EXPERIMENTAL RESEARCH ON CONSTANT-AMPLITUDE FATIGUE CHARACTERISTICS OF 8.8 GRADE M24 HIGH-STRENGTH BOLTS

In order to study the constant-amplitude fatigue performance of 8.8 grade high-strength bolts under axial tension-tension condition, 3 static tensile tests and 15 M24 bolts with 35K material were carried out. S-N curves were fitted and the fatigue fracture surfaces of representative specimens were analyzed macroscopically and microscopically. In addition, all the test results were compared with those calculated based on the relevant formula of Standard for Classification of Steel Structures (GB 50017—2017). The conclusions are as follows: The fatigue test data were generally discrete, but all within 95% confidence interval; The S-N curves could basically reflect the fatigue life of specimens under different stress amplitudes; At the root of the screw thread, the stress concentration was especially serious, punctiform fatigue source was easy to expand to form linear fatigue source, the notch effect of the specimen was evident; Comparing the test results with the recommended values of allowable fatigue strength stipulated in the national standards, the corresponding fatigue strength of 2×10⁶ times was 1.61 times of the recommended value.