A leading autonomous drone delivery OEM approached Dongguan Flex Precision Composites to redesign their payload platform. The original 7075-T6 aluminum design weighed 1.2 kg and could withstand a 3.5 J impact from a dropped payload. The goal: reduce weight by at least 50% while maintaining or improving impact resistance and stiffness. This case study details the material selection, FEA-driven design, manufacturing process, and validation testing that achieved a 55% weight reduction with a CFRP payload platform.
Design Requirements and Constraints
The payload platform is a critical structural component that supports the cargo bay and transfers loads to the drone fuselage. Key requirements included:
- Maximum weight: 0.6 kg (1.32 lb) target, from original 1.2 kg (2.65 lb)
- Impact resistance: Withstand a 3.5 J impact from a 2 kg payload dropped from 180 mm (7.1 in) without permanent deformation or failure
- Stiffness: Maximum deflection under 5 kg static load < 2 mm (0.079 in)
- Fatigue life: > 10,000 cycles at 80% of ultimate load
- Environmental: Operating temperature -20°C to +60°C, 95% RH
Material Selection: Toray T800H / Hexcel 8552
After evaluating multiple material systems, we selected a unidirectional prepreg of Toray T800H carbon fiber (5,490 MPa tensile strength, 294 GPa tensile modulus) with Hexcel 8552 epoxy resin (Tg > 190°C). This system offers an excellent balance of strength, stiffness, and impact resistance. The laminate was designed with a quasi-isotropic layup [(0/90/±45)]2S to provide isotropic in-plane properties.
The density of the CFRP is 1.58 g/cm³, compared to 2.81 g/cm³ for 7075-T6 aluminum, giving a theoretical weight reduction of 44% for equal volume. However, by optimizing the geometry with sandwich construction and ribs, we achieved 55% weight reduction.
FEA-Driven Design Optimization
We performed finite element analysis (FEA) using Abaqus to model the platform under static and impact loads. The baseline aluminum design had a mass of 1.2 kg and a safety factor of 2.5 under the 5 kg static load. The CFRP design iteration reduced mass to 0.54 kg while maintaining a safety factor of 2.8.
Worked Example: Static Deflection Calculation
For a simply supported rectangular plate with a central point load, the maximum deflection is given by:
w_max = (α * P * a²) / (E * t³)
Where α = 0.126 for a/b = 1.5, P = 5 kg × 9.81 m/s² = 49.05 N, a = 300 mm (0.3 m), E = 70 GPa (aluminum) or 55 GPa (CFRP quasi-isotropic), t = 4 mm (aluminum) or 3 mm (CFRP).
For aluminum: w_max = (0.126 × 49.05 × 0.3²) / (70e9 × 0.004³) = 0.00062 m = 0.62 mm
For CFRP: w_max = (0.126 × 49.05 × 0.3²) / (55e9 × 0.003³) = 0.00112 m = 1.12 mm
The CFRP deflection is 1.12 mm, still well under the 2 mm requirement. The impact simulation used a 2 kg mass at 2.0 m/s (3.5 J) and showed a peak stress of 320 MPa, below the material's compressive strength of 1,200 MPa.
Manufacturing and Quality Assurance
The CFRP payload platform was manufactured using autoclave cure at 135°C and 6 bar pressure, with a vacuum bag. The laminate was laid up on a 5-axis CNC-machined aluminum tool (DMG Mori DMU 80). After cure, the part was trimmed and drilled using a 5-axis CNC router with diamond-coated tooling to achieve ±0.05 mm tolerance. Each part was inspected with a Zeiss Contura CMM and ultrasonic C-scan to verify thickness and detect delaminations.
Comparison: Aluminum vs. CFRP Payload Platform
| Parameter | 7075-T6 Aluminum | CFRP (Toray T800H/8552) |
|---|---|---|
| Weight | 1.20 kg | 0.54 kg (55% reduction) |
| Density | 2.81 g/cm³ | 1.58 g/cm³ |
| Static Deflection (5 kg load) | 0.62 mm | 1.12 mm (within spec) |
| Impact Energy Absorption | 3.5 J (no failure) | 3.5 J (no failure) |
| Safety Factor (static) | 2.5 | 2.8 |
| Fatigue Life (80% load) | 10,000 cycles (no failure) | 10,000 cycles (no failure) |
| Cost per unit (low volume) | $45 | $68 |
Validation Testing Per ASTM D3039
To validate the material properties, we conducted tensile testing per ASTM D3039 (Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials) on five coupons taken from the production part. The results confirmed the design assumptions:
- Average tensile strength: 2,450 MPa (355 ksi) – 98% of theoretical
- Average tensile modulus: 54 GPa (7.83 Msi) – 98% of theoretical
- Poisson's ratio: 0.31
- Strain to failure: 1.8%
Impact testing was performed per ASTM D7136 (Drop-Weight Impact Test) with a 2 kg impactor at 1.87 m/s (3.5 J). The CFRP platform showed no visible damage and less than 0.1 mm permanent indentation, meeting the requirement.
Results and Client Benefits
The final CFRP payload platform achieved a weight of 0.54 kg, a 55% reduction from the original 1.2 kg aluminum design. This weight saving allowed the drone to carry an additional 0.66 kg of payload or extend flight time by 18%. The platform also demonstrated superior fatigue performance and corrosion resistance, extending service life in humid environments. The client has since adopted the CFRP design for their next-generation delivery drone fleet.
Key Takeaways
- CFRP payload platform reduced weight by 55% (1.2 kg to 0.54 kg) while meeting 3.5 J impact requirement.
- Toray T800H carbon fiber with Hexcel 8552 epoxy provides excellent strength-to-weight ratio for UAV structures.
- FEA optimization and quasi-isotropic layup achieved safety factor of 2.8 under static load.
- ASTM D3039 tensile testing confirmed material properties within 2% of theoretical values.
- 55% weight reduction translates to 18% longer flight time or 0.66 kg additional payload capacity.
Looking to reduce weight in your UAV or robotics application? Contact our engineering team at +86 130 2680 2289 or sales@flexprecisioncomposites.com for a design review and free feasibility study.
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