EXPERIMENTAL STUDY ON DELAYED FRACTURE OF ULTRA HIGH STRENGTH BOLT UNDER ACCELERATED TEST : Part 1 As to bolt's material and shape

Abstract

Accelerated delayed fracture tests were carried out on the subject of the ultra high strength bolts in number of 1480. Experimental parameters were 8 kinds of metal materials and 6 kinds of strength level as well as shape of thread. Each test bolt was inserted into the test cylinder and loaded. The cylinder was coated by epoxy resin to eliminate corrosion, further it has load cell function putting the wire strain gages on both sides. The loaded assemblies were exposed to alternate immersion cycle in sulfuric acid solution accomplished by subjecting the specimens to the solution for period of 10 minutes per hour, followed by drying in air for a period of 50 minutes. We got conclusions as follows, the development of cracks or failures of bolts were caused mainly by tempering temperature, which was able to be related to carbon equivalent value of bolts material. On the other hand, the effect of shape of thread and bolts strength level accordance with the quality of the material and tempering temperature, themselves were of secondary importance.