Farmers have The Old Farmer’s Almanac and parents have the famous book Baby and Childcare. Have you ever wondered what the ‘Bible’ of aircraft engineering is? For more than six decades, a guide has been the essential design and maintenance guide for aircraft engineers – the MMPDS. These initials stand for Metallic Materials Properties Development Standardization. It is the most important source of design allowables used in aerospace structure design within the United States and beyond. In this article, you will learn about the contents of this handbook, preceded by a brief history.
The Journey of the Handbook
The first version of the guide was published in 1934. It was then referred to as the Army-Navy-Commerce Handbook 5 (ANC-5). When the United States Air Force (USAF) took control of the publication in 1954, they consequently coined a new name “MIL-HDBK-5 in 1956”. For the last six decades, the Handbook has undergone tremendous revisions to update design properties, methodologies and material properties. In estimation, there have been more than 50 revisions and re-issuances.
Over this period, the document has predictably undergone several milestones. For instance, the first release of the Army-Navy-Commerce Handbook 5 was in 1937. It was a free issue. In 1954, the Battelle became the MMPDS Secretariat, upon the shift of proponency to the Air Force.
MMPDS Handbook Contents
The current version of the Handbook is an improvement of MMPDS-12. It covers all other information in previous versions. Its development was a collaboration of different entities including material suppliers/users and certifying agencies. NASA, DoD, and FAA are at the centre of this ongoing process.
The handbook came with three specific changes as compared to the previous release:
- New/updated alloy sections for Alclad, Toughmet 3, Ferrium, and multiple fasteners
- Stress-Strain curves usage guidance
- Modification of Chapter 9 criteria and guidelines
As you would expect, there are many chapters in this Handbook so we will list just a few of them:
- Steel alloys
- Aluminium alloys
- Magnesium alloys
- Heat resistant alloys
- Miscellaneous alloys and hybrid materials
This handbook offers comprehensive properties about each of the featured alloys. Chapter 8 is about structural joints, whereby mechanically fastened joints and metallurgical joints are covered in detail. Specific mechanically fastened joints discussed are solid rivets, blind fasteners, threaded fasteners and upset-pin fasteners. Welded joints are the featured metallurgical joints. Towards the end of the chapter, there is a section dedicated to wire rope, bearings and pulleys.
Updates to the Document
We have highlighted a few changes captured in the handbook above. There is a reason that such changes have been and will continue to be there. The revisions ensure the following:
- Availability of reliable design properties for as many materials and forms as possible
- Identification of cancelled specifications
- Representation of supporting data-fracture toughness, fatigue growth, temperature effect etc.
Today, there are numerous aerospace companies manufacturing military and commercial products. Owing to this fact, both governmental agencies and manufacturers need a standard for data used in the design of metallic materials in the aerospace industry. Yes, military and commercial products may differ in design, but the requirements for the strength of materials and several other characteristics rarely change. Therefore, the data in the current handbook is applicable across the board.
Metallic components of an aircraft must meet technical specifications stringently. The suitability of one material can be based on tens of thousands of lot release test points. Because the questions can be so many, the Handbook serves as the most definite guide for engineers.
For the FAA, the Handbook is one irreplaceable document. It is a reliable guide for ensuring aircraft worthiness and certifying aircraft. Some content that is crucial for the industry includes:
- Fatigue life curves
- Stress-strain curves
- Joints and fasteners
- Mechanical property design allowables
Note that materials and metals used in the aviation industry are also present in other industries. While design requirements in the aviation industry can be unique, they rarely differ from the general design values for strength of materials and material characteristics.
Aircraft manufacturers and maintenance teams have two options for certification: create their own data, or refer to the handbook. Different government agencies and departments recognise this document as a rich source of allowables for metals and fasteners. Have you gone through the releases?