Battery Enclosure Drop Test Simulation

The problem

Portable and swappable packs are dropped during handling, and fixed packs can be dropped during assembly or service. A drop can crack housings, dislodge modules or damage cells. Physical drop testing is destructive and expensive, so simulation is used to find weak points and choose protective features before prototypes are built.

Objectives

• Build a simplified but representative pack model for impact analysis.
• Set up Drop Test studies for several orientations and heights.
• Use elastic-plastic material where yielding is expected and study mesh and time sensitivity.
• Assess enclosure stress, permanent deformation and internal accelerations.
• Redesign corners and module mounts and compare results.

What you need

Key concepts

Drop Test study

A SOLIDWORKS Simulation study that calculates the response of a part or assembly hitting a floor from a given height or velocity, over a short time after impact.

Defeaturing

Removing small details that do not affect the global response, such as logos and tiny fillets, to make a model that meshes and solves efficiently.

Elastic-plastic material

A material model that yields above a stress and keeps permanent strain. It is needed when impact stresses exceed yield.

Peak deceleration

The maximum acceleration of internal parts during impact, often expressed in g. It drives loads on module mounts and cells.

Step-by-step guide

1. 1

   Define the drop scenario

   Define an example pack of 12 kg with a polymer or aluminium housing, and drop heights such as 0.5 m and 1.0 m onto concrete, representing handling. List orientations: flat on the base, on an edge, and on a corner, which is usually worst. Note that standards such as AIS-156 include mechanical requirements for traction batteries and that test heights and conditions must be taken from the current standard.

   Checkpoint: A test matrix of heights and orientations, with the source of each value stated.

2. 2

   Build a simplified model

   Defeature the pack: keep housing walls, ribs, corners, module mounts and lid fasteners, and replace each module with a solid block of the correct mass and an equivalent stiffness. Remove logos, small holes and cosmetic fillets. Join lid and housing with bonded contact or bolts depending on what matters. Check total mass and centre of gravity with Mass Properties against the detailed model.

   Checkpoint: Simplified model mass and centre of gravity within about 2 per cent of the detailed model.

3. 3

   Assign materials

   Assign the housing an elastic-plastic von Mises material using yield strength and tangent modulus or a stress–strain curve from the datasheet. Keep module blocks linear elastic with an equivalent modulus chosen to give a realistic stiffness. Note which properties are assumed. For polymers, remember that properties depend on temperature and strain rate, which the Drop Test study does not fully capture.

   Checkpoint: A material table with sources and assumptions for every body.

4. 4

   Set up the Drop Test

   Create a Drop Test study, set drop height and gravity direction, and set the target orientation for the first case, such as corner impact. Choose a rigid target for a concrete floor. Set the solution time after impact long enough to capture the first rebound, checking by inspecting the displacement plot. Request results at enough plot steps to see the peak.

   Checkpoint: The study solves and the time history shows impact, peak deformation and rebound.

5. 5

   Check mesh and time sensitivity

   Run the corner case with a coarse, medium and fine mesh, refining at the impact corner with mesh control. Compare peak von Mises stress, plastic strain and module peak acceleration. Also extend the solution time to check that the peak is captured. Choose the mesh where results change by less than about 10 per cent, accepting that impact results converge more slowly than static.

   Checkpoint: A sensitivity table for three meshes and a justified choice.

6. 6

   Run the test matrix

   Run every height and orientation in the matrix with the chosen mesh. For each, record peak von Mises stress, maximum plastic strain in the housing, permanent deformation after rebound and peak acceleration of each module block from a sensor or probe. Save animations for the worst cases to show how the housing deforms. Keep all other settings fixed so differences come from height and orientation only.

   Checkpoint: A results table for the full matrix with the worst orientation and height identified.

7. 7

   Check module mounts

   Take the peak module deceleration from the worst drop case and apply it as an acceleration load in a Static study of the module mounts and fasteners. Use Bolt connectors and check bolt and boss factor of safety. Compare with a hand calculation of the force as module mass times deceleration. This shows whether modules would tear free. Include bolt preload, since loose bolts let modules hammer their mounts.

   Checkpoint: Mount and bolt factor of safety under the peak deceleration, confirmed by a hand calculation.

8. 8

   Redesign for impact

   Create a configuration with protective changes: larger corner radii, corner ribs or bumpers in a softer material, thicker walls at the impact corner and compliant module mounts that lower peak acceleration. Rerun the worst cases. Track mass added against the reduction in plastic strain and module acceleration. Keep the redesign within the original envelope so the pack still fits the vehicle. Check that softer bumpers do not lower the pack stiffness so much that modules move further in the drop.

   Checkpoint: Redesign reduces plastic strain and peak module acceleration in the worst case, with mass added recorded.

9. 9

   Interpret results honestly

   Compare predicted permanent deformation and stresses with material limits, and state where cracking is likely. Explain that cells are represented as blocks, so cell damage is not predicted; module acceleration is a proxy. Plan a physical drop test with a dummy pack and accelerometers to validate the corner case. Mark predicted crack locations on the drawing so they can be inspected after a physical test. Compare plastic strain with the material's elongation at break as a rough failure indicator.

   Checkpoint: A written interpretation listing what the model predicts, what it cannot predict and a validation test plan.

10. 10

    Report

    Report the scenario, model simplifications, materials, mesh and time sensitivity, test matrix results, mount check, redesign comparison and limitations. Include time-history plots of module acceleration and contour plots of plastic strain at the worst corner. Provide drawings of the redesigned corner and mount features. Present the test matrix as a heat map of plastic strain and module acceleration so the worst cases stand out. List all simplifications in one table so a reader can judge how far the model can be trusted.

    Checkpoint: A complete report with sensitivity, results, redesign and a validation plan.

Testing & validation

• Simplified model mass and centre of gravity match the detailed model.
• Mesh and solution-time sensitivity reported.
• Mount loads confirmed by hand calculation.
• Redesign compared with baseline on identical cases.
• Physical drop test plan included.

Expected results

A drop-test study of an example battery pack across heights and orientations, with mesh sensitivity, the worst case identified, a module mount check and a redesign that lowers plastic strain and internal acceleration.

Take it further

• Run a physical drop with a dummy pack and accelerometers and compare peaks.
• Study the effect of a flexible floor such as wood or rubber.
• Compare aluminium and glass-filled polymer housings for drop performance and mass.

Viva and review questions

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