Carbon Fiber-reinforced Laminates Research Articles

Impact Behavior and Residual Strength of PEEK/CF-Laminated Composites with Various Stacking Sequences.

Carbon fiber-reinforced composites are popular due to their high strength and light weight; thus, the structures demonstrate high performance and specific strength. However, these composites are susceptible to impact damage. The objective of this research was to study the behavior of carbon fiber-reinforced laminates based on a polyetheretherketone (PEEK) matrix with six stacking sequences under static and impact loading. Four-point bending, short-beam bending, drop weight impact, and compression after impact tests were carried out. The results were complemented with digital shearography to estimate the damaged areas. Finite element modeling served to assess the failure mechanisms, such as fiber and matrix failure, in different layers due to tension of compression. Three behavior pattern of layups under drop-weight impact were found: (i)-energy redistribution due to mostly linear behavior (like a trampoline) and thus lower kinetic energy absorption for damage initiation, (ii)-moderate absorption of energy with initiation and propagation of concentrated damage with depressed redistribution of energy in the material, (iii)-moderate energy absorption with good redistribution due to initiation of small, dispersed damage. The results can be used to predict the mechanical behavior of composites with different stacking sequences in materials for proper structural design.

Material characterization of cyanate ester material for structures with high dimensional stability requirements

The degradation temperature, cure kinetics, viscosity, shrinkage, thermal expansion, and the modulus of RS-36-1 (modified epoxy), RS-3C and RS-3 (cyanate esters) are measured to evaluate the dimensional stability of these materials. L-shape carbon fibre-reinforced laminates with these polymer matrices are manufactured using Out-of-Autoclave (OoA) Vacuum Bag Only (VBO) processing and the spring-in angle is measured. Upon heating, cyanate ester resins experience expansion followed by shrinkage, which brings the overall shrinkage close to zero. Their coefficient of thermal expansion is found to be lower in comparison to the epoxy material, showing the lowest amount of spring-in. Finite Element simulation using COMPRO CCA is performed and the results are compared to the measurements performed on L-shape laminates. The methodology described herein shows phenomenological insight on the cyanate ester materials and the possibility to predict the effect of residual stresses during processing of composite parts, demonstrating high dimensional stability of cyanate esters.

A Machine Learning Model for Flaw Identification in Fibre-Reinforced Composites

A Haar cascade classifier is a machine learning (ML) algorithm used for object detection. In this paper, the Haar algorithm is introduced in the context of a non-destructive evaluation of fibrereinforced composite (FRC) structures. The Haar learning model is used for flaw identification from thermal images. Thermal images are created from cross-ply (CP) carbon fibre-reinforced laminates with flat-bottomed holes (6–10 mm) of different depths from the surface (0.5–1.5 mm). After training is complete, the model successfully detects similar artificial flaws in previously unseen thermal images. In doing so, the feasibility of Haar classifiers for automatic evaluation of FRCs is established.

Numerical investigation of the Mode I/Mode II fracture behavior of the hybrid composite joints with a hybrid bondline

In this study, the fracture behavior of fracture characterization bonded joints consisting of hybrid composite adherends and hybrid bondlines under Mode I and Mode II loadings were investigated numerically. Numerical analysis was performed using LS-DYNA. Hybrid composite laminates (HCGFRE) obtained by sequencing plain woven glass fiber reinforced epoxy (GFRE) and plain woven carbon fiber reinforced laminates (CFRE) as adherends. Araldite AV138M and Araldite 2015 epoxy adhesives were also used to create the hybrid bondline. Mode I and mode II fracture behaviors were determined by numerical modeling of the Double Cantilever Beam (DCB) and End Notched Flexural (ENF) tests, respectively. In the numerical model, firstly, the fracture parameters of the relevant adhesives were found in the literature, and verification was made utilizing the numerical model. Then, the fracture behavior in both two modes was examined by forming a hybrid bondline. In the literature, there are restricted studies examining the fracture behavior of fracture characterization bonded joints with hybrid bondlines. Additionally, it is not encountered any study determining the both mode I and mode II fracture behavior of composite fracture characterization bonded joints with hybrid bondlines. Therefore, it is thought that this study will gain significant novelties to the existing literature.

Structural health monitoring of carbon fiber-reinforced laminate composites with torsional loads by using acoustic emission

Structural health monitoring of carbon fiber-reinforced laminate composites with torsional loads by using acoustic emission

Low-cost fabrication of high-performance composite structures using external compaction pressure

In the composite industry, wet lay-up and vacuum bagging are widely used, low-cost manufacturing processes. This paper investigates the mechanical performance of wet layup and vacuum bagged carbon fibre-reinforced laminates compressed in a hydraulic press at different compaction pressures. The external compaction pressure is shown to significantly reduce void content, and increase the fibre volume fraction and mechanical performance of tested laminates. The tensile and flexural properties of tested specimens subjected to high levels of external compaction pressure are found to be comparable to those of out-of-autoclave (OOA) prepreg specimens. It is summised that the use of external compaction pressure over wet layup and vacuum bagged composites offers a low-cost (and low-energy) industrial processing route for manufacturing high-performance carbon fibre-reinforced components.

Effects of laminate thickness and ply-stacking sequence on the low velocity impact resistance of carbon fiber-reinforced laminates

Carbon/epoxy pre-impregnated has become one of the most demanded materials for some aeronautics structures. Boeing 787 and Airbus A350 are pioneers in incorporating carbon fiber-reinforced composite materials in primary structures as wings and airframe. Tailoring the laminate ply sequence involves a difficult challenge owing to the rigorous design and operational criteria. Given that composite materials present a high sensitivity to impact loads, it has been indispensable to examine the influence of different factors in the failure mechanisms after an impact event. In this work, the effect of impact energy, stacking sequence and thickness on the impact damage resistance of CFRP composites was investigated. Damage response parameters as peak force, absorbed energy and delamination threshold were obtained from the impact curves. Then, a C-Scan imagen showed the damage extension using the non-destructive inspection Phased Array.

Bio-Inspired Laminates of Different Material Systems

Abstract Helicoidal laminates mimicking the laminar structure of the exoskeleton of crustaceans have been reported to resist higher out-of-plane loads than the common cross-ply and quasi-isotropic fiber-reinforced laminates. Some have reported that smaller inter-ply angle improves strength of helicoidal laminates but others have reported the opposite. A few important material parameters that dictate the failure mechanism of helicoidal laminates have recently been proposed based on proof-of-concept carbon fiber-reinforced laminates, which is not the best material system to benefit from a helicoidal configuration. This study investigates the out-of-plane loading performance of helicoidal laminates with various inter-ply angles, ply thicknesses, and materials. Result shows that the failure mechanism is dictated by the competition between spiraling matrix split and delamination followed by fiber breakage regardless of the laminate material system. Spiraling matrix split resistance decreases as pitch (ratio of inter-ply angle to ply thickness) and matrix toughness decreases. This study provides guidelines for the optimization of helicoidal laminates. Coexistence of spiraling matrix split and fiber damage is often seen on the failed laminate with the highest peak load. The optimal inter-ply angle provides the optimal spiraling matrix split resistance; so, neither spiraling matrix split nor fiber/delamination damage becomes dominant. Since resistance to spiraling matrix split decreases as pitch or matrix toughness decreases, the optimal inter-ply angle will increase for laminates with weaker matrix or thicker plies and vice versa.

Micromechanisms of Failure and Damage Evolution in Low-Thickness Composite Laminates Under Tensile Loading

In this work, failure mechanisms and damage evolution in low-thickness composite laminates are numerically simulated. The effect of thinning ply on the strength and damage evolution of composite laminates is investigated. Micromechanical modeling is performed to study damage initiation and propagation mechanisms and ply thickness or in situ effect in thin-ply carbon fiber-reinforced laminate under transverse tension loading. Two different sets of models are examined. The first set of the thin-ply laminate models contains a representative volume element (RVE) of 90° lamina constrained between two homogenized 0° plies. Thicknesses of models with embedded 90° lamina were 30, 60, 90 and 120 μm. In the second set, two models with 30 and 90 μm of 90° thin ply as the outer layers with embedded homogenized 0° layer are considered. Micromechanical analysis is combined with augmented finite element method to provide high-fidelity results of damage evolution. Random fibers’ arrangement and interface toughness and strength normal distribution are considered to capture the composite stochastic behavior. It is shown that the damage initiation and propagation locations are affected by the thickness of 90° lamina and distributions of fracture properties within the RVE.

Artificial Neural Network Approach to Determine Elastic Modulus of Carbon Fiber-Reinforced Laminates

Recognized as a prominent material for engineering applications, carbon fiber-reinforced laminated composites require significant effort to characterize due to their anisotropic structure and viscoelastic nature. Dynamic mechanical analysis has been used to accelerate the testing process by transforming the measured viscoelastic properties to elastic modulus. To expand the transformation to anisotropic materials, artificial neural network approach is used to build the master relationship of the storage modulus in three in-plane directions. Using rotation transformation, the stiffness tensor can be calculated to extrapolate the frequency domain viscoelastic properties in any orientation with respect to the fiber direction. The viscoelastic properties are transformed to time domain relaxation function using the linear relationship of viscoelasticity. Stress response with a certain strain history is predicted and the elastic modulus is extracted. Compared to the experimental flexural test results, the artificial neural network-based method achieved an error of less than 7.3%. The results show that the transformation can predict the anisotropic material behavior at a wide range of temperatures and strain rates.

Load-carrying capacity of the GFRP and CFRP composite beams subjected to three-point bending test – numerical investigations

Abstract The subject of this article is the finite element method (FEM) simulation of the multi-layered rectangular composite beam subjected to three-point bending test. The study is focused on the composite beams made of glass or carbon fibre-reinforced laminates (glass fibre-reinforced polymer [GFRP] and carbon fibre-reinforced polymer [CFRP]) for which different laminate stacking were addressed. Three beam geometries with various length-to-thickness ratios included short beam shear (SBS) test, provided the beam is short relative to its thickness, which maximised the induced shear stresses. Simulation included the application of Tsai–Hill, Hoffman, Tsai–Wu, Hashin and Puck failure criteria to perform the composite beam failure analysis wherein the matrix and fibre failure were considered separately. Numerical failure studies also aimed to verify the beam failure modes and the participation of stress tensor elements in material failure.

Effect of Curing Agent on the Compressive Behavior at Elevated Test Temperature of Carbon Fiber-Reinforced Epoxy Composites.

The aim of the underlying research is to understand the effect of elevated test temperatures on the mechanical properties of carbon fiber-reinforced laminates based on three different hardeners. A high-temperature stable adhesive was developed for the end tabs of the specimen. Bifunctional bisphenol A diglycidyl ether (DGEBA) epoxy cured with triethylenetetramine (TETA), isophorone diamine (IPDA), and 4,4′-diaminodiphenylsulfone (DDS) were cured and tested in a Celanese compressive test up to 250 °C. A model by Feih was applied, and sufficient accordance (R2 > 97%) with the compressive data was found. We showed that the network density and the chemical structure of the thermoset network influenced the compressive behavior.

Carbon nanotube fibres for CFRP-hybrids with enhanced in-plane fracture behaviour

Carbon nanotube (CNT) assemblies such as vertical arrays and mats have been investigated for their potential to provide additional interlaminar toughness for carbon fibre-reinforced laminates, although the achieved improvement in mechanical properties has not always been consistent so far. In this study, we introduced thin interlayers of continuous unidirectional CNT fibres for additional in-plane reinforcement and toughening of conventional autoclave-cured carbon fibre composites. Double notched specimens with and without CNT fibre reinforcing layers were tested to failure in tension. The results show that the introduction of relatively thin interlayers of continuous CNT fibres at local regions close to the notch tip increased the failure load and stress by 9% and the failure strain by 15% respectively, suggesting the toughening potential of CNT fibres. The observed mechanical behaviour is discussed with respect to the strength and compaction of pristine CNT fibres during the autoclave processing and their contributions towards the reinforcing efficiency.

X-ray computed tomography analysis of damage evolution in open hole carbon fiber-reinforced laminates subjected to in-plane shear

The deformation and damage mechanisms during tensile deformation of [±45]2s open hole carbon fiber composite materials were quantitatively analyzed by means of image analysis of XCT data. Damage developed progressively in each ply with deformation in two shear bands (parallel and perpendicular to the fiber direction) at ±45° with respect to the loading direction, i.e. cracking started from these shear bands and grew following the fiber direction until encompassing the whole laminate width. Matrix cracking and fiber rotation in both types of shear bands presented different features, which were quantified by means of image processing from XCT data. A small delamination developed around the hole at the intersection from +45° and −45° cracks directions in adjacent plies. However, this delamination does not progress excessively with deformation until the end of the test, when fracture was triggered by the sudden propagation of two main delamination cracks tangent to opposite sides of the hole in the shear band parallel to the fiber direction.

Toughening effect of carbon nanotubes and carbon nanofibres in epoxy adhesives for joining carbon fibre laminates

The effect of carbon nanotubes (CNTs) and carbon nanofibres (CNFs) on mode I adhesive fracture energy (GIC) of double cantilever beam (DCB) joints of carbon fibre-reinforced laminates bonded with an epoxy adhesive has been studied. It was observed that the presence of carbon nanofillers in the epoxy adhesive results in a significant increase in the propagation value of mode I adhesive fracture energy with CNTs producing the largest increase. The toughening mechanisms, analysed using scanning electron microscopy (SEM), for the two nanofiller systems differed: pull-out with CNFs, and pull-out and crack bridging with CNTs. At the macroscopic level there was also a change in the failure mode, with an increased proportion of delamination occurring in the nanoreinforced joints in comparison with the unreinforced. Two different surface treatments were also applied to the laminates: grit blasting and atmospheric plasma. The highest fracture energy was obtained in the grit blasted joints.

Improving the through-thickness thermal and electrical conductivity of carbon fibre/epoxy laminates by exploiting synergy between graphene and silver nano-inclusions

Fibre-reinforced polymer composites typically feature low functional (e.g., electric and thermal conductivity) and structural (e.g. mechanical strength and fracture toughness) properties in the laminate’s thickness direction. In the event of lightning strikes, overheating, and impact by foreign objects, composite laminates may suffer wide spread structural damage. This research explores the synergistic physical interaction between two-dimensional nanostructured (graphene nano-platelets) and, zero- or one-dimensional conductive fillers (silver nanoparticles or silver nanowires, respectively) when both are dispersed in fibre–polymer laminates. The results reveal a synergistic improvement in the through-thickness thermal conductivity that is more than the additive improvements by each constituent. Specifically, the simultaneous inclusion of graphene nano-platelets and silver nanoparticles/nanowires at a combined loading of 1vol% resulted in approximately 40% enhancement in the through-thickness thermal conductivity while the inclusion of graphene nano-platelets alone at the same loading resulted only in 9% improvement. Similarly, the through-thickness electrical conductivity of carbon fibre/epoxy laminates incorporating graphene nano-platelets together with silver nanoparticles/nanowires was notably higher (⩾70%) than can be achieved by graphene nano-platelets alone (∼55%). These results demonstrate that the presence of nano-reinforcements exhibiting varied phonon transport and electron transfer pathways, and geometric aspect ratios promote synergistic physical interactions. Small improvements were found in the mechanical properties, including tensile, flexural or compressive properties of the carbon fibre-reinforced laminates, due to the relatively low concentrations of the nano-fillers.

Carbon fiber-reinforced composites using an epoxy resin matrix modified with reactive liquid rubber and silica nanoparticles

Abstract Carbon fiber-reinforced composites are gaining importance and are about to play a very prominent role in automotive applications. In structural applications mainly epoxy resins are used as matrix materials. The properties of epoxy resins and laminates made thereof can be improved by tougheners like reactive liquid rubbers. Further improvements can be achieved by adding surface-modified silica nanoparticles, with 20 nm in size and a very narrow particle size distribution. In this study carbon fiber-reinforced laminates made from epoxy resins modified with reactive liquid rubber and silica nanoparticles have been prepared and investigated. A very fast amine cure of 15 min has been chosen to match industrial needs. Mechanical properties for bulk resins and laminates are compared and the mechanisms responsible for the property improvements are discussed. Structure property relationships between the neat resin fracture toughness and the interlaminar G Ic and G IIc of the reactive liquid rubber and silica nanoparticles modified resins were established. Tough laminates could be prepared. However, CAI performance of the hybrid laminates was slightly inferior as compared to the rubber-toughened laminates, most probably due to agglomerates of nanoparticles found in the cured resin systems. The reason for the nanoparticle aggregation was detected and their influence on laminate performance discussed.

Ply level failure prediction of carbon fibre reinforced laminated composite panels subjected to low velocity drop-weight impact using adaptive meshing techniques

This work is concerned with physical testing and numerical simulations of flat and round nose drop-weight impact of carbon fibre-reinforced laminate composite panels to predict ply level failure. Majority of the existing studies on impact of composites by spherical nose impactors are experimental, computational models are simplified, and based on classical laminated plate theories where contributions of through-thickness stresses are neglected. Present work considers flat nose impact and contributions from through-thickness stresses and is mainly simulation based. A computational model was developed in ABAQUS™ software using adaptive meshing techniques. Simulation produced (2D model) stresses were numerically integrated using MATALB™ code to predict through-thickness (3D) stresses. Through-the-thickness stresses were then utilised in advanced failure criteria coded in MATLAB™ software to predict ply level failures. Simulation produced results demonstrate that the computational model can efficiently and effectively predict ply-by-ply failure status of relatively thick laminates.

Automatic quantification of matrix cracking and fiber rotation by X-ray computed tomography in shear-deformed carbon fiber-reinforced laminates

Abstract The deformation and damage mechanisms of carbon fiber-reinforced epoxy laminates deformed in shear were studied by means of X-ray computed tomography. In particular, the evolution of matrix cracking, interply delamination and fiber rotation was ascertained as a function of the applied strain. In order to provide quantitative information, an algorithm was developed to automatically determine the crack density and the fiber orientation from the tomograms. The investigation provided new insights about the complex interaction between the different damage mechanisms (i.e. matrix cracking and interply delamination) as a function of the applied strain, ply thickness and ply location within the laminate as well as quantitative data about the evolution of matrix cracking and fiber rotation during deformation.

Optimization of curing cycle in carbon fiber-reinforced laminates: Void distribution and mechanical properties

A strategy is presented to optimize out-of-autoclave processing of quasi-isotropic carbon fiber-reinforced laminates. Square panels of 4.6 mm nominal thickness with very low porosity ( ⩽ 0.2 % ) were manufactured by compression molding at low pressure (0.2 MPa) by careful design of the temperature cycle to maximize the processing window. The mechanisms of void migration during processing were ascertained by means of X-ray microtomography and the effect of ply clustering on porosity and on void shape was explained. Finally, the effect of porosity and ply clustering on the compressive strength before and after impact was studied.