J.I.R. Blake

Progressive damage analysis of tee joints with viscoelastic inserts

The purpose of this paper is to investigate the static structural response of a new type of composite tee joint containing a viscoelastic insert. The introduction of this material has proven benefits in terms of noise and vibration attenuation across the joint. The effects of introducing this new material on the structural response of the joint are numerically examined by using a progressive damage model. Application of this method allows the initiation and progression of failure and ultimate failure load to be predicted. Experimental results show good qualitative and quantitative agreement with the predictive damage model.

Integrity of hybrid steel-to-composite joints for marine application

There are many instances where the use of weight-saving polymer composite material for an entire structure is either too complex, too expensive or unfeasible. In these circumstances the use of a hybrid structure can incorporate the benefits of traditional (e.g. steel) construction coupled with the advantages of composite materials [e.g. glass-reinforced polymers, glass-reinforced plastic (GRP)] in weight-critical areas. A number of studies have been carried out on the static strength of hybrid steel-to-composite joints. In the present study, an experimental investigation was undertaken into the fatigue life characterization of a hybrid steel-to-GRP joint. It was found that the fatigue data correlated well with the statistical-based Weibull cumulative distribution function. In addition, post fatigue (in-plane and out-of-plane) residual strength tests were undertaken to ascertain the joint structural performance after cyclic loading. Finite-element-based progressive damage analyses incorporating damage initiation and propagation characteristics, showed good correlation with experimental results.

Strength modelling in stiffened FRP structures with viscoelastic inserts for ocean structures

The purpose of this paper is to investigate the static structural response of a new type of composite stiffener containing a viscoelastic insert. The introduction of this material has proven benefits in terms of noise and vibration attenuation across the joint. House, 1997 describes the use of this material in sonar dome/hull connections — equipment sensitive to noise and vibration. Structural stiffeners incorporating this material would have positive implications for not only marine and ocean structures but for structural applications in general. The effects of introducing this new material on the structural response of the joint are numerically examined by using a progressive damage model. Application of this method allows the initiation and progression of failure and ultimate failure load to be predicted. Experimental results show good qualitative and quantitative agreement with the predictive damage model.

Monte Carlo reliability analysis of tophat stiffened composite plate structures under out of plane loading

Composite materials are often utilised for their high strength to weight ratio, excellent corrosion resistance, etc. but are also characterised by variabilities and uncertainties in their mechanical properties owing to the material make-up, process and fabrication techniques. It is essential that modelling techniques continue to be developed to take account of these variabilities and uncertainties and as more complicated structures are developed it is important to have rapid assessment methods to determine the reliability of these structures. Grillage analysis methods have been previously used for assessment of tophat stiffened composite structures using simple failure criteria. As new criteria are introduced, such as by the World Wide Failure Exercise, the response of more complex topologies must be introduced. This paper therefore assesses the reliability of composite grillages using Navier grillage method incorporating up to date failure criteria. An example, taken from boatbuilding, is used to show the results of using these more complex assessment methods showing that it is of high importance to use the correct assessment criteria.

Path Following of an Underactuated AUV Based on Fuzzy Backstepping Sliding Mode Control

This paper addresses the path following problem of an underactuated autonomous underwater vehicle (AUV) with the aim of dealing with parameter uncertainties and current disturbances. An adaptive robust control system was proposed by employing fuzzy logic, backstepping and sliding mode control theory. Fuzzy logic theory is adopted to approximate unknown system function, and the controller was designed by combining sliding mode control with backstepping thought. Firstly, the longitudinal speed was controlled, then the yaw angle was made as input of path following error to design the calm function and the change rate of path parameters. The controller stability was proved by Lyapunov stable theory. Simulation and outfield tests were conducted and the results showed that the controller is of excellent adaptability and robustness in the presence of parameter uncertainties and external disturbances. It is also shown to be able to avoid the chattering of AUV actuators.

Nature in Engineering for Monitoring the Oceans: Towards a Bio-Inspired Flexible Autonomous Underwater Vehicle Operating in an Unsteady Flow:

It has long been understood that swimming marine animals have evolved capabilities in terms of speed, manoeuvrability, and efficiency which are desirable for underwater vehicles. Despite this, solutions inspired by nature, or bio-inspiration, are very rarely applied to solve engineering challenges. In particular, it is understood that fish have the ability to alter their mode of swimming to interact with naturally produced vortices as a method of conserving energy and in certain instances extracting energy from a flow. This paper considers whether a bio-inspired flexible autonomous underwater vehicle (AUV) could exploit unsteady flow features to reduce its cost of transport. An analytical model is developed which allows an AUV designer to predict which flow frequencies excite the natural vibration modes of a flexible cylinder. It is demonstrated that by placing a flexible cylinder in an unsteady flow, such as downstream of a bluff body, a similar mechanism to that used by fish may be exploited to move the cylinder upstream with no power input except that extracted from the flow.

Optimisation Approaches to Design Synthesis of Marine Composite Structures

Abstract This paper develops a method of structural optimisation for stiffened FRP panels allowing optimisation between cost and mass. The approach uses genetic algorithms for optimisation combined with elastic stress modified grillage theory for stiffener structural analysis and third-order shear deformation theory for the plate structural analysis. For top-hat stiffened panels, optimum designs following first principles and classification society rules are compared, showing considerable potential for cost savings by using a first principle approach.

Composite materials for marine applications – key challenges for the future

This chapter presents the key challenges for the future use of composite materials for marine applications. Five technical challenges have been identified: load transfer mechanisms, safety, life cycle assessment, concurrent engineering and structural health monitoring. These are discussed in the following sections of the chapter. The mechanical behaviour of layered orthotropic structures is considered for both adhesively bonded and hybrid joints, and the strength, fatigue, failure prediction, ageing and optimisation of the connections are described. The safety section discusses the challenge of managing variability and uncertainty when constructing bespoke marine craft, where extensive testing and prototyping are not possible, considering fabrication, strength and through-life behaviour. In the life cycle assessment section, environmental impact is considered using an embodied energy approach. Concurrent engineering approaches that incorporate both the design and production functions in a non-sequential manner are particularly important in the marine industry. A future requirement in this field will be the ability to incorporate design history in optimised design solutions. The structural health monitoring section focuses on state-of-the-art inspection techniques such as vibration-based damage identification approaches and other data-rich experimental mechanics techniques for use in repair intervention strategies. The chapter concludes with comments on the future use of polymeric composite materials for structural marine applications.

Damage mechanisms of hat-shaped GRP beams

In this study, the behaviour of hat-shaped glass-reinforced plastic (GRP) composite beams was investigated experimentally and numerically to predict the effect of different material composition on: • Flexural stiffness of the beams • Ultimate collapse strength of beams • Failure mechanisms of the beams The materials used in this study were chopped strand mat (CSM) in different weight e.g., 600, 450 and 225 g/m2 and 1600 g/m2 unidirectional (UD) glass fibre, 600 g/m2 woven rowing (WR) and 600 g/m2 biaxial [±45°] with polyester resin (isopthalic and orthopthalic) and polyurethane (PU) foam. Two types of top hat composite beam have been tested under four-point bending loads. The finite element predictions were compared with the test data and good agreement was obtained.

Fatigue life and residual strength analysis of steel-composite joints

There are many instances where the use of weight saving composite materials for an entire structure is either; too complex, too expensive or unfeasible. In these circumstances the use of a hybrid structure can incorporate the benefits of traditional construction materials, for example steel, coupled with the advantages of composite materials in weight critical areas. In the present study, an investigation was undertaken into the fatigue life characterisation of a hybrid joint for marine application. In addition the residual strength of the joint, after a fixed number of fatigue cycles, was assessed under axial compression and bending loads. A progressive damage model was developed to predict the location of major stress concentrations, the path of damage and subsequent loss in stiffness of the joint under axial compression.