Engineering Design -5

Material Selection in Design

Material selection is a crucial part of the design process, as it directly impacts the performance, cost, sustainability, and overall success of a product or project. Choosing the right material involves understanding the specific needs of the design, its functional requirements, and the environmental conditions it will face. This process ensures that the final product is both effective and economically viable, while also meeting safety, aesthetic, and environmental standards.

Key Factors in Material Selection

1. Mechanical Properties:

   • Strength: The material's ability to withstand forces without failure (tensile, compressive, shear strength).

   • Stiffness: The resistance of a material to deformation (elastic modulus).

   • Hardness: The material's resistance to surface indentation or scratching.

   • Fatigue Resistance: Ability to resist failure under repeated loading conditions.

   • Toughness: The ability to absorb energy before fracturing, important for materials subjected to impact loads.

2. Thermal Properties:

   • Thermal Conductivity: The ability of a material to conduct heat.

   • Thermal Expansion: How much a material expands or contracts with changes in temperature.

   • Heat Resistance: The material’s ability to withstand high temperatures without degrading or losing strength.

3. Corrosion and Wear Resistance:

   • Corrosion Resistance: Materials must be chosen based on their ability to resist deterioration from environmental conditions (moisture, chemicals, salt, etc.).

   • Wear Resistance: Materials should be selected based on their ability to withstand abrasive forces or friction.

4. Electrical Properties:

   • Electrical Conductivity: The ability of the material to conduct electricity (important for wiring, circuits, etc.).

   • Insulation: The material's ability to resist electrical flow (important in applications requiring isolation or protection).

5. Environmental Factors:

   • Exposure Conditions: Consideration of the environmental conditions where the product will be used (e.g., extreme temperatures, humidity, UV exposure).

   • Sustainability: Choosing materials that are renewable, recyclable, or have a lower environmental impact.

   • Biodegradability: In some applications (especially in packaging), materials that are biodegradable may be important.

6. Cost:

   • Material Cost: The raw material cost is crucial to ensure that the design stays within budget.

   • Fabrication Cost: The ease or difficulty of processing the material also affects its cost, including cutting, shaping, joining, and finishing.

7. Availability:

   • Material Supply: The availability of materials in the required quantity and the geographical location where they are sourced from.

   • Lead Time: Time taken for material delivery, which can impact project timelines.

8. Manufacturing Processes:

   • Formability: Some materials may be easier to shape and form than others. For example, plastics are often easier to mold than metals.

   • Joinability: How easily a material can be welded, bonded, or otherwise joined with other materials.

   • Machinability: The ability of the material to be cut, drilled, or finished with ease.

9. Aesthetic and Design Requirements:

   • Appearance: Materials contribute to the product's look and feel. For consumer products, texture, color, and surface finish can be essential factors.

   • Transparency/Opacity: Materials may need to have particular optical properties (e.g., glass, plastics, or metals with coatings).

Material Selection Process

The process of selecting materials typically involves the following steps:

1. Define Requirements:

• Begin by clearly defining the functional requirements and performance criteria of the product, including load-bearing capacities, environmental exposure, and other constraints such as size, weight, and budget.

2. Generate Material Options:

• Create a list of potential materials that meet the functional and performance requirements. This list can include metals, polymers, ceramics, composites, and more.

3. Apply Selection Criteria:

• Assess each material based on key factors such as mechanical properties, environmental resistance, cost, and manufacturing compatibility. This can involve detailed calculations, simulations, and using material databases to narrow down the best options.

4. Analyze Alternatives:

• Evaluate the trade-offs between different materials. For example, a material with high strength may be more expensive or harder to process. Consider alternatives that balance all criteria.

5. Prototype and Testing:

• Once a material is selected, a prototype or sample product is made and tested under real-world conditions to ensure it performs as expected. The testing phase may reveal issues that require reevaluating the material choice.

6. Finalize Material Selection:

• Based on prototype testing and further refinements, finalize the material choice. This may involve fine-tuning the design to make use of the selected material's strengths.

Material Selection Tools and Techniques

1. Ashby Charts:

   • One of the most widely used tools in material selection, Ashby charts plot material properties like strength vs. density or stiffness vs. cost. These charts help designers quickly visualize trade-offs between materials.

2. Material Property Databases:

   • Many engineers use material databases (e.g., MatWeb or CES EduPack) that provide detailed material properties. These databases allow easy comparison of thousands of materials.

3. Finite Element Analysis (FEA):

   • FEA can be used to simulate how different materials will perform in a specific design under various loads and conditions.

4. Life Cycle Assessment (LCA):

   • A tool that evaluates the environmental impact of materials across their entire lifecycle—from extraction and manufacturing to use and disposal. This is increasingly important in the context of sustainability.

Examples of Material Selection in Different Industries

1. Automotive Industry:

• In car manufacturing, materials must meet stringent safety, weight, and durability standards. The selection of metals (like steel or aluminum) versus composite materials for body panels depends on performance goals such as strength, weight reduction for fuel efficiency, and cost.

2. Aerospace:

• Materials in aerospace must have high strength-to-weight ratios, resistance to heat, and corrosion resistance. Common materials used in aircraft design include titanium alloys and composite materials for wings and fuselages, while high-temperature metals like nickel-based superalloys are used in engines.

3. Consumer Electronics:

• Materials used in electronics need to be conductive (for circuit boards) or insulating (for casings). The selection of plastics (for lightweight and aesthetic appeal) and metals (for internal components and heat dissipation) must balance electrical properties, durability, and cost.

4. Construction:

• In construction, materials like concrete, steel, and timber are commonly used. Concrete is selected for its compressive strength and durability, while steel is chosen for its high tensile strength and ability to resist bending.

Conclusion

Material selection in design is a complex, multi-faceted process that requires careful consideration of a variety of factors. By understanding the properties and applications of materials, designers can ensure that the final product performs well, is cost-effective, and meets safety, environmental, and aesthetic requirements. Whether in automotive, aerospace, consumer products, or construction, selecting the right material is key to the success of any design.