A rod-inserted design approach to delay failure and improve Mode II fracture toughness in metallic cylinders

Currently, the rod-inserted design strategy focuses on enhancing Mode II (in-plane shear) fracture toughness and retarding crack propagation in metallic cylinders, as shear-dominated failure plays a critical role in a wide range of engineering applications. Hence this paper presents a rod-inserted tube design as a practical strategy to improve Mode II fracture toughness and delay catastrophic failure in cylindrical metallic components. A new analytical expression for the Mode II stress intensity factor (K_II) was derived using strain energy release principles and validated against benchmark solutions. Experimental shear tests were conducted on Al 6061-T6 alloy, M.S. Bright steel, and EN31 steel, comparing plain solid rods with layered rod tube specimens. The results revealed consistent, statistically significant gains in fracture resistance (low scatter with CV ≤ 3.6 %). Al 6061-T6 showed the largest improvements, with apparent Mode II fracture toughness (K_II) increasing by 17–28 % and time to failure by 37–53 %. The layered rod tube interface introduced a novel geometry driven toughening mechanism, retarding crack propagation and producing a two-stage failsafe response. These findings establish the rod inserted configuration as a viable, scalable design strategy for damage tolerant cylindrical components.