Propiedades Mecánicas de los Materiales PDF

## Propiedades mecánicas de los materiales - **Elasticidad:** The ability of materials to regain their original shape when the load that deformed them is removed. If the elastic limit is exceeded, the deformation is permanent. - **Plasticity:** The ability of materials to acquire permanent defor...

## Propiedades mecánicas de los materiales - **Elasticidad:** The ability of materials to regain their original shape when the load that deformed them is removed. If the elastic limit is exceeded, the deformation is permanent. - **Plasticity:** The ability of materials to acquire permanent deformations without breaking. If the deformation takes place in the form of sheets, it is called malleability. If it takes place in the form of filaments, it is called ductility. - **Cohesion:** The resistance that atoms offer to being separated. This resistance depends on the type of bonding between atoms. Metals can be separated slightly, which is the reason for their elasticity. - **Hardness:** The greater or lesser resistance that bodies offer to being scratched or penetrated. It depends on the atomic cohesion. - **Toughness:** The ability to resist fracture under the action of external forces. - **Brittleness:** The opposite property of toughness. The plastic interval is very short, and the elastic and fracture limits are very close. - **Fatigue resistance:** The resistance of a material to repeated stresses. - **Resilience:** The energy absorbed during a fracture caused by impact. ### Medida de las propiedades mecánicas Mechanical properties can be quantified and measured through different industrial tests, which help determine the technical characteristics of materials. These tests are classified based on three main criteria: #### Rigor of execution - **Technical control tests:** Executed during the production process. They are characterized by their speed and simplicity, and by being accurate, reliable and practical. - **Scientific tests:** Executed to study the technical properties of new materials. They are characterized by their high accuracy. The production speed does not matter in this case. #### How the tests are conducted - **Destructive tests:** The material undergoes changes in its shape and initial presentation. - **Non-destructive tests:** The material does not undergo changes in its shape or initial presentation. #### Methods used to determine the properties - **Chemical tests:** Determine the qualitative and quantitative chemical composition of the material, and its behavior with chemical regents. - **Metallographic tests:** Study the internal structure of the material using a metallographic microscope. This allows us to learn about the thermal and mechanical treatments that the material has undergone. - **Physical and physicochemical tests:** Determine the physical properties (density, melting point, specific heat, thermal and electrical conductivity, etc.), as well as any imperfections and deformations, both internal and external. - **Mechanical tests:** Determine the elastic characteristics and the resistance of the materials subjected to forces or deformations similar to those found in reality. These tests include static tensile, compressive, shear, bending and torsional tests; hardness tests; impact tests; fatigue and creep tests; and technological tests such as bending, folding, pressing, forging, etc. ## Ensayos técnicos de los materiales Technical tests are used to measure the properties of technological materials. They are standardized and allow the selection of the most suitable materials for a specific application. The most commonly performed tests are the tensile test, hardness test, resilience test, fatigue test and technological tests. ### Ensayo de tracción (UNE 7-474) This mechanical test involves subjecting a specimen of standard shape and dimensions to a system of external forces (tensile force) in the direction of its long axis until it breaks. There are two types of specimens: - **Cylindrical specimens:** Used for tests on materials that have been forged, cast, bars, rolled rounds and thick sheets. - **Prismatic or flat specimens:** Used on sheets of medium and small thickness. Specimens have a calibrated central section that widens at the ends. The ends, called heads, are gripped by clamps on the tensile testing machine. The tensile testing machines that are used to conduct the test are mechanical or hydraulic devices that subject the specimens to an increasing tensile force or stress in all cross sections. This produces a displacement of the clamps that grip the specimen and causes it to stretch. The machine detects, quantifies and correlates the applied forces and the deformations (elongations) that are produced. **A. Elastic and plastic deformations** When a material is subjected to tensile stress, it deforms. If, upon removing the stress, the material recovers its original dimensions, it is said to have undergone elastic deformation. The elastic deformation that any material can withstand is small because the atoms are only displaced from their original positions until the stress is applied, but not to the point of taking on new positions. When the stress is removed, the atoms return to their original positions. If a material is deformed to such an extent that it cannot fully recover its original dimensions, it is said to have undergone plastic deformation. We must not confuse plastic and elastic deformation with the plasticity properties of materials, which classify them into plastic, elastic and brittle materials. **Vocabulary** - **Stress in engineering (σ):** The value of the quotient obtained by dividing the uniaxial force by the initial cross-sectional area (σ = F/S). - **Strain in engineering (ε):** The variation in the length of the specimen divided by its original length (ε = Δ / - **Uniaxial:** The direction of the axis of symmetry of the specimen.