machine design of welded joints

1. DESIGN OF MACHINE ELEMENTS-1
(MEPC-301)
Presented by:
Dr Saurabh Kango
Lecture-33 & 34

2. WELDED JOINTS
STRENGTH OF BUTT WELDS
Butt Weld in Tension
A gas tank consists of a cylindrical shell of 2.5 m inner diameter.
It is enclosed by hemispherical shells by means of butt welded
joint as shown in Fig. The thickness of the cylindrical shell as
well as the hemispherical cover is 12 mm. Determine the
allowable internal pressure to which the tank may be subjected,
if the permissible tensile stress in the weld is 85 N/mm2. Assume
efficiency of the welded joint as 0.85.

3. STRENGTH OF PARALLEL FILLET WELDS STRENGTH OF TRANSVERSE FILLET WELDS
The length of each of the two equal sides is called a leg. As a
rule, the leg length h is equal to the plate thickness
The throat is the minimum cross-section of the weld located at
45° to the leg dimension
failure due to tensile stress will occur at the throat section.
Double parallel fillet welds
Double transverse fillet welds

4. A steel plate, 100 mm wide and 10 mm thick, is welded to
another steel plate by means of double parallel fillet
welds as shown in Fig. The plates are subjected to a static
tensile force of 50 kN. Determine the required length of
the welds if the permissible shear stress in the weld is 94
N/mm2.
Adding 15 mm of length for starting and stopping of the weld
run, the length of the weld is given by,
l = 37.62 + 15 = 52.62 or 55 mm
Two steel plates, 120 mm wide and 12.5 mm thick, are
joined together by means of double transverse fillet
welds as shown in Fig. The maximum tensile stress for
the plates and the welding material should not exceed
110 N/mm2. Find the required length of the weld, if the
strength of weld is equal to the strength of the plates.

5. MAXIMUM SHEAR STRESS IN PARALLEL FILLET WELD
symbol cross indicates a force perpendicular to the plane of
paper, which goes away from the observer. The symbol dot
indicates a force perpendicular to the plane of paper, which is
towards the observer.
The welds are cut at an angle q with the horizontal. t’ is the
width of plane that is inclined at angle q with the horizontal.
If l = 1 mm

6. MAXIMUM SHEAR STRESS IN TRANSVERSE FILLET WELD

7. ECCENTRIC LOAD IN THE PLANE OF WELDS
The force P acting through the centre of gravity causes direct shear stress in the welds. It is called the primary shear stress. It
is assumed that the primary shear stress is uniformly distributed over the throat area of all welds. Therefore,
The couple M causes torsional shear stresses in the throat area of welds. They are called secondary shear stresses and given by

8. A welded connection, as shown in Fig. is subjected to an
eccentric force of 7.5 kN. Determine the size of welds if the
permissible shear stress for the weld is 100 N/mm2. Assume
static conditions.

9. Suppose t is the throat of each weld. There are two welds W1 and
W2 and their throat area is given by,
The two welds are symmetrical and G is the centre of gravity of
the two welds.
The distance r of the farthest point in the weld from the centre
of gravity is given by

10. WELDED JOINT SUBJECTED TO BENDING MOMENT
The bending stresses are assumed to act normal to the throat
area. The resultant shear stress in the welds is given by,
The throat dimension is very small compared to b or d.
Therefore, the first term in the above expression is neglected.

11. A bracket is welded to the vertical column by means of two fillet welds as shown in Fig. Determine the size of the welds, if the
permissible shear stress in the weld is limited to 70 N/mm2.

12. WELDED JOINT SUBJECTED TO TORSIONAL MOMENT
Consider an elemental section in the weld having an area dA. It
is located at an angle q with X-axis and subtends an angle dq.
The area of the elemental section is given by,
The moment of inertia of the annular fillet weld is obtained by integrating the above
expression. Therefore,

13. A circular shaft, 50 mm in diameter, is welded to the support by means of circumferential fillet weld as shown in Fig.
It is subjected to torsional moment of 2500 N-m. Determine the size of the weld, if the permissible shear stress in the weld is
limited to 140 N/mm2.

14. WELDED JOINTS SUBJECTED TO FLUCTUATING FORCES
Stress Concentration in Welds

15. Reference
Thank You
Design of Machine Element by V B Bhandari
Machine Design Data Book by V B Bhandari