Ramzi Othman

Critical impact velocity for ice fragmentation

The fragmentation process is a main concern in many engineering applications such as preventing flameouts of aircraft engines. The authors of this article are interested in measuring the critical impact velocity for ice fragmentation. Precisely, a dropweight technique was applied to study the ice ball impacts on glass plates. The influence of ice ball temperature, diameter and impact angle is also investigated. The after-impact ice ball state was found to be classified into two cases: an altered state and a non-altered state. The critical impact velocity is defined as the minimum impact velocity for which the ice ball is altered after impact or the maximum impact velocity for which the ice ball is not altered after impact. The experimental results are analysed by a model, assuming that the alteration regime is observed as soon as the ice ball normal kinetic energy is higher than a critical value of its deformation energy. This model depends on one parameter which is determined in this study. This last result is the major achievement of this article as there is almost no measurement of this parameter in the literature.

Compression and shear behavior of epoxy SA 80 bulk adhesive over wide ranges of strain rate

Abstract This paper deals with the experimental characterization of a bulk adhesive fracture in the quasi-static range using a conventional machine and at high strain rates using the Hopkinson bar technique. For very high strain rates, the direct impact Hopkinson bar technique is used. The studied adhesive is a toughened epoxy which can be used for impact resistance in bonded assemblies. It is worth studying the adhesive sensitivity to strain rate as a bulk material in order to distinguish between its response within a structure when used to bond substrates and its response as pure material. Experiments were carried out under compression and shear loadings. A special grip was conceived to mount the specimen for shear tests. In both loading types, this adhesive was found to be highly strain-rate-sensitive. The adhesive strength increases with strain rate until reaching a maximum value then it drops for very high strain rates. Although this behavior is uncommon, it has been reported already in three previous works.