Failures Modes of Riveted Joints

Failures modes of riveted joints Riveted joints:  A rivet is a permanent mechanical fastener fastener.. Before being installed a rivet consists of a smooth cylindrical cylindrical shaft  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 a#is of the shaft$% however! it is much more capable of supporting shear loads "loads perpendicular to the a#is of the shaft$. Bolts and screws are better suited for tension applications. Types of riveted joints: •

Butt joint!

•

&ingle lap joint !

•

'ouble lap joint

Types of failures: (. &hear failure of rivets! ). Bearing failure! *. Tearout failure! +. Tension failure. The objective in joint design is to ma#imi,e the joint efficiency!

-fficiency 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.

&hear failure of a rivet:

Basic Assumption: The crossshearing stress! in the rivets is uniformly distributed over all shear areas. All rivets take e0ual loads. The joint efficiency is

 1here A sheet 2is the cross sectional area of the sheet!  A r is the cross sectional area of one rivet!

Bearing failure

 Assumption: 3ltimate bearing stress between the rivets and the plates is assumed to be uniformly distributed over the projection of the contact area. 4ontact Area is the plate thickness! t! multiplied by the rivet diameter! d)r. The joint efficiency is

Tearout failure:

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

 1here 5e5umber 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. 6ust consider all rows and both sheets7 8oint efficiency for row r is

 Applications: Before welding techni0ues and bolted joints were developed! metal framed buildings and structures such as the -iffel Tower! &hukhov Tower and the &ydney 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. 6any 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.