Headed fastener with precisely calculated groove under head to accommodate O'ring sealing member as a self-sealing assembly

A method of securing a rivet to at least one workpiece, comprising:

• providing a rivet having a first head and a shank, said first head and said shank having a first aperture passing therethrough providing a collar having a bore passing therethrough, said collar being disposed at an upper surface of said fastener head and extending partially into the aperture of said fastener head;
• providing a mandrel having an upper end and a lower end, said mandrel having a precalculated breaking area and having locking means for mating with said collar, said breaking area being disposed above said locking means and said breaking area being a relatively weakened area whereby when a pull tool applies a tensile stress to said mandrel, said tensile stress required for separation of said mandrel is achieved at said breaking area before said tensile stress causes separation of said mandrel at another area of said mandrel;
• placing said shank through an opening in said at least one workpiece;
• collapsing a lower portion of said shank to form a second head so that said first and second heads engage upper and lower surfaces of said at least one workpiece;
• sealing said aperture by compressing a sealing member between said collar and a wall of said apertures, placing said collar into locking engagement with said mandrel within said aperture to maintain said sealing member in a compressed state, and breaking said mandrel at said breaking area.

A fastener, comprising:

• a fastener head having an upper surface and a lower surface;
• a shank extending from said lower surface of said fastener head, said shank and said fastener head having an aperture passing therethrough;
• a collar having an inner wall forming a bore, said inner wall having a first plurality of locking teeth, and said collar being disposed at said upper surface of said fastener head and extending partially into the aperture of said fastener head;
• a mandrel having an upper end and a lower end, said mandrel extending through at least a portion of said aperture and extending through at least a portion of said bore, said mandrel having a precalculated breaking area and having locking means for mating with said collar, said breaking area being disposed above said locking means and said breaking area being a relatively weakened area whereby when a pull tool applies a tensile stress to said mandrel, said tensile stress required for separation of said mandrel is achieved at said breaking area before said tensile stress causes separation of said mandrel at another area of said mandrel;
• and
• a first sealing member disposed between said collar and said mandrel.