Impact absorber and method of manufacture

An impact absorber of the type comprising two aligned parts of a tubular overall shape, each part having a different cross section, and the two aligned parts being joined together by a joining zone, such that:

• the aligned part of the impact absorber which has a smaler surface area cross section is a plunger tube,
• the aligned part of the inpact absorber which has a larger surface area cross section is an abosorber tube in which as the absorber tube is turned-back under the action of the plunger tube at the region of the joining zone, with a turned-back portion of the impact absorber freely sliding about said plunger tube, said turned-back portion begins at the region of the joining zone,
• wherein, for any plane of section passing through the axis of the tube formed by the two aligned parts,
• Dp denotes the outside diameter of said plunger tube and Da denotes the outside diameter of said absorber tube,
• Ep denotes the thickness of the plunger tube and Ea denotes the thickness of the absorber tube,
• Rr.p is the natural outside radius of the turned-back portion of the tubular casing of the plunger tube and Rr.a is the natural outside radius of the turned-back portion of the tubular casing of the absorber tube,
• and, said joining zone, prior to turning back the absorber tube, connects inwardly with said plunger tube, forming an outside radius of curvature Rp, and connects outwardly with said absorber tube, forming an outside radius of curvature Ra, such that the following five relationships are simultaneously satisfied:
• Ep>Ea;
• Rp<Rr.p;
• Ra>Rr.a ½(Da-Dp)>2×Rr.a;
• Ra>Rp.