256 WIRE ROPE TESTS. 



assumed that there was a hemp core or centre, around 

 which the strands were laid. Instead of testing all the 

 wires of one strand, and assuming all the strands to be of 

 the same strength, the less reliable plan was here adopted 

 of testing six wires from any part of the rope, and taking 

 the average of these as the nominal strength of one wire. 



The average diameter of the wires is given as 0'04 in., 

 which is equivalent to a sectional area of O'OOIS in. The 

 average breaking load of one wire is 200 lb., so that the 

 breaking stress of the wire per square inch of sectional 

 area is 



200 

 f t ~ 0-0013x2240 



= 68*68 tons per square inch. 



There are 72 wires whose average strength is 200 lb. 

 So that the total nominal strength of the whole rope will 



be 



72 x 200 



2240 

 = 6*43 tons. 



When placed in the testing machine, the rope itself 

 fractured at a load of 5 '85 tons. If this load be called W A , 

 then the " efficiency," or the percentage which the strength 

 of the whole rope is of the sum of the strengths of the 

 individual wires, is 



W 



' - w; 100 

 -Us 100 



= 91 per cent. 



The reasons why the strength of the whole rope is less 

 than the sum of the strengths of its component parts are 

 several. In the first place, in its original state the wires 

 composing the rope are not all in the same state of tight- 

 ness, and therefore, when the load comes upon the rope, 

 all do not have to withstand the same tension. This fault 

 may be aggravated by the way in which the rope is held, 

 and it is extremely important that the wires may be so held, 

 that there is as much uniformity in the tension on the 

 different wires as possible. This is probably why embed- 

 ding the individual wires in a matrix of metal is better 

 than relying on wedges alone. Possibly slight damage 



