266 SCIENCE PROGRESS 



supplied by the Cambridge Scientific Instrument Co. is 0-05 inch 

 deep and 0*05 inch wide, is made round the centre of the bar, 

 the corners of the notch being practically square. This bar 

 receives blows from a hammer weighing 4*7 lb., the height of 

 fall of which can be varied. The test-piece is rotated through 

 180 after each blow, about 100 of which are given per minute. 

 The number of blows endured before fracture occurs at the 

 groove is recorded. In the paper by Hatfield to which refer- 

 ence has already been made, results are given which reveal a 

 very close connection between the resistance of steels to the 

 Stanton test and their true elastic limits. Something much 

 more than this is required if the impact test is to justify its 

 existence, with the result that this modification of the test 

 finds but limited application, the single-blow variety being far 

 more commonly employed. The results obtained from these 

 two types of impact tests are often widely discordant, materials 

 which, according to one test, show marked resistance to impact 

 making a poor show when tested by the other. 1 



In all the machines in common use for conducting impact 

 tests a bend test is employed. Other types have been suggested, 

 but have found little or no support. Stanton and Bairstow 

 (Proc. Inst. Mech. Eng., 1908, p. 889) have described and 

 figured an apparatus designed for carrying out impact tensile 

 tests. Four forms of impact bend test are in fairly common 

 use. The two best known of these, the Izod and Charpy types, 

 both employ a falling pendulum to strike the blow. The 

 Fremont machine has a vertically-falling weight, while in the 

 Guillery apparatus a rapidly revolving fly-wheel is used to 

 impart the blow. The essentials of each form are as follows : 



In the Izod test the piece, 10 mm. square with a V notch 

 2 mm. deep at an angle of 45 °, is clamped vertically with the 

 notch on a level with the face of the die and facing the pendulum. 

 This is released by a spring attachment from a given height, 

 and at the lowest point of its swing a knife edge which it carries 

 strikes and breaks the test-piece. The residual energy is 

 measured by a pointer which is moved over a graduated scale as 

 the pendulum rises. The height of fall of the centre of mass of 

 the pendulum is 2-5 feet, the striking velocity 13-6 foot-seconds. 



1 A considerable amount of information concerning the relationship of the 

 Stanton to other tests will be found in the Journ. Iron and Steel Inst., Carnegie, 

 vol. vi, p. 94. 



