LET'S TALK ABOUT MATERIALS!

Hello friends, greetings to the whole community of steemit, in this opportunity I want to talk a little about the properties of the materials, both physical and mechanical. I am a lover of engineering and for me it is essential to know the types of materials and their properties.

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Material is denominated to each one of the different types of elements with which are formed the pieces of the machines or any apparatus in general. The materials must have adequate composition and homogeneity, as well as present suitable shapes and dimensions for their transformation into machine parts, appliances or other objects.

The number of materials used in engineering is very large and includes both solids and liquids and gases. The selection of the materials for the design and manufacture of machines and appliances is based on the weighted evaluation of their properties in each case, it is necessary to take into account, among other things: the resistance and rigidity, in structural elements and transmission; the superficial properties, in the joints and bonds.

PROPERTIES OF MATERIALS

Each of the materials behaves differently in the face of different types of experimentation. For example: some materials float in water, while others do not; this behavior is related to the property we call density. Some materials conduct electricity and others do not: this characteristic is related to the property we call electrical conductivity.

The properties of the materials can be grouped into two main streams: physical properties and mechanical properties. Below I will present some of the most significant properties

PHYSICAL PROPERTIES:

Among the physical properties of the materials that have the most influence in their application, density stands out, which is defined as the relationship between the mass and the volume it occupies. Density is a determining factor in all applications in which weight or mass must be minimized, such as in the construction of vehicles or in parts that move with enormous acceleration. For example: aluminum, almost three times less dense than steel, is used in aviation, in engine pistons and in vehicle bodies. Plastics, less dense than aluminum, are used in analogous applications but with demands on minor stiffness or resistance.

Other important physical properties are the conduction of electricity and heat. The first property is determinant in the electrical applications, being the metals good conductors and the polymers good isolators.

Among the most commonly used metals, copper and aluminum are the best conductors of electricity, although silver, better conductor than the previous ones, is only used in very specific applications because of its high price.

The conduction of the heat is determinant in applications like the transmission of heat, in the thermal sensors isolation and in the perception of cold and heat to the tact with the objects. Finally we must mention the thermal expansion, which is the increase in the dimensions of the bodies due to the increase in temperature. In some applications, thermal expansion is used, as in mercury thermometers, or in the difference of dilations of two metals, such as the radiator thermostat of automobiles, however in other applications the dilation produces undesired effects, such as in bridges and buildings.

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MECHANICAL PROPERTIES:

Are the properties that are related to the behavior of materials subjected to external forces.

If the forces affect the entire volume of the material, they are known as volumetric mechanical properties among which stand out: the elastic limit, the resistance to breakage, the rigidity and elasticity. On the other hand, if they only affect its surface, they take the name of superficial mechanical properties, among which are: hardness, friction and adhesion, and resistance to wear, among others.

Volumetric Mechanical Properties: For moderate forces, limited by a characteristic value of each material, which is called the elastic limit, all materials undergo deformations. If the force is increased beyond the elastic limit, the behavior of the material can be different depending on whether the material is ductile or brittle.

The ductile materials undergo new deformations, much greater than the elastic ones, which no longer recover if the forces are no longer exercised. If the force continues to increase, there comes a time when breakage occurs for a value called resistance to breakage.

Fragile materials hardly suffer any new deformations after the elastic limit and break when exceeding just such a limit, so we can say that the ductile materials have greater resistance to breakage than the fragile ones. The rigidity evaluates the difficulty to elastically deform a material and is measured by means of the modulus of elasticity.

Finally, the tenacity measures the capacity of the materials to resist blows without breaking, and increases at the same time, with the resistance to breakage and the capacity of deformation of the material.

Surface Mechanical Properties: These are properties related to phenomena that take place between surfaces in contact. In spite of its complexity and difficult evaluation, they are of great importance in the behavior of the articulations and links of the machines, elements that constitute one of its most critical points.

The hardness of a material measures the resistance that its surface offers to be marked or deformed by an external penetrating object, this property is important when exerting high forces through very small surfaces such as in rolling contacts or with rolling and sliding, Example: bearings, linear guides, gears and cams.

The friction and the adhesion are related to the resistance offered by two surfaces in contact with the mutual sliding, and the wear is the loss of material from the surface of the materials caused by the movement of mutual sliding in time.

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