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Composite Materials Qualification at Airbus UK - ESUEC
20 Nov 2003
Qualification of Materials and Use of Data in Design of Aerospace Structures
A view from Airbus UK Composites Research
MMS IAG, NPL Teddington
Presented by
Rob FergusonComposites Test Specialist
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t.Outline
• This presentation only looks at
• Composites
• Airbus UK.
• Outline of Presentation
• Brief overview of composites in Airbus aircraft
• Regulatory Requirements and Certification Approach
• Generating Design Allowables from Qualification Data
• Conclusions
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t.History of Composites in Airbus Aircraft
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t.State of the Art for Composites at Airbus
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t.Immediate Future for Composites at Airbus: A380
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t.Composites Research at Airbus UK: TANGO
TANGO Lateral wingbox assembly
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t.Regulatory Requirements for Materials
• JAR 25.603 Materials
The suitability and durability of materials used for parts, the failure of which could adversely affect safety, must –
(a) Be established on the basis of experience or tests;
(b) Conform to approved specifications (such as industry or military specifications, or Technical Standard Orders) that ensure their having the strength and other properties assumed in the design data; and
(c) Take into account the effects of environmental conditions, such as temperature and humidity, expected in service.
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t.Regulatory Requirements for Materials
• JAR 25.613 Material Strength Properties And Design Values(a) Material strength properties must be based on enough tests of material
meeting approved specifications to establish design values on a statistical basis.
(b) Design values must be chosen to minimise the probability of structural failures due to material variability...Compliance with this sub-paragraph must be shown by selecting design values which assure material strength with the following probability:
(1) Where applied loads are eventually distributed through a single member within an assembly, the failure of which would result in loss of structural integrity of the component, 99% probability with 95% confidence.
(2) For redundant structure, in which the failure of individual elements would result in applied loads being safely distributed to other load carrying members, 90% probability with 95% confidence.
(c) The effects of temperature on allowable stresses used for design in an essential component or structure must be considered where thermal effects are significant under normal operating conditions.
(d) …
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t.Airbus UK Certification Approach
• Composite structure is designed to withstand Ultimate Loads…- In all environmental conditions.- Throughout the operating life of the aircraft.… “Ultimate Load” = maximum anticipated load (“Limit Load”) x safety
factor (usually 1.5), defined in JAR 25.303
• Full scale structural tests demonstrate:- Proof of Ultimate Load capability (static strength).- No fatigue damage initiation and propagation.- Manufacturing defects do not grow during aircraft life and do not
reduce allowable in-service damage
• Coupon and element tests are used to generate design data complying with JARs 25.603 and 25.613.
• Use “Pyramid of Test” approach to support design and analysis of aircraft structure.
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t.
Component e.g.Complete wingset
Sub-components e.g.Outer wingbox
Landing gear support
Details, e.g.Stiffened skin panelsSpar or rib box test
Elements, e.g.Bolted joint groupL-pull and T-pull
Coupons, e.g.Tension / compression / shear
Strength Tests
• Generic specimens
• Understand deformations and failure modes
• Determine strength and strain limits
• Establish Design
Proof Tests
• Aircraft-specific specimens
• Demonstrate Ultimate Load or fatigue capability
• Include defects, damage, environmental effects.
• Validate Design
Mechanical Tests
(Material properties)
Manufacturing Tests
(Process, quality)
Pyramid of Test
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t.Material Property Data Required
• Property information required for structural materials:
- Mechanical properties e.g.• Ply: Strength, stiffness etc. in tension, compression and shear.• Laminate: Strength in tension and compression with and without
holes; bearing strength; Compression After Impact strength.
- Physical properties, e.g.• Density, Tg, volume fraction, cured ply thickness, CTE.
- Environmental response, e.g.• -55°C to +120°C dry and “wet” (saturated with water)• Contaminants (hydraulic fluid, jet fuel, solvents, paint stripper)
- Requirements for storage, handling, processing, machining etc.
• Qualification forms part of the process of generating this data in compliance with JAR 25.
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t.Process for Generation of Design Allowables
1. Generate Data
- Airbus Industrie Material Specification (AIMS) defines tests to• Demonstrate material quality (for procurement / quality control).• Provide data used to generate some structural analysis
allowables.
- Additional tests for cases not covered by the AIMS are also carried out.
2. Apply statistics to create “material allowables”
- Statistical requirements for calculation of A and B-basis defined in JAR 25.613.
3. Apply “engineering judgement” to create “design allowables”
- Ensures dataset is coherent and applicable for intended analysis tools.
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t.Qualification Requirements: History
• Material qualification activity “owned” by M&P department
- Key qualification driver is material and process reliability.
- Qualification data provides statistical base for calculation of specification data.
• Design activity “owned” by Stress department
- Key design driver is mechanical performance.
- Calculation of design allowables requires a statistical base.
• Airbus material specifications have expanded over time to generate basic design data in addition to qualification data.
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t.Step 1: Generate the Raw Data
• AIMS test matrix:
- Provides strength (and modulus where required) data for up to 5 batches of material with 6 specimens per batch (usually).
- Repeated across:
• Temperature envelope(-55°C to +120°C) for dry and saturated.
• Contaminants e.g. fuel, MEK, paint stripper.
• Layup variations (QI, shear bias, directed).
- Also physical property tests. Extract of test matrix from AIMS
• Additional test matrix for cases not covered by AIMS, e.g. additional layups, notch or countersink factor generation.
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t.Step 2: Calculate the Material Allowables
• JAR 25.613 states that “Design values must be chosen … which assure material strength with the following probability:
(1) Where applied loads are eventually distributed through a single member within an assembly … 99% probability with 95% confidence.
(2) For redundant structure … 90% probability with 95% confidence.”
Case (1) is known as “A-basis”; case (2) as “B-basis”.
• Airbus UK approach based on MIL-HDBK-17, with an additional approach for small datasets where appropriate.
• The resulting mean, A- and B-basis values are “material allowables” and are used for material specification, quality control and procurement activities.
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t.Step 3: Generate the Design Allowables
• Generate “design allowable” dataset based on
- Calculated B-basis values from:
• AIMS tests (“material allowables”).• Additional data generated outside the AIMS.
- Applying consistency across:
• Environmental parameters.• Large/small datasets.
- Fatigue and damage tolerance requirements (e.g. strain limits).
- Procurement requirements e.g. harmonisation with second source.
- Adjustments for use with specific analysis methods / tools.
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t.Conclusions
• Qualification and use of material property data is driven by JAR25, especially JARs 25.603 and 25.613.
• The qualification process provides data for procurement and some structural analysis.
• Further testing is carried out to provide additional design data for structural analysis.
• “Material allowable” values are not necessarily the same as “design allowable” values due to the different requirements of quality control and structural analysis.
• To satisfy certification requirements, component designs are validated through large-scale structural tests (validates data, methodology and analysis tools).
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t.Full Scale Structural Test on A320
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