Multi-criteria Decision Analysis for Supporting the Selection of Engineering Materials in Product Design (eBook)

1.1 Introduction to Materials Selection

The selection of the most appropriate material for a particular purpose is a crucial function in the design and development of products. Materials influence product function, customer satisfaction, production systems, product life cycle, who is going to use or produce it, usability, product personality, operating environment, and costs in a complex way.

Materials selection either can be carried out to choose alternative materials for changes to the design of an existing product in order to reduce say cost or weight, meet new legal requirements, overcome failure occurrence, or satisfy different market demands, or it can be used to choose materials for the design of a completely new product. The materials selection process is similar for existing and new products although the starting point and information requirements may differ. The interdisciplinary effort required in most cases is nontrivial and the engineering designer not only requires detailed, accessible, and timely information about the properties of the materials but also knowledge of multi-criteria decision-making (MCDM).

This book describes the main principles and strategic application of MCDM techniques to support engineering designers compare the performance of established materials, new materials, and hybrid materials when selecting the most appropriate materials for product design.

1.2 Background and Justification for Formalized Materials Selection

There are an enormous number of materials available, each with a range of different properties and behaviors. New materials are also constantly being developed with enhanced properties, expanding the list of options available to the engineering designer. The material properties, and combination of properties in the form of performance indices, can be mapped on to materials’ selection charts, pioneered by Ashby [1]. In the charts, the materials naturally cluster into different classes of metals, polymers, elastomers, glasses, and ceramics. However, only parts of the charts are populated with materials, leaving holes or gaps in the selection space. New materials with enhanced properties can reduce the size or fill gaps within clusters, or expand the boundary of clusters, or the gaps between clusters can potentially be filled or “bridged” with hybrid or multimaterials such as composite materials, as shown schematically in Figure 1.1.

The historical evolution in the use and development of materials reflects the progress of the interdisciplinary science from early civilizations until today [2]. The strategy with respect to materials usage started with the Stone Age (greater than 10,000 BC) by using the available materials such as stone and wood and then later copper and bronze (Bronze Age, 4,000 BC to 10,000 BC), and iron (Iron Age, 1,000 BC to AD 1620). Afterward, the strategy gradually focused on the optimization of specific classes of materials. This led to the development of tools for comparing and selecting materials from different classes of materials already optimized in terms of their engineering potential. Today can be followed by (2013), the emphasis has shifted more toward the consideration of economical aspects and environmental impact. This has created a tendency toward the development of materials using design strategies with an increased importance of modeling and multifunctionality of materials [2]. However, there is still a lot of fundamental materials research being conducted without careful consideration being given to its practical application [3]. This not only justifies the need for the greater use of materials selection tools, but also the importance of supporting decision-making to better understand and manage the multiobjective product design process.

1.3 Decision-Making and Concession in Product Design

Introducing a completely new product or improving an existing product involves a complex chain of interdependent activities including design, analysis, materials selection, and consideration of manufacturing processes, and all depend on MCDM. Besides influencing material properties, process selection is a prerequisite to manufacturing equipment selection. However, materials selection used to be only a minor part of the design process [4] and has therefore not received the same level of research and development as other fields of design. The selection of suitable materials for a specific purpose is a difficult, time-consuming, and expensive process because of the large number of available materials with complex relationships and various selection parameters. As a consequence, approximations are made with materials frequently being chosen by “trial and error” or simply on the basis of what has been successfully used in the past. This approach can lead to compromise and unpredictable outcomes, possible premature failures, and limits the ability to achieve an optimal choice of materials.

The stage reached in the design process is important because the nearer a product is to manufacture level, the greater is the cost of making any design change [5]. It has been estimated that the relative cost of a design change after manufacture is 10,000 times more than at the conceptual stage of design [5]. Therefore, it is worth making decisions carefully and spending enough time early on in the design process using systematic selection techniques. This makes it easier to manage the “trade-offs” between design, materials, shape, and manufacturing processes and lead to an optimum design solution.

To satisfy customer requirements, manufacturing organizations must be continually aware of product costs, reliability, durability, recyclability, and market trends. These attributes should be addressed strategically by manufacturers through a continuous process of improvement in an ongoing effort to improve their products [6]. This will only be fully achieved through optimum decision-making about design, materials, and manufacturing processes [7,8] and provides the opportunity for sustainable and profitable growth. To support this process, MCDM techniques have developed dramatically in both theory and practice, especially in the fields of design and manufacturing, with growing interest in their application to materials selection.

1.4 The Position of Materials Selection in the Engineering Design Process—from Concept to Detail Stages

The successful design of an engineering component is integral to satisfying the functional and customer specified requirements for the overall product it forms a part, utilizing material properties, and capabilities of suitable manufacturing processes [9]. The behavior of a material used to create a component will be affected by component geometry, external forces, properties of stock material before processing, and the effect of manufacturing (or fabrication) method [10]. The evaluation of the typically large number of design solutions (altering the size, shape, and mass of the component) and suitability of an even larger number of different materials rapidly becomes too complicated to be intuitive. This highlights the value of being able to use MCDM to support decision-making in the engineering design process. Although experimental-based selection of a material, for example, testing and prototyping, for a specific design solution is the most accurate; it quickly becomes unreasonable due to the time required and the high costs of experiments, especially if several materials have to be considered. Alternatively, other more viable options can be considered such as computer-based simulations, but the ranking of materials should have already been successfully completed during the initial stage of the design process [6].

Figure 1.2 shows the connection of materials selection and continuous improvement in product development. There is the option to develop a new material but this adds cost and risk to the design efforts and has been highlighted here for the occasion when there is no acceptable material options [11,12]. However, the added cost and risk may be worthwhile if there is an innovation that provides a product with a competitive advantage compared to products produced by other companies. In Figure 1.3, quality tools such as quality function deployment (QFD) [13,14] helps marketing and design teams incorporate the voice of the customer in product designs, increasing the likelihood that the final product will successfully satisfy the customer’s needs. Failure modes and effects analysis (FMEA) [15] will indicate the material’s attributes that must be investigated, controlled, and monitored to ensure the reliability of the component in which the material is used. It will also indicate the manufacturing process steps and controls that are required to make a product, subassembly, or component that will consistently meet its design requirements. Therefore, QFD and FMEA, used as quality tools in design, can dramatically improve product development efficiency because it leads to systematic design, materials selection, and manufacture.

Ashby [16] and Ashby et al. [17] map...