4.1 Properties of materials Notes

Properties of Materials

1. Designers must choose materials carefully to optimize their product's performance, durability, and usability.
2. The right material can enhance a product’s strength, weight, safety, comfort, and longevity.
3. Understanding material properties helps designers innovate and refine their products for real-world applications.

Physical Properties of Materials

Mass vs. Weight: Why They Matter in Design

Mass

1. What It Means:
   1. The amount of matter in an object, measured in kilograms (kg).
   2. Mass is constant regardless of location. A 2kg bicycle frame has the same mass on Earth as it does on Mars.
2. Design Relevance:
   1. Mass affects how a product handles and performs.
   2. Bicycles, drones, and racing cars must balance mass with stiffness and strength for optimal efficiency.

Weight

1. What It Means:
   1. Weight is a force that depends on gravity, measured in Newtons (N).
   2. A 2kg object on Earth weighs about 19.6N, but on Mars, where gravity is weaker, it weighs only 7.4N.
2. Design Relevance:
   1. Aircraft, rockets, and spacecraft must consider weight differences in different gravitational environments.
   2. Backpacks and luggage are designed to be lightweight while maximizing storage capacity.

Volume: Space Considerations in Design

1. What It Means:
   1. The amount of 3D space an object occupies (measured in liters or cubic meters).
2. Design Relevance:
   1. Volume is crucial for storage products like backpacks, suitcases, or food packaging.
3. Interior designers and architects optimize volume for space efficiency.
   1. In industrial design, fuel tanks, water bottles, and containers must be compact yet hold sufficient material.

Density: Balancing Mass and Volume

1. What It Means:
   1. The mass per unit of volume (kg/m³). A material with high density is heavy for its size, while a low-density material is lightweight.
2. Design Relevance:
   1. Protective equipment like bicycle helmets uses low-density foam to absorb impact without adding weight.
   2. Aerospace materials use lightweight, high-strength composites to reduce weight while maintaining durability.

Electrical Resistivity: Designing for Safety and Conductivity

1. What It Means:
   1. A material’s ability to conduct or resist electricity.
      1. Low resistivity = good conductor (e.g., copper).
      2. High resistivity = good insulator (e.g., rubber, fiberglass).
2. Design Relevance:
   1. Electrical components must use conductors for wiring and insulators for safety.
   2. Tools and equipment for electricians must be made from high-resistivity materials.

Thermal Conductivity: Heat Management in Design

1. What It Means:
   1. A material’s ability to transfer heat.
   2. Metals like aluminum and copper conduct heat quickly.
   3. Wood and plastic are poor conductors and act as insulators.
2. Design Relevance:
   1. Cooking utensils often combine materials to manage heat transfer.
   2. Thermal insulation in buildings prevents heat loss or excessive heating.

Thermal Expansion: Designing for Temperature Changes

1. What It Means:
   1. Materials expand when heated and contract when cooled.
   2. Different materials expand at different rates, which can cause structural failures if not accounted for.
2. Design Relevance:
   1. Bridges and railway tracks include expansion joints to prevent buckling in heat.
   2. Glass cookware like Pyrex is designed to resist sudden expansion, preventing cracks.

Hardness: Scratch and Wear Resistance in Materials

1. What It Means:
   1. Hardness is a material’s resistance to scratching, cutting, or denting.
   2. Harder materials resist wear and tear but may be brittle.
2. Design Relevance:
   1. Floor tiles in high-traffic areas must be highly scratch-resistant.
   2. Smartphone screens use hardened glass (e.g., Gorilla Glass) to prevent scratches and cracks.

Mechanical Properties in Design

1. Mechanical properties describe how materials respond to forces like pulling, pushing, bending, and impact.
2. Unlike physical properties, these are often measured using destructive testing, meaning the material is tested until it breaks or deforms.
3. Understanding these properties allows designers to choose the best material for durability, strength, flexibility, and safety in their products.

Tensile Strength: Resisting Pulling Forces

1. What It Means:
   1. A material’s ability to withstand pulling (tensile) forces without breaking.
2. Design Relevance:
   1. Suspension bridge cables must have high tensile strength to support the bridge’s weight.
   2. Elevator cables must hold heavy loads safely and reliably.

Compressive Strength: Resisting Pushing Forces

1. What It Means:
   1. A material’s ability to resist being squashed or compressed without failing.
2. Design Relevance:
   1. Concrete foundations in buildings must have high compressive strength to support weight.
   2. Skyscraper glass panels are designed to withstand compression while holding structural loads.

Stiffness: Maintaining Shape Under Force

1. What It Means:
   1. A material’s ability to resist bending or deformation when force is applied.
2. Design Relevance:
   1. Airplane wings need to be stiff enough to maintain aerodynamic shape while withstanding air pressure.
   2. Bicycle frames must be stiff to transfer pedaling energy efficiently while allowing some flex for comfort.

Toughness: Absorbing Impact Without Breaking

1. What It Means:
   1. A material’s ability to deform without cracking or shattering when impacted.
2. Design Relevance:
   1. Car bumpers need to absorb impact energy without breaking into pieces.
   2. Sports helmets must be tough enough to protect against repeated impacts.

Ductility: Stretching Into Wire-Like Shapes

1. What It Means:
   1. A material’s ability to be stretched into a wire-like form without breaking.
   2. Different from malleability, which refers to reshaping materials without cracking.
2. Design Relevance:
   1. Electrical wiring relies on ductile metals like copper, which can be stretched into long, thin wires.
   2. Extruded aluminum parts in construction benefit from aluminum’s ductility.

Elasticity: Bending and Returning to Shape

1. What It Means:
   1. A material’s ability to flex and then return to its original shape after the force is removed.
2. Design Relevance:
   1. Pole vaulting poles need to flex under force and snap back to propel the athlete over the bar.
   2. Car suspension springs absorb shocks and return to their original shape.

Plasticity: Permanently Changing Shape Without Breaking

1. What It Means:
   1. A material’s ability to be reshaped and hold its new form permanently.
   2. When stretched beyond its yield point, it does not return to its original shape.
2. Design Relevance:
   1. Metal casting and plastic molding rely on plasticity to shape materials into final products.
   2. Car body panels are stamped into shape due to metal’s plasticity.

Understanding Young’s Modulus, Stress, and Strain in Design

1. Engineers and designers use Young’s Modulus, stress, and strain to understand how materials respond to forces.
2. This helps in selecting the right materials for structural integrity, flexibility, and durability in a given design context.

Young’s Modulus: Measuring Stiffness

1. What It Means:
   1. Young’s Modulus is a measure of a material’s stiffness—how much it resists bending or stretching when a force is applied.
   2. It is the ratio of stress to strain, meaning it shows how much a material deforms for a given applied force.
2. Design Relevance:
   1. High Young’s Modulus = Very stiff material (e.g., steel, carbon fiber) → Used in structures that must not flex, like bridges or airplane wings.
   2. Low Young’s Modulus = Flexible material (e.g., rubber, plastics) → Used in products requiring elasticity, like shoe soles or elastic bands.

Stress and Strain: Understanding Material Deformation

1. What They Mean:
   1. Stress → The force applied to a material over a given area (measured in Pascals, Pa).
   2. Strain → The amount a material stretches or compresses relative to its original length (expressed as a percentage).
2. Design Relevance:
   1. High-stress materials are used in applications requiring strength and load-bearing capacity (e.g., suspension bridges, aerospace components).
   2. High-strain materials are used in products that must stretch or flex without breaking (e.g., rubber seals, flexible electronics).

The Stress-Strain Graph: The Journey of a Material Under Force

1. Think of the stress-strain graph as a material’s life cycle under force.
2. It shows how a material deforms as force increases and eventually fails (breaks).
3. It helps designers and engineers predict material behavior under tension, compression, and load-bearing applications.

Key Regions of the Stress-Strain Graph

1. O to A: Linear (Elastic) Region
   1. The material stretches proportionally to the applied force.
   2. If the force is removed, the material returns to its original shape (elastic behavior).
   3. Design Relevance:
      1. Important for springs, rubber bands, and shock absorbers, where flexibility and recovery are needed.
   4. Example:
      1. A diving board flexes when someone jumps but returns to its original position.
2. A to B: Proportional Limit and Yield Stress
   1. Proportional Limit (A): The last point where stress and strain are directly proportional (Hooke’s Law).
   2. Yield Stress (B): The material begins to deform permanently and won’t return to its original shape.
   3. Design Relevance:
      1. High-yield materials (like structural steel) resist permanent deformation, making them ideal for bridges and skyscrapers.
   4. Example:
      1. A bent paperclip no longer returns to its straight shape.
3. B to C: Perfect Plasticity (Plastic Deformation Begins)
   1. The material can deform without breaking but won’t return to its original shape.
   2. Useful in manufacturing (e.g., metal stamping, forging).
   3. Example:
      1. Aluminum sheets can be shaped into soda cans due to their plasticity.
4. C to D: Strain Hardening & Ultimate Tensile Strength (UTS)
   1. C to D: The material becomes stronger as it is stretched (strain hardening).
   2. D (Ultimate Stress Point): The material withstands its maximum load before weakening.
   3. Design Relevance:
      1. Strong, durable materials are used in high-performance applications like aerospace and automotive engineering.
   4. Example:
      1. Suspension bridge cables require materials with high ultimate tensile strength.
5. D to E: Necking & Failure
   1. Necking: The material begins to thin and weaken.
      1. E (Fracture Point): The material breaks completely under stress.
   2. Design Relevance:
      1. Materials that fail suddenly (like glass) must be used in controlled environments.
   3. Example:
      1. Ceramic plates shatter upon impact because they lack ductility.

Material Behavior Based on Graph Shape

1. Brittle Materials (Glass, Ceramics):
   1. Short elastic region, no plastic deformation.
   2. Breaks suddenly at Point B (little warning before failure).
   3. Used in: Insulators, cutting tools, laboratory glassware.
2. Ductile Materials (Copper, Aluminum):
   1. Large plastic region, stretches significantly before breaking.
   2. Can be drawn into wires or shaped into complex forms.
   3. Used in: Electrical wiring, aircraft fuselages.
3. High-Strength Materials (Steel, Titanium):
   1. High ultimate tensile strength (D).
   2. Used in: Bridges, automotive parts, heavy machinery.

Comparison of Different Stress-Strain Profiles

1. The stress-strain graph helps designers and engineers understand how materials behave under tension.
2. Different materials exhibit unique stress-strain characteristics, which influence their suitability for structural, mechanical, and industrial applications.

Material Types and Their Stress-Strain Behavior

1. Material A: Brittle (e.g., Glass, Ceramics)
   1. Characteristics:
      1. Withstands a high amount of force but fails suddenly.
      2. No plastic deformation—once stress reaches a critical point, it shatters.
   2. Design Relevance:
      1. Used in applications requiring hardness and wear resistance but not flexibility.
   3. Examples:
      1. Glass windows in skyscrapers.
      2. Ceramic tiles in high-traffic areas.
2. Material B: Strong but Not Ductile (e.g., Steel Wires)
   1. Characteristics:
      1. Can handle high stress but does not stretch much before breaking.
      2. Small elastic zone—once deformed, it quickly reaches failure.
   2. Design Relevance:
      1. Used in applications requiring strength with some flexibility but not extreme stretching.
   3. Examples:
      1. Steel cables in suspension bridges.
      2. Piano strings, which need high tensile strength but break if overstretched.
3. Material C: Ductile (e.g., Copper, Aluminum)
   1. Characteristics:
      1. Can stretch significantly before breaking.
      2. Large plastic zone, meaning it deforms without sudden failure.
   2. Design Relevance:
      1. Used where materials need to absorb stress and be shaped into different forms (e.g., wire, sheets).
   3. Examples:
      1. Copper wires used in electrical applications.
      2. Aluminum body panels in vehicles.
4. Material D: Very Plastic (e.g., Polymers, Soft Metals)
   1. Characteristics:
      1. Does not return to its original shape after force is applied.
      2. Has almost no elastic zone, meaning it permanently deforms easily.
   2. Design Relevance:
      1. Used for soft, moldable materials that need to be shaped or molded.
   3. Examples:
      1. Plastic bottles, formed using blow molding.
      2. Clay and soft metals, which can be pressed into shape without breaking.

Understanding the Material Selection Chart (Young’s Modulus vs. Density)

1. This Ashby Material Selection Chart plots different material categories based on:
   1. Young’s Modulus (E) (GPa) → Measures stiffness (how much a material resists bending).
   2. Density (kg/m³) → Measures mass per unit volume (how heavy a material is for its size).
2. The chart helps engineers and designers compare materials to balance strength, weight, and flexibility for specific applications.

Key Material Groups on the Chart

1. Metals and Alloys (Top Right, High Density & High Stiffness)
   1. Characteristics: High Young’s Modulus (stiff), dense, strong.
   2. Uses: Structural applications requiring strength, such as bridges, aircraft, and machinery.
   3. Examples: Steel, aluminum, titanium.
2. Ceramics (Top Right, High Stiffness & Moderate Density)
   1. Characteristics: Very stiff and brittle, moderate-to-high density.
   2. Uses: Cutting tools, high-temperature components, biomedical implants.
   3. Examples: Glass, porcelain, silicon carbide.
3. Composites (Upper Middle, High Stiffness & Low-Medium Density)
   1. Characteristics: High strength-to-weight ratio, customizable properties.
   2. Uses: Aerospace, automotive parts, sports equipment.
   3. Examples: Carbon fiber, fiberglass.
4. Woods (Middle Left, Low-Medium Density & Moderate Stiffness)
   1. Characteristics: Stiff but lightweight, natural variability in properties.
   2. Uses: Furniture, construction, musical instruments.
   3. Examples: Oak, pine, plywood.
5. Porous Ceramics (Middle, Moderate Stiffness & Density)
   1. Characteristics: Brittle but can be lightweight due to porosity.
   2. Uses: Thermal insulation, filters, lightweight construction.
   3. Examples: Brick, aerogels.
6. Polymers (Middle-Lower, Low Stiffness & Low Density)
   1. Characteristics: Flexible, lightweight, moderate strength.
   2. Uses: Plastic packaging, consumer goods, medical devices.
   3. Examples: Polyethylene, polycarbonate, nylon.
7. Rubbers (Bottom Right, Very Low Stiffness & Moderate Density)
   1. Characteristics: Extremely flexible, absorbs energy well.
   2. Uses: Tires, seals, vibration dampening.
   3. Examples: Natural rubber, silicone.
8. Foams (Bottom Left, Very Low Density & Low Stiffness)
   1. Characteristics: Ultra-lightweight, shock-absorbing.
   2. Uses: Insulation, cushioning, protective packaging.
   3. Examples: Styrofoam, memory foam.

How to Use This Chart in Material Selection

1. Need something lightweight but stiff? → Composites (e.g., carbon fiber).
2. Need extreme strength and stiffness? → Metals & ceramics.
3. Need flexibility and energy absorption? → Rubbers & polymers.
4. Need thermal insulation & low weight? → Foams & porous ceramics.

Aesthetic Properties of Materials

1. Aesthetic properties influence how users perceive and interact with a product.
2. These properties determine a material’s visual appeal, texture, sound, and even scent, shaping user experience and emotional response.

Form and Shape: How a Material Defines Structure

1. What It Means:
   1. The shape and form of a material affect usability, aesthetics, and user interaction.
   2. Materials can be shaped in organic (curved, natural) or geometric (sharp, structured) forms.
2. Design Relevance:
   1. Rigid materials like plywood lead to structured, geometric designs (e.g., flat-pack furniture).
   2. Flexible materials like plastic allow for smooth, flowing organic shapes (e.g., ergonomic chair designs).
3. Examples:
   1. Bent plywood furniture like the Eames Lounge Chair has a structured but elegant look.
   2. Soft, curved plastic shells in modern consumer electronics create a futuristic and seamless aesthetic.

Sound: The Role of Acoustics in Material Perception

1. What It Means:
   1. The sound a material makes when touched or manipulated adds to the sensory experience of a product.
2. Design Relevance:
   1. Product packaging sound (e.g., a chip bag crinkle) can heighten user anticipation.
   2. Automobile manufacturers design door-closing sounds to convey quality and luxury.
3. Examples:
   1. Luxury car doors are engineered to have a deep, solid "thud" when closed, reinforcing a premium feel.
   2. Musical instruments like violins and guitars rely on the resonant properties of wood and strings.

Smell: Emotional and Psychological Associations

1. What It Means:
   1. Smell connects strongly to memory and emotions, affecting user perception.
2. Design Relevance:
   1. Luxury products use signature scents to enhance brand identity (e.g., the "new car smell").
   2. Plastic materials with strong chemical odors may deter users due to health and sensory concerns.
3. Examples:
   1. Cadillac engineers a leather scent called "Nuance" to enhance the luxurious feel of their car interiors.
   2. Inexpensive plastic toys made from PVC can have an off-putting, artificial smell, discouraging purchases.

Texture: How Materials Feel to the Touch

1. What It Means:
   1. Texture refers to both physical feel and visual texture (e.g., smooth vs. rough surfaces).
2. Design Relevance:
   1. Soft textures enhance comfort (e.g., upholstered seats).
   2. Rough textures improve grip (e.g., rubberized handles on tools).
3. Examples:
   1. Matte vs. glossy finishes on smartphone cases change tactile feel and visual perception.
   2. Wood grain surfaces in furniture create natural visual texture, even if the surface is smooth.

Appearance: Color and Pattern in Material Selection

1. What It Means:
   1. Color and pattern influence perception, psychology, and cultural meaning.
2. Design Relevance:
   1. Designers must consider cultural associations with color in different markets.
   2. Patterns and finishes (e.g., marble, brushed metal) affect perceived material quality.
3. Examples:
   1. Red is associated with excitement and urgency (used in sales promotions).
   2. Cool-toned metals (e.g., silver, chrome) convey a modern, high-tech aesthetic in electronics.

Smart Materials

1. Smart materials are reactive materials that change their properties when exposed to external stimuli like electricity, temperature, light, or magnetism.
2. They allow designers to create innovative, adaptive, and high-performance products across various industries.

Piezoelectricity: Generating Electricity from Movement

1. What It Means:
   1. Piezoelectric materials produce an electric charge when deformed.
   2. They can also expand or vibrate when an electric current is applied.
2. Design Relevance:
   1. Used in sensors, impact measurement, and energy harvesting.
3. Examples:
   1. Airbag sensors → Detect sudden impact and trigger deployment.
   2. Piezoelectric shoe soles → Generate electricity while walking.

Shape Memory Alloys (SMAs): Returning to Original Shape

1. What It Means:
   1. SMAs "remember" their original shape and return to it when exposed to heat or electricity.
   2. They are highly elastic and durable.
2. Design Relevance:
   1. Used for flexible, self-repairing, or adaptive structures.
3. Examples:
   1. Eyeglass frames → Can bend and return to shape without breaking.
   2. Nitinol stents → Medical devices that expand inside blood vessels when heated by body temperature.

Photochromicity: Changing Color with Light

1. What It Means:
   1. Photochromic materials change color when exposed to UV light.
2. Design Relevance:
   1. Used for adaptive, light-sensitive products.
3. Examples:
   1. Transition lenses → Automatically darken in bright sunlight and lighten indoors.
   2. UV-sensitive fabrics → Can indicate sun exposure and help prevent overexposure.

Magneto-Rheostatic Fluids: Changing from Liquid to Solid with Magnetism

1. What It Means:
   1. These fluids thicken or solidify instantly when exposed to a magnetic field.
2. Design Relevance:
   1. Used for shock absorption and impact protection.
3. Examples:
   1. Car shock absorbers → Adjust stiffness based on road conditions.
   2. Flexible body armor → Stays soft for movement but hardens upon impact.

Electro-Rheostatic Fluids: Changing from Liquid to Solid with Electricity

1. What It Means:
   1. These fluids harden when exposed to an electric current.
2. Design Relevance:
   1. Useful for controlling fluid flow in small-scale devices.
3. Examples:
   1. Small, adjustable valves → Used in precision medical equipment and robotics.

Thermoelectricity: Generating Power from Heat

1. What It Means:
   1. When two different conductors are joined, they generate electricity when exposed to heat.
2. Design Relevance:
   1. Converts waste heat into usable power, improving energy efficiency.
3. Examples:
   1. Space probes → Use thermoelectric materials to power radio transmitters.
   2. Hybrid and electric cars → Capture heat from engines to recharge batteries.

Reflection