Static and Dynamic Fracture Toughness Properties of High-Strength Low-Alloy Steel for Naval Application

In the present investigation, static and dynamic fracture toughness properties of HSLA steel (DMR 292A grade) have been evaluated. Standard fracture mechanics CT (compact tension)-type specimens for static fracture toughness, CVN (Charpy V-notch) specimens for dynamic fracture toughness have been extracted from the industrial plate in LT and TL directions. Elastoplastic fracture toughness tests (J_IC) have been performed using single-specimen unloading compliance technique. For the dynamic elastoplastic fracture toughness (J_ID) tests, CVN samples have been fatigue precracked to different crack lengths levels. These samples are further tested under impact loads in an instrumented impact machine. Crack initiation energies have been deduced from dynamic load–deflection curves. Subsequently, J_ID have been evaluated using these energies. No significant difference is observed in the dynamic fracture toughness properties w.r.t. orientations. The dynamic fracture toughness values of materials are consistently lower than static values due to the increased strength of the material under dynamic conditions. This paradoxically leads to lower fracture resistance and, as a result, a decrease in dynamic toughness. Further, SEM-based fractographic analysis has been performed on all the tested samples to identify various fracture micro-mechanisms.