Properties of materialz

Material Properties

• Understanding material properties is essential as they have definite meanings; key terms include:

  • Strength

  • Stiffness

  • Brittle vs. Tough

  • Malleable

  • Ductile

  • Density

Strength

• Definition: A strong material needs a large force to break it.

  • Example: Steel cables are used in suspension bridges because steel is strong and can handle heavy loads (e.g., trucks).

  • Non-Example: Copper is not as strong, hence unsuitable for cables in heavy-load structures.

  • Conclusion: Strength relates to a material's resistance to breaking.

Stiffness

• Definition: Stiffness is the resistance to deformation (changing shape).

  • A stiff material does not deform much when stretched or compressed.

  • Types of stiffness:

    • Tensile Stiffness: Resistance when stretching.

    • Compressive Stiffness: Resistance when squashing.

    • Additional types include bending and torsional stiffness depending on the shape and forces applied.

  • Comparison: Steel (stiff) vs. rubber (not stiff but strong).

  • Young's Modulus (E): A measure of stiffness for materials like steel, copper, or rubber.

Brittleness vs. Toughness

• Brittle Materials: Prone to cracking easily.

  • Example: Glass and cast iron are brittle; cast iron can crack if struck hard.

• Tough Materials: Resistant to cracking.

  • Example: Wrought iron (like horseshoes) is tough and does not crack easily.

Malleability

• Definition: Ability of a material to be hammered or pressed into shape.

  • Materials: Copper and iron are malleable, making them useful in various applications.

  • Terminology: "Mallet" is derived from "malleable."

Ductility

• Definition: Ductile materials can be drawn into wires through tensile deformation.

  • Example: Copper and gold can be stretched into thin wires, demonstrating ductility.

  • Comparison: Thick objects decrease in thickness while the length increases when stretched.

Density

• Definition: Density is mass per unit volume (measured in kilograms per meter cubed).

  • Formula: ( \rho = \frac{m}{v} ) (where ρ = density, m = mass, v = volume)

  • Example: Density of aluminum is approximately 2,710 kg/m³; uranium is 18,900 kg/m³, about 7 times denser than aluminum.

  • Applications: Aluminum is used in airplanes for its low density, while depleted uranium is used in weaponry because of its high density, allowing for greater impact damage.

Study Thoughts

• Write definitions for each term: strength, stiffness, brittle, tough, malleable, ductile, density.

• Example Calculation: To practice density, calculate the density of iron (0.15 meters³ volume, 1180 kg mass) and verify against standard values.