Calibration of Alloy Steel Bolts

摘要

The report is based on results of tests of a large sample of A354 and A490 bolts studied to determine the performance of the alloy steel structural bolt when subjected to various conditions of installation and load. Variables included bolt diameter, grip length, thread length under nut, and thread lubrication. Conclusions: (1) Coupon tests do not accurately reflect the true strength of a bolt. (2) The elastic behavior of high strength bolts in direct and in torqued tension can be predicted using the simple theory for deformation of axially loaded members. (3) All bolts had lower ultimate loads when tested in torqued tension than in direct tension. (4) A decrease in the length of thread under the nut results in increased ultimate strength and reduced elongation capacity for both direct and torqued tension tests of alloy steel bolts. (5) The use of heavy grease or wax as a thread lubricant had little apparent effect on the torqued tension characteristics. (6) Direct tension tests after preloading the bolt indicate that preloading with a wrench does not reduce the tensile strength. (7) Alloy steel bolts torqued continuously to a given nut rotation does not differ from that of incrementally-tightened bolts. (8) Repeated tightening of alloy steel bolts into the inelastic range resulted in a marked reduction in induced tension with each installation and a marked increase in installation time. (Author)