Allowable Strain of Aluminum Alloy
Aluminum alloy is a type of metal composed of aluminum and other elements and is used in various industries including construction, aerospace, automotive and so on. Aluminum alloys have many unique applications that take advantage of its high strength to weight ratio and formability; they are lightweight, corrosion resistant, and conductive of electricity. Aluminum alloy can be hot forged, extruded and cold formed. However, with cold forming processes, special attention has to be paid to the strain limits of the material, since strain in excess of these limits will lead to irregular flow of the material.
The allowable strain of aluminum alloy depends on the type of alloy and its temper. The permanent strain limit, otherwise known as the yield strength, is defined as the strain at which aluminum alloy permanently deforms. This phenomenon is known as yielding. Different aluminum alloys have different yield strengths based on their composition, temper and workability.
Types of temper affect the strain limit as well. Annealed temper is the process of heating and cooling liquid aluminum alloy to reduce its strength and make it potentially more ductile, which allows for larger allowable strain limits. Heat-treating is a process that involves the use of heat and special coatings to strengthen and harden an aluminum alloy and reduce the allowable strain limits.
The strain limit can be determined through tests in the laboratory or in practice. The method used in the laboratory is known as tensile testing. Tensile testing involves stretching a specimen of the aluminum alloy until it fractures and measuring the strain during the process. Through this method, the yield strength of any aluminum alloy can be determined. In practice, strain gauges are used to measure strain on real-life structures, such as bridges and aircraft.
For some aluminum alloys, manufacturers provide information regarding the strain limit, known as the “ultimate strain.” However, it is important to take into account that strain limits vary depending on the material and its temper.
Heat treatments and welds also affect the allowable strain of aluminum alloy. Annealing processes create higher permanent strain limits, while heat treating to strengthen the aluminum alloy can reduce the allowable strain. Furthermore, heat treatments are used to reduce brittleness, whereaswelding can introduce local plasticity and irregular strain.
Given the variety of aluminum alloy and its tempers, it is important to take into account the strain limit in order to avoid failure when using the material. The strain limit of aluminum alloy can range from 20-35%, depending on its composition and temper. A material with a lower strain limit will be stronger and less ductile, while higher strain limits result in a softer material that is more ductile. It is important to remember, regardless of the strain limit, that an aluminum alloy should not be strained beyond its ultimate strength, as this could lead to cracking, brittleness and eventual rupture.
