The Effect of Strain Rate on the Impact Behaviour of Fe–2 mass% Ni Sintered Alloy

Abstract

The impact behaviour of Fe–2 mass% Ni sintered alloy as a function of strain rate has been studied using a material testing system at strain rate of 10⁻³, 10⁻² and 10⁻¹ s⁻¹ and a split Hopkinson bar at strain rates ranging from 2.5×10³ s⁻¹ to 6.8×10³ s⁻¹. The mechanical properties of the sintered alloy, including its impact strength, rate of work hardening and strain rate sensitivity are found to be significantly influenced by the strain rate at which deformation takes place. A constitutive law based on the Khan–Huang–Liang model is applied to predict the rate-dependent plastic flow behaviour of the sintered alloy. The model predictions are found to be in good agreement with the observed experimental response. Even under heavy deformation conditions, none of the specimens were observed to fracture. Microstructural observations reveal that the grain size of the deformed specimen decreases as the strain rate increases. The reduction of the grain size can lead to an increase of the flow stress due to the enhancement of the grain boundary area.