Lap joints of TC1 Ti alloy and LF6 A1 alloy dissimilar materials were fabricated by friction stir welding and corresponding interface characteristics were investigated. Using the selected welding parameters, excellent...Lap joints of TC1 Ti alloy and LF6 A1 alloy dissimilar materials were fabricated by friction stir welding and corresponding interface characteristics were investigated. Using the selected welding parameters, excellent surface appearance forms, but the interface macrograph for each lap joint cross-section is different. With the increase of welding speed or the decrease of tool rotation rate, the amount of Ti alloy particles stirred into the stir zone by the force of tool pin decreases continuously. Moreover, the failure loads of the lap joints also decrease with increasing welding speed and the largest value is achieved at welding speed of 60 mm/min and tool rotation rate of 1500 r/min, where the interracial zone can be divided into 3 kinds of layers. The microhardness of the lap joint shows an uneven distribution and the maximum hardness of HV 502 is found in the middle of the stir zone.展开更多
Corrosion behavior of friction stir lap welded AA6061-T6 aluminum alloy was investigated by immersion tests in sodium chloride + hydrogen peroxide solution. Electrochemical measurement by cyclic potentiodynamic polari...Corrosion behavior of friction stir lap welded AA6061-T6 aluminum alloy was investigated by immersion tests in sodium chloride + hydrogen peroxide solution. Electrochemical measurement by cyclic potentiodynamic polarization, scanning electron microscopy, and energy dispersive spectroscopy were employed to characterize corrosion morphology and to realize corrosion mechanism of weld regions as opposed to the parent alloy. The microstructure and shear strength of welded joint were fully investigated. The results indicate that, compared with the parent alloy, the weld regions are susceptible to intergranular and pitting attacks in the test solution during immersion time. The obtained results of lap shear testing disclose that tensile shear strength of the welds is 128 MPa which is more than 60% of the strength of parent alloy in lap shear testing. Electrochemical results show that the protection potentials of the WNZ and HAZ regions are more negative than the pitting potential. This means that the WNZ and HAZ regions do not show more tendencies to pitting corrosion. Corrosion resistance of parent alloy is higher than that for the weldments, and the lowest corrosion resistance is related to the heat affected zone. The pitting attacks originate from the edge of intermetallic particles as the cathode compared with the Al matrix due to their high self-corrosion potential. It is supposed that by increasing intermetallic particle distributed throughout the matrix of weld regions, the galvanic corrosion couples are increased, and hence decrease the corrosion resistance of weld regions.展开更多
Friction stir lap joints of LY12 aluminum alloy plates with a thickness of 3 mm were fabricated using several tools with different pin profiles. The effects of tool pin profile on the interface migration of friction s...Friction stir lap joints of LY12 aluminum alloy plates with a thickness of 3 mm were fabricated using several tools with different pin profiles. The effects of tool pin profile on the interface migration of friction stir lap joints were investigated with the comparison of weld morphologies. The results show that the screw thread of the pin plays an important role in the migration of weld interface in the thickness direction. The interface between the sheets will move upwards to the top of the plate when the pin with left hand thread was used. Conversely, the interface will move downwards to the tip of the pin when the pin with right hand thread was used: As for a stir pin with smooth surface was used, the upward or downward migration of the weld interface was largely reduced, but the extension of weld interface to the weld center line from the retreating side becomes more serious. By analyzing the force on the pin according to the sucking-extruding theory for the weld formation, the obtained results have been well explained.展开更多
Penetration and non-penetration lap laser welding is the joining method for assembling side facade panels of railway passenger cars,while their fatigue performances and the difference between them are not completely u...Penetration and non-penetration lap laser welding is the joining method for assembling side facade panels of railway passenger cars,while their fatigue performances and the difference between them are not completely understood.In this study,the fatigue resistance and failure behavior of penetration 1.5+0.8-P and non-penetration 0.8+1.5-N laser welded lap joints prepared with 0.8 mm and 1.5 mm cold-rolled 301L plates were investigated.The weld beads showed a solidification microstructure of primary ferrite with good thermal cracking resistance,and their hardness was lower than that of the plates.The 1.5+0.8-P joint exhibited better fatigue resistance to low stress amplitudes,whereas the 0.8+1.5-N joint showed greater resistance to high stress amplitudes.The failure modes of 0.8+1.5-N and 1.5+0.8-P joints were 1.5 mm and 0.8 mm lower lap plate fracture,respectively,and the primary cracks were initiated at welding fusion lines on the lap surface.There were long plastic ribs on the penetration plate fracture,but not on the non-penetration plate fracture.The fatigue resistance stresses in the crack initiation area of the penetration and non-penetration plates calculated based on the mean fatigue limits are 408 MPa and 326 MPa,respectively,which can be used as reference stress for the fatigue design of the laser welded structures.The main reason for the difference in fatigue performance between the two laser welded joints was that the asymmetrical heating in the non-penetration plate thickness resulted in higher residual stress near the welding fusion line.展开更多
Dissimilar stir welding (FSW) lap joints were produced by friction out of Ti6A14V titanium alloy and AA2024 aluminum alloy sheets. The joints, welded with varying tool rotation and feed rate, were studied by ana- ly...Dissimilar stir welding (FSW) lap joints were produced by friction out of Ti6A14V titanium alloy and AA2024 aluminum alloy sheets. The joints, welded with varying tool rotation and feed rate, were studied by ana- lyzing the maximum shear strength, Vickers microhardness and optical observations. A dedicated numerical model, able to take into account the presence of the two different alloys, was used to highlight the effects of the process parameters on temperature distribution, strain distribution, and material flow. The combined analysis of experimental measurements and numerical predictions allowed explaining the effects of tool rotation and feed rate on the material flow. It was found that tool rotation had a larger impact on the joint effectiveness with respect to feed rate. A competition between material mixing and heat input occurs with increasing tool rotation, resulting in higher joint strength when lower values of tool rotation are used.展开更多
With the explosive growth of computational resources and data generation,deep machine learning has been successfully employed in various applications.One important and emerging scientific application of deep learning ...With the explosive growth of computational resources and data generation,deep machine learning has been successfully employed in various applications.One important and emerging scientific application of deep learning involves solving differential equations.Here,physics-informed neural networks(PINNs)are developed to solve the differential equations associated with a specific scientific problem.As such,algorithms for solving the differential equations by embedding their initial and boundary conditions in the cost function of the artificial neural networks using algorithmic differentiation must also be developed.In this study,various PINNs are adopted to estimate the stresses in the tablets and the interphase of a single lap joint.The proposed model is represented by two fourth-order non-homogeneous coupled partial differential equations,with the axial stresses in the upper and lower tablets adopted as the dependent variables.The axial stresses are a function of the tablet length,which presents the independent variable.Therefore,the axial stresses in the tablets are estimated by solving the coupled partial differential equations when subjected to the boundary conditions,whereas the remaining stress components are expressed in terms of axial stresses.The results obtained using the developed methodology are validated using the results obtained via MAPLE software.展开更多
The welding of aluminum(Al)and steel has attracted more and more interest due to the weight reduction trend in vehicle and aerospace manufacturing industries.5182-O/HC260YD+Z lap joint was produced by friction stir we...The welding of aluminum(Al)and steel has attracted more and more interest due to the weight reduction trend in vehicle and aerospace manufacturing industries.5182-O/HC260YD+Z lap joint was produced by friction stir welding(FSW),and the microstructure and mechanical property of the joint were systemically characterized.The microstructure in horizontal direction of the Al and steel near interface was similar to their corresponding conventional friction stir welded joint.The joint was divided into stir zone of Al(ST-Al),stir zone of interface(ST-I),thermal-mechanically affected zone of steel(TMAZ-Fe)and base material of steel(BM-Fe)according to their distinct microstructure vertically.Three kinds of intermetallic compounds(IMCs)of FeAl_(3),FeAl and Fe_(3)Al were formed at the interface.The horizontal micro hardness distribution exhibited a hat shape and“M”shape in Al and steel,respectively.The hardest region of the joint was located at the ST-I,with a hardness of 175 HV−210 HV.The joint was fractured along the hook structure,with an average shear strength of 73.9 MPa.Fractural morphology of Al and steel indicted a cleavage fracture mode.展开更多
The effect of through-thickness reinforcement by composite pins (Z-pins) on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite (CMC) is investigated. Overlap length...The effect of through-thickness reinforcement by composite pins (Z-pins) on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite (CMC) is investigated. Overlap length of the single lap joint is 15 mm, 20 mm, 23 mm, 37 mm, and 60 mm, respectively. The experimental results indicate that the final failure modes of the joints can be divided into two groups, (a) the bond-line stops debonding until crack encounters Z-pins; and then the adherends break at the location of Z-pins, when overlap length is more than 20 mm; (b) the bond-line detaches entirely and Z-pins are drawn from adherends, when overlap length is equal to 15 mm. A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints. Here, the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of complete failure mechanisms, for example, bond-line initial delamination and ultimate failure associated with Z-pin pullout, ultimate failure of the adherends. The paper simulates connecting performance of the single lap joints with different Z-pins' diameter, spacing and overlap length; the numerical results agree with the experimental results; the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints. By numerical analysis method, the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm, when Z-pins' diameter and spacing are 0.4 mm, 5 mm, respectively.展开更多
The joining of metal and polymer is an increasingly important method to get lightweight components in the development of manufacturing industry- nowadays. In this artiele, metal and polymer lap joint was achieved by m...The joining of metal and polymer is an increasingly important method to get lightweight components in the development of manufacturing industry- nowadays. In this artiele, metal and polymer lap joint was achieved by means of resistance spot welding (RSW) and ultrasonic assistance welding (UAW). The joining mechanism of lap joint was analyzed by OM, TEM on microstructure at the interface of lap joints and XPS and IR spectra was discussed based on the following different ones: mechanical-interlocking, diffusion bond and coordination bond. The results showed that it was the combined action that played an important role in the effective joining work. Besides, ultrasonic assistance was used in the study to aid welding process based on its high-frequency ultrasonic vibration, which made joints shaping better and improved tensile strength visibly contrast to joints with the same lower heat input parameters.展开更多
GMT-sheet is used in automobile bumper with high rigidity and strength, and its joining strength is influenced by lap length, one of the joined molding conditions. Fracture strength was calculated by dividing fracture...GMT-sheet is used in automobile bumper with high rigidity and strength, and its joining strength is influenced by lap length, one of the joined molding conditions. Fracture strength was calculated by dividing fracture load with cross-sectional area. Total five repeated measurements were made to obtain the average value. Tensile test was conducted at room temperature for 10 specimens. In addition, the effect of compression ratio on creep and tensile performance during lap joined molding was discussed. With increasing lap length, the lap joining efficiency of GMT-sheet was increased. However, higher compression ratio reduced the joining efficiency. Creep test on GMT-sheet showed abrupt fracture without tertiary creep. This can be explained by the weak thermal resistance of the resin. If GMT-sheet was exposed to high temperature for a long time, it was easily failed by external force.展开更多
In this paper, the closure-welded joint is studied through experiment after canceling telescopic joint of penstock in the hydropower station at dam toe. The closure-welded joint includes butt joint and lap joint and e...In this paper, the closure-welded joint is studied through experiment after canceling telescopic joint of penstock in the hydropower station at dam toe. The closure-welded joint includes butt joint and lap joint and each has its own characteristics. According to calculation and experiment, these two joints can meet the requirements of design. There are little axial contraction and low restraint stress in the lap joint. Using some technologies, the restraint stress in butt joint can be reduced and cracks can be prevented. The lap joint has more complex stress distribution and higher stress concentration factor than butt joint. It is advantageous for safe running of penstock to use butt joint.展开更多
Friction stir lap welds were produced in 3 mm thick Alclad sheets of Al alloy 2014-T4 using two different tools (with triangular and threaded taper cylindrical pins). The effects of tool geometry on weld microstruct...Friction stir lap welds were produced in 3 mm thick Alclad sheets of Al alloy 2014-T4 using two different tools (with triangular and threaded taper cylindrical pins). The effects of tool geometry on weld microstructure, lap-shear performance and failure mode were investigated. The pin profile was found to significantly influence the hook geometry, which in turn strongly influenced the joint strength and the failure mode. Welds produced in alloy 2014-T4 Alclad sheets by using triangular and threaded taper cylindrical tools exhibited an average lap-shear failure load of 16.5 and 19.5 kN, respectively, while the average failure load for standard riveted joints was only 3.4 kN. Welds produced in alloy 2014-T6 Alclad sheets and in alloy 2014-T4 bare sheets (i.e., no Alclad) were comparatively evaluated with those produced in alloy 2014-T4 Alclad sheets. While the welds made (with threaded taper cylindrical tool) in T6 and T4 conditions showed very similar lap-shear failure loads, the joint efficiency of the welds made in T6 condition (43%) was considerably lower (because of the higher base material strength) than those made in T4 condition (51%). The Alclad layers were found to present no special problems in friction stir lap welding. Welds made with triangular tool in alloy 2014-T4 Alclad and bare sheets showed very similar lap-shear failure loads. The present work provides some useful insights into the use of friction stir welding for joining Al alloys in lap configuration.展开更多
An easy-to-implement yet practical single-camera microscopic stereo-digital image correlation(stereo-DIC) technique is proposed for surface three-dimensional(3D) deformation measurement of singe lap joint(SLJ) samples...An easy-to-implement yet practical single-camera microscopic stereo-digital image correlation(stereo-DIC) technique is proposed for surface three-dimensional(3D) deformation measurement of singe lap joint(SLJ) samples subjected to mechanical loads. The basic principles, optical configurations and implementation procedures of the proposed technique are described in detail. Compared with existing single-camera 2D-DIC technique, which has been regularly used for in-plane deformation measurement of a SLJ specimen, the proposed technique offers the special merit of simultaneously determining all the three displacement components by simply adding two additional optical elements to existing single-camera 2D-DIC systems. The accuracy and effectiveness of the proposed technique is demonstrated by measuring the 3D deformation of a SLJ specimen subjected to quasi-static tensile loads.展开更多
Adhesive Single Lap Joints have been subjected to tensile and bending investigations by many researchers. However, the joint is also likely to experience buckling loading in some aerospace applications. The aim of thi...Adhesive Single Lap Joints have been subjected to tensile and bending investigations by many researchers. However, the joint is also likely to experience buckling loading in some aerospace applications. The aim of this work is to investigate the joint behaviour under quasi-static buckling conditions. For this purpose, the joints with three different adherend thicknesses and 25 mm overlap length were tested using two different types of adherends and an adhesive film. They were modelled using a non-linear Finite Element Method via the ABAQUS Explicit package programme.Load to failure and stress distributions in the joints were predicted and compared with the experimental results, which were found in a good agreement. The adhesive layer in the joint was assumed to experience shear stresses under the buckling mode, similar to that in tensile loading, yet, the stress concentrations at the ends of the overlap, the main cause of the failure, resulted in different effects on the joint performance;for the buckling mode the critical stresses were in compression but for the tensile case in peeling. Unlike the latter, the former was found to prevent failure of the layer depending on the adherend thickness, causing different failure mechanisms. There were two different failure modes of the joints;a complete failure in the adhesive layer and large plastic deformation of adherends which could be a good source for crashworthiness situations. Mechanical properties of the adherends were found to play important roles on the joint performance.展开更多
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 stre...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.展开更多
The shear modulus of the adhesive layer and the failure mode of adhesive structure on single lap joint specimens under tensile tests are investigated in this paper.The aluminum-aluminum adherends are bonded by two dif...The shear modulus of the adhesive layer and the failure mode of adhesive structure on single lap joint specimens under tensile tests are investigated in this paper.The aluminum-aluminum adherends are bonded by two different adhesives:polydimethylsiloxane (PDMS) and epoxy.The full deformation fields are measured using the digital image correlation (DIC) method with the images on the middle part of the adhesive layer recorded by a high resolution microscope.Then,the shear modulus values of the two adhesives are calculated with a simple pure shear strain model.A numerical model is proposed to simulate the single lap joint structure under tensile load in comparison with the experimental results.The results show that this method can successfully estimate the shear modulus of the adhesive layer.The failure behavior of epoxy adhesive/adherend interface is also analyzed and discussed.展开更多
基金Project (2011BAB206006) supported by the Natural Science Foundation of Jiangxi Province,ChinaProject (2009ZE56011) supported by the Aviation Science Funds of ChinaProject (GJJ12411) supported by the Education Department of Jiangxi Province,China
文摘Lap joints of TC1 Ti alloy and LF6 A1 alloy dissimilar materials were fabricated by friction stir welding and corresponding interface characteristics were investigated. Using the selected welding parameters, excellent surface appearance forms, but the interface macrograph for each lap joint cross-section is different. With the increase of welding speed or the decrease of tool rotation rate, the amount of Ti alloy particles stirred into the stir zone by the force of tool pin decreases continuously. Moreover, the failure loads of the lap joints also decrease with increasing welding speed and the largest value is achieved at welding speed of 60 mm/min and tool rotation rate of 1500 r/min, where the interracial zone can be divided into 3 kinds of layers. The microhardness of the lap joint shows an uneven distribution and the maximum hardness of HV 502 is found in the middle of the stir zone.
文摘Corrosion behavior of friction stir lap welded AA6061-T6 aluminum alloy was investigated by immersion tests in sodium chloride + hydrogen peroxide solution. Electrochemical measurement by cyclic potentiodynamic polarization, scanning electron microscopy, and energy dispersive spectroscopy were employed to characterize corrosion morphology and to realize corrosion mechanism of weld regions as opposed to the parent alloy. The microstructure and shear strength of welded joint were fully investigated. The results indicate that, compared with the parent alloy, the weld regions are susceptible to intergranular and pitting attacks in the test solution during immersion time. The obtained results of lap shear testing disclose that tensile shear strength of the welds is 128 MPa which is more than 60% of the strength of parent alloy in lap shear testing. Electrochemical results show that the protection potentials of the WNZ and HAZ regions are more negative than the pitting potential. This means that the WNZ and HAZ regions do not show more tendencies to pitting corrosion. Corrosion resistance of parent alloy is higher than that for the weldments, and the lowest corrosion resistance is related to the heat affected zone. The pitting attacks originate from the edge of intermetallic particles as the cathode compared with the Al matrix due to their high self-corrosion potential. It is supposed that by increasing intermetallic particle distributed throughout the matrix of weld regions, the galvanic corrosion couples are increased, and hence decrease the corrosion resistance of weld regions.
基金This work was sponsored by the National Natural Science Foundation of China (50875119 ) , the Aerospace Science Foundation of China (20081156009) and the Natural Science Foundation of Jiangxi Province, China (0450090).
文摘Friction stir lap joints of LY12 aluminum alloy plates with a thickness of 3 mm were fabricated using several tools with different pin profiles. The effects of tool pin profile on the interface migration of friction stir lap joints were investigated with the comparison of weld morphologies. The results show that the screw thread of the pin plays an important role in the migration of weld interface in the thickness direction. The interface between the sheets will move upwards to the top of the plate when the pin with left hand thread was used. Conversely, the interface will move downwards to the tip of the pin when the pin with right hand thread was used: As for a stir pin with smooth surface was used, the upward or downward migration of the weld interface was largely reduced, but the extension of weld interface to the weld center line from the retreating side becomes more serious. By analyzing the force on the pin according to the sucking-extruding theory for the weld formation, the obtained results have been well explained.
基金Supported by Scientific Research and Development Projects of China Railway Corporation(Grant No.2017J011-C).
文摘Penetration and non-penetration lap laser welding is the joining method for assembling side facade panels of railway passenger cars,while their fatigue performances and the difference between them are not completely understood.In this study,the fatigue resistance and failure behavior of penetration 1.5+0.8-P and non-penetration 0.8+1.5-N laser welded lap joints prepared with 0.8 mm and 1.5 mm cold-rolled 301L plates were investigated.The weld beads showed a solidification microstructure of primary ferrite with good thermal cracking resistance,and their hardness was lower than that of the plates.The 1.5+0.8-P joint exhibited better fatigue resistance to low stress amplitudes,whereas the 0.8+1.5-N joint showed greater resistance to high stress amplitudes.The failure modes of 0.8+1.5-N and 1.5+0.8-P joints were 1.5 mm and 0.8 mm lower lap plate fracture,respectively,and the primary cracks were initiated at welding fusion lines on the lap surface.There were long plastic ribs on the penetration plate fracture,but not on the non-penetration plate fracture.The fatigue resistance stresses in the crack initiation area of the penetration and non-penetration plates calculated based on the mean fatigue limits are 408 MPa and 326 MPa,respectively,which can be used as reference stress for the fatigue design of the laser welded structures.The main reason for the difference in fatigue performance between the two laser welded joints was that the asymmetrical heating in the non-penetration plate thickness resulted in higher residual stress near the welding fusion line.
文摘Dissimilar stir welding (FSW) lap joints were produced by friction out of Ti6A14V titanium alloy and AA2024 aluminum alloy sheets. The joints, welded with varying tool rotation and feed rate, were studied by ana- lyzing the maximum shear strength, Vickers microhardness and optical observations. A dedicated numerical model, able to take into account the presence of the two different alloys, was used to highlight the effects of the process parameters on temperature distribution, strain distribution, and material flow. The combined analysis of experimental measurements and numerical predictions allowed explaining the effects of tool rotation and feed rate on the material flow. It was found that tool rotation had a larger impact on the joint effectiveness with respect to feed rate. A competition between material mixing and heat input occurs with increasing tool rotation, resulting in higher joint strength when lower values of tool rotation are used.
基金Project supported by the Science and Engineering Research Board(SERB),Department of Science and Technology(DST),India(No.SRG/2019/001581)。
文摘With the explosive growth of computational resources and data generation,deep machine learning has been successfully employed in various applications.One important and emerging scientific application of deep learning involves solving differential equations.Here,physics-informed neural networks(PINNs)are developed to solve the differential equations associated with a specific scientific problem.As such,algorithms for solving the differential equations by embedding their initial and boundary conditions in the cost function of the artificial neural networks using algorithmic differentiation must also be developed.In this study,various PINNs are adopted to estimate the stresses in the tablets and the interphase of a single lap joint.The proposed model is represented by two fourth-order non-homogeneous coupled partial differential equations,with the axial stresses in the upper and lower tablets adopted as the dependent variables.The axial stresses are a function of the tablet length,which presents the independent variable.Therefore,the axial stresses in the tablets are estimated by solving the coupled partial differential equations when subjected to the boundary conditions,whereas the remaining stress components are expressed in terms of axial stresses.The results obtained using the developed methodology are validated using the results obtained via MAPLE software.
文摘The welding of aluminum(Al)and steel has attracted more and more interest due to the weight reduction trend in vehicle and aerospace manufacturing industries.5182-O/HC260YD+Z lap joint was produced by friction stir welding(FSW),and the microstructure and mechanical property of the joint were systemically characterized.The microstructure in horizontal direction of the Al and steel near interface was similar to their corresponding conventional friction stir welded joint.The joint was divided into stir zone of Al(ST-Al),stir zone of interface(ST-I),thermal-mechanically affected zone of steel(TMAZ-Fe)and base material of steel(BM-Fe)according to their distinct microstructure vertically.Three kinds of intermetallic compounds(IMCs)of FeAl_(3),FeAl and Fe_(3)Al were formed at the interface.The horizontal micro hardness distribution exhibited a hat shape and“M”shape in Al and steel,respectively.The hardest region of the joint was located at the ST-I,with a hardness of 175 HV−210 HV.The joint was fractured along the hook structure,with an average shear strength of 73.9 MPa.Fractural morphology of Al and steel indicted a cleavage fracture mode.
基金supported by the National Natural Science Foundation of China (No. 90405015)the Research Fund forthe Doctoral Program of Higher Education (No. 20030699040).
文摘The effect of through-thickness reinforcement by composite pins (Z-pins) on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite (CMC) is investigated. Overlap length of the single lap joint is 15 mm, 20 mm, 23 mm, 37 mm, and 60 mm, respectively. The experimental results indicate that the final failure modes of the joints can be divided into two groups, (a) the bond-line stops debonding until crack encounters Z-pins; and then the adherends break at the location of Z-pins, when overlap length is more than 20 mm; (b) the bond-line detaches entirely and Z-pins are drawn from adherends, when overlap length is equal to 15 mm. A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints. Here, the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of complete failure mechanisms, for example, bond-line initial delamination and ultimate failure associated with Z-pin pullout, ultimate failure of the adherends. The paper simulates connecting performance of the single lap joints with different Z-pins' diameter, spacing and overlap length; the numerical results agree with the experimental results; the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints. By numerical analysis method, the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm, when Z-pins' diameter and spacing are 0.4 mm, 5 mm, respectively.
文摘The joining of metal and polymer is an increasingly important method to get lightweight components in the development of manufacturing industry- nowadays. In this artiele, metal and polymer lap joint was achieved by means of resistance spot welding (RSW) and ultrasonic assistance welding (UAW). The joining mechanism of lap joint was analyzed by OM, TEM on microstructure at the interface of lap joints and XPS and IR spectra was discussed based on the following different ones: mechanical-interlocking, diffusion bond and coordination bond. The results showed that it was the combined action that played an important role in the effective joining work. Besides, ultrasonic assistance was used in the study to aid welding process based on its high-frequency ultrasonic vibration, which made joints shaping better and improved tensile strength visibly contrast to joints with the same lower heat input parameters.
文摘GMT-sheet is used in automobile bumper with high rigidity and strength, and its joining strength is influenced by lap length, one of the joined molding conditions. Fracture strength was calculated by dividing fracture load with cross-sectional area. Total five repeated measurements were made to obtain the average value. Tensile test was conducted at room temperature for 10 specimens. In addition, the effect of compression ratio on creep and tensile performance during lap joined molding was discussed. With increasing lap length, the lap joining efficiency of GMT-sheet was increased. However, higher compression ratio reduced the joining efficiency. Creep test on GMT-sheet showed abrupt fracture without tertiary creep. This can be explained by the weak thermal resistance of the resin. If GMT-sheet was exposed to high temperature for a long time, it was easily failed by external force.
文摘In this paper, the closure-welded joint is studied through experiment after canceling telescopic joint of penstock in the hydropower station at dam toe. The closure-welded joint includes butt joint and lap joint and each has its own characteristics. According to calculation and experiment, these two joints can meet the requirements of design. There are little axial contraction and low restraint stress in the lap joint. Using some technologies, the restraint stress in butt joint can be reduced and cracks can be prevented. The lap joint has more complex stress distribution and higher stress concentration factor than butt joint. It is advantageous for safe running of penstock to use butt joint.
基金the Indian Space Research Organization (ISRO) for providing financial support forcarrying out this work
文摘Friction stir lap welds were produced in 3 mm thick Alclad sheets of Al alloy 2014-T4 using two different tools (with triangular and threaded taper cylindrical pins). The effects of tool geometry on weld microstructure, lap-shear performance and failure mode were investigated. The pin profile was found to significantly influence the hook geometry, which in turn strongly influenced the joint strength and the failure mode. Welds produced in alloy 2014-T4 Alclad sheets by using triangular and threaded taper cylindrical tools exhibited an average lap-shear failure load of 16.5 and 19.5 kN, respectively, while the average failure load for standard riveted joints was only 3.4 kN. Welds produced in alloy 2014-T6 Alclad sheets and in alloy 2014-T4 bare sheets (i.e., no Alclad) were comparatively evaluated with those produced in alloy 2014-T4 Alclad sheets. While the welds made (with threaded taper cylindrical tool) in T6 and T4 conditions showed very similar lap-shear failure loads, the joint efficiency of the welds made in T6 condition (43%) was considerably lower (because of the higher base material strength) than those made in T4 condition (51%). The Alclad layers were found to present no special problems in friction stir lap welding. Welds made with triangular tool in alloy 2014-T4 Alclad and bare sheets showed very similar lap-shear failure loads. The present work provides some useful insights into the use of friction stir welding for joining Al alloys in lap configuration.
基金supported by the National Natural Science Foundation of China(Grant Nos.1127203211322220 and 11427802)+2 种基金the Program for New Century Excellent Talents in University(Grant No.NCET-12-0023)the Science Fund of State Key Laboratory of Automotive Safety and Energy(Grant No.KF14032)Beijing Nova Program(Grant No.xx2014B034)
文摘An easy-to-implement yet practical single-camera microscopic stereo-digital image correlation(stereo-DIC) technique is proposed for surface three-dimensional(3D) deformation measurement of singe lap joint(SLJ) samples subjected to mechanical loads. The basic principles, optical configurations and implementation procedures of the proposed technique are described in detail. Compared with existing single-camera 2D-DIC technique, which has been regularly used for in-plane deformation measurement of a SLJ specimen, the proposed technique offers the special merit of simultaneously determining all the three displacement components by simply adding two additional optical elements to existing single-camera 2D-DIC systems. The accuracy and effectiveness of the proposed technique is demonstrated by measuring the 3D deformation of a SLJ specimen subjected to quasi-static tensile loads.
文摘Adhesive Single Lap Joints have been subjected to tensile and bending investigations by many researchers. However, the joint is also likely to experience buckling loading in some aerospace applications. The aim of this work is to investigate the joint behaviour under quasi-static buckling conditions. For this purpose, the joints with three different adherend thicknesses and 25 mm overlap length were tested using two different types of adherends and an adhesive film. They were modelled using a non-linear Finite Element Method via the ABAQUS Explicit package programme.Load to failure and stress distributions in the joints were predicted and compared with the experimental results, which were found in a good agreement. The adhesive layer in the joint was assumed to experience shear stresses under the buckling mode, similar to that in tensile loading, yet, the stress concentrations at the ends of the overlap, the main cause of the failure, resulted in different effects on the joint performance;for the buckling mode the critical stresses were in compression but for the tensile case in peeling. Unlike the latter, the former was found to prevent failure of the layer depending on the adherend thickness, causing different failure mechanisms. There were two different failure modes of the joints;a complete failure in the adhesive layer and large plastic deformation of adherends which could be a good source for crashworthiness situations. Mechanical properties of the adherends were found to play important roles on the joint performance.
基金The project supported by the National Natural Science Foundation of China. The major part of this paper was reported at the International Conference of Composite Materials and Structures, June 10-13, 1986, Beijing.
文摘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.
基金support by the National Basic Research Program of China(Grant Nos. 2010CB631005 and 2011CB606105)the National Natural Science Foundation of China(Grant Nos. 10625209,10732080 and 90916010)+2 种基金China Postdoctoral Science Foundation(Grant No. 20090460335)Specialized Research Fund for the Doctoral Program of Higher Education(Grant No. 20090002110048)the opening funds from the State Key Laboratory of Explosion Science and Technology(Grant No. KFJJ10-18Y)
文摘The shear modulus of the adhesive layer and the failure mode of adhesive structure on single lap joint specimens under tensile tests are investigated in this paper.The aluminum-aluminum adherends are bonded by two different adhesives:polydimethylsiloxane (PDMS) and epoxy.The full deformation fields are measured using the digital image correlation (DIC) method with the images on the middle part of the adhesive layer recorded by a high resolution microscope.Then,the shear modulus values of the two adhesives are calculated with a simple pure shear strain model.A numerical model is proposed to simulate the single lap joint structure under tensile load in comparison with the experimental results.The results show that this method can successfully estimate the shear modulus of the adhesive layer.The failure behavior of epoxy adhesive/adherend interface is also analyzed and discussed.