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Chapter 9 PowerPoint Presentation

Chapter 9

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Chapter 9

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  1. Chapter 9 Welding, Bonding, and the Design of Permanent Joints Dr. A. Aziz Bazoune King Fahd University of Petroleum & Minerals Mechanical Engineering Department Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  2. Chapter Outline 9-1 Welding Symbols 9-2 Butt and Fillet Welds 9-3 Stresses in Welded Joints in Torsion 9-4 Stresses in Welded Joints in Bending 9-5 The Strength of Welded Joints 9-6 Static Loading 9-7 Fatigue Loading 9-8 Resistance Welding 9-9 Bolted and Riveted Joints Loaded in Shear 9-10 Adhesive Bonding Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  3. LECTURE-40 9-1 Welding Symbols 9-2 Butt and Fillet Welds 9-3 Stresses in Welded Joints in Torsion 9-4 Stresses in Welded Joints in Bending 9-5 The Strength of Welded Joints Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  4. Introduction Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints • Welding is the process of joining two pieces of metal together by hammering, pressure or fusion. Filler metal may or may not be used. • The strongest and most common method of permanently joining steel components together. • Arc welding is the most important since it is adaptable to various manufacturing environments and is relatively cheap. • A weldment is fabricated by welding together a collection of metal shapes.

  5. Introduction Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints • A pool of molten metal in which the components and electrode material coalesce, forming a homogeneous whole (ideally) when the pool later resolidifies. • The materials of components and electrode must be compatible from the point of view of strength, ductility and metallurgy.

  6. The form of a welded joint is dictated largely by the layout of the joined components. • Two most common forms are: • the buttjoint • the filletjoint Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  7. 9-1 Welding Symbols • A weld is fabricated by welding together a collection of metal shapes, cut to particular configurations. • The weld must be precisely specified on working drawing and this is done by welding symbol, Fig. 9-1. • The arrow of this symbol points to the joint to be welded. • The body of the symbol contains as many of the following elements as are deemed necessary: • Reference line • Arrow • Basic weld symbols in Fig. 9-2 • Dimensions and other data • Supplementary symbols • Finish symbols • Tail • Specification or process. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  8. Welding Symbols WELD Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  9. Types of Welding • There 2 general types of welds: • Fillet weldsfor general machine elements. • Butt or groove welds for pressure vessels, piping systems,... • There are also others such as: , Fillet welds groove welds Bead Plug or slot groove Plug or slot Bead Fillet Figure 9-2 Arc and gas-weld symbols Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  10. Parts to be joined must be arranged so that there is sufficient clearance for welding operation. • Due to heat, there are metallurgical changes in the parent metal in the vicinity of the weld. • Residual stresses may be introduced because of clamping or holding. • These residual stresses are not severe enough to cause concern. • A light heat treatment after welding is done to relive these stresses. • When the parts to be welded are thick, a preheating will also be of benefit. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  11. Figure 9-3 Fillet welds Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  12. Figure 9-4 The circle on the weld symbol indicates that the welding is to go all around. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  13. Figure 9-5 Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  14. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  15. Figure 9-6 Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  16. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  17. 9-2 Butt and Fillet Welds where h is the weld throat and l is the length of the weld. Notice that the value of h does not include the reinforcement. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  18. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints The reinforcement can be desirable, but it varies somewhat and does produce stress concentration at point A in the figure. If fatigue loads exist, it is good practice to grind or machine off the reinforcement.

  19. Stresses in Fillet Welds • Fig. 9-8 illustrates a typical transverse fillet weld. • In Fig. 9-9 a portion of the welded joint has been isolated from Fig. 9-8 Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints • At angle q the forces on each weldment consists of a normal force Fnand a shear force Fs

  20. Stresses in Fillet Welds Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints • The nominal stresses at the angle θ in the weldment, τ and σ, are

  21. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints • The von Misesstresseσ’at angle θ is • σ’maxoccurs at θ = 62.5o with a value of σ’max = 2.16 F/(hl). • The corresponding values of τ and σ, are τ = 1.196 F/(hl) and σ = 0.623 F/(hl). • τmaxcan be found by solving the equation [d(τ)/dθ]=0. • The stationary point occurs at θ = 67.5o with a corresponding τmax = 1.207 F/(hl) andσ = 0.5 F/(hl).

  22. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  23. We have no analytical approach that predicts the existing stresses. • The geometry of the fillet is crude by machinery standards. • The approach has been to use a simple and conservative model, verified by testing as conservative. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  24. The approach has been to: • Consider the external loading to be carried by shear forces on the throat area of the weld. By ignoring the normal stress on the throat, the shearing stresses are inflated sufficiently to render the model conservative. • Use the distortion energy for significant stresses • Circumscribe typical cases by code • For this model, the basis for weld analysis or design employs • which assumes the entire force F is accounted for by a shear stress in the minimum throat area. (9.3) Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  25. Notice that this inflates the maximum estimated shear stress by a factor of 1.414/1.207=1.17. • Further, consider the parallel fillet welds shown in Fig. 9-11 where, as in Fig.9-8, each weld transmits a force F. However, in the case of Fig. 9-11, the maximum shear stress is at the minimum throat area and corresponds to Eq. (9-3). Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  26. Under circumstances of combined loading we: • Examine primary shear stresses due to external forces. • Examine secondary shear stresses due to torsional and bending moments. • Estimate the strength(s) of the parent metal (s). • Estimate the strength of the deposited weld metal. • Estimate the permissible load(s) for parent metal(s). • Estimate permissible load for deposited weld metal. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  27. 9-3 Stresses in Welded Joints in Torsion • Figure 9-12 illustrates a cantilever of length l welded to a column by 2 fillet welds. • The reaction at the support of a cantilever always consists of shear force V and a moment reaction M. • The shear force produces a primary shear in the welds of magnitude • where A is the throat area of the welds. (9.4) Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  28. The moment at the support produces secondary shear or torsion of the welds, and this stress is given by • where • r: distance from the centroid of the weld group to the point in the weld of interest. • J: second polar moment of area of the group about the centroid of the group. (9.5) Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  29. Figure 9-13 shows 2 welds in a group. The rectangles represent the throat areas of the welds. • Weld 1 has a throat width b1 = 0.707 h1 • Weld 2 has a throat width d2 = 0.707 h2 • Throat area of both welds together is • A = A1 + A2 = b1d1 + b2d2 • which is the area to be used in Eq. (9-4) Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  30. The x-axis passes through the centroid G1of the weld 1. • The second moment of area about this axis is • Similarly, the second moment of area about an axis passing through G1parallel to the y-axis is • The second polar moment of areas of weld 1 and weld 2 about their centroids are Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  31. The centroid G of the weld group is located at • The distances r1and r2 from G1 and G2 are respectively given by • Using the parallel axis theorem, the second polar moment of area of the weld group is • This is the quantity to be used in Eq. (9-5). The distance r must be measured from G and the moment M computed about G. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  32. (9.6) Ju : is found from table 9.1 Page 472 Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints • The quantities and , which represent the weld width are small and hence can be neglected. • The terms and Makes JG1and JG2linear in the weld width. • Setting weld widths b1 and d2 to unity leads to the idea of treating each fillet weld as line. • The resulting second moment of area is then a unit second polar moment of area. • The value of Ju same regardless of weld size. • Since throat width of a fillet weld is 0.707h, the relation between J and the unit value is

  33. Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints

  34. QUESTIONS ? Thank U ! Dr. A. Aziz Bazoune Chapter9: Welding, Bonding, and the Design of Permanent Joints