Design of Welded Joints for mechaical branch
- 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