Current Issue : October - December Volume : 2015 Issue Number : 4 Articles : 6 Articles
Background: Self-piercing riveting (SPR) is a new performing technology able to joint several kinds of metal and\nnon-metal supports together. The combined effect of joint configuration and environmental conditions could have\ndetrimental effect on the ageing effect on mechanical behaviour of dissimilar metal SPR joints.\nMethods: The joining of dissimilar materials, such as steel and aluminium, realized by self-piercing riveting (SPR)\ntechnique was studied to evaluate the ageing effects on its mechanical behaviour in critical environmental conditions.\nThe investigation was carried out on symmetrical or unsymmetrical joints at varying total thicknesses (i.e. 2.0, 2.5 and\n3.0 mm). The joint resistance was determined by single-lap shear tests. A design of experiment (DoE) has\nbeen performed by using Minitab�® followed by the statistical analysis (ANOVA) of the experimental data.\nLong-term ageing tests in salt spray environment were performed to evaluate the durability of the mechanical joint.\nResults: The experimental results evidenced that the corrosion degradation phenomena influenced significantly both the\nperformance and failure mechanisms of the joints; also, the joint configuration is a significant factor for the corrosion\neffect. In the salt spray, the aluminium sheet undergoes a noticeable degradation due to galvanic Al/Fe corrosion. The set\ncharacterized by thinner aluminium sheet evidenced a gradual reduction of the mechanical strength with\nincreasing ageing time due to the prevalence of thinning induced by aluminium corrosion. Instead, for S10-A15 samples\n(characterized by a thicker thickness of aluminium sheet) during the first 7 weeks, stable mechanical performances were\nobserved.\nConclusions: The experimental results evidenced that the corrosion degradation phenomena influence significantly both\nperformances and failure mechanisms of SPR joints. Furthermore, the durability of the SPR joint is strongly affected by the\njoint configuration, and the best results were observed in the unsymmetrical joint with thicker aluminium sheet....
Background: The clinching is one of the most common metal joining processes in the manufacturing of metal plate\nbased products (similar or dissimilar, pre-coated or galvanized), especially when the assembly without adding major\njoining elements is required. When the clinched joints work in an aggressive environment, particular attention would be\nplaced on the electrochemical stability and corrosion resistance of the metal constituents (Mizukoshi and Okada 1997). In\njoining design, an appropriate material selection reduces the electrochemical potential differences and prevents\nsignificant galvanic currents (Kruger and Mandel 2011; Calabrese et al. 2014). The durability of the metal joints could be\nheavily influenced in a corrosive environment, whereas the less noble material will tend to increase its corrosion rate;\ninstead the more noble one will reduce its electrochemical dissolution (He et al. 2008; Bardal 2004). Accelerated ageing\ntests (i.e. salt fog test) were carried out to evaluate the durability of the joints in highly aggressive environments\n(Calabrese et al. 2013; LeBozec et al. 2012). Although the durability for a long time of the clinched joint in a corrosion\nenvironment is a known problem, few works focus the attention on the relationship between durability of joints and\nelectrochemical behaviour of the metal constituents. The aim of the present work is to evaluate the durability at long\nageing time in salt spray test (according to ASTM B117) of carbon steel/aluminium alloy joints, obtained by clinching.\nMethods: The investigation has been conducted on one total thickness (2.5 mm) of unsymmetrical joints (i.e. thickness\nsheets of 1.5 mm and 1 mm) to inquire about the effect of corrosion on the two different unsymmetrical configurations\n(St1.5/Al1 and St1/Al.5). The joint resistance has been determined, by means of shear tests of single-lap joints in\naccording to ISO/CD 12996. The samples were exposed to critical environmental conditions following the ASTM B 117\nstandard. To inquire the damage evolution of the samples, 0, 1, 2,3, 5, 7, 10 and 15 weeks of ageing time have been\nchosen. Seven samples for each combination and for each ageing time were realized. A Design of Experiment has been\nperformed, followed by the ANOVA of the results to analyse the influence of the two factors, thickness combinations\nand ageing time, on the mechanical properties of the joints.\nResults: The two sets of joints show a different behaviour at increasing ageing time: the St1.5/Al1 batch shows a\nconstant decay of the load values, instead the St1/Al1.5 set maintains acceptable values of resistance for several weeks\nof ageing, at tenth week the mechanical stability is strongly impaired. In the latter case the presence of the thin oxide\nlayer at the overlapping interface, which behaves as an adhesive interlayer, and the larger thickness of the aluminium\nplate improve the resistance of the St1/Al1.5 joints. Statistical analysis confirms that the two thickness combinations and\nageing time are the significant factors. At zero weeks, neglecting the effect of ageing, the maximum load values of all\nsamples belong to the same population. This means that the resistance of the clinched joints is the same regardless the\ncombination of thicknesses, but by considering both the ageing and thickness, the analysis of variance shows that both\nthickness and weeks are significant parameters distinguishing two different populations in the distribution of loads.\n(Continued on next page)...
The constitutive behavior and failure of ductile materials are described in the present work for a general case of\nloading in terms of the secant moduli, which depend on the first (dilatational) and second (deviatoric) strain\ninvariants. This approach exposes the distinct behavior of materials to the equivalent normal and shear stresses. The\nsecant moduli enable the establishment of two (instead of one) constitutive equations necessary for the complete\ndescription of these materials. Emphasis is given in the accuracy of the resulting constitutive equations in terms of\ntheir predictions relative to actual experimental data for two materials systems. Failure predictions, according to\nT-criterion, are derived for two materials under combined torsion and tension, which are in good agreement\nwith experimental data. Finally, the associated failure surfaces in a stress space are presented as well....
In this research work, experimental analyses have been done for helical tube type heat exchanger. For these analyses, helical concentric tubes have been designed and fabricated. This heat exchanger contains two tubes of 6.0 meters length which are helical in shape. And these dimensions have been checked on CAD Tool Cero Parametric 2.0. Two sets of concentric tubes have been fabricated with copper and mild steel tube materials. After fabrication effectiveness, entropy generation, exergy destruction, entransy dissipation and entransy dissipation-based thermal resistance have been evaluated. All these thermodynamic analyses have been completed at various working conditions. Finally bar charts have been generated for various working conditions which show performance of the heat exchangers. All analysis have been performed for counter and parallel flow heat exchanger....
Background: The structural integrity of welds carried out in underwater wet environment is very key to the\nreliability of welded structures in the offshore environment. The soundness of a weld can be predicted from the\nweld bead geometry.\nMethods: This paper illustrates the application of artificial neural network approach in the optimization of the\nwelding process parameter and the influence of the water environment. Neural network learning algorithm is the\nmethod used to control the welding current, voltage, contact tube-to-work distance, and speed so as to alter the\ninfluence of the water depth and water environment.\nResults: The result of this work gives a clear insight of achieving proper weld bead width (W), penetration (P), and\nreinforcement (R).\nConclusions: An interesting implication of this work is that it will lead to a robust welding activity so as to achieve\nsound welds for offshore construction industries....
Background: The effect of mixed size of recycled-copper-filled epoxy composites on mechanical, electrical, thermal\nand physical properties was investigated.\nMethods: The recycled copper was collected as a waste from the milling machine. The recycled copper-filled epoxy\ncomposite was mixed using a mechanical stirrer.\nResults: The effect of volume fraction of recycled copper of the epoxy composites were studied based on the\nflexural properties, coefficient of thermal analysis (CTE), electrical conductivity, hardness and density.\nConclusions: The incorporation of recycled copper has decreased the CTE of the composites. The flexural\nproperties, electrical conductivity, hardness and density of the composites increased with increasing volume\nfraction and filler loading....
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