head and the fiber bragg grating sensors were used for obtaining the clamping forces of high strength bolts. Based on the results of numerical simulation and experiments, it is found that fiber bragg grating sensors are reliable and stable for monitoring the clamping forces of high strength bolts while they are installed at the proper location and the clamping forces of high strength bolts are significantly influenced by the bolt head corrosion. The formula for evaluate the clamping force of the high strength bolt with bolt head corrosion is proposed by this study. [ABSTRACT FROM AUTHOR]

Due to its strength advantage, high strength bolts are able to provide larger clamping force. However, the changing behavior of friction coefficient during repeated tightening will adversely affect the tightening torque - clamping force relationship. To ensure reliable clamping force of high strength bolts, an easy implement experimental method to investigate the changing behavior of friction coefficient is put forward in this work. The constraint torque of bolt head, as well as the tightening torque and clamping force, was measured during tightening. Friction coefficient interval of bolt underhead is obtained according to the preset assumptions and experimental results. Based on the mechanical equilibrium relationship of the bolt during tightening, thread reaction torque can be obtained to calculate the friction coefficient of threads and bearing surface. Three cases are considered, namely without lubricant, lubrication at threads and nut surface. Statistical analysis was carried out through replicated experiments to investigate the effect of clamping force on the changing behavior of friction coefficient. Without lubrication, repeated tightening caused the increasing of friction coefficient, which resulted in a reduction of clamping force. When using a lubricant, it can protect the contact surface, and the obtained clamping force during repeated tightening was more stable. Experimental results showed that the proposed method can be used to investigate the changing behavior of friction coefficient during repeated tightening. • An easy implement experimental method to investigate the changing behavior of friction coefficient is put forward in this work. • Based on the mechanical equilibrium relationship of the bolt during tightening, thread reaction torque can be obtained to calculate the friction coefficient of threads and bearing surface. • Statistical analysis was carried out through replicated experiments to investigate the effect of clamping force on the changing behavior of friction coefficient. • The friction and wear of the threaded fasteners during repeated tightening was observed and analyzed. [ABSTRACT FROM AUTHOR]

• Fine particle peening was used to improve fatigue properties of high strength bolts under transverse loading. • Surface roughness, compressive residual stress and micro-hardness was measured. • A finite element analysis combined with equivalent stress method was performed. In order to avoid the fatigue failure of high strength bolt under cyclic transverse loading, fine particle peening (FPP) treatment was conducted to the bolt using steel beads. The surface roughness, residual stress and surface hardness of the treated bolts were examined. Fatigue tests were performed for bolts with or without FPP treatment under transverse loading. The test results show that FPP treatment effectively improves the fatigue resistance of high strength bolt through reducing the surface roughness, increasing the surface hardness and introducing high compressive residual stress in the surface layer. For the FPP treated bolts, failure location changes from the bolt head fillet to thread root as loading displacement decreases to 0.3 mm. A finite element analysis was performed to analyze the failure behavior before and after FPP treatment. [ABSTRACT FROM AUTHOR]