Validated Aerospace Metallic Materials Properties
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Design engineers can spend a great deal of time rigorously developing models, analyzing structures and simulating product performance and good reliable design data is critical to the design process. The design engineer faces an ever-increasing demand for products with a performance that must be substantiated under stringent conditions of cost and environment. If invalid material property data are utilized, then valuable engineering time will be wasted. If the error is detected early during development or testing, then the design and structures will have to be reanalyzed with validated data and new prototypes built and tested. In the worst case, field failures could result in costly corrective actions such as scrapping of raw materials, alternative materials selection, new supplier identification and approval, product redesign or retooling of production lines.
The output or results of structural design or finite element method (FEM) models are only as good as the design input data, which include physical or material properties. After the design is verified with prototyping and testing or virtual simulations, the design can be optimized by assessing alternative part geometries or new material selections from the MMDH materials database in the validated model and/or through additional prototyping and testing.
Data concerning aerospace structural materials are widely scattered and, when located, are of variable quality and relevance to industrial applications. The task of collecting and evaluating all the relevant data available on a particular material property is time consuming and therefore expensive. While is some cases mechanical testing is used on products or material samples to assure quality. With all of the test factors, material condition and lot variation involved, the engineer may question the validity of internal or local data compared to materials data from a significant cross-section of the engineering and scientific community. The design or materials engineer would need to have the alloy property tests validated through round robin or proficiency test with other established testing laboratories, which is a time consuming and costly process. ESDU Metallic Materials Data Handbook provides validated material property data that can be used with confidence in finite element method models and with other engineering analysis techniques.
Collection, Validation and Presentation of Data on Metallic Materials
ESDU 00932, The Metallic Materials Data Handbook (MMDH) first came into being in May 1981 as Def Stan 00-932 following 10 years of data collection, collation and evaluation by, amongst others, Paul Johnson and Bob Obee then of BAe Woodford. The content of MMDH is based on the Society of British Aerospace Companies (SBAC) Technical Specification 95, “Recommendations for metallic materials specifications to be used for new designs”. SBAC is now part of ADS, which publishes standards for the aerospace industry based in the United Kingdom.
The compiler of MMDH and assisting members of Panel M obtain materials data from a wide variety of commercial or company and standard designations, compositions, forms, heat treatments and orientations in order to construct an MMDH material Data Sheet. Before metallic properties are issued in a datasheet, a great deal of statistical analysis and rigorous evaluation are applied to ensure the validity of the property data and the status of data. Depending on the quantity, quality and origins of the raw data, any of 17 methods might be used to obtain the values ultimately quoted in MMDH.
A, B and S are three statistical "basis" used to group the data by confidence limits. "A basis" data has a 95 per cent probability that at least 99 per cent of the material released will exceed the A value. "B basis" data has a 95 per cent probability that at least 90 per cent of the material released will exceed the B value. "S basis" data specified the minimum values or min-max value range from an appropriate material specification or standard.
Once all the values that can be have been derived for a particular material, a draft Data Sheet is submitted to Panel M for approval. Panel M meets four times each year to examine draft Data Sheets, review existing Data Sheets, and discuss any other matters pertinent to MMDH. At the meetings, draft Data Sheets are either approved for issue, often subject to further minor changes and/or corrections being made, or they are held back pending further work or until additional data become available.
Following the approval of a Data Sheet, the data are added to the master database and that is then checked to ensure that the data have been incorporated correctly. Bespoke software is then used to generate, from the master database, the html and image files for the internet version of MMDH.
MMDH Data Status Levels
Material property data quoted in the MMDH data can have varying status or levels of validation depending on the amount and availability of the data. Aerospace alloys accepted and established in the industry will have a large amount of data available while newer alloys under development will have limited test data. Some of conventions used to indicate the status of the data being presented are:
“Grey Paper” (GP) Data
- Values and figures printed on a grey background (Grey Paper data).
- Typically, GP data are data from the barest minimum of tests, possibly from pre-production samples or manufacturer’s catalogue values. They also include values based on tests not in accordance with or meeting all the requirements of the procedures specified in Section 5 of MMDH. They are applicable only to preliminary design studies, and are for use with great caution and are included to provide advance information on new materials and properties likely to become of importance.
White Paper Bracketed (WPB) data
- Bracketed values and figure curves displayed as dashed lines ().
- WPB data are less well substantiated than White Paper Full data, but have been approved by Panel M as being acceptable for use in showing compliance with design and airworthiness requirements.
White Paper Full (WPF) data:
- Values without brackets on a white background and figure curves displayed as full lines on a white background ().
- WPF data are acceptable to show compliance with design and airworthiness requirements. Typically they include A, B and S values either obtained directly or derived from well substantiated property relationships.
The initial sections of the Metallic Materials Database Handbook provide detailed information on derivation and use of design data, conversion factors, property relationships, notation and definitions, limitations and variations of allowable stresses and the standardized test procedures used for validation of the material properties.
Range of Alloy and Metallic Material Properties
The database can provide data on a range of material properties such as:
- Mechanical properties – (Ultimate strength, modulus, elongation, poisson's ratio in tensile, Shear, Torsion Bearing, or Compression)
- Elevated temperature properties (Heat Factors)
- Composition / Principle Alloying Elements
- Thermal and physical properties (CTE, thermal conductivity, density)
- Fatigue or cyclic stress and fracture toughness properties
- Creep and stress-rupture properties
- Toughness (Charpy or Izod)
- Weldability and brazing characteristics
- Corrosion resistance and stress corrosion cracking susceptibility (KIscc)
- Magnetic properties
The specific properties in the database depend on the applicability and availability related to the specific metal alloy. The data
Sections 6, 9 and 12 contain material properties information on the low density or light weight alloys including aluminum alloys, magnesium alloys and titanium alloys. Low maintenance or corrosion resistant alloys are covered in sections 10 and 12. Ferrous alloys and aircraft quality steels are listed in sections 10 and 11. Section 8 contains data on heat resisting alloys. Section 7 provides data on copper alloys.
ESDU Aerospace Materials Data Sets
MMDH - Metallic Materials Data Handbook
MMPDS - Metallic Materials Properties Development and Standardization
ESDU Design Collections
Additional Engineering Reference from ESDU