Lec 5 (Welded Joint)

COURSE OUTLINE Permissible & actual stresses

Ch-10 KHURMI

Design of a simple machine element Design of keys, cotters and couplings

Design of riveted, welded and bolted joints Design of helical and leaf springs

Design of shafts Design standards

Metal fits & tolerances

Ch-9 SHIGLEY

DESIGN OF WELDED JOINT Permanent fastenings

Riveted Joints

Welded Joints

Require the knowledge of  Manner of Loading  Geometry of the joint  Pattern of the joint

DESIGN OF WELDED JOINT

DESIGN OF WELDED JOINT Types of the welded Joint

DESIGN OF WELDED JOINT General nomenclature

DESIGN OF WELDED JOINT Types of the Weld joint

1.Lap joint or fillet joint 2.Butt joint.

DESIGN OF WELDED JOINT Types of the Weld joint

DESIGN OF WELDED JOINT Other types of the Weld joint

DESIGN OF WELDED JOINT Main considerations involved in the selection of weld joint type

• The shape of the welded component required • The thickness of the plates to be welded • The direction of the forces applied

DESIGN OF WELDED JOINT Welding Symbols

DESIGN OF WELDED JOINT Welding Symbols

DESIGN OF WELDED JOINT Welding Symbols

DESIGN OF WELDED JOINT Welding Electrodes

DESIGN OF WELDED JOINT APPLICATIONS

DESIGN OF WELDED JOINT APPLICATIONS

DESIGN OF WELDED JOINT Stress analysis of transverse fillet (lap) joint

Throat thickness

t sin 45  s o

Size or leg of the weld (thickness of the plate)

t  0.707 s Since the weld is weaker than the plate due to slag and blow holes, therefore the weld is given a reinforcement which may be taken as 10% of the plate thickness.

DESIGN OF WELDED JOINT Stress analysis of transverse fillet (lap) joint

Minimum throat area

Throat thickness

A  t l Length of the weld

DESIGN OF WELDED JOINT Stress analysis of transverse fillet (lap) joint

Applied Force

Throat Area

P  0.707 sl t Single transverse fillet (lap) Weld

Permissible tensile stress

DESIGN OF WELDED JOINT Stress analysis of transverse fillet (lap) joint

Applied Force

Throat Area

P  2 0.707 sl t Double transverse fillet (lap) Weld

Permissible tensile stress

DESIGN OF WELDED JOINT Stress analysis of parallel fillet (lap) joint

Applied Force

Minimum throat Area

P  2 0.707 sl Parallel transverse fillet (lap) Weld

Permissible shear stress

DESIGN OF WELDED JOINT Stress analysis of transverse & parallel fillet (lap) joint

Applied Force

P  (0.707 sl1 t )  (2  0.707 sl2 ) Combination of fillet (lap) Weld In order to allow for starting and stopping of the bead, 12.5 mm should be added to the length of each weld obtained by the above expression.

DESIGN OF WELDED JOINT Circular fillet weld subjected to torsion

𝐽 = 𝜋ൗ4 𝑡𝑑 3

2𝑇 𝜏= 𝜋𝑡𝑑2 𝑡

DESIGN OF WELDED JOINT Circular fillet weld subjected to bending moment

When the shaft is subjected to a bending moment only, the maximum stress is given by the bending equation. 𝑍 = 𝐼/𝑦

𝑍 = 𝜋ൗ4 𝑡𝑑 2

𝑡

DESIGN OF WELDED JOINT Eccentrically Loaded Welded Joints

CASE-1 The joint will be subjected to the following two types of stresses: 1. Direct shear stress due to the shear force P acting at the welds 2. Bending stress due to the bending moment P× e.

Applied Force

  P (2  0.707  sl ) Permissible shear stress

Area of weld

DESIGN OF WELDED JOINT Eccentrically Loaded Welded Joints

CASE-1 The joint will be subjected to the following two types of stresses: 1. Direct shear stress due to the shear force P acting at the welds 2. Bending stress due to the bending moment P× e.

Bending stress

b  M Z

P×𝑒

2 𝑡𝑙 ( ൗ6) × 2

Where t=0.707s

DESIGN OF WELDED JOINT Eccentrically Loaded Welded Joints

CASE-1

DESIGN OF WELDED JOINT Eccentrically Loaded Welded Joints

CASE-2 The joint will be subjected to the following two types of stresses:

1. Direct or primary shear stress 2. Shear stress due to turning moment.

Applied Force

 1  P (2  0.707  sl ) Area of weld Permissible shear stress

DESIGN OF WELDED JOINT Eccentrically Loaded Welded Joints

CASE-2 The joint will be subjected to the following two types of stresses:

1. Direct or primary shear stress 2. Shear stress due to turning moment.

𝑃×𝑒

2

r2

T

J Polar moment of inertia

Permissible shear stress

DESIGN OF WELDED JOINT

DESIGN OF WELDED JOINT

DESIGN OF WELDED JOINT Eccentrically Loaded Welded Joints

CASE-2

DESIGN OF WELDED JOINT EXAMPLE-1 A rectangular steel plate is welded as a cantilever to a vertical column and supports a single concentrated load of 60 KN.

Determine the weld size if shear stress in the same is not to exceed 140 MPa.

DESIGN OF WELDED JOINT EXAMPLE-2 A plate 75 mm wide and 12.5 mm thick is joined with another plate by a single transverse weld and a double parallel fillet weld. The maximum tensile and shear stresses are 70 MPa and 56 MPa respectively. Find the length of each parallel fillet weld, if the joint is subjected to both static and fatigue loading.

DESIGN OF WELDED JOINT EXAMPLE-3 A 50 mm diameter solid shaft is welded to a flat plate. If the size of the weld is 15 mm, find the maximum normal and shear stress in the weld.

EXAMPLE-4 Design the circular fillet weld subjected to load of 10KN with a eccentricity distance of 500mm and rod diameter of 55mm and rod length of 800mm. Use E70 electrodes for welding.

Weld joint

𝜋𝑡𝑑 3 𝐽= 4 𝜋𝑡𝑑 2 𝑍= 4

NUMERICAL PROBLEMS Chapter # 10: Welded Joints From A Textbook of Machine Design by R.S.KHURMI AND J.K.GUPTA PRACTICE YOURSELF Examples

10.1, 10.2, 10.4, 10.5, 10.6, 10.9, 10.10, 10.11, 10.13, 10.14, 10.15, 10.16 Exercise Problems

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

NUMERICAL PROBLEMS

Chapter # 9: Welding, Bonding, and the Design of

Permanent Joints From SHIGLEY’S MECHANICAL ENGINEERING DESIGN PRACTICE YOURSELF Examples

9.1, 9.2, 9.4 Exercise Problems

9-1 to 9-31