L03 Materials properties

Materials Selection Process

  • Key Steps in Materials Selection:

    • Defining the engineering problem

    • Determining critical materials properties

    • Establishing relationships between critical materials properties

    • figure of merit

    • selection diagrams

Ashby Plot: Materials Selection

Material Characteristics

  • Material Behavior:

    • Elastic Behavior: Metals exhibit elasticity under load.

    • Elastic-Plastic Behavior: Polymers may show both elastic and plastic deformation.

Stiffness in Materials

  • Definition of Stiffness:

    • High bonding strength between atoms leads to high interatomic stiffness, resisting disturbances from the equilibrium spacing.

    • High elastic moduli are indicative of the material's rigidity.

    • nteratomic stiffness will resultin the material having high values of elastic moduli

Strength of Materials

  • Definition of Strength:

    • Material strength refers to the ability to withstand applied loads without failure or plastic deformation.

    • The field of strength of materials deals with forces and deformations that result from their acting on a material

Fracture Toughness

  • Definition:

    • Fracture toughness measures a material's ability to resist fracture, critical for design applications.

Hardness Measurement

  • Definition of Hardness:

    • Hardness relates to resistance to localized plastic deformation due to either mechanical indentation or abrasion.

    • high Ka meansrapid wear at agiven bearingpressure.

    • Strong interatomic bonds typically correlate with high hardness and high strength values.

Importance of Material Properties

  • Multiple Properties for Selection:

    • One material property is insufficient for optimal mechanical performance; consider weight density, specific stiffness, and strength.

    • Specific mechanical properties are often a good guide to identifying the “best” material.

    • Specific stiffness =Young’s modulus/density

    • Specific strength =strength/density

Ashby Plot Overview

  • Ashby Plot Functionality:

    • a scatter plot whichdisplays two or more properties of many materialsor classes of materials

    • These plots are useful tocompare the ratio between different properties.

Summary of Materials Selection

  • Critical Takeaways:

    • A single material property is not enough to make a selection

    • Important to define a figure of merit that describes the relative performance of different materials

    • Selection diagrams can speed up the selection process, but are not essential

    • Many real life situations will require multiple diagrams/large materials data tables.