Ductility and energy dissipation of partially threaded and fully threaded A4-80 bolts under cyclic tension

The thread forming process in austenitic stainless steel bolts results in significant strength gains in the threaded bolt region at the expense of ductility. Thus, contrary to carbon steel bolts, failure under monotonic tension in partially threaded austenitic stainless steel bolts may occur in the shank despite having a larger cross-sectional area than the threaded part of the bolt. Failure of the shank is accompanied by significantly higher ductility compared to failure in the threads, which may be beneficial in earthquake resisting applications where energy dissipation is of paramount importance. This paper reports an experimental study on fully threaded high strength 8.8 bolts and fully and partially threaded A4-80 bolts under cyclic tension. All bolts are M16 and have the same nominal ultimate tensile stress. In addition to monotonic tension, two variable cyclic amplitudes were applied. The obtained loading and unloading cycles are used to extract the energy dissipation for each loading cycle, whilst the reduction in diameter of the fractured bolt is used to obtain the true plastic strain at fracture. It is observed that there is a significant increase in the observed energy dissipation of partially threaded A4-80 bolts compared to their fully threaded counterparts, the ductility and energy dissipation characteristics of which are closer to those of grade 8.8 bolts. Thus, the possibility to obtain a more ductile failure mode for T-stubs emerges, if partially threaded A4-80 bolts are used, as is numerically demonstrated.