CROSS-BREAKING TESTS. 



173 



cylinders which are fixed in the two separate standards 

 shown. By this means, beams of very much greater span 

 than could be taken by the usual appliances can be tested. 

 In the ordinary machines of 100 tons capachy, provision is 

 usually made for testing beams up to spans of 5 ft. or 6 ft. 

 In the Sydney machine the maximum span is 15 ft. 



On Fig. 81 is shown the form of beam testing shackle 

 as applied to a 100-ton vertical machine designed primarily 

 for tension, and having no provision for compression or 

 cross-breaking. Here the lower frame or beam A is 

 attached, by means of a pin, to the lower tension shackle, 

 and the stirrup, carrying the central knife-edge B, is hung 



FIG. 82. 



from the upper tension shackle. The supports for the ends 

 of the specimen beams are knife edges pointing downwards, 

 as shown. This is the form of shackle made for Professor 

 Unwin, by Messrs. Buckton. 



In all bending shackles provision is made whereby the 

 span can be varied at will. The load is generally a concen- 

 trated one applied in the middle of the beam, which is 

 itself supported at the two ends, but by a slight modifica- 

 tion the load can be applied in a distributed form, or on 

 two or more points. This, however, is rarely done. 



At the present day, testing machines are so numerous 

 that they can nearly always be obtained for beam testing 

 purposes ; but where a machine is not available, the beam 

 may rest on fixed supports, and the load may be applied 

 by hanging on a number of dead weights. This plan is 

 illustrated on Fig. 82. 



