Correct materials selection means that products have the optimum performance, longevity in use and cost as well as meeting sustainability requirements.
When deciding which material is best for an engineering project, there are various criteria to take into consideration, including:
- Mechanical Properties: These properties include factors such as ductility, strength, hardness, toughness and stiffness. They determine how the material will respond to issues such as loads and stresses.
- Physical Properties: These properties include electrical resistance, density and thermal conductivity. They show how the material will interact with the physical world.
- Chemical Properties: These properties demonstrate how a material will be affected by matters like corrosion or reactivity.
- Cost: The cost of a material is also important in materials selection, with some applications requiring and deserving higher-cost materials than others.
- Availability: Rarer materials may not only be more costly, but they can also be harder to source.
- Sustainability: The environmental impact of a material is also an important consideration and means answering questions around life expectancy and ease of recycling.
To make the materials selection process easier, a materials selection chart (also known as an Ashby Chart) can be used. This offers a graphical representation of different materials and their properties and allows for an impartial, systematic and speedy selection by comparing various materials based on different criteria.
For example, for applications requiring lightweight, low density and high strength materials, like those in the aerospace industry, you can search the relevant family of materials for the desirable properties on the chart.
However, before a selection chart can be used it is important to understand the required properties for the specific application. The complexity of this task depends upon how many different properties are required from the material. An engineer needs to identify and list the requirements before they can be matched to the available materials, while taking factors such as cost, safety and environmental impact into consideration. The materials shortlist is then narrowed down to find the most suitable materials, after which, samples can be tested to ensure they are suitable for the required application.
The materials selection process can be broken down into stages, as follows:
- Define Requirements: The first step involves identifying the needs of the application –including operating temperatures, pressure, corrosion, and loading.
- Identify Materials: List potential materials that meet the requirements, whether ceramics, metals, polymers, or composite materials.
- Create Shortlist: Analyse the materials you have identified to create a shortlist by assessing factors like cost and availability. This step can be made easier by using an Ashby Chart.
- Evaluation: The shortlisted materials can now undergo an in-depth evaluation. This can include testing against the requirements set out in step one.
- Selection: The final step is to select your chosen material, which may include quality assurance checks to be certain of the selection.
The final selection is not actually the end of the process as it is worth conducting ongoing monitoring and evaluation to ensure that your chosen material is still the best for your given application. The requirements may change with time or new and better materials may become available.
Materials selection is important for engineering as it acts as the foundation for every part of the design process, from which a final product’s capabilities are determined. It influences how a product will function, its manufacture, lifecycle, and whether it can be readily recycled.
The choice of material also determines factors such as thermal and electrical conductivity, strength, density and how a product responds to environmental conditions. Different properties can be gauged by measurements such as Young's modulus, which shows elasticity for tension or axial compression.
Selecting an unsuitable material can have negative consequences for the required application and also health and safety. For example, an insufficient yield strength could lead to a structure failing while inadequate chemical or corrosion resistance could cause an object to fail sooner than intended.
Of course, materials selection may require two or more materials to be considered together to determine how they will react when used alongside each other. Carbon steel, for example, will suffer from galvanic corrosion at a much faster rate if it is placed in contact with stainless steel in an electrolytic solution than it would if used in isolation.
Using the right materials can also impact cost, with some being more expensive than others while sustainability is also a factor, with environmental issues related to production, recycling and emissions to be considered.
All of these considerations are important in assessing the suitability of candidate materials.
Whether you are considering materials selection in mechanical design or for any other application, choosing the correct material for your needs is a vital part of industry, manufacture and engineering. The material chosen should not only have the desired properties for your application, but should also be assessed according to how it interacts with any other material under the given service conditions, how sustainable it is, its impact on the environment and its cost.
Getting any of these factors wrong might not only be financially costly, but could also be detrimental to the environment or lead to catastrophic failure and dangerous health and safety problems.
There are a number of tools available to assist with making the right choice for your materials selection, but choosing a given material is not the end of the process. Materials need to be continually assessed to ensure they are still the best fit for your application, as new alternatives may become available or outside factors may impact the cost, availability or suitability of those chosen.