FSAE Segment Structural HandCalcs

Original work: early 2024 (MATLAB, pre-design of the UV26 accumulator segment). Ported to Python and re-run against SES 2026 load cases. I've been grounding segment design decisions in this calculation set for two years.

Battery Module Structural Analysis

These hand calcs, translated into a Python script, let me iterate quickly on the structural design of the UV26 accumulator segment. This page covers the current SES calculations, calculations expected for 2026, and sanity checks I wanted for solid mechanical design.

Design verdict:Governing case is lid bending under SES 20g vertical load, SF 1.75. That set the polycarbonate lid at 3/8" thickness. All seven load cases pass SES crash requirements. Bolts, bond, and buckling all clear with margin. No redesign needed, the existing geometry and bolt scheme hold.

Open interactive notebook

Open the Colab notebook to change dimensions, materials, or load factors and re-run.

1. Constants and Geometry

Segment assembly

             ____________________________________________________________
            /                                                           /|
           /                     POLYCARBONATE LID                     / |
          /___________________________________________________________/  |
         |                                                           |   | <-- EneSegHeight
         |                                                           |   |       (105.6 mm)
         |___________________________________________________________|   |
         |                                                           |  /
         |                                                           | / <-- EneSegmentWidth
         |___________________________________________________________|/        (81.2 mm)
           <------------------- EneSegmentDepth ------------------->
                                 (417.0 mm)

Cell layout (top view)

      _________________________________________________________
  |  | [ o o ]   [ o o ]   [ o o ]   [ o o ]   [ o o ]   [ o o ] |
  |  | [ o o ]   [ o o ]   [ o o ]   [ o o ]   [ o o ]   [ o o ] |
  |  | [ o o ]   [ o o ]   [ o o ]   [ o o ]   [ o o ]   [ o o ] |   (81.2 mm) WIDTH
  |  | [ o o ]   [ o o ]   [ o o ]   [ o o ]   [ o o ]           |
  |  |_________________________________________________________| |
  |                                                                |
     <----------------------- DEPTH (417.0 mm) -------------------->

Input parameters

Material properties

2. Load Cases and Bending Stress

Calculated for 20g vertical and 40g lateral crash loads per SES requirements. Assuming a uniformly distributed load where total force relates to distributed load by :

Maximum bending moment

Bending stress

Maximum deflection

Results — polycarbonate lid

Verifies the polycarbonate lid survives a 20g vertical crash load. Cells stay in.

3. Fasteners

Tensile stress area

For a threaded rod in pure tension, strength is defined by the average of minor and pitch diameters. The tensile-stress area is:

For ISO metric threads (M6):

Where = major diameter (6.0 mm), = thread pitch (1.0 mm).

Axial tensile stress:

Ref: Norton, R. L. (2020). Machine Design: An Integrated Approach, 6th ed., p. 907.

Fastener results (M6 bolts)

4. Bond Strength

How strong is the bonded G10 under simple loading? This doesn't account for finger joints (which add more strength).

5. Euler-Johnson Buckling

Critical slenderness ratio and radius of gyration:

Johnson (inelastic) buckling if :

Euler (elastic) buckling if :

Ref: Norton, Machine Design, 6th ed., p. 231.

Results

6. Passive Thermal

Conductive heat dissipation capacity through the segment casing.

7. Summary

All safety factors > 1.0. Structure passes SES crash load requirements.

Code

Sources

1. Enepaq VTC6 Module Datasheet — module dimensions and weight.
2. Laminated Plastics G-10 / FR4 Data — material strengths, bonding, tear-out.
3. MatWeb Polycarbonate Data — mechanical properties for the lid.