R. Zaera

Analytical modelling of normal and oblique ballistic impact on ceramic/metal lightweight armours

Abstract This paper presents a new analytical model developed to simulate ballistic impact of projectiles on ceramic/metal add-on armours. The model is based on Tate and Alekseevskii’s equation for the projectile penetration into the ceramic tile, whilst the response of the metallic backing is modelled following the ideas of Woodward’s and den Reijer’s models. The result is a fully new analytical model that has been checked with data of residual mass and residual velocity of real fire tests of medium caliber projectiles on ceramic/metal add-on armours. Agreement observed between experimental and analytical results confirmed the validity of the model. Therefore, the model developed can be a useful tool for optimisation of ceramic/metal armour design.

Modelling of the adhesive layer in mixed ceramic/metal armours subjected to impact

Abstract The effect of the adhesive layer, used to bond ceramic tiles to a metallic plate, on the ballistic behaviour of ceramic/metal mixed armours is analysed mathematically and experimentally. Two types of adhesives, polyurethane (soft adhesive) and rubber-modified epoxy resin (rigid adhesive), and different thicknesses, are considered in the study. Numerical simulations were made of low calibre projectiles impacting on alumina tiles backed by an aluminium plate, using a commercial finite difference code. Full-scale tests were carried out to check the influence of the adhesive. An engineering model was also developed to provide a preliminary design tool taking account of the influence of the adhesive.

Numerical modeling of the impact behavior of new particulate-loaded composite materials

Ballistic efficiency and cost are the main considerations in the design of lightweight armors. Metallic materials have the drawback of their high density. Mixed armors, of ceramic tiles backed by a metallic plate, are an efficient shield against low and medium caliber projectiles since they combine the light weight and high resistance of a ceramic with the ductility of a metal. The drawback is their high cost. The authors developed a new material composed of ceramic particles and a polymeric matrix. It fills the gap between metallic and ceramic materials and could be interesting for applications in which weight is not the primary concern and cost benefits are welcome. A model of the mechanical behavior of this composite is presented in this paper, implemented in a numerical code and validated by experimental results.

Residual Stresses in Orthogonal Cutting of Metals: The Effect of Thermomechanical Coupling Parameters and of Friction

The generation of residual stresses in orthogonal machining is analysed by using an Arbitrary Lagrangian Eulerian (ALE) finite element approach. It is shown that a substantial level of tensile residual stresses can be obtained in the vicinity of the machined surface without any contribution of thermal effects. This motivates the development of a parametric study to analyse the effects of the thermomechanical coupling parameters on residual stresses. The roles of thermal expansion, of thermal softening and of the Taylor–Quinney coefficient (controlling the heat generated by plastic flow) are considered separately. The influence of friction is also analysed by assuming dry cutting conditions and a Coulomb friction law. The friction coefficient has a complex effect by controlling heat generation (frictional heating) along the tool rake and clearance faces and the propensity for the chip to stick to the tool. Geometrical effects such as the tool rake angle and the tool edge radius are also discussed.

Analytical modelling of metallic circular plates subjected to impulsive loads

This paper presents an analytical approach to the dynamic response of metallic circular plates subjected to impulsive loads. It is based on the plate energy balance equation and assumes that the plate material behaves viscoplastically. The proposed method permits a consideration of the influence of the different terms of the kinetic energy and the plastic work of the plate. A yield criterion is proposed, which involves the coupled effect of the radial and circumferential internal force resultants. By applying the normality rule, the distribution of the bending moments and membrane forces inside the plate are computed. For model validation, its analytical predictions are compared with experimental results.

Cost-effective optoelectronic system to measure the projectile velocity in high-velocity impact testing of aircraft and spacecraft structural elements

We present a microcontrolled optoelectronic system to mea- sure online the average velocity of a projectile impacting on aircraft and spacecraft structures. The projectile velocity can vary in the range from subsonic to supersonic. The implemented optical system is based on three optical barriers that are crossed by the projectiles before impacting on the structural elements. A simple optoelectronic prototype is con- structed and tested. The flight times among the three optical barriers are obtained by the microcontroller system. The measured velocity accuracy in test conditions is better than 1%. A high-brightness liquid crystal dis- play is used to show messages of the system configuration and also the measured projectile velocity. To ensure safety in the experimental impact tests, serial RS-232 communication can be used to monitor this informa- tion using a remote computer. The system is highly robust since it is able to measure projectile velocity even when an optical barrier is missed by failure in either the optical transmitter or the receptor.

Uncovering changes in spider orb-web topology owing to aerodynamic effects.

An orb-weaving spiders likelihood of survival is influenced by its ability to retain prey with minimum damage to its web and at the lowest manufacturing cost. This set of requirements has forced the spider silk to evolve towards extreme strength and ductility to a degree that is rare among materials. Previous studies reveal that the performance of the web upon impact may not be based on the mechanical properties of silk alone, aerodynamic drag could play a role in the dissipation of the preys energy. Here, we present a thorough analysis of the effect of the aerodynamic drag on wind load and prey impact. The hypothesis considered by previous authors for the evaluation of the drag force per unit length of thread has been revisited according to well-established principles of fluid mechanics, highlighting the functional dependence on thread diameter that was formerly ignored. Theoretical analysis and finite-element simulations permitted us to identify air drag as a relevant factor in reducing deterioration of the orb web, and to reveal how the spider can take greater—and not negligible—advantage of drag dissipation. The study shows the beneficial air drag effects of building smaller and less dense webs under wind load, and larger and denser webs under prey impact loads. In essence, it points out why the aerodynamics need to be considered as an additional driving force in the evolution of silk threads and orb webs.

Numerical Analysis of the Hydrodynamic Ram Phenomenon in Aircraft Fuel Tanks

Hydrodynamic Ram (HRAM) is a phenomenon that occurs when a high-energetic object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure increasing the risk of catastrophic failure and an excessive structural damage on adjacent components. It is of particular concern in the design of wing fuel tanks for aircraft because it has been identified as one of the important factors in aircraft vulnerability. In order to study the aforementioned phenomenon, water filled aluminium tubes (to different volume percentages) were subjected to impact of spherical projectiles. This work is focused on the analysis of energies, momenta and pressure contours obtained by means of a previously developed and validated numerical model in order to achieve a better understanding of the fluid/structure interaction problem that takes place during the HRAM phenomenon.

Ballistic Impacts on Polymer Matrix Composites, Composite Armor, Personal Armor

Throughout recorded history, humans have used various types of materials to protect themselves from injury in combat or other dangerous situations. In recent decades, the appearance of high-performance fibers and ceramics has allowed the development of protection against ballistic impact, with some exceptionally lightweight and protective characteristics. This chapter, divided in two parts, provides a review of the design and use of lightweight composite amours. The first part contains preliminary information of interest for the understanding of the second part, in which the characteristics of the various composite armours are described, as well as the methodologies for analysis and simulation.

Tuning the instrument: sonic properties in the spider's web

Spider orb webs are multifunctional, acting to absorb prey impact energy and transmit vibratory information to the spider. This paper explores the links between silk material properties, propagation of vibrations within webs and the ability of the spider to control and balance web function. Combining experimental and modelling approaches, we contrast transverse and longitudinal wave propagation in the web. It emerged that both transverse and longitudinal wave amplitude in the web can be adjusted through changes in web tension and dragline silk stiffness, i.e. properties that can be controlled by the spider. In particular, we propose that dragline silk supercontraction may have evolved as a control mechanism for these multifunctional fibres. The various degrees of active influence on web engineering reveals the extraordinary ability of spiders to shape the physical properties of their self-made materials and architectures to affect biological functionality, balancing trade-offs between structural and sensory functions.