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 À3 , 10 À2 and 10 À1 s À1 and a split Hopkinson bar at strain rates ranging from 2:5 Â 10 3 s À1 to 6:8 Â 10 3 s À1 . 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 ratedependent 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.
In this paper, the experimental system using the NHAT (New Hybrid Aerodynamic vibration Technique) is introduced. This technique can verify the interactions between the oscillating 2D square prism and the surrounding flow. Moreover the accuracy verifications of dynamic behaviors for the mechanism of NHAT without the non-linear effect due to the aerodynamic force is conducted, and then, the aerodynamic characteristics of the stasis and the oscillating cylinders (i.e. characteristics of pressure distributions and aerodynamic forces, the damping and mass ratio dependent of the response displacement', 'the lock-in', and `the hysteresis of the response displacement') are verified using NHAT. The experimental results are compared with the results of the previous wind tunnel tests to argue the validities of the results using NHAT. On NHAT, the dynamic characteristics of the square prism such as the mass, the damping, and the stiffness can be set easily and precisely. Especially, in case of the non-linear restoring force is set on the equation of motion of the square prism, It is possible to simulate the aerodynamic behaviors of the elastoplastic structure, too. The interactions between the elastic structure and the surrounding 2D flow are simulated here.
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