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This book presents selected papers from the 2nd Workshop on “Durability of Composites in a Marine Environment”, which was held in Brest, France in August 2016. Providing an overview of the state of the art in predicting the long-term durability of composite marine structures, it addresses modelling water diffusion; damage induced by water accelerated testing, including durability in design; in-service experiences; ocean energy; and offshore applications. Ensuring long-term durability is not only necessary for safety reasons, but also determines the economic viability of future marine structures, and as such, the book is essential reading for all those involved with composites in the marine industry, from initial design and calculation through to manufacture and service exploitation. It also provides information unavailable elsewhere on the mechanisms involved in degradation and how to take account of them.



Nonempirical Kinetic Modeling of Non-fickian Water Absorption Induced by a Chemical Reaction in Epoxy-Amine Networks

In the last two decades, several studies made in our laboratory have shown that hydrolytic reactions may occur during water absorption and may be responsible for behavioral deviations from the classical Fick’s law in epoxy-amine networks. On one hand, water is chemically consumed by specific groups initially present in the repetitive structural unit (e.g., unreacted epoxies and amides) or formed by oxidation under operating conditions. On the other hand, water establishes strong molecular interactions (hydrogen bonds) with new highly polar groups resulting from hydrolysis (alcohols and acids). Due to both contributions, the kinetic curves of water absorption no longer tend towards an equilibrium value, i.e., a final saturation plateau, but display a slow and continuous increase over time in the water mass uptake. On this basis, a diffusion/reaction model has been developed for predicting such a peculiar water sorption behavior. In addition, the classical Henry’s law has been modified for describing the changes in boundary conditions during the course of the hydrolytic reaction. This chapter provides an overview of the recent theoretical advances made in this field and demonstrates, through two case studies, the good predictive value of the kinetic modeling approach set up in our laboratory.
Xavier Colin

Influence of Glass Fibre Sizing and Storage Conditions on Composite Properties

This paper describes a major component of glass fibre reinforcements, the sizing, and its impact on mechanical properties of epoxy or polyester laminates. First the basics of the glass fibre manufacturing process and the types of silanes used for direct rovings are briefly described. The important feature of these coatings is that they can be affected by storage conditions. The study focuses on the effect of roving storage time, temperature and humidity as well as packaging type on the fibre/matrix interphase and on the inter-fibre properties of the composites. The conclusions show that not all fibre sizings offer the same storage stability and that warehousing and packaging details can have a significant impact on the final composite performance.
Luc Peters

Water Uptake in Polymer Composites with Voids

Long-term durability assessment of polymer matrix composite materials exposed to humid air or liquid water requires a firm understanding of the mechanisms governing water uptake and the chemical interactions involved in degradation of the matrix and the fiber/matrix interface. The added mass of water will cause swelling of the matrix, which tends to degrade bonding between fiber and matrix. Voids provide space where water may accumulate, and if they are located at the fiber/matrix interface, the accumulated water may cause hydrolysis. Voids, furthermore, are geometrical irregularities that cause stress concentration, and reduction of strength. Fickian diffusion is considered valid to analyze the moisture uptake in polymers and void-free composites. For composites containing voids, however, deviations from Fickian diffusion are observed. Voids in the form of capillaries along the fibers define flow channels and promote ‘wicking’, which is a rapid water uptake mechanism. Experimental studies on water uptake in polymer matrix composites show a strong dependence of voids. A composite containing even a small void volume fraction will absorb moisture in excess of that contained in the matrix resin. The moisture uptake in a composite immersed in seawater has been modeled using a combination of diffusion of moisture in the matrix resin, combined with the capillary flow in the voids. The predictions qualitatively agree with experiments, but saturation times are off. More detailed characterization of the void structure and improved flow modeling are required to accurately predict the dynamics of water uptake in a composite.
Leif A. Carlsson, E. Du

Durability of US Naval Composites and Sandwich Structures: Science Framework Considering Multiscale Response in Harsh Sea Environment

Deformation behavior of carbon fiber-reinforced polymer composites involves mechanisms at multiple length scales with a strong dependency on the carbon fiber type and quality, fiber sizing, choice of polymer matrix, form of reinforcement, and manufacturing process. Naval structures typically employ sandwich materials including low-density foam core materials. Given the large amount of variables associated with materials and processing methods, a systematic science based framework is needed for predictive capabilities to model static, fatigue, and fracture behavior and its dependency on seawater and temperature. Using materials of high interest to US Navy, such a framework is proposed considering T700 carbon fibers specifically sized for vinylester resin system having brominated additives for improved fire performance. Textile composites manufactured utilizing VARTM process with suitable post-cure were utilized throughout the experimental campaign. The sandwich lay-up for this study consists of a closed cell polymeric (PVC) foam core placed between thin carbon fiber-reinforced vinylester facings. A fundamental study to evaluate the environmental degradation associated with long-term exposure on mechanical properties of carbon fiber-(Toray T700 3K tow-based stitched fabric) reinforced vinylester (CF/VE) facings at different orientations and various specimen sizes was implemented. The tension–tension fatigue effects, which simulate the splash load in marine environment, are shown to be more notable in composite facings with orientation of lay-ups that are resin dominated (for example, [±45]2S). The seawater absorption in the carbon fiber/vinylester composite leads to several deleterious effects resulting in new failure modes and deterioration in long-term durability.
Dayakar Penumadu

Statistical Long-Term Creep Failure Time of Unidirectional CFRP

A method for statistical prediction of the long-term creep failure time of CFRP using the statistical static strengths of CFRP at various temperatures and the viscoelasticity of matrix resin is proposed based on Christensen’s model of viscoelastic crack kinetics. The tensile strength along the longitudinal direction of unidirectional CFRP constitutes important data for the reliable design of CFRP structures. The authors developed a reliable method for testing creep and fatigue strengths as well as static strength at elevated temperatures for resin-impregnated carbon fiber strands (CFRP strands) as unidirectional CFRP. Two kinds of CFRP strands with two types of PAN-based carbon fibers with high strength and high modulus were examined on the viewpoint of failure mechanism. The statistical static strengths of these CFRP strands and the creep compliances of matrix resins were measured at various temperatures. The tensile creep failure times of these CFRP strands are predicted statistically based on a prediction method using measured data. The predicted creep failure times of these CFRP strands were compared with the creep failure times of these CFRP strands measured experimentally and statistically. Additionally, the statistical temperature-dependent static strengths are also discussed for CFRP strands of two types of pitch-based carbon fibers with low modulus and high modulus.
Yasushi Miyano, Masayuki Nakada

Multiphysics Modeling of the Hygro-Mechanical Behavior of Heterogeneous Materials

The present chapter investigates the modeling of the hygro-mechanical behavior of composites used in marine environment. The purpose of the proposed models is to analyze the effect of water absorption on a composite structure through mechanical quantities such as stress fields. The case of non-Fickian diffusion processes is first addressed with the Langmuir model allowing representing anomalies of diffusion. The elastic constitutive equations thus depend on the moisture content involving a hygroscopic strain field. The capabilities of the model are shown with a numerical study on a composite material. Second, we propose to introduce couplings between the water diffusion and the mechanical states. To achieve this, we mix the classical Fick model with the free volume theory and implement the model in a finite element software. A numerical study regarding the impact of such coupling on a pure resin case is carried out. We finally propose to take into account the uncertainties sometimes observed on the experimental data which enable the characterization of the diffusion properties. Some of the material properties of the hygro-elastic model thus become random and are modeled with random variables. The propagation of these uncertainties is made with a stochastic spectral approach based on polynomial chaos expansions. The efficiency of the proposed technique is shown with a numerical application involving a polyamide neat resin.
Alexandre Clément, Sylvain Fréour, Frédéric Jacquemin

Reliability of Composite Marine Structures

Traditional engineering design takes a deterministic view of the world. This type of analysis has provided a safe method for designing structures for many years. However, reliability analyses have been developed to account for the stochastic loads encountered in service and the variation in geometries and material properties seen after production. There are a range of techniques available for this analysis each with their own advantages and disadvantages. This chapter explores methods for composite analysis using simplified methods and simulation techniques.
A. J. Sobey, J. I. R. Blake, R. A. Shenoi

Multiscale Modelling of Environmental Degradation—First Steps

Fibre-reinforced plastics are praised for their good corrosion resistance. However, when this resistance needs to be documented for safety-critical applications extensive and time-consuming test programmes are needed. A better quantitative understanding of the fundamental mechanisms behind degradation should help to reduce the testing effort. A multiscale approach for modelling degradation in water and hydrocarbons is described. The environmental degradation happens on the scale of the constituent materials: fibres, matrix and sizing (interface). Local concentration profiles of the fluid inside the material need to be known to predict degradation. The global engineering properties are then calculated from the constituents using finite element analysis and homogenisation. Describing degradation with the multiscale approach is a promising method for reducing the current test effort. Much more work is needed to create enough confidence in the models that then can be used for designing real components. The first steps are described here showing the models and how they can be connected.
Andreas T. Echtermeyer, Abedin Gagani, Andrejs Krauklis, Tobiasz Mazan

Present and Future Composites Requirements for the Offshore Oil and Gas Industry

The aim of this paper is to review some of the main applications of composite and polymer materials in the oil and gas industry. It starts with the basics of material selection and the methods used for corrosion mitigation of carbon steel which is the base case and material of choice due to its low cost and ease of installation. Some specific business cases are identified for composite materials and some typical applications are described in more details.
Denis Melot

Composite Materials in Tidal Energy Blades

Composite materials are the natural choice for the construction of tidal energy blades; their high strength, good environmental resistance and the ease with which they may be used to form complex shapes means that they are well suited to the application. The design of MW-scale tidal energy blades has evolved over a number of years, keeping step with the requirements of turbine developers as their emphasis shifts from prototyping to production. In parallel, it has been necessary to develop a rigorous approach to materials testing and qualification. The specifics of the blade structure and the operational environment mean that it has been necessary to solve a number of complications that arise during such a qualification programme. These issues are discussed and efforts to mitigate their consequences are explained. Although this chapter is written particularly with tidal energy blades in mind, much of the content will be applicable to a wide range of other applications where composite materials are used in the marine environment.
Matthew Dawson, Peter Davies, Paul Harper, Simon Wilkinson

Influence of Composite Fatigue Properties on Marine Tidal Turbine Blade Design

The structural design of marine tidal turbine blades is governed by the hydrodynamic shape of the aerofoil, extreme loadings and composite material mechanical properties. The design of the aerofoil, chord and twist distribution along the blade is generated to optimise turbine performance over its life time. Structural design gives the optimal layout of composite laminae such that ultimate strength and buckling resistance requirements are satisfied. Most structural design approaches consider only extreme static loads, with a lack of dynamic load-based fatigue design for tidal blades. Approaches for tidal turbine blade design based on dry and immersed composite material fatigue life are studied.
Vesna Jaksic, Ciaran R. Kennedy, David M. Grogan, Sean B. Leen, Conchúr M. Ó. Brádaigh

Marine Ageing Behaviour of New Environmentally Friendly Composites

In recent years several new materials have been proposed for marine applications. These include liquid infusible acrylics, basalt fibre and plant fibre-reinforced composites, and thermoplastic polyamide composites. In order to assess the long-term durability of such materials accelerated tests are used but the validity of this approach, widely accepted for traditional marine composites, must be checked. This presentation will describe results from ageing tests on these four materials, specifically developed for particular applications: acrylic composites and basalt and flax fibre composites for surface structures, and carbon-reinforced polyamides for deep sea pressure vessels.
Peter Davies, Pierre-Yves Le Gac, Maelenn Le Gall, Mael Arhant

Erratum to: Durability of Composites in a Marine Environment 2

Peter Davies, Yapa D. S. Rajapakse
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