1. Mechanical Joints

2. Methods of joining materials
 Welding
 Mechanical joints
– Screw fasteners
– Rivets
 Adhesives

3. Uses of welding:
 Ship building, industrial and
commercial buildings.
 Oil pipe -line construction.
 Automobile, railways and bridges.
 Machine tools.
 Farm equipment, home appliances, and
air-conditioning units.
 Computer components.
 Mining equipment.
 Boilers, furnaces and vessels.
 Maintenance and repair of equipment

4. Welding and cutting processes:
Oxy-fuel gas welding (OFW)
oxygen and acetylene
Shield metal arc welding (SMAW)
it is the most popular method
because:
 High quality weld
 Excellent uniformity
 High rate
 It can be used for variety of
materials and thickness.

5. • Gas tungsten arc welding (GTAW):
Clean
 High quality weld
 No post weld finishing is required
 Performed on variety of material
• Gas metal arc welding
(GMAW):
 Fast
 Economical
 Welding on thin as well as thick
plates
 Reduced post-weld cleanup

6. • Pressure welding or resistance
welding
Spot welding
Seam welding

7. Welding joints:
Butt joint Lap joint
Double butt joint
Edge joint
Tee joint
Corner joint

8. Welding terminology

9. Welding strength:
• Welding joints are classified according to the
stress exerted on the joint:
Class 1- Longitudinal shear
Class2- transverse shear+ tension
Class3 - pure tension

10. Class 1-
Longitudinal shear
Area of shear = 2 a L
Where, a = 0.707 h L
L
h
a

11. Class2
-transverse shear+ tension
Area of shear = 2 h L
Area of tension = 2 h L
L h h

12. Class3
– pure tension
Area of tension = h L
h

13. Design of welding joint:
 Welding rods coated with flux table (7.1), (7.3)
 Uncoated welding rods 80% of table (7.1)
 ½ inch should be added to the length of weld
 compensate for the defects which may occur at
the beginning and end of welding
 Stress concentration factors should be taken
from table (7.2)
 For reinforced weld increase the weld area by
20%

14. Eccentric loads: F
L
 Thewelds will be subjected to a
combination of shear:
– Shear caused by direct load
– Shear caused by torque. (F L)

15. Approximate value of the significant stress
dA
l
Oc
S
r1
r
T
O
 Torsional shear stress is proportional to its distance
from centroid
 Assume, on element dA
 s = nr
 where:
 n: constant of proportionality
 r: distance from the element to O

16. The external torque
 dT = (s dA ) r
 Integrated over all the welds in the
joint. Thus,
T sdAr
2
T n r dA nJ
• J is the second polar moment
of area of the weld
Tr
• Substituting for n we get, s
J

22. Thank You