Material selection
It is essential that a designer should have a thorough knowledge of the properties of the materials and their behavior under working conditions.
Some of the important characteristics of materials are : strength, durability, flexibility, weight, resistance to heat and corrosion, ability to cast, welded or hardened, machinability, electrical conductivity, etc.
[3] In contemporary design, sustainability is a key consideration in material selection.
[4] Growing environmental consciousness prompts professionals to prioritize factors such as ecological impact, recyclability, and life cycle analysis in their decision-making process.
Systematic selection for applications requiring multiple criteria is more complex.
For example, when the material should be both stiff and light, for a rod a combination of high Young's modulus and low density indicates the best material, whereas for a plate the cube root of stiffness divided by density
is the best indicator, since a plate's bending stiffness scales by its thickness cubed.
The cost of the ideal material, depending on shape, size and composition, may be prohibitive, and the demand, the commonality of frequently utilized and known items, its characteristics and even the region of the market dictate its availability.
On such a plot, it is easy to find not only the material with the highest stiffness, or that with the lowest density, but that with the best ratio
Using a log scale on both axes facilitates selection of the material with the best plate stiffness
[citation needed] However, the geography- and time-dependence of energy, maintenance and other operating costs, and variation in discount rates and usage patterns (distance driven per year in this example) between individuals, means that there is no single correct number for this.
For commercial aircraft, this number is closer to $450/kg, and for spacecraft, launch costs around $20,000/kg dominate selection decisions.
[6] Thus as energy prices have increased and technology has improved, automobiles have substituted increasing amounts of lightweight magnesium and aluminium alloys for steel, aircraft are substituting carbon fiber reinforced plastic and titanium alloys for aluminium, and satellites have long been made out of exotic composite materials.
For example, if the key design objective was the stiffness of a plate of the material, as described in the introductory paragraph above, then the designer would need a material with the optimal combination of density, Young's modulus, and price.
Optimizing complex combinations of technical and price properties is a hard process to achieve manually, so rational material selection software is an important tool.
First, three different sets of variables are identified: Next, an equation for the performance index is derived.
This equation numerically quantifies how desirable the material will be for a specific situation.
Using the weight equation above and solving for the free variables, the solution arrived at is
The first step is to create a log-log plot and add all known materials in the appropriate locations.
However, the performance index equations must be modified before being plotted on the log-log graph.
First, the best bending materials can be found by examining which regions are higher on the graph than the
In this case, some of the foams (blue) and technical ceramics (pink) are higher than the line.
tension line can be used to "break the tie" between foams and technical ceramics.
Therefore, the overall best material is a technical ceramics in the top-left of the pink region such as boron carbide.
The performance index can then be plotted on the Ashby chart by converting the equation to a log scale.
By moving the line up the Ashby chart, the performance index gets higher.
So, moving to the top of the chart while still touching a region of material is where the highest performance will be.
As seen from figure 3 the two lines intercept near the top of the graph at Technical ceramics and Composites.
When taking into consideration the cost of the engineering ceramics, especially because the intercept is around the Boron carbide, this would not be the optimal case.
A better case with lower performance index but more cost effective solutions is around the Engineering Composites near CFRP.
