Search Results (393)

The aim of this research was to develop a lightweight armor that could be used in bulletproof vests or vehicle protection, offering an alternative to the disadvantageous properties of high-strength steel plates. Specifically, the study focused on investigating the properties of different binders to identify the most suitable one for further development. The bulletproof characteristics of Kevlar (aramid) fiber fabric (200 g/m², plain weave, CT709) were examined using both the Ansys simulation environment and ballistic laboratory testing. In the experiments, three different layer configurations were tested on 300 × 300 mm specimens, each consisting of 20 layers of Kevlar. The layers were arranged as follows: dry lamination for the first specimen, epoxy binder for the second, and polyurethane binder for the third. Laboratory tests were conducted using 9 mm Parabellum bullets, in accordance with the parameters defined in the MSZ K 1114-1:1999 standard. Both the ballistic and simulation tests indicated that the Kevlar laminated with polyurethane resin demonstrated the most promising performance and is suitable for further development. Full article

Fiber-reinforced resin matrix composites are generally composed of fibers and matrix with significantly different properties, which are non-uniform and anisotropic in nature. Macro-failure criteria generally view composite plies as a uniform whole and do not accurately reflect fiber- and matrix-scale failures. In this study, the interface phase effect between fiber and matrix has been introduced into the frame of trans-scale analysis to better model the failure process, and the equivalent mechanical property characterization model of the interface phase has also been established. Combined with the macro–micro-strain transfer method, the trans-scale correlation of the mechanical response of the composite laminates between the macro scale and the fiber, matrix and interface micro scale has been achieved. Based on the micro-scale failure criterion and the stiffness reduction strategy, the trans-scale failure analysis method of composite materials incorporating the interface phase effect has been developed, which can simultaneously predict the failure modes of the matrix, fiber and interface phase. A numerical implementation of the developed trans-scale failure analysis method considering interface phase was carried out using the Python and Abaqus 2020 joint simulation technique. Case studies were carried out for three material systems, and the prediction data of the developed trans-scale failure analysis methodology incorporating interface phase effects for composite materials, the prediction data of the Linde failure criterion and the experimental data were compared. The comparison with experimental data confirms that this method has good prediction accuracy, and compared with the Linde and Hashin failure methods, only it can predict the failure mode of the fiber–matrix interface. The case analysis shows that its prediction accuracy has been improved by about 2–3%. Full article

Carbon fiber-reinforced plastics (CFRPs) offer excellent in-plane mechanical performance, but their relatively low interlaminar fracture toughness makes them vulnerable to delamination, particularly around intralaminar discontinuities such as resin-rich regions or fiber gaps. This study investigates the effectiveness of polyamide (PA) mesh inserts in improving interlaminar toughness and suppressing delamination in CFRP laminates with such features. Two PA mesh configurations were evaluated: a fully embedded continuous layer and a 20 mm cut mesh strip placed between continuous and discontinuous plies near critical regions. Fracture toughness tests showed that PA mesh insertion improved interlaminar toughness approximately 2.4-fold compared to neat CFRP, primarily due to a mechanical interlocking mechanism that disrupts crack propagation and enhances energy dissipation. Uniaxial tensile tests with digital image correlation revealed that while initial matrix cracking occurred at similar stress levels, the stress at which complete delamination occurred was approximately 60% higher in specimens with a 20 mm mesh and up to 92% higher in specimens with fully embedded mesh. The fully embedded mesh provided consistent delamination resistance across the laminate, while the 20 mm insert localized strain redistribution and preserved global mechanical performance. These findings demonstrate that PA mesh is an effective interleaving material for enhancing damage tolerance in CFRP laminates with internal discontinuities. Full article

In engineering practice, liquid droplet impingement typically occurs at an oblique angle relative to the target surface, yet the influence of impact orientation on damage outcomes remains contentious and exhibits target-material dependency. In this paper, a typical single-waterjet-generating technique is applied to liquid impact tests on a unidirectional carbon fiber-reinforced polymer (CFRP) laminate, with special focus on the effects of the impingement angle and the fiber orientation. Finite-element simulation is employed to help reveal the failure mechanism of oblique impacts. The results show that, in most cases, the damage caused by a 15° oblique impact is slightly larger than that of a normal impact, while the increase amplitude varies with different impact speeds. Resin removal is more prone to occur when the projection of the waterjet velocity on the impact surface is perpendicular (marked as the fiber orientation PE) rather than parallel (marked as the fiber orientation PA) to the fiber direction of the top layer. A PE fiber orientation can lead to mass material peeling in comparison with PA, and the damage range is even much larger than for a normal impact. The underlying mechanism can be attributed to the increased lateral jet-particle velocity and resultant shear stress along the impact projection direction. The distinct damage modes observed on the CFRP laminate with the different fiber orientations PE and PA originate from the asymmetric tensile properties in the longitudinal/transverse directions of laminates coupled with dissimilar fiber–matrix interfacial characteristics. A theoretical model for the surface damage area under a single-jet impact was established through experimental data fitting based on a modified water-hammer pressure contact-radius formulation. The model quantitatively characterizes the influence of critical parameters, including the jet velocity, diameter, and impact angle, on the central area of the surface failure ring. Full article

Automated fiber placement (AFP) composites exhibit complex mechanical behaviors due to manufacturing-induced mesostructural variations, including resin-rich regions and tow gaps that significantly influence both local stress distributions and global material responses. This study presents a hierarchically nested modeling framework based on the Parametric High-Fidelity Generalized Method of Cells (PHFGMC) to predict the effective elastic properties and nonlinear mechanical response of AFP composites. The PHFGMC model integrates micro- and meso-scale analyses using representative volume elements (RVEs) derived from micrographs of AFP composite laminates to capture these manufacturing-induced characteristics. Multiple RVE configurations with varied gap patterns are analyzed to quantify the influence of mesostructural features on global stress–strain response. Predictions for linear and nonlinear elastic behaviors are validated against experimental results from carbon fiber/epoxy AFP specimens, demonstrating good quantitative agreement with measured responses. A cohesive extension of the PHFGMC framework further captures damage initiation and crack propagation under transverse tensile loading, revealing failure mechanisms specifically associated with tow gaps and resin-rich areas. By systematically accounting for manufacturing-induced variability through detailed RVE modeling, the nested PHFGMC framework enables the accurate prediction of global mechanical performance and localized behavior, providing a robust computational tool for optimizing AFP composite design in aerospace and other high-performance applications. Full article

This research paper employed the recently developed Elium thermoplastic resin and basalt fabrics as an alternative to thermoset/synthetic fibre composites to reduce their environmental impact. Elium^® 191 XO/SA and Epoxy Prime^TM 37 resin were reinforced with mineral-based semi-unidirectional basalt fibre (BF). Physical, chemical, tensile, and flexural performance was investigated under the effect of hydrothermal seawater ageing at 45 °C for 45 and 90 days. The results show that the BF/Elium composite exhibited superior tensile and flexural strength, as well as good stiffness, compared with the BF/Epoxy composite. Digital images and scanning electron microscope images were used to describe the fracture and failure mechanisms. The tensile and flexural strength values of the BF/Elium composite were 1165 MPa and 1128 MPa, greater than those of the BF/Epoxy composite by 33% and 71%, respectively. The tensile and flexural modulus values of the BF/Elium composite were 44.1 GPa and 38.2 GPa, which are 30% and 12% greater than those of the BF/Epoxy composite. The result values for both composites were normalised with respect to the density of each composite laminate. Both composites exhibited signs of resin decomposition and fibre surface degradation under the influence of seawater ageing, resulting in a more recognisable reduction in flexural properties than in tensile properties. Full article

The current study demonstrates the buckling properties of composite laminates reinforced with MWCNT fillers using a novel higher-order shear and normal deformation theory (HSNDT), which considers the effect of thickness in its mathematical formulation. The hybrid HSNDT combines polynomial and hyperbolic functions that ensure the parabolic shear stress profile and zero shear stress boundary condition at the upper and lower surface of the plate, hence removing the need for a shear correction factor. The plate is made up of carbon fiber bounded together with polymer resin matrix reinforced with MWCNT fibers. The mechanical properties are homogenized by a Halpin–Tsai scheme. The MATLAB R2019a code was developed in-house for a finite element model using C⁰ continuity nine-node Lagrangian isoparametric shape functions. The geometric nonlinear and linear stiffness matrices are derived using the principle of virtual work. The solution of the eigenvalue problem enables estimation of the critical buckling loads. A convergence study was carried out and model efficiency was corroborated with the existing literature. The model contains only seven degrees of freedom, which significantly reduces computation time, facilitating the comprehensive parametric studies for the buckling stability of the plate. Full article

In recent times, fiber reinforced polymer composite materials have become more popular due to their remarkable features such as high specific strength, high stiffness and durability. Particularly, Carbon Fiber Reinforced Polymer (CFRP) composites are one of the most prominent materials used in the field of transportation and building engineering, replacing conventional materials due to their attractive properties as mentioned. In this work, a CFRP laminate is fabricated with carbon fiber mats and epoxy by a hand layup technique. Alumina (Al₂O₃) micro particles are used as a filler material, mixed with epoxy at different weight fractions of 0% to 4% during the fabrication of CFRP laminates. The important objective of the study is to investigate the influence of alumina micro particles on the mechanical performance of the laminates through characterization for various physical and mechanical properties. It is revealed from the results of study that the mass density of the laminates steadily increased with the quantity of alumina micro particles added and subsequently, the porosity of the laminates is reduced significantly. The SEM micrograph confirmed the constituents of the laminate and uniform distribution of Al₂O₃ micro particles with no significant agglomeration. The hardness of the CFRP laminates increased significantly for about 60% with an increase in weight % of Al₂O₃ from 0% to 4%, whereas the water gain % gradually drops from 0 to 2%, after which a substantial rise is observed for 3 to 4%. The improved interlocking due to the addition of filler material reduced the voids in the interfaces and thereby resist the absorption of water and in turn reduced the plasticity of the resin too. Tensile, flexural and inter-laminar shear strengths of the CFRP laminate were improved appreciably with the addition of alumina particles through extended grain boundary and enhanced interfacial bonding between the fibers, epoxy and alumina particles, except at 1 and 3 wt.% of Al₂O₃, which may be due to the pooling of alumina particles within the matrix. Inclusion of hard alumina particles resulted in a significant drop in impact strength due to appreciable reduction in softness of the core region of the laminates. Full article

This paper deals with an important issue, which is the influence of failure caused by the quality of matrix post-curing on the strength of complex and difficult materials of the “new generation” such as fibre composites, particularly with a polymer matrix. In recent years, significant advances in the field of adhesive materials chemistry have led to the constant development of bonding technology. The effectiveness of bonding depends, to a large extent, on the suitable selection of the adhesive and the use of appropriate surface treatment technology. It is difficult to imagine virtually any modern industry without adhesive joints, be it the aircraft, aerospace or automotive industries, which simultaneously highlights the great importance of adhesives and adhesive materials for the present-day economy. In modern technology, it is extremely important to obtain the right combination of modern construction materials. The statistical analysis of the components showed the complexity of the layered composite structure. The proposed model of the weakest micro-volume developed in this study indirectly reflects the experimentally based curing variables that affect the stresses of the components in the composite (laminate) structure. The strength of fibrous composite structures based on the Markov chain theory considers technological aspects during hardening. The model proposed in the paper was validated on the basis of examples from the literature and experimental data obtained in the research project. The numerical results are in good agreement with the literature database and measurement data. The presented model could be a novel method, which allows better insight into the curing process of epoxy resins. Full article

Titanium alloy/carbon fiber-reinforced polymer (TA1/CFRP) laminates, representing the latest fourth generation of fiber metal laminates (FMLs), is a kind of high-performance composite material. However, the fragility of the fiber/resin and metal/resin interface layers in these composites directly impacts their mechanical properties. To enhance these properties, this paper investigates the preparation process of multi-walled carbon nanotube (MWCNT)-reinforced ultra-thin TA1/CFRP laminates and explores the impact of MWCNT content on the interlayer properties of these ultra-thin TA1/CFRP laminates. Initially, the challenge of dispersing carbon nanotubes using ultrasonic dispersion devices and dispersants was addressed. Vacuum-curing pressure studies revealed minimal overflow at 0.8 bar vacuum. Subsequently, the impact of MWCNT content on interlayer properties was investigated. The results indicated a significant increase in interlayer shear strength and interlayer fracture toughness with MWCNT additions at 0.5 wt% and 0.75 wt%, whereas the interlayer properties decreased at 1.0 wt% MWCNT. Fracture morphology analysis revealed that MWCNT content exceeding 0.75 wt% led to agglomeration, resulting in resin cavity formation and stress concentration. Full article

The thermal stability and flammability behavior of an epoxy resin, modified by the addition of Posidonia oceanica (PO) at three concentration levels (8%, 10%, 12% wt.), were investigated by performing thermogravimetric and cone calorimetry tests. The plant was preliminarily dried and milled to obtain a powder with an average size of 80 μm, then dispersed within the resin prior to curing. Scanning electron microscopy and spectroscopic FT-IR analysis on both PO and hybrid composites were carried out to verify the dispersion and the mechanisms of action of the plant within the resin. Results from TGA and cone calorimetry tests showed that the incorporation of PO reduced the thermal degradation rate by simultaneously increasing the residual weight and significantly affected the flammability of the epoxy resin, with a strong reduction in PHHR of up to 52%. Thus, the PO-modified resin at 12% wt was used to realize basalt laminate composites that demonstrated an improvement in fire performance with respect to the neat resin composites. Full article

During the machining of unidirectional carbon fiber-reinforced polymers (UD-CFRPs), their anisotropic characteristics and the complex cutting conditions often lead to defects such as delamination, burrs, and surface/subsurface damage. This study systematically investigates the effects of different fiber orientation angles (0°, 45°, 90°, and 135°) on cutting force, chip formation, stress distribution, and damage characteristics using a coupled macro–micro finite element model. The model successfully captures key microscopic failure mechanisms, such as fiber breakage, resin cracking, and fiber–matrix interface debonding, by integrating the anisotropic mechanical properties and heterogeneous microstructure of UD-CFRPs, thereby more realistically replicating the actual machining process. The cutting speed is kept constant at 480 mm/s. Experimental validation using T700S/J-133 laminates (with a 70% fiber volume fraction) shows that, on a macro scale, the cutting force varies non-monotonically with the fiber orientation angle, following the order of 0° < 45° < 135° < 90°. The experimental values are 24.8 N/mm < 35.8 N/mm < 36.4 N/mm < 44.1 N/mm, and the simulation values are 22.9 N/mm < 33.2 N/mm < 32.7 N/mm < 42.6 N/mm. The maximum values occur at 90° (44.1 N/mm, 42.6 N/mm), while the minimum values occur at 0° (24.8 N/mm, 22.9 N/mm). The chip morphology significantly changes with fiber orientation: 0° produces strip-shaped chips, 45° forms block-shaped chips, 90° results in particle-shaped chips, and 135° produces fragmented chips. On a micro scale, the microscopic morphology of the chips and the surface damage characteristics also exhibit gradient variations consistent with the experimental results. The developed model demonstrates high accuracy in predicting damage mechanisms and material removal behavior, providing a theoretical basis for optimizing CFRP machining parameters. Full article

Natural composites find application in various fields because of their low specific weight and low investment cost. But due to their inherent nature, natural composites have lower strength and tend to absorb moisture, which makes them weak. In this work, woven glass, mono-bi-filament polypropylene, and polyester fibers in an epoxy matrix were developed with four and five different stacking layers of texture utilizing the hand-layup procedure. However, understanding the directional dependence of material properties is necessary for the application of these new materials. Three distinctive plates were fabricated for the purpose of the investigation. The laminated plates were tested on a universal testing machine (UTM) and a flexible test setup to examine the mechanical properties of the polymer fiber. By adding short fibers such as polypropylene, polyester fibers in a random manner improved the mechanical strength of the polymer composite compared to the other fiber types such as woven glass fiber sheets and woven polypropylene sheets placed in the middle of the composite. This is because short polymer fibers bond well with epoxy resin and have very good bonding strength. Full article

In today’s aviation industry, research and studies are carried out to manufacture and design lightweight, high-performance materials. One of the materials developed in line with this goal is glass laminate aluminum-reinforced epoxy (GLARE), which consists of thin aluminum sheets and S2-glass/epoxy layers. Because of its high impact resistance and excellent fatigue and damage tolerance properties, GLARE is used in different aircraft parts, such as the wing, fuselage, empennage skins, and cargo floors. In this study, a survey was carried out and a low-velocity impact model for GLARE materials was developed using the ABAQUS (2014) version V6.14 software and compared with the results of low-velocity impact tests performed according to the American Society for Testing and Materials (ASTM) D7136 standard. This article introduces a novel integrated approach that combines detailed numerical modeling with experimental validation of GLARE 4A FMLs under low-velocity impact. Leveraging ABAQUS, a robust FEM featuring explicit analysis, cohesive resin interfaces, and custom VUMAT subroutines was developed to accurately simulate energy absorption, dent depth, and delamination. The precise model’s predictions align well with test results performed according to ASTM D7136 standards, exhibiting less than a 0.1% deviation in the displacement (dent depth)–time response, along with deviations of 4.3% in impact energy–time and 5.2% in velocity–time trends at 5.5 ms. Full article

In this work, the mechanical properties of jute fiber-reinforced polymers were investigated, considering two manufacturing technologies—wet layups and vacuum-assisted resin infusion—with the aim of developing cost-effective composite materials based on natural fibers. In the manufacturing process, two different types of resins were used, specific to each technology. Specimens measuring 25 mm × 200 mm were cut from the resulting laminates at three orientations (0°, 45° and 90° with respect with the weft orientation), and they were subjected to tensile tests. The results showed that resin infusion yielded superior stiffness and strength values when compared to the wet layup. Multi-scale modeling techniques were applied in order to estimate the properties of the fibers and evaluate the orthotropic properties of the composites, and virtual material models that included orthotropic elasticity and the anisotropic Hill plasticity formulation were developed and evaluated, managing to reproduce the experimental data using finite element analyses with decent accuracy. Full article