Investigation of the high velocity impact behavior of grid cylindrical composite structures

In this paper, the experimental behavior of grid cylindrical composite structures, which are used widely in engineering structures, under ballistic impact is investigated. For this purpose, some grid cylindrical composite specimens were manufactured by the filament winding process and perforated by projectile using the ballistic gas gun. Incident impact velocity and exit velocities of projectile were recorded in each test. The results show that the presence of the ribs prevents pervading of damaged area of one cell to its adjacent cells. The structure behaves differently against projectile with velocity near ballistic limit and higher velocities. The results demonstrated that, by getting close to the ribs location, ballistic limit velocity was increased. However, due to reduction in energy absorption mechanisms in grid composite structures which are impacted in higher velocity than ballistic limit, projectile was exited of grid samples at higher velocity than unstiffened composite shells. Also, investigation of delamination in composite shell and ribs, debonding between ribs and shell (or separation of ribs and shell), residual velocity of projectile, damaged area of the grid specimens and the effects of curvature in two different velocities are presented and the results are discussed. POLYM. COMPOS., 38:2603–2608, 2017. © 2015 Society of Plastics Engineers     

Multi-walled carbon nanotube-filled polypropylene nanocomposites: high velocity impact response and mechanical properties

Polymer nanocomposites containing 0.75, 1.0 and 1.5 wt% of multi-walled carbon nanotubes (MWNTs) in a polypropylene (PP) matrix were studied in relation to their low and high velocity impact performances. PP nanocomposites reinforced MWNTs were prepared via melt compounding in an internal mixer followed by injection molding. Transmission electron microscopy analysis confirmed well dispersed 1?wt% MWNT in the polymer nanocomposites. The same analysis showed agglomeration and cluster formation in 1.5?wt% MWNT specimens. Results showed increase in Izod impact strength in nanocomposites containing 1?wt% MWNT, which attained the highest value (with 33.4?% increment). A single stage gas gun was used to carry out high velocity impact test in velocity range of 20?C150?m/s using hard steel hemispherical tip projectile of 11.34?g weight and 8.1?mm diameter. Results showed better ballistic limit velocity (the average of highest impact velocity causing perforation but unable to go through and lowest impact velocities with no residual velocity recording) and energy absorption for specimens, each containing 1?wt% MWNT, showing the highest value (with 100?% increment), compared with neat PP. Considerable increases were observed in tensile and flexural strengths and modulus for the MWNT-containing specimens as compared with neat PP.     

Flame retardant and the degradation mechanism of high impact polystyrene/Fe-montmorillonite nanocomposites

High impact polystyrene/Fe-montmorillonite (HIPS/Fe-MMT) nanocomposites were successfully prepared by melting intercalation. The nanostructures of HIPS/Fe-MMT were testified by X-ray diffraction (XRD) and transmission electron microscope (TEM). Corresponding to pure HIPS, the thermal stability of HIPS/Fe-MMT nanocomposites was notably improved. The peaks of heat release rate (PHRR) and the mass loss rate (MLR) were significantly reduced after the formation of the HIPS/Fe-MMT nanocomposites from cone calorimetry. And nanocomposites PHRR was further lower with the increase of Fe-MMT content in the range of 1 to 5 wt%. The degradation mechanism of HIPS and HIPS/Fe-MMT nanocomposites was conducted by pyrolysis gas chromatography mass spectrometry (Py-GC-MS). And the reason of the enhancement of thermal stability maybe is that structural iron is the operative site for radical trapping in the Fe-MMT and the nanostructure enhances the interaction of the chains of the HIPS.     

Studies on mechanical behavior high impact polystyrene/vinyl clay nanocomposites: Comparison between in situ polymerization and melt mixing

A comparative study on various synthesis methods like melt mixing (MM) and in situ polymerization (ISP) of high impact polystyrene/vinyl clay nanocomposites (HIPS/VNCs) is attempted here. In ISP, nanocomposites were prepared by mixing vinyl clay (VC) and poly butadiene rubber (PBR) in styrene with the initiator, azo bis isobutyronitryle. Melt compounding was conducted in two ways–commercial melt mixed blend where Commercial HIPS was mixed with VC and in situ melt mixed blend, where, nanocomposites were prepared by mixing polystyrene, PBR, and VC. The effect of dispersion of the nanoclay on the morphology and material properties of HIPS/VNCs was compared for all the methods, and it is found that the product obtained by ISP gives better properties when compared with MM. Moreover, the dispersion of the clay in the matrix is greater by in situ method, which is evident from X‐ray diffraction pattern and scanning electron microscopic analysis. Statistical analysis of ISP was carried out by design expert software version 8.0.7.1. Modeling and Optimization of the mechanical properties were done by using central composite design of response surface methodology. POLYM. COMPOS., 38:68–76, 2017. © 2015 Society of Plastics Engineers     

Effects of some liquids on the creep behavior of high impact polystyrene

The effects of seventeen different fluids on polystyrene is investigated. The fluids are divided into three groups by their effect on the unstressed polymer, namely dissolving, softening, and non-softening fluids. The accelerated rates of creep of the polymer when immersed in the dissolving fluids are shown to be due to the reduction in the load-bearing area resulting from dissolution at the surface, The increase in creep strain rates (relative to that in air) when exposed to the softening fluids result from the combined effects of: (i) the accumulated deformation of numerous crazes; (ii) the reduction in stiffness of the surface layer due to the softening effect of the fluid; and (iii) the swelling of the softened layer. In the case of the non-softening fluids, the creep rates “accelerated” after a specific delay time which is a function of the applied stress. For these fluids there exists a critical stress below which crazing does not occur. This critical stress is shown to increase with increasing difference between fluid and polymer solubility parameters.     

Single-source-precursor synthesis,microstructure and high temperature behavior of TiC-TiB2-SiC ceramic nanocomposites

Newly developed TiC-TiB₂-SiC ceramic nanocomposites were successfully synthesized by a novel single-source-precursor approach, with allylhydridopolycarbosilane (AHPCS), bis(cyclopentadienyl) titanium dichloride (Cp₂TiCl₂) and triethylamine borane (TEAB) as starting materials. The obtained single-source-precursor was characterized by Fourier transform infrared spectra (FT-IR), which confirms that hydroboration (C=C/B-H) and dehydrochlorication (Si-H/Cp₂TiCl₂) reactions were involved to introduce B and Ti elements into the AHPCS chains. The structural evolution of single-source-precursors, phase composition and chemical composition of the obtained ceramics were investigated by FT-IR, X-ray diffraction (XRD) and elemental analysis. High temperature behavior of the resultant TiC-TiB₂-SiC ceramic nanocomposites with respect to decomposition as well as crystallization was carefully checked by XRD and mass loss after annealing at high temperatures of 1600 and 1800 °C. Transmission electron microscopy (TEM) was used to further observe the microstructure of TiC-TiB₂-SiC nanocomposites, which again confirms the crystalline phases consist of nanoscaled β-SiC, TiC and TiB₂.     

Investigation of the influence of processing conditions on the thermal,rheological and mechanical behavior of polypropylene nanocomposites

The use of polypropylene (PP)‐layered silicate nanocomposite has attracted great interest in the polymer industry over the last years. On one hand, PP is widely used in many fields of applications because of good performance and cost. On the other hand, the major advantage of layered silicate nanofiller in the polymer matrix is the small amount of filler (<5 wt%) needed to enhance various properties such as Young's modulus. The most commonly used layered silicates are organomodified montmorillonite (MMT). In this study, a PP/organoclay nanocomposite, filled with layered silicate Nanofil SE3010 (1 and 5 wt%), provided by Rockwood Additives, USA, was used. The polymer nanocomposites were prepared via melt intercalation in a laboratory kneader. The compatibilizer (PP grafted with maleic acid anhydride) admixture content relative to the organoclay content (1 and 5 wt%) was chosen at a ratio of 1:1 (clay:compatibilizer). The influence of different processing conditions (rotation speed and residence time) on the thermal, rheological, and mechanical properties and the interlayer distance was investigated. It was the target to determine whether a short and intensive or a long and soft process performs better. Different properties prefer different states of dispersion of MMT in the polymer matrix. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Low velocity impact behavior of glass/epoxy cross-ply laminates with different fiber treatments

This paper deals with the influence of the fiber/matrix adhesion quality on the impact behavior of cross-ply glass/epoxy laminates. Glass fibers with two different treatments (one to promote and one to prevent adhesion to the matrix) were embedded in epoxy matrix systems and subjected to low velocity impacts at energies below perforation energy. It will be shown that the laminates with good fiber/matrix adhesion are significantely more damage resistant than the plates with poor adhesion. It will be pointed out that the composites with the more brittle matrix system show the lower damage resistance. For all materials, the absorbed energy correlates well with the amount of impact induced damage. Furthermore, an experimental/mathematical model is introduced that gives the possibility of predicting the maximum deflection and maximum force for any given impact energy. Only one experiment is needed for each material to identify the model parameters. These parameters describe the real material behavior and can be used as characteristic values to classify materials with respect to their impact stiffness and damage resistance.     

High velocity impact behavior of GRP panels containing coarse‐sized sand filler

Ballistic performance of glass reinforced plastic (GRP) composite plates containing coarse sized sand filler was investigated as an attempt towards developing a low cost armored system. In all, 10 different types of plates from 4 to 12 layers of E‐glass chopped strand mat reinforced polyester resin containing 0, 10, and 20% of 600‐ to 700‐μm sized sand filler were tested. A smooth barrel gas gun was used to conduct high velocity tests in the range of 70–185 m/s. Results indicated higher ballistic performance for GRP plates with sand filler in terms of higher ballistic limits (velocity at which at least 50% of samples were partially or fully penetrated the target plates with zero residual velocity), particularly for plates with highest sand filler loadings. Energy absorption associated with these specimens also showed higher performance. Delamination was identified as dominant failure mode, in particular for thicker specimens with highest sand filler loading. Specific energy absorption per weight per unit area for the composite plates indicated diminishing effectiveness with increase in sand filler loading, thereby limiting its possible application to armored system for stationary objects only. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Crystallization behavior of nylon 6 nanocomposites

The crystallization behavior of nylon 6 nanocomposites formed by melt processing was investigated. Nanocomposites were produced by extruding mixtures of organically modified montmorillonite and molten nylon 6 using a twin screw extruder. Isothermal and non-isothermal crystallization studies involving differential scanning calorimetry (DSC) were conducted on samples to understand how organoclay concentration and degree of clay platelet exfoliation influence the kinetics of polyamide crystallization. Very low levels of clay result in dramatic increases in crystallization kinetics relative to extruded pure polyamide. However, increasing the concentration of clay beyond these levels retards the rate of crystallization. For the pure nylon 6, the rate of crystallization decreases with increasing the molecular weight as expected; however, the largest enhancement in crystallization rate was observed for nanocomposites based on high molecular weight polyamides; this is believed to stem from a higher degree of platelet exfoliation in these nanocomposites. Wide angle X-ray diffraction (WAXD) and DSC were further used to characterize the polymer crystalline morphology of injection molded nanocomposites. The outer or skin layer of molded specimens was found to contain only γ-crystals; whereas, the central or core region contains both the α and γ-forms. The presence of clay enhanced the γ-structure in the skin; however, the clay has little effect on crystal structure in the core. Interestingly, higher levels of crystallinity were observed in the skin than in the core for the nanocomposites, while the opposite was true for the pure polyamides. In general, increasing the polymer matrix molecular weight resulted in a lower degree of crystallinity in molded samples as might be expected.     

Fatgiue behavior of metal matrix nanocomposites

Light-weight high-strength composites (particularly with aluminum and magnesium base alloys) have principal applications in a wide variety of fields ranging from automotive and aerospace structures to medical and energy applications wherein the materials undergo both static and dynamic (fatigue) loading conditions. Conventional metal matrix composites (MMCs), i.e. those filled by micro-sized reinforcements, have usually poor ductility and insufficient mechanical performance made them, therefore, unreliable to be used in some critical applications. Instead, those composites strengthened by nano-sized reinforcing agents, namely metal matrix nano-composites (MMNCs), have newly been developed in order to boost the mechanical properties. The current paper aims to study the fatigue behavior of the MMCs with a particular attention on recent investigations made on MMNCs. It is believed that the materials selection, microstructural features, manufacturing and processing parameters, etc. have a dominant influence on the fatigue response of MMNCs.     

Wear behavior of metal matrix nanocomposites

Metal matrix nanocomposites (MMNCs), a unique class of metallic materials having superior mechanical, chemical, thermal or tribological properties, are commonly used in critical applications Those light-weight aluminum and magnesium alloys usually working in harsh wear conditions are susceptible to surface attacks. Although a lot of investigations have already been performed on those conventional composites reinforced by micro-particles, the wear behavior of the nanocomposites has not yet been fully understood. The surface properties associated with MMNCs are presented in this paper focusing mostly on manufacturing & processing routes, nano-particles as well as the dominant wear mechanisms. Studying wear behavior of MMNCs shows that no quantitative comparison of different existing studies is available as it is aimed to be done in the present review. To this end, wear reports have been categorized and discussed wherein the following results has been obtained: (i) it is found that ceramics reinforced composites usually exhibit a relatively better wear resistance behavior compared to those filled by carbon-based nanomaterials, (ii) hybrid MMNCs with two or more reinforcement types are promising materials to improve the surface resistance, particularly when the combination of ceramic and carbon-based particles are employed, (iii) solid-state processes like powder metallurgy usually provide superior wear resistance as compared to those liquid processing methods like casting, (iv) the use of smaller reinforcement size may almost always result in superior response, (v) abrasion is the most governing wear mechanism amongst the abrasion, adhesion and delamination mechanisms being frequently observed in MMNCs. A comprehensive review is made with particular attention on the composites reinforced by nano-sized reinforcing agents in order to evaluate the current research activities, discuss the pitfalls and provide a roadmap for future endeavors. It is believed that still countless research opportunities exist in order to fill the existing voids and fulfill the challenges with MMNCs.     

Investigation of sandwich structures with innovative cellular metallic cores under low velocity impact loading

Abstract

Sandwich panels are widely used for energy absorbing applications in cases of low and high velocity impacts. The core itself is capable of absorbing energy by progressive collapse, while the skins are necessary for uniformly distributing the local vertical load over the impacted area as well as for the introduction of overall panel bending resistance. In the present work, the failure response of sandwich panels with open lattice cellular cores subjected to low velocity impact is investigated. Experimental tests are performed using a mass drop testing machine. Additionally, a three-dimensional finite element model of the sandwich panels–impactor system is developed using commercial Finite Element (FE) codes. The core homogenisation is introduced in order to improve the efficiency of the FE analysis by reducing the computational time. Numerical results correlate well with experimental data, enabling detailed understanding of the parameters affecting the initiation and propagation of impact damage.     

Network model for the viscoelastic behavior of polymer nanocomposites

A theoretical network model reproducing some significant features of the viscoelastic behavior of unentangled polymer melts reinforced with well dispersed non-agglomerated nanoparticles is presented. Nanocomposites with low filler volume fraction (∼10%) and strong polymer-filler interactions are considered. The model is calibrated based on results obtained from discrete simulations of the equilibrium molecular structure of the material. This analysis provides the statistics of the network of chains connecting fillers, of dangling strands having one end adsorbed onto fillers, and that of the population of loops surrounding each nanoparticle. The network kinetics depends on the attachment-detachment dynamics of grafted chains of various types and is modeled by using a set of convection equations for the probability distribution functions. The overall viscoelastic response depends strongly on the lifetime of the polymer-filler junctions. The largest reinforcement is observed at low strain rates and low frequency oscillations. A solid like behavior is predicted for systems in which the polymer molecules interact strongly with the nanoparticles, effect which is associated with the behavior of the network of bridging segments.     

Influence of adhesive thickness on high velocity impact performance of ceramic/metal composite targets

Influence of adhesive thickness on high velocity impact (HVI) performance of ceramic (Al₂O₃-99.5)/aluminium (Al5083 H116) composite targets is critically examined in this paper through numerical investigations. Detailed parametric studies are carried out by choosing a practical problem and for a range of adhesive thickness between 0.1 mm and 1.5 mm. Studies are focussed on normal impact of the composite target by ogive nosed projectile with a velocity of 830 m/s. Numerical simulation is carried out by adopting the Lagrangian approach and an axisymmetric finite element model. Impact responses are compared in relative terms among different cases of analysis to highlight the role played by adhesive thickness. Various response parameters such as shear strain developed at the interface of adhesive layer, target deformation, energy transformation, depth of penetration and deflection profile of back plate are considered in the investigations. These response parameters are observed to be influenced to different degree by the adhesive thickness. In particular, the depth of projectile penetration into the aluminium back plate is found to have non-monotonic variation with the thickness of adhesive layer.     

Investigation of nano-SiO2 impact on mechanical and biocompatibility properties of cyanoacryalate based nanocomposites for dental application

Although cyanoacrylate glues are widely used in medicine, cyanoacrylate-based nanocomposites have been recently suggested for dental restorative/filling applications. In the present research, SiO₂ nanoparticles were used as filler for development of a novel dental nanocomposite base on alkoxy-ethyl-cyanoacrylate. The mechanical properties of nanocomposite samples filled with different levels of nano-sized SiO₂ (wt%) were evaluated and comparisons were made with the neat cyanoacrylate. The hardness and wear behavior of the samples were measured using Vickers hardness and pin-on-disk tester, respectively. The wear mechanism of the samples was also evaluated using scanning electron microscopy (SEM). Furthermore, cell biocompatibility of the samples using MTT and LDH assays as well as inflammatory cytokine expression interleukin-6 (IL-6) from L929 cells was investigated. The results showed that an increase in nano-sized SiO₂ content improves hardness and wear resistance of the cyanoacrylate-based nanocomposites and changes the wear mechanism from adhesive to abrasive. The results of cytotoxicity analysis showed a significant reduction in cell viability and IL-6 produced from the samples-exposed L929 cells compared with untreated control cells. Moreover, increasing the nano SiO₂ powder content caused a decrease in the released formaldehyde.     

Impact fracture behavior of clay-reinforced polypropylene nanocomposites

The micromechanism of plastic deformation during impact loading of polypropylene-clay nanocomposites is examined and compared with the unreinforced polypropylene under identical conditions of processing to underscore the determining role of clay. The addition of clay to polypropylene increases the impact strength in the temperature range of 0 to +70 °C. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques provided an understanding of the micromechanism of plastic deformation in terms of the response of the polymer matrix, nucleating capability of the reinforcement, crystal structure, percentage crystallinity, lamellae thickness, and particle-matrix interface. The enhancement of toughness on reinforcement of polypropylene with nanoclay is associated with change in the primary mechanism of plastic deformation from crazing and vein-type in neat polypropylene to microvoid-coalescence-fibrillation process in the nanocomposite.     

Intumescent-like behavior of polystyrene synthetic clay nanocomposites

A synthetic Li-fluorohectorite with typical aspect ratios around 1000 shows superior thermal, fire and mechanical properties. A comparison between Li-fluorohectorite and MMT underlines the crucial role of the aspect ratio in particular for flame retardancy. Furthermore, solution blending yields a better dispersion of the filler, as compared to melt compounding, which directly transforms into superior properties. Quite surprisingly, the homogenous clay surface layer built during burning of the PS fluorohectorite nanocomposite has such a high gas barrier that an intumescent-like behavior of the char is detectable.     

SBS／蒙脱土纳米复合材料的流变行为

用毛细管流变仪测定并研究了热塑性丁苯三嵌段共聚物（SBS）／蒙脱土纳米复合材料的熔体的稳态剪切流变行为，研究结果表明：温度和压力一定的条件下，加入一定量的改性蒙脱土可以降低熔体的粘度；在较低的剪切速率下，即出现剪切变稀现象；在高剪切速率下，粘度对剪切速率的敏感性是降低的，改性蒙脱土加入量对熔体的剪切粘度影响较小，主要是由基体材料所决定的；随温度的升高熔体粘度对剪切速率的敏感性是降低的。采用转矩流变仪对材料的加工性能进行研究，发现复合材料的加工性能基本上保持了纯SBS的加工性能。     

Investigation of thermal behavior and decomposition kinetic of PET/PEN blends and their clay containing nanocomposites

Blends of Poly(ethylene terephthalate), (PET), and poly(ethylene naphthalene 2,6-dicarboxylate), (PEN), were prepared in a twin-screw extruder. Samples were investigated by differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (¹H NMR) measurements to evaluate the extent of transesterification reaction. X-ray diffraction (XRD) test was performed to examine the effect of transesterification reactions on crystalline structure of the blends. Thermogravimetry analysis (TGA) was used to study thermal decomposition of the blends which could be explained by the level of transesterification reaction for various blend compositions. The kinetic of the decomposition reaction was analyzed by Freeman-Carroll and Chang models. It was found that these two methods were acceptable models for describing the thermal decomposition of the blends however, the Chang model showed better correlation with the experimental data as compared to the other model. Results revealed that progress of transesterification reaction in blends depends on temperature and mixing time, which have dominant role in thermal behavior and decomposition kinetic of the blends. Effect of nanoclay on transesterification reactions and degradation behavior was also investigated. It was found that the nanoclay inhibited the transesterification reactions and reduced the thermal stability of the blends. PET degraded much faster than PEN in O₂ environment while, an opposite trend was observed in N₂ atmosphere.