64 Mr. P. W. Bridgmai) on Breaking Tests under 



be handled, many cases of rapture have been observed. 

 Several of these appear to he of types not observed before, 

 and they have special bearing on tne present question. In 

 this paper three of these types of rupture will he described 

 somewhat in detail, and a discussion given of the bearing of 

 these tests on theories of rupture. No attempt will be made 

 to develop a new theory. All that it is desired to do is to 

 point out that in consequence of these tests the true criterion 

 of rupture must be a much more complicated affair than is 

 ordinarily supposed, and that considerations must he intro- 

 duced which have been so Bar neglected, for these tests 

 enable us to summarily dismiss all the conditions of rupture 

 hitherto proposed 



The tests to be described in this paper fall naturally it to 

 three types, and the conditions of rupture to which they 

 have application are also three in number, there being one 

 other generally recognized possibility beside- the two 

 mentioned in the first, paragraph. Each of the three types 

 of tests gives some evidence on the validity of each of the 

 three conditions of rupture, but it will be found that each of 

 the three types of test has its most direct bearing on only 

 one of the conditions. The argument of the paper is grouped 

 about the three different types of test. The nature of the 

 test is first described, then the hearing on the corresponding 

 condition of rupture, and finally the incidental bearing on 

 the other conditions of rupture. The argument is further- 

 more somewhat complicated by the necessity for keeping in 

 mind the possibility of different criteria holding for brittle 

 and ductile bodies. 



The three conditions of rupture to be considered are the 

 condition of maximum principal stress, of maximum stress 

 difference, and of maximum strain. The first demands that 

 rupture occur when either principal str< ss exceeds u certain 

 value, whether this stress is compressive or tensile. The 

 second demand.- that Pail ure occur when the greatest shearing 

 stress, or what is the same Lhing the difference between the 

 greatest and the least principal stress, exceeds a certain value. 

 The third criterion demands that rupture occur if the exten- 

 sion in any direction exceeds a critical value. 



Another question o\' much practical interest, and under 

 ordinar} condition- closelj related to the question of rupture, 

 is the question as to the conditions under which a material 

 will receive a permanent set. The three criteria jus! 

 enumerated are very often n-cd interchangeably as either 

 criteria of rupture or as criteria of set. 



Tne first criterion, as origin alh stated, evidently cannot 



