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Today, the demand for joining dissimilar metals of aluminium and steel to reduce the vehicle weight in the automotive, aerospace and shipbuilding industries has witnessed a rapid growth. In the present study, 5083 aluminium alloy was joined to galvanized steel and plain carbon steel with 4043 and 4047 filler metals by using the welding-brazing hybrid method. The brittle intermetallic compound (IMCs) layer formed in the interface of steel-weld seam was found to have a significant influence on the joint strength. The results also indicated that increasing heat input enhanced the thickness of IMCs layer. The thickness of IMCs layers, as measured from microstructural images, was in a range of 2-6 μm. Further, the results obtained from microstructural observation showed that with equal weld heat input, the thickness of IMCs layer for the joint produced with 4047 filler metal was approximately half of that obtained for the joint produced with 4043 filler metal. The highest mechanical resistance (of about 170 MPa) was obtained for aluminum to galvanized steel joint with 4047 filler metal. Moreover, in this joint, the failures occurred in the welded seam and for aluminum to plain carbon steel joint, it was in the interface of steel‌-‌weld seam.‌ The results obtained by Energy dispersive x-ray spectrometry analysis of IMCs layer for aluminum to galvanized steel joint showed the presence of the FeAl3 intermetallic compound. This was confirmed by x-ray diffraction analysis of the fracture plane.

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In the case of presence of deep micro-cracks within the composite structures, they must be replaced. The self-healing phenomenon which is inspired from the biological systems such as vascular networks in plants or capillary networks in animals, is an appropriate strategy to control the defects and micro-cracks. In the present research, by taking accounts the advantages of self-healing concept, an attempt has been made to control the micro-cracks and damages which were created in composite structures. To do so, series of micro glass tubes were employed to provide a self-healing system. These micro-tubes were filled with epoxy resin/anhydride hardener as a healing agent. When the structure is subjected to loading conditions, some damages or micro-cracks are created. In this situation, the micro glass tubes will rupture and the healing agent flows in the damage area, leading to the elimination of the defects over a time span. The aim of this study is to find out the appropriate self-healing material volume fraction and healing time to obtain an efficient healing. For this purpose, glass micro-tubes containing various healing agent loadings of 0.75, 1.65 and 2.5 vol.% were incorporated in epoxy-carbon fibers composites and the tensile behavior of the specimens were assessed during different time span from defect creation. The highest tensile strength recovery of 89% was observed for the specimen with 1.65 vol.% healing agent. Also the results show presence of micro tube decrease the fracture strain and over the time span fracture strain recovered.

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The occurrence of damage is considered as an unavoidable fact in fibrous polymers. For this reason, the self-healing systems could extend the service life time of materials by implementing the concept of autonomous or induced repair. In the present study, a self-healing E-glass fibers/epoxy composite based on micro-vascular channels has been designed and fabricated. The specimens were fabricated via the hand lay-up route, while the fabrication of micro-vascular channels was conducted through the removing of solid preforms. Due to the lack of previous studies about the utilization of anhydride resin-hardener system with lower viscosity and also their controllable miscibility in comparison to the amine systems, in the present work, these materials were selected as healing agent for repairing the primary defects created in the structure. For this purpose, mico vascular channels containing two various parts of epoxy resin and anhydride hardener (2, 3.2, and 3.7 Vol.% with respect to the matrix part) were incorporated in the structure of composites. The flexural behavior of the specimens was assessed during the different time span (0, 4, 8 and 11 days) from the primary damage creation. After the defect creation in the structure, the healing agents present in the micro vascular channels are flow into the defects and after the combining with catalysis dispersed in the matrix, local polymerization process and restoring of properties are started. According to the obtained results in this research, the highest flexural strength recovery of 46% was observed for the specimen with 3.2% healing agent after 8 days.

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In this study, microstructure and mechanical properties of 7068 aluminum alloy matrix nanocomposite reinforced with 0.1, 0.3, 0.5, 0.7 and 1 wt.% graphene nano plates (GNPs) produced by stir casting and ultrasonic treatment have been investigated. Ultrasound device equipped with a cooling system with high power was used for mixing alloy and nanoparticles. Also the microstructure was investigated by scanning electron microscope. The microstructural studies revealed that GNPs addition reduces the grain size, but adding high GNPs content (1 wt.%) does not change the grain size considerably. Further investigations revealed that the addition of GNPs increases tensile strength. At high GNPs contents (1 wt.%), the presence of GNPs agglomerates on grain boundaries were found that causes decrease the tensile strength. The optimum amount of nanoparticles is 0.5 wt.% GNPs. The average ultimate tensile strength (UTS) of the specimens before and after extrusion processes increases from 212 MPa to 374 MPa. Adding of 0.5 wt.% GNPs and extrusion process make about 76% enhancement in tensile strength compared to that of unreinforced aluminum alloy.