The aim of this study was to optimize the geometry and the design of metallic/composite single bolted joints subjected to tension-compression loading. For this purpose, it was necessary to evaluate the stress state in...The aim of this study was to optimize the geometry and the design of metallic/composite single bolted joints subjected to tension-compression loading. For this purpose, it was necessary to evaluate the stress state in each component of the bolted join. The multi-material assembly was based on the principle of double lap bolted joint. It was composed of a symmetrical balanced woven glass-epoxy composite material plate fastened to two stainless sheets using a stainless pre-stressed bolt. In order to optimize the design and the geometry of the assembly, ten configurations were proposed and studied: a classical simple bolted joint, two joints with an insert (a BigHead<sup>R</sup> insert and a stair one) embedded in the composite, two “waved” solutions, three symmetrical configurations composed of a succession of metallic and composites layers, without a sleeve, with one and with two sleeves, and two non-symmetrical constituted of metallic and composites layers associated with a stair-insert (one with a sleeve and one without). A tridimensional Finite Element Method (FEM) was used to model each configuration mentioned above. The FE models taked into account the different materials, the effects of contact between the different sheets of the assembly and the pre-stress in the bolt. The stress state was analyzed in the composite part. The concept of stress concentration factor was used in order to evaluate the stress increase in the highly stressed regions and to compare the ten configurations studied. For this purpose, three stress concentration factors were defined: one for a monotonic loading in tension, another for a monotonic loading in compression, and the third for a tension-compression cyclic loading. The results of the FEM computations showed that the use of alternative metallic and composite layers associated with two sleeves gived low values of stress concentration factors, smaller than 1.4. In this case, there was no contact between the bolt and the composite part and the most stressed region was not the vicinity of the hole but the end of the longest layers of the metallic inserts.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
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
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
Bolt connection is one of the main fixing methods of cylindrical shell structures.A typical bolted connection model is considered as a tuned system.However,in the actual working conditions,due to the manufacturing err...Bolt connection is one of the main fixing methods of cylindrical shell structures.A typical bolted connection model is considered as a tuned system.However,in the actual working conditions,due to the manufacturing error,installation error and uneven materials of bolts,there are always random errors between different bolts.To investigate the influence of non-uniform parameters of bolt joint,including the stiffness and the distribution position,on frequency complexity characteristics of cylindrical shell through a statistical method is the main aim of this paper.The bolted joints considered here were simplified as a series of springs with random features.The vibration equation of the bolted joined cylindrical shell was derived based on Sanders’thin shell theory.The Monte Carlo simulation and statistical theory were applied to the statistical analysis of mode characteristics of the system.First,the frequency and mode shape of the tuned system were investigated and compared with FEM.Then,the effect of the random distribution and the random constraint stiffness of the bolts on the frequency and mode shape were studied.And the statistical analysis on the natural frequencies was evaluated for different mistuned levels.And some special cases were presented to help understand the effect of random mistuning.This research introduces random theory into the modeling of bolted joints and proposes a reference result to interpret the complexity of the modal characteristics of cylindrical shells with non-uniform parameters of bolt joints.展开更多
2G-NPR bolt (the 2nd generation Negative Poisson’s Ratio bolt) is a new type of bolt with high strength, high toughness and no yield platform. It has signifcant efects on improving the shear strength of jointed rock ...2G-NPR bolt (the 2nd generation Negative Poisson’s Ratio bolt) is a new type of bolt with high strength, high toughness and no yield platform. It has signifcant efects on improving the shear strength of jointed rock mass and controlling the stability of surrounding rock. To achieve an accurate simulation of bolted joint shear tests, we have studied a numerical simulation method that takes into account the 2G-NPR bolt's tensile–shear fracture criterion. Firstly, the indoor experimental study on the tensile–shear mechanical properties of 2G-NPR bolt is carried out to explore its mechanical properties under diferent tensile–shear angles, and the fracture criterion of 2G-NPR bolt considering the tensile–shear angle is established. Then, a three-dimensional numerical simulation method considering the tensile–shear mechanical constitutive and fracture criterion of 2G-NPR bolt, the elastoplastic mechanical behavior of surrounding rock and the damage and deterioration of grouting body is proposed. The feasibility and accuracy of the method are verifed by comparing with the indoor shear test results of 2G-NPR bolt anchorage joints. Finally, based on the numerical simulation results, the deformation and stress of the bolt, the distribution of the plastic zone of the rock mass, the stress distribution and the damage of the grouting body are analyzed in detail. The research results can provide a good reference value for the practical engineering application and shear mechanical performance analysis of 2G-NPR bolt.展开更多
A Double Shear Model(DSM) was used in a numerical simulation on bolted rock joint shearing performance.An entire bolt deformed as the letter'U'under a shear load between two joints.Near the bolt-joint intersec...A Double Shear Model(DSM) was used in a numerical simulation on bolted rock joint shearing performance.An entire bolt deformed as the letter'U'under a shear load between two joints.Near the bolt-joint intersection,the bolt partly deformed as the letter'Z'.There were two critical points along the bolt:one was at the bolt-joint intersection with zero bending moment and the other at the maximum bending moment(plastic hinge) with zero shear stress.The blocks on two sides slid along the bolt as it deformed. A separation area was found between the two joint contact surfaces of the middle rock block and sided block.This area of separation was related to bolt diameter and external forces.We assume that this area is related to the work of external forces.Further research is needed.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
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
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
For up-to-date bolted joints, first of all in vehicles, high strength bolts of 10.9 or even 12.9 are used, which are preloaded up to 90% or even 100% of the yield strength. The primary aim of this high degree utilizat...For up-to-date bolted joints, first of all in vehicles, high strength bolts of 10.9 or even 12.9 are used, which are preloaded up to 90% or even 100% of the yield strength. The primary aim of this high degree utilization is the weight reduction. For the analytic dimensioning of bolted joints, the VDI 2230 Richtlinien German standard [1] provides support. However, the analytic model can mostly consider the true structural characteristics only in a limited way. The analytic modeling is especially uncertain in case of multiple bolted joints when the load distribution among the bolts depends reasonably upon the elastic deformation of the participating elements in the joints over the geometry of the bolted joint. The first part of this paper deals with the problems of numerical modeling and stress analysis, respectively specifying the analytic dimensioning procedure by applying elastic or rather elastic-plastic material law. The error magnitude in bolted joint calculation was examined in case of omitting the existing threaded connection—between the bolt and the nut—in order to simplify the model. The second part of the paper deals with the dimensioning of stands and cantilevers’ multi-bolt fixing problems, first of all, with the load distribution among the bolts keeping in view the analysis of the local slipping relations. For demonstrating the above technique, an elaborated numeric procedure is presented for a four-bolted cantilever, having bolted joints pre-tightened to the yield strength.展开更多
Numerical and experimental study was conducted to investigate the failure mode and strength performance of stiffened composite panel repaired by bolted joints under compressive load, and the results were then compared...Numerical and experimental study was conducted to investigate the failure mode and strength performance of stiffened composite panel repaired by bolted joints under compressive load, and the results were then compared with those from virgin stiffened composite panel without any damage. A finite element analysis model was established for repaired and virgin stiffened composite panels under compressive load, the 3D Hashin criteria was applied to identify the composite structure failure, and the secondary stress criteria was adopted to identify the adhesive failure between the base laminate and the stiffener. The failure modes of repaired stiffened composite panels were stiffened composite panels breaking off along the bolt joints. The experimental results were consistent with the finite element analysis results, indicating the reliability of the finite element analysis model.展开更多
For up-to-date bolted joints, first of all in vehicles, high strength bolts of 10.9 or even 12.9 are used, which are pre-tightened up to 90% or even 100% of the yield strength. The primary aim of this high degree util...For up-to-date bolted joints, first of all in vehicles, high strength bolts of 10.9 or even 12.9 are used, which are pre-tightened up to 90% or even 100% of the yield strength. The primary aim of this high degree utilization is the weight reduction. For the analytic dimensioning of bolted joints, the VDI 2230 Richtlinien German standard provides support. However, the analytic model can mostly consider the true structural characteristics only in a limited way. The analytic modeling is especially uncertain in case of multiple bolted joints when the load distribution among the bolts depends reasonably upon the elastic deformation of the participating elements in the joints over the geometry of the bolted joint. The first part of this paper deals with the problems of numerical modeling and stress analysis, respectively specifying the analytic dimensioning procedure by applying elastic or rather elastic-plastic material law. The error magnitude in bolted joint calculation was examined in case of omitting the existing threaded connection—between the bolt and the nut—in order to simplify the model. The second part of the paper deals with the dimensioning of stands and cantilevers’ multi-bolt fixing problems, first of all, with the load distribution among the bolts keeping in view the analysis of the local slipping relations. For demonstrating the above technique, an elaborated numeric procedure is presented for a four-bolted cantilever, having bolted joints pre-tightened to the yield strength.展开更多
This paper studies the effects of fiber orientaion and holes position on stress concentration and the determination of weakened areas in the composite of glass fiber reinforced epoxy resin around the hole for joints b...This paper studies the effects of fiber orientaion and holes position on stress concentration and the determination of weakened areas in the composite of glass fiber reinforced epoxy resin around the hole for joints by using the finite element method.In this study,for the observation of areas affected by stress concentration Tsai-Wu failure criterion is used to determine the failed elements and ANSYS Software is implemented for modeling.In order to compare the effect of geometric parameters on stress concentration around the holes,two types of hole position arrangement along with fibers orientation have been studied.Results show that the stress concentration coefficient is lower in the second type of holes arrangement in comparison with the first type for the same component dimensions.Increasing the distance from hole center to upper or lower edge of the sample and also decreasing the distance between holes,would result in an increase in the stress concentration.展开更多
As the controlled research of Dynamic Installation(DI)and Static Installation(SI),a new interference installation method was developed based on electromagnetic loading to enhance the mechanical properties of composite...As the controlled research of Dynamic Installation(DI)and Static Installation(SI),a new interference installation method was developed based on electromagnetic loading to enhance the mechanical properties of composite structures.Four different interference-fit sizes were considered,ranging from a net fit to 2.0%.The experiments were conducted to evaluate the installation resistance and the mechanical behavior of the joint under external loads.Meanwhile,an FFA model to model the stress distribution and damage behavior of the bolt-hole contact interface was established.The load-displacement curve and damage modes of experiments were used to verify the FEA results.The results show that the installation resistance during DI process was remarkably lower than that of SI process corresponding to all interference-fit sizes,and the stress amplitudes induced by interference were larger and widely distributed.The damage of the hole wall was positively correlated with interference fit size,but DI can significantly reduce the damage compared to SI.In performance tests,DI enhanced the static bearing capacity and extended longer fatigue life of the joints than SI.DI methods can be an effective way to achieve highly reliable interference joints in composite structures.展开更多
Since most current seismic capacity evaluations of reinforced concrete (RC) frame structures are implemented by either static pushover analysis (PA) or dynamic time history analysis, with diverse settings of the p...Since most current seismic capacity evaluations of reinforced concrete (RC) frame structures are implemented by either static pushover analysis (PA) or dynamic time history analysis, with diverse settings of the plastic hinges (PHs) on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints (BCJs) during major earthquakes is commonly neglected. This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. To verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements. By considering shear failure at BCJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.展开更多
In order to study the influence of the bolt joint mode on low-velocity projectiles penetrating the composite protective structure,two bolt joint models which connect the composite target to the fixed frame were design...In order to study the influence of the bolt joint mode on low-velocity projectiles penetrating the composite protective structure,two bolt joint models which connect the composite target to the fixed frame were designed,the ballistic test of the bolted composite protective structure with limited span was carried out,and the bearing and failure characteristics of the bolted region,as well as the energy dissipation of each part of the structure,were analyzed.The results show that in the condition of lowvelocity impact,there are three failure modes for the bolted composite protective structure subjected to projectile penetration,including failure of the impact point of the composite target,failure of protective structure connecting components and failure of the holes in the bolted region of the composite target;the failure mode of bolt holes in the bolted region has a great influence on the protection performance,and the allowable value of the bearing capacity of the bolted region depends on the sum of the minimum failure load in the failure modes and the friction force;shear-out failure occurring in the bolt holes in the bolted region exerts the greatest effect on ballistic performance,which should be avoided;When simultaneous failure occurs in the bolted region and the free deformation region of the composite protective structure,the energy absorption per unit surface density of the composite protective structure reaches the maximum,which can give full play to its anti-penetration efficiency.展开更多
Presented a new analytical model for studying the shear-tensile large deforma-tion behavior near the vicinity of joint interface for bolted rough discontinuous rock, and presented the formulation estimating global she...Presented a new analytical model for studying the shear-tensile large deforma-tion behavior near the vicinity of joint interface for bolted rough discontinuous rock, and presented the formulation estimating global shear strength for bolted joints under shear-ing-tensile loads. The analytical strength curves of bolts contribution on reinforced discon-tinuous rocks as the function of joint displacements or deformation angle of a bolt at rock joints was obtained. Based on Barton’s equation on JRC roughness profiles, the theoreti-cal shearing strength of bolted rough joints was also established. Test results on bolted granite and marble specimen confirm the validity of the analytical approach.展开更多
In order to obtain the optimal parameters of anchor bolt supporting system for large-span and jointed rock mass in Kaiyang Phosphor Mine, it is expensive and unavailable with the method of in-situ experiments. This pa...In order to obtain the optimal parameters of anchor bolt supporting system for large-span and jointed rock mass in Kaiyang Phosphor Mine, it is expensive and unavailable with the method of in-situ experiments. This paper describes a numerical modeling with discrete element method for the supporting effects of different type of anchor bolts. The anchor bolts with variant length of 0.5m, 0.8m, 1.0m, diameter of 10mm, 15mm, 20mm, setting spacing of 3.0m, 2.5m, 2.0m, and setting angle of 10°, 20°, 30°, are simulated respectively. The results show that there exist optimal parameters of anchor bolt support for large-span and jointed rock mass. For the bolt support of the concerning, the optimal length is 2.53.5m, the diameter is 2535mm, the spacing is 0.50.6m, and the setting angle is 105°.展开更多
A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is locate...A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is located in the core joint region and the connections between concrete members. This paper presents an experimental study of a series of PPSRC specimens. These specimens are tested under low cyclic loading.Experimental results demonstrate that the bearing capacity of the PPSRC specimens is 3 times that of the ordinary reinforced concrete( RC) beam-column joints. The strength and stiffness degradation rates are slower compared with that of the RC beam-column joints. In addition,the strength of the core joint region and the connections is higher than other parts of the PPSRC specimens. Beam failure occurs firstly for the PPSRC specimens,followed by column failure and connections failure. The failure of the core joint region occurs finally.Test results show that the seismic performance of the PPSRC is better than that of the ordinary RC beam-column joints.展开更多
文摘The aim of this study was to optimize the geometry and the design of metallic/composite single bolted joints subjected to tension-compression loading. For this purpose, it was necessary to evaluate the stress state in each component of the bolted join. The multi-material assembly was based on the principle of double lap bolted joint. It was composed of a symmetrical balanced woven glass-epoxy composite material plate fastened to two stainless sheets using a stainless pre-stressed bolt. In order to optimize the design and the geometry of the assembly, ten configurations were proposed and studied: a classical simple bolted joint, two joints with an insert (a BigHead<sup>R</sup> insert and a stair one) embedded in the composite, two “waved” solutions, three symmetrical configurations composed of a succession of metallic and composites layers, without a sleeve, with one and with two sleeves, and two non-symmetrical constituted of metallic and composites layers associated with a stair-insert (one with a sleeve and one without). A tridimensional Finite Element Method (FEM) was used to model each configuration mentioned above. The FE models taked into account the different materials, the effects of contact between the different sheets of the assembly and the pre-stress in the bolt. The stress state was analyzed in the composite part. The concept of stress concentration factor was used in order to evaluate the stress increase in the highly stressed regions and to compare the ten configurations studied. For this purpose, three stress concentration factors were defined: one for a monotonic loading in tension, another for a monotonic loading in compression, and the third for a tension-compression cyclic loading. The results of the FEM computations showed that the use of alternative metallic and composite layers associated with two sleeves gived low values of stress concentration factors, smaller than 1.4. In this case, there was no contact between the bolt and the composite part and the most stressed region was not the vicinity of the hole but the end of the longest layers of the metallic inserts.
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Supported by Anhui Provincial Natural Science Foundation of China (Grant No.2108085QE223)Universities Natural Science Research Project of Anhui Province of China (Grant No.KJ2021A0156)National Natural Science Foundation of China (Grant Nos.52075086,52205078)。
文摘Bolt connection is one of the main fixing methods of cylindrical shell structures.A typical bolted connection model is considered as a tuned system.However,in the actual working conditions,due to the manufacturing error,installation error and uneven materials of bolts,there are always random errors between different bolts.To investigate the influence of non-uniform parameters of bolt joint,including the stiffness and the distribution position,on frequency complexity characteristics of cylindrical shell through a statistical method is the main aim of this paper.The bolted joints considered here were simplified as a series of springs with random features.The vibration equation of the bolted joined cylindrical shell was derived based on Sanders’thin shell theory.The Monte Carlo simulation and statistical theory were applied to the statistical analysis of mode characteristics of the system.First,the frequency and mode shape of the tuned system were investigated and compared with FEM.Then,the effect of the random distribution and the random constraint stiffness of the bolts on the frequency and mode shape were studied.And the statistical analysis on the natural frequencies was evaluated for different mistuned levels.And some special cases were presented to help understand the effect of random mistuning.This research introduces random theory into the modeling of bolted joints and proposes a reference result to interpret the complexity of the modal characteristics of cylindrical shells with non-uniform parameters of bolt joints.
基金supported by the National Natural Science Foundation of China(NSFC)(41941018).
文摘2G-NPR bolt (the 2nd generation Negative Poisson’s Ratio bolt) is a new type of bolt with high strength, high toughness and no yield platform. It has signifcant efects on improving the shear strength of jointed rock mass and controlling the stability of surrounding rock. To achieve an accurate simulation of bolted joint shear tests, we have studied a numerical simulation method that takes into account the 2G-NPR bolt's tensile–shear fracture criterion. Firstly, the indoor experimental study on the tensile–shear mechanical properties of 2G-NPR bolt is carried out to explore its mechanical properties under diferent tensile–shear angles, and the fracture criterion of 2G-NPR bolt considering the tensile–shear angle is established. Then, a three-dimensional numerical simulation method considering the tensile–shear mechanical constitutive and fracture criterion of 2G-NPR bolt, the elastoplastic mechanical behavior of surrounding rock and the damage and deterioration of grouting body is proposed. The feasibility and accuracy of the method are verifed by comparing with the indoor shear test results of 2G-NPR bolt anchorage joints. Finally, based on the numerical simulation results, the deformation and stress of the bolt, the distribution of the plastic zone of the rock mass, the stress distribution and the damage of the grouting body are analyzed in detail. The research results can provide a good reference value for the practical engineering application and shear mechanical performance analysis of 2G-NPR bolt.
基金Financial support from the National Natural Science Foundation of China(No.50978251)the National Government Building High-Level University Graduate Programs of the China Scholarship Council
文摘A Double Shear Model(DSM) was used in a numerical simulation on bolted rock joint shearing performance.An entire bolt deformed as the letter'U'under a shear load between two joints.Near the bolt-joint intersection,the bolt partly deformed as the letter'Z'.There were two critical points along the bolt:one was at the bolt-joint intersection with zero bending moment and the other at the maximum bending moment(plastic hinge) with zero shear stress.The blocks on two sides slid along the bolt as it deformed. A separation area was found between the two joint contact surfaces of the middle rock block and sided block.This area of separation was related to bolt diameter and external forces.We assume that this area is related to the work of external forces.Further research is needed.
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.
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.
文摘For up-to-date bolted joints, first of all in vehicles, high strength bolts of 10.9 or even 12.9 are used, which are preloaded up to 90% or even 100% of the yield strength. The primary aim of this high degree utilization is the weight reduction. For the analytic dimensioning of bolted joints, the VDI 2230 Richtlinien German standard [1] provides support. However, the analytic model can mostly consider the true structural characteristics only in a limited way. The analytic modeling is especially uncertain in case of multiple bolted joints when the load distribution among the bolts depends reasonably upon the elastic deformation of the participating elements in the joints over the geometry of the bolted joint. The first part of this paper deals with the problems of numerical modeling and stress analysis, respectively specifying the analytic dimensioning procedure by applying elastic or rather elastic-plastic material law. The error magnitude in bolted joint calculation was examined in case of omitting the existing threaded connection—between the bolt and the nut—in order to simplify the model. The second part of the paper deals with the dimensioning of stands and cantilevers’ multi-bolt fixing problems, first of all, with the load distribution among the bolts keeping in view the analysis of the local slipping relations. For demonstrating the above technique, an elaborated numeric procedure is presented for a four-bolted cantilever, having bolted joints pre-tightened to the yield strength.
文摘Numerical and experimental study was conducted to investigate the failure mode and strength performance of stiffened composite panel repaired by bolted joints under compressive load, and the results were then compared with those from virgin stiffened composite panel without any damage. A finite element analysis model was established for repaired and virgin stiffened composite panels under compressive load, the 3D Hashin criteria was applied to identify the composite structure failure, and the secondary stress criteria was adopted to identify the adhesive failure between the base laminate and the stiffener. The failure modes of repaired stiffened composite panels were stiffened composite panels breaking off along the bolt joints. The experimental results were consistent with the finite element analysis results, indicating the reliability of the finite element analysis model.
文摘For up-to-date bolted joints, first of all in vehicles, high strength bolts of 10.9 or even 12.9 are used, which are pre-tightened up to 90% or even 100% of the yield strength. The primary aim of this high degree utilization is the weight reduction. For the analytic dimensioning of bolted joints, the VDI 2230 Richtlinien German standard provides support. However, the analytic model can mostly consider the true structural characteristics only in a limited way. The analytic modeling is especially uncertain in case of multiple bolted joints when the load distribution among the bolts depends reasonably upon the elastic deformation of the participating elements in the joints over the geometry of the bolted joint. The first part of this paper deals with the problems of numerical modeling and stress analysis, respectively specifying the analytic dimensioning procedure by applying elastic or rather elastic-plastic material law. The error magnitude in bolted joint calculation was examined in case of omitting the existing threaded connection—between the bolt and the nut—in order to simplify the model. The second part of the paper deals with the dimensioning of stands and cantilevers’ multi-bolt fixing problems, first of all, with the load distribution among the bolts keeping in view the analysis of the local slipping relations. For demonstrating the above technique, an elaborated numeric procedure is presented for a four-bolted cantilever, having bolted joints pre-tightened to the yield strength.
文摘This paper studies the effects of fiber orientaion and holes position on stress concentration and the determination of weakened areas in the composite of glass fiber reinforced epoxy resin around the hole for joints by using the finite element method.In this study,for the observation of areas affected by stress concentration Tsai-Wu failure criterion is used to determine the failed elements and ANSYS Software is implemented for modeling.In order to compare the effect of geometric parameters on stress concentration around the holes,two types of hole position arrangement along with fibers orientation have been studied.Results show that the stress concentration coefficient is lower in the second type of holes arrangement in comparison with the first type for the same component dimensions.Increasing the distance from hole center to upper or lower edge of the sample and also decreasing the distance between holes,would result in an increase in the stress concentration.
基金co-supported by the National Commercial Aircraft Manufacturing Engineering Innovation Fund,China(No.COMAC-SFGS-2-22-1816)Shaanxi Province Key Research and Development Program Projects,China(No.2022GXLH-02025)Shaanxi Province 100 Scientific and Technological Achievements Transformation Action Projects,China(No.2021CGBX-11)。
文摘As the controlled research of Dynamic Installation(DI)and Static Installation(SI),a new interference installation method was developed based on electromagnetic loading to enhance the mechanical properties of composite structures.Four different interference-fit sizes were considered,ranging from a net fit to 2.0%.The experiments were conducted to evaluate the installation resistance and the mechanical behavior of the joint under external loads.Meanwhile,an FFA model to model the stress distribution and damage behavior of the bolt-hole contact interface was established.The load-displacement curve and damage modes of experiments were used to verify the FEA results.The results show that the installation resistance during DI process was remarkably lower than that of SI process corresponding to all interference-fit sizes,and the stress amplitudes induced by interference were larger and widely distributed.The damage of the hole wall was positively correlated with interference fit size,but DI can significantly reduce the damage compared to SI.In performance tests,DI enhanced the static bearing capacity and extended longer fatigue life of the joints than SI.DI methods can be an effective way to achieve highly reliable interference joints in composite structures.
文摘Since most current seismic capacity evaluations of reinforced concrete (RC) frame structures are implemented by either static pushover analysis (PA) or dynamic time history analysis, with diverse settings of the plastic hinges (PHs) on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints (BCJs) during major earthquakes is commonly neglected. This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. To verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements. By considering shear failure at BCJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.
基金the financial support of the National Natural Science Foundation of China(Grant nos.51679246)。
文摘In order to study the influence of the bolt joint mode on low-velocity projectiles penetrating the composite protective structure,two bolt joint models which connect the composite target to the fixed frame were designed,the ballistic test of the bolted composite protective structure with limited span was carried out,and the bearing and failure characteristics of the bolted region,as well as the energy dissipation of each part of the structure,were analyzed.The results show that in the condition of lowvelocity impact,there are three failure modes for the bolted composite protective structure subjected to projectile penetration,including failure of the impact point of the composite target,failure of protective structure connecting components and failure of the holes in the bolted region of the composite target;the failure mode of bolt holes in the bolted region has a great influence on the protection performance,and the allowable value of the bearing capacity of the bolted region depends on the sum of the minimum failure load in the failure modes and the friction force;shear-out failure occurring in the bolt holes in the bolted region exerts the greatest effect on ballistic performance,which should be avoided;When simultaneous failure occurs in the bolted region and the free deformation region of the composite protective structure,the energy absorption per unit surface density of the composite protective structure reaches the maximum,which can give full play to its anti-penetration efficiency.
基金Supported by National Nature Science Foundation of China(50304012)the "973" Program of China(2002CB412701)
文摘Presented a new analytical model for studying the shear-tensile large deforma-tion behavior near the vicinity of joint interface for bolted rough discontinuous rock, and presented the formulation estimating global shear strength for bolted joints under shear-ing-tensile loads. The analytical strength curves of bolts contribution on reinforced discon-tinuous rocks as the function of joint displacements or deformation angle of a bolt at rock joints was obtained. Based on Barton’s equation on JRC roughness profiles, the theoreti-cal shearing strength of bolted rough joints was also established. Test results on bolted granite and marble specimen confirm the validity of the analytical approach.
文摘In order to obtain the optimal parameters of anchor bolt supporting system for large-span and jointed rock mass in Kaiyang Phosphor Mine, it is expensive and unavailable with the method of in-situ experiments. This paper describes a numerical modeling with discrete element method for the supporting effects of different type of anchor bolts. The anchor bolts with variant length of 0.5m, 0.8m, 1.0m, diameter of 10mm, 15mm, 20mm, setting spacing of 3.0m, 2.5m, 2.0m, and setting angle of 10°, 20°, 30°, are simulated respectively. The results show that there exist optimal parameters of anchor bolt support for large-span and jointed rock mass. For the bolt support of the concerning, the optimal length is 2.53.5m, the diameter is 2535mm, the spacing is 0.50.6m, and the setting angle is 105°.
文摘A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is located in the core joint region and the connections between concrete members. This paper presents an experimental study of a series of PPSRC specimens. These specimens are tested under low cyclic loading.Experimental results demonstrate that the bearing capacity of the PPSRC specimens is 3 times that of the ordinary reinforced concrete( RC) beam-column joints. The strength and stiffness degradation rates are slower compared with that of the RC beam-column joints. In addition,the strength of the core joint region and the connections is higher than other parts of the PPSRC specimens. Beam failure occurs firstly for the PPSRC specimens,followed by column failure and connections failure. The failure of the core joint region occurs finally.Test results show that the seismic performance of the PPSRC is better than that of the ordinary RC beam-column joints.