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This preliminary investigation has shown that the programme load method of testing provides more useful information than single load level tests enabling a more reliable estimate of a structural joint fatigue life to be obtained.

It is well known that notches have a deleterious influence on the fatigue strength of parts. A constant, the sensitivity index, is commonly used to relate the fatigue stress concentration factor to the elastic stress concentration factor. The author outlines a simpler hypothesis, which he claims to be a more reliable guide to fatigue behaviour in notches. Briefly it assumes that the elastic stress concentration factor gives the reduction in the fatigue strength due to the notch, but because of the local nature of the stress concentration, the endurance limit is increased according to a simple law. This increase in the fatigue strength depends on the smallness of the notch.

NOTWITHSTANDING the fact that there exists a considerable amount of literature published in various forms on the subject of brittle lacquers and their applications to a multitude of diverse problems a brief resume of some of the general principles involved would seem not to be out of place.

IN Part I, some aspects of the technique of stress determination by photo‐elastic analysis were recommended which, it was considered, would overcome certain difficulties. Let us now have a look at the other side, and consider a few applications of the method, and so to examine its usefulness or otherwise to the designer.

PHOTO‐ELASTICITY is not a new subject. In recent years much progress has been made towards a simplified technique, so that this method of stress analysis is now becoming popular in industry, and is giving valuable information about the failure of engineering parts. There is no mystery about the method; the application of photo‐elasticity is found to require not so much the learned scientist for its satisfactory execution, but rather the man with a sound common sense and a knowledge of the fundamental principles underlying engineering problems. It is found, too, that if the method is intelligently applied it is comparatively cheap and can well repay itself by saving thousands of pounds worth of damage caused by failures under service conditions. To the practical designer photo‐elasticity provides him with one of the most powerful weapons by which he may analyse the stresses existing in complicated engineering parts. In effect the responsibility of a design is passed from the intuitive thought within a designer's mind to the certainty of facts.

THE design of aircraft instruments is a highly specialized art, and unless the principles are well understood a great wastage of time and money can occur before a successful instrument is evolved. The reasons for this will be clear after a consideration of the conditions which must bo satisfied to ensure useful service. These may be summarized under the following headings:—

THIS note proposes a new type of empirical alternating/mean stress diagram for plain fatigue specimens, which combines the merits of the Modified Goodman Line and the Gerber Parabola, with increased accuracy.

The technique described in this paper consists of the examination of surface strains in a metal component with optically sensitive material bonded to the component and the analysis of the photoelastic pattern produced under load by means of polarized light reflected from the surface of the metal. The original investigations cover in considerable detail the development of the technique and the results obtained, using the photoelastic materials Catalin 800, C.R.39, and the Marco Resin, S.B.26C, and S.B.28C, in conjunction with light alloy, magnesium and mild steel. The fundamental problem of producing good adhesion between the photoelastic material and the metal surface coupled with satisfactory light reflexion from the latter comprised the major part of the initial investigations. Results of the measurement of both elastic and plastic stress concentrations at holes in plates subjected to uniform tension are presented, together with a qualitative analysis of the effect on stress distribution of the variation of the pin to hole clearance in lugs. Owing to the fairly extensive nature of the original investigations it has only been possible to outline the more salient features of the work undertaken. The term ‘Metaplastic’ is suggested to describe concisely the use of compound specimens for the photoelastic applications considered.

IN 1968, Dowry Rotol Ltd., Staverton, Gloucester, were awarded a contract by McDonnell Douglas Corporation to implement a surface stress survey on the DC‐10 Nose Undercarriage Assembly.

Forty‐six milks were submitted for analysis. Five of these were reported against for added water or fat deficiency. The leaky churn appeared on the scene in one case, but this did not save the vendor from fine and costs amounting to over thirteen pounds.