466 WEAR

Systematic Abstracts of Current Literature

I. DEFOR~WTION AND FRACTURE

The High-speed Photography of Fracture in Sapphire and Diamond. J. E. Field, 6th International Coxgress ox High-speed Photography, September, 1962. pp. 514-521; 4 figs., 10 refs. Headings of sections are : Introduction; Experimental: Results: Conclusion. From sequences described it has been possible to study the injtiation and growth of frac- tures in sapphire and diamond. Cleavage in- variably occurred in diamond on the (III) planes, except in the case of horizontal fracture (illustrated). Fracture appeared in sapphire in three forms, and examples of simple cleavage, stepped cleavage, and con- choidal fractures were recorded. The maximum velocities measured for sap- phire and diamond were 4400 and 7200 mjscc respectively. It is convenient to obtain the ratio of these velocities with the stress wave velocities, since several theoretical treatments of fracture predict relationships for these ratios. Using the published elastic constants for sapphire and diamond it is possible to cal- culate the appropriate stress wave values. Evaluated in this way, the ratios V,/C, and VF/CZ for sapphire are 0.4 and 0.7’; for diamond they arc 0.4 and 0.6, respectively. I’p is the maximum fracture velocity meas- ured, and Cl and CZ are the longitudinal and transverse stress wave velocities. Mott’s theory predicts for l’p/Cl a value of 0.38 (varying slightly depending on the Poisson’s ratio), while Poncelet’s theory predicts for VF/CZ a value of 0.5, ngrecment appears closest with Mott’s predicted ratio.

Fracture of Solids. J. E. Field, The Times Science Review, (19h4) 5-g; 8 figs. Headings of sections are: Types of fracture; Strength of solids: Transmission of stress; Fracture velocity.

The fact that fractures propagate less casill in materials in which some plastic work occurs as the fracture advances may prove useful. Indications are that reinforced solids can bc devised which, while retaining many of the good properties that brittle solids have, will inhibit fracture growth of catastrophic nature. Certainly a large amount of information about the strength properties of solids has been assembled in the comparatively short time since the original paper by Griffith. In the last few years understanding of the cause of fracture and the mechanism of its propa- gation has advanced considerably. It is reasonable to expect that in the near futurr new and exciting materials will be developed.

The Behavior of Materials in a High-speed Environment. I;. P. Rowden and J. H. Wonton, Higiz Tempevatuve Structuves a?zd Materials, Pro- ceedings gvd Symposium on Naval Structztval Mechanics, Pergamon Press, New York, 1903, pp. 214-244; 27 figs., 21 rcfs. The headings of the individual srctions arc: Introduction; Friction at high sliding speeds; The behavior of materials at high tempcra- tures; High-speed liquid impact; Conclusion. A number of experimental investigations into the properties and behavior of materials un- der the extrcmc conditions associated with present-day high-speed travel arc described. It is apparent in the casts considered that the experiments have not produced an)- rcatly- made solutions to the materials problem. However, the purpose of these studies has been to examine the basic mechanisms under- lying the behavior of materials in a high- speed environment. Given an understanding of the various mechanisms it then becomes easier to choose, and even to design, new materials which are capable of lvithstanding these conditions more effectively.

2. :YDHESION AKD FRICTION

On a Sliding Friction Mechanism, Comple- contrast. The part plavcd by this bulge in the mentary to the Adhesion Process. (in French) process of sliding friction is briefly analysed.

R. Courtel, Compt. Rend., 253 (1961) 19oG- 1908. On the Contact Stress of Two Cylinders with The frontal bulge formed in the course of the Parallel Axes Normally and Tangentially preliminaq+ displacement and at the end of Loaded. (in French) sliding was revealed and examined by inter- II. Hecms, F. I,agarde, R. (‘ourtcl and I’.

ferometry and by interfercntial Nomarski Sorin, Compt. Rrjzd., 2.57 (19b3) 3~93-3~90.