Understanding Aerospace Materials: AMS SpecificationsMatt Kerster
The field of aerospace materials can be said to have begun with the production and sale of the Wright Flyer to the U.S. Army in 1909. At that time, the principal consideration for selecting materials was essentially maximum strength with minimum weight.
As other builders and manufacturers joined the budding industry of “aeroplane” manufacturing, other critical considerations for materials selection began to take equal prominence. The included stiffness, toughness and durability and consisted of fabrics, wood, guy wires and hardware. However, the main consideration of high strength-to-weight was still paramount as the overall weight of a craft had to be kept to an absolute minimum because of the low power of early aircraft engines.
According to an entry at Wikipedia,
“Aviation in the United States was not regulated during the early 20th century. A succession of accidents during the pre-war exhibition era (1910–16) and barnstorming decade of the 1920s gave way to early forms of federal regulation intended to instill public confidence in the safety of air transportation.
To that end, the Air Commerce Act became law on May 20, 1926.
The Act created an Aeronautic Branch assigned to the United States Department of Commerce, and vested that entity with regulatory powers to ensure a degree of civil air safety. Among these powers were: testing and licensing pilots, issuing certificates to guarantee the airworthiness of aircraft, making and enforcing safety rules, certificating aircraft, establishing airways, operating and maintaining aids to air navigation, and investigating accidents and incidents in aviation.”
What Constitutes Aerospace Materials?
120 years ago aircraft materials were largely fabric, wood, wire and fasteners. Today, aerospace materials are mostly metal alloys, although they can include polymer-based materials specifically developed for aerospace purposes.
Aircraft construction, and the parts used, often require exceptional performance, strength or heat resistance. In addition, many materials require long-term reliability for characteristics such as resistance to fatigue loading, for example.
The engineering and manufacture of aerospace materials is defined by the international standards bodies who maintain standards for the materials and processes involved. One of the primary organizations for this is ASTM International, formerly known as American Society for Testing and Materials.
ASTM was originally called the “American Society for Testing Materials” in 1902. Today it is an international standards organization that develops and publishes “voluntary consensus technical standards for a wide range of materials, products, systems, and services.”
ASTM’s aerospace material standards are instrumental in evaluating materials, components, and devices primarily used in aerospace and aircraft industries. The aerospace material standards allow various companies around the world to test these materials in order to evaluate their thermal, optical, mechanical, chemical, and electrical properties.
Another important standards body is the American National Standards Institute (ANSI). Although the ANSI does not develop standards itself, it does oversee the development and use of standards by accrediting the procedures of standards developing organizations. ANSI also designates specific standards as American National Standards, or ANS.
And, if all this isn’t confusing enough, there is also the Society of Automotive Engineers, or SAE, which began in 1905 and expanded in 1936 with their first National Aircraft Production meeting is. SAE publishes technical documents for the aerospace industry and including Aerospace Recommended Practices, which are recommendations for engineering practice, and Aerospace Information Reports that contain general accepted engineering data and information.
A Look at Part Designations and AMS Specifications
For this post we want to focus on two important aspects of identifying specific extruded aircraft parts using the AND (Army Navy Drawing) part shapes designations and the desired AMS Standards or Specifications (Aerospace Materials Specification) for a particular part, or shape.
AMS stands for Aerospace Material Specifications that are established by the Society of Automotive Engineers or SAE. AMS specifications are compiled in a comprehensive database of individual directives that standardize procedures, equipment and processes related to aerospace material processing. These are continuously updated and revised to stay up-to-date with advances in material science and processes technologies.
There are a several standard aerospace and aircraft extruded aluminum shapes with AND (Army Navy Drawing) shape designations. Each designation describes a specific part shape such “10133”, for example, which refers to an equal leg angle. (Illustration 1a)
AND10133 is an aluminum extrusion available in many different alloys and finishes such as 7075, 2024 and 6061 in both tempered condition and 0 condition. AND10133 extrusion is used in maintenance applications and new build applications throughout the aviation and aerospace industry.
While there are a number of other shapes available, the most common are listed below. (Illustration 1b)
An AMS specification covers the general requirements for aluminum alloy bar, rod, shapes, structural shapes, tube and wire, extruded. Specific requirements for these products in a particular alloy are covered by the applicable detailed specification.
For example, the part AND10133-0401 is made with the aluminum alloy 7075 and has a T6511 temper. This temper is achieved as the aluminum is solution heat-treated, stress relieved, then artificially aged. Stretching the metal by an amount that depends on the type of standard wrought product being made, either extrusion or tube, results in stress relief. The metal is straightened after the stretching operation.
This particular part has a specification of AMS QQ-A-200/11. This specification, according the SAE, covers the specific requirements for aluminum alloy 7075 bar, rod, shapes, tube, and wire produced by extrusion. It also has the second highest strength compared to the other variations of 7075 aluminum.