Product Design for the Environment: A Life Cycle Approach - Chapter 12 pot

325 Chapter 12 Environmental Characterization of Materials and Optimal Choice A product’s environmental impact is directly infl uenced by the environmental properties of the materials used, such as energy costs, emissions involved in production and manufacturing phases, and recyclability. The choice of materi- als, therefore, assumes strategic importance and requires an extension of the characterization of materials, integrating conventional characterization (aimed at defi ning physical–mechanical properties) with a complete characterization of environmental behavior. To enable the designer to make an optimal choice of materials that harmonizes performance characteristics and properties of eco-compatibility, the selection process must take account of a wide range of factors: constraints of shape and dimension, required performance, techno- logical and economic constraints associated with the manufacturability of materials, and environmental impacts of all the phases of the life cycle. In accordance with the Life Cycle Design approach, this chapter proposes a defi nition of the environmental characterization of materials and processes, and a systematic method that introduces environmental considerations in the selection of the materials used in components. This defi nition and method are directed at meeting functional and performance requirements while minimizing the environmental impact associated with the product’s entire life cycle. The proposed selection procedure elaborates data on the conven- tional and environmental properties of materials and processes, relates this data to the required performance of product components, and calculates the values assumed by functions that quantify the environmental impact over the whole life cycle and the cost resulting from the choice of materials. As shown in the case study presented, the results can then be evaluated using multiobjective analysis techniques. 12.1 Materials Selection and Environmental Properties “New materials inspire designers; but even more, design drives material development” (Ashby, 2001). This statement highlights the close connection 2722_C012_r02.indd 3252722_C012_r02.indd 325 11/30/2005 1:51:56 PM11/30/2005 1:51:56 PM © 2006 by Taylor & Francis Group, LLC between materials and the design activity, confi rmed by the signifi cance of the issues related to the effi cient integration of materials selection in the product development process (Edwards, 2003; Lu and Deng, 2004). The enormous variety of materials available for engineering applications and the complexity of the requirements conditioning the choice of the most appro- priate materials and processes lead to a taxing problem of multiple-criterion optimization (Brechet et al., 2001). In recent years, several systematic methods have been proposed to help the designer in the selection of materials and processes (Charles et al., 1997; Farag, 1997; Asbhy et al., 2004). Of the more com- monly used quantitative selection methods, that developed by Ashby is based on the defi nition of material indices consisting of sets of physical–mechanical properties which, when optimized, maximize certain performance aspects of the component under examination (Ashby and Cebon, 1995). Defi ning these indices makes it possible to compile selection charts summarizing the relations between properties of materials and engineering requirements (Ashby, 1999). Usually taking into consideration the physical-mechanical properties of materials, these selection charts can be extended to introduce some environ- mental properties (Navin-Chandra, 1991). From this standpoint, several impor- tant studies have been based on the development of indices able to express the environmental performance of materials by introducing the energy consump- tion and emissions (into the atmosphere or water) associated with the materi- als (Holloway, 1998), or eco-indicators developed on the basis of Life Cycle Assessment methods (Wegst and Ashby, 1998). An alternative approach is that of translating environmental impact in terms of economic cost of production, introducing functions of environmental cost such as energy consumption and toxicity that depend on the properties of the materials (Chen et al., 1994). All the methods proposed are limited to quantifying the environmental impact of the choice of materials on the basis of their environmental properties associated with the production phase. Only a few studies have considered the infl uence of the choice of materials on the impact associated with the working life of the component (Kampe, 2001). To date, the problem of choice of materials from the viewpoint of Life Cycle Design (taking into account the environmental impacts involved in all phases of the life cycle, from production to retirement) has been considered only in general terms, with the aim of defi ning guidelines for choices that integrate properties of materials, manufacturing demands, and end-of-life impacts, and suggesting a distinction of selection criteria between component design and assembled product design (Stuart, 1998). 12.2 Environmental Characterization of Materials and Processes The infl uence that the materials used to manufacture a product have on its envi- ronmental impact is manifested in the energy costs and emissions associated 326 Product Design for the Environment 2722_C012_r02.indd 3262722_C012_r02.indd 326 11/30/2005 1:51:56 PM11/30/2005 1:51:56 PM © 2006 by Taylor & Francis Group, LLC Environmental Characterization of Materials and Optimal Choice 327 with the production and end-of-life processes of the material, and in the intrinsic properties of the material and production process that constrain its level of recy- clability. Complete environmental characterization of a material should, there- fore, consist of defi ning the environmental impact linked to its production and disposal, and of evaluating the margins of recyclability in terms of decline in performance of the recycled material and recovery costs. Therefore, the optimal choice of materials, in relation to environmental demands, requires this complete environmental characterization, with particular regard to the following aspects: • Environmental impact associated with production processes (energy costs and overall impact) • Environmental impact associated with phases of end-of-life (recy- cling or disposal) • Suitability for recycling (expressed by the recyclable fraction) Information on the energy costs and recyclable fractions of more common materials can be obtained from commercially available databases, such as that of the CES ® (Cambridge Engineering Selector, Granta Design Ltd., Cambridge, UK) materials selection software. Overall environmental impact can be evalu- ated using the techniques of Life Cycle Assessment (LCA), the analysis method used to quantify the environmental effects associated with a process or prod- uct through the identifi cation and quantifi cation of the resources used and the using these resources and of the emissions produced. Quantifi cation of the impacts is based on inventory data that is subsequently translated into eco- indicators such as those used here. These are evaluated according to the Eco- SimaPro 5.0 ® software (Pré Consultants BV, Amersfoort, The Netherlands). Environmental characterization is also extended to common primary (forming) and secondary (machining) manufacturing processes, evaluating the indicators that quantify the impacts of standard processes per unit of process parameter or of the volume or weight of material processed. 12.2.1 Data on Materials and Processes For each material it is necessary to integrate the information used in conven- tional design with that regarding environmental properties to obtain: • General properties (density, cost) • Mechanical properties (e.g., modulus of elasticity, hardness, fatigue limit) • Thermal and electrical properties (e.g., conductivity and thermal expansion, operating temperature, electrical resistance) 2722_C012_r02.indd 3272722_C012_r02.indd 327 11/30/2005 1:51:57 PM11/30/2005 1:51:57 PM © 2006 by Taylor & Francis Group, LLC waste generated. As was discussed in Chapter 4, LCA evaluates the impact of indicator 99 method (Chapter 4, Section 4.2 and Table 4.3) and calculated using 328 Product Design for the Environment • Environmental properties (energy cost, environmental impact, recyclability) As an example, the datasheet in Figure 12.1 relates to a widely used plastic material (polypropylene) and shows the data on its environmental proper- ties. Eco-indicators were evaluated with SimaPro 5.0 software, using the Eco- indicator 99 method and expressing impacts in mPt (milliPoint). With this software it is possible to select the inventory data to be used for impact eval- uation, in this specifi c case Buwal 250 data (Pré, 2003). Likewise, the following information must be obtained for the primary and secondary manufacturing processes: • Physical attributes of the fi nal product • Economic cost of standard process (fi xed and variable costs) • Environmental properties (energy consumption, environmental impact of standard process) 12.3 Summary of Selection Method that quantify and interrelate the various performances required of the material FIGURE 12.1 Material datasheet: Polypropylene. 2722_C012_r02.indd 3282722_C012_r02.indd 328 11/30/2005 1:51:57 PM11/30/2005 1:51:57 PM © 2006 by Taylor & Francis Group, LLC The reference method depicted in Figure 12.2 is based on calculation models Environmental Characterization of Materials and Optimal Choice 329 in order to identify potential solutions, and a successive, multiobjective analysis aimed at harmonizing the conventional performance, costs, and environmen- tal performance of the product. The fi rst phase consists of defi ning the set of design requirements and parameters: • Primary performance (Pf1), in relation to the specifi c functionality of the component • Secondary performance (Pf2), which can impose further restrictions to guide the selection • Geometric parameters, distinguishing between fi xed (Gf) and vari- able (Gv) geometric parameters • Typology of shape and relative level of complexity (Sh), which greatly affects the choice of forming processes • Use of component (Us), which can infl uence an initial selection of materials The set of design requirements constitutes the input for the procedure of selecting potential solutions. This procedure is based on two different types of each hypothetical solution is evaluated by analyzing some of the informa- tion given in the set of design requirements (in particular, the typology of FIGURE 12.2 Summary of method. 2722_C012_r02.indd 3292722_C012_r02.indd 329 11/30/2005 1:51:57 PM11/30/2005 1:51:57 PM © 2006 by Taylor & Francis Group, LLC of analysis, shown in Figure 12.3. In the fi rst stage, the production feasibility 330 Product Design for the Environment shape required and the intended use). The solutions identifi ed in the analysis of production feasibility must then be evaluated in terms of the required performances (Pf1, Pf2). The potential solutions obtained are then analyzed in subsequent phases of the selection method. Each potential solution S is defi ned by pairs of material–primary forming process (M, FPr), and by the performance volume (PfV), representing the minimum volume needed to meet the requirements of primary performance. If appropriate, the defi nition of the generic solution S can also include any processes of secondary machining required after the initial forming. In the following phase, the calculation models are applied to each potential solution in order to evaluate the indicators of environmental impact and cost over the entire life cycle. The fi nal phase of the method involves analyzing the results and identifying the optimal choice. 12.4 Analysis of Production Feasibility The fi rst stage of the selection procedure must correlate material, process, shape, and function. The problem of the interaction between these factors is considered central to the selection of materials and has been thoroughly investigated (Ashby, 1999). In the method proposed here, this problem is addressed by considering shape (Sh) and use (Us) to be design requirements, expressed using binary FIGURE 12.3 Procedure for selection of potential solutions. 2722_C012_r02.indd 3302722_C012_r02.indd 330 11/30/2005 1:51:57 PM11/30/2005 1:51:57 PM © 2006 by Taylor & Francis Group, LLC Environmental Characterization of Materials and Optimal Choice 331 vectors V Sh and V Us , and introducing binary matrices correlating shape– process, material–use, and material–process: ⌽⌽ ⌽ ⌽ SP sp SP s,,ns p1, ,np UM um UM u1, ,nu m1, − ϭϭ Ϫ ϭ ϭ ϪϪ ϭ ϭ ⎡ ⎣ ⎤ ⎦ ⎡ ⎣ ⎤ ⎦ 1 … … … …… … … ,nm PM pm PM p1, ,np m1, ,nm ⌽⌽ ϪϪ ϭ ϭ ϭ ⎡ ⎣ ⎤ ⎦ (12.1) where nm, np, ns, and nu are the numbers of, respectively, possible materi- als, processes, shape typologies, and uses. Considering processes of primary manufacture only, on the basis of the correlation matrices (12.1) and vectors V Sh and V Us , and following the calculation scheme summa- Pr and V Mt , indicat- ing, respectively, the primary processes able to produce the required typology of shape, and the materials suitable for the intended use. The subsequent application of the material–process correlation matrix gives a matrix of producible solutions: ⍀⌽⌽⌽ϭϭ ϭ ϭ ϪϪ Ϫ ␻␻␻ pm pnp m1, ,nm pm pm Sh Us S P U M P where V V ⎡ ⎣ ⎤ ⎦ 1, , ,, , , … … MM ( ) (12.2) This matrix indicates all the pairs of material–primary process that constitute the set of producible solutions. The material–use correlation matrix constitutes a fi lter in the preselection of possible solutions in that it limits the choice to those materials convention- ally employed for the intended use. For a broader preselection, it is possible to bypass this fi lter. In this case, the terms of matrix (12.2) would depend solely on V Sh , ⌽ S-P , and ⌽ P-M . Using the above approach in the analysis of production feasibility, it is possible to: • Produce an analytical and exhaustive selection of all the possible solutions that can satisfy the intended form and use. FIGURE 12.4 Summary of production feasibility analysis. 2722_C012_r02.indd 3312722_C012_r02.indd 331 11/30/2005 1:51:58 PM11/30/2005 1:51:58 PM © 2006 by Taylor & Francis Group, LLC rized in Figure 12.4, it is possible to obtain the vectors V 332 Product Design for the Environment • Separate the selection conditioned by production feasibility from that conditioned by performance requirements, thereby evidencing the relationships between choice of material and effect on life cycle impacts; such relationships, as shown below, depend on the different performance capacities of the materials. This approach requires the prior compilation of the correlation matrices (12.1). Given the ever-greater variety of engineering materials and related manufac- turing processes, it is reasonable to consider compiling these matrices by typol- ogy of material. Alternatively, for a fi rst selection of material–process pairs, it is possible to use existing software tools such as CES, which implements Ashby’s methodology. It must be remembered, however, that tools of this type allow a selection that already takes account of the performances required. 12.5 Analysis of Performance The second stage of the selection procedure identifi es producible solutions that respect the required performance characteristics. In this way a set of potential solutions is obtained, which are then analyzed by applying the calculation models to evaluate their environmental and economic impacts over the entire life cycle. In general, the analysis of performance can be simplifi ed by considering three different typologies of mathematical relations: • Function of performance volume (PfV)—Expresses the minimum volume necessary to meet the primary performance requirements. Generally, it is a function of the primary performance (Pf1), the geomet- ric parameters (Gf, Gv), and the properties of the material (MtPp): PfV PfV(Pf1, Gf, Gv, MtPp)ϭ (12.3) • Geometric conditions of performance—If the variable geometric parameters Gv are directly correlated with primary performance Pf1, the geometric conditions of performance can be expressed by functions constrained by a range of values (defi ned by the design requirements): Gv Gv (Pf1, Gf, MtPp) Gv (Gv , Gv ) 12 ϭ ∈ (12.4) • Secondary conditions of performance—Conditions of this type can be generally expressed using functions dependent on the properties 2722_C012_r02.indd 3322722_C012_r02.indd 332 11/30/2005 1:51:58 PM11/30/2005 1:51:58 PM © 2006 by Taylor & Francis Group, LLC Environmental Characterization of Materials and Optimal Choice 333 of the materials and the performance volume, to be compared with assumable limit values: Pf2 Pf2 PfV , MtPp Pf2 Pf2 LI M ϭՅՆ ( ) (12.5) In conclusion, if a producible solution meets all the performance constraints and requirements, it then becomes a performing solution and can be selected consists of all the performing material–primary process pairs, integrated by the corresponding performance volume . The latter parameter acquires particular relevance in the proposed method because it directly conditions the values assumed by the life cycle indicators which, defi ned below, guide the optimal choice. Using this approach, it is possible to correlate the search for environmentally and economically convenient solutions with the perfor- mance characteristics of the materials. Only in the case of particularly simple design problems can the functions of type (12.3) be defi ned in analytical form (Giudice et al., 2001). More generally, the performance volume cannot be explicitly ascribed to the factors affecting it; it is the result of design procedures employing modern methods of engineering design, implemented in commonly used tools based on parametric CAD and FEM software for structural performance analyses. 12.6 Life Cycle Indicators The fi nal phases of the selection method consist of applying the calculation models to the set of potential solutions, evaluating the indicators of environ- mental impact and cost relative to the entire life cycle (Life Cycle Indicators), and then analyzing the results and identifying the optimal choice. The indi- cators are functions of the quantities of material necessary to produce the component, expressed by the performance volume. 12.6.1 Environmental Impact Functions The Environmental Impact of the Life Cycle (EI LC ) is expressed by: EI EI EI EI EI LCMatMfctUseEoL ϭϩ ϩϩ (12.6) where EI Mat is the environmental impact of the material needed to produce the component; EI Mfct is the impact associated with its manufacture; EI Use is 2722_C012_r02.indd 3332722_C012_r02.indd 333 11/30/2005 1:51:58 PM11/30/2005 1:51:58 PM © 2006 by Taylor & Francis Group, LLC for fi nal evaluation. As shown in Figure 12.3, the set of potential solutions 334 Product Design for the Environment the impact related to the entire phase of use (which can depend on the choice of material); and EI EoL is the impact of the end-of-life (recycling, disposal). The fi rst two terms of Equation (12.6) constitute the Environmental Impact of Production (EI Prod ), which can be expressed by: EI EI EI ei W ei ei Prod Mat Mfct Mat Prss Mchg ϭϩ ϭ ϩ ␮ϩ ␩⋅⋅ ⋅ () (12.7) where ei Mat is the eco-indicator per unit weight of material (expressed by W); ei Pcss is the eco-indicator of the primary forming process per unit of µ, which can represent the characteristic parameter of the process or the quantity of material processed; and ei Mchg is the eco-indicator of the secondary machining process per unit of characteristic parameter of process ␩. As mentioned above, these eco-indicators can be evaluated using the Eco-indicator 99 method. The Environmental Impact of End-of-Life (EI EoL ) can be expressed by: EI ei 1 W ei W EoL Dsp Rcl ϭϪ␰ϩ␰·· ·· ( ) (12.8) where ei Dsp and ei Rcl are, respectively, the environmental impact of disposal and of recycling processes per unit of weight of material (ei Rcl generally includes a quota of environmental impact recovered), and ␰ is the recyclable fraction. So defi ned, Equation (12.8) refers to the optimal condition where, at the end-of-life, all of the recyclable fraction of material is recovered. Consider- ing a more realistic scenario, it is possible to introduce an appropriate coeffi - cient of reduced recyclability to obtain the fraction actually recycled. Finally, the Environmental Impact of Use (EI Use ) cannot be expressed in general terms and must be defi ned each time, according to the specifi c case under examination. In this chapter, it will be defi ned in relation to the partic- ular case study discussed below. 12.6.2 Cost Functions Similar to the fi rst life cycle indicator, which quantifi es the environmental impact, the second life cycle indicator quantifi es the economic cost related to the entire life cycle. Hypothesizing that both production and disposal costs are paid by a single entity (the manufacturer), the Cost of the Life Cycle (C LC ) can be expressed as: CC C LC Prod EoL ϭϩ (12.9) The Cost of Production (C Prod ) can be expressed in a form analogous to Equation (12.7), as a function of the quantity of material to be employed and 2722_C012_r02.indd 3342722_C012_r02.indd 334 11/30/2005 1:51:58 PM11/30/2005 1:51:58 PM © 2006 by Taylor & Francis Group, LLC [...]... of the materials • Global strain state (due to the superimposition of mechanical and thermal loading) within the elastic limit of the materials Given the complexity of the problem, the performance analysis was conducted using the finite element software MSC Patran/Nastran® (MSC Software Corporation, Santa Ana, CA), which allowed the correlation of performance properties of the materials, variable geometric... parameters, and the corresponding structural and thermal loading As an example, Figure 12. 6 shows some results of the stress and thermal analyses on the disk These FEM analyses were calibrated on the basis of experimental data available in the literature (Bassignana et al., 1984; Brembo, 1998) Both of the producible solutions under examination were found to function Table 12. 1 shows the values that... materials and engineering systems design integration, Materials and Design, 25, 459–469, 2004 Navin-Chandra, D., Design for environmentability, in Proceedings of ASME Design Theory and Methodology Conference, Miami, FL, 1991, DE-31, 119 125 Pré, SimaPro 5 Database Manual: The BUWAL 250 Library, Pré Consultants BV, Amersfoort, The Netherlands, 2003 Sawaragi, Y., Nakayama, H., and Tanino, T., Theory... of an aluminum matrix compound (F3K20S Duralcan®, Alcan Aluminum Ltd., San Diego, CA) as the material, and squeeze casting (liquid metal forging) as the primary forming process 12. 8.3 Analysis of Performance By defining the weight of the automobile and imposing the required braking capacity, it was possible to determine the braking moment required on each wheel and the pressures at the disk–pad contact... Duralcan) 12. 8.4 Evaluation of Life Cycle Indicators and Analysis of Results Equations (12. 6) and (12. 9) were used to calculate the indicators of environmental impact and cost for each performing solution The results of the calculation models are reported in Table 12. 2 The general models were simplified as follows: • In the calculation of production impacts and costs, only the primary manufacturing processes... necessary to produce this moment The primary performance was thus translated into the following conditions of correct functioning that must be ensured by the thermal– mechanical characteristics of the material: • Thermal peaks below the maximum operating temperature of the materials • Global stress state (due to superimposition of mechanical and thermal loading) below the mechanic resistance limits of the. .. more advantageous than that in cast iron (since the lower value of EILC due to the reduced weight tends to increase with the distance traveled) 12. 9 Acknowledgments The main contents of this chapter were previously published (Giudice, F., La Rosa, G., and Risitano, A. , Materials selection in the life- cycle design process: A method to integrate mechanical and environmental performances in optimal choice,... choice, Materials and Design, 26[1], 9–20, 2005), and are reproduced with permission from Elsevier 12. 10 Summary The proposed selection procedure elaborates data (both conventional and environmental) regarding the properties of materials and processes It relates this data to the performance requirements demanded of the product and calculates the values assumed by functions that quantify the environmental... properties (in cases where the multiobjective function and all properties are to be minimized): Bq ϭ Vq V max q (12. 12) where Vq is the value assumed by the q-th property for the solution under examination and Vmaxq is the maximum value assumed by the q-th property among all the solutions to be compared A set of Bq coefficients is obtained for each of the potential solutions to be evaluated The optimal solution... is that with the minimum value of the function ␥ 12. 8 Case Study: Selection of Material for an Automobile Brake Disk The following case study illustrates the application of this method of selection and choice of materials and of the supporting calculation models The design problem consists of the optimum choice for the material of an automobile brake disk, depicted in Figure 12. 6 A preliminary meaningful . parameters, and the corre- some results of the stress and thermal analyses on the disk. These FEM anal- yses were calibrated on the basis of experimental data available in the litera- ture (Bassignana. environmental impacts of all the phases of the life cycle. In accordance with the Life Cycle Design approach, this chapter proposes a defi nition of the environmental characterization of materials and processes,. F., La Rosa, G., and Risitano, A. , Materials selection in the life- cycle design process: A method to integrate mechanical and environmental performances in opti- mal choice, Materials and Design,