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To design and iteratively optimise a prosthetic running blade using Finite Element Analysis (FEA), evaluating woven CFRP against an Aluminium 2014-T4 baseline to balance structural performance, durability, and weight under dynamic loading.

Project Brief

Initial C-Blade Design

Final C-Blade Design

Project Brief

To design and iteratively optimise a prosthetic running blade using Finite Element Analysis (FEA), evaluating woven CFRP against an Aluminium 2014-T4 baseline to balance structural performance, durability, and weight under dynamic loading.


Initial C-Blade Design

Final C-Blade Design

Focus

FEA · Fatigue Analysis · Modal Analysis

Timeline

8 Weeks · 2026

Toolkit

Fusion 360 · ANSYS Mechanical · Overleaf

Key Design Criteria

Design Criteria

Requirement

Materials

  • Epoxy Carbon Woven Prepreg Composite (230 GPa)

  • Aluminium Alloy 2014-T4

Lightweight Structure

Under 750 g

Durability

Minimum fatigue life of 1 million cycles or a 3x safety factor against peak stress

Vibrational Stability

Fundamental frequency > 50 Hz to minimise the risk of resonance during running

Boundary Conditions & Loading

  • Fixed Constraint: The upper attachment face was fixed to represent the connection between the blade and prosthetic socket.


  • Combined Loading: A 2100 N vertical force and 500 N horizontal force were applied to the contact region to represent combined ground-reaction loading during running.

Boundary Conditions on the initial Blade Design

Mesh Refinement

  • Global Mesh: A 2.5 mm quadratic mesh was used across the blade to capture its curved geometry.


  • Local Refinement: Element size was reduced to 1.5 mm around critical geometric transitions to better resolve stress concentrations.


  • Mesh Independence: Mesh density was progressively refined to verify that further refinement produced negligible changes in the key simulation results.

Mesh Refinement on the Final Blade Design

Mesh Refinement

  • Global Mesh: A 2.5 mm quadratic mesh was used across the blade to capture its curved geometry.


  • Local Refinement: Element size was reduced to 1.5 mm around critical geometric transitions to better resolve stress concentrations.


  • Mesh Independence: Mesh density was progressively refined to verify that further refinement produced negligible changes in the key simulation results.

Mesh Refinement on the Final Blade Design

Final Outcome: CFRP Running Blade

Iteration 1:
Cd ~ 0.3823, Cl ~ 0.0887

0.685kg

Mass of product

Iteration 1:
Cd ~ 0.3823, Cl ~ 0.0887

3.30x

safety factor against peak stress

Iteration 1:
Cd ~ 0.3823, Cl ~ 0.0887

78.9Hz

Fundamental Frequency

Iteration 1:
Cd ~ 0.3823, Cl ~ 0.0887

Final Outcome: CFRP Running Blade

0.685kg

Mass of product

3.30x

safety factor against peak stress

78.9Hz

Fundamental Frequency

Modal Analysis on the CFRP C-Blade

Safety Factor Analysis on the CFRP C-Blade

Lightweight Dynamic Performance: At 0.685 kg, the CFRP blade achieves a 78.9 Hz natural frequency, well above the ~50 Hz running excitation frequency, showing an effective stiffness-to-weight balance.

Reduced Stress Concentration: Increasing the fillet at the blade's straight-to-curve transition by 15% reduced peak stress to 244.16 MPa, resulting in a 3.30× safety factor against material failure.

Final Outcome: Aluminium Alloy Running Blade

Iteration 1:
Cd ~ 0.3823, Cl ~ 0.0887

1.35kg

Mass of product

Iteration 1:
Cd ~ 0.3823, Cl ~ 0.0887

111Hz

Fundamental Frequency

Iteration 1:
Cd ~ 0.3823, Cl ~ 0.0887

3.5x10⁶ Cycles

Predicted Fatigue Life

Iteration 1:
Cd ~ 0.3823, Cl ~ 0.0887

Final Outcome: Aluminium Alloy Running Blade

1.35kg

Mass of product

111Hz

Fundamental Frequency

3.5x10⁶ Cycles

Predicted Fatigue Life

Modal Analysis on the Aluminium Alloy C-Blade

Fatigue Analysis on the Aluminium Alloy C-Blade

Stiffness-to-Mass: The 111.08 Hz natural frequency reflects aluminium's high stiffness relative to its mass, consistent with ( fₙ ∝ √(k/m) ).

Fatigue Performance: The 3.5 million cycle fatigue life results from reduced stress concentrations at the critical bending transition, providing substantial durability under repeated loading.

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Click here to read the full report ↗

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