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

It is well known that the properties of the materials may be different as t he strain rate increases. Advanced ceramic materials such as aluminas, coul d 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 r ate on the tensile strength of alumina. The influence of this variable on t his property is experimentally analysed by means of two different kind of t ests carried out from low to high strain rates. The splitting test of britt le materials is a testing technique widely used at low strain rates. It has been recently extended to dynamic conditions using the Hopkinson split pre ssure bar. In this work this method is used both in static and dynamic cond itions with servohydraulic machines and a Hopkinson bar. The tensile streng th of alumina has been measured at three different strain rates. The spalli ng test of long bars is an additional technique that provides the dynamic t ensile strength of brittle materials in uniaxial conditions. The test proce dure and the experimental derails are also presented and discussed in a sep arate paper. This technique has also been used to measure dynamic tensile s trength 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 th e failure, a microscope analysis of fracture surfaces using SEM has also be en 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 resu lts of the fractographic analysis are presented and discussed.