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Polyurea (PU) elastomers have become increasingly popular in recent years due to their exceptional blast mitigation, ballistic protection, and wear resistance properties. However, their applications as protective materials are often limited as a result of their high flammability. In this study, aromatic dianhydrides (ArDAs) were employed to capture the thermal decomposing products of PU during combustion and facilitate the generation of highly heat-resistant aromatic polyimides (i.e., end group capturing effect), thus enhancing the material's char-forming ability and improving its flame retardancy. The ArDAs were found to significantly reduce the peak heat release rate (PHRR), total heat release (THR), total smoke release (TSR), and total CO release (TCO) of PU, and meanwhile increased the amount of char residue. At 20 wt% content of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), PHRR, THR, TSR and TCO of PU were reduced by 70.6%, 32.5%, 44.7% and 58.8%, respectively, the char residue was increased by 405%, and the mechanical properties of PU were well maintained (88.5% tensile strength and 91.0% elongation at break of pure PU). These findings demonstrate that ArDAs could serve as a new kind of halogen/phosphorus-free flame retardant for PU elastomers. [Display omitted] • Novel halogen/phosphorus-free flame retardants were designed for PU elastomers. • The flame retardant mechanism is end group capturing by aromatic dianhydrides (ArDAs). • PHRR, THR, TSR and TCO were simultaneously reduced, and char residue was improved. • Both excellent flame retardant property and high mechanical property were achieved. [ABSTRACT FROM AUTHOR]

The ballistic performance of Glass Fiber Reinforced Polymer (GFRP) composite [0°/90°] s target has been studied against 19 mm diameter conical nosed steel projectiles. The effects of target thicknesses, geometry and boundary conditions have been studied on contact force, residual velocity and induced damage. The ballistic tests have also been reproduced by carrying out three dimensional finite element simulations on AUTODYN hydro code. The nonlinear material behaviour of GFRP has been modeled employing shock effect for studying the different modes of failure in the target. The energy absorbing capacity and ballistic limit velocity of the target have also been discussed with varying target thickness, aspect ratio and boundary conditions. The numerical results show the significant contribution of aspect ratio and boundary condition on the ballistic perforation characteristic of the target. The propagation of pressure wave that causes the generation of various stresses in laminate due to projectile impact has been discussed and the numerical results thus obtained in terms of residual velocities and damage have been found to have close correlation with the experimental results. [ABSTRACT FROM AUTHOR]

This paper concerns the ballistic resistance of hybrid composite shields. The analysis covers three types of two-layer composites. The first shield layer were plates of tungsten carbide (WC), ceramic balls Al 2 O 3 (aluminum oxide 92) or steel balls (100Cr6 steel) embedded in a polymer matrix. The second layer was a laminate consisting of 10 layers of aramid fabric in a matrix of styrene-butadiene-styrene (SBS) copolymer. The study presents the analysis of damage caused by a ballistic impact, further compared to the results of computer simulations conducted using the finite element method (FEM). Samples were overshot along the ballistic track from the Beryl rifle. The 5.56 × 45 mm ammunition with the bullet of SS109 MESCO type was used. [ABSTRACT FROM AUTHOR]

A constitutive model based on the concept of continuum damage mechanics has been proposed to study the progressive damage behavior of composite laminates under ballistic impact. The proposed model is investigated in five steps: First, the quadratic form of damage initiation criteria are presented to predict the initiation of failure in different modes. Second, an exponential form damage evolution law combined with characteristic length based fracture energy approach has been presented. Stiffness degradation is characterized by a variable determined by the equivalent displacement for each failure mode. Third, an experimentally verified strain rate model that considers the rate dependency of the strength and modulus of the composite laminate is considered. Fourth, cohesive elements are inserted at every inter-layer for modeling the delamination evolution. Fifth, the constitutive model has been combined with an element erosion algorithm for the removal of highly distorted elements. Simulations have been performed using reduced integration hexahedra elements (RIHE) and full integration hexahedra elements (FIHE). Implementation of cohesive elements exhibited better delamination progression. Experimentally verified strain rate model enhanced the efficiency of the model showing good correlation between the present simulations and experimental observations, in terms of damage patterns, residual velocity, kinetic energy and ballistic limit. [ABSTRACT FROM AUTHOR]

An investigation on the ballistic impact behaviour of tungsten blunt projectiles on Kevlar ® 29 plain-woven fabrics with an epoxy matrix has been carried out for the purpose of gaining an insight in the phenomena at the level of the composite components. Numerical models have been developed and have then been compared with experimental results. The numerical models have been developed in LS-DYNA adopting two different approaches: a Macro-homogeneous model, in which each layer is modelled as an orthotropic equivalent, and a Meso-heterogeneous one, based on the definition of all the details of the fabric architecture in the area of impact of the projectile's tip (in this case, yarns and matrix have their own properties). In both models, the projectile is considered a rigid body. An in-depth analysis of the macro parameters, such as the residual velocities, their dependency upon the yaw impact angle and delamination has been performed. Also the stress state inside the layers and the morphological features of the damaged plates has been studied and interesting results regarding the behaviour of different layers of Kevlar ® 29 plain-woven fabrics during impact have been obtained. Performances and the pros/cons of the different numerical approaches have also been discussed. [ABSTRACT FROM AUTHOR]

This study evaluates the ballistic impact resistance of soda-lime silicate glass strengthened by ion exchange for application in lightweight and thin bulletproof materials. The maximum flexural strength values of the strengthened glass with thicknesses of 3, 4, 8, and 10 mm were 0.63, 0.68, 0.73, and 0.77 GPa, respectively, values that were 3.5 times higher than that of the parent glass. By laminating polycarbonate and multilayer defense film with the strengthened glass, we achieved a ballistic limit velocity of 973.8 m/s, which was 16% higher than the standard. Also, the transmittance satisfied the standard for bulletproof windows. [ABSTRACT FROM AUTHOR]

This work investigates balsa core sandwich composites with thin carbon fiber skins subjected to single and multi-site sequential ballistic impacts. For the sandwich composite composed of core and facesheet thicknesses of 0.95 cm and 0.25 mm respectively. The ballistic limit was determined to be 96 m s −1 , indicating that it was capable of withstanding impacts from small projectiles such as, secondary debris from blast, hurricane, tornado and foreign object debris from roads and runways. The visual inspection and non-destructive evaluation (NDE) tests showed that the damage was relatively localized. A neat perforation was observed on the strike side facesheet whereas the back facesheet indicated greater spread of damage. The effect of prior damage in terms of residual and absorbed energies became more pronounced as the number of impacts increased. Damage areas were measured in order to quantify the extent of visible failure and/or perforations, while NDE tap testing was implemented to extract the information regarding interfacial damage. [ABSTRACT FROM AUTHOR]