ESDU Engineer
Issue 08
MMDH - How it all works
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. Paul remains the force majeure behind the Handbook in his role as its compiler and secretary to Panel M, the committee that monitors and guides the methods of analysis and material data provided in MMDH.
The content of MMDH is based on the Society of British Aerospace Companies Technical Specification 95, “Recommendations for metallic materials specifications to be used for new designs” (with the exception of fastener data which are not included in MMDH owing to the wide variation in properties resulting from the numerous possible post-production treatments to which fasteners may be subjected).
As compiler of MMDH, Paul, with the assistance of the members of Panel M and ESDU, is responsible both for the maintenance of the data already in MMDH and for adding new data to it. Unlike the situation for Mil-Hdbk-5 (the US equivalent of MMDH), there is no formal programme of testing to obtain data for publication and therefore Paul begs and borrows (though never steals) data from any source where he can lay his hands on them (the tired, haggard-looking fellow in the materials testing laboratory who has bags under his eyes and a hunted look on his face and who starts at sudden noises, particularly the ring of a telephone, is the chap whose name and number have been given to Paul when he’s in the middle of a data collection exercise). From the resulting chaos and welter of commercial, company and standard designations, compositions, forms, heat treatments and orientations, Paul creates the order of a material Data Sheet.
Between obtaining data and issuing properties in a Data Sheet there is a great deal of statistical analysis and rigorous evaluation to ensure the validity of the data and to determine not only the actual property value that is quoted in MMDH, but also the status with which it is quoted. Depending on the quantity, quality and origins of the raw data, any of 17 methods might be used to obtain the value ultimately quoted in MMDH. These methods range from simply quoting an S (specification) value from the parent material standard to using a combination of order statistics and particular property relationships to derive a ‘grey paper’ B value.
The ‘status’ of data is mentioned above. Throughout MMDH can be seen values and figures printed on a grey background (Grey Paper data), bracketed values and figure curves displayed as dashed lines (White Paper Bracketed data), and values without brackets on a white background and figure curves displayed as full lines on a white background (White Paper Full data). These are the conventions used to indicate the status of the data being presented (full details are given in Section 1, Paragraphs 2.1 to 2.3, of MMDH).
Typically, Grey Paper 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 materials and properties likely to become of importance.
White Paper Bracketed 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. They include B basis values derived from test results that do not meet the full requirements of Appendix A of Section 1 of MMDH. They also include values based on tests not in accordance with the procedures specified in Section 5.
White Paper Full 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. Relevant data previously in AvP 970, Leaflets 401/1, 401/7 and 401/8, or the corresponding leaflets of AvP 32, are also included as White Paper Full data.
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 on which the CD version of MMDH is based and that is then checked to ensure that the data have been incorporated correctly. The modified database and the CD interface are then wrapped up in a set-up program and the whole is tested prior to the CDs being produced and issued. A tailored version of the CD package is also used to produce the printed Data Sheets required for the paper supplements and another program is used to generate, from the database, the html and image files for the internet version of MMDH.
Adam Quilter is the Group Head responsible for MMDH. He can be contacted at aqui@esdu.com
Also available from IHS
MMPDS (formerly Mil-Hdbk-5) presents design data for a large number of US aerospace specification materials. The data presented include composition and physical and mechanical properties. The mechanical properties consist of design allowable values for tensile strength, tensile and compressive proof stresses, Young’s modulus, shear and bearing strengths et cetera. Graphical data covering heat factors and fatigue, amongst other things, are also included, as is information on joints and fasteners. In essence MMPDS is similar to ESDU 00932 (MMDH) and the two handbooks are complementary, the former covering US aerospace materials, the latter covering British and European specifications.