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The ballistic behavior of four different armor ceramic materials with thicknesses varying from 3 mm to 14 mm has been investigated. These are two types of alumina Al2O3 armor grades and two types of SiC armor grades produced by different armor ceramic producers. The ballistic study has been performed using the standard DoP technique with two types of AP projectiles. The microstructure and the mechanical properties of the armor ceramics are investigated with SEM (Scanning Electron Microscopy), X-ray microanalysis, impulse excitation methods and Vickers hardness method. The microstructures are characterized by the number and chemical nature of the phases, the grain size, the type of fracture mode identified from SEM investigation of fragments. The measured mechanical properties are hardness, fracture toughness, flexural strength and the speed of sound (transversal and longitudinal). The ballistic tests are performed with two 7.62 mm projectiles AP8 (WC core) at 930 m/s and APM2 (hard steel core) at 800 m/s. The mass efficiency factor has been determined for each of the armor ceramics. The difference in the ballistic performance of the two alumina types is marginal. The two silicon carbide types are indistinguishable from ballistic point of view. The gained knowledge can be used two-fold: first, to understand better the influence of the microstructure on the ballistic performance of armor ceramics and second, as reference material for the development of a new class of armor ceramics.

Damage containment is one of the key factors for optimising operational readiness of warships after an internal warhead detonation. Ship designers currently have no other option than to rely on state of the art solutions applied in vehicle and personal protection; mainly ballistic composites. These solutions are prone to being traded off during the design process due to cost of the bulk material. Areas to protect are in the order of magnitude of hundreds of square meters. This called for development of a cost efficient, but lightweight protection against fragments. TNO has teamed up with industrial partners to develop understanding of the physical phenomena involved in pre-layers on armour steels [1], in order to optimise protective solutions. Goal of the project was to assess the potential of using polymer coated armour steels in combination with blast bulkheads. The project consisted of three iterations of testing and analysis. The first test programme was aimed at understanding the physics explaining why armour steels perform significantly better against blunt projectiles when covered with an additional thin layer of a relatively soft material. Knowledge from the preliminary tests was applied to protective concepts for blast bulkheads. The pre-layer on the armour steel allows it to dissipate the energy over a wider area of the steel. In the experiments extreme stretching of the armour plate occurred and about twice the amount of energy is dissipated in the armour steel compared to the uncoated situation. The work resulted in protective concepts that fulfilled the mass requirements and are based on affordable materials. The project team considers this technology to be promising for future application in warships. Solutions from this project will be engineered further into a prototype concept. There is spin-off possible to other platforms like vehicles and offshore rigs, where mass and cost are equally important.

At TNO several energy-based engineering models have been created for various failure mechanism occurring in ballistic testing of materials, like ductile hole growth, denting, plugging, etc. Such models are also under development for ceramic and fiberbased materials (fabrics). As the models are energy-based they can be directly compared to experimental results of ballistic tests as the mass and velocities of projectiles are regularly measured. This allows the models to be validated, as has been done for the ductile hole growth model. Using AP-rounds on ductile target materials like many metals, clay and polymers, ductile hole growth (DHG) normally is the major failure mechanism during projectile penetration. When the core of the projectile remains rigid (which is often the case in ductile materials) the loss in kinetic energy of the core is easily measured from its initial and residual velocity. In the DHG-engineering model this energy loss is also calculated but requires that the flow stress at high strain rates is known. Using the experimental results in combination with this engineering model the dynamic flow stress of the target has been quantified. This procedure has been done for several material (metals, clay types and polymers) and allows the determination of dynamic material properties that are otherwise not easily measured. This method requires a rigid penetration of a projectile through a (thick) plate of the material to be characterized. Hence, no special sample shape or dimension is required. The dynamic flow stresses that are obtained have been compared to high strain rate (order 1000/s) strength values of the same materials determined by other techniques. As the values are very close to each other, this provides confidence in the approach to use ballistic test results of targets failed by DHG in combination with the engineering model for the characterization of materials at high strain rates.