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Experimental study of friction in aluminium bolted joints  [cached]
Croccolo D.,De Agostinis M.,Vincenzi N.
EPJ Web of Conferences , 2010, DOI: 10.1051/epjconf/20100608003
Abstract: This study aims at developing an experimental tool useful to define accurately the friction coefficients in bolted joints and, therefore, at relating precisely the tightening torque to the bolt preloading force in some special components used in front motorbike suspensions. The components under investigation are some clamped joints made of aluminium alloy. The preloading force is achieved by applying a torque wrench to the bolt head. Some specific specimens have been appropriately designed and realized in order to study the tribological aspects of the tightening phase. Experimental tests have been performed by applying the Design of Experiment (DOE) method in order to obtain a mathematical model for the friction coefficients. Three replicas of a full factorial DOE at two levels for each variable have been carried out. The levels include cast versus forged aluminium alloy, anodized versus spray-painted surface, lubricated versus unlubricated screw, and first tightening (fresh unspoiled surfaces) versus sixth tightening (spoiled surfaces). The study considers M8x1.25 8.8 galvanized screws.
Strength of aluminium resistance spot welded and weldbonded joints
Pereira,A.M.; Ferreira,J.A.M.; Antunes,F.V.; Bártolo,P.J.;
Ciência & Tecnologia dos Materiais , 2010,
Abstract: the increasing restrictions in terms of safety and energy consumptions imposed in the transport vehicles construction promotes the use of new materials and new processes searching weight reduction. lighter materials and better joining processes, like adhesive bonding can contribute to obtain some weight gain. present work studies the shear strength obtained with weldbonding technique and compares it with the traditional resistance spot welding. the single lap joints were obtained with thin plates of 6082-t6 alloy and a high strength epoxy adhesive of two components (araldite 420 a/b). the strength of weldbonded joints was found to be significantly higher than equivalent spot welded joints. numerical models were developed replicating experimental work. nugget diameter was found to have a major influence in stiffness and stress level, while thickness reduction showed a much lower influence. the adhesive reduced significantly the stress level at the nugget root.
Strength of aluminium resistance spot welded and weldbonded joints  [cached]
A.M. Pereira,J.A.M. Ferreira,F.V. Antunes,P.J. Bártolo
Ciência & Tecnologia dos Materiais , 2010,
Abstract: The increasing restrictions in terms of safety and energy consumptions imposed in the transport vehicles construction promotes the use of new materials and new processes searching weight reduction. Lighter materials and better joining processes, like adhesive bonding can contribute to obtain some weight gain. Present work studies the shear strength obtained with weldbonding technique and compares it with the traditional resistance spot welding. The single lap joints were obtained with thin plates of 6082-T6 alloy and a high strength epoxy adhesive of two components (araldite 420 A/B). The strength of weldbonded joints was found to be significantly higher than equivalent spot welded joints. Numerical models were developed replicating experimental work. Nugget diameter was found to have a major influence in stiffness and stress level, while thickness reduction showed a much lower influence. The adhesive reduced significantly the stress level at the nugget root. As crescentes restri es em termos de seguran a e consumo de energia impostas na constru o de veículos de transporte promove o uso de novos materiais e processos procurando reduzir o peso. Materiais mais leves e melhores processos de liga o, como as liga es adesivas, podem contribuir para obter algum ganho no peso. O presente trabalho estuda a resistência ao corte em juntas soldo-coladas e compara com a tradicional soldadura de resistência por pontos. As juntas de sobreposi o simples foram obtidas com placas finas de liga 6082-T6 e um adesivo epóxido de alta resistência de dois componentes (Araldite 420 A/B). A resistência das juntas soldo-coladas é significativamente mais elevada do que das juntas soldadas por resistência por pontos. Foram desenvolvidos modelos numéricos para reproduzir o trabalho experimental. Verificou-se que o diametro do ponto de soldadura tem uma grande influência na rigidez e resistência, enquanto que a indenta o do eléctrodo tem uma influência muito menor. O adesivo reduziu significativamente o nível de tens o na raiz do ponto de soldadura.
CFRP加固火灾后RC梁柱节点抗震性能试验
Experiment on seismic behavior of RC beam??column joints??after fire and strengthened with CFRP
 [PDF]

徐玉野,高伟,罗漪,胡杰
- , 2018,
Abstract: 为评估折线形粘贴碳纤维增强复合材料(CFRP)布加固火灾后钢筋混凝土梁柱节点抗震性能的效果,分别进行未受火、火灾后和CFRP布加固火灾后带正交梁和楼板翼缘的钢筋混凝土梁柱中节点抗震性能的拟静力试验。火灾试验时采用ISO 834标准升温曲线、梁柱节点的受火方式为楼板下方受火,拟静力试验时柱子的轴压比为0.25。基于试验结果,考察火灾高温后CFRP布加固对混凝土梁柱节点的破坏形态、滞回曲线、骨架曲线、承载力、延性、刚度及滞回耗能的影响。研究结果表明:梁柱节点核心区均发生了剪切破坏;未受火和受火后梁柱节点分别在3/100和??4/100??位移角时达到最大承载力,该位移角下节点核心区可见最大斜裂缝宽度分别达到??2.0??、??1.9 mm??;未受火梁柱节点和CFRP布加固后梁柱节点核心区箍筋发生屈服,90 min的火灾高温作用会显著降低梁柱节点的抗震性能,受火后梁柱节点的开裂荷载、屈服荷载、极限荷载和延性系数分别降低了41.3%、18.5%、15.8%和14.8%;节点区折线形粘贴CFRP布加固对受火后混凝土梁柱节点抗震性能的提高有限,加固后梁柱节点的承载力未能恢复至未受火时情况;CFRP布加固火灾后梁柱节点开裂荷载、屈服荷载和极限荷载分别比火灾后未加固梁柱节点提高了16.5%、4.0%和3.4%,比未受火梁柱节点的降低了31.6%、15.2%和12.9%。火灾后钢筋混凝土梁柱节点抗震加固方案及其设计方法还有待进一步深入研究。
This paper presents an experimental study of the seismic behavior of reinforced concrete (RC) beam column joints after fire and strengthening with fold??line CFRP sheets. Pseudo??static loading was applied to RC beam column joints with orthogonal beams and floor flanges. Experimental tests were conducted on three specimens: one with no fire, one subjected to fire, and one subjected to both fire and strengthening with CFRP sheets. The ISO 834 standard temperature rise curve was used for the fire test, and the part beneath the floor of the joint was subjected to fire. The axial compression ratio of the column was maintained at 0.25. The effects of high temperature (due to the fire) and CFRP strengthening on the failure mode, hysteretic curve, skeleton curve, load bearing capacity, ductility, stiffness, and hysteretic energy of the joints were investigated. The results show that shear failure occurred in the core area of each joint. The maximum bearing capacities of the joint without fire and the joint subjected to fire are achieved at the displacement angles of 3/100 and 4/100, respectively. The corresponding maximum widths of the inclined cracks are 2.0 and 1.9 mm, respectively, in the core area of the joints under the displacement angles. The stirrups in the core area of the joint which is not subjected to fire, and that of the joint after fire and with CFRP reinforcement are founded to have yielded. The seismic performance of the joint is significantly reduced after a fire lasting 90 min. Specifically, the cracking load, yield load, ultimate load, and ductility coefficient of the joint are reduced by ??41.3%??, ??18.5%??, ??15.8%??, and ??14.8%??, respectively. Furthermore, strengthening the joint that is subjected to fire with CFRP sheets provided only limited improvements in the seismic performance of the joint, and this strengthening could not restore the bearing capacity to the same level as that of the specimen that is not
Microstructure and properties of FSW joints of 2017A/6013 aluminium alloys sheets  [PDF]
K. Mroczka,J. Dutkiewicz,L. Lityńska-Dobrzyńska,A. Pietras
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: The aim of the studies was to analyse the structure and mechanical properties of FSW joints. Experiment were perform in order to study possibilities to join different aluminium alloys 2017A and 6013. The alloys differ one from the other with respect to chemical composition and mechanical properties especially, therefore the ability to perform the correct joints may be useful for special constructions.Design/methodology/approach: The joints were produced applying different parameters and temperatures. The microstructure was studied using optical, scanning electron and transmission electron microscopes. The mechanical properties are discussed with regard to microhardness profiles on the cross-sections of the joints.Findings: No cracks were found in the joints. Weld nuggets were formed in the 2017A alloy which was located on the advancing side during welding. Mixing process of the materials within the joints was observed as a formation of separate regions of the materials being joined. The hardness profiles showed sudden changes of hardness what correlates with structure observations. In the vicinity of the weld nugget higher dislocation density was observed. Lowering the temperature of sheets and welding with intensive cooling caused a decrease in size of the weld nugget.Research limitations/implications: In the further studies, tensile and bending tests are planned. Moreover, an attempt of explaining the influence of precipitates at the regions boundaries on the fracture process.Practical implications: Good quality of the joints can be stated on the basis of structure analysis. The chosen parameters of welding can be considered as proper ones.Originality/value: Comparison of the welding of the alloys2017A and 6013 are not common. The results of studies and conclusions presented in the paper are consecutive data complementing knowledge on FSW of the aluminium alloys. The applied welding parameters ensure good quality of joints with respect to the technology.
Effect of the Welding Parameters on the Structural and Mechanical Properties of Aluminium and Copper Sheet Joints by Electromagnetic Pulse Welding  [PDF]
Irene Kwee, Verena Psyk, Koen Faes
World Journal of Engineering and Technology (WJET) , 2016, DOI: 10.4236/wjet.2016.44053
Abstract: Aluminium-copper hybrid parts, as a substitution to copper parts, result in weight and cost reduction, and are relevant in applications related to the electronic, heating and cooling sector. However, aluminium to copper joined by thermal welding processes presents challenges in terms of achieving good joint quality. This is attributed to their dissimilar mechanical and thermal properties which result in large stress gradients during heating. This study investigated joining of aluminium to copper sheets by electromagnetic pulse welding, which is a solid-state process that uses electromagnetic forces for joining of dissimilar materials. Hybrid sheet welds were obtained for all parameters conditions, selected according to a Taguchi L18 design. The structural and mechanical characteristics were examined and related to the welding parameters by means of a Pareto analysis and response graphs. The welded zone started with a wavy interface with interfacial layers and defects and evolved to a flat interface without interfacial layers. The maximum transferable force depended on the minimum specimen thickness and the strength of the hybrid sheet weld. In case of aluminium sheet thickness reduction, the maximum transferable force was linearly correlated with the aluminium sheet thickness. High quality joints were obtained for no aluminium sheet thickness reduction and for a sheet weld strength which was at least as high as that of the base material. The most effective way to increase the transferable force was to lower the initial gap and to increase the free length, which resulted in no aluminium sheet thickness reduction. Alternatively, the use of a rounded spacer decreased the effect of the aluminium sheet thickness on the transferable force. An increase in weld width was achieved for an increase in capacitor charging energy and gap, whereas an increase in weld length was obtained for a decrease in gap. An increase in weld width did not necessarily result in an increase in the transferable force. In the regarded cases, a hybrid sheet with narrow weld width could therefore have higher quality.
Investigation of Repeated Low Velocity Impact Behaviour of GFRP /Aluminium and CFRP /Aluminium Laminates  [PDF]
G R Rajkumar,M Krishna,H N Narasimha Murthy,S C Sharma
International Journal of Soft Computing & Engineering , 2012,
Abstract: The objective of this research was to investigate esponse of repeated low velocity impact tests on glass fibre/ epoxy-Al metal laminates (GEAML) and carbon fibre/ epoxy-Al metal laminates (CEAML) at the same location using drop-weight tester. CEAML, GEAML as well as monolithic Al panels of the same thickness were impacted repeatedly up to four impacts. The effect of repeated impacts on specimen is studied on peak load, absorbed energy, decelerated velocity and impact time with respect to deflection at impactor load of 5.2 kg under gravity fall. The result shows the Al plates, GEAML and CEAML exhibit different behaviour for both loading bearing capacity and damage pattern. The maximum load bearing capacity is higher in case of monolithic aluminium but damage spread throughout the specimen, which contribute to the energy-absorbing capacity of these Al plates. In the case of GEAML and CEAML the damage is concentrated only at impact area hence lower energy-absorbing capacity
The Rivet Parameter Influence in Fatigue Strength
Ion Fuiorea , Daniela Bartis , Roxana Nedelcu , Adrian Mocanu
Fatigue of Aircraft Structures , 2009, DOI: 10.2478/v10164-010-0005-y
Abstract: The paper deals with the experimental analysis of the influence of the rivet parameters upon the fatigue strength of aircraft structures. Different riveted samples were tested on fatigue machine taking into account the diameter of the rivet and the forming pressure influence. By superposing the resulting W hler curves on the same graphic, some interesting conclusions were pointed.
EXPERIMENTAL INVESTIGATION ON REHABILITATION OF REINFORCED CEMENT CONCRETE INTERIOR BEAM-COLUMN JOINTS USING CFRP AND GFRP SHEETS
R.V.S.RAMAKRISHNA,V.RAVINDRA
International Journal of Engineering Science and Technology , 2012,
Abstract: This paper proposes a rapid rehabilitation scheme for moderately damaged reinforced concrete interior beam - column joints under the static loading. Eight interior beam - column joints were casted and designated as virgin specimens and tested up to failure . Out of eight specimens, four of the specimens were externally wrapped with glass fibre reinforced polymer sheets and other four specimens with carbon fibre reinforced polymer sheets. These rehabilitated specimens were tested up to failure. The performances of the rehabilitatedbeam-column joint specimens were compared with the virgin beam-column joint specimens. Experimental results illustrated that the rehabilitated specimens of glass fibre reinforced polymer and carbon fibre reinforced polymer beam-column joint specimens exhibited an improved load carrying capacity and a higher rate of stiffness than the virgin specimens.
Failure load prediction of adhesive joints under different stressstates over the service temperature range of automobiles  [PDF]
Qin Guofeng, Na Jingxin, Mu Wenlong, Tan Wei, Liu Haolei, Pu Leixin
- , 2018, DOI: 10.3969/j.issn.1003-7985.2018.04.014
Abstract: To predict the failure loads of adhesive joints under different stress states over the service temperature range of automobiles, adhesively bonded carbon fiber reinforced plastic(CFRP)/aluminum alloy joints under shear stress state(thick-adherend shear joints, TSJ), normal stress state(butt joints, BJ)and combined shear and normal stress states(scarf joints with scarf angle 45°, SJ45°)were manufactured and tested at -40, -20, 0, 20, 40, 60 and 80 ℃, respectively. The glass transition temperature Tg of the adhesive and CFRP, failure loads and fracture surfaces were used to analyze the failure mechanism of CFRP/aluminum alloy joints at different temperatures. A response surface, describing the variations of quadratic stress criteria with temperature, was established and introduced into the cohesive zone model(CZM)to carry out a simulation analysis. Results show that the failure of CFRP/aluminum alloy joints was determined collectively by the mechanical performances of adhesive and CFRP. Besides, reducing temperature or increasing the proportion of normal stress of adhesive layer was more likely to cause fibre tear or delamination of CFRP, resulting in a more obvious effect of CFRP. The validity of the prediction method was verified by the test of scarf joints with the scarf angle of 30°(SJ30°)and 60°(SJ60°)at -10 and 50 ℃.
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