Materials Selection & Life Cycle Analysis

σY = strength

K1C = toughness

E = stiffness

I = area moment-of-inertia

σFρ = strenght-to-weight ratio

Eρ = stiffness-to-weight ratio

C_m = Price-per-kilo

Performance metric (P) = f(F,G,M)

F = functional requirement (force, load etc.)

G = geometric parameter (size, shape etc.)

M = material properties

In most cases, these are all independent of each other, and hence separable;

P = f₁(F) x f₂(G) x f₃(M)

This means the optimum material may well be independent of the DETAILS of the design, so the performance can be maximised by maximising the Material Performance Index, f₃(M).

Example - Performance Metric for a light, stiff beam:

Function - beam, must support a vertical load between two points.

Objective - minimise mass.

Constraints - must not deflect more than d_M, beam must have square cross-section.

Variables - cross-sectional area, A, material (properties).

Common Materials Indices:

Embodied Energy (H_m) is the sum of the energies required to make 1kg of material from its raw sources. These energies can include; thermal energy needed to transform materials, energies used to run the plant, transport costs etc.

Processing energy (H_p) is the sum of the energies required to transform 1kg of material into a completed component/product, via machining, bending, casting, moulding etc.