No abstract

Fusion welding of dissimilar aluminum alloys is very challenging. In the present work, Al-Cu alloy AA2219-T87 was friction stir welded to Al-Mg alloy AA5083-H321. Weld microstructures, hardness, and tensile properties were evaluated in as-welded condition. Microstructural studies revealed that the nugget region was primarily composed of alloy 2219, which was placed on the advancing side. No significant mixing of the two base materials in the nugget region was observed. Hardness studies revealed that the lowest hardness in the weldment occurred in the heat-affected zone on alloy 5083 side, where tensile failure were observed to take place. Tensile tests indicated a joint efficiency of around 90%, which is substantially higher than what can be achieved with conventional fusion welding. Overall, the results show that satisfactory butt welds can be produced between AA2219-T87 and Al-Mg alloy AA5083-H321 sheets using friction stir welding.

In the recent past, the substantial structural strength, light weight and stiffness properties of polymer based composite materials find its application in aircraft and automotive structures at prodigious rate. Fibre glass Reinforced Plastic (FRP) composites are partially elastic and brittle. The present study evaluates the ballistic limit, energy absorbed and the damage area caused by different projectile nose shapes on the composite plates made of glass fibre and vinyl ester resin with the orientation of (0/90)s. The number of plies in the plates is varied to 4, 6 and 8 and thus lead to different thicknesses. The projectile nose geometry is varied (hemispherical, conical, truncated conical, ogival and truncated ogival) to have realistic effect on the impact. The influence of projectile nose shape over ballistic limit is found experimentally and compared with the analytical predictions by H. M. Wen [5,6]. The ballistic limit, perforation mechanism, energy absorption at ballistic limit and the damage area at ballistic limit velocity has been studied. The influence of thickness of the composite plate over the ballistic limit have also been discussed. It is found that the truncated conical nose shaped projectile resulted in highest ballistic limit and largest damage area dominated by delamination. Experimental results showed that the analytical method [5,6] could satisfactorily predict the ballistic limit.

Dynamic mechanical properties of cyanate modified epoxy/glass fiber composites are investigated under varied temperatures. The tensile strength increased with an increase in cyanate content (EP, 20EPCY, 40EPCY and 60EPCY) from 320 MPa to 401 MPa. The fracture toughness values also increased from 0.7671 kJ/m2, for neat epoxy resin to 0.9315 kJ/m2 for 60% cyanate ester modified epoxy system. Free vibration method is used to experimentally measure frequency response. Natural frequency of 20EPCY, 40EPCY and 60EPCY increase by 1.2 times, 1.5 times and 1.74 times respectively at 150°C when compared to neat EP system. The damping properties, in terms of the damping factor and dynamic tensile modulus are determined theoretically. The increase in tensile modulus of cyanate modified epoxy system with increase in cyanate loading is 3.8 GPa(EP) to 5.3 GPa(60EPCY) at 30°C and 2.75 GPa(EP) to 4.36 GPa(60EPCY) at 150°C. The neat epoxy system has a damping factor of 0.01326 and 0.01668 at 30°C and 150°C. The damping factors of 20EPCY, 40EPCY and 60EPCY systems at 150° C are found to increase by 1.1times, 1.2 times and 1.4 times respectively when compared with EP system.