Volume Fraction Of Core Research Articles

A simplified predictive model for the compression behavior of self-healing microcapsules using an empirical coefficient

Abstract This study is dedicated to predicting the compression behavior of microcapsules, a key aspect in self-healing applications. Understanding the compression behavior of microcapsules, mainly due to their liquid cores, is a complex task. Equally challenging is the evaluation of the shell properties. We aimed to streamline this prediction process by introducing the empirical coefficient C core, which accounts for core influence. We conducted experiments on microcapsules with MUF (Melamine–Urea–Formaldehyde) shells, compressing them between two plates and recording their responses to load and displacement. The empirical coefficient, influenced by capsule size, shell properties, and core volume fraction, was then analyzed in terms of microcapsule size and Young’s modulus. The research results showed that as the diameter of microcapsule and Young’s modulus of the shell increased, the Ccore also increased. This relationship could be represented in a three-dimensional surface. These findings could significantly contribute to estimating shell properties and modeling matrices with dispersed microcapsules.

Silk-inspired architectured filament with enhanced stiffness and toughness for Fused deposition modelling (FDM)

Architectured materials, those capable of manipulating the spatial configurations of two or more material phases, have recently gained substantial attention, primarily due to their unprecedented material properties (e.g., exceptional strength-to-weight ratio and intriguing negative Poisson's ratio). Most architectured materials draw inspiration from the microstructure of natural solutions. One of fascinating examples are spider silk and cocoon silk. Their multimaterial core-shell fibrous structure exhibits remarkable mechanical properties—high stiffness, strength, and toughness. In this study, silk-inspired dual-phase Core-Shell Architectured Filament (CSAF), which combines a rigid Polylactic Acid (PLA) core with a soft Thermoplastic Polyurethane (TPU) shell, was developed as feedstock for additive manufacturing. The mechanical testing of dual-phase CASF printed samples reveal intriguing results. Notably, the optimized CASF in this study, whose volume fraction of rigid core was set as 52 %, was observed a substantial improvement of the printed specimens in initial stiffness and energy absorption capacity—up to a remarkable 14-fold increase in initial stiffness and a ∼9 % enhancement in energy absorption when compared to the pure TPU filament. To gain a deeper understanding of the synergistic effects arising from geometrical and material configurations on the structure's damage mechanism, a theoretical model of this core-shell structure was developed. Computational models have been built to validate theoretical model, and the results from finite element analysis are in excellent agreement with experimental results. These discoveries offer valuable insights to enhance mechanical performance of the feedstock for additive manufacturing.

A novel method of fabricating designable polylactic acid (PLA)/thermoplastic polyurethane (TPU) composite filaments and structures by material extrusion additive manufacturing

Multi-material 3D printing enables the creation of complex parts with tailored mechanical properties, which expands the potential of material extrusion additive manufacturing (MEAM). A promising approach to realise multi-material printing is to manufacture a composite filament, integrating multiple materials into a filament that can be further processed on a single extruder machine. However, making such composite filaments typically requires specialised equipment, which in turn limits its application in multi-material printing and increases costs. This study presents a novel and cost-effective approach for fabricating composite structures with enhanced mechanical properties. In this method, a commercially available 3D printer is employed to manufacture polylactic acid (PLA) and thermoplastic polyurethane (TPU) into core-shell composite filaments. The fabricated core-shell filaments are further used as feedstocks in the re-extrusion process to make composite specimens. In addition, the effects of multiple process parameters and geometrical design strategies on re-extruded materials are comprehensively evaluated by microscopy analysis, nanoindentation and tensile testing. The design with the best mechanical properties has a volume fraction of the PLA core (Vf) of 36 %, which results in a 63 % higher in toughness than the neat TPU and 27 times higher than neat PLA. Overall, the approach offers a promising way for rapid prototyping and testing of various material configurations.

Enhanced near-field radiative heat transfer between core-shell nanoparticles through surface modes hybridization

Core-shell nanoparticles (CSNPs) are widely used in energy harvesting, conversion, and thermal management due to the excellent physical properties of different components. Because of the synergistic interaction between the core and the shell, the thermal radiative properties are expected to be further enhanced. In this work, we achieve near-field radiative heat transfer (NFRHT) enhancement between SiC@Drude CSNPs. Numerical results show that the total heat flux between NPs is 1.47 times and 9.98 times higher than homogeneous SiC and Drude NPs at the same radius when the core volume fraction is 0.76. Surface modes hybridization arising from the interfaces of the shell-core and shell-air contributes to the improved thermal radiation. The effect of shift frequency on the NFRHT between SiC@Drude CSNPs is studied, showing that the enhancement ratio of NFRHT between CSNPs can reach 4.34 at a shift frequency of 1 × 1014 rad/s, which is 38.34 times higher than the previous work. This study demonstrates that surface modes hybridization in CSNPs can significantly improve NFRHT and open a novel path for high-efficiency energy transport at the nanoscale.

Cluster-counterpart Voids: Void Identification from Galaxy Density Field

We identify cosmic voids from galaxy density fields under the theory of void–cluster correspondence. We extend the previous novel void-identification method developed for the matter density field to the galaxy density field for practical applications. From cosmological N-body simulations, we construct galaxy number- and mass-weighted density fields to identify cosmic voids that are counterparts of galaxy clusters of a specific mass. The parameters for the cluster-counterpart void identification such as Gaussian smoothing scale, density threshold, and core volume fraction are found for galaxy density fields. We achieve about 60%–67% of completeness and reliability for identifying the voids of corresponding cluster mass above 3 × 1014 h −1 M ⊙ from a galaxy sample with the mean number density, . When the mean density is increased to , the detection rate is enhanced by ∼2%–7% depending on the mass scale of voids. We find that the detectability is insensitive to the density weighting scheme applied to generate the density field. Our result demonstrates that we can apply this method to the galaxy redshift survey data to identify cosmic voids corresponding statistically to the galaxy clusters in a given mass range.

Probing the atomic-scale deformation mechanism of single-crystal nanowires coated with a multi-component alloyed shell

Metallic nanowires have attained considerable attention as applied for the building blocks in nano-electromechanical systems. Surface coating is needed for nanowires to prevent their degradation from the external environment. Multi-component alloys (MCAs) exhibit a combination of exceptional fracture tolerance and desirable corrosion resistance, which are promising coating materials for nanowires. However, few attempts have been made to investigate the deformation mechanisms of nanowires coated with an MCA shell. To address this gap, we employ atomic simulations on investigating the tensile deformation of single-crystal nickel nanowires coated with MCA shells, and study the microstructural features governing the necking behavior of these specimens. The results indicate that the dislocation nucleation method controlling the incipient plasticity of the nanowire turns from a typical homogeneous surface nucleation mode to another interface nucleation one after coating, lowering the maximum stress during the tensile loading. Ductile necking with dispersed plastic events prevails in the uncoated nanowire, while severely localized shear dominates the necking mode of the single- and poly-crystalline MCA nanowire due to their lower dislocation contents as well as the sluggish dislocation mobility caused by lattice distortion and high-entropy effect. The necking mode of nanowires is not altered by the MCA coating due to the predominant volume fraction of the nickel core in the present configurations. Noteworthily, the deformation stability is highly enhanced by polycrystalline MCA coating, thus the stress no longer drops to zero before the final fracture. This work gives new insights into developing reliable nanowires with enhanced deformability via using MCA coating.

Complex Phase Behavior in Binary Blends of AB Diblock Copolymer and ABC Triblock Terpolymer

Blending block polymers with different block compositions provides an opportunity to create nanostructures that are not accessible from neat block copolymer melts. In this study, we investigate the equilibrium phase behavior in binary blends composed of an AB diblock copolymer and an ABC triblock terpolymer, using self-consistent field theory (SCFT). Blending these simple linear block polymers results in complex phase behaviors, including unusual core–shell network phases with asymmetric core and shell volume fractions and a new cylinder-in-O70 hybrid network phase. The phase diagrams with respect to segregation strength and blend composition reveal an unexpected morphological richness, including 15 ordered phases, illustrating the potential inherent in blending these relatively simple components.

Accessing the Frank–Kasper σ Phase of Block Copolymer with Small Conformational Asymmetry via Selective Solvent Solubilization in the Micellar Corona

Large conformational asymmetry has been considered as an essential ingredient for accessing the Frank–Kasper (FK) phase in a neat block copolymer (bcp) melt. This criterion can be relaxed by blending the bcp with the corresponding homopolymer, where the homopolymer is incorporated into the micellar core in the dry-brush regime. While the solubilization of the homopolymer in the micellar corona in the wet-brush regime has also been demonstrated to yield the FK σ phase in a bcp system bearing a large conformational asymmetry parameter (ε > 1.5), we demonstrate here that this is also true for the system with small conformational asymmetry. A cylinder-forming poly(ethylene oxide)-block-poly(1,2-butadiene) (PEO-b-PB) with a ε of 1.2 was blended with a small amount of selective solvent, which was either a PB homopolymer (h-PB) or dodecylbenzene (DB) to yield the mixtures forming the spherical micelles composed of the PEO core and the corona containing the wet-brush mixture of PB blocks and the selective solvents. Both types of mixtures were found to form the FK σ phase in a narrow region near the cylinder-sphere phase boundary. We argue that, under a given volume fraction (fPEO) and size of the PEO core, the shorter PB coronal blocks in the bcp/solvent mixtures are more strained than the longer PB blocks in the corresponding neat diblock; therefore, the spherical phase is accessed at a higher PEO core fraction to alleviate the excess entropic penalty. The formation of a larger core (at a higher fPEO) and the stronger propensity to alleviate the packing frustration of the more strained PB coronal blocks in the bcp/selective solvent mixture creates an effect equivalent to increasing the conformational asymmetry and hence promotes the core to adopt the polyhedral geometry templated by the Voronoi cells of the lattice. The micelles approaching the polyhedral interface limit then favor the packing in the FK σ phase to minimize the total free energy.

Tuning Diblock Copolymer Particle Packing Symmetry with Variable Molecular Weight Core-Homopolymers

We report the sensitivity of diblock copolymer particle packing symmetry to the ratio α = Nhomo/Ncore, where Nhomo and Ncore are the respective homopolymer and core-block degrees of polymerization. Three poly(ethylene oxide)-b-poly(2-ethylhexyl acrylate) (OA) diblock copolymers with O volume fractions fO = 0.15, 0.16, and 0.20 were blended with O homopolymers characterized by α = 0.23, 0.42, 0.80, and 1.00. Small-angle X-ray scattering revealed rich phase behavior as a function of α, the overall particle core volume fraction (fcore), and temperature. BCC, HCP, and Frank–Kasper σ, C14, C15, and dodecagonal quasicrystal phases, were all identified. “Dry-brush” homopolymer distribution (α = 0.80 and 1.00) favor C14 and C15 phases with macrophase separation at high homopolymer loadings. “Wet-brush” homopolymer distributions in the particle cores (α = 0.42) lead to narrow σ or C15 windows and cylinders at greater O concentrations. Solvent-like swelling (α = 0.23) favors widespread σ phase formation.

Molecular Dynamics Study of Melting Behavior of Planar Stacked Ti–Al Core–Shell Nanoparticles

Selective laser sintering (SLS) is one of the most commonly used methods in additive manufacturing, due to its high prototyping speed and applicability to various materials. In the present work, molecular dynamics (MD) simulations were performed to study the thermodynamic behaviors of the planar stacked nanoparticles (NPs) model and explore the potential capability of the SLS process with nano-sized metal powders in the zero-gravity space environment. A multi-particle model of titanium–aluminum (Ti–Al) core–shell NP with a particle radius of 50 Å was constructed to investigate the characteristics of the melted pattern during sintering. Two patterns with different spatial densities were considered to study the influence of particle stacking on the melting process. Various core volume fractions and heating rates were examined to investigate their effects on the quality of the final sintered product. The stacked-NPs models with core volume fractions (CVFs) of 3%, 12%, and 30% were linearly heated up to 1100 K from room temperature (298 K) with heating rates of 0.04, 0.2, 0.5, and 1.0 K ps−1. The initial fusion temperature and final sintering temperature for each stacking pattern were obtained via the validation from the radial distribution function, mean squared displacement, and the radius of the gyration analysis. The 30% CVF yields the largest neck size before the melting point, while beyond the melting point, a larger core helps delay the formation of the fully-melted products. It is observed that using the close-packed stacked-NPs model under a slow heating rate (long melting duration) would help form a stable, completely sintered product with a relatively low final sintering temperature.

中Mn鋼の中断焼入-二相域焼鈍により形成されるコア-シェル型第二相組織の制御

Medium manganese steel (Fe-5.0%Mn-1.2%Si-0.10%C alloy) was subjected to interrupted quenching from the austenite single-phase region to a temperature between Ms and Mf followed by intercritical annealing in the ferrite and austenite dual-phase region at 923 K. As a result, a core-shell type second phase, which consisted of a fresh martensite core surrounded by a film-like retained austenite shell, was formed. The mechanism and kinetics of reversion for the interrupted-quenched specimens were analyzed with DICTRA simulation and TEM observation. With regard to the effect of the core-shell type second phase on mechanical properties, it was inferred that the fresh martensite core functioned as a hard second phase and enhanced work hardening by stress partitioning similar to DP steel, while the film-like retained austenite contributed to improved ductility due to the TRIP effect. As the interrupted quenching temperature decreased, the volume fraction of the fresh martensite core decreased, while the stability of the retained austenite shell increased. This showed potential for controlling the strength and ductility balance of medium manganese steel. A possible beneficial effect of the core-shell type second phase on the ductile fracture behavior was also discussed in terms of stress/strain relaxation at the interfaces between hard martensite and ferrite matrix.

Effect of morphology on the phonon thermal conductivity of Si, Ge, and Si/Ge core/shell nanowires

An additional factor in reducing thermal conductivity for thermoelectric applications of semiconductor nanowires is a change in morphology. In this paper, for Si, Ge and core/shell Si/Ge nanowires the effect of the volume fraction and the type of core material on thermal conductivity at 300 K is investigated by means of nonequilibrium molecular dynamics. Nanowires with experimentally observed <100>, <110>, <111> and <112> orientations and different cross sections were taken into account. It was found that for <112>-oriented Si-core/Ge-shell nanowires with a core volume fraction of ~30% the thermal conductivity is the lowest (5.76 W/(m · K)), while the thermal conductivity values for pure Si and Ge nanowires are 13.8 and 8.21 W/(m · K), respectively. Keywords: nanowire, core/shell structure, morphology, silicon, germanium, thermal conductivity, molecular dynamics.

Влияние морфологии на фононную теплопроводность нанопроволок Si, Ge и Si/Ge типа ядро/оболочка

An additional factor in reducing thermal conductivity for thermoelectric applications of semiconductor nanowires is a change in morphology. In this paper, for Si, Ge and core/shell Si/Ge nanowires the effect of the volume fraction and the type of core material on thermal conductivity at 300 K is investigated by means of nonequilibrium molecular dynamics. Nanowires with experimentally observed <100>, <110>, <111> and <112> orientations and different cross sections were taken into account. It was found that for <112>-oriented Si-core/Ge-shell nanowires with a core volume fraction of ~ 30% the thermal conductivity is the lowest (5.76 W/(m∙K)), while the thermal conductivity values for pure Si and Ge nanowires are 13.8 and 8.21 W/(m∙K), respectively.

Inorganic-organic nanocomposite networks: Structure, curing reaction, properties, and hard coating performance

This study reports the first structure and morphology details of octakis(acryloyloxypropyl)-octasilsesquioxane (POSS-Acryl8), a reactive inorganic-organic hybrid molecule, before and after photochemically crosslinked. POSS-Acryl8 was confirmed as an oblate ellipsoidal nanoparticle consisting of inorganic cage core (0.774 nm diameter) and chemically-bonded organic shell (1.447 nm thickness). The core volume fraction is only 0.95% in a single molecule, but drastically increases up to 18.8% in the neat bulk state and 31.9% in the photocured film state; the individual inorganic cores are eventually encapsulated with the networked shells (0.176 nm thickness) chemically interconnected with the neighbors. Based on such the highly networked structure and inorganic core reinforcement, the photocured POSS-Acryl8 exhibited exceptionally high optical transparency, glass transition temperature, surface hardness, and abrasion resistances. Due to the superior properties, clear hard POSS-Acryl8 coatings solved completely inherently poor surface hardness and abrasion resistances of conventional polymer window substrates and, furthermore, serious drawbacks in the eraser and steel wool abrasion resistances of glass window substrate. In addition, POSS-Acryl8 was found miscible with pentaerythritolylethyl tetraacrylate (PEEO-Acryl4) and thereby enhanced substantially the surface hardness and abrasion resistances of PEEO-Acryl4 through nanocomposite network formations. It turns out that the photocurable inorganic-organic POSS-Acryl8 hybrid and its composites with fully organic PEEO-Acryl4 are so suitable for optically clear hard top coating applications in advanced telecommunication, defense, automobile, and smart home appliance (smart and foldable phones, display devices, sensor windows, etc.).

Sintered Ti/Al core/shell nanoparticles: computational investigation of the effects of core volume fraction, heating rate, and room-temperature relaxation on tensile properties

Molecular dynamics simulations were performed to roughly imitate the conditions of selective laser sintering during additive manufacturing. The role of core volume fraction on the resultant uniaxial tensile properties of sintered Ti/Al bimetallic core/shell nanoparticles (NPs) was investigated during various sintering states. A chain model was created from five single thermally equilibrated Ti/Al NPs with weak neck connections by a solid-state sintering process at room temperature (298 K). The chains were heated to 800 K with two heating rates (0.04 and 0.2 K ps−1), underwent high-temperature relaxation, and were cooled to 298 K with a cooling rate of 0.08 K ps−1. They were then relaxed at 298 K for different periods (i.e. 1, 4, and 10 ns). In a follow-up procedure, those sintered NPs were subjected to uniaxial tension at different strain rates (i.e. 0.001, 0.01, and 0.1% ps−1). The thermodynamic properties and the structural evolutions of atomic configurations were investigated during the sintering process. The tensile responses were also obtained to examine the final product quality. The results indicate a strong correlation between the tensile strength of the final sintered chain product and the Ti core volume fraction. A larger Ti core volume fraction yields a stronger chain structure, resulting in higher tensile strength. The effect of heating rate on the tensile strength of final products with larger core volume fraction is more pronounced. The effect of room-temperature relaxation is not obvious on the tensile strength except for two products, which were sintered with the fast heating rate and tested under the lowest/highest strain rate. Also, high strain rates improve the tensile strength, and low strain rates will lead to enhanced ductility of the final products, especially with residual single atomic chain.

Long-lasting accretion-powered chemical heating of millisecond pulsars

ABSTRACT We analyse the effect of magnetic field in superconducting neutron star (NS) cores on the chemical heating of millisecond pulsars (MSPs). We argue that the magnetic field destroys proton superconductivity in some volume fraction of the stellar core, thus allowing for unsuppressed non-equilibrium reactions of particle mutual transformations there. The reactions transform the chemical energy, accumulated by an NS core during the low-mass X-ray binary stage, into heat. This heating may keep an NS warm at the MSP stage (with the surface temperature $\sim 10^5\, \rm K$) for more than a billion of years after ceasing of accretion, without appealing to the rotochemical heating mechanism.

Universal Polymeric-to-Colloidal Transition in Melts of Hairy Nanoparticles.

Two different classes of hairy self-suspended nanoparticles in the melt state, polymer-grafted nanoparticles (GNPs) and star polymers, are shown to display universal dynamic behavior across a broad range of parameter space. Linear viscoelastic measurements on well-characterized silica-poly(methyl acrylate) GNPs with a fixed core radius (Rcore) and grafting density (or number of arms f) but varying arm degree of polymerization (Narm) show two distinctly different regimes of response. The colloidal Regime I with a small Narm (large core volume fraction) is characterized by predominant low-frequency solidlike colloidal plateau and ultraslow relaxation, while the polymeric Regime II with a large Narm (small core volume fractions) has a response dominated by the starlike relaxation of partially interpenetrated arms. The transition between the two regimes is marked by a crossover where both polymeric and colloidal modes are discerned albeit without a distinct colloidal plateau. Similarly, polybutadiene multiarm stars also exhibit the colloidal response of Regime I at very large f and small Narm. The star arm retraction model and a simple scaling model of nanoparticle escape from the cage of neighbors by overcoming a hopping potential barrier due to their elastic deformation quantitatively describe the linear response of the polymeric and colloidal regimes, respectively, in all these cases. The dynamic behavior of hairy nanoparticles of different chemistry and molecular characteristics, investigated here and reported in the literature, can be mapped onto a universal dynamic diagram of f/[Rcore3/ν0)1/4] as a function of (Narmν0f)/(Rcore3), where ν0 is the monomeric volume. In this diagram, the two regimes are separated by a line where the hopping potential ΔUhop is equal to the thermal energy, kBT. ΔUhop can be expressed as a function of the overcrowding parameter x (i.e., the ratio of f to the maximum number of unperturbed chains with Narm that can fill the volume occupied by the polymeric corona); hence, this crossing is shown to occur when x = 1. For x > 1, we have colloidal Regime I with an overcrowded volume, stretched arms, and ΔUhop > kBT, while polymeric Regime II is linked to x < 1. This single-material parameter x can provide the needed design principle to tailor the dynamics of this class of soft materials across a wide range of applications from membranes for gas separation to energy storage.

Nanoscale Engineering of Optical nonlinearity Based on a Metal Nitride/Oxide Heterostructure.

The abilities to modulate linear and nonlinear optical response of materials in the nanoscale are of central importance in the design and fabrication of photonic devices for applications like optical modulators. Here, based on a simple transition metal oxide/nitride (TiO2/TiN) system, we show that it is possible to tune the optical properties by controlling the nanoscale architecture. Through controlled oxidation of the plasmonic TiN nanoparticle surfaces, we observe a continuous change of linear and nonlinear optical (NLO) properties with the increase of the thickness of the oxide layer in the TiN/TiO2 heterogeneous architecture. The NLO response is manifested by the strong saturable absorption with a structurally tunable negative NLO absorption coefficient. The variation in the NLO absorption coefficient by up to 7-fold can be connected to the relative change in the volume fraction of the metallic core and the dielectric shell. We demonstrate further that the optimized TiN-TiO2 heterostructures can be used to drive an optical switch for pulse laser generation in the 1.5 μm wavelength region. Our results delineate a topochemical process for optimization of the NLO properties of common plasmonic materials for photonic applications based on simple materials chemistry.

Formation of a C15 Laves Phase with a Giant Unit Cell in Salt-Doped A/B/AB Ternary Polymer Blends.

Salt-doped A/B/AB ternary polymer blends, wherein an AB copolymer acts as a surfactant to stabilize otherwise incompatible A and B homopolymers, display a wide range of nanostructured morphologies with significant tunability. Among these structures, a bicontinuous microemulsion (BμE) has been a notable target. Here, we report the surprising appearance of a robust C15 Laves phase, at compositions near where the BμE has recently been reported, in lithium bis(trifluoromethane) sulfonimide (LiTFSI)-doped low-molar-mass poly(ethylene oxide) (PEO)/polystyrene (PS)/symmetric PS-b-PEO block copolymer blends. The materials were analyzed by a combination of small-angle X-ray scattering (SAXS), 1H NMR spectroscopy, and impedance spectroscopy. The C15 phase emerges at a high total homopolymer volume fraction ϕH = 0.8 with a salt composition r = 0.06 (Li+/[EO]) and persists as a coexisting phase across a large area of the isothermal phase diagram with high PS homopolymer compositions. Notably, the structure exhibits a huge unit cell size, a = 121 nm, with an unusually high micelle core volume fraction (fcore = 0.41) and an unusually low fraction of amphiphile (20%). This unit cell dimension is at least 50% larger than any previously reported C15 phase in soft matter, despite the low molar masses used, unlocking the possibility of copolymer-based photonic crystals without compromising processability. The nanostructured phase evolution from lamellar to hexagonal to C15 along the EO60 isopleth (ϕPEO,homo-LiTFSI/ϕH = 0.6) is rationalized as a consequence of asymmetry in the homopolymer solubility limit for each block, which leads to exclusion of PS homopolymer from the PS-b-PEO brush prior to exclusion of the PEO homopolymer, driving increased interfacial curvature and favoring the emergence of the C15 Laves phase.

Experimental and analytical studies of syntactic foam core composites for impact loading

Sandwich composites with polymeric open-celled foams or honeycomb structures as core materials have been used widely in low-weight naval, aerospace and structural applications in the past. One major drawback of such foams is skin-core debonding. To overcome this, core materials with the same matrix as the skin are studied in this paper. Sandwich composites with fibre composite skins and a hollow glass particle-filled syntactic foam core are fabricated and tested under ballistic impact loading. Both the constituents have an epoxy matrix and are fabricated using a co-curing method which improves the skin-core debonding considerably. Parameters such as ballistic limit and energy absorbed by the samples are obtained for different core volume fractions and varying skin thicknesses. The effect of skin layup sequence has also been studied. It is found that samples with thicker back skins have better impact-resistant properties. The external and internal damage in the samples subject to different impact velocities is studied by visual means and CT scans. An energy-based analytical model is used to predict the ballistic limit of the samples, and to study the individual energy-absorption modes. The evolution of the contribution of the modes with time as well as the velocity profile of the projectile as it penetrates the composites are also obtained from the model. The experiments and the model show comparable ballistic limit results.