Knowledge of materials and their properties is very important for designers. Mechanical elements should be made of materials with suitable properties for the operating conditions. Additionally, designers need to know how manufacturing processes and heat treatments affect material properties. This article describes construction materials commonly used in the manufacture of machinery and their properties.
What are Engineering Materials?
Engineering materials refer to a group of materials used in the construction of man-made structures and components. The main function of engineering materials is to withstand the applied loading without failure (breaking and excessive deflection). Carbon steel, Aluminum, Cast Iron, Stainless Steel, Copper alloys, Plastics, Composites, Nickel alloys, DSS, etc all are examples of engineering materials.
Classification of Engineering Materials
Engineering materials are generally grouped into two parts i.e., Metals & Non-Metals. Metals include Ferrous, Non-Ferrous, and Non-Metals include Glass, Rubber, Plastic, etc. However, there are many other engineering materials which are Ceramics, Polymers, Semiconductors, Composite, Biomaterials, and Advance Materials. Let’s understand these materials one by one:
Metals have a large number of delocalized electrons. That is, these electrons are not attached to any specific atom. Metals are very good conductors of electricity and heat and are opaque to visible light. The polished metal surface has a glossy appearance.
In addition, the metal is fairly strong yet malleable, making it widely used in structural applications. Metals are classified into ferrous metals (carbon steel, alloy steel, stainless steel, tool/mild steel, etc.) and nonferrous metals (Al, Mg, Cu, Ni, Ti, refractory metals, Be, Zr, superalloys, etc. Alloying elements together have created a wide variety of metallic materials that can be engineered for specific properties.
Iron and Carbon are the main constituents of Ferrous metals and due to the presence of Iron, ferrous metals are having magnetic properties. For example, Cast Iron, Wrought Iron, Steel, etc.,
Non-Ferrous metals do not have Iron content and thus these are non-magnetic and rust resistant. For example, Aluminium, Copper, Lead, Brass, Bronze, Gold, Zinc, etc.
Alloys are the combination of two or more alloying elements. For example, Brass is an alloy of Copper and Zinc. Bronze is an alloy of Copper and Tin.
Typical Uses & Applications of Alloys
- For making Needles & Surgical Blades due to the toughness property and ability to sterilize at elevated temperature.
- Metals like Gold, Silver in Jewellery making.
- Used in Machines & Automobiles and other construction work.
Ceramics are compounds of metallic and non-metallic elements. They are mainly oxides, nitrides, and carbides. A wide range of materials that fall into this category includes ceramics composed of clay minerals, cement, and glass. These materials typically insulate the passage of electricity and heat and are more tolerant of high temperatures and harsh environments than metals or polymers. Regarding mechanical behavior, ceramics are hard but very brittle. MgO, SiC, BaTiO3, silica, glass, concrete, cement, ferrite, garnet, Al2O3, granite, calcite, magnesite, etc. Ceramics.
Uses & Applications of Ceramics as Engineering Materials
- In the making of Ceramic Tiles and Bricks.
- Silicon Carbide, Alumina, and Silica are used in making tools.
- In the making of Insulations and Optical Instruments.
Polymers are large molecules made up of repeating small simple chemical units. In some cases, the iterations are linear, like a chain made up of its links. In other cases, the chains are branched or linked to form a 3D network. The repeating units of the polymer are usually the same or nearly the same as the monomers or starting materials from which, the polymer is formed.
Polymers include familiar plastic and rubber materials. Many of them are chemically organic compounds based on carbon, hydrogen, and other non-metallic elements. Moreover, they have a very large molecular structure. These materials are typically low density and very flexible. PVC, PTFE, polyethylene, terylene, nylon, rubber, etc. are polymers.
Polymers are generally divided into three types:
- Thermoplastic Polymer
- Thermosetting Polymer
The classification of thermoplastics and thermosets is based on their thermal behavior. When heat is applied to thermoplastics, they soften and melt. When cooled, it returns to its original solid state. Thermoplastics can be repeatedly heated and cooled without undergoing a chemical change (unless the temperature is hot enough to break molecular bonds). Therefore, it is very suitable for injection molding.
Thermosets are typically heated during initial processing and then permanently hardened. Thermosets do not melt when reheated. However, if the heat applied becomes extreme, the thermoset will degrade due to the breaking of molecular bonds. Thermosets are typically harder and stronger than thermoplastics. They are also typically more dimensionally stable than thermoplastics, retaining their original dimensions better when exposed to changes in temperature and humidity.
Elastomers are highly elastic polymers with rubber-like mechanical properties. Elastomers are widely used in seals, adhesives, hoses, belts, and other flexible parts. The strength and stiffness of rubber can be increased through a process called vulcanization. Vulcanization is the addition of sulfur and subjecting the material to high temperature and pressure. This process forms crosslinks between polymer chains.
Uses & Applications of Elastomers
- In the making of carrying Bags.
- In the making of Pipes and Plumbing items.
- Used as an Insulation
Many composite materials have been developed that consist of multiple types of materials. Glass fibers are a well-known example of glass fibers embedded in polymeric materials. Composite materials are designed to have the best combination of properties from each constituent material. Fiberglass gets its strength from glass and its flexibility from polymer. Many recent materials developments involve composite materials.
Generally, composites are the following types:
A fiber composite is a material in which the fibers of the material are embedded in a matrix. The fibers carry most of the stress and the matrix holds them in place and serves to transfer stress between them. The fibers can be short and randomly oriented or long and continuous.
Particulate composites are made by adding particles of the material to a matrix (filler). Particles typically occupy less than 15% of the total volume of the material. Particles are added to remedy some deficiencies of the matrix material.
Laminated composites are made by combining layers of composite materials. The layers usually have different fiber orientations or are different materials themselves. Sandwich materials are common, where a lightweight material (such as foam or honeycomb) is placed between layers of strong, rigid material.
Uses & Applications of Composites
- Glass Fiber Reinforced Plastics are used in Automotive Parts and in GRP Piping systems.
- Carbon Fiber Reinforced Plastics are used in Chasis of Vehicle.
- Bumper systems of Automobiles are also made up of Composite materials.
Semiconductors have electrical properties intermediate between those of conductors and insulators. Moreover, the electrical properties of these materials are highly sensitive to the presence of trace concentrations of impurities. Semiconductors have enabled the emergence of integrated circuits and have completely revolutionized the electronics and computer industry over the past few decades. Semiconductor materials include Si, Ge, CdS, CdSe, and GaAs.
Uses & Applications of Semiconductors
- Semiconductors are widely used in Mother Board of Electronic devices.
Biomaterials are used for components that are implanted in the human body to replace diseased or damaged body parts. These materials must not produce toxic substances and must be compatible with body tissue (ie, not cause adverse biological reactions). All the materials mentioned above (metals, ceramics, polymers, composites, and semiconductors) can be used as biomaterials.
Uses & Applications of Biomaterials
- Used in implantation of Damaged Body parts or damaged Tissues.
Advanced Engineering Materials
Materials used in high-tech (or hi-tech) applications are sometimes called advanced materials. Advanced technology means devices or products that operate or function according to relatively complex and sophisticated principles. Examples include electronic devices (VCRs, CD players, etc.), computers, fiber optic systems, spacecraft, aircraft, and military missiles.
These advanced materials are typically either conventional materials with improved properties or newly developed high-performance materials. Additionally, they can be made of all sorts of materials (metals, ceramics, polymers, etc.) and are usually relatively expensive.
These materials are used in thermal protection systems for lasers, integrated circuits, magnetic information storage, liquid crystal displays (LCDs), optical fibers, and space shutter orbiters. This category includes materials such as process electricals, ferroelectrics, high-temperature superconductors, super refractory materials, magnetic alloys, and shape memory alloys.
Material Selection for Engineering Purposes
Choosing the right material for engineering purposes is one of the most difficult problems for designers. The best materials are those that serve their intended purpose at the lowest cost.
The choice of material for a particular application is determined by the working conditions to which it will be exposed, ease of manufacture, and cost considerations. Pure metal has very few applications in engineering, firstly because it is difficult to manufacture in its pure state, and secondly, it generally has low strength in its pure state. can achieve a variety of desirable special properties. Alloys consist of a base metal (usually a content of 50% or more) and one or more alloying elements. Typical properties related to working conditions are toughness, elasticity, toughness, and hardness, and typical properties related to the manufacturing process are ductility, deformability, and plasticity.
Various properties can be determined by test methods. Tensile strength is a tensile test, ductility is a bending test, wear resistance is a hardness test, toughness is an impact test, and fatigue and creep tests determine other special properties such as fatigue and creep.
Materials can be manipulated in a number of ways. The choice depends on the material, the desired properties, the shape to be manufactured, the accuracy required, the quantity to be manufactured, and the cost aspect.
The following factors should be considered when choosing materials:
- Material Availability
- Suitability of the Engineering material for the required working conditions
- The load to which a workpiece or component is exposed.
- The resistivity of the Engineering Material against Corrosion
- The resistivity of the Engineering Materials against Temperature, Wear & Tear.
- Flexibility and Rigidity are required for the material.
- Ease in manufacturing.
- Cost-effectiveness to manufacture.
The key properties that determine a material’s usefulness are its physical, chemical, and mechanical properties which we will discuss separately.