Qualification of Materials and Use of Data in Design of ... · PDF fileComposite Materials...

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

20 Nov 2003Composite Materials Qualification at Airbus UK - ESUEC

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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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This document and all information contained herein is the sole property of AIRBUS UK LTD. No intellectual property rights are granted by the delivery of this document or the disclosure of its content. This document shall not be reproduced or disclosed to a third party without the express written consent of AIRBUS UK LTD. This document and its content shall not be used for any purpose other than that for which it is supplied.

The statements made herein do not constitute an offer. Theyare based on the mentioned assumptions and are expressedin good faith. Where the supporting grounds for these statements are not shown, AIRBUS UK LTD will be pleased to explain the basis thereof.

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