Metallographic study of non-homogenous armour impacted by armour-piercing incendiary ammunition

In this paper, the influence of impact and incendiary effect on the microstructure changes and crack development in non-homogenous add-on armour is studied. The main objective was to determine the parameters that may cause the yielding of the material, leading to a possible decrease in multi-hit resistance. For that purpose, patented wire fence and perforated plates made from two types of high strength steel, Hardox 450 and 50CrV4 tempered at 170 °C were tested. Various techniques were applied: high speed video camera was used, visual macroanalysis, light microscopy, scanning electron microscopy and energy dispersive X-ray analysis. It was found that incendiary effect, being of a brief nature, does not have any influence on microstructure of the add-on armour. However, impact greatly influences crack development and propagation, which occurs in 50CrV4 steel, the material with lower ductility, diminishing its multi-hit resistance. In accordance with obtained results, non-homogenous add-on armour behaviour models were devised, describing the influence of material ductility and geometry on fracture mode, stresses and deformability.     

Geometry,mechanical properties and mounting of perforated plates for ballistic application

In this paper, the ballistic resistance of perforated plates made of different types of steel, mounting and geometry was investigated. Different types of steel in various heat treatment conditions were tested. Target mounting was also varied: rigid, oblique and hanging. Furthermore, four different perforated plate geometries were tested: two plate thicknesses and two hole diameters. Their behaviour was tested using impact from firing 12.7 mm M-8 API ammunition at eleven perforated plate samples. These samples were placed by means of a steel frame over a 13 mm RHA plate, at two distances. Damaged area on targets was correlated to ballistic resistance of the whole armour to find the optimal perforated plate. It was found that perforated plates, in optimized case offer a frequent fracture of the penetrating core in up to five parts. This debris is unable to penetrate the basic plate, offering mass effectiveness of the whole armour model of 1.76 and the mass effectiveness of the perforated plate of 5.91.     

Microstructure and cavitation behaviour of alloyed austempered ductile irons

In this paper, the study of cavitation behaviour of austempered ductile iron (ADI) alloyed with copper, as well as copper and nickel with a fully ausferritic microstructure, is presented. The ADI materials used were austenitized at 900 °C and austempered at 350 °C having an ausferrite microstructure with 16 and 19% of austenite, respectively. The experimental investigations were conducted using the ultrasonically induced cavitation test method. The results show that the cavitation damage was initiated at graphite nodules, as well as in the interface between a graphite nodule and an ausferrite matrix. The cavitation rate revealed that the ADI material alloyed with Cu + Ni austempered at 350 °C/3 h has a higher cavitation resistance in water than ADI alloyed with Cu. An increased cavitation resistance of the ADI material alloyed with Cu and Ni is due to the matrix hardening by stress assisted phase transformation of austenite into the martensite (SATRAM) phenomenon.     

Wire fence as applique armour

In this paper, the behaviour of wire fence was investigated for potential as applique armour. The wire fence used was made from commercial high-strength patented wire and the supporting frames were made of mild steel L-profiles. Both patented wire and L-profiles are of-the-shelf materials. The fence was tested by firing 12.7 mm M8 API ammunition at four applique armour models: two of these models use a parallel wire arrangement, with one mounted at a 90° angle from the incoming projectile and the other at 70°; and two of these models use a zig-zag wire arrangement, one mounted at a firm 90° angle and the other is left in a hanging arrangement. Fence damage was correlated with RHA basic plate damage, on both the face and back. Wire fence has considerable potential as an improvised applique armour, except if the projectile impacts near the center of the wire or near the center between two wires. The latter case was successfully overcome by placing the armour model at an angle and by using a zig-zag wire arrangement. The lowest basic RHA plate damage level was found using the hanging armour model. However, from the point of view of ease of attachment, the most convenient was found to be the armour model with the zig-zag wire arrangement fixed at 90° angle from the incoming projectile. SEM fracto graphy revealed that the fracture surface was predominantly ductile, with dimples filled with debris from the incendiary effect of the projectile.     

Microdeformation of soft particles in metal matrix composites

In this study, microdeformation of soft particles in metal matrix composites was investigated. For that purpose, two different types of ductile iron having different metal matrix microstructures were tensile stressed and compressed. It was found that graphite nodules do not change their shape during tensile stressing, only decohesion occurs on the graphite and metal matrix interface. However, compression testing at room temperature resulted in a significant change in graphite shape. A relationship between average aspect ratio of graphite after various degrees of compression and bulk material deformation was devised. Furthermore, graphite nodule and metal matrix microdeformation was compared to bulk material deformation. This implies that deformation process is not homogenous. It strongly depends on metal matrix microstructure and can be represented with deformation ratio (K). Deformed or deformed and cracked graphite nodules were found on the fractured surface of compressed specimens, indicating that the graphite does not turn into powder during compression at room temperature, as other previous researches found.