EV.4.8 Tractive System Part Positioning

All parts belonging to the Tractive System must meet F.10.5.8

Rules Reference - F.10.5.8

F.10.5 Attachment

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F.10.5.8 Accumulator Attachment – All Types

a. Every fastener must withstand the Test Load in pure shear, using the minor diameter if any threads are in shear

b. Every Accumulator bracket, chassis bracket, or monocoque attachment point must withstand the Test Load in bending, in pure tearout, pure pullout, pure weld shear if welded, and pure bond shear and pure bond tensile if bonded.

c. Monocoque attachment points must meet F.7.8.8

d. Fasteners must be spaced minimum 50 mm apart to be counted as separate attachment

points

This rule requires that components belonging to the High Voltage (Tractive) System also comply with F.10.5.8, which determines the attachment requirements of the Accumulator Container. Outlined there are specifications for each fastener, bracket, and monocoque attachment point (if applicable). While a full explanation of these rules can be found on the UNCA Chassis Rules Site, a brief overview of each subsection of this rule is provided below.

Graphic - Mohr's Circle

F.10.5.8.a stipulates that each fastener used for the Tractive System be able to withstand a test load in pure shear. Further, if the fasteners are threaded, the smallest diameter of its thread (measured at a right angle to the thread axis) is what should be used.

But what is pure shear?

Pure shear is a specific type of deformation where an object is distorted but not rotated, and the volume remains unchanged. In this deformation, the principal axes of stress or strain are aligned with the material axes, and the deformation can be described by stretching along one axis and compressing along the perpendicular axis equally. The principal axes of stress or strain remain fixed in direction and coincide with the axes of the material, and the stress tensor in pure shear has a specific symmetric form where the shear components are equal and opposite on the diagonal.

Diagram - Test Load (Attachment)

In F.10.5.8.b, it is stated that any accumulator or chassis bracket must be capable of handling a test load applied on a multitude of different axes. As shown in the picture on the left, the bracket must be able to withstand bending in the Z-direction and the Y-direction.

In this diagram, shear tear-out is also defined along the X-axis.

Furthermore, the bracket must handle being subject to pull-out in the Y-direction (through the pocket).

In the cases of pull-out and tear-out, there are special considerations to be made of the mounting site. If welded, calculations should be representative of weld-shear, whereas if the mount is bonded, they should be representative of bond-shear and bond-tensile.

Note that the leverage point is shown relative to the mounting of the component.

Diagram - Test Load (Segment)

For monocoque attachments, F.10.5.8.c requires that each point follow in suit with F.7.8.8. Essentially, each attachment point should have a solid insert which fully encloses and eliminates gaps between the inner and outer skin.

In monocoque or tube frame, F.10.5.8.d discusses spacing of the attachments. In order to justify being separate, each attachment must be at least 50 millimeters away from the nearest attachment. This is most likely to ensure that a load is distributed evenly among each component.

Rules Reference - F.7.8.8 (Referenced in F.10.5.8.c)

F.7.8.8 Each Roll Hoop or Accumulator Container to Chassis attachment point must contain one of the two:

a. A solid insert that is fully enclosed by both the inner and outer skin

b. Local elimination of any gap between inner and outer skin, with or without repeating skin layups

Article - Chassis and Attachment Suggestions

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