Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relat...Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relationship between load amplitude,fatigue life,and damage progression in low-carbon steel assemblies.Design/methodology/approach–An experimental approach was adopted using MTS specimens fabricated from St 1203 cold-rolled steel,joined with Grade 8.8 M4 bolts.Cyclic fatigue tests were conducted under zerobased loading at seven distinct force levels.Fracture surfaces were visually analyzed to identify dominant failure mechanisms.Findings–The results revealed a strong inverse correlation between applied cyclic load and fatigue life.Three distinct failure modes were identified:bolt shear at high loads(5.4 kN),interface cracking and slippage at moderate loads(4.9–5.1 kN),and plate tearing or stable fatigue behavior at lower loads(54.1 kN).The results highlight a progressive transition in failure mechanisms,from bolt shear at high loads to plate tearing and interface cracking at lower loads,providing essential insights for fatigue-resistant bolted joint design.Originality/value–This study offers original insights into the fatigue behavior of bolted lap joints using MTS,a relatively underexplored configuration in fatigue assessment.By experimentally evaluating failure modes under varied cyclic load levels,the authors uncover critical transitions in damage mechanisms—from bolt shear to interface cracking and plate tearing—depending on the applied load.Unlike many existing studies focused on numerical modeling or bonded joints alone,this work provides empirical data rooted in real-world fastening conditions using cold-rolled low-carbon steel.展开更多
The wet-assembly hybrid bonded/bolted(WHBB)joint is increasingly employed in aircraft fuel tank structures owing to its advantageous mechanical strength and sealing performance.However,the integral tank is susceptible...The wet-assembly hybrid bonded/bolted(WHBB)joint is increasingly employed in aircraft fuel tank structures owing to its advantageous mechanical strength and sealing performance.However,the integral tank is susceptible to leakage during service,particularly at the joint,which seriously endangers the flight safety of the aircraft.In this paper,a leakage prediction method of WHBB joint based on porous media theory is proposed,in which the shape and characteristic length of the sealant layer are taken into consideration.The model parameters are determined by the analysis and treatment of the defect state of the WHBB joint section.The prediction results agree well with the experimental data,which were acquired by self-designed sealing leakage rate measurement system,and the deviation between the predicted results and the average value of the experimental data is less than 20%.Furthermore,in order to verify the environmental adaptability,the prediction results based on 2D cutting sections of the joints and experimental results under three different loading conditions are compared.The comparison results not only prove the accuracy of the prediction model,but also reveal the important influence of tensile fatigue load on the sealing performance of the structure.The tensile fatigue loads lead to two orders of magnitude increase in leakage rate,and the reason is that the repeated stretching and compression process lead to an increase in interfacial cracks between the adhesive layer and the hole wall,thereby accentuating the defects within the adhesive layer.展开更多
This study investigates the vibration characteristics of bolted-flange-joined conical-cylindrical shells(BFJCCSs)through both theoretical analysis and experimental testing.The proposed model incorporates the pressure ...This study investigates the vibration characteristics of bolted-flange-joined conical-cylindrical shells(BFJCCSs)through both theoretical analysis and experimental testing.The proposed model incorporates the pressure distribution within the bolted joint and accounts for the flange effect.The energy expressions for the conical and cylindrical shells are derived from Donnell's shell theory,while those for the flanges are obtained from the Euler-Bernoulli beam theory.The Lagrange equation is used to derive the dynamic equation,and the experimental studies on the BFJCCS are conducted to validate the accuracy of the model.Subsequently,the comprehensive effects of bolt loosening and bolt number on the frequency parameters are analyzed.Additionally,the effects of the flange dimensions and cone angle on the vibration behavior of the BFJCCS are discussed.In particular,the dynamic differences between the welded conical-cylindrical shell(WCCS)and BFJCCS are investigated.It is found that compared with the WCCS,the fundamental frequency of the BFJCCS is reduced by 7.6%,and the corresponding modal damping ratio is reduced by 21.0%.However,the high-order frequencies of the BFJCCS are higher than those of the WCCS,accompanied by a higher modal damping ratio.Compared with the bolt loosening degree,the bolt number has a more significant effect on frequencies.As the bolt number decreases,the impact of the bolt loosening degree diminishes gradually.展开更多
The shear characteristics of bolted rock joints are crucial for the stability of tunneling and mining,particularly in deep underground engineering,where rock bolt materials are exposed to high stress,water pressure,an...The shear characteristics of bolted rock joints are crucial for the stability of tunneling and mining,particularly in deep underground engineering,where rock bolt materials are exposed to high stress,water pressure,and engineering disturbance.However,due to the complex interaction between bolted rock joints and various geological contexts,many challenges and unsolved problems arise.Therefore,more investigation is needed to understand the shear performance of bolted joints in the field of deep underground engineering.This study presents a comprehensive review of research findings on the responses of bolted joints subjected to shearing under different conditions.As is revealed,the average shear strength of bolted rock joints increases linearly with the normal stress and increases with the compressive strength of rock until it reaches a stable value.The joint roughness coefficient(JRC)affects the contact area,friction force,shear strength,bending angle,and axial force of bolted rock joints.A mathematical function is proposed to model the relationship between JRC,normal load,and shear strength.The normal stress level also influences the deformation model,load-carrying capacity,and energy absorption ratio of bolts within bolted rock joints,and can be effectively characterized by a two-phase exponential equation.Additionally,the angle of the bolts affects the ratio of tensile and shear strength of the bolts,as well as the mechanical behavior of both bolted rock joints and surrounding rock,which favors smaller angles.This comprehensive review of experimental data on the shear behavior of bolted rock joints offers valuable theoretical insights for the development of advanced shear devices and further pertinent investigations.展开更多
The bolted flange structure finds significant applications in fields such as aerospace,shipbuilding,and pipeline transportation.The investigation of its dynamic characteristics has consistently been a focal point for ...The bolted flange structure finds significant applications in fields such as aerospace,shipbuilding,and pipeline transportation.The investigation of its dynamic characteristics has consistently been a focal point for researchers;however,there remains a deficiency in the development of robust analytical models.This paper introduces a novel analytical model based on the finite element methods and the Timoshenko beam theory to accurately simulate the bolted flange structure.The stiffness,mass,damping,and inertia matrices of the rotor system are individually derived,and the dynamic equation is subsequently formulated.The model’s validity and accuracy are validated through both the experimental testing and the finite element analysis.This study aims to elucidate the relationship between the external loads and the influence of the geometric configuration on the stiffness and contact behavior of the bolted flange structure,thereby enabling a thorough and precise prediction of the static and dynamic load transfer pathways,as well as the distribution of vibrational energy within the structure,while also facilitating the incorporation of friction and slip effects.Simultaneously,this work provides a foundational framework for the optimization design of bolted flange structures,addressing the factors such as the number,size,and geometric distribution of bolts.展开更多
Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting perfo...Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting performance.In this study,a new artificial molding method based on 3D scanning and printing technology was first proposed to prepare bolted joints with an inclined bolt.Then,the effects of the bolt inclination angle and boundary conditions on the shear behavior and failure characteristic of bolted joints were addressed by conducting direct shear tests under both CNL and CNS conditions.Results indicated that rock bolt could significantly improve the shear behavior of rock joints,especially in the post-yield deformation region.With the increase of bolt inclination angle,both the maximum shear stress and the maximum friction coefficient increased first and then decreased,while the maximum normal displacement decreased monotonously.Compared with CNL conditions,the maximum shear stress was larger,whereas the maximum normal displacement and friction coefficient were smaller under the CNS conditions.Furthermore,more asperity damage was observed under the CNS conditions due to the increased normal stress on the shear plane.展开更多
Efficient and accurate strength analysis of bolted connections is essential in analyzing the integral thermal protection system（ITPS） of hypersonic vehicles, since the system bears severe loads and structural failur...Efficient and accurate strength analysis of bolted connections is essential in analyzing the integral thermal protection system（ITPS） of hypersonic vehicles, since the system bears severe loads and structural failures usually occur at the connections. Investigations of composite mechanical properties used in ITPS are still in progress as the architecture of the composites is complex. A new method is proposed in this paper for strength analysis of bolted connections by investigating the elastic behavior and failure strength of three-dimensional C/C orthogonal composites used in ITPS. In this method a multi-scale finite element method incorporating the global–local method is established to ensure high efficiency in macro-scale and precision in meso-scale in analysis.Simulation results reveal that predictions of material properties show reasonable accuracy compared with test results. And the multi-scale method can analyze the strength of connections efficiently and accurately.展开更多
Interference fit has advantages in improving fatigue behaviors of composite bolted joints,however, interference fit bolt insertion tends to cause damages in laminates weakening joint mechanical properties. Therefore, ...Interference fit has advantages in improving fatigue behaviors of composite bolted joints,however, interference fit bolt insertion tends to cause damages in laminates weakening joint mechanical properties. Therefore, an experimental study was conducted to investigate bolt insertion damages of Carbon Fiber Reinforced Polymer(CFRP)/CFRP interference fit bolted joints.Mechanical behaviors of joints were also evaluated experimentally under both quasi-static loads and cyclic loads. Scanning Electron Microscope(SEM) and high-resolution X-ray micro-CT scan were used to examine micro damages in laminates. Damage and failure behaviors of joints were characterized. The results demonstrated that the hole entrance in upper laminate and the laminate boundary near the hole wall were the most critical regions for damages during bolt insertions. However, the influence of those damages on quasi-static failure loads and fatigue failure modes of joints was minimal. Delamination and matrix cracking occurred first in laminates following fiber and matrix fracture in quasi-static tensile tests. Interference fit could improve the fatigue resistance of the laminate hole, however, the bolt seemed to suffer a more critical local fatigue loading condition.This paper can contribute to composite structure designs, especially in understanding damage and failure behaviors of composite bolted joints.展开更多
Quasi-NPR(negative Poisson’s ratio)steel is a new type of super bolt material with high strength,high ductility,and a micro-negative Poisson’s effect.This material overcomes the contrasting characteristics of the hi...Quasi-NPR(negative Poisson’s ratio)steel is a new type of super bolt material with high strength,high ductility,and a micro-negative Poisson’s effect.This material overcomes the contrasting characteristics of the high strength and high ductility of steel and it has significant energy-absorbing characteristics,which is of high value in deep rock and soil support engineering.However,research on the shear resistance of quasi-NPR steel has not been carried out.To study the shear performance of quasi-NPR steel bolted rock joints,indoor shear tests of bolted rock joints under different normal stress conditions were carried out.Q235 steel and#45 steel,two representative ordinary bolt steels,were set up as a control group for comparative tests to compare and analyze the shear strength,deformation and instability mode,shear energy absorption characteristics,and bolting contribution of different types of bolts.The results show that the jointed rock masses without bolt reinforcement undergo brittle failure under shear load,while the bolted jointed rock masses show obvious ductile failure characteristics.The shear deformation ca-pacity of quasi-NPR steel is more than 3.5 times that of Q235 steel and#45 steel.No fracture occurs in the quasi-NPR steel during large shear deformation and it can provide stable shear resistance.However,the other two types of control bolts become fractured under the same conditions.Quasi-NPR steel has significant energy-absorbing characteristics under shear load and has obvious advantages in terms of absorbing the energy released by shear deformation of jointed rock masses as compared with ordinary steel.In particular,the shear force plays a major role in resisting the shear deformation of Q235 steel and#45 steel,therefore,fracture failure occurs under small bolt deformation.However,the axial force of quasi-NPR steel can be fully exerted when resisting joint shear deformation;the steel itself does not break when large shear deformation occurs,and the supporting effect of the jointed rock mass is effectively guaranteed.展开更多
In this paper,a failure evaluation criterion was proposed for the bolted casing-flange structure under impact loading.Subsequently,ballistic tests with eighteen bolted casing-flange structure specimens were conducted ...In this paper,a failure evaluation criterion was proposed for the bolted casing-flange structure under impact loading.Subsequently,ballistic tests with eighteen bolted casing-flange structure specimens were conducted to validate the failure evaluation criterion.Parameter studies were then carried out using the validated FE models.Both the experimental and numerical results demonstrated the accuracy of the failure evaluation criterion.The failure evaluation criterion provided a quick and easy way to determine the failure mode of the casing connection area by using the materials and dimensions of the structure.Based on the failure evaluation criterion,designing the structural failure mode of the bolted casing-flange structure to be between flange failure and bolt failure can improve the impact resistance of the connection area of the aero-engine casings.This investigation revealed that the impact failure is not the unique criterion in evaluating the containment of the casing connection area,structural failure should also be involved in the evaluation criteria.展开更多
This paper is focused on the structural behavior of the single shear bolted connections with thin-walled ferritic stainless steel.The purpose of this study is to investigate the ultimate behaviors,such as ultimate str...This paper is focused on the structural behavior of the single shear bolted connections with thin-walled ferritic stainless steel.The purpose of this study is to investigate the ultimate behaviors,such as ultimate strength and fracture mode of the single shear bolted connections of thin-walled ferritic stainless steel(low cost steel) rather than austenitic stainless steel(high cost steel).Bolt arrangement and end distance parallel to the direction of applied load are considered as main variables of the test specimens for bolted connections.Specimens have a constant dimension of edge distance perpendicular to the loading direction,bolt diameter,pitch,and gauge.A monotonic tensile test for specimens has been carried out and some bolted connections with long end distance showed curling(out of plane deformation) occurrence which led to strength reduction.The ultimate behaviors such as fracture mode,ultimate strength are compared with those predicted by current design codes.Further,conditions of curling occurrence and the strength reduction due to curling are investigated and modified strength equations are suggested considering the curling effect.展开更多
Hybrid bonded/bolted(HBB) joint has been widely used in engineering practice because it can overcome the potential weakness of pure bonded and pure bolted joints. However, studies on HBB joint are still at the initial...Hybrid bonded/bolted(HBB) joint has been widely used in engineering practice because it can overcome the potential weakness of pure bonded and pure bolted joints. However, studies on HBB joint are still at the initial stage. In this paper, tensile properties of a composite–metal singlelap HBB joint was investigated experimentally. And a detailed finite element model(FEM) was established to simulate the tensile behavior of the joint. The model was verified by the experimental results. Then the damage propagation and load transfer mechanism were explored based on the FEM. The results show that the HBB joint can provide multi-load transmission paths and resist damage propagation in the adhesive. The HBB joint has higher strength and energy absorption capacity than the pure bonded joint. And the HBB joint has greater initial damage load and tensile stiffness than pure bolted joint. Adhesive fillets can obviously improve the tensile performances of the HBB joint. Lateral stiffness of the joint boundary and testing machine show obvious effects on tensile performances of single-lap hybrid joints.展开更多
Efficient bolted joint design is an essential part of designing the minimum weight aerospace structures, since structural failures usually occur at connections and interface. A comprehensive numerical study of three-d...Efficient bolted joint design is an essential part of designing the minimum weight aerospace structures, since structural failures usually occur at connections and interface. A comprehensive numerical study of three-dimensional(3D) stress variations is prohibitively expensive for a large-scale structure where hundreds of bolts can be present. In this work, the hybrid composite-to-metal bolted connections used in the upper stage of European Ariane 5ME rocket are analyzed using the global-local finite element(FE) approach which involves an approximate analysis of the whole structure followed by a detailed analysis of a significantly smaller region of interest. We calculate the Tsai-Wu failure index and the margin of safety using the stresses obtained from ABAQUS. We find that the composite part of a hybrid bolted connection is prone to failure compared to the metal part. We determine the bolt preload based on the clamp-up load calculated using a maximum preload to make the composite part safe. We conclude that the unsuitable bolt preload may cause the failure of the composite part due to the high stress concentration in the vicinity of the bolt. The global-local analysis provides an efficient computational tool for enhancing 3D stress analysis in the highly loaded region.展开更多
The fatigue behavior of aluminum alloy 7050-T7451 single lap four-bolted joints was studied by high- frequency fatigue test and finite element （FE） methods. The fatigue test results showed that a better enhancement ...The fatigue behavior of aluminum alloy 7050-T7451 single lap four-bolted joints was studied by high- frequency fatigue test and finite element （FE） methods. The fatigue test results showed that a better enhancement of fatigue life was achieved for the joints with highlocked bolts by employing the combinations of cold expansion, interference fit, and clamping force. The fractography revealed that fatigue cracks propagated tortuously; more fatigue micro-cliffs, tearing ridges, lamellar structure were observed, and fatigue striation spacing was simultaneously reduced. The evaluation of residual stress conducted by FE methods confirmed the experimental results and locations of fatigue crack initiation. The extension of fatigue lives can be attributed to the evolution of fatigue damage and effect of beneficial compressive residual stresses around the hole, resulting in the delay of crack initiation, crack deflection, and plasticityinduced crack closure.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.展开更多
The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional(3 D)st...The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional(3 D)structural solid elements assembled model of a carbon fiber-reinforced polymer(CFRP)-aluminum single-lap joint with a titanium(Ti-6 Al-4 V)fastener and a washer generated with the commercial finite element(FE)software package,ABAQUS/Standard.A progressive failure algorithm written in Fortran code with a set of appropriate degradation rules was incorporated as a user subroutine in ABAQUS to simulate the non-linear damage behavior of the composite component in the composite-aluminum bolted aerospace structure.The assembled 3 DFE model simulated,as well as the specimen for the experimental testing consisted of a carbon-epoxy IMS-977-2 substrate,aluminum alloy 7075-T651 substrate,liquid shim(Hysol EA 9394),solid peelable fiberglass shim,a titanium fastener,and a washer.In distinction to previous investigations,the influence of shim layers(liquid shim and solid peelable fiberglass shim)inserted in-between the faying surfaces(CFRP and aluminum alloy substrates)were investigated by both numerical simulations and experimental work.The simulated model and test specimens conformed to the standard test configurations for both civil and military standards.The numerical simulations correlated well with the experimental results and it has been found that:(1)The shimming procedure as agreed upon by the aerospace industry for the resolution of assembly gaps in bolted joints for composite materials is the same for a composite-aluminum structure;liquid shim series(0.3,0.5 and 0.7 mm thicknesses)prolonged the service life of the composite component whereas a solid peelable fiberglass shim most definitely had a better influence on the 0.9 assembly gap compared with the liquid shim;(2)The shim layers considerably influenced the structural strength of the composite component by delaying its ultimate failure thereby increasing its service life;and(3)Increasing the shim layer′s thickness led to a significant corresponding effect on the stiffness but with minimal effect on the ultimate load.展开更多
A contact bolt model is proposed as a new modeling technique to investigate the complex structure with bolted joints for modal analysis and compared with the coupled bolt model, and the test results are given. Among t...A contact bolt model is proposed as a new modeling technique to investigate the complex structure with bolted joints for modal analysis and compared with the coupled bolt model, and the test results are given. Among these models, the coupled bolt model provides the best accurate responses compared with the experimental results. The contact bolt model shows the best effectiveness and usefulness in view of operational time. The bolt models proposed in this study are adopted for a dynamic characteristic analysis of a large diesel engine consisting of several parts which are connected by many bolts. The dynamic behavior of the entire engine structure was investigated by experiment. The coupled bolt model and the contact bolt model were applied to model the assembly of engine with high preload. The experimental results are in good agreement with the finite element method （FEM） results. Compared with the other models, the contact bolt model presented in this paper is more effective and useful in view of operational time and experience of analysts.展开更多
Rock bolts have been widely used in slopes as a reinforcement measure.Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shea...Rock bolts have been widely used in slopes as a reinforcement measure.Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shear force on the bolts.Rock bolts under shear action exhibit the guide rail effect;that is,the rock mass slides along the rock bolt as if the rock bolt is a rail.The normal stress can inhibit the guide rail effect and reduce the axial force on bolts.However,this factor is not considered by the existing analysis models.Shear tests of bolted joints under different normal stresses were carried out in the laboratory.During the test,the axial force on each point monitored on the bolt was recorded by a strain gauge,and the attenuation trend of the strain was studied.An analytical model that considers the inhibition of the bolt rail effect due to an increase in the normal stress was proposed to predict the shear mechanical behaviour of rock bolted joints.The new model accommodates the bolt shear behaviours in the elastic stage and plastic stage,and the estimated values agree well with the results of the direct shear tests in the laboratory.The validation shows that the proposed model can effectively describe the deformation characteristics of the bolts in the shear tests.展开更多
The high demands for load-carrying capability and structural efficiency of composite-metal bolted joints trigger in-depth investigations on failure mechanisms of the joints in hygrothermal environments.However,few stu...The high demands for load-carrying capability and structural efficiency of composite-metal bolted joints trigger in-depth investigations on failure mechanisms of the joints in hygrothermal environments.However,few studies have been presented to exhaustively reveal hygrothermal effects on the failure of CFRP-metal bolted joints,which differ from CFRP-CFRP or metal-metal bolted joints because of the remarkably different material properties of CFRPs and metals.In this paper,hygrothermal effects on tensile failures of single-lap and double-lap CFRP-aluminum bolted joints were experimentally and numerically investigated.A novel numerical model,in which a hygrothermal-included progressive damage model of composites was established and elastic-plastic models of metals were built,was proposed to predict the failures of the CFRP-metal bolted joints in hygrothermal environments and validated by corresponding experiments.Different failure mechanisms of single-lap and double-lap CFRP-aluminum bolted joints,under 23°C/Dry and 70°C/Wet conditions,were revealed,respectively.It follows that both the collapse failures of the single-lap and double-lap bolted joints were dominated by the bearing failure of the CFRP hole laminate in the two conditions,indicating that the hygrothermal environment did not change the macro failure modes of the joints.However,the hygrothermal environment considerably shortened the damage propagation processes and reduced the strength of the joints.Besides,the hygrothermal environment weakened the load-transfer capability of the single-lap joint more severely than the double-lap joint because it aggravated the secondary bending effects of the single-lap joint obviously.展开更多
To minimize the mass and increase the bearing failure load of composite double-lap bolted joints,a three-step optimization strategy including feasible region reduction,optimization model decoupling and optimization wa...To minimize the mass and increase the bearing failure load of composite double-lap bolted joints,a three-step optimization strategy including feasible region reduction,optimization model decoupling and optimization was presented.In feasible region reduction,the dimensions of the feasible design region were reduced by selecting dominant design variables from numerous multilevel parameters by sensitivity analyses,and the feasible regions of variables were reduced by influence mechanism analyses.In model decoupling,the optimization model with a large number of variables was divided into various sub-models with fewer variables by variance analysis.In the third step,the optimization sub-models were solved one by one using a genetic algorithm,and the modified characteristic curve method was adopted as the failure prediction method.Based on the proposed optimization method,optimization of a double-lap single-bolt joint was performed using the ANSYS®code.The results show that the bearing failure load increased by 13.5%and that the mass decreased by 8.7%compared with those of the initial design of the joint,which validated the effectiveness of the three-step optimization strategy.展开更多
Ceramic matrix composite(CMC)and superalloy bolted joints are commonly used high temperature connection structures in aerospace and aeronautical fields.In this paper,a finite element model coupled with progressive dam...Ceramic matrix composite(CMC)and superalloy bolted joints are commonly used high temperature connection structures in aerospace and aeronautical fields.In this paper,a finite element model coupled with progressive damage analysis of 2D C/SiC composites and superalloy bolted joint was implemented to simulate the uniaxial tensile loading process by using the ABAQUS finite element software.The parametric effects of raised head bolt on stress distribution,tensile performance,and damage process were studied for the CMC⁃superalloy bolted joint structures.The results showed that the final failure load increased first to the maximum value,and then decreased with the rise of bolt diameter,bolt head diameter,and bolt head thickness,respectively.When the three parameters were 5.0 mm,9.5 mm,and 2.8 mm for the current studied bolt configuration,the joint structure gave the maximum load bearing capacity for the considered parameter ranges.It was also found that around 42%potential improvement in load bearing capacity could be achieved by very small adjustments in bolt parameters of the joints.展开更多
文摘Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relationship between load amplitude,fatigue life,and damage progression in low-carbon steel assemblies.Design/methodology/approach–An experimental approach was adopted using MTS specimens fabricated from St 1203 cold-rolled steel,joined with Grade 8.8 M4 bolts.Cyclic fatigue tests were conducted under zerobased loading at seven distinct force levels.Fracture surfaces were visually analyzed to identify dominant failure mechanisms.Findings–The results revealed a strong inverse correlation between applied cyclic load and fatigue life.Three distinct failure modes were identified:bolt shear at high loads(5.4 kN),interface cracking and slippage at moderate loads(4.9–5.1 kN),and plate tearing or stable fatigue behavior at lower loads(54.1 kN).The results highlight a progressive transition in failure mechanisms,from bolt shear at high loads to plate tearing and interface cracking at lower loads,providing essential insights for fatigue-resistant bolted joint design.Originality/value–This study offers original insights into the fatigue behavior of bolted lap joints using MTS,a relatively underexplored configuration in fatigue assessment.By experimentally evaluating failure modes under varied cyclic load levels,the authors uncover critical transitions in damage mechanisms—from bolt shear to interface cracking and plate tearing—depending on the applied load.Unlike many existing studies focused on numerical modeling or bonded joints alone,this work provides empirical data rooted in real-world fastening conditions using cold-rolled low-carbon steel.
基金co-supported by the National Natural Science Foundation of China(NSFC)(No.52035011)the Fundamental Research Funds for the Central Universities,and the Research Project of the Ministry of Industry and Information Technology,China(No.MJZ4-4N22)。
文摘The wet-assembly hybrid bonded/bolted(WHBB)joint is increasingly employed in aircraft fuel tank structures owing to its advantageous mechanical strength and sealing performance.However,the integral tank is susceptible to leakage during service,particularly at the joint,which seriously endangers the flight safety of the aircraft.In this paper,a leakage prediction method of WHBB joint based on porous media theory is proposed,in which the shape and characteristic length of the sealant layer are taken into consideration.The model parameters are determined by the analysis and treatment of the defect state of the WHBB joint section.The prediction results agree well with the experimental data,which were acquired by self-designed sealing leakage rate measurement system,and the deviation between the predicted results and the average value of the experimental data is less than 20%.Furthermore,in order to verify the environmental adaptability,the prediction results based on 2D cutting sections of the joints and experimental results under three different loading conditions are compared.The comparison results not only prove the accuracy of the prediction model,but also reveal the important influence of tensile fatigue load on the sealing performance of the structure.The tensile fatigue loads lead to two orders of magnitude increase in leakage rate,and the reason is that the repeated stretching and compression process lead to an increase in interfacial cracks between the adhesive layer and the hole wall,thereby accentuating the defects within the adhesive layer.
基金supported by the National Natural Science Foundation of China(No.12272088)the Out-standing Youth Science Foundation of Liaoning Province of China(No.2024JH3/50100013)。
文摘This study investigates the vibration characteristics of bolted-flange-joined conical-cylindrical shells(BFJCCSs)through both theoretical analysis and experimental testing.The proposed model incorporates the pressure distribution within the bolted joint and accounts for the flange effect.The energy expressions for the conical and cylindrical shells are derived from Donnell's shell theory,while those for the flanges are obtained from the Euler-Bernoulli beam theory.The Lagrange equation is used to derive the dynamic equation,and the experimental studies on the BFJCCS are conducted to validate the accuracy of the model.Subsequently,the comprehensive effects of bolt loosening and bolt number on the frequency parameters are analyzed.Additionally,the effects of the flange dimensions and cone angle on the vibration behavior of the BFJCCS are discussed.In particular,the dynamic differences between the welded conical-cylindrical shell(WCCS)and BFJCCS are investigated.It is found that compared with the WCCS,the fundamental frequency of the BFJCCS is reduced by 7.6%,and the corresponding modal damping ratio is reduced by 21.0%.However,the high-order frequencies of the BFJCCS are higher than those of the WCCS,accompanied by a higher modal damping ratio.Compared with the bolt loosening degree,the bolt number has a more significant effect on frequencies.As the bolt number decreases,the impact of the bolt loosening degree diminishes gradually.
基金Open Fund of Badong National Observation and Research Station of Geohazards,Grant/Award Number:BNORSG202315Key R&D Program of Xinjiang Uygur Autonomous Region,Grant/Award Number:2021B03004-3+1 种基金National Natural Science Foundation of China,Grant/Award Numbers:42207169,U22A20569Natural Science Foundation of Jiangsu Province,Grant/Award Number:BK20221126。
文摘The shear characteristics of bolted rock joints are crucial for the stability of tunneling and mining,particularly in deep underground engineering,where rock bolt materials are exposed to high stress,water pressure,and engineering disturbance.However,due to the complex interaction between bolted rock joints and various geological contexts,many challenges and unsolved problems arise.Therefore,more investigation is needed to understand the shear performance of bolted joints in the field of deep underground engineering.This study presents a comprehensive review of research findings on the responses of bolted joints subjected to shearing under different conditions.As is revealed,the average shear strength of bolted rock joints increases linearly with the normal stress and increases with the compressive strength of rock until it reaches a stable value.The joint roughness coefficient(JRC)affects the contact area,friction force,shear strength,bending angle,and axial force of bolted rock joints.A mathematical function is proposed to model the relationship between JRC,normal load,and shear strength.The normal stress level also influences the deformation model,load-carrying capacity,and energy absorption ratio of bolts within bolted rock joints,and can be effectively characterized by a two-phase exponential equation.Additionally,the angle of the bolts affects the ratio of tensile and shear strength of the bolts,as well as the mechanical behavior of both bolted rock joints and surrounding rock,which favors smaller angles.This comprehensive review of experimental data on the shear behavior of bolted rock joints offers valuable theoretical insights for the development of advanced shear devices and further pertinent investigations.
基金Project supported by the National Defense Technology Foundation Under the State Administration of Science,Technology,and Industry for National Defense of China(No.JSZL2022213A001)the Special Funds for Basic Research in Central Universities of China(No.HYGJZN202322)。
文摘The bolted flange structure finds significant applications in fields such as aerospace,shipbuilding,and pipeline transportation.The investigation of its dynamic characteristics has consistently been a focal point for researchers;however,there remains a deficiency in the development of robust analytical models.This paper introduces a novel analytical model based on the finite element methods and the Timoshenko beam theory to accurately simulate the bolted flange structure.The stiffness,mass,damping,and inertia matrices of the rotor system are individually derived,and the dynamic equation is subsequently formulated.The model’s validity and accuracy are validated through both the experimental testing and the finite element analysis.This study aims to elucidate the relationship between the external loads and the influence of the geometric configuration on the stiffness and contact behavior of the bolted flange structure,thereby enabling a thorough and precise prediction of the static and dynamic load transfer pathways,as well as the distribution of vibrational energy within the structure,while also facilitating the incorporation of friction and slip effects.Simultaneously,this work provides a foundational framework for the optimization design of bolted flange structures,addressing the factors such as the number,size,and geometric distribution of bolts.
基金Project(U1865203)supported by the Key Projects of the Yalong River Joint Fund of the National Natural Science Foundation of ChinaProject(51279201)supported by the National Natural Science Foundation of ChinaProjects(2019YFC0605103,2019YFC0605100)supported by the National Key R&D Program of China。
文摘Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting performance.In this study,a new artificial molding method based on 3D scanning and printing technology was first proposed to prepare bolted joints with an inclined bolt.Then,the effects of the bolt inclination angle and boundary conditions on the shear behavior and failure characteristic of bolted joints were addressed by conducting direct shear tests under both CNL and CNS conditions.Results indicated that rock bolt could significantly improve the shear behavior of rock joints,especially in the post-yield deformation region.With the increase of bolt inclination angle,both the maximum shear stress and the maximum friction coefficient increased first and then decreased,while the maximum normal displacement decreased monotonously.Compared with CNL conditions,the maximum shear stress was larger,whereas the maximum normal displacement and friction coefficient were smaller under the CNS conditions.Furthermore,more asperity damage was observed under the CNS conditions due to the increased normal stress on the shear plane.
基金co-supported by the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe National Natural Science Foundation of China (No. 11302105)
文摘Efficient and accurate strength analysis of bolted connections is essential in analyzing the integral thermal protection system（ITPS） of hypersonic vehicles, since the system bears severe loads and structural failures usually occur at the connections. Investigations of composite mechanical properties used in ITPS are still in progress as the architecture of the composites is complex. A new method is proposed in this paper for strength analysis of bolted connections by investigating the elastic behavior and failure strength of three-dimensional C/C orthogonal composites used in ITPS. In this method a multi-scale finite element method incorporating the global–local method is established to ensure high efficiency in macro-scale and precision in meso-scale in analysis.Simulation results reveal that predictions of material properties show reasonable accuracy compared with test results. And the multi-scale method can analyze the strength of connections efficiently and accurately.
基金funded by China Postdoctoral Science Foundation(No.2020M673227)NSAF,China(No.U1830122)Sichuan Science and Technology Program,China(No.2020YFG0109)。
文摘Interference fit has advantages in improving fatigue behaviors of composite bolted joints,however, interference fit bolt insertion tends to cause damages in laminates weakening joint mechanical properties. Therefore, an experimental study was conducted to investigate bolt insertion damages of Carbon Fiber Reinforced Polymer(CFRP)/CFRP interference fit bolted joints.Mechanical behaviors of joints were also evaluated experimentally under both quasi-static loads and cyclic loads. Scanning Electron Microscope(SEM) and high-resolution X-ray micro-CT scan were used to examine micro damages in laminates. Damage and failure behaviors of joints were characterized. The results demonstrated that the hole entrance in upper laminate and the laminate boundary near the hole wall were the most critical regions for damages during bolt insertions. However, the influence of those damages on quasi-static failure loads and fatigue failure modes of joints was minimal. Delamination and matrix cracking occurred first in laminates following fiber and matrix fracture in quasi-static tensile tests. Interference fit could improve the fatigue resistance of the laminate hole, however, the bolt seemed to suffer a more critical local fatigue loading condition.This paper can contribute to composite structure designs, especially in understanding damage and failure behaviors of composite bolted joints.
基金This study has been funded by the National Natural Science Foundation of China(Grant No.41941018)and the Second Tibetan Plateau Scientific Expedition and Research Grant(Grant No.2019QZKK0708).
文摘Quasi-NPR(negative Poisson’s ratio)steel is a new type of super bolt material with high strength,high ductility,and a micro-negative Poisson’s effect.This material overcomes the contrasting characteristics of the high strength and high ductility of steel and it has significant energy-absorbing characteristics,which is of high value in deep rock and soil support engineering.However,research on the shear resistance of quasi-NPR steel has not been carried out.To study the shear performance of quasi-NPR steel bolted rock joints,indoor shear tests of bolted rock joints under different normal stress conditions were carried out.Q235 steel and#45 steel,two representative ordinary bolt steels,were set up as a control group for comparative tests to compare and analyze the shear strength,deformation and instability mode,shear energy absorption characteristics,and bolting contribution of different types of bolts.The results show that the jointed rock masses without bolt reinforcement undergo brittle failure under shear load,while the bolted jointed rock masses show obvious ductile failure characteristics.The shear deformation ca-pacity of quasi-NPR steel is more than 3.5 times that of Q235 steel and#45 steel.No fracture occurs in the quasi-NPR steel during large shear deformation and it can provide stable shear resistance.However,the other two types of control bolts become fractured under the same conditions.Quasi-NPR steel has significant energy-absorbing characteristics under shear load and has obvious advantages in terms of absorbing the energy released by shear deformation of jointed rock masses as compared with ordinary steel.In particular,the shear force plays a major role in resisting the shear deformation of Q235 steel and#45 steel,therefore,fracture failure occurs under small bolt deformation.However,the axial force of quasi-NPR steel can be fully exerted when resisting joint shear deformation;the steel itself does not break when large shear deformation occurs,and the supporting effect of the jointed rock mass is effectively guaranteed.
基金support from the National Natural Science Foundation of China(Nos.11772158,11502113)the Fundamental Research Funds for Central Universities,China(No.30917011103)。
文摘In this paper,a failure evaluation criterion was proposed for the bolted casing-flange structure under impact loading.Subsequently,ballistic tests with eighteen bolted casing-flange structure specimens were conducted to validate the failure evaluation criterion.Parameter studies were then carried out using the validated FE models.Both the experimental and numerical results demonstrated the accuracy of the failure evaluation criterion.The failure evaluation criterion provided a quick and easy way to determine the failure mode of the casing connection area by using the materials and dimensions of the structure.Based on the failure evaluation criterion,designing the structural failure mode of the bolted casing-flange structure to be between flange failure and bolt failure can improve the impact resistance of the connection area of the aero-engine casings.This investigation revealed that the impact failure is not the unique criterion in evaluating the containment of the casing connection area,structural failure should also be involved in the evaluation criteria.
基金Project supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education,Science and Technology(MEST)(No.2012-00-2110)the Sustainable Building Research Center of Hanyang University funded by the SRC/ERC Program of MEST(No.2012-0000-723)
文摘This paper is focused on the structural behavior of the single shear bolted connections with thin-walled ferritic stainless steel.The purpose of this study is to investigate the ultimate behaviors,such as ultimate strength and fracture mode of the single shear bolted connections of thin-walled ferritic stainless steel(low cost steel) rather than austenitic stainless steel(high cost steel).Bolt arrangement and end distance parallel to the direction of applied load are considered as main variables of the test specimens for bolted connections.Specimens have a constant dimension of edge distance perpendicular to the loading direction,bolt diameter,pitch,and gauge.A monotonic tensile test for specimens has been carried out and some bolted connections with long end distance showed curling(out of plane deformation) occurrence which led to strength reduction.The ultimate behaviors such as fracture mode,ultimate strength are compared with those predicted by current design codes.Further,conditions of curling occurrence and the strength reduction due to curling are investigated and modified strength equations are suggested considering the curling effect.
文摘Hybrid bonded/bolted(HBB) joint has been widely used in engineering practice because it can overcome the potential weakness of pure bonded and pure bolted joints. However, studies on HBB joint are still at the initial stage. In this paper, tensile properties of a composite–metal singlelap HBB joint was investigated experimentally. And a detailed finite element model(FEM) was established to simulate the tensile behavior of the joint. The model was verified by the experimental results. Then the damage propagation and load transfer mechanism were explored based on the FEM. The results show that the HBB joint can provide multi-load transmission paths and resist damage propagation in the adhesive. The HBB joint has higher strength and energy absorption capacity than the pure bonded joint. And the HBB joint has greater initial damage load and tensile stiffness than pure bolted joint. Adhesive fillets can obviously improve the tensile performances of the HBB joint. Lateral stiffness of the joint boundary and testing machine show obvious effects on tensile performances of single-lap hybrid joints.
基金Project(282522)supported by the European Union's Research and Innovation Funding Programme
文摘Efficient bolted joint design is an essential part of designing the minimum weight aerospace structures, since structural failures usually occur at connections and interface. A comprehensive numerical study of three-dimensional(3D) stress variations is prohibitively expensive for a large-scale structure where hundreds of bolts can be present. In this work, the hybrid composite-to-metal bolted connections used in the upper stage of European Ariane 5ME rocket are analyzed using the global-local finite element(FE) approach which involves an approximate analysis of the whole structure followed by a detailed analysis of a significantly smaller region of interest. We calculate the Tsai-Wu failure index and the margin of safety using the stresses obtained from ABAQUS. We find that the composite part of a hybrid bolted connection is prone to failure compared to the metal part. We determine the bolt preload based on the clamp-up load calculated using a maximum preload to make the composite part safe. We conclude that the unsuitable bolt preload may cause the failure of the composite part due to the high stress concentration in the vicinity of the bolt. The global-local analysis provides an efficient computational tool for enhancing 3D stress analysis in the highly loaded region.
基金supported by Key Research and Development Plan of Shandong Province, China (2017GGX20140)Natural Science Foundation of Shandong Province, China (No. ZR2014JL031)
文摘The fatigue behavior of aluminum alloy 7050-T7451 single lap four-bolted joints was studied by high- frequency fatigue test and finite element （FE） methods. The fatigue test results showed that a better enhancement of fatigue life was achieved for the joints with highlocked bolts by employing the combinations of cold expansion, interference fit, and clamping force. The fractography revealed that fatigue cracks propagated tortuously; more fatigue micro-cliffs, tearing ridges, lamellar structure were observed, and fatigue striation spacing was simultaneously reduced. The evaluation of residual stress conducted by FE methods confirmed the experimental results and locations of fatigue crack initiation. The extension of fatigue lives can be attributed to the evolution of fatigue damage and effect of beneficial compressive residual stresses around the hole, resulting in the delay of crack initiation, crack deflection, and plasticityinduced crack closure.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.
基金the Innovation Foundation of National Research Center for Commercial Aircraft Manufacturing Engineering Technology in China (No. SAMC13-JS-13-021)Jiangsu Key Laboratory of Precision and Micro-Manufacturing Technology for the provision of financial support
文摘The influence of varying shim layers on the progressive damage/failure of a composite component in a bolted composite-aluminum aerospace structural assembly was investigated using a non-linear three-dimensional(3 D)structural solid elements assembled model of a carbon fiber-reinforced polymer(CFRP)-aluminum single-lap joint with a titanium(Ti-6 Al-4 V)fastener and a washer generated with the commercial finite element(FE)software package,ABAQUS/Standard.A progressive failure algorithm written in Fortran code with a set of appropriate degradation rules was incorporated as a user subroutine in ABAQUS to simulate the non-linear damage behavior of the composite component in the composite-aluminum bolted aerospace structure.The assembled 3 DFE model simulated,as well as the specimen for the experimental testing consisted of a carbon-epoxy IMS-977-2 substrate,aluminum alloy 7075-T651 substrate,liquid shim(Hysol EA 9394),solid peelable fiberglass shim,a titanium fastener,and a washer.In distinction to previous investigations,the influence of shim layers(liquid shim and solid peelable fiberglass shim)inserted in-between the faying surfaces(CFRP and aluminum alloy substrates)were investigated by both numerical simulations and experimental work.The simulated model and test specimens conformed to the standard test configurations for both civil and military standards.The numerical simulations correlated well with the experimental results and it has been found that:(1)The shimming procedure as agreed upon by the aerospace industry for the resolution of assembly gaps in bolted joints for composite materials is the same for a composite-aluminum structure;liquid shim series(0.3,0.5 and 0.7 mm thicknesses)prolonged the service life of the composite component whereas a solid peelable fiberglass shim most definitely had a better influence on the 0.9 assembly gap compared with the liquid shim;(2)The shim layers considerably influenced the structural strength of the composite component by delaying its ultimate failure thereby increasing its service life;and(3)Increasing the shim layer′s thickness led to a significant corresponding effect on the stiffness but with minimal effect on the ultimate load.
基金Sponsored by the Ministerial Level Foundation(40402020105)
文摘A contact bolt model is proposed as a new modeling technique to investigate the complex structure with bolted joints for modal analysis and compared with the coupled bolt model, and the test results are given. Among these models, the coupled bolt model provides the best accurate responses compared with the experimental results. The contact bolt model shows the best effectiveness and usefulness in view of operational time. The bolt models proposed in this study are adopted for a dynamic characteristic analysis of a large diesel engine consisting of several parts which are connected by many bolts. The dynamic behavior of the entire engine structure was investigated by experiment. The coupled bolt model and the contact bolt model were applied to model the assembly of engine with high preload. The experimental results are in good agreement with the finite element method （FEM） results. Compared with the other models, the contact bolt model presented in this paper is more effective and useful in view of operational time and experience of analysts.
基金Projects(41931295,41877258)supported by the National Natural Science Foundation of ChinaProject(2017YFC1501305)supported by the National Key Research and Development Program of China。
文摘Rock bolts have been widely used in slopes as a reinforcement measure.Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shear force on the bolts.Rock bolts under shear action exhibit the guide rail effect;that is,the rock mass slides along the rock bolt as if the rock bolt is a rail.The normal stress can inhibit the guide rail effect and reduce the axial force on bolts.However,this factor is not considered by the existing analysis models.Shear tests of bolted joints under different normal stresses were carried out in the laboratory.During the test,the axial force on each point monitored on the bolt was recorded by a strain gauge,and the attenuation trend of the strain was studied.An analytical model that considers the inhibition of the bolt rail effect due to an increase in the normal stress was proposed to predict the shear mechanical behaviour of rock bolted joints.The new model accommodates the bolt shear behaviours in the elastic stage and plastic stage,and the estimated values agree well with the results of the direct shear tests in the laboratory.The validation shows that the proposed model can effectively describe the deformation characteristics of the bolts in the shear tests.
基金supported by the National Science Foundation of China(11772028,11872131,11702012,U1864208,11572058 and 11372020)the Academic Excellence Foundation of BUAA for PhD Students.
文摘The high demands for load-carrying capability and structural efficiency of composite-metal bolted joints trigger in-depth investigations on failure mechanisms of the joints in hygrothermal environments.However,few studies have been presented to exhaustively reveal hygrothermal effects on the failure of CFRP-metal bolted joints,which differ from CFRP-CFRP or metal-metal bolted joints because of the remarkably different material properties of CFRPs and metals.In this paper,hygrothermal effects on tensile failures of single-lap and double-lap CFRP-aluminum bolted joints were experimentally and numerically investigated.A novel numerical model,in which a hygrothermal-included progressive damage model of composites was established and elastic-plastic models of metals were built,was proposed to predict the failures of the CFRP-metal bolted joints in hygrothermal environments and validated by corresponding experiments.Different failure mechanisms of single-lap and double-lap CFRP-aluminum bolted joints,under 23°C/Dry and 70°C/Wet conditions,were revealed,respectively.It follows that both the collapse failures of the single-lap and double-lap bolted joints were dominated by the bearing failure of the CFRP hole laminate in the two conditions,indicating that the hygrothermal environment did not change the macro failure modes of the joints.However,the hygrothermal environment considerably shortened the damage propagation processes and reduced the strength of the joints.Besides,the hygrothermal environment weakened the load-transfer capability of the single-lap joint more severely than the double-lap joint because it aggravated the secondary bending effects of the single-lap joint obviously.
基金This work was supported by the National Natural Science Foundation of China(11772028,11872131,11702012,U1864208,11572058 and 11372020).
文摘To minimize the mass and increase the bearing failure load of composite double-lap bolted joints,a three-step optimization strategy including feasible region reduction,optimization model decoupling and optimization was presented.In feasible region reduction,the dimensions of the feasible design region were reduced by selecting dominant design variables from numerous multilevel parameters by sensitivity analyses,and the feasible regions of variables were reduced by influence mechanism analyses.In model decoupling,the optimization model with a large number of variables was divided into various sub-models with fewer variables by variance analysis.In the third step,the optimization sub-models were solved one by one using a genetic algorithm,and the modified characteristic curve method was adopted as the failure prediction method.Based on the proposed optimization method,optimization of a double-lap single-bolt joint was performed using the ANSYS®code.The results show that the bearing failure load increased by 13.5%and that the mass decreased by 8.7%compared with those of the initial design of the joint,which validated the effectiveness of the three-step optimization strategy.
基金Sponsored by the Pre⁃Research Foundation of Shenyang Aircraft Design and Research Institute,Aviation Industry Corporation of China(Grant No.JH20128255).
文摘Ceramic matrix composite(CMC)and superalloy bolted joints are commonly used high temperature connection structures in aerospace and aeronautical fields.In this paper,a finite element model coupled with progressive damage analysis of 2D C/SiC composites and superalloy bolted joint was implemented to simulate the uniaxial tensile loading process by using the ABAQUS finite element software.The parametric effects of raised head bolt on stress distribution,tensile performance,and damage process were studied for the CMC⁃superalloy bolted joint structures.The results showed that the final failure load increased first to the maximum value,and then decreased with the rise of bolt diameter,bolt head diameter,and bolt head thickness,respectively.When the three parameters were 5.0 mm,9.5 mm,and 2.8 mm for the current studied bolt configuration,the joint structure gave the maximum load bearing capacity for the considered parameter ranges.It was also found that around 42%potential improvement in load bearing capacity could be achieved by very small adjustments in bolt parameters of the joints.
