Material Classification: Properties & Origin

• Materials can be classified based on their properties, origin, and use

Classification Based on Properties

• Materials are often classified based on their mechanical, thermal, electrical, magnetic, and optical properties
• Mechanical properties include strength, stiffness, toughness, ductility, and hardness, describing how a material responds to applied forces
• Thermal properties include thermal conductivity, thermal expansion, and heat capacity, describing how a material responds to changes in temperature
• Electrical properties include conductivity, resistivity, dielectric constant, describing how a material interacts with electric fields and currents
• Magnetic properties include permeability, coercivity, and saturation magnetization, describing how a material interacts with magnetic fields
• Optical properties include refractive index, reflectivity, and transmissivity, describing how a material interacts with light

Classification Based on Origin

• Materials can be classified based on their origin, whether natural or synthetic (man-made)
• Natural materials include wood, stone, cotton, and rubber, obtained directly from the environment
• Synthetic materials include plastics, synthetic rubber, and composite materials, created through chemical processes

Classification Based on Use

• Materials can be classified based on their application or use, such as structural, electronic, or biomedical materials
• Structural materials are used in construction and engineering for their mechanical strength and stability
• Electronic materials are used in electronic devices for their electrical conductivity or semiconducting properties
• Biomedical materials are used in medical applications for their biocompatibility and interaction with biological systems

Mechanical Properties

• Strength is a material's ability to withstand stress without breaking
• Yield strength is the stress at which a material begins to deform permanently
• Tensile strength is the maximum stress a material can withstand while being stretched before breaking
• Stiffness is a material's resistance to deformation under stress, quantified by Young's modulus (elastic modulus)
• Toughness is a material's ability to absorb energy and plastically deform before fracturing
• Ductility is a material's ability to be stretched into a wire without breaking
• Malleability is a material's ability to be deformed into a sheet without fracturing
• Hardness is a material's resistance to localized plastic deformation, often measured by indentation tests like Rockwell, Vickers, or Brinell

Thermal Properties

• Thermal conductivity is a material's ability to conduct heat
• Thermal expansion is a material's tendency to change in volume in response to temperature changes, quantified by the coefficient of thermal expansion
• Heat capacity is the amount of heat required to raise the temperature of a material by a certain amount, also known as specific heat capacity
• Melting point is the temperature at which a solid material changes to a liquid
• Boiling point is the temperature at which a liquid material changes to a gas

Electrical Properties

• Electrical conductivity is a material's ability to conduct electric current, measured in Siemens per meter (S/m)
• Resistivity is a material's resistance to the flow of electric current, measured in ohm-meters (Ω⋅m), the inverse of conductivity
• Dielectric constant (permittivity) is a material's ability to store electrical energy in an electric field
• Conductors have high electrical conductivity (low resistivity), allowing electric current to flow easily
• Insulators have low electrical conductivity (high resistivity), preventing electric current from flowing
• Semiconductors have intermediate electrical conductivity, which can be controlled by doping or external factors

Magnetic Properties

• Permeability is a material's ability to support the formation of magnetic fields
• Coercivity is the magnetic field required to reduce the magnetization of a ferromagnetic material to zero
• Remanence (remanent magnetization) is the magnetization remaining in a ferromagnetic material after the applied magnetic field is removed
• Saturation magnetization is the maximum magnetization a material can achieve in a strong magnetic field
• Ferromagnetic materials (e.g., iron, nickel, cobalt) exhibit strong magnetism due to the alignment of magnetic moments
• Paramagnetic materials are weakly attracted to magnetic fields
• Diamagnetic materials are weakly repelled by magnetic fields

Optical Properties

• Refractive index is a measure of how much light is bent when passing from one medium to another
• Reflectivity is the fraction of incident light reflected by a material's surface
• Transmissivity is the fraction of incident light transmitted through a material
• Absorption is the process by which a material absorbs light energy
• Transparent materials allow light to pass through with little or no scattering or absorption
• Translucent materials allow light to pass through but scatter it, so objects are not clearly visible
• Opaque materials do not allow light to pass through

Material Types

• Metals are typically strong, ductile, and good conductors of heat and electricity e.g. steel, aluminum, copper, and gold
• Ceramics are typically hard, brittle, and good insulators of heat and electricity e.g. oxides, carbides, and nitrides
• Polymers (plastics) are typically flexible, lightweight, and can be molded into various shapes e.g. polyethylene, polypropylene, and PVC
• Composites are made of two or more materials to combine their properties, often consisting of a matrix and reinforcement e.g. fiber-reinforced polymers and concrete
• Semiconductors have electrical conductivity between conductors and insulators, used in electronic devices e.g. silicon, germanium, and gallium arsenide

Material Selection

• Material selection involves choosing the right material for a specific application based on its properties and cost
• Consider mechanical, thermal, electrical, magnetic, and optical properties
• Consider environmental factors, such as temperature, humidity, and chemical exposure
• Consider manufacturing processes, such as casting, machining, and welding
• Cost is a significant factor in material selection, balancing performance with affordability

Material Testing

• Material testing validates that a material meets requirements
• Destructive testing methods involve testing the material to failure to determine its properties e.g. tensile tests, impact tests, and fatigue tests
• Non-destructive testing methods evaluate the material without causing damage e.g. ultrasonic testing, radiography, and magnetic particle inspection
• Hardness tests include Rockwell, Vickers, and Brinell hardness tests, measuring resistance to indentation
• Microstructural analysis techniques include microscopy and spectroscopy, examining the material's structure and composition

Factors affecting material properties

• Temperature: Material properties can change significantly with temperature
• Composition: Adding different elements to a material can change its properties.
• Processing: The way a material is processed can affect its properties.
• Environment: Exposure to certain environments can degrade a material's properties.