Assessing the mechanical properties of materials at intermediate strain rates (1-200/s) is one of the major concerns in impact engineering. Servo-hydraulic machines are usually used at this range of strain rates. However, detrimental oscillations appear on the measured load for strain rates above 10/s. In this paper, we present a modified servo-hydraulic machine. The load is measured by a Hopkinson bar-like technique. Besides, the BCGO wave separation method is used to overcome the limited test duration problem. Moreover, the strain in the sample is measured using Digital Speckle Photographs (DSP) which are captured via high-speed video camera. This modified machine is an equivalent and alternative solution to the slow bar technique. It is applied to aluminium 2017 T4 alloy at strain-rates of approximately 100/s. Compared to the piezoelectric force sensor, the Hopkinson bar-like method gives less-oscillating signals. The sample attaching device is also taken into account. It is considered as a rigid mass. This simple assumption is valid up to strain-rates

International audienceStress and strain homogeneity, in tested samples, is a crucial assumption during a dynamic test. Whenever this assumption is true, the conventional recovery of the mean strain and stress is valid. However, when the stress and strain fields in the sample are not homogeneous, more sophisticated treatment must be considered. Inverse problem techniques are then proposed. Nevertheless, they may yield a non-physical result. In this paper, a non-parametric solution to the problem of non-homogeneity in dynamic tests is presented. The stress field is deduced from the displacement field measured via a Digital Speckle Photography (DSP) technique and a force boundary condition

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.