Influence of the strain rate on the tensile strength in aluminas of different purity

Abstract
It is well known that the properties of the materials may be different as the strain rate increases. Advanced ceramic materials such as aluminas, could present an increase in their strength as the strain rate becomes higher. In this paper the investigation is focused on the influence of the strain rate on the tensile strength of alumina. The influence of this variable on this property is experimentally analysed by means of two different kind of tests carried out from low to high strain rates. The splitting test of brittle materials is a testing technique widely used at low strain rates. It has been recently extended to dynamic conditions using the Hopkinson split pressure bar. In this work this method is used both in static and dynamic conditions with servohydraulic machines and a Hopkinson bar. The tensile strength of alumina has been measured at three different strain rates. The spalling test of long bars is an additional technique that provides the dynamic tensile strength of brittle materials in uniaxial conditions. The test procedure and the experimental details are also presented and discussed in a separate paper. This technique has also been used to measure dynamic tensile strength of alumina at higher strain rates. The influence of the strain rate on the tensile strength is presented and a comparison between the two kind of tests is also discussed. To identify the physical mechanisms causing the failure, a microscope analysis of fracture surfaces using SEM has also been performed. The study has been applied to the different specimens tested at low and high strain rates with the two different kind of tests. The results of the fractographic analysis are presented and discussed.