Fuzzy Logic Approach for Material Selection in Mechanical Engineering Design

Introduction

The importance of materials in Engineering Design can never be underestimated. It is a well-known fact that materials have a very significant role in the process of engineering design (Figure 1). In an engineering design process, the most important stage after conceptual design stage is the selection of materials (Figure 2). A design engineer needs to select a material having certain specific properties which can assure him of an optimal performance by satisfying the various constraints required by the system/product. With numerous amounts of material being developed and researched each and every day, the question arises how do we select a material and how do we begin to choose a specific material with so much of information around us. The basic answer to this lies in the fact that we need to look at the function of the product – Product Analysis. But, with product analysis arises another few question which needs to be resolved like what is the basic need of the product? how does it function? what does it do? who all uses it? and what should be its ideal cost?

Figure 1.

Relation between process, design and material

Figure 2.

Engineering design process

Consider the example of a bicycle. Questions like what does it do? who uses it? what type of bicycle it is – racing, touring, for child, mountaineer, etc., how can it be easily maintained? is it comfortable for riding? what should it look like – colors, aesthetically, etc. how does different parts of the bicycle interact and work together as a unit? is it one component or a system? whenever we analyses a system, we further need to break down the system into various individual components and then analyze each component. The bicycle parts could be broken down into various components like – frame, saddle, forks, wheel, etc. On system analysis, we need to give importance to the following questions for each part like Requirement – (ergonomic, mechanical, aesthetic, etc.)? Function? What manufacturing method will we use for making it? and what quantity (how many in numbers) will be manufactured for the first lot/batch?

All these questions have a great impact on selection of materials. For example, consider the frame of bicycle (Figure 3) – what are the materials we could possibly use?

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  Steel: Stiff, strong, heavy but cheap and easily available.

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  Aluminum: Lighter, weaker but expensive when compared to steel.

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  Composite (CRPF): Stiff, strong, very light, but pretty expensive and difficult to fabricate.

Figure 3.

Frame of bicycle

Apart from this, there are questions which also needs to be addressed like properties.

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  Mechanical: Strength, modulus

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  Electrical: Conductivity, resistivity

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  Physical: Density, melting point

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  Processability: Ductility, mouldability

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  Aesthetic: Appearance, texture, color

and most important of all cost.