Camanho / Hallett Composite Joints and Connections

Principles, Modelling and Testing
1. Auflage 2011
ISBN: 978-0-85709-492-6
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 544 Seiten

Reihe: Woodhead Publishing Series in Composites Science and Engineering

The growing use of composites over metals for structural applications has made a thorough understanding of the behaviour of composite joints in various applications essential for engineers, but has also presented them with a new set of problems. Composite joints and connections addresses these differences and explores the design, modelling and testing of bonded and bolted joints and connections.Part one discusses bolted joints whilst part two examines bonded joints. Chapters review reinforcement techniques and applications for composite bolted and bonded joints and investigate the causes and effects of fatigue and stress on both types of joint in various applications and environments. Topics in part one include metal hybridization, glass-reinforced aluminium (GLARE), hybrid fibre metal laminates (FML), glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) composites. Topics in part two include calculation of strain energy release rates, simulating fracture and fatigue failure using cohesive zone models, marine and aerospace applications, advanced modelling, stress analysis of bonded patches and scarf repairs.Composite joints and connections is a valuable reference for composite manufacturers and composite component fabricators, the aerospace, automotive, shipbuilding and civil engineering industries and for anyone involved in the joining and repair of composite structures. - Explores the design, modelling and testing of bonded and bolted joints and connections - Reviews reinforcement techniques and applications for composite bolted and bonded joints - Investigates the causes and effects of fatigue and stress on bolted and bonded joints in various applications and environments

Autoren/Hrsg.

Camanho, P.

Hallett, Stephen R.

Leseproben

2 Bolted joints in glass reinforced aluminium (Glare) and other hybrid fibre metal laminates (FML)
C.D. Rans,     Delft University of Technology, The Netherlands Abstract:
Fibre metal laminates (FMLs) are a family of hybrid metallic–polymer matrix composite materials with superior fatigue and damage tolerance behaviour. Although technically a composite material, they share many behaviour features more in common with their metallic constituents. This chapter introduces the FML material concept and discusses the static and fatigue design considerations needed in the design of bolted FML joints. Key words fibre metal laminates fatigue joining 2.1 Introduction
Fibre metal laminates (FMLs) are a family of hybrid laminates consisting of alternating layers of monolithic metallic sheet and fibre reinforced composite layers as illustrated in Fig. 2.1. A key characteristic of the FML concept is the high resistance against fatigue cracking and the significant residual strength in case of fatigue damage (Alderliesten, 2005). The material technology also exhibits superior impact resistance and fire resistance, and does not have the electrical conductivity or moisture absorption issues of conventional composite materials (Alderliesten et al., 2003). Currently, the most common FML variant in commercial use is an aluminium and glass fibre-epoxy variant known as Glare (GLAss REinforced aluminium). 2.1 Illustration of the FML concept. This chapter examines the FML concept and the design considerations needed in the design of bolted FML joints. This chapter differs significantly from the other chapters of this book in that it deals with a hybrid metal–composite material. Designing structures with such a material requires understanding of both its metallic and composite constituents. This is emphasized throughout the chapter where discussions of the relative contributions of the constituents are made. Given the composite focus of this book, particular attention is paid to describing the metal-like behavioural features of FMLs and how treatment of FMLs differs from the more traditional composite materials described in the remainder of the book. To begin with, the chapter provides a brief overview of the FML concept, how it came into being, and how it has been developed and applied in the aerospace industry. The remaining sections focus on design of bolted FML joints. Methods for examining the load distribution and division of loading components in a bolted lap joint are considered first. Based on knowledge of these loads, the static strength and fatigue strength of an FML joint are then discussed. This chapter provides only a brief glimpse of the complexity and potential of FMLs and bolted FML joints, and the reader is encouraged to look further into the references provided in order to develop a deeper understanding of the technology. 2.2 Glare and the fibre metal laminate (FML) concept
Glare, and other members of FML material family, are promising metal–polymer matrix composite hybrid materials that successfully combine the best of the metals and composites worlds and make up for many of their shortcomings. Composites provide the promise of tailorability, high specific strength and stiffness, and relative fatigue insensitivity compared to metals, but suffer from their brittle nature which makes them susceptible to damage – either accidental or designed in the form of fastener holes and cut-outs. Metals, on the other hand, are very forgiving due to their ductility, and thus are tolerant to damage, cut-outs and holes. Despite this advantage, however, metals are susceptible to fatigue cracking and have relatively short fatigue lives compared with composites. FMLs can be described in the way the metal and composite constituents compensate for each other’s shortcomings. In the face of fatigue cracking of the metal constituents of an FML, the composite layers act as a bonded repair patch, providing an alternative load path around the crack. This effectively reduces the crack growth driving force and slows (or in some cases completely arrests) crack growth under fatigue loading. It also improves the residual (as well as undamaged) strength of FML structures relative to their metal counterparts. Effectively, from a metals perspective, FMLs can be viewed as pre-repaired metallic structures. From a composites standpoint, the presence of the metallic layers provides ductility which absorbs energy in the event of impact or other damage scenarios, making the composite more forgiving. Furthermore, the metal layers behave in a well-defined and visible manner when subjected to impact damage or fatigue loading. Impact damage results in the formation of a plastic dent while fatigue loading produces fatigue cracks, both of which are known factors requiring attention from a maintenance and inspection standpoint, and do not require complicated structural health monitoring systems. As a result, from a composites standpoint, FMLs can be viewed as composite materials with an analogue structural health monitoring system. The history behind the development of the FML concept has shaped its perception by the materials world and influenced further development of the technology. Despite having obvious composite material features, the technology has its roots in the metals world and is often viewed as a damage tolerant metal rather than a composite. This has greatly influenced the development of FMLs, in particular Glare, and their design and analysis methodologies, as discussed in the following sections. The discussion is divided into two viewpoints on FMLs: one as a damage tolerant metal; and a more recent research trend for FMLs as tailorable hybrid metal–composite structures. 2.2.1 FMLs: a damage tolerant metal
FMLs can be considered an evolutionary technology with roots firmly placed in metal-to-metal bonding technology (Vlot, 2001). After World War II, the Dutch aircraft manufacturer, Fokker, needed to find a cheap solution for producing variable thickness wing skins for its aircraft designs. Not being able to afford the large gantry milling machines their competitors were using to machine variable thickness wing skins from large aluminium ingots, Fokker utilized adhesive bonding technology to create built-up wing skins from multiple thin metal sheets. These built-up bonded wing skins showed excellent fatigue performance that could be attributed to three factors: • The plane–stress state of the thin metal sheets. • The barrier to through-thickness crack growth provided by the adhesive interface between bonded sheets. • The load bridging effect of the uncracked metal layers bonded to a crack metal layer, reducing the crack tip stress intensity factor. In the early 1970s, a breakthrough which vastly improved the damage tolerance of these bonded built-up metal laminates was made when reinforcing fibres were added to the adhesive bond line. These fibres produced a similar bridging effect to the intact metal layers in the bonded laminates (Fig. 2.2), but were less sensitive to fatigue and could sustain the bridging role longer than additional metal layers. 2.2 Illustration of the fibre bridging mechanism. At Delft University of Technology in the Netherlands, the first generation of these fibre reinforced metal laminates, or fibre metal laminates as they were called, were studied consisting of bonded 2024-T3 aluminium sheets reinforced with aramid fibres. In the late 1980s, glass fibres were introduced as a reinforcing fibre, resulting in the variant of FMLs commonly known as Glare (GLAss REinforced aluminium). These laminates exhibited superior fatigue damage growth performance compared with monolithic and bonded metal structures (Fig. 2.3) and the technology continued to be studied as means of improving the damage tolerance of metal structures. 2.3 Typical crack growth behaviour of Glare compared to monolithic 2024-T3 (van Hengel, 2001). In the mid-1990s, Airbus Industries began investigating FML technology which led to the eventual application of Glare as a fuselage skin material on the Airbus A380 super jumbo jet (Gunnink et al., 2002). In applying Glare on this aircraft, Airbus reinforced the notion of FMLs as a damage tolerant metal by choosing to certify Glare used in its structures as a metal material. This choice was made due to the ease and reduced cost of this approach compared with certifying a tailorable composite system and could be made due to the following six common features between metals and FMLs: • Ductility: FMLs yield and are capable of absorbing energy with gradual and predictable strength degradation. Ductility is related to the metal applied. • Oxidation: The sensitivity of an FML to corrosion relates to the sensitivity of the metal applied. • Fatigue sensitivity: The sensitivity of an FML to crack initiation relates to the sensitivity of the metal...