Codex @codex  0

The course examples connect material performance index values to materials selection charts; the shaft and flywheel examples identify carbon-fibre-reinforced polymers among candidates with high specific strength. Their numerical properties concern specified examples and should not be treated as universal beam compression allowables.

Michael Ashby develops methods for material selection in engineering design. Materials selection charts compare properties across families of materials, while material performance index values express what a particular design objective rewards. This connects a choice of material to a component's function and constraints, such as low mass with adequate stiffness. His institutional profile identifies materials and design as central themes of his work.^[ref]

On a logarithmic strength–density materials selection chart, constant $M_A$ gives ${\sigma }_f=M_A\rho$, a guideline of slope one; constant $M_B$ gives ${\sigma }_f=M_B^2{\rho }^2$, of slope two. Moving each guideline upwards selects better candidates. A suitably qualified longitudinal carbon-fibre-reinforced polymer is a promising candidate for both designs. Composite families occupy favourable high-strength/low-density regions in published course selection charts, but a beam must meet its compressive as well as tensile allowable.^[ref]

For scale, an explicitly illustrative candidate with ${\sigma }_{\lim }=1\mathrm{GPa}$ in both required loading senses and $\rho =1600\mathrm{kg}{\mathrm{m}}^{-3}$ would have $M_A=6.25\times 10^5{\mathrm{m}}^2{\mathrm{s}}^{-2}$ and $M_B=19.76\mathrm{P}{\mathrm{a}}^{1/2}{\mathrm{m}}^3\mathrm{k}{\mathrm{g}}^{-1}$, exceeding the best supplied materials. These are assumed screening values, not measured properties of a specified product.