Design and Manufacture of Composite Structures

G C Eckold

• Publisher: Woodhead Publishing
• Year: 1994
• Print ISBN: 9781855730519
• eBook ISBN: 9781845698560
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

A practical book of value to those in the automotive, chemical, aerospace and offshore industries. Case studies are included and as well as covering flexible manufacturing systems and non-destructive evaluation, the author looks ahead to metal matrix composites and ceramic matrix composites.

1

Introduction

Materials and their application are the fundamental constituents of any engineering design. Regardless of whether or not the calculations for stress and strain are accurate, the fabrication is performed according to proper quality-assured procedures, and installation and commissioning are completed as specified, the incorrect selection of materials will ultimately lead to the component or structure not achieving its potential in terms of performance or lifetime. As a consequence, the concept of tailoring materials at a fundamental level to meet specific design requirements has intrigued engineers for many years. Whilst the principle is by no means new, it is only comparatively recently that the use of ‘materials design’ has been fully incorporated in the overall product development process. Examples range from the macroscopic, such as steel reinforcing bars in concrete for tensile strength, through the microscopic and molecular, for example whisker reinforcement of ceramics for enhanced toughness and the copolymerization of polypropylene and polyethylene for good mechanical behaviour below ambient temperatures, to the atomic, such as ion implantation of surfaces to increase wear properties.

This book is concerned with one family of designer materials – fibre reinforced composites. In many respects they represent excellent examples of the principles of material design where the performance of the whole is greater than the sum of its parts. Fibres, lightweight, immensely strong and stiff (in some cases not too distant from the theoretical maximum), but easily damaged and in a form of limited engineering application, and the matrix, comparatively weak and often brittle and not usually attractive for structural load-bearing applications. Together, however, they offer a vast array of materials and great scope for optimization in the true sense of the word. This is not only limited to mechanical characteristics but also extends to thermal properties, acoustic and electromagnetic response, creep and fatigue, ballistic performance and chemical resistance. Indeed, for the great majority of parameters in which an engineer may be interested, fibre reinforced composites provide alternatives often only limited by the imaginations of the designers themselves. Of course, it would be misleading to suggest that these systems supply answers to all problems: where there are advantages, there are also disadvantages. It is for this reason that this new class of materials needs a complement – a new breed of engineers, not only familiar with the principles of mechanics and design, but also conversant with fabrication science, chemistry, materials physics, and new test and inspection procedures (Fig. 1.1). Only with an appreciation of all these facets of the composites’ equation will the required levels of structural efficiency and reliability be achieved. It is the purpose of the following chapters to introduce these issues in a design-orientated context and, while claiming not to be exhaustive, to cover the main points of the engineering process from conceiving the materials to completing the component.

1.1 Considerations in composite design (NDT, non-destructive testing).

Historical perspective

Amongst the earliest applications of the use of particulate or fibrous material to reinforce another material are natural fibres such as grass or animal hair which were used to improve the strength and to alleviate shrinkage of pottery prior to firing.¹ In a similar way potters were able to modify the porosity of their finished artefacts to produce receptacles that would provide cooling by evaporation. Modified polymeric materials also featured in ancient times. Evidence dating to around 3000 BC suggests reinforced bitumen/pitch building products, and bitumen embedded with papyrus reeds for boat building were in widespread application. An example of what must be one of the first exercises in surface modification is in the use of stone or fired clay cones hammered into building walls (Fig. 1.2).² This would have had the effect of improving erosion and weathering resistance.

1.2 Reinforcement of soft mud brick walls.

Applications can also be found in early armaments. In this period powerful composite bows were fabricated from wood and horn lamallae or even more exotic combinations such as animal tendons, wood and silk bonded together using adhesive.² The makers of armour made use of the perforation resistance of laminated structures fabricated from alternate layers of iron and steel. In one example³ of the many variants of compound blade, three types of steel were used. Edge steel was folded up to 20 times, core steel 8 times and the three layers of skin steel folded by a similar amount. All were hammered out and welded together into a blade containing many thousands of layers. Special heat treatment utilizing quenching and slow cooling of different parts of the structure converted the edge into a very hard material indeed. Similarly, oriental gunsmiths utilized different kinds of iron and steel fashioned into strips, wound into a helix and then welded to form the barrel of a gun.

In terms of the modern exploitation of composite materials, this was essentially pioneered following the work of Griffiths’ in the 1920s;⁴ who reported strengths of freshly drawn glass fibres of up to 900000 psi (6000 MPa). Since this time research and development have been intensive. The initial work centred on the defence uses of glass reinforced plastics (GRPs) such as aircraft radomes, boat hulls and seaplane floats.⁵ Up to that time the cost of the basic resin and glass materials precluded general application and it was not until the late 1940s with the advent of cold setting resin systems and cheaper forms of reinforcement that the industry expanded beyond specialist uses. Translucent sheeting, boat hulls, chemical-resistant process equipment and car bodies all became ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Preface
• 1: Introduction
• 2: Materials and Properties
• 3: Mechanics of Material Behaviour
• 4: Beams, Plates and Shells
• 5: Aspects of Design
• 6: Manufacture
• 7: Metal and Ceramic Matrix Composites
• 8: Examples of Composite Applications
• Index