Photoelasticity for Designers

Photoelasticity for Designers 100s. R. B. Heywood’s previous book “Designing by Photoelasticity”, published in 1952, has gained a justified reputation and has helped many students and young engineers to understand photoelasticity, to put its technique to good use, and to improve design by the intuitive understanding that photoelasticity does so much to promote. The new book is a completely revised edition of the older book, has taken over much of its text and has added new matter and new references high-lighting the progress since 1952. After a summary of definitions, symbols, S.I. conversion factors, the author devotes 40 pages to planepolarising and 20 pages to circularly polarising systems, 30 pages to polariscopes and their components, 50 to photoelastic materials and 35 pages to preparation and testing of two-dimensional models. These 175 pages compare with 110 pages on the same topic in the earlier book. Discussion of the transfer of results to the prototype has been expanded from 15 to 20 pages, and the separation of principal stresses now merits a chapter for itself (13 pages). The frozen-stress technique (33 pages) is described separately from its applications (20 pages) and materials (15 pages). A chapter on photoelastic layers has been newly added (17 pages). A substantial part of the earlier book dealt with stress concentration factors and included original contributions by the author, but only a single chapter called “Improvement of designs”, has been taken over and expanded with emphasis on the feature of “streamline fillets” (50 pages). This chapter shows how qualitative understanding of photoelastic results improves design by the technique of “shaping” engineering components. Finally, a “New Distorted Model Technique” and some results are described in 20 pages. This technique of observing deflections on low-modulus models is old and not directly related to photoelasticity, but the author adds some pertinent clarifications. The bibliography (826 references in the earlier, 1134 references in the new book) is a gold mine, and a very good subject and author index contributes much to the value of the book. The classical basis of photoelasticity has been so well described in so many books that a repetition should have been very brief. The discussion of various types of polaristers (10 pages!) appears dated, and the 238 space could have been used in a forward looking discussion of newer discoveries and developments. The automatic polariscopes of Robert and of Redner would have .deserved mention. Dynamic photoelasticity is now a serious tool for qualitative analysis and its demonstration of dynamic events should have appealed to the author, whose remarks do not do justice to this topic and in some instances are apt to mislead. The sandwich technique might have been described by examples, embedded polaroids are not even mentioned. The author concludes that various such techniques “are useful but none compare with the flexibility and versatility of the frozen-stress method”. Not so! It would have been the author’s duty to compare and point out individual advantages and disadvantages as has been done in an article in this issue of “Strain”. The reviewer would have preferred a deeper discussion of the lessons to be drawn from design for strength in living nature whose technical accomplishments still leave us near the starting post. The chapter on the “new” technique of distorted models brings some excellent instructive examples but the contention that tensile deformation indicates improved shapes is not true in every case. The silicone-rubber technique with household paint as a strain-sensitive coating has already gone far beyond the simple two-dimensional aspects discussed in the book. The author is not always critical enough in describing methods known from literature. The technique of passing light through a surface layer in a direction parallel to the surface stlffersfrom the inherent defect that strain normal to a free surface is not zero layer may therefore develop bending stresses through its thickness. Criticism of such detail is already a recommendation of the book because the critic wishes it could have been even better in many respects. The author has collected with extraordinary persistence a very great amount of useful data and the new book, like the earlier one, is certain to give instruction and pleasure to many students-formal and informal-of the subject and to provide a valuable source of reference and a compendium of work in this field for the research worker and expert. The style is unhurried, the conclusions are general and always qualitatively instructive so that the reader who browses through it at leisure and he who works through it with diligence will both draw profit. M.L.M. “Strain”, October, 1969 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Strain Wiley

Photoelasticity for Designers

Strain, Volume 5 (4) – Oct 1, 1969

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Publisher
Wiley
Copyright
© 1969 Blackwell Publishing Ltd
ISSN
0039-2103
eISSN
1475-1305
D.O.I.
10.1111/j.1475-1305.1969.tb01629.x
Publisher site
See Article on Publisher Site

Abstract

100s. R. B. Heywood’s previous book “Designing by Photoelasticity”, published in 1952, has gained a justified reputation and has helped many students and young engineers to understand photoelasticity, to put its technique to good use, and to improve design by the intuitive understanding that photoelasticity does so much to promote. The new book is a completely revised edition of the older book, has taken over much of its text and has added new matter and new references high-lighting the progress since 1952. After a summary of definitions, symbols, S.I. conversion factors, the author devotes 40 pages to planepolarising and 20 pages to circularly polarising systems, 30 pages to polariscopes and their components, 50 to photoelastic materials and 35 pages to preparation and testing of two-dimensional models. These 175 pages compare with 110 pages on the same topic in the earlier book. Discussion of the transfer of results to the prototype has been expanded from 15 to 20 pages, and the separation of principal stresses now merits a chapter for itself (13 pages). The frozen-stress technique (33 pages) is described separately from its applications (20 pages) and materials (15 pages). A chapter on photoelastic layers has been newly added (17 pages). A substantial part of the earlier book dealt with stress concentration factors and included original contributions by the author, but only a single chapter called “Improvement of designs”, has been taken over and expanded with emphasis on the feature of “streamline fillets” (50 pages). This chapter shows how qualitative understanding of photoelastic results improves design by the technique of “shaping” engineering components. Finally, a “New Distorted Model Technique” and some results are described in 20 pages. This technique of observing deflections on low-modulus models is old and not directly related to photoelasticity, but the author adds some pertinent clarifications. The bibliography (826 references in the earlier, 1134 references in the new book) is a gold mine, and a very good subject and author index contributes much to the value of the book. The classical basis of photoelasticity has been so well described in so many books that a repetition should have been very brief. The discussion of various types of polaristers (10 pages!) appears dated, and the 238 space could have been used in a forward looking discussion of newer discoveries and developments. The automatic polariscopes of Robert and of Redner would have .deserved mention. Dynamic photoelasticity is now a serious tool for qualitative analysis and its demonstration of dynamic events should have appealed to the author, whose remarks do not do justice to this topic and in some instances are apt to mislead. The sandwich technique might have been described by examples, embedded polaroids are not even mentioned. The author concludes that various such techniques “are useful but none compare with the flexibility and versatility of the frozen-stress method”. Not so! It would have been the author’s duty to compare and point out individual advantages and disadvantages as has been done in an article in this issue of “Strain”. The reviewer would have preferred a deeper discussion of the lessons to be drawn from design for strength in living nature whose technical accomplishments still leave us near the starting post. The chapter on the “new” technique of distorted models brings some excellent instructive examples but the contention that tensile deformation indicates improved shapes is not true in every case. The silicone-rubber technique with household paint as a strain-sensitive coating has already gone far beyond the simple two-dimensional aspects discussed in the book. The author is not always critical enough in describing methods known from literature. The technique of passing light through a surface layer in a direction parallel to the surface stlffersfrom the inherent defect that strain normal to a free surface is not zero layer may therefore develop bending stresses through its thickness. Criticism of such detail is already a recommendation of the book because the critic wishes it could have been even better in many respects. The author has collected with extraordinary persistence a very great amount of useful data and the new book, like the earlier one, is certain to give instruction and pleasure to many students-formal and informal-of the subject and to provide a valuable source of reference and a compendium of work in this field for the research worker and expert. The style is unhurried, the conclusions are general and always qualitatively instructive so that the reader who browses through it at leisure and he who works through it with diligence will both draw profit. M.L.M. “Strain”, October, 1969

Journal

StrainWiley

Published: Oct 1, 1969

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