48 



TESTING MACHINES. 



and constant in their application, whether the specimen is 

 deformed or not. 



(6) The magnitude of the applied load must be capable 

 of measurement to a reasonable degree of accuracy. 



FIG. 17. 



(c) The magnitude or extent of the deformations pro- 

 duced by the loads must also be capable of being measured. 



Of these three conditions the two first are necessary in 

 all cases, and the appliances for carrying them out form 

 the main features of all testing machines. The last con- 

 dition is not indispensable, and is generally fulfilled by 

 some piece of apparatus apart from the testing machine 

 itself. It is with the two first that we are at present con- 

 cerned, and the manner of carrying them into effect, which 

 is employed in all the chief types of testing machines, will 

 next be described. 



20. Simple Forms. The simplest kind of test that can 

 be applied to almost any material is that under a tensile 

 load, and as tensile tests form the greater proportion of 

 testing work, most testing machines are arranged, in the 

 first instance, for this kind of test, and usually slight 

 modifications in the arrangement of the machine are added 

 to enable tests of other kinds to be made. 



We have seen that it is necessary in a tension test to be 

 able to apply such loads as may be desired, and at the 

 same time to be in a position to accurately measure these 

 loads as they are applied. It will be fairly obvious that 

 the simplest way of thus applying loads to a specimen, 

 and at the same time measuring them, is by fixing the 

 specimen to be tested in a vertical position, with the upper 



