1. Mechanical Design Lecture (2) Chapter (2) : Welding and Welded JointsBy
Dr. Abdel-Rahman Ibrahim Abdel-Bary

2. References
Dan B Marghitu, Mechanical Engineerʹs Handbook, Department of Mechanical Engineering, Auburn University, Auburn, Alabama, 2001.
Peter R. N. Childs, Mechanical Design, University of Sussex UK, 2004.
Bodynas & Nisbett, Mechanical Engineering design, Mc Graw-Hill, New York
B. J. Hancock, B. Jaconson, and S. R. Schmid, Fundamentals of Machine Elements, McGraw-Hill, New York, 1999.
W. H. Middendorf and R. H. Englemann, Design of Devices and Systems. Marcel Dekker, New York, 1998.
R. L. Mott, Machine Elements in Mechanical Design. Prentice-Hall, Upper Saddle River, NJ, 1999.
R. L. Norton, Machine Design. Prentice-Hall, Upper Saddle River, NJ, 2000
C. W. Wilson, Computer Integrated Machine Design. Prentice Hall, Upper Saddle River, NJ, 1997.
D. B. Marghitu and M. J. Crocker, Analytical Elements of Mechanisms, Cambridge University Press, 2001.

3. Welding and Welded Joints
Lecture (2)
Welding and Welded Joints
Objectives of lecture (2) :
Studying lecture (2) , the student should :
Learn the importance applications of welding.
Learn The types of welded joints
Design of welded joints
Analyze the stresses due to different types of loading
Check the safety of welded joints

4. Lecture (2) Welding and Welded Joints
t: Plate thickness
W: Width of weld = t
l : Length of weld (design parameter)
0.707 t l: Shearing area
0.707 t l τ: Resistance force of welded joint
τ, σ: Shear and tensile Stress
P: Load force = t l τs

5. l
In case of automated process the permissible shearing stress τs in the weld is assumed as 70% of permissible tensile stress σt of parent metal. For manual weld the joints τs = 50% of σt. If P varies between Pmin and Pmax , the permissible stress is multiplied by a factor ɤ. ɤ = 1/(4/3 – 1/3 × (Pmin/Pmax))
l = P/0.707 t τs

6. ***

7. Fig. 2.4 T- Joint under Axial and Eccentric Load
2.4 T- Joint A fillet weld of a plate welded to another at right angle. The joint may be subject a tension, P or bending due to P acting parallel to weld, as seen in Figure 2.4. Two loads are shown in this figure for convenience but they will be analyzed separately.
Fig. 2.4 T- Joint under Axial and Eccentric Load

8. 1. Axial Tension in T-joint Fillet weld
The depth of the throat of the weld h = 0.7 t.
The length of the weld is l
The cross-section of fillet is an isosceles triangle. Thus
The areas to resist shearing failure:
The leg of the weld = thickness of the plate t and
τs The permissible shearing stress in the weld.

9. 2. Eccentric load P :
e Eccentricity distance measured between line of action of force P and the line joining the centers of gravity of triangular sections of fillet welds.
P The load have two actions on the fillet:
- shearing along the throat plane
- bending of throat plane of the weld
The shearing stress due to P acting on the area:
Bending stress:
a. Z modulus of section
b. Width of section = 0.7 t and depth =l.
c. The sections are considered perpendicular to the axis

10. d. The bending stress σ occurs at top of the fillet at point A in Figure 2.4. e. At these points the shearing stress is given by: τ = P/1.4 t l f. The maximum shearing stress: Here σx = σ, τxy = τ and σy = 0
τmax = permissible shearing stress τs
For design purposes:
τmax = 50% of permissible tensile stress for manual welding
= 70% of permissible tensile stress for automatic welding.

11. Thanks