Multi-stage inversion tube mounting system
Methods and apparatus are provided for a mounting system for attaching a container to a vehicle adapted to resist loads imparted by the container to the mounting system in sequential stages. In one exemplary mounting system a first spring is configured to elastically compress when subjected to an initiation load that exceeds a load imparted to the first spring by the container under static conditions. The first spring may have a useable load range from the initiation load to a maximum load at which the first spring is fully bottomed out. A first deformable member is disposed serially with respect to the first spring, and configured to remain substantially un-deformed until subjected to a first deformation threshold load that equals or exceeds the maximum load at which the first spring is fully bottomed out. A second deformable member may be disposed serially with respect to the first deformable member, and configured to remain substantially un-deformed until subjected to a second deformation threshold load that substantially exceeds the first deformation threshold load.
1. A multi-stage energy attenuating mounting system adapted for attaching a container to a vehicle at a plurality of discrete mounting points on the container:
a bracket adapted for being securely attached to the container at the mounting points, the bracket having a flange configured to extend away from the container;
a rod extending through a hole in the flange, wherein the hole is sized to have clearance around the rod;
a base plate spaced apart from the flange in a parallel orientation thereto, wherein a first end of the rod is securely attached to a center portion of the base plate, and wherein the base plate is adapted to be rigidly fixed to a vehicle at a perimeter portion of the base plate;
a first compression spring disposed about the rod between the flange and the base plate, and a second compression spring disposed about the rod on an opposite side of the flange from the first compression spring; and
an inversion tube disposed about the rod between the second compression spring and a second end of the rod, the inversion tube having an open end abutting the second compression spring, and a substantially closed end fixed to the second end of the rod.
2. The multi-stage energy attenuating mounting system of claim 1 , wherein the base plate comprises a deformable region separating the center portion from the perimeter portion.
3. The multi-stage energy attenuating mounting system of claim 2 , wherein the deformable region comprises a plurality of concentric rings of elongated slots through the plate, each slot having a length and a width.
4. The multi-stage energy attenuating mounting system of claim 3 , wherein the elongated slots of adjacent ones of said rings are offset such that a said slot in any one said ring is aligned with a space between ones of said slots on immediately adjacent ones of said rings.
5. The multi-stage energy attenuating mounting system of claim 3 , wherein a spacing between two adjacent ones of said rings of elongated slots is equal to or less than the width of the slots in another two adjacent ones of said rings.
6. The multi-stage energy attenuating mounting system of claim 3 , wherein the length of a space separating two adjacent ones of said slots in a said ring is equal to or less than the width of either slot.
7. The multi-stage energy attenuating mounting system of claim 1 , wherein the first and second springs are stacks of Belleville washers.
8. The multi-stage energy attenuating mounting system of claim 7 , wherein the first and second springs are installed in a pre-compressed state with a pre-load calculated to exceed by a pre-defined amount a static load applied to the first and second springs.
9. The multi-stage energy attenuating mounting system of claim 1 , further comprising a drive washer between the second spring and the open end of the inversion tube, and a nut threaded onto the rod fixing the substantially closed end of the inversion tube on the rod.
10. The multi-stage energy attenuating mounting system of claim 1 , wherein the inversion tube is configured such that a deformation threshold of the inversion tube is reached, and plastic deformation of the inversion tube ensues when a load imparted by the flange in a direction toward the open end of the inversion tube exceeds by a pre-defined amount a load sufficient to fully compress the second spring.
11. The multi-stage energy attenuating mounting system of claim 10 , wherein the amount of pre-defined load in excess of the amount of load sufficient to fully compress the second spring is zero.
12. The multi-stage energy attenuating mounting system of claim 10 , wherein the base plate is configured such that a deformation threshold is reached, and plastic deformation of the base plate ensues when the load imparted by the flange toward the open end of the inversion tube substantially exceeds the deformation threshold of the inversion tube.
13. The multi-stage energy attenuating mounting system of claim 1 , further comprising:
a second rod extending through a second hole in the flange, wherein the second hole is sized to have clearance around the second rod, and wherein a first end of the second rod is securely attached to the center portion of the base plate;
a third compression spring disposed about the second rod between the flange and the base plate, and a fourth compression spring disposed about the second rod on an opposite side of the flange from the third compression spring; and
a second inversion tube disposed about the second rod between the fourth compression spring and a second end of the second rod, the second inversion tube having an open end abutting the fourth compression spring, and a substantially closed end fixed to the second end of the second rod.