A3.1 / Material Classification & Properties
A3.1 / Material Classification & Properties
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How do material properties and classifications aid material selection for a specified manufacturing process or product?
3.1.1 - Material classification
3.1.1 - Material classification
Materials are selected for manufacturing products based primarily on their properties. The rapid pace of scientific discovery and new technologies has had a major impact on material science, giving designers many more materials from which to choose for their products. These new materials have given scope for “smart” new products or enhanced classic designs. Choosing the right material is a complex and difficult task with physical, aesthetic, mechanical and appropriate properties to consider. Environmental, moral and ethical issues surrounding the choice of materials for use in any product, service or system also need to be considered.
The five intial classicfcations of materials are, metals and metalic alloys, Timbers, Ceramics and glass, Plastics and Textiles.
Composite materials and smart materials are additional classifciations.
3.1.1a - Metals and metallic alloys
3.1.1a - Metals and metallic alloys
3.1.1b - Timber
3.1.1b - Timber
3.1.1c - Ceramics
3.1.1c - Ceramics
3.1.1d - Plastics
3.1.1d - Plastics
3.1.1e - Textiles
3.1.1e - Textiles
3.1.2 - Sources & origins of materials
3.1.2 - Sources & origins of materials
More detail can be found about specific materials in each materials category. As a general overview the following can be used.
Metallic ore
Hardwood forest
Silica Sand
Crude Oil
Sheep herd
Carbon Fibre
Metals and Metallic Alloys
Metals and Metallic Alloys
Origin: Metals are typically extracted from ores found within the Earth's crust.
Classification: While the ores are natural, the extraction and refinement process is a human-made industrial activity.
Metallic Alloys: Most pure metals are either too soft or chemically reactive for practical use, so they are often combined with other elements to form alloys.
Example: Market gold is often an alloy of pure gold and copper to increase its hardness for use in jewellery.
Timber
Timber
Origin: Timber is a natural, renewable resource derived from trees that utilize the Sun's energy to grow in a continuous cycle.
Classification: Natural (though "man-made timbers" like plywood involve human processing).
Categories:
Natural Timbers: Classified into hardwoods (usually from broad-leaved trees) and softwoods (usually from coniferous trees).
Man-made Timbers: These are engineered products, such as MDF or particleboard, created by bonding wood fibres or particles with adhesives.
Glass and Ceramics
Glass and Ceramics
Origin: Glass is primarily made from silica (sand) and other natural minerals that are melted and cooled rapidly. Ceramics are typically made from clay and other earthen minerals that are shaped and fired at high temperatures.
Classification: Human-made (processed from natural minerals).
Note: While glass was once considered a luxury item, it has evolved through technological discovery to become a staple in building materials and interactive electronic devices.
Plastics (Polymers)
Plastics (Polymers)
Origin: Most traditional plastics are produced from petrochemicals (oil), which is a finite, non-renewable resource.
Classification: Human-made.
Modern Shift: Due to environmental pressures, designers are increasingly using bioplastics/biomaterials derived from natural sources like fungi (mycelium) or plants, which are often biodegradable.
Structures: Plastics are categorized into thermoplastics (which can be reheated and reshaped) and thermosetting plastics (which remain rigid once set).
Textiles
Textiles
Origin: Textiles can originate from both natural and synthetic sources.
Classification: Mixed (Natural and Human-made).
Types of Fibres:
Natural Fibres: Derived from plants or animals, such as cotton, wool, and silk.
Synthetic Fibres: Human-made polymers such as nylon, polyester, and Lycra®.
Process: These fibres are converted into yarns and then into fabrics through techniques like weaving, knitting, or felting.
Composites
Composites
Origin: Composites are human-made materials created by combining two or more distinct materials—typically a reinforcing fibre (like carbon or glass) and a matrix (like plastic, metal, or ceramic).
Classification: Human-made.
Purpose: They are engineered to have specific properties that the individual component materials do not possess on their own, such as the high strength-to-weight ratio found in carbon-fibre reinforced plastic used in aerospace.
Examples: Concrete (sand/gravel in a cement matrix), plywood (layers of wood veneer), and fibreglass.
3.1.3 - Material considerations & Suitability
3.1.3 - Material considerations & Suitability
Material selection charts compare two material properties. The materials are plotted on the chart and displayed in groups. Material selection charts help designers choose suitable materials for their designs.
Aesthetic properties of materials aren't as clearly defined as physical or mechanical properties. They deal with how a material appeals to our senses, and perception can be subjective. However, some common characteristics contribute to a material's aesthetic appeal:
Visual (appearance): This includes properties like colour, gloss, transparency, and pattern. These properties can be influenced by factors like:
Surface finish: Polishing, sanding, or etching can alter a material's visual and tactile qualities.
Light interaction: How a material reflects, absorbs, or transmits light can affect its perceived colour and texture.
Tactile (texture): How a material feels to the touch, such as smooth, rough, soft, hard, cool, or warm.
Auditory: Some materials have unique sounds associated with them, like the crackle of wood burning or the clink of glass.
While taste and smell are technically senses involved with materials, they're often associated with consumption rather than inherent material properties.
Mixing materials with different aesthetic properties can create interesting contrasts or complements.
3.1.4 - Physical Properties
3.1.4 - Physical Properties
Physical properties are inherent characteristics of a material that can be observed or measured without applying external forces. These properties describe the material itself, regardless of how it will behave under stress. Physical properties commonly considered in design are weight, mass, volume, density, electrical resistivity, thermal conductivity, thermal expansion and hardness.
Mass: The amount of matter an object contains, constant regardless of location (measured in kilograms, kg).
Weight: The force exerted on an object due to gravity (depends on location, measured in Newtons, N). Think of weight as the heaviness you feel.
Volume: The amount of space an object occupies (measured in cubic meters, m³).
Density: How much mass is packed into a unit volume (mass per unit volume, kg/m³). High density means more mass in a smaller space. Opposite: Friability.
Electrical resistivity: How strongly a material opposes electric current (measured in ohm-meters, Ω⋅m). High resistivity means a material is a good insulator. Low resistivity means a material is a good conductor.
Thermal conductivity: How well a material conducts heat (measured in watts per meter-kelvin, W/(m⋅K)). High conductivity means heat flows easily.
Thermal expansion: How much a material's dimensions change with temperature (usually a unitless ratio). Higher expansion means it grows more when heated.
Hardness: A material's resistance to permanent indentation (various scales like Rockwell, Vickers or Mohs). Harder materials scratch softer ones more easily. Opposite: softness.
Weight and Mass are often confused and used interchangeably. Mass is the amount of matter contained in a space. Mass is measured in kg. The mass of an object is constant, regardless of where it is measured. A 2kg object on Earth will have the same mass of 2kg on Mars.
Wood-handled cooking utensils are poor conductors of heat, and so are comfortable to use while cooking--metal-handled cooking utensils conduct heat quickly and can be a safety hazard. Metal utensils are more durable but they conduct heat readily.
3.1.5 - Chemical Properties
3.1.5 - Chemical Properties
Coming soon..
3.1.6 - Mechanical Properties
3.1.6 - Mechanical Properties
Mechanical properties tell you how a material responds to external forces. They describe the material's behaviour under stress or strain. Mechanical properties commonly considered in design are tensile strength, compressive strength, stiffness, toughness, hardness, ductility, elasticity, plasticity and Young’s modulus. Think of it this way: physical properties are like a material's identity card, while mechanical properties are like its report card on how it performs under pressure.
Strength: More specifically tensile strength, compressive strength, shear strength, yield strength or breaking strength. Strength is a general term describing the ability of a material to withstand stress without breaking.
Tensile strength: The maximum stress a material can withstand before pulling apart. High tensile strength is crucial for suspension cables in bridges and elevators, which need to bear weight without snapping.
Compressive strength: The maximum stress a material can withstand before crushing. Concrete has excellent compressive strength, making it ideal for building foundations that support massive structures.
Stiffness: Resistance to elastic deformation under load. It describes how much a material bends before breaking. I-beams used in buildings are designed with high stiffness to minimize bending under heavy loads placed on floors.
Ductility: The ability to deform plastically under tension without breaking (drawability as opposed to brittleness. Imagine stretching a wire. Copper wires are ductile, allowing them to be drawn into thin wires for electrical applications.
Toughness: The ability of a material to absorb energy before fracturing (impact resistance or fracture resistance as opposed to brittleness). It combines both strength and ductility. Steel is a tough material because it can withstand a significant impact without breaking, making it suitable for car frames.
Elasticity: Ability of a material to return to its original shape after deformation (resilience or springiness as opposed to plasticity). Think of a rubber band snapping back. Springs rely on elasticity to store and release energy, using their ability to return to their original shape. Pole-vaulting poles need to flex when a force is applied to it in order to propel the athlete over the bar.
Plasticity: The ability of a material to deform permanently under stress, without breaking (yielding as opposed to elasticity). Imagine bending clay to a new shape. Aluminum is a good example of a plastic material. It can be bent and moulded into different shapes without breaking.
Malleability: Ability of a material to be hammered or pressed into thin sheets without breaking (pliability as opposed to brittleness ).
Fatigue Strength or endurance limit: Maximum stress a material can withstand for a specific number of loading cycles without failure.
Creep: Tendency of a material to deform slowly under a constant load over time.
Abrasion resistance: Ability of a material to resist wear and tear from friction.
Young's Modulus: A measure of stiffness that relates stress to strain in the elastic region. A higher Young's Modulus indicates a stiffer material. Piano wires require a high Young's Modulus to maintain their tight tension and vibrate at precise frequencies when struck, producing clear musical notes.
Bicycle frames need to maintain their shape so the rider can transfer as much of their pedal energy to the road. If the frame is too "soft" it will flex, absorbing some of the energy. However, frames need to be flexible for comfort and handling. For this reason, frame designers may alter the thickness or shape of tubes in different parts of the bike frame.
Young's Modulus is a measure of the stiffness of an elastic material. It is the ratio of stress to strain of a material as force is applied along its length.
A low Young's modulus value means a solid is elastic.
A high Young's modulus value means a solid is inelastic or stiff.
Each material has its own unique modulus.
As a designer or an engineer, it is necessary to understand what the graph represents, and how it would influence the choice of materials. As a designer, the goal is to find the ideal material for a design.
Material A represents a material that can withstand a great amount of force but then fails suddenly. It is brittle, and would likely break into many small pieces. Glass or ceramics would be a good example. There is no elastic zone.
Material B represents a material that is strong, but not ductile. Steel wires are very strong but break suddenly. There is a small elastic zone.
Material C represents a material that is ductile and could be extruded to create wires or cables. Gold and silver are good examples.
Material D represents a very plastic material. It has almost no elastic zone, and a very large plastic zone. Clingwrap would be an example.
Stress and Strain are usually plotted on a graph that shows the relationship between the amount of force applied (Stress) and how much the materials change in length (or deform in a different way).
Think of the graph of telling a journey. As more force (often tension) is applied to the material sample, it will undergo a series of changes. It will move through different zones, each affecting its performance characteristics, until it reaches a fracture point (it breaks).
The linear first part of the graph indicates the elastic region. If the material was stretched and then the force was released, it would return to its original shape.
The Yield Point is the point at which the material will no longer return to its original shape. It has now entered the plastic region.
The Ultimate (Tensile) Strength (UTS) is the point at which the material can maintain a maximum load. After this point, the material is moving towards its fracture or failure point. Necking occurs between the ultimate strength and fracture.
3.1.7 - Composite materials
3.1.7 - Composite materials
Composites are an important material in an intensely competitive global market. New materials and technologies are being produced frequently for the design and rapid manufacture of high-quality composite products. Composites are replacing more traditional materials as they can be created with properties specifically designed for the intended application. Carbon fibre has played an important part in weight reduction for vehicles and aircraft.
Form: fibres/sheet/particles and matrix/reinforcement
Form: fibres/sheet/particles and matrix/reinforcement
Mixes of different Fibres can be spun into thread or heated and extruded as filament. Threads or filament of different 'pure' materials can also be woven (matted) into sheet material to make fibre composites. Commonly used examples of fibre composites are carbon fiber and kevlar.
Particle reinforcement in particle composites is a less effective means of strengthening than fibre reinforcement. Particle-reinforced composites achieve gains in stiffness, but can also achieve increases in strength, toughness and wearability. A commonly used example concrete.
Laminar composites layer different materials to obtain the combined properties of the of the materials. The sheet material in the layers can in itself be composite materials again. Commonly used examples of laminar composites are shatterproof glass and plywood.
With fibre and particle composites, there are usually two types of constituent materials - matrix (or embedding) and reinforcement. The matrix provides a medium for binding and holding reinforcements together as a solid. The matrix for carbon fibre is epoxy resin, that surrounds and supports the reinforcement material: The woven carbon fibre fabric.
There are endless ways to combine matrix and reinforcement materials. And therefore many different composites have been engineered. Many industries are very protective of the particular composites they use. Many are patented.
In tungsten tooltips, hard tungsten carbide particles are located in a softer matrix
Process: weaving, moulding, pultrusion and lamination
Process: weaving, moulding, pultrusion and lamination
Composites can be constructed by weaving different materials into one fabric. The thread that is woven can already be a composite in itself. Note that weaving can be done in two dimensions, but also in three. This allows the weaving of thicker fabrics. In the textiles subtopic, we learned that there are different weaving patterns as well.
Composites can also be formed by using moulds. Again the cast or moulded material can be a composite in itself or the combination of matrix and embedding happens in the mould. Moulds can be hollow negatives of the part to be produced or they can be positives that are used for spray or hand layup. Spray layup is commonly used to form fibreglass products such as swimming pools. Hand layup is commonly used to create custom carbon fibre car parts. Depending on the production process, the production volume per mould can be low, and labour intensive.
Pultrusion is a continuous process for the forming of composite materials with consistent cross-sections. The term combines the words ‘pull’ and ‘extrusion’. As opposed to extrusion which pushes the material, pultrusion works by pulling the raw materials through a heated steel die using a continuous pulling device. Before the reinforcement is pulled through the die, it is impregnated with for instance a resin as the matrix. Curing of the composite might happen during or after the pultrusion.
In lamination, usually, a fabric (the reinforcement) is impregnated (with a matrix) before being pulled through a set of (hot) rollers. The process can be used to create flexible composite sheets such as those used to form the bottom of pools and ponds. The process can also be used to create more solid products. Formica©️ is a well-known example of that. Formica originally consisted of layers of fabric bonded together with resin. Later, it was made with thick pieces of paper laminated with melamine. These tough substances can resist heat and abrasion. By using paper in its manufacture, it opened a wealth of colour possibilities and proved key to its success. Formica is still used extensively in kitchen counters and cabinet doors.
Composition and structure of composites
Composition and structure of composites
Concrete is a particle composite material composed of aggregate (sand and small stones) bonded with a fluid cement that hardens over time. Often additives and reinforcements, such as steel bars known as ‘rebar’ are included in the mixture to achieve different properties of the finished material. When these ingredients are mixed together, they form a fluid mass that is easily moulded into shape. Over time the cement forms a hard matrix which binds the rest of the ingredients together into a stone-like material of many uses.
Fibreglass or Glass reinforced plastic (GRP) is a fibre-reinforced polymer made of a plastic reinforced by fine fibres made of glass. The material comes in sheets, mats or small strands. It can even be sprayed. Like carbon-fibre reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibres - fibreglass. Benefits of fibreglass:
Very high strength-to-weight ratio.
Corrosive resistant.
Water-resistant.
Relatively cheap to produce.
Charles and Ray Eames were early pioneers of GRP technology. Plastics were struggling for an authentic form during the 1950’s and 1960’s due to reputation of cheap plastic toys.
Fibreglass is now widely used in many applications and products; surfboards, wind turbine blades, kayaks, water slides, auto body parts, helmets and other protective products to name but a few.
Kevlar fabric
Kevlar®️ (para-aramid)[2] is a strong, heat-resistant synthetic fibre. Developed by Stephanie Kwolek at DuPont in 1965 the high-strength material was first used commercially in the early 1970s as a replacement for steel in racing tires. It is typically spun into ropes or fabric sheets that can be used as such, or as an ingredient in composite material components. Its natural toughness helps allow fabrics and threads to stand up to repeated abuse. Kevlar®️ helps minimise vibration transfer and can sustain deformation without breaking. Its very high strength to weight is also an important property.
Carbon Reinforced Plastic (CRP) or Carbon fibre is stiff and strong but very light carbon-fibre (organic polymers consisting of long strings of molecules held together by carbon atoms) reinforced thermoplastic (FRTP). Replacing steel in many applications, it is up to five times stronger and two-thirds lighter. CFRTP can be expensive to produce but is commonly used wherever high strength-to-weight ratio and rigidity are required. Aerospace, automotive, civil engineering, sporting goods and ever-increasing commercial and applications are being found for this amazing material. The binding polymer is often a thermoset resin such as epoxy and the carbon fibre is there for strength and stiffness. Beyond its incredible strength and weight properties carbon fibre products have a distinct aesthetic appeal. Carbon fibre can be moulded into complex shapes, woven into ropes, cable and fabric sheets.
Kevlar and Carbon Fibre are two good examples of fibres that are woven in specific ways to produce very strong textiles. On their own, these fabrics do not possess strength beyond that of any woven fabric, but once they are combined with a resin, their strength can be astonishing.
Carbon fibre fabric
3.1.8 - Smart materials
3.1.8 - Smart materials
Smart materials, also called intelligent or responsive materials, are a group of engineered materials that can significantly change one or more of their properties in a controlled and reversible way. This change happens in response to external stimuli, such as:
Physical: Stress, moisture, temperature
Electrical: Electric fields, voltage
Magnetic: Magnetic fields
Chemical: Chemical compounds, pH
Light
These changes allow smart materials to act as sensors, actuators, or even mimic biological muscles. Smart materials can open up new and innovative possibilities for product designs. Here are some cool properties of some smart materials:
Piezoelectricity: Generates electricity when mechanically stressed (pressure, vibration). Piezoelectric crystals are used in pressure sensors, like those in car airbags, which detect a collision and trigger airbag deployment.
Shape Memory: Returns to a pre-defined shape upon heating or exposure to another stimulus. Shape memory alloy (SMA) eyeglass frames can be adjusted to fit perfectly and then "remember" that shape when heated by body temperature.
Photochromicity: Changes color reversibly in response to light. Photochromic lenses in eyeglasses darken in sunlight, acting like sunglasses, and lighten indoors for better vision.
Magneto-rheostatic fluids: Fluid whose viscosity changes dramatically in a magnetic field. Magneto-rheostatic dampers are used in high-performance car suspensions, adjusting fluid viscosity to control shock absorption based on driving conditions.
Electro-rheostatic fluids: Fluid whose viscosity changes dramatically when an electric field is applied. The change can be almost instantaneous. The change can change from a thick fluid to a solid almost instantaneously. The rapidly changing viscosity of ER fluids has potential applications in haptic devices, which provide users with tactile feedback. By controlling the electric field and thus the stiffness of the ER fluid, these devices could simulate different textures or sensations during interaction with virtual objects.
Thermoelectricity: Converts heat into electricity or vice versa.Thermoelectric generators can be used in remote areas to convert waste heat from car engines or power plants into electricity
Medical devices such as Nitinol stents use SMAs to repair damaged blood vessels. to allow a thin device to be inserted into a vein. As the device heats up because of the body heat, it changes shape and keeps the blood vessel open. Nitinol is also used in dental braces to straighten teeth.
3.1.8 - Biomaterials
3.1.8 - Biomaterials
Coming soon...
3.1.9 - Sustainability in materials
3.1.9 - Sustainability in materials
Coming soon...
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