SHEET NON-FERROUS METALS 805 



Note. — In some cases, it may be found that the thickness of the material near 

 the fillets is so much less than the thickness in the plane of minimum width that the 

 minimum area of cross-section occurs near the fillet. In measuring specimens, the 

 operator should be on the lookout for this condition and, in case it is found, the 

 width of the specimen at the point of minimum width should be further reduced by 

 grinding with a stone until the minimum cross-section is brought to the middle of 

 the specimen. 



(f) Cross-Section of Test Specimen Over \ in. in Width. — -For specimens over \ in. 

 wide as described in Section 3 {b), the measurements shall be made as on the standard 

 specimen, as described in Paragraph {b) above. 



Method of Testing 

 8. Testing Machine. — ■ 



(a) Design. — Testing machines shall be of a design in which the applied load is 

 balanced by increasing the lever arm of a movable weight or by some other means 

 employing weights without the use of springs. 



(b) Method of Mounting. — -The testing machine shall be installed on a solid 

 foundation of such a nature that the machine is maintained in a level position. 



(c) Range. — -It is desirable that the testing machine should be capable of applying 

 and measuring a load about 50 per cent greater than the normal anticipated breaking 

 strength of the test specimen. 



(d) Sensitivity. — ^AU bearings and knife edges of the testing machine shall be so 

 proportioned and adjusted that the position of the beam, when balanced at the 

 normal breaking load of the specimen, shall be perceptibly changed by a change 

 of load of 0.1 per cent. 



(e) Accuracy. — The machine shall be calibrated with dead weights so that a load 

 equal to the breaking load of the material tested shall be indicated with an error 

 of less than ±0.1 per cent. 



(/) Method of Applying Load. — The mechanism for applying load to the test 

 specimen shall be such as to advance the pulling head of the machine at a uniform 

 rate, such as may be obtained by a motor drive operating from a well regulated 

 source of power. The machine shall be capable of being operated at different 

 uniform rates of speed, including the rate of approximately 0.05 in. per minute 

 of the moving head. Unless otherwise specified in individual specifications, the 

 maximum speed of the moving head in making a test shall be 0.025 in. per inch 

 free length of specimen per minute. 



(g) Jaws. — -The jaws or grips of the testing machine shall be designed so as to 

 produce and maintain axial alignment of the specimen without producing tearing 

 stresses. The edges of the jaws shall be rounded so as not to noticeably deform 

 the specimen near the borders of the region where the specimen comes in contact 

 with the jaws. 



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