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V. Breaking Tests under Hydrostatic Pressure and 

 Conditions of Rupture. By P. W. Bridgman *. 



[Plate II.] 



WITHIN the last few years a number of papers -j- have 

 appeared, either written by engineers or else of 

 engineering interest, dealing with the conditions under 

 which rupture is produced in the materials of ordinary 

 practice. The objects of these papers has been to find if 

 possible some criterion by which rupture may be predicted, 

 whatever the type of applied stress. The present state of 

 opinion seems to be that for ductile materials the maximum 

 shearing stress plays the principal part, but that for brittle 

 materials the maximum principal stress is the determining- 

 factor. At the same time it is pretty generally recognized 

 that neither of these criteria is likely to be actually correct, 

 but is at best only an approximation likely to give fairly 

 good results for the materials of ordinary engineering 

 practice under ordinary practical systems of load. 



A general consideration of what may be the determining 

 factors in producing rupture under so wide a variation in 

 the nature of the applied stress that there is no immediate 

 relation to the needs of engineering seems to have been 

 neglected. Yet it is precisely such a consideration of the 

 conditions of rupture under as wide a range of the conditions 

 as possible that is likely to lead to a true theory of rupture, 

 and so to a better formulation of the conditions for the range 

 of ordinary practice. 



In the course of a number of experiments on very high 

 hydrostatic pressures, the author has observed many cases 

 of rupture which have a bearing on the present question. 

 The pressures which it has been found possible to reach are 

 considerably in excess of any hitherto produced in fluids, 

 pressures of 30,000 atmos. having been repeatedly attained. 

 Under these pressures all ordinary theories as to the behaviour 

 of elastic solids break down completely, and the entire 

 subject had to be approached from the beginning. During 

 the two or three years of preliminary work spent in acquiring 

 familiarity with the methods by which these pressures might 



* Communicated by the Author 



t Scoble, Phil. Ma-r. xii. pp. 533-547 (1906) ; Hancock, Phil. Mag. 

 xii. pp. 418-425, 426-430 (1906), and xvi. pp. 720-725 (1908) ; Gulliver, 

 Proc. Roy. Soc. Edin. xxix. pp. 427-431 (1909) ; Smith, Eng. lxxxviii. 

 pp. 238-243 (1909); Scoble, Phys. Soc. Lond., Nov. 26, U909 j xxii. 

 pp. 130-146 (1910). 



