Ductility

Scheme of the response of a metal cylindrical bar to a steering traction force opposed to its ends. (a) Fracture fragile. (b) Ductile fracture. (c) Fully ductile fracture.

Ductility is a property of some materials, such as metal alloys or asphalt materials, which under the action of a force, can sustainably plastically deform without breaking, allowing wires to be obtained. or threads of said material. Materials with this property are called ductile. Non-ductile materials are classified as brittle. Although ductile materials can also break under adequate stress, this break only occurs after large deformations.

Some examples of very ductile materials are gold, silver, copper, bronze, and brass.

In other words, a material is ductile when the relationship between the longitudinal elongation produced by traction and the decrease in the cross section is very high.

Introduction

In the field of metallurgy, ductile metal is understood to be one that undergoes great deformation before breaking, being the opposite of brittle metal, which breaks with hardly any deformation. Note that ductility is an observable phenomenon only in the plastic regime.

Do not confuse ductile with soft, since ductility is a property that manifests itself once the material is supporting a considerable force, sufficient to produce plasticization. That is, as long as the load is small, the deformation will also be small and in general the deformation will be elastic and reversible, however, once a certain point is reached, the material yields and flows due to plasticization, deforming to a much greater extent than it had done up to then. but without breaking.

In a tensile test, ductile materials present a creep phase characterized by a large deformation with hardly any increase in load. From a technological point of view, apart from economic considerations, the use of ductile materials has advantages:

• In manufacturing: they are suitable for the methods of manufacturing by plastic deformation.
• In use: they present noticeable deformations before breaking. On the contrary, the biggest problem presented by the fragile materials is that they break without notice, while the ductile materials first suffer a marked deformation, still retaining a certain reserve of resistance, so then it will be necessary that the applied force continue to increase so that the breakage is provoked.

The ductility of a metal is assessed indirectly through resilience. Ductility is the property of metals to form wires or threads of different thicknesses. Metals are characterized by their high ductility, which is explained by the fact that the metal atoms are arranged in such a way that it is possible for them to slide over each other and therefore they can be stretched without breaking.

Ductility measurements

After a tensile test, or tensile test, there are two measurements that provide us with information about the ductility of a material: the elongation percentage and the percentage reduction in area.

• The Percentage of elongation quantifies permanent deformation in the breakage (plastic deformation), i.e., the deformation recovered after the fracture (elastic deformation). This way, the distance between the measurements calibrated in the sample before and after the test is measured. It is observed that deformation after failure (red) is less than deformation at the breaking point, because the elastic effort recovers when the load ceases. The percentage of elongation can be written as:

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Where L_f is the distance between the calibrated marks after sample failure.

• La Percentage reduction of area consists of measuring the change in the cross section area in the fracture point before and after the test. Thus, the amount of slimming suffered by the specimen during the test is described:

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where Af is the final cross-sectional area at the fracture surface.