B787 Wing Material Selection

Overview

Project Summary

This project focuses on the optimal material selection for the Boeing 787-8 Dreamliner wing structure using Ashby's systematic methodology implemented through CES EduPack software. The wing was decomposed into three essential parts: primary structure, leading edge, and trailing edge (aileron and flap), and each was analyzed independently through performance index derivation, constraint-based filtering, and cost-performance comparison. The results were validated against the actual materials used in the real B787 aircraft.

Three essential parts of the wing: primary structure, leading edge, and aileron/flap

My Role

My Contributions

I was responsible for the entire material selection analysis and the validation against real B787 materials, from deriving performance indices to running CES EduPack simulations and comparing results with actual Boeing data.

Performance Index Derivation

Derived performance indices for all 3 wing parts.

CES EduPack Analysis

Used CES EduPack to generate Ashby charts for each wing part, applying mechanical, thermal, and cost constraints to filter from thousands of materials down to optimal candidates.

Material Comparison

Compared aluminum alloys vs. stainless steels for the leading edge, evaluating performance index, cost per unit performance, machinability, and corrosion resistance.

Validation Against Real B787

Compared selected materials with actual Boeing 787 data, confirming EP-CF70 composites for structure and aluminum alloys for leading edge match real aircraft.

Approach

Methodology

Step 1: Wing Decomposition

The wing was treated as a semi-monocoque structure and decomposed into three essential parts: primary structure (main load-bearing), leading edge (impact protection), and aileron/flap (control surfaces). Each part has different functional requirements and loading conditions.

Step 2: Geometry Simplification

Each wing part was simplified into an equivalent structural element: the primary structure as a cantilever beam with hollow rectangular cross-section, the leading edge as a half-tube, and the aileron as a triangular cantilever beam. These simplifications enabled analytical derivation of performance indices.

Step 3: Performance Index Derivation

For each wing part, the objective function (minimize mass) was expressed in terms of material properties using the constraint equations. Free variables were eliminated to derive material performance indices combining density, Young's modulus, fatigue strength, and fracture toughness as appropriate.

Step 4: CES EduPack Filtering

The derived performance index equations were plotted as iso-performance lines on logarithmic Ashby charts using CES EduPack. Constraints (service temperature ≤ −80°C, thermal expansion limits, minimum fracture toughness) were applied progressively to narrow candidate materials.

Step 5: Material Comparison and Selection

Remaining candidates were compared on performance index, cost per unit performance, machinability, corrosion resistance, and ductility. The AND method was used to combine multiple performance indices for the primary structure.

Step 6: Validation Against Real B787 Data

Selected materials were compared with the actual materials used in the Boeing 787 Dreamliner to validate the methodology. Results showed excellent agreement: composites for structure/trailing edge and aluminum for leading edge.

Primary Structure

Main Wing Structure Selection

Geometry and Simplification

The primary structure carries the bending moment from aerodynamic lift. It was modeled as a cantilever beam with a hollow rectangular cross-section (h = b/4), where the wing root acts as the fixed support (fuselage junction). The distributed load along the wing was approximated as a triangular distribution representing the combined effect of lift and self-weight.

Simplified primary wing structure geometry: cantilever beam model

Performance Indices

Two mechanical constraints were derived, fatigue resistance and stiffness, leading to two performance indices combined using the AND method with equal weighting (m₁ = ½):

Final Performance Index Expression: Primary Structure

Using the AND method with base b as free variable:

log(σ_f^½ / ρ) = −log(E^⅓ / ρ) + 2·log(W*)

Where W₁ = σ_f^½/ρ (fatigue index) and W₂ = E^⅓/ρ (stiffness index), combined into the iso-performance line: y = −x + p

Constraint Limits

Constraint	Limit
Maximum thermal expansion α	≤ 10⁻⁶ µstrain/°C
Minimum fracture toughness K_c	≥ 30 MPa·m^½
Minimum service temperature	≤ −80°C

CES EduPack Results

CES results without constraints : composites and alloys dominate

CES results with constraints : zoomed view on remaining candidates

Candidate Material Properties

Property	BMI-CF65	Cyanate-CF65	EP-RF50	EP-CF70
Density (kg/m³)	1570–1610	1620–1670	1380	1550–1580
Young's Modulus (GPa)	110–130	299–376	60–80	129–154
Yield Strength (MPa)	1710–1740	1890–2530	1100–1380	1740–2170
Fatigue Strength 10⁷ cycles (MPa)	940–1130	1040–1650	605–897	959–1410
Fracture Toughness (MPa·m^½)	56.9–73.9	48.3–59	56.3–68.8	60.2–73.5
Min Service Temp (°C)	−67 to −47	−51 to −31	−48 to −28	−123 to −73
Thermal Expansion (µstrain/°C)	−0.17	−1.6	−0.83	−0.6
Price (EUR/kg)	89.2–107	196–219	44.6–73.4	34.9–38.8

At the B787's maximum cruising altitude of 43,100 ft (~13,137 m), the standard ISA temperature is approximately −56.5°C, but can drop to −70°C or even −80°C in polar/winter conditions. This eliminates BMI-CF65, Cyanate-CF65, and EP-RF50, leaving only EP-CF70.

Selected Material: EP-CF70

Property	Value
Fatigue Strength σ_f (MPa)	959–1410
Young's Modulus E (GPa)	129–154
Yield Strength R_e (MPa)	1740–2170
Price (EUR/kg)	34.9–38.8
Density ρ (kg/m³)	1550–1580
Fracture Toughness K_c (MPa·m^½)	60.2–73.5
Thermal Expansion α (µstrain/°C)	−0.6
Min Service Temperature (°C)	−123 to −73
Performance Index P (N·m/kg)	7.69–7.95
Cost/Performance C/P (EUR/N·m)	4.38–5.04

Leading Edge