Section III., 1903 [ S9 ] Trans. R. S. C 



VIII. — A Laboratory Apparatus for Applying Bending and Torsional 

 Moments Simultaneously. 



By E. G. CoKEK, M.A., D.Sc. 



Assistant Professor of Civil Engineering, McGill University. 

 (Communicated by Dr. H. T. Bovey, and read May 19, 1903.) 



The d'etenninatioii of the behaviour of materials under various 

 kinds of stress forms an essential part of the laboratory training of the 

 engineering student, and various forms of testing machines are used 

 for applying stresses, such as simple tension, compression, bending, 

 shear, and the particular case of shear produced in twisting a bar by 

 an applied torque. Incidentally, cases of compound stress occur, 

 such as in the bending of beams, where it is not usually thought worth 

 while to eliminate the shearing stress from the bending stress on 

 account of its small effect in beams of moderate length in relation to 

 itheir depth, but in general suitable means for the application of com- 

 pound stress are rarely found in the laboratory, and in particular the 

 important case of bending combined with twisting is rarely experi- 

 mented upon, chiefly because the types of machine used for applying 

 bending or torsional moments, are not applicable for applying these 

 stresses simultaneously. The present paper describes an apparatus 

 for applying both kinds of stress in any desired proportion and uniform 

 in amount over the whole length of the specimen and is a modified 

 form of one described in a previous paper.^ 



The principle of the machine is illustrated by Hgure 1, in wliich 

 a rod A B oi circular section is suspended by rings C D from a bar E, 

 and twisting couples are applied by levers F G oi equal length and 

 loaded to the same degree, whereby a uniform twisting moment is 

 produced on the specimen between the levers. In practice, if the 

 outer end of the lever F is anchored to the ground the effect is the 

 same, and the twisting moment can be applied by a single weight sus- 

 pended from the lever G. 



The ends of the specimen are produced and at suitable distances 

 from each supporting ring loads are applied, so that the bending 

 moment at each ring is the same, and it therefore follows that the 

 bending moment between the supports will be of uniform amount. It 

 it usually preferable to have separate levers for applying the bending 

 moment which can be attached to the ends of the specimen. 



' Apparatus for measuring strain and applying stress. Trans. Roy. Sot-. 

 Edin., 1901. 



