What is meant by the structure of the materials?

The word ‘structure’ means the thing that is built or constructed from combining the different interrelated parts on a definite location on the ground surface. The structure should be able to possess sufficient rigidity against the external loads that are applied to it.

There are several essential components that are used in civil engineering for the design of the structures like beams, columns, bridges, tunnels, highways, etc. It is very important to decide the suitable material because the performance and reliability of every structure, as they are dependent on materials choices and materials behaviors. The behavior of structural materials can be understood by their structure and the bonding of their atoms.

The behavior of the atoms of the material is affected by their electronic configuration and bonding that also affects their characteristics and potential applications. The bonding of the materials can be attractive or repulsive. It develops additive forces or energies and brings the atoms to interact and reach the equilibrium point. Therefore, these energies can be compressive or tensile. The bond energies of the materials are dependent on the molecular properties that bind the atoms together.

Types of bonds

Primary bonds

These bonds are developed when the atoms of the elements interact to change their valence electrons to gain stability.

• Ionic bonds: This occurs when the electrons are transferred from one atom to another atom of the element.
• Covalent bonds: This occurs when the electrons are shared from one atom to another atom of the element.
• Metallic bonds: This occurs when the electrons are transferred from one atom to several other atoms of the element.

Secondary bonds

These bonds are developed when the atoms of the molecules are bonded together by electrostatic forces. There is a positive charge on one molecule and a negative charge on another molecule.

The structure and behavior of the materials can be determined based on the type of bonding of the atoms. These engineering materials have distinguishing characteristics.

Metallic materials

The metal is an element that has one, two, or three valence electrons. These materials are formed by the cooling process of the molten materials. During the cooling process, crystals grow from multiple nuclei. As this material continues to cool, they grow together with the grain boundaries. They have a very regular, crystalline state and are perfectly defined structures. They possess metallic bonds. The atoms of the metals are packed in a dense configuration. This regular geometric pattern of the atoms is called a unit cell. The continuous combination of the unit cells forms a space lattice of the materials. The atoms of the metals are arranged into definite structures depending on the size of the atoms and the number of valence electrons. It includes materials like steel, iron, and aluminum.  

A good understanding of the types of lattice structure helps in the determination of the mechanical behavior, material property, physical property, and the potential application of the metallic material. The unit cells, grain structure, and crystalline structure describe the structure of the metal. The grain boundaries affect the overall behavior of the material. It strengthens the pure crystal structure. They are at much higher levels than the atoms away from the grain boundary. The grain boundaries are categorized into four types: 

1. Coherent Boundary
2. Coherent Strain Boundary
3. Semi-Coherent Boundary
4. Incoherent Boundary

In-organic solids

The in-organic solids are materials that are composed of five, six, and seven valence electrons. They are non-metallic elements or can be a combination of metallic and non-metallic elements. In-organic solids are also termed ceramic materials which are formed by the combination of ionic and covalent bonds. They possess high strength, stiffness, and wear, and corrosion resistance. They have a well-defined, complicated unit cell structure. The drawback is their cost and lack of fracture toughness for design purposes. 

The in-organic metals include materials like glass, vitreous ceramics, high-performance ceramics, cement, concrete, rocks, and minerals. Glasses are the special type of inorganic solids that do not develop crystalline structure because they are composed of silica that possesses a high softening point and low thermal expansion. Glass has an amorphous structure. Vitreous ceramics are the clay materials that are used for manufacturing pottery and bricks. High-performance ceramics are the highly refined inorganic solids that are compensated for their high cost. Cement and concrete are widely used structural materials used in civil engineering.

Organic solids

Organic solids are materials that are composed of molecules that have a chain-to-chain combination of Carbon and Hydrogen atoms and other radial components. They have carbon atoms that are bonded by secondary bonds or cross-linked with covalent bonds. The organic solids are categorized as-

Thermoplastics

These are the organic solids that become very soft when they are heated and are very hard when they are cooled. They come in the liquid state when they are heated to their melting point due to the melting of the secondary bonds. They are composed of linear carbon chain-to-chain that are not cross-linked. They include materials like polyethylene, polypropylene, polytetrafluoroethylene (Teflon), polystyrene, and polyvinyl chloride. 

Thermosets

These are the organic solids that create a three-dimensional network due to the cross-linking reaction of the carbon atoms. They remain in their hardened state and do not soften on heating. They include materials like epoxies, polyesters, and phenol-formaldehyde. 

Elastomers

They are the organic solids that are linear polymers with limited cross-linking of the Carbon atoms that possess the material to regain its original shape when the external forces are removed. They are also termed rubbers. They include materials like polyisoprene, polybutadiene, and polychloroprene. 

Natural organic materials

They are the organic materials that are obtained from plants and trees. The primary natural organic material is wood that contains cellulose, lignin, and protein.

Context and Applications

The behavior of the materials used in the construction project is directly proportional to material property, their physical property, and the potential application. The behavior and structure of these materials are highly influenced by the bonding of the atoms and their arrangements. The structure of materials is an important topic in the field of material science, design, structures, and materials. Materials are the most essential elements that are used by designers, engineers, and architects. There are varieties of materials that are used in the modern world. The materials should be selected wisely and appropriately while designing the structures. This topic plays an important application in-

• Bachelors in Technology (Civil Engineering)
• Masters in Technology (Civil Engineering)

Practice Problems

Q1. Which bond is developed when the electrons are shared from one atom to another atom of the element?

1. Ionic Bond
2. Covalent Bond
3. Metallic Bond
4. Secondary Bond

Answer: Option b

Explanation: Covalent Bonds occur when the electrons are shared from one atom to another atom of the element.

Q2. Identify the given image. 

1. Coherent Boundary
2. Coherent Strain Boundary
3. Semi-Coherent Boundary
4. Incoherent Boundary

Answer: Option b

Explanation: The grain boundaries are represented as-

Q3. Which is the incorrect category for metallic materials?

1. Steel
2. Aluminum
3. Iron 
4. Glass

Answer: Option d

Explanation: Metals include the materials like steel, iron, and aluminum.  

Q4. What is not responsible for defining the structure of a metal?

1. Unit cells
2. Covalent Bond
3. Grain structure 
4. Crystalline structure

Answer: Option b

Explanation: The unit cells, grain structure, and crystalline structure describe the structure of the metallic materials. 

Q5. Which is an example of a thermoplastic?

1. Epoxies
2. Teflon
3. Polyesters
4. Phenol-formaldehyde

Answer: Option b

Explanation: Thermoplastic includes the materials like polyethylene, polypropylene, polytetrafluoroethylene (Teflon), polystyrene, and polyvinyl chloride.