Surendran Sankunny

Aluminium alloys provide many benefits and challenges for use in marine environment. Attention on lightweight hulls leads to power saving, better handling and easy transportation. The stiffness and mass of the structure or member is responsible for its natural vibration. The hull panels and stiffeners vibrate at different frequencies when their stiffness is reduced by formation of a crack or any structural problems. If there is a monitoring system on board and by using a sensor detecting the modified vibrations, the maintenance crew senses the spot where urgent repair is needed. Application of composite laminates is convenient in view of portability and simplicity in procedure such as hand lay-up. In this study, the edge-cracked aluminium plates were repaired with one-sided composite patches and their temperature were varied to both low and high temperature levels. Dynamic fracture toughness was determined using Charpy impact test. Three different types of materials were used for composite patching: GFRP (glass-fibre-reinforced plastic), CFRP (carbon-fibre-reinforced plastic) and Kevlar. For each temperature level, two lay-ups were used, viz. three layered and five layered. Aluminium specimens with edge cracks of two different lengths, keeping the width of the crack constant, were prepared. Impact tests were performed for the prepared specimens at different temperatures. The fracture toughness of aluminium strips reinforced with patches was determined and compared with the energy absorbed during the impact of the corresponding specimen without the patch. It was observed that the specimen with patches gave a higher fracture toughness value when compared with that without the patch; corresponding observation on aluminium has been made along with patch at these temperatures. The patch using Kevlar was found to be the best among the three composites. Followed by these experiments, simulations using FRANC 2D software were carried out for finding stress intensity factor at different crack lengths with and without patches. The research has a spin-off application in the selection of materials used for patching and hence in the maintenance of LPG (liquefied petroleum gas) and LNG (liquefied natural gas) storage tanks under cryogenic conditions. © 2013 Copyright Taylor and Francis Group, LLC.

Light-weight metals like aluminium are preferred to for building of high speed crafts, naval ships, superstructures of commercial ships and offshore platforms. In plate joining, the efficiency of joint is a measure of its impact resistance and structural-integrity. The plates welded together should function effectively against any external loads under emergencies. An ideal welded joint should possess superior weld strength with good impact resistance. Cold metal transfer (CMT) is a proven type of welding technique which is proposed for marine fabrications. Plates of aluminium alloys with grade AA5086-H111 and AA6061-T6 are welded together using a filler, AA4043. For the purpose of plate joining, parameters like current, voltage, arc length, shield gas pressure, etc. are varied to arrive at a continuous weld without any crack. In this study, welded thin plates are subjected to tensile test and thereafter impact loads are applied. The plates are subjected to impact loads in the range of sub-ordinance level velocities, feasibility of ordinance and ultra-ordinance can be scaled and compared. Thus, various ballistic loads are applied at the welded joints. Response and terminal ballistics limit are determined for thin plates of thickness 1.2 and 3 mm plates. This study consists of simulation in Abaqus software and experiments using a gun prepared in the laboratory. It was observed that, there was petaling in very thin plates and perforations by plugging for lower ballistic loads and thinner plates. The work gives new insights in the application of CMT in joining of plates of different metals with varied thickness values. The experimental results can be used as bench marks to compare results of simulations for thin plates. While experiments were done for thin plates, only computer simulation was done for thicker plate of 12 mm which is usually accepted for fabrication in industry.

It is well known that during the operating condition of any metallic structural system the dynamic crack growth speed is in the order of 1-2 km/s. Industrial finishes like coating which form the integral part of manufacturing is adopted to improve fracture toughness of metals. These coated samples coated with thin films are mechanically tested by Charpy V-notch impact tester for estimating dynamic fracture toughness. Coatings improve the wear and corrosion resistance of materials; they tend to reduce the strength of materials, because of the increased residual stresses due to the coating process. Defects cannot be precluded from these coated and treated components; strength of those components in the presence of these defects can be analyzed by fracture mechanics approach. An attempt has been made to analyze the effectiveness of coating methods like electroplating, PVD (Physical Vapour Deposition), coating thickness and the service temperature on the fracture behaviour of metals. Experiments have been carried out on EN8 steel and aluminium for different temperatures and the later samples were corroded for 2400 h and tested for corrosion resistance. The specimen preparation and experimentations were carried out according to the ASTM standard E-23. Finite element analysis was done by FRANC 2D (Fracture Analysis Code) for estimating the stress intensity factor at different crack lengths along with influence of temperature and corrosion. PVD coated samples of Al-N (aluminium nitride) and nano-crystalline layer of Ti-Al-N (titanium aluminium nitride) showed improved dynamic fracture toughness properties. The same set of samples showed decrease in stress intensity factors and excellent corrosion resistance compared to conventional Ni (nickel) and Cr (chromium) coated samples. Mechanical behaviour of selected metals under heat affected zone is of also discussed in this paper, the study aims at both coated and uncoated cases. Performances of metals in cryogenic condition are also paid attention in this paper. © 2013 Elsevier Ltd.