Effect of Threaded Fastener Condition on Low Cycle Fatigue Failures in Metric Bolts Under Transverse Loading

This paper presents an experimental investigation of the effect of threaded fastener condition on the low cycle fatigue behavior of a tightened metric fastener under a fully reversed, cyclic transverse load. The test set-up subjects tightened, threaded fasteners to the combined effect of axial, torsional, bending, and transverse shear loading. The two conditions of the fasteners were “as received” and “ultrasonically cleaned and oiled”. Fatigue performance at three different bolt tension levels was investigated. Based on preliminary testing arbitrarily selected amplitude of 0.05 inches was used for the cyclic transverse displacement, at a frequency of 10 Hz. A Scanning Electron Microscope (SEM) was used to assess the failure mode on a bolt fracture surface. The bolt stresses are sensitive to both thread and under head friction characteristics. As a result, the low cycle fatigue life of the tested bolts was slightly influenced by the surface condition, “as received” versus “cleaned and oiled” and initial bolt tension.