Temperature measurements on ES steel sheets subjected to perforation by hemispherical projectiles

Abstract

a b s t r a c tIn this paper is reported a study on the behaviour of ES mild steel sheets subjected to perforation by hemispherical projectiles. Experiments have been conducted using a pneumatic cannon within the range of impact velocities 5m=s V 0 60m=s. The experimental setup allowed evaluating initial velocity, failure mode and post mortem deflection of the plates. The tests have been recorded using high speed infrared camera. It made possible to obtain temperature contours of the specimen during impact. Thus, special attention is focussed on the thermal softening of the material which is responsible for instabilities and failure. Assuming adiabatic conditions of deformation, the increase of temperature may be related to the plastic deformation. The critical strain leading to target failure is evaluated coupling temperature measurements with numerical simulations and with analytical predictions obtained by means of the Rusinek Klepaczko constitutive relation [Rusinek, A., Klepaczko, J.R. Shear testing of sheet steel at wide range of strain rates and a constitutive relation with strain rate and temperature dependence of the flow stress. Int J Plasticity. 2001; 17, 87 115]. It has been estimated that the process of localization of plastic deformation which leads to target failure involves local values close to 3 p f z1 for the boundary value problem approached. Subsequently, this failure strain level has been applied to simulate the perforation process and the numerical results obtained show satisfactory agreement with the experiments in terms of ballistic limit, temperature increase and failure mode of the target.

Experimental study on the martensitic transformation in AISI 304 steel sheets subjected to tension under wide ranges of strain rate at room temperature

“…The integration time is within the range 1 ms ≤ t int ≤ 20 ms. Such features allow having high definition and elevated frame-rates [19].…”

“…In order to get the maximum emissivity from the sample, the steel specimens were covered with soot the emissivity of which was estimated Á = 0.95 (before loading, the temperature registered by the camera on the soot-coated target-surface must fit the room temperature) [19][20][21]. …”

Influence of projectile shape on dynamic behavior of steel sheet subjected to impact and perforation

“…The material behavior has been modeled using the Johnson-Cook constitutive equation sðe p , _ e p ,TÞ [16,17] which takes into account strain hardening, strain-rate sensitivity, and thermal softening. It is important to emphasize that during perforation, an impact velocity of V 0 ¼120 m/s allows to reach locally in the impacted zone a strain rate around 600 s À 1 and a local heating of 500 K [18,19]. As the duration of the impact is very short, it is necessary to take into account an adiabatic heat transformation inside the elements in the numerical model.…”

On the Taylor–Quinney coefficient in dynamically phase transforming materials. Application to 304 stainless steel

“…In these conditions, the thermodynamic process deviates from the isothermal state and approaches adiabaticity, leading to large and sometimes very rapid variations in the temperature field. The analysis should then use temperaturedependent mechanical properties where thermal softening of the material should be considered since dynamic plastic instabilities, such as adiabatic shear bands or necking, are known to be temperature dependent (Molinari, 1997;BonnetLebouvier et al, 2002;Rodríguez-Martínez et al, 2010c).…”