Failures modes of riveted joints

Riveted joints:

A rivet is a permanent mechanical fastener. Before being installed a

rivet consists of a smooth cylindrical shaft with a head on one end. The end

opposite the head is called the buck-tail.

To distinguish between the two ends of the rivet, the original head is

called the factory head and the deformed end is called the shop head or

buck-tail.

Because there is effectively a head on each end of an installed rivet, it

can support tension loads (loads parallel to the axis of the shaft); however,

it is much more capable of supporting shear loads (loads perpendicular to

the axis of the shaft). Bolts and screws are better suited for tension

applications.

Types of riveted joints:

• Butt joint,

• Single lap joint ,

• Double lap joint

Types of failures:

1. Shear failure of rivets,

2. Bearing failure,

3. Tear-out failure,

4. Tension failure.

The objective in joint design is to maximize the joint efficiency,

Efficiency= Failure load of the joint/Failure load of the

surrounding sheet

The actual efficiency of a joint is the minimum of all the

possible joint efficiencies you could calculate for all the possible failure

modes of the joint.

Shear failure of a rivet:

Basic Assumption:

The cross-shearing stress, in the rivets is uniformly distributed over

all shear areas. All rivets take equal loads. The joint

efficiency is

Where A sheet –is the cross sectional area of the sheet,

Ar -is the cross sectional area of one rivet,

Bearing failure

Assumption: Ultimate bearing stress between the rivets and the plates is

assumed to be uniformly distributed over the projection of the contact area.

Contact Area is the plate thickness, t, multiplied by the rivet diameter,

d=2r. The joint efficiency is

Tear-out failure:

Shear failure of the sheet along the indicated lines. The joint efficiency is

Where Ne=Number of rivets in the row closest to the edge of either plate,

t = thickness of the plate,

e = distance from rivet center to the edge of the plate.

Tension failure:

Assumption: Tensile stress in the plate is assumed to be uniformly

distributed over the net area of the plate at each row of rivets. Must

consider all rows and both sheets! Joint efficiency for row r is

Applications: Before welding techniques and bolted joints were developed,

metal framed buildings and structures such as the Eiffel Tower, Shukhov

Tower and the Sydney harbour Bridge were generally held together by

riveting. Also automobile chassis were riveted. Riveting is still widely used

in applications where light weight and high strength are critical, such as in

an aircraft. Many sheet-metal alloys are preferably not welded as

deformation and modification of material properties can occur.

Blind rivets are used almost universally in the construction of plywood road

cases.