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THE TEACHING OF MATERIALS SCIENCE TO HONOURSDEGREE LEVEL IN A GENERAL ENGINEERING COURSEL.Q. HAWEPublished online: 30 Nov 2011.

To cite this article: L.Q. HAWE (1979) THE TEACHING OF MATERIALS SCIENCE TO HONOURS DEGREE LEVEL IN A GENERALENGINEERING COURSE, European Journal of Engineering Education, 4:1, 35-42, DOI: 10.1080/03043797908903458

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European Journal o f Engineering Education. 4 ( 1979 ) 35-42 Q Elsevier Scientific Publishing Company, Amsterdam -The Netherlands

THE TEACHING OF MATERIALS SCIENCE TO HONOURS DEGREE LEVEL IN A GENERAL ENGINEERING COURSE

L.Q. HAWE

INTRODUCTION

The objective of a broadly based engineering degree course -as distinct from a degree in one of the specialist areas of engineering such as aeronauti- cal, electrical, electronic, mechanical, production or shipbuilding - might be stated as: 'The equipping of students with sufficiently broad technological expertise and with adequate understanding of business, management and production methods so that they are able t o adapt to technical changes of increasing complexity and able to contribute - t o problem-solving and decision-making - with due regard to wide-ranging restraints and implica- tions'.

Such a course will be concerned primarily with the bekaviour of integrated systems, including man-machine systems. The student will be trained in the analysis of, and t o some extent the optimisation of, a range of interacting functions. Essential constituents of the course will be Mathematics and Com- puting, so that the student can model and hence examine system behaviours. However, the behaviour of a system is not dictated only by its component parts and their inventive combinations. Basically, engineering function derives from the behaviour of the material (or, more likely, the materials) as designed into the component and as influenced by the required manufacturing history. The capability function of the transformer, of the micro-processor, of the turbine owe much to the skills of the designer and the production engineer, but the capability -and not the least the capability limits -derive from an understanding of the behaviour of the iron-nickel alloy within the lamina- tions of the transformer; the behaviour of the silicon within the chip; the behaviour of the fibre-reinforced polymer within the rotor.

Some knowledge of Engineering Materials is then a pre-requisite t o the mathematical analysis of engineering systems. There is indeed good argument for the adoption of a course-framework in which Materials (providing basic. behaviour-data) and Mathematics (providing the tools to analyse behaviour) form a twin.stem serving all the applied engineering subjects.

Not all readers will agree, however, as to the amount of time which should be devoted to these stem -or core -subjects. In the case of Materials, if their behaviour can be represented by a series of constants -possibly drawn

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from an 'accepted' data source -then i t might be said that the student need only be familiarised with appropriate definitions and directed to the sources of collected data. This notion of discrete values has indeed been encouraged in some cases by the very terms which are - or were -employed. If the ,

behaviour of a capacitor material can be defined by a dielectric 'constant', can a single table, in a prescribed data source (covering the likely range of design materials), not serve as the requisite 'tuition'? In fact, the data-source would need t o provide -as a very minimum - a separate contour map, or 3-dimensional diagram, for each material (the evident misnomer giving way nowadays t o the term, 'permittivity'). The amount of time to be given to Materials as a subject will be dictated by such xariations of behaviour and the interaction of their controlling factors, and by whether or not the beha- viour parameters -including time -are of functional significance.

A knowledge of the behaviour of 'materials' is no less important in the study of man-machine systems; in this case a knowledge of the behaviour of industrial workers, as individuals and as groups. No material has more variation.

A TEACHING STRATEGY

In the teaching of any subject, a wide range of topics can be covered (and very usefully covered in Engineering Certificate and Diploma Courses) by presenting appropriate formulae - with a minimum of fundamental deriva- tion or emphasis of underlying assumptions -and taking the student through a series of graded worked-examples. The student learns how to per- form quite complex manipulations but, as some with more perception have remarked, '"~e have learned how to put in the numbers and turn the handle!" Clearly in this method of teaching any reasonably consistent 'set' of num- bers - including those purporting t o define material behaviour - will be satisfactory. After a period in industry however some students have discov- ered: "We must decide which numbers, and choose between alternative handles or, even worse, attempt to fit a handle!".

When teaching Engineering-Degree students, the aim must be t o train and equip them to mathematically model, and define the boundary condi- tions for, non-standard problems. The graduate must not only know a range of standard formulae but know also their deriv'ations and their associated assumptions, so that an appropriate analysis can be chosen or developed for each new problem of engineering practice.

This objective can be very effectively contributed to in the area of Materials Science, using appropriate syllabuses, teaching methods and assess- ment techniques. The syllabuses, the scope of the present paper, will focus progressively on the derivation of behaviour, the restraints imposed on be- havioui and finally on the analysis of behavioural reliability.

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INHERENT BEHAVIOUR

In First Year, tuition will concentrate not on property definitions but rather on a coverze of the structural features which account for property - - - differences. Definitions of relevant engineering properties will be a logi& startpoint. with indeed some brief indications of the denee of significance - - in a range of typical engineering applications e.g. that modulus of elasticity is relevant in the sag of an overhead cable, in the response and vibration characteristics of a mechanical control system, in the load transfer within a fibre-reinforced composite, in the springback allowance during sheet- metal forming, etc. The bulk of the First Year Syllabus should, however, concentrate on explanations of the distinctive structural features of mate- rials, metals, ceramics and polymers, and then on the correlation of these features with engineering properties, physical, mechanical, electrical, mag- netic and manufacturing. The behaviour of engineering materials must not only be defined: the basis of behaviour must be explained, the student needs the 'formula' and the 'derivation'.

The structural features to be covered will include: the atom, the molecule, the grain, the chain, the network. The correlation should be as wide ranging as possible e.g. having defined the origin of dipoles they should be shown t o be significant in the design of the capacitor, the effectiveness of the water- proofing agent and of adhesives, the ease of manufacturing of thermoplastics and the effectiveness of plasticisers, the resistance of polymers t o chemical attack, the permeability of gases and general diffusion in polymers. The wider the range of applications, the more thought will be provoked and the more the subject becomes phenomena based rather than property based.

The above coverage will be restricted however t o what might be termed the 'inherent properties' of materials and i t will certainly be concerned with the science of properties, in general, rather than a discussion of particular materials. There will not be sufficient time, nor should it be necessary, t o cover even representative materials but only to take appropriate examples.

BEHAVIOUR OPTIMISATION

The First Year coverage will have introduced the basic capabilities of materials and in the opinion of some - as expressed below -nothing further is necessary. "Heat treatment is an established procedure; the Degree student only needs to be aware of i t and then consult the appropriate Standard". Hence, property-development procedures in general, not just heat treatment, are, in effect, 'shelved'.

To draw an analogy, could i t be said that the medical profession only needs dispensing chemists? Is it true to say, "Cortisone is an established drug for the treatment of arthritis; the doctor only needs to be aware of it and to know, for example, that the trade product, Sintisone, his been ap- proved by the British Medical Association." The practitioner attempts to

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match case and cure -and not always with success. Drugs, whose beha- viours were not fully understood have had to be taken off the shelves !

Engineers, no less than medical practitioners, have too often implemented a prescription that focused on too narrow an objective. The'following are some of the more headline-capturing examples of recent years - cases where the 'patient died'!

The initial. design for the outer blades of the RB211 engine, using carbon fibre reinforcement, was hailed as a great achievement in terms of strength- to-weight ratio. The blades shattered during early trials; the limitations of the resin in terms of erosion resistance were not fully understood.

By adopting an 'improved' structural steel for the Point Pleasant bridge, the construction engineers claimed that an eyebar suspension design would be 'less expensive' than a cable suspension-member design. The bridge failed in 1967 with the loss of 46 lives; the inevitable non-homogeneity of the microstructure, as heat treated, and the subsequent failure-mechanism inter- actions were not fully understood.

When low-density polyethylene insulation was adopted for underground power cables, the design life was anticipated as '30 years or more'. Failure occurred 'due to unknown causes, when in service for approximately eight years'; polyethylene being non-polar, there was good reason to believe (as taught in First Year!) that the insulation would be hydrophobic but the implications of the extrusion and post-extrusion processes, with regard t o subsequent dielectrophoresis, were not fully understood.

Major service failures (such as those quoted above), where the engineers involved appear to have made gross miscalculations, have perhaps three broad explanations, related to the field of Materials Science. Some failures can be attributed t o the inevitable area of uncertainty a t the 'frontiers' of engineering. The avoidance of this category requires more fundamental re- search, the importance of which has been emphasised by other writers [ I ] but this research is the province of post-graduate studies. Some failures - a second group -have, in fact, been due to an earlier failure, that of prac- ticing engineers to keep up.to date with the progress of knowledge. This is a major problem but it is the province of short-courses. As has been stated elsewhere, "Perhaps no facet of technology has advanced so rapidly during the past two decades as has that of engineering materials" [2]. There is a need for readily available data-banks but to merely collate supposedly essen- tial data is certainly not the province of Materials Science tuition -at any level.

Some failures - in a third category comprising a disturbingly large num- ber -have been due to the failure of system-design engineers to appreciate one or more of what might be called the fundamental 'laws' of property development and evaluation. The seeming lack of awareness of these 'laws' is no less disturbing than the actual service failures. I t is this area that is the province of undergraduate training. These 'laws' must be effectively covered and illustrated during the training of all engineers who will be involved in

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the design, operation or maintenance of engineering systems. In the scheme of tuition suggested here, coverage would begin in the Second Year syllabus and carry through into a Third Year.

The coverage will introduce a wide range of property development tech- niques including: grain boundary surface area control; sub-recrystallisation plastic deformation; alloying and heat treatment; crystal growth; doping; ion implantation; degassing; impregnation; copolymerisation; crosslinking; compounding; chemical additives; fillers; fibre reinforcement; surface modi- fication. There will be no attempt t o teach the implementation of each tech- nique or t o define the related procedures as applied t o particular materials. As already stated, the emphasis in a general engineering degree course should not be on numerous worked examples but rather on models and boundary conditions. This applies no less t o Materials Science than it does to Engineer- ing Science.

Tuition will aim t o explain the operative mechanisms in property devel- opment - to define the 'models'; and to indicate the potential of altemative techniques applied to representative materials but, not least, to highlight any anomalies and likely adverse 'side effects' - to define the 'boundary conditions'. Selected properties whose origins have been explained in First Year will be used as a means of comparing the effectiveness and identifying the limitations of seemingly suitable altemative techniques. For example, having explained the origin of elasticity and plasticity, in First Year, further t o explain the extent to which the stress-strain behaviour of metals, ceram- ics or polymerscan be tailored t o achieve a limited objective, such as form- ability plus static'strength plus fracture toughness. A-further illustration of conflicting objectives would be the use of thermoplastics for cable insula- tion because of their inherent extrudability and high resistivity albeit not inflammable. The mechanisms of f i e retardance will be explained but again showing that while some techniques, or combination of techniques which are synergistic, may appear to be a solution, in fact, to achieve retardance at the expense of toxicity has only changed -indeed perhaps aggravated - the problem. To come nearer to a solution requires further additives, adding t o the expense of the product not only in terms of raw materials but prob- ably also in terms of added difficulties during extrusion.

The method of tuition and the examples chosen must serve t o emphasise (i) that property development cannot be assessed by data values averaged across a test section and(ii) that the enhancement of one property is usually with detriment to another. These are two of what have been termed earlier 'the fundamental laws of property development and evaluation'. The would- be practitioner must be taught the hazards of oversimplified prescriptions!

CAPABILITY LIMITS

All engineering components and systems have a finite period of usefulness; their performance deteriorates beyond acceptability or total breakdown

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occurs. In meanindul desien and analvsis it is not sufficient therefore to de- sign-in and quantiiy what is in effect only the initial performance. From an adeauate knowledge of the modes and rates of subseauent deterioration in the Eonstituent materials, the graduate engineer mui<be able to quantify also - with acce~table certaintv to the customer -the nett life a ~ ~ r o ~ r i a & . * * *

to the need served, either the life t o overhaul, or t o replacement, or to fail- ure. Taking up again the earlier analogy, death is a certainty but the effec- tive medical practitioner should be a t least able to minimise the 'downtime' meanwhile.

If in a particular case the available knowledge does not allow the predic- tion of a 'safe life' or a t least a safe life between overhauls - then alterna- tively i t may be possible to design some form of 'fail safe' system, by in- corporating redundancies or - being even more ingenious - by exploiting some additional material behaviour e.g. as in self-healing capacitor film. In general, however, 'fail safe' is an over statement; the aim can only be t o design-in a specified (perhaps as small as 0.0001) probability of failure.

If the redundancy is in the form of a stand-by system then relevant forms of deterioration may still need t o be considered, the life t o be predicted being the period of stand-by, with or without periodic run-up, beyond which the speed of, or degree of, functional response would be unacceptably lowered.

The analysis of functional systems must cany through then to a considera- tion of deterioration and reliability. Deterioration in the form of dissipat- ing goodwill is no less vital a consideration in man-machine systems. .

One simple approach -still all too entrenched among designers and in- deed perhaps still encouraged by the would-be guidance of standard speci- fications - is t o adopt a 'derating factor' for electrical systems (e.g. 'de- rate i t by 10°C and the life will double') and a 'safety factor' (more honestly an 'ignorance factor') for mechanical systems. In any functional system, however -even where function depends on only a single component - duty and capability will each have a statistical variation. I t follows that re- liability cannot be guaranteed by simple procedures.

Any adequate consideration of reliability necessarily involves cost. Total reliability, even assuming it could be designed into a system, may in- cur a prohibitive cost but i t does not follow that unreliability must be ac- cepted. I t may'be, and especially so in to-day's high investment technolo- gies, that unreliability represents a no less prohibitive cost, in the form of lost production or lost investment-earning due to unscheduled shut-downs.

I t was estimated (in 1972) that a 1% increase in the Forced Outage Rate of the four 750 MW units a t the Bruce Generating Station in Canada, over its 3 0 year life span, would result in a penalty of $20 million. The cost of the shut downs, in November 1976 and January 1977, of the 660 MW units at'the Drax station in Yorkshire, arising from the early development of cracks in the 90 ton rotors, has been reported as 6 2 million for replace- ment of the rotors and a further 6 6 million t o cover the emergency mea-

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sures necessary t o maintain supplies. An immeasurable cost is introduced in cases where premature failure endangers l i e ; faildangerous probabilities may need t o be of the order of 0.000 001 -as, for example, in the auto- matic landing system of an airliner.

There are, by contrast, many areas of application where customers have in the past largely accepted unreliability at the attendant costs; suppliers have not given due attention to deterioration and failure analysis and have 'got away with it' in terms of market acceptance. Governments are now reacting, however, and legislation on product liability has already been introduced in some countries. In the future, customers will not need to be, and are certainly not likely to be, so tolerant. This legislation, and the threat of even more demanding enactments in line with EEC policies, has added a new impetus to the application of reliability engineering.

The study of risk and reliability involves many areas of engineering practice -the area of creativity and design; the techniques of functional analysis; the technology of shaping and fabrication; the area of materials selection and treatment; the methods of preliminary testing and evaluation. Post-mortems on past service failures have adversely reported on all of these areas but the order of the above listing is some indication of those shown to be most suspect.

I t is this suspect behaviour - its origin and hence appropriate testing and functional analysis -which will be the subject matter of Materials Science 111.

Students will not altogether welcome a focus on 'suspect behaviour'. They will have been conditioned by studies which in general have involved definable responses and unique right-answer type outcomes. Indeed, in the earlier studies of Material Science, comparative behaviours will have been defined by discrete property values. Moreover by the very units (MN/m2 and kV/mm) in which these were defined i t will have been inferred that they can be applied as design data on the basis merely of area or thickness factors. The idea of breakdown strength as proportional to corss-sectional area (as in a tie rod) or to thickness (as in insulation) will be firmly en- trenched.

An appropriately provocative introduction, therefore, to the syllabus coverwe will be a consideration of selected service failures. These ~ o s t - mortems will certainly highlight the alarmingly suspect behaviour bf fabri- cated components subject to interacting environments and in turn drama- tise the necessity to reappraise, at least to some extent and perhaps even to a revolutionary extent, some former approaches to design and evaluation. It will be seen that typical service failures rather than occurring instantane- ously across a plane or through a thickness are activated a t a point e.g. as a crack due to some stress concentration around an impurity; as a tree due to some field enhancement factor at a contaminant; as erosion due to the discharge across an internal void. I t will be noted that engineers;during post-mortem hearings, have admitted they attempted t o use data derived

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from overload conditions in designing for working conditions or, in effect, that they designed against overload which they envisaged would never occur and merely hoped for indefinite, or a t least acceptable life under the condi- tions that would occur! The student will be made t o realise that the analysis of load-carrying systems cannot, as often in the past, be based on the notion of 'allowable' stresses and voltage gradients related t o geometry but must instead be based on the 'concept of cumulative damage' and, furthermore, must take account of the likelihood that the accumulation of 'damage' will in many cases be far advanced during the process cycle, before ever the system reaches functional service.

Tuition must cover therefore the likelihood of, and the distinctive fea- tures of, contaminant pick-up, stress fields and micro structural damage in materials subjected t o the principal manufacturing techniques e.g. casting and vacuum deposition of metals; extrusion of polymers.

This identification of the 'origin' of suspect behaviour logically leads on t o the second main area of tuition viz. 'appropriate testing'. The student will by this stage appreciate that single-point property values, averaged a- cross a thickness and based on a single application of load - this load being of a distinctive type- are a t best irrelevant and a t wor;t misleading. Tuition will demonstrate that meaningful data can only be derived from a test sec- tion which is representative both statistically (i.e. is large rather. than small) and historically (i.e. has been subject to actual process conditions). The data envisaged is of course not failure magnitudes but rather the significance of typical non-homogeneities, critical in either magnitude, constitution or position e.g. in the case of cable insulation, the significance of small rather than large size, of water filled rather than gas pocket, of a position near a bend rather than along a straight length, of a position near the conductor rather than near the sheath.

The final area of tuition t o which all the course has been aimed will be failure analysis and the prediction, quantitatively, of service reliability. Predictions will be made directly and by perceptive deductions from acceler- ated-life tests. The analytical techniques will cover: defect propagation; ther- mal degradation; diffusion and cumulative damage due to both load-frequency and load-duration spectrums. In all cases the student will be encouraged t o critically appraise the adequacy of the technique -its underlying assump- tions, its over-simplifications, its omissions of operative interactions.

The aim is t o equip the student with a knowledge of probabilistic design but not as just another 'handle t o be turned'. Exercise of judgement be- tween alternative approaches must be cultivated.

REFERENCES

1 Finniston, M. (1971). "Materials research must grow in scale to show benefits," Design Engineering (June).

2 Evans, R.K. (1973). "Advanced materials spearhead technology's growth," Chartered Mechanical Engineering (January).

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