Crashworthiness Concept for an EV Front Structure: Energy Absorption

The problem

EVs lose the engine block that helps absorb frontal crash energy, while the battery must be protected from intrusion. Front rails and crash boxes must absorb energy in a controlled, progressive way. SOLIDWORKS is not an explicit crash solver, so a research project must combine what it can do with analytical models and tests, and be honest about limits.

Objectives

• Define a frontal crash energy target for an example EV and allocate it to structures.
• Design crash box and rail concepts with triggers for progressive folding.
• Study quasi-static crush with large-displacement nonlinear analysis and compare with analytical mean crush force models.
• Validate with quasi-static or drop-weight tests on tube specimens and plan an explicit model.

What you need

Key concepts

Specific energy absorption

Energy absorbed per unit mass of the structure, a key measure for comparing crash box designs.

Crush force efficiency

Mean crush force divided by peak force. High efficiency means a flat force curve, which limits peak deceleration.

Progressive folding

A tube folding in a controlled series of lobes absorbs energy steadily. Triggers such as beads or notches start folding at the right place.

Implicit versus explicit

Implicit solvers suit slow, quasi-static loads; explicit solvers handle fast, contact-heavy events like full crashes.

Step-by-step guide

1. 1

   Set the crash energy target

   Take an example compact EV with a stated mass and a frontal impact speed for your study. Calculate kinetic energy and decide what share the front structure must absorb, as an assumption. Note that Indian frontal crash requirements are set by the current AIS and CMVR rules and rating programmes, which you should check. Set targets for mean crush force, stroke and peak force.

   Checkpoint: An energy budget with assumptions and targets for crash box and rail force and stroke.

2. 2

   Lay out the front structure

   In SOLIDWORKS, lay out the bumper beam, crash boxes, front rails, the motor and subframe envelope and the battery pack envelope behind. Mark the stroke available before the battery would be reached. Use configurations for two or three rail section concepts. Make sure the load path from crash box to rail to floor is direct. Add a simple envelope for the motor and subframe that must not block folding.

   Checkpoint: A layout showing available crush stroke and the load path, with the battery protected by a stated margin.

3. 3

   Use analytical crush models

   For square and circular tubes, calculate mean crush force with published analytical models, such as those based on Alexander's model for circular tubes and Wierzbicki and Abramowicz's model for square tubes. Use them to size wall thickness and section width for your target force. Calculate specific energy absorption for each. Check that each formula applies to your wall thickness and section width range, since these models assume thin walls. Compare circular and square sections at equal mass.

   Checkpoint: Analytical mean crush forces and SEA for candidate sections, with references for each formula.

4. 4

   Design crash box concepts

   Model crash boxes as sheet metal or extruded tubes with triggers: beads, notches or tapered ends to start folding at the front. Make three concepts: plain tube, beaded tube and multi-cell section. Assign steel or aluminium from the material library, and add a stress-strain curve from your data. Keep the mass of each concept similar so SEA comparisons are fair. Check the triggers can be made by pressing or machining. Save each concept as a configuration.

   Checkpoint: Three crash box concepts modelled with mass and section properties recorded.

5. 5

   Run quasi-static crush

   Set up a nonlinear static study with large displacement and an elasto-plastic von Mises material. Fix the rear of the crash box and push a rigid plate into the front with displacement control. Use contact between the plate and the box and self-contact for folds where your version allows. Run to as much stroke as converges and plot force against displacement.

   Checkpoint: Force-displacement curves for each concept through at least the first one or two folds.

6. 6

   Assess limits and convergence

   Implicit nonlinear studies can struggle as folds contact themselves. Record how far each run goes and whether peak force and first-fold mean force converge with mesh refinement. Report results only for the converged part. Be clear that full crush with many folds needs an explicit solver. Note any warnings about contact and element distortion. Try a finer mesh in fold zones and see whether the run goes further. Keep a log of settings for each run.

   Checkpoint: A table of converged peak force and first-fold mean force with mesh sizes, and the stroke reached.

7. 7

   Compare with analytical models

   Compare simulated peak force and first-fold mean force with analytical predictions. Compute SEA and crush force efficiency where possible. Rank concepts by SEA and efficiency and check that the triggered designs reduce peak force. Explain differences in terms of model assumptions. Separate implicit results clearly from analytical and test results in every table. Do not extrapolate the force curve beyond the converged stroke, and say clearly where each run stopped and why.

   Checkpoint: A comparison table of analytical and simulated forces with ranked concepts.

8. 8

   Test specimens

   Make tube specimens of the best two concepts and crush them quasi-statically in a universal testing machine, or dynamically on a drop tower, under supervision and with safety guards. Record force and displacement and photograph folding. Compare with analytical and simulated results, and note strain-rate effects in dynamic tests. Check in the photos that folding starts at the trigger, and compare the measured fold length with the analytical and simulated values.

   Checkpoint: Measured force-displacement curves and fold photos compared with predictions.

9. 9

   Protect the battery

   Using the validated crash box force and rail sizing, estimate whether the front structure absorbs the energy budget within the available stroke. Check the rails for buckling under the crash box force with a linear buckling study. Add a load path check for the subframe and battery front member. Revise designs if the battery margin is not met. Include the subframe and motor mounts as possible extra load paths in the energy sum.

   Checkpoint: An energy-stroke check showing the battery margin is met, and rail buckling factors above the crash box force.

10. 10

    Plan the explicit model and report

    Prepare geometry and material data for an explicit crash model, and define the test-matched crash box case as the first validation. Write the thesis chapter covering energy targets, analytical sizing, implicit studies and their limits, tests and the explicit plan. Clearly separate what was simulated, what was tested and what remains. Include the test data and photos in an appendix. Say what an explicit model will need, such as strain-rate data and contact settings, and how it will first be validated against the crash box tests.

    Checkpoint: A report with validated crash box results, clear limits and a ready explicit model plan.

Testing & validation

• Analytical crush forces calculated and referenced.
• Implicit crush results reported only within converged range.
• Tube specimen tests compared with predictions.
• Battery stroke margin checked with the energy budget.

Expected results

A front-structure crash concept for an EV with sized crash boxes and rails, analytical and implicit simulation results, specimen test validation and a plan for full explicit crash analysis.

Take it further

• Run the explicit crash model and compare with tests.
• Study foam-filled or composite crash boxes.
• Add a small-overlap load case and side-rail design.

Viva and review questions

Learn it at DIYguru

These DIYguru courses and programmes teach what this project needs.