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.

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.

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.

Effect of Interference Fits on the Fatigue Lives of Bolted Composite Joints

The effect of interference fits on the fatigue lives of bolted composite joints is investigated by conducting mechanical tests.Static and fatigue tests are carried out on specimens made of carbon-bismaleimide composites joined together as double-lap single-bolt joints.The bolts having interference fits ranging of 0(neat fit),0.5%,0.75% and 1% are performed.The results demonstrate the relationship between fatigue life and different values of interference fits.After the fatigue tests,non-destructive evaluation(NDE) and scanning electron microscope(SEM) are used to observe the damage of the surrender and surface of the hole.The test results show that the interference fitted specimens have improved fatigue life compared to the neat fitted specimen.The NDE and SEM results reveal that the damage degree of interference fitted specimen is weaker than that for the neat fitted one.

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.

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.

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.

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.

Research review on steel–concrete composite joint of railway hybrid girder cable-stayed bridges

Purpose–This study aims to research the development trend,research status,research results and existing problems of the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge.Design/methodology/approach–Based on the investigation and analysis of the development history,structure form,structural parameters,stress characteristics,shear connector stress state,force transmission mechanism,and fatigue performance,aiming at the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge,the development trend,research status,research results and existing problems are expounded.Findings–The shear-compression composite joint has become the main form in practice,featuring shortened length and simplified structure.The length of composite joints between 1.5 and 3.0 m has no significant effect on the stress and force transmission laws of the main girder.The reasonable thickness of the bearing plate is 40–70 mm.The calculation theory and simplified calculation formula of the overall bearing capacity,the nonuniformity and distribution laws of the shear connector,the force transferring ratio of steel and concrete components,the fatigue failure mechanism and structural parameters effects are the focus of the research study.Originality/value–This study puts forward some suggestions and prospects for the structural design and theoretical research of the steel–concrete composite joint of railway long-span hybrid girder cable-stayed bridge.

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.

Investigation of stress distribution and damage behavior caused by forced installation of a composite bolted joint with a hole-location error

In this paper,the influence of forced installation caused by a hole-location error on the 3D stress distribution and damage of a composite bolted joint is investigated.An analytical model of stress distributed on composite holes is promoted,in view of non-uniform extrusion caused by forced installation.At first,non-uniform extrusion of the hole edge caused by forced installation is analyzed.According to the contact state,expression of hole deformation is given.Then,based on Hertz theory,the maximum extrusion load is obtained with help of deformation expression.By constructing an elastic foundation beam model,3D stress distributed on a hole could be analyzed according to the extrusion load.Then,stress distribution predicted by the above analytical method is compared with that provided by FE considering composite damage.Finally,a forced installation experiment is carried out to analyze the damage distribution of the joint.Results show that a central-symmetrically distributed stress is introduced by the hole-location error.With an increment of the error,strength of composite decreases due to extrusion damage.Therefore,stress presents a concave distribution on the hole.As the hole-location error exceeding 3%,stress decreases gradually due to failure of composite.Damage of holes does not exhibit a centrosymmetric distribution.Serious damage is mainly distributed on the entrance of the hole at the lower sheet.

Modeling on mechanical behavior and damage evolution of single-lap bolted composite interference-fit joints under thermal effects

This paper reports the modeling method and outcomes of mechanical performance and damage evolution of single-lap bolted composite interference-fit joints under extreme temperatures.The anisotropic continuum damage model involving thermal effects is established on continuum damage mechanics which integrates the shear nonlinearity constitutive relations characterized by Romberg-Osgood equation.The temperature-induced modification of thermal strains and material properties is incorporated in stress-strain analysis,extended 3 D failure criteria and exponential damage evolution rules.The proposed model is calibrated and employed to simulate behavior of composite joints in interference fitting,bolt preloading,thermal and bearing loading processes,during which the influence of interference-fit sizes,preload levels,laminate layups and service temperatures is thoroughly investigated.The predicated interfacial behavior,bearing response and failure modes are in good agreement with experimental tests.The numerical model is even capable of reflecting some non-intuitive experimental findings such as residual stress relaxation and matrix softening at elevated temperatures.

A novel virtual material layer model for predicting natural frequencies of composite bolted joints

A novel virtual material layer model based on the fractal theory was proposed to predict the natural frequencies of carbon fiber reinforced plastic composite bolted joints.Rough contact surfaces of composite bolted joints are modeled with this new proposed approach.Numerical and experimental modal analyses were conducted to validate the effectiveness of the proposed model.A good consistence is noted between the numerical and experimental results.To demonstrate the necessity of accurately modeling the rough contact surfaces in the prediction of natural frequencies,virtual material layer model was compared with the widely used traditional model based on the Master-Slave contact algorithm and experiments,respectively.Results show that the proposed model has a better agreement with experiments than the widely used traditional model(the prediction accuracy is raised by 8.77%when the pre-tightening torque is 0.5 N·m).Real contact area ratio A*of three different virtual material layers were calculated.Value of A*were discussed with dimensionless load P*,fractal dimension D and fractal roughness G.This work provides a new efficient way for accurately modeling the rough contact surfaces and predicting the natural frequencies of composite bolted joints,which can be used to help engineers in the dynamic design of composite materials.

Discontinuities effect on drilling condition and performance of selected rocks in Nigeria

The study examined joint discontinuity spacing effect on drilling condition and performance in selected rocks in llorin and Ibese areas, Nigeria. Five samples for each rock type （gneiss and limestone） were tested in the laboratory for chemical, physical and mechanical properties. Dip direction and joint spacing were measured using compass clinometers. The chemical composition was determined using X-ray Fluores- cence （XRF） spectrometer. The results show that gneiss has SiO2 of 61.88g and limestone has CaO content of 52.3g. The average dry density of gneiss and limestone are 2.6 and 2.39 g/cm^3, respectively. The uniaxial compressive strength of gneiss and limestone are 195 and 93.83 MPa, respectively. These rocks are classified as strong and moderately strong rock. Gneiss and limestone have mean joint discontinuity spacing of 0.79 and 0.25 m, which classified them as moderate and wide joint spacing respectively. Joint spacing was correlated with specific energy, bit wear and uniaxial compressive using Statistical Package for Social Science （SPSS）. The regression model has multiple coefficient of correlation of R^2 = 0.791 and R^2 =0.995 for gneiss and limestone, respectively. The variation in joint spacing could be attributed to spe- cific energy, bit wear and uniaxial compressive strength which affect drilling condition and performance. Ultimately, as joint spacing gets closer, the drilling velocity increases, drill string will be stable.

Effect of Bonding Temperature on the Microstructures and Strengths of C/C Composite/GH3044 Alloy Joints by Partial Transient Liquid-Phase(PTLP) Bonding with Multiple Interlayers

With the use of Ti/Ni/Cu/Ni multiple foils as interlayer,carbon/carbon（C/C） composite was bonded to Nibased superalloy GH3044 by partial transient liquid-phase bonding technique.The effect of bonding temperature on the microstructures and strengths of the joints was investigated.The results showed that gradient structural multiple interlayers composed of ‘‘C–Ti reaction layer/Ti–Ni intermetallic compound layer/Ni–Cu sosoloid/residual Cu layer/Ni-GH3044 diffusion layer＇＇ were formed between C/C composite and GH3044.The shear strength of the C/C composite/GH3044 joint reached the highest value of 26.1 MPa when the bonding temperature was 1,030 °C.In addition,the fracture morphology showed that the fracture mode changed with the increase of bonding temperature.

Laser welding process and strength enhancement of carbon fiber reinforced thermoplastic composites and metals dissimilar joint:A review

Carbon fiber reinforced thermoplastic composites(CFRTP)and metals hybrid structures have been widely used in aircraft lightweight manufacturing.However,due to the significant difference in physical and chemical properties between CFRTP and metals,there are lots of challenges to connect them with high quality.Laser welding has a good application prospect in CFRTP and metals connection,and a significant research progress has been made in the exploration of CFRTP-metal laser joining mechanism,joining process optimization,joining strength improvement and joining defects controlling.However,there are still some problems need to be solved for this technology application.In this paper,the research progress of CFRTP-metal laser joining was summarized in three major aspects:theoretical modeling and simulation analysis,process exploration and parameter optimization,joint performance improvement and process innovation.And,problems and challenges of this technology were discussed,and the outlook of this research was provided.

Joining of C_f/SiBCN composite with two Ni-based brazing fillers and interfacial reactions

G/SiBCN ceramic composite was joined using Ni-19Cr-10Si （BNi5） and Ni-33Cr-24Pd-3.5Si-0.5B filler alloys at 1170 ℃ for 10 min. Two kinds of Ni-based filler alloys exhibited good wettability on the CdSiBCN com- posite, with a contact angle of 13° and 4°, respectively, The microstructures of the brazed joints were investigated by electron-probe microanalysis （EPMA）, and three-point bend test was conducted for the joints at room temperature. When being brazed with BNi5 filler alloy, no evident reaction layer was ob- served at the surface of the joined composite, and the joint microstructure was characterized by Ni2Si matrix with scatteringly distributing mixture compounds of Cr23C6, Ni2Si and CrB. While Ni-Cr-Pd（Si,B） brazing alloy was used, a Cr23C6 reaction layer with a thickness of 11 μm was formed at the surface of the base composite. In the central part of the brazed joint, the phases were composed of Ni（Cr, Si） solid solution and complex compounds including Pd2Si, （Ni,Pd）2Si and Ni-B. The strength of Cf/SiBCN joint brazed with BNi5 filler alloy was 62.9 MPa at room temperature, whereas that with Ni-Cr-Pd（Si,B） filler alloy was at the same level.

Evaluation of tensile properties of a compositemetal joint with a novel metal insert design by experimental and numerical methods

Composite-metal joints with a metal insert are one kind of connecting structure.In this paper,tensile experimental tests were carried out to investigate tensile properties of a compositemetal joint with a novel metal insert design.Finite element models of the joint were established,and strain distribution and tensile strength were analyzed.The numerical results are in good agreement with the experimental results.Results show that the joint failure is dominated by shear properties of the resin layer.Increasing the resin layer thickness in a certain range will improve the tensile strength of the joint,while increasing the radius of the fillet on the ending side of the metal insert will decrease the joint strength.Increasing the resin layer plasticity will improve the joint strength.The effect of the embedded depth of the metal insert can be ignored.

INTERLAMINAR STRESSES OF A LAMINATED COMPOSITE LAP JOINT

The energy method has been successfully applied to solving interlaminar stresses of laminated composite lap joint with an adhesive layer of a certain thickness. This method has the merit of reckoning not only the stress component σ_y, in adherents but also the variation of stresses through the thickness of the adhesive layer. Thus we have the possibility to rectify some mistakes that have long frustrated the solution to joint problems. As all the series encountered can be summed, the solutions are, as usual, neat in closed forms. Furthermore, solutions can be confirmed by the load to be taken by the joint.