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Fracture mechanics in design and service
Int. J. Pres. Ves. & Piping 10{t982)481-483
BOOK REVIEW
Fracture Mechanics in Design and Service. The Royal Society, 1981. 239 pp, £23.00. The seventeen papers (not twenty, as stated by the Publisher) and associated discussions in this volume, together with opening and closing remarks, respectively by Sir Hugh Ford, FRS, and Sir Peter Hirsch, FRS, were first published in Philosophical Transactions of the Royal Society, Series A, Vol. 299, 1981. The papers, originally contributions to a Royal Society Discussion Meeting held in December, 1979, cover the fundamental fracture behaviour of metallic and nonmetallic materials under repeated and sustained loads, testing and assessment and, perhaps most importantly, experience in the application of fracture mechanics in various industries--petroleum, rubber, gas, wood and power generation, including nuclear. Contributors of papers, and also written discussions, are mainly fracture mechanics specialists from the United Kingdom representing industrial, government and private research and development organisations, university departments and, in one case, an insurance company. It would clearly be an impossible task within the space normally granted to a reviewer to comment meaningfully on each of these papers. However, it is noted that the Discussion Meeting started with the maxim that 'defects of many kinds exist in every real structure, and the engineer has to learn to live with them' and, accordingly, aimed at assessing the extent to which fracture mechanics in itspresent state ofde1'elopment is being successfully applied by engineers and designers to the solution of real problems. Significantly, a number of the papers, by reference to case histories and (or) by describing the application of fracture mechanics in a particular industry, evince the extent to which the Discussion Meeting as a whole achieved this objective. It is therefore appropriate that some of these are mentioned here. In 'Materials Defects and Service Performance', G. P. Smedley considers, with due reference to case histories of failures in marine structures, pressure vessels and storage tanks, whether recent brittle failures have stemmed from a misinterpretation of the results of major researches since World War 2, or from fundamental deficiencies in the scope of these researches. No conclusion regarding this point is 481 Int. J. Pres. Ves. & Piping
Printed in Great Britain
(10) (1982)--© Applied Science Publishers Ltd, England, 1982
482
BOOK REVIEW
explicitly given, however--rather, the reader is left to form his own opinion. Nevertheless, a number of points are clearly made, notably: great uncertainties remain in designing against crack arrest; the development of notch tough steels has provided the means of solving most of the problems of brittle fracture for C Mn steel weldments, although Post-yield Fracture Mechanisms (PYFM) is not sufficiently advanced that it can be used in the proper determination of minimum toughness requirements for rules and codes of practice governing the design and construction of important weidments and future research should concentrate on solutions to the serious deficiencies of weld zones, principally in terms of gaining a better understanding of factors affecting defect tolerance. A small error appears in this paper: C. P. Sandberg reported the results of drop weight tests on the cold brittleness of iron and steel in 1869 n o t 1969 as printed--although, of course, in engineering terms the phenomenon remains as significant today as when it was first scientifically investigated over a hundred years ago! A more sanguine attitude towards welded connections is adopted by H.C. Cotton in 'Experience in the Petroleum Industries', in describing the pragmatic approach adopted by British Petroleum Ltd to the application of fracture mechanics (notably PYFM in terms of COD) for the selection of materials and development of optimum welding and stress relieving procedures for storage tanks, oil and gas pipelines and offshore structures. There is also an interesting discussion in this paper as to why the petroleum industry as a whole is reluctant to adopt fracture mechanics methods at the design stage in favour of more empirically based methods; e.g. Charpy V, culminating with the generalisation: ' . . . In short, the use of fracture mechanics at the design stage is currently more likely to compound a problem than to solve it.' It is only fair to point out that, against this, the value of fracture mechanics in materials selection and as an aid/to investigating service failures is acknowledged. Moreover, much of the discussion has a wider significance in being equally relevant to industry in general. As a third, and perhaps less contentious, example, J. M. Coffey and M. J. Whittle in 'Non-destructive Testing: Its Relation to Fracture Mechanics and Component Design', consider the implications that the inherent limitations of N D T techniques have for component design and fracture mechanics and give two illustrative examples where the joint application of fracture mechanics and ultrasonics has proved beneficial (repair to a large pressure vessel involving the replacement of ~t forged nozzle; development of in-service inspection of certain components in the 1500 MW Dinorwic Pumped Storage Power Station). Notwithstanding the more contentious points of view, the book leaves no doubt that some industries, at least, are successfully learning to live with defects by appropriate application of existing fracture mechanics technology. It is a pity, however, that none of the contributions are specially concerned with applications in the aerospace industry: this constitutes an unfortunate omisssion in what is otherwise a well balanced collection of papers. The volume nevertheless does great service to fracture mechanics as an engineering discipline by showing very clearly the
BOOK REVIEW
483
benefits accruing to particular industries from relatively modest investments in fracture mechanics expertise. For example, H. D. Williams and G. J. Neate, in their paper, 'Fracture Mechanics: the CEGB Approach', report that as a result of a fracture mechanics based assessment, an extensively cracked alternator rotor continued safely in operation for 2 years, thus saving the Central Electricity Generating Board £ 16M in replacement generation costs. Another snippet gleaned from the book in the same context, and which is clearly worth recording here, is the cost-effectiveness enj~oyed by British Petroleum Ltd with reputedly only three fracture mechanics experts on its staff. There is little doubt that the benefits of fracture mechanics can be reaped by many more industries than at present--a point made by Sir Peter Hirsch in his Concluding Remarks. There are problems to be overcome, however, not the least of which is the effective dissemination of practical fracture mechanics 'know-how' in suitably simple and convincing terms. The present volume makes a valuable and timely contribution in this direction. D. P. G. LIDBURY
BOOK REVIEW
Fracture Mechanics in Design and Service. The Royal Society, 1981. 239 pp, £23.00. The seventeen papers (not twenty, as stated by the Publisher) and associated discussions in this volume, together with opening and closing remarks, respectively by Sir Hugh Ford, FRS, and Sir Peter Hirsch, FRS, were first published in Philosophical Transactions of the Royal Society, Series A, Vol. 299, 1981. The papers, originally contributions to a Royal Society Discussion Meeting held in December, 1979, cover the fundamental fracture behaviour of metallic and nonmetallic materials under repeated and sustained loads, testing and assessment and, perhaps most importantly, experience in the application of fracture mechanics in various industries--petroleum, rubber, gas, wood and power generation, including nuclear. Contributors of papers, and also written discussions, are mainly fracture mechanics specialists from the United Kingdom representing industrial, government and private research and development organisations, university departments and, in one case, an insurance company. It would clearly be an impossible task within the space normally granted to a reviewer to comment meaningfully on each of these papers. However, it is noted that the Discussion Meeting started with the maxim that 'defects of many kinds exist in every real structure, and the engineer has to learn to live with them' and, accordingly, aimed at assessing the extent to which fracture mechanics in itspresent state ofde1'elopment is being successfully applied by engineers and designers to the solution of real problems. Significantly, a number of the papers, by reference to case histories and (or) by describing the application of fracture mechanics in a particular industry, evince the extent to which the Discussion Meeting as a whole achieved this objective. It is therefore appropriate that some of these are mentioned here. In 'Materials Defects and Service Performance', G. P. Smedley considers, with due reference to case histories of failures in marine structures, pressure vessels and storage tanks, whether recent brittle failures have stemmed from a misinterpretation of the results of major researches since World War 2, or from fundamental deficiencies in the scope of these researches. No conclusion regarding this point is 481 Int. J. Pres. Ves. & Piping
Printed in Great Britain
(10) (1982)--© Applied Science Publishers Ltd, England, 1982
482
BOOK REVIEW
explicitly given, however--rather, the reader is left to form his own opinion. Nevertheless, a number of points are clearly made, notably: great uncertainties remain in designing against crack arrest; the development of notch tough steels has provided the means of solving most of the problems of brittle fracture for C Mn steel weldments, although Post-yield Fracture Mechanisms (PYFM) is not sufficiently advanced that it can be used in the proper determination of minimum toughness requirements for rules and codes of practice governing the design and construction of important weidments and future research should concentrate on solutions to the serious deficiencies of weld zones, principally in terms of gaining a better understanding of factors affecting defect tolerance. A small error appears in this paper: C. P. Sandberg reported the results of drop weight tests on the cold brittleness of iron and steel in 1869 n o t 1969 as printed--although, of course, in engineering terms the phenomenon remains as significant today as when it was first scientifically investigated over a hundred years ago! A more sanguine attitude towards welded connections is adopted by H.C. Cotton in 'Experience in the Petroleum Industries', in describing the pragmatic approach adopted by British Petroleum Ltd to the application of fracture mechanics (notably PYFM in terms of COD) for the selection of materials and development of optimum welding and stress relieving procedures for storage tanks, oil and gas pipelines and offshore structures. There is also an interesting discussion in this paper as to why the petroleum industry as a whole is reluctant to adopt fracture mechanics methods at the design stage in favour of more empirically based methods; e.g. Charpy V, culminating with the generalisation: ' . . . In short, the use of fracture mechanics at the design stage is currently more likely to compound a problem than to solve it.' It is only fair to point out that, against this, the value of fracture mechanics in materials selection and as an aid/to investigating service failures is acknowledged. Moreover, much of the discussion has a wider significance in being equally relevant to industry in general. As a third, and perhaps less contentious, example, J. M. Coffey and M. J. Whittle in 'Non-destructive Testing: Its Relation to Fracture Mechanics and Component Design', consider the implications that the inherent limitations of N D T techniques have for component design and fracture mechanics and give two illustrative examples where the joint application of fracture mechanics and ultrasonics has proved beneficial (repair to a large pressure vessel involving the replacement of ~t forged nozzle; development of in-service inspection of certain components in the 1500 MW Dinorwic Pumped Storage Power Station). Notwithstanding the more contentious points of view, the book leaves no doubt that some industries, at least, are successfully learning to live with defects by appropriate application of existing fracture mechanics technology. It is a pity, however, that none of the contributions are specially concerned with applications in the aerospace industry: this constitutes an unfortunate omisssion in what is otherwise a well balanced collection of papers. The volume nevertheless does great service to fracture mechanics as an engineering discipline by showing very clearly the
BOOK REVIEW
483
benefits accruing to particular industries from relatively modest investments in fracture mechanics expertise. For example, H. D. Williams and G. J. Neate, in their paper, 'Fracture Mechanics: the CEGB Approach', report that as a result of a fracture mechanics based assessment, an extensively cracked alternator rotor continued safely in operation for 2 years, thus saving the Central Electricity Generating Board £ 16M in replacement generation costs. Another snippet gleaned from the book in the same context, and which is clearly worth recording here, is the cost-effectiveness enj~oyed by British Petroleum Ltd with reputedly only three fracture mechanics experts on its staff. There is little doubt that the benefits of fracture mechanics can be reaped by many more industries than at present--a point made by Sir Peter Hirsch in his Concluding Remarks. There are problems to be overcome, however, not the least of which is the effective dissemination of practical fracture mechanics 'know-how' in suitably simple and convincing terms. The present volume makes a valuable and timely contribution in this direction. D. P. G. LIDBURY