Numerical Optimization by Finite Element Method of Stainless Steel/Glass-Epoxy Composite Bolted Joint under Tension and Compression

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 BigHeadR 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.

Evaluation of microstructure and mechanical properties of squeeze overcast Al7075-Cu composite joints

Al7075-Cu composite joints were prepared by the squeeze overcast process.The effects of melt temperature,die temperature,and squeeze pressure on hardness and ultimate tensile strength(UTS)of squeeze overcast Al7075-Cu composite joints were studied.The experimental results depict that squeeze pressure is the most significant process parameter affecting the hardness and UTS.The optimal values of UTS(48 MPa)and hardness(76 HRB)are achieved at a melt temperature of 800℃,a die temperature of 250℃,and a squeeze pressure of 90 MPa.Scanning electron microscopy(SEM)shows that fractured surfaces show flatfaced morphology at the optimal experimental condition.Energy-dispersive spectroscopy(EDS)analysis depicts that the atomic weight percentage of Zn decreases with an increase in melt temperature and squeeze pressure.The optimal mechanical properties of the Al7075-Cu overcast joint were achieved at the Al2Cu eutectic phase due to the large number of copper atoms that dispersed into the aluminum melt during the solidification process and the formation of strong intermetallic bonds.Gray relational analysis integrated with the Taguchi method was used to develop an optimal set of control variables for multi-response parametric optimization.Confirmatory tests were performed to validate the effectiveness of the employed technique.The manufacturing of squeeze overcast Al7075-Cu composite joints at optimal process parameters delivers a great indication to acknowledge a new method for foundry practitioners to manufacture materials with superior mechanical properties.

Progressive Failure Analysis of Composite/Aluminum Riveted Joints Subjected to Pull-Through Loading

Out-of-plane mechanical properties of the riveted joints restrict the performance of the wing box assembly of airplane.It is necessary to investigate the pull-through performance of the composite/metal riveted joints in order to guide the riveting design and ensure the safety of the wing box assembly.The progressive failure mechanism of composite/aluminum riveted joint subjected to pull-through loading was investigated by experiments and finite element method.A progressive damage model based on the Hashin-type criteria and zero-thickness cohesive zone method was developed by VUMAT subroutine,which was validated by both open-hole tensile test and three-point bending test.Predicted load-displacement response,failure modes and damage propagation were analysed and compared with the results of the pull-through tests.There are 4 obvious characteristic stages on the load-displacement curve of the pull-through test and that of the finite element model:first load take-up stage,damage stage,second load take-up stage and failure stage.Relative error of stiffness,first load peak and second load peak between finite element method and experiments were 8.1%,-3.3%and 10.6%,respectively.It was found that the specimen was mainly broken by rivet-penetration fracture and delamination of plies of the composite laminate.And the material within the scope of the rivet head is more dangerous with more serious tensile damages than other regions,especially for 90°plies.This study proposes a numerical method for damage prediction and reveals the progressive failure mechanism of the hybrid material riveted joints subjected to the pull-through loading.

Mechanical characteristic and failure mechanism of joint with composite sucker rod

Composite sucker rods are widely used in oil fields because of light weight,high strength,and corrosion resistance.Bonded technology becomes the primary connection method of composites.However,the joints with composite sucker rods are prone to debone and fracture.The connected characteristics are less considered,so the failure mechanism of the joint is still unclear.Based on the cohesive zone model(CZM)and the Johnson-Cook constitutive model,a novel full-scale numerical model of the joint with composite sucker rod was established,and verified by pull-out experiments.The mechanical properties and slip characteristics of the joint were studied,and the damaged procession of the joint was explored.The results showed that:a)the numerical model was in good agreement with the experimental results,and the error is within 5%;b)the von Mises stress,shear stress,and interface stress distributed symmetrically along the circumferential path increased gradually from the fixed end to the loading end;c)the first-bonded interface near the loading end was damaged at first,followed by debonding of the second-bonded interface,leading to the complete shear fracture of the epoxy,and resulted in the debonding of the joint with composite sucker rod,which can provide a theoretical basis for the structural design and optimization of the joint.

Theoretical study and numerical simulation of the stress fields of the Al_2O_3 joints brazed with composite filler materials

Non-linear finite element code MSC. Marc was utilized to analysis the field of stress of the Al2O3 joints brazed with composite filler materials. The properties of the filler materials were defined by using the mixing law, method of Mori-Tanaka and theory of Eshelby to ensure the accuracy and reliability of results of finite element method （FEM）. The results show stress in brazed beam is higher than that in base material. The maximal stress can be found in the interface of joint. And the experimental results show that the shear strength of joints increases from 93.75 MPa （ Al2O3p Ovol. % ） to 135.32 MPa （ Al2O3p 15vol. % ） when composition of titanium is 3wt% in the filler metal.

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber Reinforced Epoxy Resin Composite Joints

To determinate the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints, energy dispersive X-ray spectroscopy analysis（EDX） is used to establish the content change of oxy- gen in the adhesive in adhesive/carbon fther reinforced epoxy resin composite joints. As water is made up of oxygen and hydrogen, the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging, via EDX analy-sis. The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of beth energy dispersive X-ray spectroscopy and elemental analysis. The de- termined results with EDX analysis are almost the same as those determined with elemental analysis and the results al- so show that the durability of the adhesive/carbon fther reinforced epoxy resin composite joints subjected to silane cou- pling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treat- ment.

Diffusion bonding mechanism and microstructure ofwelded joint of aluminium matrix composite Al_2O_(3p),/6061

Relationships between microstructures of welded joint and welding parameters or weld strength of aluminium matrix composite Al2O3p/6061 subjected to diffusion welding were studied. The results are as follows: key factor affecting strength of welded joint is oxide in the weld zone. The existence of oxide in the welded joint not only hinders the diffusion of the matrix atoms, but also destroys the good interface between the matrix and the reinforced phase. The oxides turn into fine particles from film with increasing welding temperature, and the destroying effect on welded joint decreases, which increases the strength of the welded joint. On the basis of this, the diffusion welding of aluminium matrix composite Al2O3p/6061 was successfully realized.

Using Walsh-m Composite Sequence and LDPC-QPSK Joint Iteration to Reduce ISI in Long-range Underwater Acoustic Systems

To reduce inter-symbol-interference (ISI) in underwater acoustic (UWA) communication systems, a method based on LDPC-QPSK joint iteration and Walsh-m composite sequence is proposed in this paper. The method is intended for use in long-range and low signal-to-noise ratio (SNR) UWA communications. At the transmitter, Walsh-m composite sequence is introduced to resist multipath effect. At the receiver, a soft-input soft-output (SISO) module is implemented in a joint iterative process between QPSK demodulator and LDPC decoder. This method is demonstrated in three types of UWA channel models: positive, negative and invariable sound velocity gradients channels. It is shown that through contrastive simulation experiments, this method is more efficient than conventional methods based on independent decoding and demodulation. After two rounds of joint iteration, the proposed method can obtain 2.5 dB over conventional method at BER of 10-5. Numerical results verify that the proposed method is a good candidate for long-range underwater acoustic communication systems.

Experimental and numerical investigation of a composite structure with frame and skin

A composite structure with frame and skin based on cabin structure in a large space telescope is studied in this paper.The frame is composed of longitudinal and transverse beams with hybrid bonded/bolted joints,and the skin is connected to the frame by bolts.Tensile tests are conducted on the structure by a set of test stand.It is observed that residual deformation occurs in the first test of the structure,which is attributed to the relative sliding between the skin and frame because of bolt-hole clearances.The high tightening torque and the increased number of the skin-frame bolts contribute to the high stiffness of the structure.A finite element model(FEM)of this composite structure is established,and the simulation model is verified by the experimental results.The FEM is contrastively analyzed with different frame joints,and it is found that adhesive joining in the hybrid bonded/bolted joints enhances the stiffness of the structure significantly.Given that adhesive plays a leading role in the stiffness of the hybrid joints,Tie contact in FEM is proposed to simulate bonded or hybrid joints when studying the stiffness performance of undamaged structure.

Damage Failure Analysis of Z-Pins Reinforced Composite Adhesively Bonded Single-Lap Joint

In order to study themechanical properties of Z-pins reinforced laminated composite single-lap adhesively bonded joint under un-directional static tensile load,damage failure analysis of the joint was carried out bymeans of test and numerical simulation.The failure mode and mechanism of the joint were analyzed by tensile failure experiments.According to the experimental results,the joint exhibits mixed failure,and the ultimate failure is Z-pins pulling out of the adherend.In order to study the failure mechanism of the joint,the finite element method is used to predict the failure strength.The numerical results are in good agreement with the experimental results,and the error is 6.0%,which proves the validity of the numerical model.Through progressive damage failure analysis,it is found that matrix tensile failure of laminate at the edge of Z-pins occurs first,then adhesive layer failure-proceeds at the edge of Z-pins,and finally matrix-fiber shear failure of the laminate takes place.With the increase of load,the matrix-fiber shear failure expands gradually in the X direction,and at the same time,the matrix tensile failure at the hole edge gradually extends in different directions,which is consistent with the experimental results.

Bearing Failure Optimization of Composite Double-Lap Bolted Joints Based on a Three-Step Strategy Marked By Feasible Region Reduction and Model Decoupling

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.

Bolt Design of Ceramic Matrix Composite and Superalloy Bolted Joint Based on Damage Failure Load

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.

Experimental and Numerical Study on Mechanical Properties of Z-pins Reinforced Composites Adhesively Bonded Single-Lap Joints

The mechanical properties of Z-pins reinforced composites adhesively bonded single-lap joints(SLJs)under un-directional tension loading are investigated by experimental and numerical methods.Three kinds of joint configurations,including SLJs with three/two rows of Z-pins and“I”array of Z-pins,are investigated by tension test.The failure modes and mechanism of reinforced joints with different Z-pins numbers and alignment are analyzed,and the comparison is performed for the failure strengths of no Z-pins and Z-pins reinforced joints.According to experimental results,failure modes of three kinds of joints are all mixed failure.It turns out that the Z-pins are pulled out ultimately.The strength of joints of more Z-pins at the end of the overlap area is relatively bigger for the joint of the same Z-pins numbers.The strength of joints with Z-pins compared with non Z-pins joints is growing at 16%.Finally,the three-dimensional distribution of interfacial stress in the lap zone of three kinds of Z-pins reinforced joints is simulated,and the numerical results are in good agreement with the experimental results.It is effective that the numerical calculation of stress analysis is verified.

Model Investigation on Composite Failure Prediction of π-Joint Structures

This paper was concerned with the tensile mechanics behavior of the composite π-joint under static tensile loading. The numerical strength analysis methodology was presented containing the basis assumption for the analysis, the material modeling, and the selected element type. It was assumed that the composite ply had transverse isotropic material properties and the adhesive had linear elastic properties. With the goal of the strength analysis to determine the onset of the damage initiation and the ultimate failure load, two stiffness degradation models were discussed and a modified maximum stress failure criteria was presented. To verify the numerical model, a pull-off test scheme was performed and the experimental data of five specimens were given. The experimental results indicate that the damage initiation location and the failure load were consistent with numerical predictions and verified the feasibility of the numerical model.

Effects of interface slip and semi-rigid joint on elastic seismic response of steel-concrete composite frames

The stiffness matrix of semi-rigidly connected composite beams considering interface slip was established and the calculation method for elastic seismic response of composite frame was derived.The corresponding calculation programs were developed.Introducing the dimensionless quantities that were related to the connector shearing stiffness and the joint rotation stiffness,the influences of interface slip and semi-rigid joint on composite frame were transferred to quantitative parameter analysis,taking account of cross sectional properties,materials and linear stiffness of composite beam synthetically.Based on the calculation programs,free vibration frequencies and seismic responses of semi-rigid joint steel-concrete composite frame considering interface slip were calculated.The influences of interface slip and semi rigid joint on dynamic characteristics and seismic response were analyzed and the seismic design advices were presented.The results show that the interface slip decreases the free vibration frequencies and increase the seismic responses of composite frame.The semi-rigid joint reduces the free vibration frequencies and increases seismic responses of composite frame compared with rigid joint.With the increase of joint rotational stiffness,the elastic seismic responses of composite frame increase firstly and then decrease.The effects are related to the ratio of joint rotation stiffness to linear stiffness of composite beam.

INTERFACIAL REACTION BEHAVIOUR AND JOINT STRENGTH OF TiC_p/Si_3N_4 COMPOSITE BONDED WITH Al FOIL

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Behaviour of a Moment Resisting Composite Steel and Concrete Joint Under Alternate Loading

The authors show the results of a study conducted on a joint connecting a concrete column to a composite steel concrete floor,subjected to tension on the beams as a result of the decomposition of sagging bending moment.The beam to column connection is achieved by means of headed studs welded to the beam and embedded in the concrete cast.Five different configurations have been tested at failure and the results are compared to formulae proposed in literature.Different degrees of ductility,reliability and strength have been obtained varying geometry and reinforcement ratio on the joints tested.

The influence of temperature on creep behavior of Cu particle enhanced SnPb based composite soldered joints

Creep property of solder alloys is one of the important factors to affect the reliabdity of soldered joints in SMT （surface mount technology）. Particle-enhancement is a way to improve the properties of solder alloys and has caused much more attention than before. Temperatures applied to soldered joints are one of the primary factors of affecting creep properties of particle enhancement composite soldered joints. In this paper single shear lap creep specimens with a 1 mm^2 cross-sectional area were fabricated using Cu particle enhancement 63Sn37 Pb based composite soldered joints and 63Sn37 Pb eutectic soldered joints to examine the influence of temperature on creep behavior of soldered joints. Results indicated that the creep resistance of soldered joints of Cu particle enhancement 63Sn37Pb based composite soldered joint was generally superior to that of the conventional 63Sn37Pb soldered joint. At the same time, creep rupture life of the composite soldered joint was declined with increasing temperature and drop faster than that of the conventional 63Sn37 Pb eutectic soldered joint.

Static behavior of semi-rigid thin-walled steel-concrete composite beam-to-column joints with bolted partial-depth flush end plate:experimental study

A new type of semi-rigid thin-walled steel-concrete composite beam-to-column joint has been proposed in this paper.Five semi-rigid composite beam-to-column joint specimens subjected to hogging moments under monotonic loading were tested to study the static behavior of this new type of joint.The main variable parameters for the five joint specimens were the longitudinal reinforcement ratio and the joint type.The experimental results designated that the magnitude of extension of the longitudinal reinforcement is the most important factor that influenced the moment-rotation characteristic of the new type of joint.The concrete slabs could resist 3.8%-19.1% of the total shear load applied to the cross-sections near the beam-to-column connection.The edge stiffened elements,such as the flange of the lipped I-section thin-walled steel beam,were capable of having considerable inelastic deformation capacity although they had comparatively large width-to-thickness ratios.The shear failure of the concrete cantilever edge strip must be taken into account in practical design because it has significant influence on the anchorage of the longitudinal reinforcement in the new type of external joints.

Influence of Shim Layers on Progressive Failure of a Composite Componentin Composite-Aluminum Bolted Joint in Aerospace Structural Assembly

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.