Notes on the design of machine elements for use in connection with Unwin's machine design Volume 1

 
9781130131598: Notes on the design of machine elements for use in connection with Unwin's machine design Volume 1
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1901 Excerpt: ... if / is increased, the stress produced becomes less for a given impulsive action; or the resistance to such action is greater for a given value of the stress. If an ordinary bolt is subjected to shock in a direction to produce tension, the stress will be a maximum at the sections through the bottom of the threads; the bolt will elongate, but the elongation will be confined largely to the very short reduced (threaded) sections, hence the stress will be much less in the larger portion of the bolt. In a Sellers bolt of one inch diameter the area, A, of the shank is.78 sq. inches, while the area, A', at the bottom of threads is only.55 sq. inches. Therefore a At c 1, 30000 x. 55 stress on A of 30000 lbs. per sq. 1n. =-JJ--21000 on the full sections. Suppose the elongation per inch of length at a stress of 30000 (taken as the E. L-) is Tjjvt". Each inch of section A' will elongate TTnnr", while each inch of full sectional ( =.78 sq. in.)will have a stress of only 2r00olbs., with a corresponding elongation of f-J X Tljvo" =-0007". Assume the thread to be 1" long, and the remainder of the bolt to be 5" long. It will appear that the mean stress on the threaded portion (1") is about the mean of 30000 and 21000, or say 25500 lbs. per square inch; as the mean section is an average of.55 and.78 square inches. Hence the elongation for this threaded 1 inch, when the stress on A' =30000, is.00085", while the other 5" (of area A) will elongate under this load 5 X.0007 =.0035". The total elongation will then be / =.00085 + 35 =.435 inches. If A=tf, W=l '= 2 n + I.55x30000 x.00435 = 82so x l6 = 344 lbs. 2.10435 Now suppose the 5" shank of this bolt were reduced in section to an area A' =.55'. Then the elongation of this...

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