DESIGN FOR MULTI-HIT CAPABILITY

doi:10.1016/S0734-743X(98)00042-6

International Journal of Impact Engineering

Volume 21, Issue 10, November 1998, Pages 905-908

https://doi.org/10.1016/S0734-743X(98)00042-6 Get rights and content

Abstract

We consider the general problem of multiple impacts onto a mosaic in which one or two cells is broken by each impact. Impact onto a broken cell or a cell interface defeats the array. Multiple impacts are defined statistically, and equations are given for calculations n₅₀, defined as the number of impacts for which the probability is 50% that:

1.
one cell is hit more than once, or
2.
an impact occurs on an interface between two cells. The value of n₅₀ is determined by the number of cells, the cell shape, and width of the interface zone.

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Cited by (12)

Enhanced bi-layer mosaic armor: experiments and simulation
2020, Ceramics International
Citation Excerpt :
The impact position affected the ballistic performance. As for the mosaic armor, the weak zones along the borders of individual tiles and the interfacial gaps among the tiles were both the regions of higher vulnerability of mosaic armor systems [12,20–22]. Although the mosaic armor system had been widely applied in the protection field [13,18,23–25], most existing studies characterized its ballistic resistance only by the performance when the ceramic tile located at the center of the armor was impacted by one single shot.
Three different alumina/aluminum bi-layer armors having different striking faces, i.e., monolithic alumina, mosaic alumina, and mosaic alumina enhanced by aluminum honeycomb, were fabricated and tested under the impact of the flat projectile. The ballistic performance of each armor type was also investigated using three-dimensional (3D) finite element (FE) simulations. Upon validating the FE simulation results with experimental measurements, the ballistic limit velocity and failure mechanisms for each type of armor, as well as the influence of ceramic tile size, impact position, border effect, and inter tile gap width were quantified. For the enhanced mosaic armor, the metallic honeycomb lattice performed as a cellular skeleton to confine the ceramic tiles and fragments, leading to enhanced ballistic resistance. Besides, the honeycomb enhanced mosaic armor was also found to have much improved multi-hit ballistic resistance in comparison with monolithic and mosaic alumina. The honeycomb preserved the structural integrity of the mosaic armor so that a high level of residual ballistic resistance remained even after impact. With the extended reliability calculation method, single shot ballistic data were used to estimate the performance of the honeycomb enhanced mosaic armor under multiple projectile impacts.
Bioinspired composite segmented armour: Numerical simulations
2019, Journal of Materials Research and Technology
Citation Excerpt :
If this hypothesis is correct, which surely warrants further investigation, it would mean that ceramics with the best ballistic performance would be the most affected by segmentation. Of course, all the above discussion has been made assuming that impacts occur at the tile centre, while it is highly probable that they occur at (or close to) the interface between plates [33]. It is a priori expected that ballistic protection will be significantly reduced when such interfacial impact occurs, but up to date there were no studies analysing how much the ballistic protection of the segmented plate is reduced when hit at inter-plate boundaries or other locations.
Nature has evolved ingenious armour designs, like the flexible carapaces of armadillo and boxfish consisting of hexagonal segments connected by collagen fibres, that serve as bioinspiration for modern ballistic armours. Here, Finite element modelling (FEM) used to analyze the effect of scale geometry and other impact parameters on the ballistic protection provided by a bioinspired segmented ceramic armour. For this purpose, the impact of cylindrical fragment simulating projectiles (FSPs) onto alumina-epoxy non-overlapping scaled plates was simulated. Scale geometrical parameters (size, thickness and shape) and impact conditions (FSP diameter, speed, location) are varied and the amount of damage produced in the ceramic tiles and the final residual velocity of the FSP after the impact are evaluated. It is found that segmentation drastically reduces the size of the damaged area without significantly reducing the ballistic protection in centred impact, provided the tile size is kept over a critical value. Such critical tile size (∼20 mm, inscribed diameter, for impacts at 650 m/s) is independent of the scale thickness, but decreases with projectile speed, although never below the diameter of the projectile. Off-centred impacts reduce the ballistic protection and increase the damaged area, but this can be minimized with an appropriate tile shape. In this sense and in agreement with the natural hexagonal tiles of the boxfish and armadillo, hexagonal scales are found to be optimal, exhibiting a variation of ballistic protection—measured as reduction of projectile speed—with impact location under 12%. Design guidelines for the fabrication of segmented protection systems are proposed in the light of these numerical results.
Ballistic performance of Al<inf>2</inf>O<inf>3</inf> mosaic armors with gap-filling materials
2017, Ceramics International
Citation Excerpt :
These interfaces have various common geometries (triangular, square, and hexagonal). Statistically, interfaces with hexagonal geometries have a slightly lower impact vulnerability than those with the other geometries [31]. A few published studies have focused on the impact performance of this configuration.
Mosaic armors are more easily adaptable to surfaces, may have a lower cost, and maximize the preservation of their ceramic tiles after an impact. Although, the tile-to-tile interfaces are vulnerable, and the expansion of the tile that receives an impact can induce damage to the adjacent tiles. In this work, the influence of filling materials on the ballistic performance of mosaics was studied. The impedance was varied to change the intensity of transmitted stress waves on adjacent tiles. The filling materials utilized were a neat epoxy resin and a quartz-filled geopolymer and they provided stress wave transmission of 9 and 20%, respectively. Eight millimeter thick alumina tiles (99 wt% Al₂O₃) were obtained from a Brazilian supplier and they were characterized. Despite the damage, there was no penetration, which suggested that the thickness and lateral dimensions of the tile were sufficient to stop the penetration of the projectile. The use of filling materials was beneficial because it prevented the expansion of the tile that received the impact, and thus, the damage to the other tiles could be reduced. Although the geopolymer-filling prevented the expansion of the tile that received the impact, it led to the detachment of the adjacent tiles. Overall, the epoxy-filled mosaics exhibited a significantly superior performance than the filling-free mosaics.
Mechanical impact behavior of polyether-ether-ketone (PEEK)
2015, Composite Structures
This paper deals with the mechanical behavior of polyether–ether–ketone (PEEK) under impact loading. PEEK polymers are the great interested in the field of medical implants due to their biocompatibility, weight reduction, radiology advantage and 3D printing properties. Implant applications can involve impact loading during useful life and medical installation, such as hip systems, bone anchors and cranial prostheses. In this work, the mechanical impact behavior of PEEK is compared with Ti6Al4V titanium alloy commonly used for medical applications. In order to calculate the kinetic energy absorption in the impact process, perforation tests have been conducted on plates of both materials using steel spheres of 1.3 g mass as rigid penetrators. The perforation test covered impact kinetic energies from 21 J to 131 J, the equivalent range observed in a fall, an accidental impact or a bike accident. At all impact energies, the ductile process of PEEK plates was noted and no evidence of brittle failure was observed. Numerical modeling that includes rate dependent material is presented and validated with experimental data.
Metallographic study of non-homogenous armour impacted by armour-piercing incendiary ammunition
2011, Materials and Design
Citation Excerpt :
Namely, ceramics are brittle and shatter upon impact, leaving some portion of basic armour unprotected and prone to penetration by a successive shots. Therefore, multi-hit resistance and careful optimization in this respect has been the subject of several studies [15–18]. On the other hand, wire fence and perforated plates, apart from being made from ductile materials (various types of steel), they are by definition non-homogenous.
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
2010, Materials and Design
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.

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