Dynamic compressive testing under confining pressure on a quasi-brittle material

A testing device has been developed to study the dynamic compressive behaviour of a quasi- brittle material under confining pressure. At the opposite of similar studies conducted with SHPB tests, this one is achieved with a crossbow system. This direct impact device is composed of a hurled mass and a measuring output bar. Moreover, a specific confinement system is developed. The specimen is confined laterally by a thin metallic sleeve and axially between two metallic plugs [1, 2]. A metallic part gathers the confining cell and the output bar together, and guides the whole during compression. High-speed camera is used to follow the cell compression, and an image post-treatment is realised. The axial strain is consequently obtained from the displacement between the input and the output plugs. In addition, the confining pressure is calculated using the ring expansion and the material constitutive law. Finally, strain gauges on the output bar are used to determine specimen axial stress. Different projectile masses, specimen diameters and ring thicknesses were tested in order to get specimen strain up to failure associated for different constant confinements. Finally, the device allows obtaining different strain rates with various confining pressures.