Unidirectional Composites Research Articles

Influence of Reinforcement Architecture on Behavior of Flax/PLA Green Composites under Low-Velocity Impact.

The main goal of this study is the comparison of different reinforcement architectures on the low-velocity impact behavior of green composites. The study includes the comparison of unidirectional, basket weave, and twill weave flax/PLA composites, they are subjected to unidirectional tensile tests, drop-weight impact tests, and after-impact compression tests. Results show that the unidirectional composite demonstrates superior tensile strength and initial modulus due to reduced fiber crimp, while basket weave exhibits the highest energy absorption capability and strain capacity attributed to its higher fiber-weight ratio and fiber crimp. Unidirectional composite also shows a larger impacted damage area compared to basket weave and twill weave, attributed to its internal architecture. Residual compressive strength across all composites decreased by 40% compared to the reference sample. However, the reduction in stiffness after impact was different, UD/PLA composite stiffness was reduced by 30% while the reduction in BW/PLA and T/PLA composites was about 20%.

Analysis of impact response and damage evolution in multi‐scale of novel 3D carbon fiber‐reinforced polyetheretherketone composites

AbstractThermoplastic composites have a high application demand in aerospace, marine military and other cutting‐edge industry. However, it poses a considerable obstacle in achieving three‐dimensional (3D) thermoplastic composites because of the inadequate infiltration of highly viscous thermoplastic resins. In this paper, high‐toughness Polyetheretherketone (PEEK) resin‐based 3D orthogonal carbon fiber thermoplastic composites were designed and obtained. Low‐velocity impact test was conducted on 3D orthogonal woven composite (3DOWC) under the energy levels of 5 and 10 J, and its performance was compared with that of the 2D unidirectional layup composite (2DULC) and the 2D plain layup composite (2DPLC). The results showed that 3DOWC possessed superior elastic energy absorption capacity and less damage morphology compared to 2D composites. 3DOWC had the highest contact force value of 2420.25 N at 10 J, which is 36.83% higher than that of 2DPLC. Furthermore, a finite element model in multi‐scale was established to investigate the damage evolution and failure mechanism of the 3D orthogonal woven CF/PEEK composites. The damage morphology observed in both experimental and numerical findings demonstrated that the matrix shedding, while the yarn fractured on the nonimpact side beneath the impact point. Additionally, enhancing the tensile strength of the yarn in the bottom layer can lead to further improvement in impact resistance. This work provides an innovative method for manufacturing 3D thermoplastic composites and lays the foundation for the impact simulation analysis of such composites.Highlights A novel approach was introduced for fabricating 3D carbon fiber/PEEK composites, which exhibits remarkable resistance to impact. A comprehensive investigation was conducted to evaluate the impact properties of 3D thermoplastic composite compared to 2D composite. A finite element model in multi‐scale including failure criteria was established to simulate the damage evolution.

Topology optimization of fiber-reinforced concrete structures using membrane-embedded model

Fiber-reinforced concrete is a typical unidirectional fiber-reinforced composite. For practicality and efficiency, fiber-reinforced concrete usually has the fiber and matrix modeled separately and then the fiber is embedded into the matrix. Therefore, this paper proposes a novel method to realize the topology and fiber orientation optimization for fiber-reinforced concrete structures. The optimization formulation considers two types of discrete variables, i.e., topology and fiber orientation, which are optimized by using the solid isotropic material with penalization method and bi-value coding parameterization method, respectively. To reduce the computational complexity, the topology and fiber orientation are independently updated at each iteration during the optimization process. Numerical examples verify the validity of the proposed method, which provides new ideas for the design of fiber-reinforced concrete structures.

Evaluation and optimization of flexural properties of anisotropic recycled carbon fiber card web reinforced thermoplastic hollow beams

The flexural properties of hollow beams are influenced by both the structural morphologies and the level of anisotropy of the materials. Card web carbon fiber-reinforced thermoplastics (CWTs), recognized as a promising composite for fabrication with recycled carbon fiber, demonstrate control over fiber alignment and robust mechanical properties, characterized by a wide distribution of fiber lengths. In this study, square-shaped, tube-shaped, and hat-shaped hollow beams are modeled with different geometries. Calculations are performed on different input data featuring CWTs with varying fiber alignments using a modified Mori-Tanaka model, and the results are verified with experimental data. The effects of fiber alignment, beam geometries, and beam types on the flexural properties of CWT hollow beams are evaluated and compared with unidirectional (UD) carbon fiber composites, aluminum alloys, and steel beams. The highest levels of flexural stiffness and specific flexural stiffness (indicative of the most effective lightweight property) in square-shaped and tube-shaped hollow beams were observed in CWTs with higher fiber alignment. The hat-shaped beams achieved the highest level of flexural properties at a relatively lower fiber alignment level. Comparisons with 1 mm wall-thickness steel hollow beams indicated that CWTs with specific fiber alignments could achieve a weight reduction of over 50 % while maintaining the same flexural stiffness. This performance surpasses that of UD composites and aluminum alloys.

The Influence of the Interface on the Micromechanical Behavior of Unidirectional Fiber-Reinforced Ceramic Matrix Composites: An Analysis Based on the Periodic Symmetric Boundary Conditions

The long-term periodicity and uncontrollable interface properties during the preparation process for silicon carbide fiber reinforced silicon carbide-based composites (SiCf/SiC CMC) make it difficult to thoroughly investigate their mechanical damage behavior under complex loading conditions. To delve deeper into the influence of the interface strength and toughness on the mechanical response of microscopic representative volume element (RVE) models under complex loading conditions, in this work, based on numerical simulation methods, a microscale representative volume element (RVE) with periodic symmetric boundary conditions for the material is constructed. The phase-field fracture theory and cohesive zone model are coupled to capture the brittle cracking of the matrix and the debonding behavior at the fiber/matrix interface. Simulation analysis is conducted for tensile, compressive, and shear loading as well as combined loading, and the validity of the model is verified based on the Chamis theory. Further investigation is conducted into the mechanical response behavior of the microscale RVE model under complex loading conditions in relation to the interface strength and interface toughness. The results indicate that under uniaxial loading, increasing the interface strength leads to a tighter bond between the fiber and matrix, suppressing crack initiation and propagation, and significantly increasing the material’s fracture strength. However, compared to the transverse compressive strength, increasing the interface strength does not continuously enhance the strength under other loading conditions. Meanwhile, under the condition of strong interface strength of 400 MPa, an increase in the interface toughness significantly increases the transverse compressive strength of the material. When it increases from 2 J/m2 to 20 J/m2, the transverse compressive strength increases by 28.49%. Under biaxial combined loading, increasing the interface strength significantly widens the failure envelope space under σ2-τ23 combined loading; with the transition from transverse compressive stress to tensile stress, the transverse shear strength shows a trend of first increasing and then decreasing, and when the ratio of transverse shear displacement to transverse tensile/compressive displacement is −1, it reaches the maximum. This study provides strong numerical support for the investigation of the interface properties and mechanical behavior of SiCf/SiC composites under complex loading conditions, offering important references for engineering design and material performance optimization.

A matrix failure criterion independent of empirical parameters for brittle fiber-reinforced composites

Based on Hashin's fracture plane assumption, a matrix failure criterion for brittle fiber-reinforced composites is proposed. The failure function is expressed as a quadratic polynomial of the stress components on the fracture plane. The unknown coefficients in the failure criterion are only calibrated by the three basic strengths of unidirectional composites, i.e., the transverse tensile strength, transverse compressive strength, and longitudinal shear strength, thus overcoming the limitation of requiring empirical parameters in most previous matrix failure criteria. Especially, under plane stress states (σ22,τ21), an analytical solution for the fracture angle of unidirectional composites can be provided. The prediction results of the proposed criterion are consistent with a large number of experimental data, confirming its applicability. In addition, the study establishes the relationship among the three transverse basic strengths (Yt, Yc and S23). It can be used to predict S23 which is difficult to measure experimentally.

Evaluating Sisal Fiber-Reinforced Gypsum Composites for Water Absorption and Mechanical Performance

There has been a great research interest for investigation of new construction materials which can reduce environmental impact and cost, with improved structural performance. Recently, sisal fiber is being used as a reinforcement material in the development of reinforced composites. Here, sisal fiber-gypsum reinforced composites were prepared using the hand lay-up method followed by the compression technique. The effects of weight percentage (Wt. %) of the sisal fiber reinforcement on the mechanical properties of the developed sisal fiber-gypsum composites were investigated experimentally by varying the Wt. % as 5, 10, and 15%. The mechanical properties were tested as per the ASTM standards. The results revealed that the long unidirectional sisal fiber-gypsum composites exhibited higher impact and hardness strengths with lower water absorption behaviour than the short-chopped sisal fiber-gypsum composites. In addition, the impact strength increased with increase in Wt. % for both short-chopped and long unidirectional sisal fiber reinforcement. While the hardness strength decreased with increase in Wt. % for both short-chopped and long unidirectional sisal fiber. The experimental investigation has established sisal fiber as an important reinforcement material for improving the performance of the neat gypsum in a wide range of architectural applications such as ceilings, decorative partitions, and light covers.

Bioabsorbable Composite Laminates of Poly‐Lactic Acid Reinforced with Surface‐Modified Mg Wires for Orthopedic Implant Applications

Unidirectional and multidirectional laminates of Mg‐wire‐reinforced poly‐lactic‐acid–matrix composites are manufactured by an improved compression molding strategy that allows excellent control on the position and orientation of the wires. Two different types of Mg wires, with and without surface modification by continuous plasma electrolytic oxidation, are used, the former to improve the interfacial strength and to reduce the degradation rate of Mg wires in biological environments. The mechanical properties of the constituents as well as of composites are measured before and after in vitro degradation by immersion in simulated body fluids and the corresponding deformation, fracture, and degradation mechanisms are analyzed in detail. It is found that the presence of the Mg wires improves the mechanical behavior in tension and compression of unidirectional composites in the longitudinal direction (close to cortical bone) and that quasi‐isotropic laminates with tailored properties can be designed from the data of unidirectional composites.

Energy transfer and release during the fracture of UD fiber-reinforced thermoplastic composites

This study delves into the complex dynamics of energy transfer and release during the fracture of unidirectional (UD) fiber-reinforced thermoplastic composites. Conducted through meticulous experimental observations and rigorous energy analysis, the research presents groundbreaking conclusions on the fracture toughness and energy conversion efficiency of UD carbon fiber composites under various loading conditions. A prominent focus is on how these mechanical properties are intricately linked to the sample’s fiber orientation angles and the external conditions applied during testing.The work employed tapered double cantilever beam (TDCB) as the far-field boundary to investigate the energy changes, transfer, and conversion processes during the crack propagation of unidirectional fiber reinforced thermoplastics (UDFRTPs) structures. It was found that throughout the entire propagation process, blunt extension occurs first followed by inertial extension. This is because in the initial stage of crack propagation, the stored elastic energy in the structure is relatively small, making the crack tip prone to blunting. This continuous blunting impedes the release of internal strain energy in the structure, with blunt extension accounting for a very small proportion of the entire fracture process. When the internal strain energy in the structure continues to increase to a certain extent, the blunting of the crack tip cannot prevent the release of a large amount of elastic energy inside the structure. At the same time, the excess released strain energy converts into kinetic energy and continually impacts the blunted region at the crack tip. At this point, the propagation transitions into the inertial extension stage, which occupies a significant portion of the entire fracture process.

Optimization of fibre orientation for composite reinforcement of circular hollow section KT-joints

PurposeComposite materials are effective alternatives for rehabilitating critical members of offshore platforms, bridges, and other structures. The structural response of composite reinforcement greatly depends on the orientation of fibres in the composite material. Joints are the most critical part of tubular structures. Various existing studies have identified optimal reinforcement orientations for a single load component, but none has addressed the combined load case, even though most practical loads are multiplanar.Design/methodology/approachThis study investigates the optimal orientation of composite reinforcement for reducing stress concentration factors (SCF) of tubular KT-joints. The joint reinforcement was modelled and simulated using ANSYS. A parametric study was carried out to determine the effect of the orientations of reinforcement in the interface region on SCF at every 15° offset along the weld toe using linear extrapolation of principal stresses. The impact of orientation for uniplanar and multiplanar loads was investigated, and a general result about optimum orientation was inferred.FindingsIt was found that the maximum decrease of SCF is achieved by orienting the fibres of composite reinforcement along the maximum SCF. Notably, the optimal direction for any load configuration was consistently orthogonal to the weld toe of the chord-brace interface. As such, unidirectional composites wrapped around the brace axis, covering both sides of the brace-chord interface, are most effective for SCF reduction.Originality/valueThe findings of this study are crucial for adequate reinforcement of tubular joints using composites, offering a broader and universally applicable optimum orientation that transcends specific joint and load configuration.

Tensile and impact properties of thermoplastic fibre hybrid composites based on air textured commingling hybrid yarns composed of carbon/aramid/polyamide 6 and carbon/glass/polyamide 6 filament yarns

This paper reports a comparison of tensile and impact properties between carbon/aramid and carbon/glass fibres reinforced unidirectional thermoplastic hybrid composites. For this purpose, different hybrid composites were produced using commingled hybrid yarns of carbon/aramid/polyamide 6 filament yarns and carbon/glass/polyamide 6 filament yarns with a defined mixing ratio based on air texturing technology. The results show that the density and specific Youngs’ modulus of the composites changes linearly with the proportion of carbon/glass and carbon/aramid fibre in hybrid composites. The specific Young’s modulus decreases linearly with decreasing carbon fibre content in the hybrid composites. On the other hand, the specific tensile strength does not change linearly according to the rule of mixture and a negative hybridization effect can be observerd for both types of hybrid composites. Furthermore, the combination of carbon/aramid and carbon/glass fibres can increase the impact strength by approximately 204% and 218%, respectively, compared to the composite reinforced by CF only. Although the specific tensile strength and specific impact strength of carbon/aramid reinforced hybrid composites are higher than those of CF/GF hybrid composites due to the lower density of carbon/glass hybrid composites, the potential impact strength achievable in hybrid composites is higher with the carbon/glass combination than with the carbon/aramid combination.

Statistical analysis, regression, and neural network modeling of the tensile strength of thermoplastic unidirectional carbon fiber-polysulfone composites

Statistical analysis, regression, and neural network modeling of the tensile strength of thermoplastic unidirectional carbon fiber-polysulfone composites

High-speed drilling mechanism study of unidirectional CoCrFeNiAl fiber-reinforced aluminum matrix composites

High-speed drilling mechanism study of unidirectional CoCrFeNiAl fiber-reinforced aluminum matrix composites

A novel modeling method to study compressive behaviors of 3D braided composites considering effects of fiber breakage and waviness defects

Fiber breakage and waviness defects are two significant and inevitable defects existing in three-dimensional braided composites (3DBCs). This work proposed a new method to create the numerical model containing fiber breakage and waviness defects at the micro-scale level according to experimental characterization results. The experimental tests of 3DBCs with various braiding angles and matrix types are then designed to verify the reliability and adaptability of the model. The results indicate that the fiber breakage and waviness defects both gave rise to an apparent decrease in the axial mechanical properties of the unidirectional and braided composites. The influences of two kinds of defects on 3DBCs are also related to the braiding angles. In addition, the effect of matrix type on the 3DBC is apparent that should not be neglected. The primary reasons of the change of compressive properties of 3DBCs with different matrix types are the variations of the matrix and interfacial properties. The proposed modeling method in this work can be extended for those composites that include a large quantity of fiber breakage and waviness defects.

Model prediction of unidirectional fiber-reinforced composites under finite deformation

The intuitive knowledge is that the mechanical modulus of unidirectional fiber-reinforced composites (UD-FRPs) decreases with higher fiber orientation angles. However, numerical results in this work and experimental results in previous literature indicate that the mechanical response of UD-FRPs has a U-shaped dependence on fiber orientation angle. To explain this phenomenon, we develop an anisotropic model to capture the mechanical behavior of UD-FRPs. The strain energy is decomposed into four components: matrix, fiber, fiber-matrix normal, and shear interactions. Each component can be determined by matching the mechanical responses of unit cells with 0°, 45°, and 90° off-axis. The results obtained from the presented model match well with the numerical response of unit cells with 15°, 30°, 60°, and 75° off-axis. With an increasing fiber orientation angle, the matrix part remains unchanged, the fiber component decreases, but the fiber-matrix normal component increases, and the fiber-matrix shear component increases and then decreases. The change in strain energy contributions explains the mechanism of the U-shaped dependence of the mechanical response on fiber orientation angle.

Response Surface Methodology Optimization of Resistance Welding Process for Unidirectional Carbon Fiber/PPS Composites.

The use of thermoplastic composites (TPCs) as one of the lightweight solutions will inevitably encounter problems in connection. Resistance welding has the characteristics of high strength, simplicity, and high reliability, and is considered a very potential hot-melt connection technology. The resistance welding technology of unidirectional carbon fiber-reinforced polyphenylene sulfide composites (UCF/PPS) was systematically studied. The experimental results show that the 100-mesh brass mesh has the best resin wetting effect and heating efficiency, and the PPS/oxidized 100-mesh brass mesh composite resistance element (Ox-RE/PPS) has the highest welding strength. The welding failure mode changes from interface failure and RE failure to interlayer structure damage and fiber fracture. The single-factor experimental results show that the maximum welding strength is reached at 310 °C, 1.15 MPa, and 120 kW/m2. According to the conclusion of the single-factor experiment, the Box-Behnken method was further used to design a three-factor, three-level experiment, and a quadratic regression model was established according to the test results. The results of variance analysis, fitting curve analysis, and perturbation plot analysis proved that the model had high fitting and prediction abilities. From the 3D surface diagram analysis, the influence of power density is the largest, and the interaction between welding temperature and power density is the most significant. Combined with the analysis of Design Expert 13 software, the optimal range of process parameters was obtained as follows: welding temperature 313-314 °C, welding pressure 1.04-1.2 MPa, and power density 124-128 kW/m2. The average strength of resistance welding joints prepared in the optimal range of process parameters was 13.58 MPa.

Tensile strength prediction of unidirectional polyacrylonitrile (PAN)-based carbon fiber reinforced plastic composites considering stress distribution around fiber break points

Recent advancements in enhancing the mechanical characteristics of carbon fibers open up new application possibilities for carbon fibre-reinforced plastic (CFRP) composites. Particularly in unidirectional CFRPs, which form the basal structure of CFRP laminates, developing a micromechanics model capable of predicting the tensile strength of unidirectional CFRPs based on carbon fiber mechanical characteristics is a current aspiration. This study conducted a stress distribution analysis around the fiber fracture point to predict the tensile strengths of unidirectional CFRPs prepared with five types of polyacrylonitrile (PAN)-based carbon fibers, each with unique mechanical characteristics. Numerical simulation results obtained using a unidirectional CFRP model that considered the stress concentration, fiber axial stress, and bimodal Weibull distribution were reasonably consistent with the experimental results for the tensile strengths of unidirectional CFRP composites, regardless of the differences in the mechanical characteristics of the fiber. Our findings can provide guidance for designing further enhanced high-performance CFRP materials.

A micromechanical study on shear performance of unidirectional composites with randomly distributed fibers in the transverse cross‐section

AbstractThe properties of unidirectional (UD) composites has been investigated by analyzing their elastic and strength characteristics under shear loading. The UD fiber‐reinforced polymer (FRP) composites usually consist of fibers randomly dispersed throughout the cross‐section in the transverse direction which is generally not accounted for. A micromechanical model based on finite element analysis (FEA) approach is utilized here to examine these properties. The study begins by identifying micro scale unit cells or repetitive unit cells (RUCs) at the micro scale, as well as representative volume elements (RVEs). The distribution of fiber volume fraction (Vf) varies among various micro scale unit cells positioned in the transverse cross‐section. The elastic properties and strength are estimated by considering the properties of the matrix and fibers, and the configuration of micro scale unit cells, which feature a fiber arrangement which is categorized as hexagonal and varying Vf at different locations (from 0.35 to 0.75). However, the overall Vf for the UD composite remains constant at 0.65. Studies are also carried out with the random distribution of fibers at micro scale unit cells. The findings reveal that the random distribution of fibers significantly impacts the shear behavior of the composite. This investigation provides valuable insights into how the mechanical properties of the UD composite are subjective by the distribution of fiber, thereby contributing to the design and development of this light weight high‐performance material.Highlights Elastic and strength analysis of UD composites is presented. Emphasis is on fiber dispersion in transverse plane. Microscale unit cells, RUCs and RVE are identified. Studies are carried out based on micromechanical model. Influence of fiber distribution on shear behavior is investigated.

Investigations on the development of impact-resistant thermoplastic fibre hybrid composites from glass and steel fibre

With the increased use of fibre reinforced composites (FRP), the design of new generation of composite structures with high stiffness and a ductile material behaviour is required to cope with complex load scenarios and high damage tolerances. This can be achieved, in particular, by a combination of conventional fibre-reinforced composites (FRP), which possess high stiffness and strength with metallic materials characterized by their high ductility and associated higher energy absorption capacity. Currently, there are no solutions for hybridisation of high performance filament yarns, metal filament yarns and thermoplastic filament yarns on micro level. Therefore, the main objective of this study is to develop a fibre hybrid composite based on hybrid yarn consisting of glass, steel and polypropylene filament yarns and to compare its tensile and impact properties with those of the composite reinforced only with glass filament yarn. The tensile and impact properties of the unidirectional hybrid composites produced from the developed multi-material hybrid yarn consisting of steel, glass and polypropylene filament yarns are compared with those of a non-hybrid composite reinforced exclusively with glass filament yarn. The results show that by hybridising with steel fibres a characteristic post-failure behaviour can be achieved, so that the developed multi-material hybrid yarns have a high potential for use in composites with high crash and impact performance requirements, where safety demands are essential.

A Comprehensive Study on the Optimization of Drilling Performance in Hybrid Nano-Composites and Neat CFRP Composites Using Statistical and Machine Learning Approaches

Carbon fiber-reinforced polymer (CFRP) composites have gradually replaced metals due to their exceptional strength-to-weight ratio compared to metallic materials. However, the drilling process often reveals various defects, such as surface roughness, influenced by different drilling parameters. This study explores the drilling quality of uni-directional CFRP composites, as well as hybrid Al2O3 alumina and hybrid SiC silicon carbide nano-composites, through experimental exploration using step, core, and twist drills. Response surface methodology (RSM) and statistical tools, including main effect plots, ANOVA, contour plots, and optimization techniques, were used to analyze the surface roughness of the hole. Optimization plots were drawn for optimal conditions, suggesting a spindle speed of 1500 rpm, feed of 0.01 mm/rev, and a 4 mm drill diameter for achieving minimum surface roughness. Furthermore, two machine learning models, artificial neural network (ANN) and random forest (RF), were used for predictive analysis. The findings revealed the robust predictive capabilities of both models, with RF demonstrating superior performance over ANN and RSM. Through visual comparisons and error analyses, more insights were gained into model accuracy and potential avenues for improvement.