CHAPTER 2

LITERATURE REVIEW

The life cycle engineering includes the entire spectrum of activities for a given

product, starting with identification of a need and extending through design and development,

production, operational use, sustenance of support and product retirement and eventually its

disposal. Concurrent engineering is a systematic approach which takes into consideration all

aspects of life cycle engineering in most appropriate manner at the product design stage. This

research study is taken to develop design methodology for the design of product from life

cycle engineering point of view. In this chapter, literature review pertaining to the study is

described. Literature review was carried out for the design and development of product from

life cycle engineering point of view and is given below.

- Product LCD modelling and evaluation

- Product LCA modelling and evaluation

- Product LCC modelling and evaluation

- Product sustainability modelling and evaluation

- Graph theoretic modelling

2.1 PRODUCT LCD MODELLING AND EVALUATION

LCD of a product is a design approach which takes into consideration all

requirements of product life cycle, at design stage of the product. Literature review indicates

various attempts that have been made for developing procedures for evaluation of product

LCD.

Xu et al. [1] proposed a decision support system for product design under concurrent

engineering environment using fuzzy decision making mathematical approach. In this

method, the evaluation of a product design is carried out on the basis of two concurrent

subsystems, i.e., an external concurrent subsystem and an internal concurrent subsystem.

These include market investigation, materials, external components, functional design,

assembly design, manufacturing design, and environment design.

Fitch and Cooper [2] proposed a methodology for the life-cycle analysis of products

at the design stage based on the cost of energy for materials used in the products. In this

research study, the authors evaluated the total energy required for reinforcing beam material

throughout life cycle.

Fitch and Cooper [3] developed LCD model (LCDM) for adaptive and variant design.

The authors used LCDM to evaluate the material substitution opportunities to minimize the

resource consumption and life-cycle air emissions and increase the recyclable mass for a Ford

C-class sedan. These researchers have also identified the vehicle design scenarios that offer

modest improvements in environmental performance and related cost trade-offs.

Contenea and Varella [4] developed a life-cycle modelling technique based on

functional analysis at the conceptual design stage using a dimensional analysis approach. In

this research study, the researchers have considered various life-cycle phases as

thermodynamic systems far from equilibrium. This means that each life-cycle phase produces

entropy and will export the same entropy to the ecosystem (e.g., the earth surface and the

space).

Eisenhard et al. [5] developed a learning surrogate life-cycle analysis methodology

using an artificial neural network. In this research study, the authors studied the effect of

materials on the environment such as greenhouse effect and ozone layer depletion at the

conceptual design stage.

Zhu and Deshmukh [6] proposed the application of Bayesian decision networks to

study the impact of design decisions on the life-cycle performance of products. In this

research study, the authors demonstrated that proper decision making at the design stage

significantly influences LCC.

Suh and Huppes [7] carried out the review of various proposed life-cycle inventory

methods for the product design. In this review, the authors compared six life-cycle inventory

methods with one another and also compared these methods with ISO standards.

Tomiyama et al. [8] proposed a holistic approach to LCD, marketing, material

acquisition, manufacturing, serviceability, and disposal/recycling.

Kato et al. [9] proposed a new product life cycle technology using the quality function

deployment (QFD). In this research work, the researchers proposed that future technologies

need to consider life-cycle aspects, such as product judgment for reuse or supply and demand

matching, by carrying out an analysis about the relationship between requirements and

technologies in the field of automobile.

Kato and Kimura [10] developed a product LCD method using a strategic analysis. In

this methodology, the authors modelled the relationship of price and cost in each process of

part exchange, transportation, remanufacture, and selling.

Hodgson and Harper [11] proposed a holistic approach of material selection for the

product LCD. In this research work, the authors demonstrated the effective use of material for

various aspects of the life cycle of the product. The authors also identified various attributes

of material selection for the LCD of a product. These are performance, impression,

manufacturability, environment, legislative compliance, reliability, maintainability, and

usability.

Ishii [12] proposed a methodology for the evaluation of the LCC of products. In this

methodology, the author estimated the cost of serviceability during the ownership period of a

product. The author has also obtained labor step cost based on labor time, labor penalty

hours, and logistic support.

Kroll and Hanft [13] developed a quantitative model for the evaluation of the LCC of

a product based on cost of serviceability and recycling. This methodology has been applied to

the CPU of a computer system.

Kainuma [14] proposed a multicriteria decision analysis for LCA on the basis of five

attributes. These are air pollution, water pollution, energy consumption, waste generated, and

customer satisfaction.

Spitzlay et al. [15] carried out the LCC analysis of a fuel tank for two different design

alternatives on the basis of design for end of product, design for manufacturing, design for

use, and design for environment (DFE). In this research methodology, multilayer high density

polyethylene (HDPE) tank and steel tank (ST) were used for comparison. It was revealed that

the design alternative (i.e., HDPE tank) has lower LCC compared with ST.

Hundal [16,17] carried out a detailed design analysis on the environment, and other

aspects of life cycle need to be considered during the product development process. In this

research study, it was revealed that consideration of ecodesign, waste prevention, innovation,

etc., at the design stage is useful for a successful development of the product.

Li and Li [18] carried out the integration of classical approaches of design, conceptual

design, detailed design, process planning, prototype manufacturing and testing in terms of

sequential processes.

Green and Mamtani [19] have developed an integrated model for the evaluation of

LCD of a product, at conceptual design stage. In this research study, the authors have used

fuzzy logic for design and evaluation of conceptual design of a wheel chair.

The recent standards of ISO-14040 have made it necessary for manufacturers and end

user of the product to carry out LCA to reduce environmental hazards, created due to solid

waste, disposal, and recycling methods of products. In addition, it also suggests ways and

means to be adopted at the design stage for designing sustainable products. The results thus

obtained from these LCA studies are useful for a decision making process at the product

design stage [20].

It is evident from these research studies that various attempts have been made for the

design and evaluation of the life cycle of a product either separately or in combination. In

addition, various LCD features/attributes of a product have been identified. Moreover, these

researchers have also considered that LCD is a multicriteria decision making process. The

various design concepts are considered as the various alternatives for product design. LCD

parameters such as design, manufacture, and safety have been considered as the design

criteria for evaluation and comparison of different concepts of product designs. However,

these researchers have not taken into consideration all aspects of LCD of a product and also

their inter-relationship/interdependence with each other.

The main requirement is the consideration of all possible features/ attributes of the life

cycle of a product. Moreover, their interrelationship/ interdependence with one another

should be well understood and properly represented. The easiest and convenient way is using

graph theory concepts in terms of digraph models. This model can be analyzed using an

appropriate matrix to develop the LCD expression and LCD index of the product.

2.2 PRODUCT LCA MODELLING AND EVALUATION

LCA addresses the environmental aspects and potential environmental impacts (e.g.

use of resources and environmental consequences of releases) throughout a product‘s life

cycle from raw material acquisition through production, use, end of life, recycling, and final

disposal [20].

Czichos [21] has shown that various triboelements are in-built in a mechanical system

to perform different functions for attaining desired output. It is a fact that triboelements

perform their functions through transfer of motion, material, and energy. The transfer of

material and energy results in loss of material and energy, which not only results in poor

performance at operational stage but also maximizes the impacts on LCA of a system.

In order to save the planet from critical damage, every technical product and process

is required to minimize impacts to environment and all living things by performing LCA,

which is often referred as the ‗cradle -to- grave approach‘ [22].

Various tribology survey reports and research studies have indicated that not only

energy losses due to poor friction and wear practices in industry can be reduced but there is

also a tremendous scope for conserving environment and materials, by adopting latest

innovative and creative tribo-techniques at design and operational stages of a product [23-

34]. In these reports, it has also been mentioned that tribology will play an increasing role as

industry strives for greater productivity through more efficient use of materials, energy,

facilities, and labour.

Kato and Ito [22] have proposed a method for LCA assessment of triboelements. In

this research study, the authors have differentiated the concepts of LCA and LCC and have

finally proposed a tribological-based impact pyramid to find impacts on environment by the

triboelements used in mechanical systems. The pyramid demonstrates a practically useful

image of the life cycle tribology (LCT).

Vag et al. [35] have carried out research studies to determine the LCA of coolants

based on fat ester. In this research study, it has been observed that native ester helps in

conserving energy as well as in reducing biotic resource depletion.

Kalnes et al. [36] carried out LCA study of the production of lubricant base oils for

regeneration. In this study, it was proved that regeneration of base oil has less impact on LCA

as compared to fresh base oil.

Desaki et al. [37,38] have developed a methodology for carrying out LCA of plain

bearing materials used in automotive transmissions. In these research studies, equivalent CO

emission (ECO) was used as the environmental index for determining impact on global

warming.

Ciantar and Hadfield [39] determined the tribological durability and environmental

impacts of domestic refrigerator. In this study, the relation among tribological characteristics,

power consumption, and environmental impact was analysed and the results indicated that

replacement refrigerant has a significant role in increasing friction and wear characteristics of

various triboelements, which leads to higher energy consumption.

Norrby [40] has discussed various issues related to the development and use of EALs.

It has been envisaged that EALs have been repeatedly heralded as one of the future growth

segments of lubricants to reduce impact on LCA.

Sarra-holm [29] has carried out an LCA from cradle to grave of base oils. In this

research study, the author has observed that the selection of base oils and their additives has a

direct and an indirect influence on the environment. Direct impact on the environment is

related to the selection of base oil and the indirect influence is caused by selection of

additives to achieve certain performance in paraffinic and naphthenic oils.

Clift [30] demonstrated how life-cycle thinking helps in identifying potential

significance of tribology, in facilitating extending the life of components, reuse of material,

and ease of assembly and disassembly. This study further revealed that tribology

developments over a period of time have a major role in material conservation (MC) and

energy conservation (EC) at the operational stage of systems.

Toshi et al. [31] have carried out a research study to explain the role of tribology in

LCA of mechanical system. In this research study, the author has supported construction of

environment management system (EMS) based on tribology.

It is clear from the above literature review that these researchers have developed

various methodologies to determine the influence of tribological properties, such as friction,

wear, and lubrication, on different aspects of LCA. These authors have however, not

recognized and envisaged the use of tribological developments in conservation of materials

and energy, preservation of environment, etc. Therefore, there is a need for developing a

holistic approach for assessing the influence of various parameters of tribology on the LCA

of a product. This means consideration of all aspects of LCA of a product based on tribology

and their interrelationship for LCA modelling through an appropriate and useful technique.

This will assist the designer to design and develop product from LCA point of view based on

tribological applications.

2.3 PRODUCT LCC MODELLING AND EVALUATION

In the present day market competition, design engineers and manufacturers are under

tremendous pressure to minimize the product cost without compromising the product quality.

Society of Automotive Engineers, (SAE) defined LCC as the total cost of ownership

of machinery and equipment including the cost of acquisition, operation, maintenance,

conversion, and/or decommissioning during its entire life [41].

LCC is an economic method to evaluate the assets which takes into consideration all

costs ranging from owning, operating, maintaining, and disposal of an asset [42].

International Electrotechnical Commission (IEC) defined LCC as the cost of

acquisition, ownership, and disposal of a product over a defined period of its life cycle [43].

LCC is a standard engineering economic approach used for choosing among

alternative products or designs that provide approximately the same service to the customer

[44].

LCC analysis is a decision making process which can substantially reduce the LCC of

products by giving due consideration to life-cycle aspects of a product [45].

The analysis of LCC gained more attention of the researchers when this concept was

implemented in the defence procurement, i.e., in the planning and acquisition of large pieces

of military equipments [46].

Cost models may range from simple to complex, and are essentially predictive in

nature. Parameters, such as the physical environment of the product, usage demand,

reliability, maintainability, labour, energy, taxes, inflation, and the time value of money, may

have a great impact on the LCC [47].

LCC assessment is a useful aid for comparing lifetime cost of mutually exclusive

assets to determine which asset provides the best value per dollars spent and it should be

performed early in the design process [48-50].

As the emphasis on LCC is increasing day by day, it is essential to consider LCC

assessment at early design stage i.e., at the conceptual design stage. In order to carry out the

LCC assessment at the conceptual design stage, it is inevitable to provide suitable and

efficient tools or methods which facilitates the designers of the product for carrying out the

LCC assessment at the design stage, in particular at the conceptual design stage.

Various LCC models have been developed by the researchers to carry out the LCC

analysis of products at conceptual design stage. Tornberg et al. [51] carried out a cost based

design evaluation process to evaluate different design alternatives in terms of costs. In this

research study, the researchers have used an activity based costing method (ABC method)

modelled in terms of graphical flowcharts representing the processes from design to

manufacture in a manufacturing industry indicating the cost related to different product

related activities.

Reich [52], carried out the economic assessment of municipal solid waste. In this

research study, the researcher has used a combination of life cycle assessment and life cycle

costing approach for the assessment of municipal solid waste.

Emblemsvag [53], proposed a life cycle costing procedure using Activity Based

Costing and Monte Carlo methods. The author has emphasised on reducing the unnecessary

product costs that are involved in the design and development of products in a product life

cycle.

H‘mida et al. [54] proposed a cost model that establishes a link between various

manufacturing and economic parameters which are modelled to carry out the cost estimation

of production products.

Qian and Arieh [55], proposed a parametric cost estimation methodology based on

activity based costing (ABC). In this research study, the authors proposed a cost estimation

model that links activity based costing with parametric cost during the design and

development phases of machined rotational parts. The authors have carried out the evaluation

on the basis of comparison of various cost models.

Chen and Wang [56], proposed a generic activity – dictionary-based method for

product cost estimation in a mass customization product environment.

Cheung et al. [57] carried out a cost modelling study for value driven design for an

aerospace component. In this research study, the researchers had considered the importance

of manufacturing costs during the early stages of product development which helps in

effective decision making. The researchers had applied the unit cost modelling approach to a

Rolls – Royce aero engine fan blade. A step by step cost breakdown structure was considered

for analysis.

Fitzpatrick and Paasch [58], suggested an analytical method for the prediction of

reliability and maintainability based life–cycle labor costs. In this research study, the

researchers carried out the life cycle cost analysis of a Bleed Air Control System (BACS) and

emphasized on the fact that reliability and maintainability greatly influences the life cycle

cost of complex systems and as a result, the more reliable and more maintainable the product

is, the lower its life-cycle cost will be.

Westkemper and Sacken [59], developed a product life cycle costing model that

takes into account various life cycle aspects of a product. In this research work, these

researchers have considered cost management aspects that influence the LCD of a

product. These are manufacturing cost, labor cost, and recycle cost or disposal cost.

Ishii [12] has proposed a methodology for evaluation of life cycle cost of products.

In this methodology, the author has estimated cost of serviceability during ownership

period of a product. The author has also obtained labor step cost based on labor time,

labor penalty (hours) and logistic support.

Ehud et al. [13] have developed a quantitative model for the evaluation of LCC of

a product, based on cost of serviceability and recycling. This methodology has been

applied to CPU of a computer system.

Fitch and Cooper [2] have proposed a methodology for life cycle analysis of products

at design stage, based on cost of energy for materials used in the products. In this research

study, the authors have evaluated total energy required for reinforcing beam material

throughout its life cycle.

Dhillon [60] have carried out the LCC analysis of many systems and has suggested a

variety of techniques to carry out the life cycle costing of systems.

Park and Seo [61] proposed a LCC analysis method which incorporates the life cycle

cost during the early stages of product development. In this research study, the researchers

have taken into consideration various aspects of maintenance and the maintenance cost

associated with the product development. The proposed methodology facilitates the product

designer in carrying out the evaluation process of LCC by considering maintenance cost and

other related costs as the factors of evaluation for different design alternatives under

consideration.

Zhu and Deshmukh, [6] proposed the application of Bayesian decision networks to

study the impact of design decisions on the life cycle performance of products. In this

research study, the authors have demonstrated that proper decision making at design stage

significantly influences the LCC.

Spitzlay et al. [15] carried out the LCC analysis of a fuel tank for two different design

alternatives on the basis of design for end of product, design for manufacturing, design for

use and design for environment. In this research methodology, multilayer high density

polyethylene (HDPE) tank and steel tank (ST) were used for comparison. The findings of the

analysis revealed that design alternative (i.e., HDPE tank), has lower LCC, as compared to

ST.

Gluch and Baumann [62] carried out the feasibility studies of LCC approach with

respect to environment. In this research study, the researchers had emphasized on the utility

of LCC approach in environmental decision making.

Newnes et al. [63] proposed a product LCC estimation method for conceptual design

stage. In this research study, these researchers have carried out a thorough analysis of various

cost modelling research issues, industrial approaches and commercial systems used for cost

estimation of products at the conceptual design stage. The researchers also developed the

relationship between cost modelling research, industrial approaches and commercial systems.

These parameters are used to carry out the prediction of LCC estimation of a product at the

system conceptual design stage. These researchers have also carried out the review of various

LCC estimation tools developed by various researchers previously.

Romanyshyn [64] carried out the LCC analysis of pumps. In this research work, the

author has considered initial cost, installation cost, commissioning cost, energy cost,

operation and maintenance cost, downtime cost, decommissioning cost, environmental cost

and disposal cost as the factors for consideration, while carrying out the life cycle cost

analysis of industrial pumps.

Fabrycky and Blanchard [65] carried out the LCC analysis of a system. In this

research study, the researchers have considered all costs related to design, manufacture,

operation, maintenance and support, retirement, and material disposal.

El-Haram et al. [66] carried out the LCC analysis of a building. In this research study,

the researchers have taken into consideration various costs associated with a building project.

These costs include acquisition cost, facility management cost, and disposal cost. It is evident

from these research studies that, various attempts have been made to carry out the LCC

analysis of a product on the basis of life cycle of a product separately or in combination.

However, these methodologies have not only considered a few parameters of a product but

are not also useful for carrying out the detailed LCC assessment at the earlier design stage

i.e., at conceptual design stage. It is also evident from the above literature review that LCC

approach is a multi-criteria decision making process as it takes into consideration various

aspects which influence the product or its components one way or the other. In addition,

various LCC features/attributes of a product have been identified individually. LCC

parameters such as, design cost, manufacture cost, operation cost, maintenance and support

cost, retirement cost, etc., have also been considered as the criteria for evaluation of life

cycle cost of a product. However, these researchers have not taken into consideration all

aspects of LCC of a product and also their interrelationship/interdependence with each other.

Main requirement is the consideration of all possible features/attributes of LCC of a

product. Moreover, their interrelationship/interdependence with one another should be well

understood and properly represented. The easiest and convenient way is using graph theory

concepts in terms of digraph models. These models can be analyzed using appropriate matrix

to develop LCC expression of a product.

2.4 PRODUCT SUSTAINABILITY MODELLING AND EVALUATION

In the present day manufacturing environment, the end user of the product evaluates

its performance not only in terms of its initial cost or service, but also evaluates the

performance in terms of its cost on environment and other costs related to disposal, recycle /

reuse [67]. A sustainable product is the one which will have little impact on the environment

during its life cycle [68].

Sustainable design or design for environment is known by several other terminologies

such as, Green Design, Eco Design, Environmental Conscious Design, LCD or even Clean

Design [69].

Sustainable design in a product design and development process refers to creation of

engineering designs to comply with the principles of technical, environmental, economic and,

social sustainability [70].

In a life cycle engineering approach, all phases of product life cycle from concept

development to product retirement are considered for successful development of product

throughout its life cycle. These include quality, cost, production feasibility, usage, servicing

and environmental aspects [71].

The companies today are enforced to design products such that they must also fulfil

environmental friendly aspects in the design and development of products at the conceptual

design stage. There is also a need to acknowledge this fact that today‘s designers and

researchers require a sustainability oriented design focus, so as to contain the problems of

sustainability on various levels [72].

The issue of environmental sustainability, which is unprecedented in both magnitude

and complexity, presents one of the biggest challenges faced by modern society [73]

Design engineers can make significant contributions to this issue by designing

products and processes that satisfy societal needs while minimizing the associated

environmental consequences. Decisions made at the initial product design phase determine

the environmental and economic impacts of future decisions [74].

However, sustainability design and development of product has not been considered

thoroughly so far. Therefore, it is essential to consider sustainability at design stage, in

particular, at conceptual design stage.

In order to take into account the sustainability aspects in the design and development

of products at design stage, in an appropriate and efficient way, the designers need to be

provided with proper tools and methods for its successful implementation at conceptual

design stage. Material selection methods have already been developed for the incorporation

of design for environment, design for conservation of energy and design for recycling at

product design stage [67-71, 75-91].

In the design and development of mechanical systems, a variety of materials are used

each signifying its own characteristics. However, to select a material for a particular

engineering application, the functional requirements must be clearly defined so as to short-list

the candidate materials. The availability of a large number of materials for any application,

together with the complex relationships between the various selection parameters, often make

the material selection process a difficult task [78].The decision to select an appropriate

engineering material is not simply a consideration of cost and basic material properties such

as strength, hardness, density, etc., it is also an integral process that requires the trade-offs

between many factors including environmental aspects [79].

A number of techniques have been developed by researchers from time to time which

aids designers and practising engineers to deal with the issue of material selection in the

design and development process of products. In a mechanical design process, the mechanical

properties are of main consideration and therefore each candidate must satisfy the basic

design requirements. The most important mechanical properties for material selection are

strength, stiffness, toughness, hardness, and density [75].

Material selection is a multi-criteria decision making process as it takes into

consideration various aspects which influence the system or its components one way or the

other. The decision to select appropriate materials is mainly influenced by the specific

application requirements, often the requirements on materials properties [80-82]. The process

of material selection can be applied to both new designs and existing designs involving

material substitution [83].

Dixon and Poli [84] suggested two approaches for material selection. These

approaches were material-first approach and, the process-first approach. In the material-first

approach, the designer begins by selecting a material class, narrowing the choices within the

class, and then considering the manufacturing processes consistent with the selected material.

Conversely, in the process-first approach, the designer begins by selecting the manufacturing

process and then the material.

Jee and Kang [85] proposed a method for optimal material selection using decision

making theory. In this research study, the researchers used an optimization technique to help

address the material selection process.

Sirisalee et al. [86] carried out a multi criteria material selection process using Pareto

Set approach. In this research study, the authors have identified the set of non linear solutions

that suggests the optimal material from and among the list of available materials. Yang et al.

[87] proposed a genetically optimized neural network system that assists the designer to

select the composite materials.

Shanian and Savadogo [88] carried out a material selection process for an engineering

application based on multi attribute decision making. In this research study, the researchers

developed an outranking relationship procedure called ELECTRE.

Liao [89] proposed a fuzzy multi criteria material selection procedure. In this research

study, the author has used the trapezoidal fuzzy numbers that helps the designer in ranking of

material alternatives.

Chen et al. [90] proposed a material selection procedure based on environmental

considerations. In this research study, the researchers suggested an alternative approach of

material selection by translating the environmental impact in terms of economic cost of

production and thereby introducing the concept of environmental cost, such as energy

consumption and toxicity.

Beitr et al. [91] carried out a material selection procedure for selection of plastic

materials. In this research study, the researchers have developed a computer program –

Hypercard to select the materials from a variety of plastic materials.

Fitch and Cooper [2] proposed a method of material selection based on life cycle

energy analysis. In this research study, the researchers have applied product analysis method

to evaluate various available materials to be used for automotive components.

Devanathan et al. [92] proposed an eco-design methodology which is a combination

of LCA and some traditionally used design tools. In this research study, the researchers have

used quality function deployment (QFD), functional-component matrix and Pugh chart. In

this methodology, the researchers have considered an office stapler redesign case study.

It is evident from these research studies, that material selection has already been used

for design and development of products for performing various functions to attain desired

output in an efficient way [68-85]. It is clear from above literature that material selection has

potential for design and development of products from sustainability point of view. Although

various attempts have been made to evaluate sustainability of product based on material

selection [86-92]. However, these researchers have not considered all the parameters of

materials which influence the sustainability of the product.

Moreover, these methodologies are not suitable to carry out sustainability modelling

and evaluation at earlier design stage i.e., at conceptual design stage of the product. It is

imperative to identify all characteristics of material which influences the sustainability of the

product in one way or the other and also their interrelationship/interdependence with each

other. Considerations of these material features and their relationship with one another will be

useful in sustainability modelling and evaluation of product at design stage The easiest and

convenient way is using graph theory concepts in terms of digraph models. These models can

be analyzed using appropriate matrix to develop sustainability evaluation expression through

material selection for sustainable design of a product.

2.5 GRAPH – THEORETIC MODELING

The concept of graph theory and its applications is prevalent for a long time, when the

long standing Konnigsberg Bridge problem was solved by Leonard Euler in the year 1736

using Graph Theory. Leonard Euler, thus became the founder of Graph Theory. It is since

then, Graph Theory has proved its mettle in various fields of science and engineering. The

major areas where the Graph Theory has been implemented intensively are:

- Communication Network [93-96]

- Mathematical Field [97-99]

- Mechanical Engineering [100-106]

- Computer Engineering [107-109]

- Artificial Intelligence and Engineering [110 - 113]

- Tribology [114-116]

The work reported in literature in the above listed areas is discussed in the following

paragraphs.

Graphs have been extensively used for analyzing the structural characteristics,

appropriate routing, congestional problems, etc. of communication networks [93,94]. The

matrix approach is used for enumeration of paths. Some graph theoretical invariants of the

network have also been identified to estimate the reliability [95,96]. Combinatorial

mathematics is enmeshed with graph theory and complex different switching functions, some

of which are often neglected in various theoretical studies.

A number of problems under operations research, particularly under economic

modelling [97-99] have been efficiently carried out using graph-theoretic computational

techniques. These include assignment model problems, production planning, sequencing and

scheduling based problems.

Graph theory has been extensively used in the field of mechanical engineering for

mechanism and machine theory, computer aided design and manufacturing [100-106]. The

applications include representation and identification of kinematic structure and for

enumeration of kinematic chains and mechanisms in a relatively simple and systematic

manner.

Matrix representation has proved to be useful in the identification of known, as well

as unknown chains. Representation and analysis of design variants is more efficient using

graph and digraph models and in particular, during the conceptual design stage of a system

[107].

In the field of computer engineering, graph theory has been used to develop various

research studies – depth, breadth, heuristic, etc., [108-109] for the development of efficient

algorithms.

Extensive use of graph theory has been carried out in the development of expert

systems [110,111]. The data structures have also been generalized in terms of

graphs/digraphs. Diagnostic rules have been developed from process models and schematics.

Two classes of rules, one related to the topological location of the faulty system, and the

other for the identification of system faults have been generated.

Fuzzy hypergraphs have been used to reduce the requirement of data in clustering

problems [112]. These are used to represent a fuzzy partition visually. The dual hypergraphs

can represent the elements, which can be grouped into a class at level 0. The strength of an

edge is useful to discriminate strong classes (subsets) from other parts.

Graph theory has been used in topological characterisation of artificial neural

networks (ANN) and structures [113].

In the recent past, graph theory has been used in the field of tribology [114-116].

Graph and digraph representations of tribo-systems, have proved to be useful for carrying

wear evaluation and analysis, and lubricant selection.

From above, it is clear that graph theory has served a great purpose in modelling of

physical systems, network analysis, functional representation, reliability and wear analysis,

conceptual modelling and failure diagnosis. Also matrix representation of graph provides an

excellent tool for qualitative or quantitative analysis and for ease in computer handling.

Moreover, graph theory is simple, convenient and flexible tool which has tremendous

potential in most applications of engineering.

In view of above, graph theory has been considered for modelling LCD, LCA, LCC,

and sustainability of a product at its design stage. Matrix representation of these graphs and

digraphs will provide a useful tool for quantitative analysis including development of the

indices.

The above literature review and the discussions in this chapter provides directions for

the development of design methodology for product life cycle engineering in the following

chapters.