During the impact by an armour-piercing projectile against a bilayer ceramic/backing protective system, dynamic tensile stresses are generated leading to the inception and the propagation of numerous and oriented cracks. This intense tensile damage, called fragmentation, affects the performances of the shielding and its capacity to resist to multiple impact. The residual confined strength of a fragmented ceramic is relatively weak compared to its undamaged compressive strength, however not negligible. Characterising the dynamic behaviour of a pre-fragmented ceramic is then of interest to design improved armour solutions. In this work, an impact configuration called tandem test, which consists in a normal impact followed by a penetrating impact, is applied to two alumina ceramics with different microstructures: a conventional 98% pure alumina compared to a bioinspired brick-and-mortar ceramic called "MAINa" (a nacre-like alumina) which exhibits higher flexural strength and fracture-toughness. Following the normal impact tests, a fragments size analysis is conducted by means of X-ray micro-computed tomography distribution, which reveals that the mean fragments size is significantly larger in the nacre-like alumina, thus demonstrating a correlation between the fragments size and the penetrating resistance of fragmented alumina ceramic. Finally, the strength of both alumina ceramics in their fragmented state is identified based on an inverse approach in which the penetrating tests are numerically simulated considering the Drucker-Prager model.

In this work the dynamic fracturing of an ultra-high strength cementitious material is probed with in-situ ultra-high speed X-ray phase-contrast diagnostics to investigate the phenomenology of dynamic fracture. Gas gun experiments were conducted on two characteristic samples with two different impact speeds, namely 80 and 190 m/s using the edge-on impact test configuration. The samples were placed within the intense X-ray beam providing an observation field of 12.8 mm in width and 8 mm in height. Thanks to equispaced 16 bunches of short X-ray pulses, the samples were imaged through an indirect detector arrangement using the Shimadzu HPV-X2 camera lens-coupled to a fast scintillator capturing through-thickness measurements with an interframe time of 1.06 µs. The comparison of fragmentation patterns between two samples revealed an important insight into velocity dependant spall formation as well as the effects of crack closure and bridging.

Ceramic materials are widely used all around the world in protective solutions as front plate of bilayered configurations, a metallic or composite material being used as backing to absorb the kinetic energy of fragments. However, during the impact, an intense fragmentation process composed of numerous oriented cracks develops in the ceramic plate due to high-loading rates tensile stresses. The edge-on impact (EOI) configurations constitute one of the best testing techniques to analysis the dynamic fragmentation process in brittle materials. A metallic cylindrical projectile hits the edge of a prismatic target of thickness smaller than the projectile diameter with an impact velocity ranging from 100 to 300 m/s. The damage process is usually observed on the lateral surface with a digital ultra-high speed camera (“open configuration”). However, the fragmentation cannot be observed in the bulk of the target except if a post-mortem analysis is conducted (“sarcophagus configuration”). In the present work, in addition to this classical testing methods, EOI experiments have been conducted in the European Synchrotron Radiation Facility (beamline ID19) with X-ray radioscopy technique using the 16-bunch operation mode. Targets, 60 × 30 × 6 mm3, made of silicon carbide were placed in an intense X-ray beam (mean photon energy about 30 keV) providing an observation field of 12.8 mm in width and 8 mm in height, and impacted with projectile velocities ranging from 150 to 200 m/s. A Shimadzu HPV-X2 camera lens-coupled to a fast scintillator (LYSO:Ce) was used to visualize the fragmentation process through the thickness with an interframe time set to 1065 ns. The fragmentation pattern was compared to data obtained in classical “open configuration” with surface visualization and to post-mortem analysis obtained in “sarcophagus configuration”.

For several decades, ceramic materials have been widely used in bilayered protective configurations. However, the impact loading produces dynamic tensile stresses that spread out the ceramic tile leading to an intense fragmentation made of short oriented cracks. To improve the design of such configurations the fragmentation process needs to be better understood. The edge-on impact (EOI) testing method constitutes one of the most used experimental techniques to investigate the fragmentation process in brittle materials at high-strain-rates. A cylindrical projectile hits the edge of a target leading to a multiple fragmentation. In classical EOI experiments, an ultra-high-speed camera is used to visualize the fragmentation process on the lateral surface. However, the fragmentation pattern in the bulk of the target can only be analysed post-mortem. In the present work, in addition to this classical optical inspection method, EOI experiments have been conducted in the European Synchrotron Radiation Facility with the means of ultra-high-speed imaging, i.e., X-ray radioscopy using the 16-bunch operation mode. The target, 60 x 30 x 6 mm(3), was placed in the intense X-ray beam (beam energy about 30 keV) providing an observation field of 12.8 mm in width and 8 mm in height, and impacted with a projectile velocity of 144 m/s. A Shimadzu HPV-X2 camera lens-coupled to a fast scintillator was used to visualise the fragmentation process through the thickness with an interframe time set to 1065 ns. This fragmentation pattern is compared to pictures of the lateral surface obtained with an ultra-high-speed camera or post-mortem analysis.

Armour-Piercing (AP) projectiles constitute a major threat to be considered for the design of bi-layer-armour configurations constructed using a ceramic front plate backed with a composite/metal layer. When they are not made of tungsten-carbide the cores of these projectiles are made of hard steel, and are the main part that defines the penetration performance of the projectile. However, due to specific testing difficulties, the dynamic behaviour of these high-strength steel AP projectiles has not been investigated in sufficient detail. In this study, a detailed experimental investigation of the dynamic behaviour of the steel used for the steel core of 7.62 mm BZ-type AP projectiles was analysed through the use of Shear-Compression Specimens (SCS). In this study, results from both quasi-static and dynamic experiments were examined. The data processing method employed was set and validated based on numerical simulations. Both quasi-static and dynamic SCS experiments were done with the steel tested which clearly indicated the steel cores exhibit a very high elastic limit, little strain-hardening, and very little strain-rate sensitivity despite the wide range of strain-rates considered. This experimental characterisation paves the way to the numerical modelling for the analysis of ballistic impact of 7.62 mm AP projectile against lightweight armour configurations.

Ceramic materials are numerically studied to understand their fracturing behaviour upon dynamic conditions and impact loadings. During a ballistic impact of a projectile against a ceramic armour system, an intense fragmentation composed of numerous oriented cracks, develops in the target. It is the reason why the conditions of crack initiation, propagation and arrest in these materials need to be investigated. In the present work, a dynamic testing configuration has been developed in order to characterise the dynamic fracture toughness ( K 1 , d ), considering a single crack that propagates from the specimen notch tip. The “Rockspall” testing technique, which employs a two-notch specimen loaded in a spalling experiment, was used. Thanks to the reflection of a compression wave into a tensile load from the sample free-end, a single dynamic crack is triggered. The sample geometry is optimised by means of a series of FE numerical simulations involving an anisotropic damage model.