Welds

Joining Processes: Permanent Joints

Objectives

By the end of this section, you should be able to:

Design welded joints to carry many types of loading conditions

Introduction to Joints

Joining Processes

For cases where portions of machine elements are more

efficiently manufactured separately

Structures too large to be made of a single material or

material stock

Joining Processes

Non-Permanent

Permanent

Efficient for joining thin members

Eliminates individual fasteners, reducing machining and

assembly cost

Welding, Brazing, Soldering, Cementing, Gluing

Welding: Types of Joints

Welding: Types of Joints

Fillet Welds

Number indicates leg size

Arrow points to one side when both sides are the same

Circle on weld symbol welding to go all round

Welding: Types of Joints

Butt or Groove Welds

Square butt welded on

both sides

Single V with 60 bevel

and root opening of 2mm

Double V

Single Bevel

Welding: Types of Joints Special Groove Welds

T Joint for thick plates

U and J welds for thick plates

Corner Weld

Edge Weld

Design Considerations for Welding

Clearance for welding operation

Heat causes metallurgical changes

Cold rolled properties transform to hot rolled properties on

the vicinity of the welds

Residual Stresses due to clamping or order of welding

Light heat treatment after welding can help

Welded Joint Design

Stresses in Welded Joints

Butt Welds

Stresses in Welded Joints

Parallel Fillet Welds

Stresses in Welded Joints

Transverse Fillet Welds

Consists of shear and

normal stresses

There have been attempts

on accurately predicting

stresses on welds (9-2 of

Shigley), however,

geometry of fillet is crude

and macrogeometry is

complex.

Stresses in Welded Joints

Conservative Model

Consider the external loading to be carried by pure shear forces

on the throat area.

=

0.707

Use distortion energy for significant stresses

= 0.577

Stresses in Welded Joints: Torsion

Stresses in Welded Joints: Torsion M, J and r should be computed using the J and r and centroid of

the weld group

Stresses in Welded Joints: Torsion

Stresses in Welded Joints: Torsion

Stresses in Welded Joints: Torsion

Stresses in Welded Joints: Torsion

Stresses in Welded Joints: Torsion

Stresses in Welded Joints: Bending

Stresses in Welded Joints: Bending

Stresses in Welded Joints: Bending

Stresses in Welded Joints: Bending

Strength of Welded Joints

Strength of Welded Joints

= 0.577

Strength of Welded Joints

Fatigue

Endurance Limit Modifying Factors

Surface Factor () Forged

Size Factor () 1 if uniform shear stress on throat

Loading Factor () - 0.59 (fillet, shear), 1 (butt, axial)

Stress Concentration Factor(reduced):

Use fatigue failure criteria

General Method

Examine primary shear stress due to external forces

Examine secondary shear stress due to torsional and bending

moments

Estimate strengths of the parent metals

Estimate strength of the weld metal

Estimate permissible loads for parent metal

Estimate permissible loads for weld metal