132 



FORMS OF SPECIMENS. 



specimens, which are generally cast with a head upon each 

 end. These heads rest upon bushes formed with spherical 

 seatings, as shown on Fig. 62. These bushes have to be 

 made in two halves, so that they can be placed in position 

 over the head of the bar. The holding devices which have 

 been described are the chief ones in use for tension speci- 

 mens of the more ordinary materials ; those used for 

 timber, cement, chains, and ropes will be described later 

 when dealing with these materials. On Fig. 63 is shown n 

 section of the Maillard type of grip, which can be used for 

 both cheese-headed specimens, and for those with screwed 

 ends. It is especially useful when the specimens are very 

 short. The holder is suspended from spherical seatings. 



FIG. 63. 



On Fig. 64 is shown the arrangement of gripping 

 wedges for flat bars used on the testing machine at the 

 Midland Locomotive Works. There it will be seen that 

 the wedges are made with rounded backs so as to dispense 

 with the use of conical seating bushes. 



73. Forms of Specimens. The form and dimensions which 

 mav be adopted for a test specimen are important in view 

 of the fact that the shape of a bar has a very definite effect 

 upon the results of the test. The forms which have been 

 most generally adopted are shown on Fig. 65. Of these, A 



