RIVET AND RIVETED JOINTS

Classes and Types of Riveted Joints
Riveted joints may be classified by application as: 1) pressure vessel; 2) structural; and 3) machine member.







For information and data concerning joints for pressure vessels such as boilers, reference should be made to standard sources such as the ASME Boiler Code. The following sections will cover only structural and machine-member riveted joints.


Basically there are two kinds of riveted joints, the lap-joint and the butt-joint. In the ordinary lap-joint, the plates overlap each other and are held together by one or more rows of rivets. In the butt-joint, the plates being joined are in the same plane and are joined by means of a cover plate or butt strap, which is riveted to both plates by one or more rows of rivets. The term single riveting means one row of rivets in a lap-joint or one row on each side of a butt-joint; double riveting means two rows of rivets in a lap-joint or two rows on
each side of the joint in butt riveting. Joints are also triple and quadruple riveted. Lap-joints may also be made with inside or outside cover plates.



General Design Considerations for Riveted Joints

Factors to be considered in the design or specification of a riveted joint are: type of joint; spacing of rivets; type and size of rivet; type and size of hole; and rivet material.


Spacing of Rivets : The spacing between rivet centers is called pitch and between row center lines, back pitch or transverse pitch. The distance between centers of rivets nearest each other in adjacent rows is called diagonal pitch. The distance from the edge of the plate to the center line of the nearest row of rivets is called margin.

Size and Type of Rivets : The rivet diameter d commonly falls between d = 1.2 t and d = 1.4 t, where t is the thickness of the plate. Dimensions for various types of American Standard large (1⁄2-inch diameter and up) rivets and small solid rivets are shown in tables that follow. It may be noted that countersunk heads are not as strong as other types.


Size and Type of Hole : Rivet holes may be punched, punched and reamed, or drilled. Rivet holes are usually made 1⁄16 inch larger in diameter than the nominal diameter of the rivet although in some classes of work in which the rivet is driven cold, as in automatic machine riveting, the holes are reamed to provide minimum clearance so that the rivet fills the hole completely.


Rivet Material : Rivets for structural and machine-member purposes are usually made of wrought iron or soft steel, but for aircraft and other applications where light weight or resistance to corrosion is important, copper, aluminum alloy, Monel, Inconel, etc., may be used as rivet material.


Simplified Design Assumptions : In the design of riveted joints, a simplified treatment is frequently used in which the following assumptions are made:

1) The load is carried equally by the rivets.
2) No combined stresses act on a rivet to cause failure.
3) The shearing stress in a rivet is uniform across the cross-section under question.
4) The load that would cause failure in single shear would have to be doubled to cause failure in double shear.
5) The bearing stress of rivet and plate is distributed equally over the projected area of the rivet.
6) The tensile stress is uniform in the section of metal between the rivets.


Formulas for Riveted Joint Design
A riveted joint may fail by shearing through the rivets (single or double shear), crushing the rivets, tearing the plate between the rivets,  crushing the plate or by a combination of two or more of the foregoing causes. Rivets placed too close to the edge of the plate may tear or shear the plate out to the edge but this type of failure is avoided by placing the center of the rivet 1.5 times the rivet diameter away from the edge.


In the following formulas, let
d=diameter of holes; t =thickness of plate; tc =thickness of cover plates; p=pitch of inner row of rivets; P=pitch of outer row of rivets; Ss = shear stress for rivets; St =tensile stress for plates; Sc =compressive or bearing stress for rivets or plates.
















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Justice Uwakwe said...

In rivet joints, the distance from the centre of one rivet to the centre of the next rivet measured parallel to the seam is called?

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