Aluminium Design and Construction John Dwight

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11.4.5 Factors affecting choice of adhesive In choosing the most suitable adhesive for a given application the following are possible factors to consider. (a) Curing time/pot-life For a mass-produced component, such as a car, the automatic choice would be for a one-component adhesive, because of a long available working time and the fast cure that is possible. With the two-component adhesives, the working time is shorter. Also the curing time is generally much longer, and varies greatly from one formulation to another. Here the choice is a compromise between the desire for a reasonable cure time and an acceptable pot-life (useable time after mixing). (b) Toughening Some adhesives are toughened. This means that they are specifically formulated so that after curing they contain an array of minute rubbery inclusions, which act as mini-crack-arresters. Such an adhesive is therefore more resistant to impact and would be selected when this is a factor. It will cost more. (c) Slumping (loss of adhesive) With a vertical joint, there is a danger that some of the adhesive will run out before it has had time to cure, leading to voids in the bonded area. This can be prevented by selecting an adhesive that does not flow in the precured condition, referred to as being thixotropic. (d) Operating temperature Many of the adhesives used on aluminium begin to lose strength at temperatures over 40°C. Some, however, are designed to operate up to 160°C. (e) Performance in a wet environment Some adhesives resist the effects of moisture better than others. (f) Ductility This can improve the strength of a joint by redistributing the load away from points of high stress. Most of the adhesives used with aluminium can be regarded as non-ductile in this respect. Copyright 1999 by Taylor & Francis Group. All Rights Reserved.
11.4.6 Creep Shear strength figures provided by adhesive manufacturers are normally based on short-term tests. When fully loaded over a long period, it is found that adhesives suffer from creep, characterized by continuing deformation and a drop in the shear strength. The effect becomes more pronounced as the temperature increases. Reliable data on this effect is not generally available, but a rough guide is that constant loading over a long period should not exceed about one-quarter of the short-term lap shear strength. 11.4.7 Peeling Bonded lap joints are inherently vulnerable to premature failure by peeling, when subjected to loading perpendicular to the plane of the adhesive. This may occur even when the tension is only a secondary or accidental effect. Manufacturers provide figures for the peel strength of their adhesives based on a standard test (the ‘roller peel test’). This is expressed as the failure force per unit width of joint and typically ranges from 3 to 10 N/ mm. An engineer should be encouraged to ignore such data and instead design joints so that peeling cannot occur. With joints between extrusions, this can be achieved by suitable design of the section. With lap joints between sheet-metal components, a possible technique is to employ occasional mechanical fasteners, strategically placed, to act as peel inhibitors, or else occasional spot welds can be used (through the adhesive). 11.4.8 Mechanical testing of adhesives The most important mechanical property of an adhesive is its ultimate strength in shear. This is normally determined by testing a standard lap-joint specimen with the dimensions shown in Figure 11.13, composed of 2014A-T6 clad sheet. The shear strength t of the adhesive is taken as the applied load at failure divided by the lap area. Such a test is simple, but not ideal. Firstly, as the load builds up the aluminium bends slightly, as shown, with the result that a peeling Figure 11.13 Adhesive lap shear test. Standard specimen. Copyright 1999 by Taylor & Francis Group. All Rights Reserved.
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Aluminium Design and Construction C
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First published 1999 by E & FN Spon
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2.2.1 Rolling mill practice 2.2.2 P
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5 Limit state design and limiting s
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8.2.6 Use of interpolation for semi
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10.3.2 Inertias for a section with
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Preface Aluminium is easily the sec
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List of symbols The following symbo
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uu, vv principal axes w effective s
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1.1.3 The industrial metal It is on
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where A is the section area (mm 2 )
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1.3.1. The good points about alumin
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Deflection Because of the lower mod
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1.4.4 Establishment of the alloys I
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1.5.2 New technology Most of alumin
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large span, where self-weight is a
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These tend to be in all-aluminium c
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Close-up of the M-dec system, which
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Aluminium glazing system for commer
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Nat West Media Centre, Lords Cricke
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The main requirements for the produ
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in which t and w are in mm. These a
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Figure 2.1 Extrusion process (direc
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Figure 2.2 Typical extrusion die. t
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Figure 2.6 ‘Semi-hollow’ profil
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especially the stronger alloys in t
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Figure 2.9 Conventional profiles. 2
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2.4 TUBES By tubes we mean hollow s
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CHAPTER 3 Fabrication 3.1 PREPARATI
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Figure 3.1 Alternative designs for
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Figure 3.2 Thread insert. a coil-sp
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3.3 ARC WELDING 3.3.1 Use of arc we
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adjusted. The technique is claimed
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For welds of minimum or fatigue qua
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Figure 3.5 Friction-stir welding: s
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are, and the designer/fabricator mu
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cartridge, and mixing takes place a
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3.7.4 Painting Alloys having durabi
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Where a range is given, as for the
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will be only slightly above that fo
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heating the metal to a temperature
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Table 4.4 Characteristics of differ
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softening in the heat-affected zone
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60 alloys, are: BSEN.485 plate and
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Firure 4.3 Nominal composition and
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popular alloys in the series are: 6
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Figure 4.6 Variation of tensile str
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undercarriages of aircraft. They ar
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Figure 4.11 Minimum stress-strain c
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AC.51400 This is another non-heat-t
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times that of the actual pits) prod
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The severity of bimetallic corrosio
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Nominal loading. Nominal loads are
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2. Material factor (� m ). In the
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design does not, because stress at
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Table 5.2 Summary of limiting stres
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Figure 5.4 Plastic strain at workin
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example, a reduced value might be t
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The parameter � depends purely on
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CHAPTER 6 Heat-affected zone soften
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area of softening. With 7xxx-type m
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Figure 6.3 Typical hardness plots a
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6.4 SEVERITY OF HAZ SOFTENING 6.4.1
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Figure 6.6 Categories of welded joi
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Figure 6.10 One-inch rule, extent o
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e allowed for in design by replacin
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Figure 6.13 Predicted area (A z ) o
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Figure 6.15 Overlapping HAZs. nomin
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In determining A zp , an appropriat
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failure plane in the HAZ, close to
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With MIG welding, an electrode-posi
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CHAPTER 7 Plate elements in compres
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(a) Compression member elements The
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Table 7.1 Classification of element
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Figure 7.4 Slender internal element
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Figure 7.7 shows curves of � ° p
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(7.9a) (7.9b) The strain gradient c
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(through the centroid) for ß S . F
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Figure 7.13 Outstands under strain-
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Figure 7.15 Reinforced elements. Th
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Figure 7.18 Stiffener location for
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Figure 7.20 Slender reinforced inte
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CHAPTER 8 Beams 8.1 GENERAL APPROAC
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8.2.2 Section classification The di
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that for the gross section. It woul
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the usual manner. Line 1 in the fig
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1. Fully compact sections. The limi
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Figure 8.8 Transverse and longitudi
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8.3.4 Shear resistance of bars and
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Figure 8.12 Tension-field action. i
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Figure 8.14 Moment/shear interactio
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depending on the estimated degree o
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where a is the stiffener spacing an
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plates (if fitted), p v =limiting m
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ending moment diagram. Two cases ar
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Figure 8.23 Sections covered in Tab
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where: I yy , I vv =inertia about m
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post (Section 8.6.4) or by some oth
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Figure 8.26 Components of deflectio
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9.1.2 Classification of the cross-s
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hole. Alternatively, it might fail
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Figure 9.2 Limiting stress p b for
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The determination of l involves a c
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Figure 9.6 Monosymmetric section. I
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Figure 9.9 Limiting stress p b for
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where s=� s /� t s =slenderness
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Figure 9.11 Type-R sections covered
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Figure 9.14 Four standardized profi
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9.7.2 Secondary bending in trusses
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Table 9.5 Necessary checks for memb
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Figure 9.18 Axial load with biaxial
Page 223 and 224: 1. Tension members. The localized f
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Page 233 and 234: 10.3.3 Product of inertia The produ
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Page 237 and 238: Table 10.2 Torsion constant. Factor
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Page 243 and 244: 10.5.3 Evaluation of warping When t
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Page 247 and 248: (10.31) where: e=distance that S li
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Page 251 and 252: CHAPTER 11 Joints This chapter cons
Page 253 and 254: the use of limiting stresses taken
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Page 259 and 260: k in order to give a fair compariso
Page 261 and 262: 3. The design is satisfactory if fo
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Page 265 and 266: 11.3.3 Weld force arising In many c
Page 267 and 268: Table 11.6 Limiting stress p w (N/m
Page 269 and 270: where p a =limiting stress for unwe
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Page 279 and 280: Table 11.7 and Figure 11.17 provide
Page 281 and 282: 11.4.11 Resistance calculations for
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Page 287 and 288: For example: The loading spectrum i
Page 289 and 290: act on the structure. However, BS.8
Page 291 and 292: Figure 12.4 Crack propagation: (a)
Page 293 and 294: 12.5 CLASSIFICATION OF DETAILS 12.5
Page 295 and 296: i.e. a joint extending in the same
Page 297 and 298: when the design life is low or when
Page 299 and 300: Methods (2) and (3) are difficult t
Page 301: it reverts to line 1. The slope s o
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Aluminium Design and Construction John Dwight

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