In securing workpieces together with a blind fastener, it is desirable to be able to maintain a high final clamp load on the workpieces. At the same time, it is desirable that the installed fastener has the capability of withstanding high shear loads. The magnitude of the clamp load is established by the relative axial force applied between the stem and shell when the blind head is formed and then engages the back surface of the workpiece. The magnitude of the shear load is primarily determined in this type of rivet by the mechanical strength of the stem, while the shear strength which can be attributed to the shell is normally less significant, and cannot be readily increased, since the shell must retain high ductility in order to be deformed during setting.
In order to achieve high shear strength, therefore, it is desirable to have a solid stem which will always shear flush with the head of the shell, and will guarantee a full plugging of the workpiece from the head of the shell on the one side, and to the blind (opposite) side of the workpiece. However, prior fasteners of this type have typically been limited in the width range of the workpieces they can fasten, since the principal engineering requirement to plug the entire workpiece in order to obtain high shear strength has not permitted the rivet to be used in multiple workpieces widths.
USPTO Backgrounds
USPTO Backgrounds