Materials testing is often the last step in the manufacturing process. Yet, quality is the result of both the process and the material. If the material that goes into the product is defective, then the product may be defective. Quality cannot be put in after the fact. In forming materials, understanding the material’s properties can help to better predict the manufacturing outcome.
For stamping and forming operations and for many products, a profile of the material will help detect variations in materials from suppliers. In fact, many of the most often-used metals and many plastics, polymers, textiles and composites exhibit Hookean behavior, which means the stress in a material is proportional to the strain that produced it. For manufacturers, it is of the utmost importance to understand the mechanical properties of materials that exhibit some Hookean behavior during loading. It is important because the performance of a structure is frequently determined by the amount of deformation permitted. A deflection of a few thousandths of an inch in an optical grinding machine will produce scrap lenses, whereas a bridge truss or joist might deflect several inches.
Some measured properties that must be considered when designing a structure include tensile strength, yield strength and Young’s Modulus of Elasticity.
Another important property is ductility, which is the ability for plastic deformation in tension or shear. Ductility controls the amount a material can be cold formed, which is the process used when forming automobile bodies or wire products. Two commonly used indices of ductility are total elongation and reduction of area. For suppliers, the mechanical properties are an important measure of product quality, and buyers often require certification of the values.