Understanding Mechanical Properties of Metals

Mechanical Properties of Metals

Mechanical properties are the properties that express the behavior of metals under forces aimed at altering their shape. A summary of the different types of fundamental forces to which any structure or machine can be subjected are: tension, compression, shear, bending, torsional buckling, or a combination of these.

Resistance

Resistance is the ability of a metal to withstand an external load of the types mentioned above without breaking. As each load type has its corresponding resistance, it is usual to work with a resistance lower than that which would cause breakage in the plastic period of the material, i.e., working within the elastic period.

Hardness

There are two types of hardness: physical, which is the ability of a metal to resist being scratched by another, and technical, which is the ability of a metal to resist being penetrated by other materials. This property has great importance in machinery, and many decisions are based on this information, such as the choice of cutting tools.

Resilience

Resilience is the resistance of a material to breaking under impact.

Creep

Creep is the property that some materials have to deform slowly and spontaneously under their own weight or small loads. This deformation is called creep.

Fatigue

If a piece is subjected to the action of periodic loads, it can break even if these loads, acting continuously, would not produce deformations. Before explaining the four following properties, it is important to know in general what happens to a specimen of a metal alloy, such as steel, when subjected to tensile stress. By applying a progressive load to a specimen, it will deform in proportion to the applied load so that upon removing the load, the specimen will return to its initial state. If we keep increasing the load, a moment will be reached when, upon removing the load, the specimen will retain a permanent deformation. Increasing the load even further will eventually break the specimen.

Elasticity

Elasticity is the ability of an elastic body to regain its form once the deforming force is removed. A term that appears here is the elastic limit, defined as the maximum load that a material can withstand without permanent deformation. This is a widely used value in machine calculations, as it is often desirable to work within the elastic period.

Plasticity

Plasticity is the ability of a material to deform permanently without breaking after the cessation of the deforming load.

Toughness

Toughness is the ability of a material to absorb energy before fracturing. To measure this property, the shape of the specimen and the manner in which the load is applied are very important.

Fragility

Fragility is a property that expresses a lack of plasticity and, therefore, toughness. In brittle metals, the break occurs at the elastic limit, i.e., failure occurs drastically just beyond the elastic limit.

Ductility

Ductility is a measure of the degree of plastic deformation a material can withstand before rupture. It can be expressed quantitatively as the elongation that occurs or the percentage reduction in area that occurs.