Composite Laminates Research Articles

The effect of glow discharge air plasma surface treatment on mechanical properties of natural fiber reinforced-epoxy sustainable biocomposites

ABSTRACT Natural fiber composites are widely explored sustainable alternative to conventional composites in many applications. However, since they are weak compared to conventional composites, various surface treatments are adopted to improve their overall mechanical properties. The effect of glow discharge air plasma treatment of banana and pineapple leaf (PALF) natural fibers is investigated and presented in this study. Fibres were treated for different time periods, their surface were analysed, and composite laminates with standalone and hybrid were fabricated. Tensile, flexural and impact tests in different combinations of reinforcements were carried out. Spectroscopic, thermal and microscopic characterisations like Fourier-transform infrared spectroscopy (FT-IR), X-Ray diffraction (XRD), Thermogravimetric analysis (TGA), Field Emission Scanning Electron Microscopy (FESEM) were used to study the fibre surface, 3D digital microscope was used to study the fractography and a water absorption test was carried out to study the hydrophilicity were carried out to characterise the fibre surface and the laminates. Significant variations in thermal stability and improvements in tensile strength (even up to 275%) and flexural properties were observed. This investigation revealed the cause of the same was due to the enhancement in crystallinity, mechanical interlocking and improved fibre-matrix adhesion, which was evident from characterizations.

Computational and Experimental Investigation & Analysis on the Effect of Milled Basalt Fibre Fillers on Static Flexural Properties of the Natural Fibre Composites for Aerospace and Automobile Industrial Applications

Academic and industry researchers are focused on developing a material that satisfies various parameters such as durability, manufacturability, low cost, lightweight, adaptability, high strength, bio-degradability, etc. to meet the current day trends across aerospace and automotive industries. In engineering and technology, fiber-reinforced matrix composites and their applications are extensive. The addition of fillers (both natural and synthetic) along with matrix and fibers is considered to be a better option to increase the efficiency and performance of the composite materials. Recently, researchers have focussed on adding fillers along with matrix and its hybridization to lift the composite properties and applications. This research paper describes the computational and experimental investigation & analysis on the effect of milled basalt fibre fillers on static flexural properties of the natural fibre composites for aerospace and automobile applications. As a first step, an optimized milled filler percentage is examined by incorporating the basalt milled filler into the epoxy laminates from 0.5% to 3% weight percentages concerning epoxy laminates. Finally, the 1% filler incorporated epoxy laminates showed better results than the base samples. Then, the 1% milled basalt filler material was incorporated into basalt fiber and areca fiber with epoxy resin and hardener to make the composite laminates for static testing. The static testing was carried out with the help of a Universal Testing Machine (UTM) i.e. the three-point bending test. The filler-incorporated basalt and areca nut epoxy composite laminates show higher flexural properties than the base samples with 0% filler material. The project work was also carried out with the help of ANSYS software with proper filler material and epoxy composite laminates for static testing. The flexural properties of the filler-incorporated composite laminates show higher properties than the base samples. Results reveal that the flexural properties of the composite laminates from experimental testing and software analysis are of less error percentage difference. Key Words: Composite materials & structures, Matrix, Fibres, Fillers, Mechanical properties, Static testing, Flexural properties and ANSYS

Simulating delamination in composite laminates with fracture process zone effects: A novel cohesive zone modeling approach

Simulating delamination in composite laminates with fracture process zone effects: A novel cohesive zone modeling approach

Resistance of CNT film toughened composite laminates under high-speed impact: Experimental and numerical study

Resistance of CNT film toughened composite laminates under high-speed impact: Experimental and numerical study

A geometry projection method for the topology optimization of additively manufactured variable-stiffness composite laminates

A geometry projection method for the topology optimization of additively manufactured variable-stiffness composite laminates

Effect of Double-Vacuum-Bag Process on the Void Evolution in Composite Laminates

Effect of Double-Vacuum-Bag Process on the Void Evolution in Composite Laminates

A Hybrid Deep Transfer Learning Framework for Delamination Identification in Composite Laminates

A Hybrid Deep Transfer Learning Framework for Delamination Identification in Composite Laminates

A Partial-Periodic Model for Predicting Structural Stiffness of Composite Laminate Beam Structures

A Partial-Periodic Model for Predicting Structural Stiffness of Composite Laminate Beam Structures

Tensile properties and failure of hybrid fiber reinforced polymer composite laminate with different fiber types, hybrid ratios, and stacking sequences

AbstractHybrid fiber‐reinforced polymer (HFRP) composites are gaining attention due to their impressive strength and stiffness with low density. However, their high‐strength often comes with reduced toughness, and achieving a balance between these properties involves combining fibers using hybrid methods. This study used fabricating HFRP laminates (carbon/Kevlar, carbon/glass, and carbon/glass/Kevlar) with different stacking sequences and hybridization ratios created through molding, followed by tensile testing to evaluate the mechanical behavior. The results showed that hybridization ratios significantly influenced the tensile strength, modulus, and elongation at break. For example, compared to the single Kevlar fiber composites, the tensile strength and tensile modulus of the laminate with the optimal configuration of carbon/Kevlar fiber‐reinforced composites increased by 102.93% and 131.65%, respectively, and the elongation at break decreased by 76.13%. This improvement was attributed to the synergistic effect of combining carbon fibers with Kevlar fibers through effective hybridization. The stacking sequences also had a significant effect on tensile strength and elongation at break, although the effect on the tensile modulus was weaker. Additionally, the different tensile properties were obtained by inter hybridization between the three types of fibers. Microscopic observations provided insights into the fracture behavior of HFRP, highlighting phenomena such as brittle/ductile fracture, delamination, fiber pullout, crack suppression, and potential interactions. These observations underscored the complex mechanics governing the mechanical performance of HFRP.Highlights The tensile properties of HFRP laminates with carbon fiber, glass fiber, and Kevlar fiber hybrids are studied. The effect of hybridization parameters on the tensile properties of HFRP are studied. Indicators of the tensile properties of HFRP laminates are compared and analyzed. The hybrid effect and interaction failure mechanism of HFRP are revealed.

Study on the measurement method of internal strain in carbon fiber laminate

Abstract Aiming at the characteristics of orthotropic anisotropy, multiangle and multilayer of carbon fiber composites, based on the relevant theories of mechanics of materials and mechanics of composites, a method of calculating the strain in the main direction of each ply inside the carbon fiber composite laminate by using the strain measured in the reverse order of the surface layer is proposed. In this study, carbon fiber composite laminates with different lay-up angles and thicknesses are selected as test objects, and the accuracy of the strain gauge measurement and rotational axis calculation method is verified by comparing the measured values of extensometer with those of the carbon fiber strain gauge that are different in the surface pasting direction. HyperMesh finite element software was used to simulate and solve the strain values in the main direction of the internal layers and compared with the strain in the main direction of the internal layers based on the surface strain measurement, which proved the validity of the method of calculating the strain in the main direction of the internal layers based on the surface strain measurement in inverse sequence.

Thermal buckling of composite laminates with elastic boundaries

AbstractThe investigation of thermal buckling in composite laminates holds significant theoretical and practical implications. For the commonly encountered rectangular thin plate structures in engineering, this study aims to explore their buckling characteristics under thermal loads in arbitrary elastic boundary conditions. To achieve this, a method based on the principle of minimum potential energy for calculating the buckling load during elastic instability is presented. Initially, transverse constraint springs and rotational constraint springs are set at the four boundaries of the plate structure model, with the stiffness values of these two types of elastic springs designated to simulate arbitrary elastic boundary conditions. The improved Fourier series is employed to address potential discontinuities in the boundary derivatives of displacement functions that may arise with the classical Fourier series form. Subsequently, the potential energy expression for the rectangular plate system is established. By combining this with the principle of minimum potential energy, a system of linear equations is derived through partial differentiation of the unknown Fourier coefficients. Finally, the critical buckling load and other parameters of the rectangular plate are obtained, with reasonable values for the spring stiffness under different boundary conditions provided. The critical buckling temperatures derived from the proposed method are compared with those obtained via finite element analysis. The results indicate that the buckling loads obtained using this method align closely with those from finite element analysis, affirming the validity and convergence of the research methodology.Highlights This study investigates the thermal buckling of composite laminate plates with elastic boundary conditions. Improved Fourier series techniques are employed to analyze thermal buckling in these laminates. The impact of intermediate stiffness on the thermal buckling response of composite materials is examined.

Experimental investigation on the impact resistance and damage mechanism of carbon/glass unidirectional and woven hybrid laminates

AbstractThe mechanical properties of hybrid fiber composite laminates are affected by the hybrid ratio as well as the stacking sequences, to investigate the effect. In this paper, the effects of the hybrid ratio and stacking sequences on the impact resistance and residual compression properties of carbon/glass unidirectional and woven hybrid laminates are investigated. The use of acoustic emission technology enables the real‐time monitoring of the impact and compression damage processes of carbon/glass composite laminates with varying hybrid ratios and stacking sequences, thereby facilitating the elucidation of the underlying failure mechanisms and the evolution of the laminates. The findings indicated that laminates with symmetrical stacking demonstrated superior impact resistance, resilience, and residual compression properties compared to those with asymmetrical stacking when subjected to high‐energy impact. Sandwich stackings demonstrate superior energy absorption properties relative to alternate‐stacking laminates, although they exhibit diminished residual compression properties. The impact resistance of laminates with a high carbon content under a sandwich stacking sequence is poor. In the context of alternating symmetric stacking, the impact resistance of the laminate is not significantly influenced by the carbon content. The results of the acoustic emission analysis indicate that the damage is minimized when the stacking sequence is alternating symmetry and the impact side is a woven material.Highlights Enhancing impact resistance of composites through hybrid structure research. Report the optimal parameters of the effects on the impact resistance of the composite. The VMD method is used to determine the percentage of damage types in the laminate.

High‐velocity impact response and damage behavior of bio‐inspired helicoidal composite laminates: Experimental and numerical investigation

AbstractBio‐inspired helicoidal composite laminates have been found to have better impact resistance and energy absorption than conventional laminates. To study the impact responses and damage behaviors of bio‐inspired helicoidal composite laminates under high‐velocity impact, the composite laminates with three helix angles were designed and tested. Two types of light‐gas gun were used to provide low and high impact energies, the velocity was measured using a velocimeter and the damage to the laminate profile was observed by scanning electron microscopy. Numerical simulation is then used to simulate the damage behavior of the helicoidal laminates based on the Hashin failure criterion and the revised dynamic increase factor. The results show that: under an impact of low energies, the helicoidal mechanism serves to absorb the impact energy through the generation of additional delamination. The laminates with the helix angle of 15° exhibits the maximum delamination area and the minimum residual velocity. However, under the impact of higher energies, the helicoidal mechanism is unlikely to improve the energy absorption and will inhibit the delamination damage. The laminates with the helix angle of 45° have the greatest inhibitory effects on delamination damage, with a delamination area reduction of 35.41%. Due to these differences, therefore, the use of helicoidal laminates should be more cautious in high‐velocity impact resistance and better avoid high‐energy situations. These findings can support the design of novel impact resistance structures.Highlights High‐velocity impact tests and FEM simulation of helicoidal laminates are carried out Damage behaviors and failure mechanism of helicoidal laminates are studied Delamination and fiber breakage are the main failure modes The laminates with the helix angle of 15° has the best impact resistance.

Critical review of interlaminar damage process and failure analysis in fiber-reinforced composite laminates encompassing fiber-bridging phenomenon

Metallic structures are increasingly being replaced by fiber-reinforced composites for the design of advanced structures with superior mechanical and physical properties. Fibrous composites offer several advantages, including lightweight feature while maintaining mechanical strength, resistance to damage evolution, and high fracture tolerance. Delamination growth in laminated composites is sometimes accompanied by fiber bridging which provides additional resistance against delamination growth. Delamination is known as one of the primary causes of premature failure in laminated composites. It is therefore necessary to gain a comprehensive understanding of interlaminar damage. Much research has been done to study various characteristics of fiber bridging yet the challenge remains an open topic for continued research. This review article aims to report the major studies on fiber bridging of composite materials in the literature. This article starts with an introduction to various modes of failure observed in fiber-reinforced laminated composites, extrinsic and intrinsic damage mechanisms, and the delamination phenomenon in the presence of fiber bridging. Next, different experimental and numerical methods for the characterization of delamination are presented. Fatigue-driven delamination, a leading cause of failure in aerospace structures, is subsequently reviewed. The paper concludes with a review of practical applications of numerical methods for delamination analysis followed by a review of recent progress in this field as well as open challenges in modeling, simulation, and experimental research works on the mechanics of fiber bridging incorporating composite damage and failure.

Mechanical and microstructural characterization of sisal fiber-reinforced polyester laminate composites for improved durability in automotive applications

This study investigates the effects of fiber concentration and the stacking sequence of laminae on the mechanical properties of a sisal-reinforced polyester composite. The mechanical properties, such as the tensile, flexural, and impact strength were characterized for laminated composite with different fiber concentrations and stacking sequences of lamina after they were processed using the hand layup weaved method. In addition to the mechanical properties, morphological analysis was done. Specimens with different fiber concentrations and stacking sequences were prepared using a manual compression molding technique that provides a flat plate with a thickness of 5 mm. The results showed that 40 wt% of sisal fiber-reinforced composites with 90/0/45 staking sequence have shown the maximum tensile (68.409 MPa), flexural (64.276 MPa), and impact (67.71 MPa) strength, and laminated composite with 90/0/45 staking sequence has shown superior tensile, flexural and impact properties as it compared with randomly oriented and non-woven fiber reinforced composite. The microstructure showed that a better interface adhesion was observed at 40 wt% of fiber and 90/0/45 staking sequence. Therefore, 90/0/45 laminated composite materials can be proposed for engineering applications that require equivalent properties, including automobile front-fender applications.

Effect of ply orientation on impact resistance of woven GFRP composites subjected to projectile impact

The focus of this paper is to present experimental and numerical investigations on the effect of fibre orientation on ballistic resistance and energy absorption capacity of glass fibre reinforced polymer (GFRP) panels. Experiments were conducted on three different GFRP laminates made of woven fabric with cross ply, angle ply and combination of cross ply and angle ply (hybrid) with dimensions of 140 mm ×140 mm ×1 mm (thick) subjected to projectile impact with 12 mm spherical projectile using single-stage gas gun setup. In each case of cross ply, angle ply and hybrid composite laminates, six experiments with nearly same velocities (52, 55, 58, 62.5, 65 and 68 m/s) were conducted and the experiments exhibited denting and perforation. The numerical analysis was carried out using LSDYNA non-linear finite-element code considering strain rate effects based on Cowper-Symonds relation. The residual velocity, ballistic limit, energy absorption capacity and damage area of GFRP laminates obtained from numerical analysis is compared with experimental results.

Laser-induced graphene as an embedded sensor for impact damage in composite structures assisted by machine learning

Laser-induced graphene (LIG) enables the creation of cost-effective sensing devices via one-step laser scribing on organic substrates. This work aims to demonstrate the feasibility of LIG as an embedded damage sensor in structural composite materials. LIG was produced on an inexpensive cork substrate using a low-power blue light laser engraving system. The LIG was characterised to establish the relationship between the LIG’s physical properties and the lasing parameters. Using the lasing parameters which offer the optimal LIG properties, a LIG mesh pattern lased on the cork substrate was embedded in a glass fibre composite laminate as the damage-sensing core material to assess its sensing capability for impact damage. By measuring the electrical resistance change in the LIG mesh pattern consisting of a series of horizontal and vertical channels before and after impact loading, it was able to define the location of internal damage and its damage size, validated by X-ray computed tomography results. It is demonstrated that the test data can be used to train a machine learning algorithm to develop a simple damage-sensing system with a high accuracy rate of 94.3%, which significantly reduces the manual effort for large-scale composite structural health monitoring. This simple damage sensing system can be used to monitor internal impact damage in composite structures, such as off-shore wind turbine blades, which are inaccessible for inspection by conventional non-destructive testing.

Enhancing structural performance of recycled fiber-reinforced thermoplastic composite part through incorporating composite laminate precuts

The mechanical recycling process of fiber-reinforced composite parts involves shredding long continuous fibers into shorter discontinuous fibers. Since the performance of the shredded short fibers is not as high as that of the original long fibers, the application of recycled composites is limited. The objective of this study is to enhance the structural performance of recycled composite parts by integrating of a set of continuous fiber composite precuts during the molding process. The 2-dimentional precuts were positioned in the structurally critical regions of the recycled composite part, and the remaining area was then filled with shredded composite material. An aircraft overhead bin door pin bracket was used as the part geometry. The mechanically recycled material and the precuts were made from 60% by weight carbon fiber reinforced polyetherketoneketone (PEKK) composite. Three different combinations of precuts were designed to create the pin bracket, and their performance was assessed by mechanical testing of the pin bracket. Additionally, digital image correlation (DIC) technology was used to analyze local strain changes and investigate the failure mechanisms of the parts throughout the testing process. The test results demonstrated that the inclusion of properly designed precuts significantly improved the performance of the recycled composite part.

Ply Optimization of Composite Laminates for Processing-Induced Deformation and Buckling Eigenvalues Based on Improved Genetic Algorithm.

The structure of thermoset composite laminated plates is made by stacking layers of plies with different fiber orientations. Similarly, the stiffened panel structure is assembled from components with varying ply configurations, resulting in thermal residual stresses and processing-induced deformations (PIDs) during manufacturing. To mitigate the residual stresses caused by the geometric features of corner structures and the mismatch between the stiffener-skin ply orientations, which lead to PIDs in composite-stiffened panels, this study proposes a multi-objective stacking optimization strategy based on an improved adaptive genetic algorithm (IAGA). The viscoelastic constitutive model was employed to describe the modulus variation during the curing process to ensure computational accuracy. In this study, the IAGA was proposed to optimize the ply-stacking sequence of L-shaped stiffeners in composite laminated structures. The results demonstrate a reduction in the spring-in angle to 0.12°, a 50% improvement compared to symmetric balanced stacking designs, while the buckling eigenvalues were improved by 20%. Additionally, the IAGA outperformed the traditional non-dominated sorting genetic algorithm (NSGA), achieving a threefold increase in the Pareto solution diversity under identical constraints and reducing the convergence time by 70%. These findings validate the effectiveness of asymmetric ply design and provide a robust framework for enhancing the structural performance and manufacturability of composite laminates.

Evaluation of Mechanical Properties of Sabai Grass (Eulaliopsis binata) Fibers and Epoxy Resin Composite Laminates Using Fly Ash as Filler Material

The integration of sabai grass fibers and fly ash in epoxy resin combines the strengths of both materials for developing a tailor-made composite laminate that balances performance, sustainability, and cost-efficiency. This innovative blend of natural fibers and industrial waste promotes environmental conservation. The laminates produced could also be used in diverse industrial and structural applications. This study investigated the mechanical properties of composite laminates reinforced with sabai grass fibers, fly ash filler, and epoxy resin as the matrix. In this work, the hand lay-up method was used to fabricate composites with two stacking configurations ((0°/0°/0°/0°) and (0°/90°/90°/0°)) and filler contents of 1.5 wt.%, 3 wt.%, and 5 wt.%. Various weight fractions of fly ash filler and sabai grass fiber were integrated into the epoxy resin to evaluate their impact on tensile strength, flexural strength, and hardness. The experimental results indicate that adding fly ash significantly improves the composite’s hardness to 27 HV in the composites containing 5 wt.% filler, while sabai grass fibers contribute to enhanced tensile strength and flexural strength. The composites with (0°/0°/0°/0°) fibers and 5 wt.% filler showed a higher tensile strength of 63.5 MPa and flexural strength of 118.5 MPa. The fractured sample was analyzed with the help of FESEM images. The XRD analysis confirmed the presence of fly ash components suitable for forming a bond with epoxy. EDX was conducted to determine the elemental composition of the fly ash. FTIR analysis verified the removal of impurities such as dust, dirt, and lignin from the fiber surface following NaOH treatment.