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Fillet weld

A fillet weld has a triangular cross-section in the corner between two plates. Its strength is based on the throat thickness a, the height of the triangle from the root to the surface. The force is spread over the weld length, and the shear stress must stay below the allowed value.

\tau = \frac{F}{a\,l}

shear stress in the weld

A_w = a\,l

load-bearing area of the weld

Symbols

$\tau$	shear stress	MPa
$F$	force	N
$a$	throat thickness	mm
$l$	weld length	mm

Example

Two 100 mm welds with $a = 5$ mm carry 60 kN:

$\tau = 60\,000/(2\cdot 5\cdot 100) = 60$ MPa.

Remember to count every weld that shares the force.

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Part of Machine Design: Bolted and welded joints.