Mechanical behaviour and failure mechanism of 7075 Aluminium alloy threaded connections under wide loading rate

Threaded connections are vital components in engineering structures due to the advantages of easy assembly, reusability and reliable performance. However, they are prone to impact loading from engineering service, and potential damage occurs via localized stress concentration, leading to premature failure. This study investigates dynamic impact response and failure mechanisms of 7075 aluminum alloy threaded connections through combined experiments and numerical simulations. Wide loading rate experiments were conducted on threaded connections of M10×1.0 and 1.5 with different lengths, by using modified Hopkinson tensile bar technique and universal mechanical machine. It is indicated that the load capacity raises significantly with increasing connection length, and failure mode shifts from thread shear-out to shank fracture. Fine-pitch thread exhibits rather higher failure load than the coarse one due to its larger minor-diameter. Under dynamic conditions, brittle shear pull-out failure occurs in fine-pitch thread connections, while the coarse-pitch threads facilitate the connections to undergo distinct plastic deformation. The failure behaviors are revealed via finite element simulation with aid of Johnson-Cook constitutive model, that pronounced stress concentrations happen near thread shank root, which initiates the damage and failure evolves progressively. The results provide practical design insights for optimizing threaded connections to enhance structural safety under dynamic loading.