Surendran Sankunny

Composite materials are a superior class of material used in almost every field of engineering like construction, military, aerospace, ocean structures, communication, and various other high-performance applications owing to their high specific strength and modulus, increased design flexibility, desirable thermal expansion characteristics good resistance to fatigue and corrosion, and economic efficiency. However, their ply-by-ply nature makes them susceptible to delamination, which originates from the propagation of microcracks in the weak resin-rich layers. Many attempts have been made to address the lack of mechanical properties of this weak interlaminar region. A particularly promising approach involves the incorporation of nanofibers between the reinforcement layers as the composite is laid up. This work involves studying the property improvements in carbon fiber epoxy composite by interleaving electrospun polyacrylonitrile (PAN) nanofibers. Experimental testing involving Tensile, Izod, Charpy and high velocity impact tests showed improved material properties for the PAN nano-interleaved composite. These improvements achieved by nanofiber interleaving shows a greater potential in addressing major concerns for critical application of composite materials in future.

Container ships move at a higher speed compared to other merchant ship types. A fin attached to the ship hull proves to be more efficient in controlling the moving ship. However, such attachments on the naked hull attract additional problems such as slamming, requirement of continuous maintenance, etc. The main objective of this study is to find the influence of fin action at various angles of attack with the incoming flow and recommend the best possible fin position for the least resistance. While experiments were performed for different angles of attacks of the fin with respect to the flow, a reduction in resistance was observed for an Fn range of 0.13–0.26. The fin was fitted at the lowest possible location of the hull surface at the bow part of the ship. Experimental investigation was done using model tests in a towing tank to determine the resistance of a scaled down model and it was compared with computer simulation. The interaction of a bow fin fitted to a container ship with its own generated and encountering waves are discussed in this paper. It was observed that at certain angles of attack of the fins favourable resistance characteristics were observed. Modifications from the expected resistance due to fin effect are paid attention in this study. Various resistance values for different angles of attack of the fin were compared and an angle of attack of 5° is found to be the best.

The very purpose of attaching fins to the hull is to reduce the roll motions of a ship. Roll minimization is a requisite for various operations in the seas. The presence of fin system provides enhanced state of stabilization especially when the vessel is performing a fast maneuvering amidst rough environmental disturbance. The fins in turn are activated by electro-hydraulic mechanism based on the in-built intelligence as per control theory like proportional-integral-derivative (PID) or fuzzy logic. As per this paper, fin system is activated using PID control algorithm. A frigate-type warship is considered for the demonstration purpose. Nonlinear roll motions are controlled using active fins. Lift characteristics of the fins in hydrodynamic flow were studied using CFD package fluent. Good amount of reduction in roll amplitude is achieved from various simulations in random sea. The approach can be used for any irregular sea conditions. © 2006 Elsevier Ltd. All rights reserved.

This study proposes a procedure to determine the optimal design parameters and target reliability based on Life cycle cost (LCC) based analysis. An iterative design procedure is performed for different levels of reserve strength ratio (RSR), and LCC is calculated. A case study is carried out for installation of the bottom fixed jacket support structure for offshore wind turbines (OWT) system subjected to extreme loading condition. To determine the ultimate capacity of the structure, static pushover analysis is integrated with the proposed design methodology. An evolutionary based particle swarm algorithm is selected for the structural design optimization of offshore jackets. The RSR evaluated from pushover analysis assists to determine the probability of failure based on the first order reliability method (FORM). Based on a set of LCC values, which are the collective sum of capital expenditure (CAPEX), operational cost (OPEX), and risk cost (RISKEX), the optimal design is reached.

In the past, there were very serious casualties under the actions of extreme waves including loss of precious lives. There are cases like loss of M V Derbyshire (Faulkner, 2001) due to hatch cover failure in extreme weather conditions. Use of composite materials in marine fields as major or minor components off floating platforms is discussed in this paper. Application of composites on board ships reduces the self weight and lowers the position of vertical centre of gravity of the floating vessel. There are advantages in using composite structures in marine environment. A link-span fitted with a composite deck and the feasibilities of using composite for hatch covers of bulk carrier ship is described in this paper. In the case of bulk carriers, failure of hatch cover especially in the forward part of the vessel leads to flooding of the forward cargo compartment and occasionally results in fatal casualty. The foremost hatch cover and the next one within 25% length of the vessel © 2010 by ASME.

The prediction of ship stability during the early stages of design is very important from the point of safety. Ships experience six modes of rigid body motions in a seaway, which can be split into two groups as translatory and oscillatory motions. Out of the six motions of a ship, the critical motion leading to capsize of a vessel is the rolling. In the present study, particular attention is paid to the performance of a ship in beam sea. The rolling motion of a ship has been described by a nonlinear differential equation taking into account the nonlinearities in both the restoring moment and the damping moment. Solution of differential equation of roll motion is sought using MATLAB. The effect of different representation of restoring moment on roll motion is investigated. It is seen that, the effect of different representation of restoring moment on roll motion depends on the characteristics of the GZ curve. A parametric investigation is undertaken to identify the effect of different parameters viz., wave steepness, encountering frequency etc., on the capsizing conditions of a ship. The rolling response of ship is determined in the frequency domain. The analysis has been carried out by varying both the wave steepness and the wave frequency. The approach has been demonstrated considering a Ro-Ro ship as test vessel.

Impact loads from incoming waves always challenge the strength of structural parts of a ship. Modern high-speed crafts including naval vessels are subjected to impact loads during high speed and sudden manoeuvre. Wave slamming may damage structural parts and cause flooding of compartments due to impact. Hydrodynamic impact load results in structural damage in conventional marine vehicles. Loads during cargo loading, unloading, shipping of green water, impact with icebergs etc. come under low-velocity impact loads. The structural parts of a ship can also be damaged due to the impact of collision with icebergs as in the case of the Titanic accident. Weapon discharge, flight operation, bulk cargo operation and collision with other structures are other examples of impact load acting on marine vehicles. Severe hydrodynamic impact load may cause damage of shell plating, collapse of bow part, damage of hatch covers, collapse of hull girder etc. Such structural parts should possess sufficient impact strength. Composite shells can be used for hull, deck or hatch covers of bulk carriers to reduce the weight of vehicle and to indirectly increase the pay load capacity. In the present work, cost-effective composites are prepared by adding fillers to improve impact strengths and tested to verify the same. The main objective of the study is to develop a cost-effective composite to be used as part of hull, deck and hatch cover of bulk carrier. Feasibility and selection of fillers to improve impact strength are established. Prior to this, different sizes of fillers and the chemical treatment of filler with acid were considered. Calcium carbonate (CaCO3), silicon carbide (SiC) and alumina (Al2O3) are considered with glass epoxy composite for the above analysis. The additional impact strength due to the application of fillers is determined using Izod impact strength tests. Contact force is considered as a scale parameter for the impact response for composite laminates. Contact force is the force against impact load on composite structures. Contact force and deflection history of composite panels are affected by a number of parameters such as fibres angle, laminate geometry, impactor energy, stiffeners, surface area of impactor and loading eccentricity. Effects of all possible parameters are included and their influence on the response is determined using the well-known package based on finite element method (FEM), ABAQUS. The FEM analysis of Khalili et al. (2011 Compos Struct 93:1363-1375) is used for comparison of results of the present numerical analysis. The study leads to many new insights to designers of cost-effective composite structures. © 2013 Taylor & Francis.

Fracture toughness is a material property in the same sense that yield strength is a material property. The determination of fracture toughness for dynamic loading conditions is not very straight-forward, as dynamic crack growth speed in supersonic speed and the speed range is 1 to 2 km/sec. The improvement of fracture toughness of metals plays a vital role in the design and manufacturing of structural components. To achieve this purpose, industries rely up on coatings which are an integral part of manufacturing. These coated samples are tested by Charpy V-notch impact testing for estimating dynamic fracture toughness. These coatings improve the wear and corrosion resistance of the materials and they tend to reduce the strength of the materials, because of the increased residual stresses due to the coating process. These defects cannot be precluded from these coated and treated components. The strength of those components in the presence of such defects can be analyzed by fracture mechanics approach. An attempt has been made to analyze the effect of coating methods like electroplating and PVD (Physical Vapour Deposition), coating thickness, heat treatment and the service temperature on the fracture behaviour of metals. The experiments have been carried out on EN8 steel and aluminium for different temperatures. The specimen preparation and experimentations were carried out according to the ASTM standard E-23. The FRANC 2D (Fracture Analysis Code) has been relied upon for estimating the stress intensity factor at different crack length and temperature. Copyright © 2012 by ASME.

Composite materials are increasingly being used as an accepted alternative to traditional structural materials throughout the globe for various engineering applications. Because of their superior properties and flexibility, these materials are beginning to find innumerable applications replacing existing materials, especially in high-performance engineering domains. The electrospinning process adds a further dimension to enhance the properties of the composite material family by incorporating fibers at their microscale to even sub-nanoscale, enabling the development of advanced composites with enhanced properties. Over the past decades, much research work has understandably been done on these exciting materials. This paper aims to comprehensively map some of the trends in electrospun nanofiber interleaved laminated composite development, marking the milestones achieved and challenges faced. A brief review of the potential applications for these materials will also be put forward in the research outlook for these advanced nanoengineered composites.

This review paper initially summarizes the latest developments in impact testing on polymer matrix composites collating the various analytical, numerical, and experimental studies performed since the year 2000. Subsequently, the scientific literature investigating nanofiller reinforced polymer composite matrices as well as self-healing polymer matrix composites by incorporating core-shell nanofibers is reviewed in-depth to provide a perspective on some novel advances in nanotechnology that have led to composite developments. Through this review, researchers can gain a representative idea of the state of the art in nanotechnology for polymer matrix composite engineering, providing a platform for further study of this increasingly industrially significant material, and to address the challenges in developing the next generation of advanced, high-performance materials.