Ongoing Researches

Material at high strain rate and temperature temperature

In recent years, interest in material characterization at high strain-rates while varying the temperature has been continuously increasing. Consequently, the study and modeling of material behavior in such conditions has been promoted. Temperature and strain-rate are variables of fundamental importance in the mechanical response of materials, playing an important role in the deformation process. In many applications such as machining, metal forming, high velocity impact or high energy deposition of metals, materials are deformed at very high rates. This will produce self heating to high temperatures due to adiabatic processes. In this case, the stress-strain response will be a balance between the effects of hardening (due to strain and strain-rate) and thermal softening.

In other cases the ambient temperature could be different from room temperature thereby changing the mechanical response of the material and the influence of strain rate. At high temperature, materials become much more ductile. By contrast, at low temperatures the material strength usually increases and the mechanical behavior changes from ductile to brittle.

In such conditions, it is necessary to define proper material models in order to obtain reliable numerical results andthis in turn implies the need to develop methodologies and facilities for the complete investigation of the mechanical response of materials. Temperature and strain-rate sensitivities are mutually related, and the thermal effects obtained from quasi-static tests cannot always be used to predict material response under dynamic loading conditions. In order to consider the coupled effects of temperature and strain-rate, material models should be used in which the thermal component of stress is also considered. It is necessary also to develop proper testing methodologies, in which the whole temperature and strain-rate field of interest is explored.

Iridium sample tested at high speed (10 m/s) and high temperature (1250°C). Video at 125000 fps