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XLV. A Laboratory Machine for Applying Bending and 

 I Twisting Moments simultaneously. By Professor E. G. 

 Coker, M.A., D.Sc.j of the City and Guilds of London 

 Technical College, Finsbury *. 



[Plates XI. & XII.] 



APPARATUS for applying simple tension or compression 

 stresses, and also for applying bending or twisting 

 moments to materials, are in common use in laboratories, 

 but such machines are, as a rule, not very well adapted for 

 experiments on combined stresses, although the frequency of 

 such cases in practice make it very desirable that experiments 

 on the effects of combinations of stresses should be carried 

 out by engineering students. This is particularly the case 

 with shafts which are generally subjected to stresses due to 

 combined bending and twisting moments. The present paper 

 describes a machine built by students of the City and Guilds 

 Technical College, Finsbury, in which uniform bending and 

 twisting moments can be applied simultaneously over the 

 w T hole length of the specimen, and in any desired proportion 

 -to each other. 



The machine is similar to one designed by the author for 

 the testing laboratory at McGill University, Montreal, but 

 with some modifications suggested by experience with the 

 earlier machine. The principle on which the design is based 

 is illustrated by fig- 1 (PL XL), in which a rod R is suspended 

 .at intermediate points A, B, by wires C, D 3 depending from 

 a fixed support E. The equal overhanging ends of the rod 

 are loaded by weights W, so that the applied couple between 

 the points of support is uniform and of amount Wa, where 

 a is the length of the lever-arm. The rod is also twisted by 

 weights Wi attached to equal arms of length b, so that there 

 is a uniform twisting moment of amount W x between the 

 points of suspension. The two systems of loading are 

 independent and their ratio can be adjusted to any value 

 desired. 



In carrying out this arrangement in practice it is con 

 venient to arrange that one of the levers for applying the 

 twisting moment shall always remain in a horizontal position, 

 and that the other shall be capable of turning through an 

 arc to bring the first lever back to zero after each application 

 of the load. The most convenient way of carrying this out 

 is to replace the adjustable lever by a worm and worm-wheel 

 gear secured in a casing and turned by a hand- wheel. To 

 allow freedom for bending the worm-wheel casing must be 



* Communicated by the Physical Society : read February 26, 1909. 



