THE TESTING OF CHAINS. 271 



(c) The chain as a whole is also tested up to some 

 specified proof load, the extension under this 

 proof load being measured. 



The two first-mentioned of these tests are usually 

 carried out in an ordinary testing machine, while the 

 tests under proof loads are made in tension machines 

 specially designed to accommodate pieces of chain of 

 considerable length. 



There is no difficulty about holding a chain specimen 

 in the machine. In the absence of special holders a 

 piece of bar iron or steel a little larger than the material 

 of the chain may be bent hot into a U shape, threaded 

 through the end link of the sample, and gripped by the 

 ordinary wedge dies which are used for flat specimens. 

 This is a simple and perfectly effective method of holding 

 the ends of the short length of chain. The arrangement 



FIG. 135. Holder for Chains. 



is shown on Fig. 135. Extensions are measured between 

 two centre-punch marks placed respectively on the middle 

 of each of the outside links of the length to be measured, 

 the actual measurements being made with a pair of 

 trammels or beam compasses. 



When a short length of chain is tested to destruction 

 the links become elongated after the elastic limit of the 

 metal has been passed, and failure generally takes place by 

 the breaking of one of the links at an end, where the 

 curvature is greatest, and most likely at the point where 

 the weld is. Before actual fracture takes place many of 

 the links begin to show signs of weakness, this being 

 most noticeable in tbe partial opening of the welds. The 

 elongation is often measured at the proof load, and also at 

 the maximum load, and the elongation due to the increase 

 of load between these points quoted in the report. 



The testing of chains under the specified proof loads is 

 generally carried out on long pieces of the actual chain, 

 the loads applied not being such as to permanently 

 damage it, but at the same time being sufficient to bring to 

 light any defects which may exist either in the material of 

 the chain or in the weld joints of the links. For instance, 



