Carbon Fiber Reinforced Epoxy Laminates Research Articles

Epoxy-functionalized polysiloxane/Nano-SiO2 synergistic reinforcement in cryogenic mechanical properties of epoxy and carbon fiber reinforced epoxy laminate

Resin matrix of carbon fiber (CF) reinforced resin laminates play a key role in transferring the external stress to carbon fibers. Especially in cryogenic environment, the mechanical properties of CF reinforced resin laminates depend largely on the mechanical properties of resin matrix. In this work, an epoxy-functional polysiloxane/Nano-SiO2 (EFPS/Nano-SiO2) was prepared to enhance the mechanical properties of epoxy resin and carbon fiber reinforced epoxy laminate at RT and cryogenic environment. The TEM images indicate that the grafting of flexible macromolecule EFPS on the surface of Nano-SiO2 can improve the dispersion of Nano-SiO2 in epoxy resin. The tensile strength of epoxy resin with 5 wt% content of EFPS/Nano-SiO2 increases by 7.95% at RT and 17.07% at 90K, fracture strain by 54.55% at RT and 26.91% at 90K, fracture toughness (KIC) by 48.82% at RT and 33.33% at 77K compared with the neat epoxy resin. The enhancement mechanism should mainly be attributed to the fact that the Nano-SiO2 particles debonding enhance the energy dissipation at crack front and the flexible EFPS significantly improves the movability of epoxy curing networks. The tensile strength of CF reinforced EFPS/Nano-SiO2 epoxy laminate shows an increase of 16.64% at RT and 25.01% at 90K, confirming that the effect of EFPS/Nano-SiO2 epoxy resin transferring the external stress from resin matrix to CF is better than that of neat epoxy resin. In addition, the mechanism of thermal cycling affecting the tensile properties of CF reinforced epoxy laminates are analyzed in detail.

Friction Stir Joining of CFRP laminates with amorphous polymers: Influence of processing speeds

The influence of the processing speeds during friction stir joining of polycarbonate sheets with carbon fiber reinforced epoxy laminates was investigated. A prototypal CNC machine equipped with load and temperature sensors was used during the experimental tests. Mechanical characterization tests were performed by conducting quasi-static single lap shear tests. In addition, the material flow and the morphology of the welds were investigated. The results indicated that the mechanical behavior of the joints was mainly determined by the temperature of the stirred material and the amount of material reflow. A predictor index given by the ratio of the plunging load by the load along the joining direction was developed to determine processing conditions that facilitate the development of large amount of material reflow. Thus, an empirical model that related the shear strength to the temperature of the stirred material and the predictor index was established. Under optimal processing conditions, the process involved the removal of the superficial layer of epoxy from the CFRP and the substitution with the polycarbonate. This enabled relatively high strength 17 MPa that corresponded to the 89 % of the Interlaminar shear strength of the CFRP.

Adapted anisomorphic model for fatigue life prediction of CFRP laminates under constant amplitude loading

A new constant life diagram (CLD) model is proposed to predict the fatigue life of carbon fibre-reinforced epoxy laminates under constant amplitude (CA) loading. The CLD is asymmetric and non-linear, and it is built upon the anisomorphic CLD model. It consists of two sub-models; one sub-model is applicable to laminates with lay-ups characterised by a larger ultimate tensile strength (UTS) than absolute ultimate compressive strength (UCS): UTS ⩾ ∣UCS∣, while the second sub-model can be applied to those exhibiting the opposite tendency: ∣UCS∣ > UTS. Combined, the sub-models can predict the fatigue life of any carbon-epoxy laminate. The CLD can be constructed using only static strength data and fatigue life data related to one stress ratio (R), defined as either R=0.1 or R=-1.0. An experimental campaign was conducted on a carbon-epoxy laminate with a lay-up of [90/0/90]2S to validate the first CLD sub-model. Additionally, a second case study from literature with a lay-up of [45/90/-45/0]2S was employed for validation. The second CLD sub-model was evaluated using two coupon case studies from literature with lay-ups of [±60]3S and [45]16. The predicted and experimentally obtained fatigue lives showed agreements for different R-ratios, and the observed prediction errors were in ranges similar to those of the original anisomorphic CLD model. Hence, the presented CLD model allows for fatigue life predictions in scales similar to experimental results while reducing the required experimental efforts with respect to the anisomorphic CLD model.

Bi-stable hybrid composite laminates containing metallic strips: an experimental and numerical investigation

This study scrutinizes the static characteristics of a new category of bi-stable hybrid composite laminates (BHCLs) that contain multiple metallic strips (aluminum) distributed along the middle layer of a carbon fiber reinforced epoxy laminate. With this new class of BHCLs, the direction of curvature of the laminates does not change during the snap-through between the two stable states, unlike the conventional bi-stable cross-ply laminates. The laminates were modeled using finite element analysis and were experimentally validated. BHCLs with two to five metallic strips were fabricated for this purpose. The effect of the number, width, and thickness of the metallic strips on the static characteristics of the laminate were numerically investigated using ABAQUS. Further, the curvatures, out-of-plane displacement, and static snap-through load of the laminates were determined experimentally. The results showed a strong relationship between the residual curvature and the load-carrying capability of the laminate and the number, width, and thickness of the metallic strips, as well as the laminate geometry. Knowledge of this characteristic will allow designers to tune the parameters for a given application and to achieve the desired performance. Good qualitative and quantitative agreement was observed between the numerical and the experimental results.

Influence of Fiber Volume Content on Thermal Conductivity in Transverse and Fiber Direction of Carbon Fiber-Reinforced Epoxy Laminates.

Thermal conductivity is an important material property for thermo-mechanical calculations, as mechanical properties strongly depend on the temperature and heat distribution in the manufactured parts. Although several suggestions for approximation formulae have been made, existing experimental data are rare and are not comparable due to different measurement methods. In addition, scarcely has the thermal conductivity in both the fiber direction and transverse direction been studied. The aim of the current research is to show the influence of carbon fiber volume content on the thermal conductivity of laminates. The values are then used to verify the micromechanical models used in the literature. A strong influence on the thermal conductivity could be determined. For the transverse thermal conductivity, the correlation was exponential; for the conductivity in the fiber direction, a linear correlation was found.

Effect of Thermal Ageing on the Impact and Flexural Damage Behaviour of Carbon Fibre-Reinforced Epoxy Laminates.

Most of the composite materials that are used in aerospace structures have been manufactured using a thermostable matrix, as epoxy resin. The region of stability of these polymers is defined by the glass transition temperature (Tg). However, operating temperatures close and above the Tg can cause a variation in the properties of the polymer and consequently, modify the mechanical properties of the composite material. Therefore, it is necessary to understand the failure mechanisms that occur in the material in order to ensure stability and durability. The effect of temperature and time of exposure on the impact and flexural mechanical responses of carbon/epoxy composites are studied in this work. For that purpose, ageing treatments at temperatures below and above the Tg have been considered and then, impact and flexural tests have been performed. It was observed that thermal ageing cause two different effects: at temperatures below the Tg, there is an increase of the maximum strength because of a post-curing effect; however, the mechanical properties decrease at higher temperatures of thermal ageing due to the thermo-oxidation of the epoxy resin and the loss of adhesion in the matrix/fibre interface.

Internal damage evaluation of composite structures using phased array ultrasonic technique: Impact damage assessment in CFRP and 3D printed reinforced composites

The application of non-destructive techniques for the evaluation of internal damage in composite materials is a challenge due to their complexity. The aim of this study is to analyse the ability of ultrasonic technique to identify and evaluate manufacturing defects and internal damage in composite laminates. Artificial object inclusions of different shapes, sizes and materials were embedded in carbon fibre reinforced epoxy (CFRP) laminates. Comprehensive investigation of non-destructive evaluation using phased array ultrasonic testing to trace and characterize the embedded defects is presented. Phased array ultrasonic technique was able to precisely locate most of the artificial inclusion in the composite laminates. Nerveless, the shape and size of the inclusions were not accurately determined due to the high signal attenuation and distortion characteristics of the carbon fibre epoxy composite.Furthermore, a major concern affecting the efficient use of composite laminates is their vulnerability to low velocity impact damage. The dynamic behaviour of composite laminates is very complex as there are many concurrent phenomena during composite laminate failure under impact loading. Thus, the practicality of the previous results is demonstrated by the evaluation of impacted carbon fibre reinforced epoxy laminates using ultrasonic testing. The influence of laminate thickness and impact energy on impact damage is also investigated. The performance of phased array ultrasonic testing for the inspection of composite laminates with barely visible impact damage is evaluated. In addition, fibre-reinforced thermoplastic composites are becoming more significant in industrial applications due to their excellent mechanical performance and potential recycling. In this study, impact damage in 3D printed continuous glass fibre reinforced thermoplastic laminates is also analysed. Phased array ultrasonic testing is performed and the amount of damage is quantified in terms of delaminated area.

Experimental study of the influence of thickness and ply-stacking sequence on the compression after impact strength of carbon fibre reinforced epoxy laminates

Composite structures are particularly vulnerable to impact which drastically reduces their residual strength [1–3]. In this work, the influence of laminate thickness, ply-stacking sequence and scaling technique on the impact damage tolerance of CFRP laminates is investigated by means of compression after impact (CAI) tests. Drop-weight impact tests were carried out to determine impact response of the different composite laminates. CAI tests were performed in a non-standard CAI device in order to obtain the compression residual strength. In addition, open-hole compression (OHC) tests were performed for comparative purposes. Ultrasonic C-scanning and cross-sections of CAI samples were examined to assess failure mechanisms of the different configurations.It was observed that damage tolerance decreases as impact energy increases. In addition, thicker laminates show higher CAI strength due to higher bending stiffness. Furthermore, angle-ply laminates depict better performance in terms of damage tolerance. Finally, the results obtained demonstrate that introducing ply blocking had a negative effect on the damage resistance but, conversely, an improvement of the CAI strength.

The effect of different curing conditions on hardness, thickness, and residual stress of carbon fiber reinforced epoxy composites

In this study, an attempt has been made to optimize the curing process of carbon fiber reinforced epoxy laminates. The effect of four factors: curing temperature, cooling method, wetting method, and resin-to-hardener ratio was studied. Custom non-regular fractional factorial design was utilized to choose the combination of these factors levels. Vickers micro-hardness test was conducted to study hardness in all the specimens. Thickness measurements were taken. The residual stresses along fiber direction were measured using Timoshenko bending beam method. Box plots were drawn to understand data variability. ANOVA was used to analyze results. It was shown that curing at 180℃ or lower, applying furnace cooling, raising resin-to-hardener ratio, and avoiding wetting the bottom side have reduced data variability, lowered thickness, and residual stress.

Damage resistance of carbon fibre reinforced epoxy laminates subjected to low velocity impact: Effects of laminate thickness and ply-stacking sequence

A major concern affecting the efficient use of composite laminates is the effect of low velocity impact damage on the structural integrity [1–3]. The aim of this study is to characterize and assess the effect of laminate thickness, ply-stacking sequence and scaling technique on the damage resistance of CFRP laminates subjected to low velocity impact. Drop-weight impact tests are carried out to determine impact response. Ultrasonic C-scanning and cross-sectional micrographs are examined to assess failure mechanisms of the different configurations.It is observed that damage resistance decreases as impact energy increases. In addition, thicker laminates show lower absorbed energy but, conversely, a more extensive delamination due to higher bending stiffness. Thinner laminates show higher failure depth. Furthermore, quasi-isotropic laminates show better performance in terms of damage resistance. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the damage resistance and on the delamination area.

Global bending response of composite sandwich plates with corrugated core. Part II: Effect of laminate construction

Global bending response of simply supported composite sandwich plates with corrugated core was studied using carbon fiber reinforced epoxy laminates in both face plates and inclined webs in the corrugated core. Two different laminate constructions were considered, namely [0/α]S and [±α]S and the fiber orientation angle was varied from 0° to 90°. Sandwich plate geometric parameters, such as face thickness, pitch and face center distance were maintained constant, but the web inclination was varied from a triangular configuration to a square configuration. The web thickness was varied with web inclination angle so that the sandwich plates had the same cross-sectional area and, therefore the same mass. This allowed a direct comparison between different laminate constructions for each web inclination angle. It was shown that for the same mass, the maximum deflection under a distributed load depends on both the web inclination angle and the laminate construction. It is significantly higher with the [±α]S construction than with the [0/α]S construction. For both laminate constructions, the largest maximum deflection occurs at a web inclination angle of 48°, which can be attributed to the combined effect of the transverse shear stiffness components.

Residual flexural strength after impact for textile carbon fiber reinforced polycarbonate laminates

This study prepared textile carbon fiber reinforced polycarbonate laminates of three kinds molded with different conditions and carbon fiber reinforced epoxy laminates consisting of the same carbon fiber textile. Drop-weight impact tests were conducted for these four laminates with three levels of impact energies. The residual flexural strengths were measured after impact. Results show that the residual flexural strengths for all laminates decrease clearly with increasing impact energy. The flexural strengths of these laminates without impact damage have mutually different values. Furthermore, the laminates exhibit a decreasing ratio of residual flexural strength by impact damage with mutually differing values. The reasons were examined through observations conducted using ultrasonic flaw detection and digital microscope.

A study of composite laminates failure using an anisotropic gradient-enhanced damage mean-field homogenization model

The failure of carbon fiber reinforced epoxy laminates is studied using an anisotropic gradient-enhanced continuum damage model embedded in a mean-field homogenization scheme.In each ply, a homogenized material law is used to capture the intra-laminar failure. The anisotropy of the homogenized material model results from the homogenization method and from the reformulation of the non-local continuum damage theory to account for the material anisotropy. As a result the damage propagation direction in each ply is predicted with accuracy as compared to the experimental results, while the problems of losing uniqueness and strain localization, which occur in classical finite element simulations when strain softening of materials is involved, can be avoided.To model the delamination process, the hybrid discontinuous Galerkin/extrinsic cohesive law method is introduced at the ply interfaces. This hybrid method avoids the need to propagate topological changes in the mesh with the propagation of the delamination while it preserves the consistency and stability in the un-cracked interfaces.As a demonstration, open-hole coupons with different stacking sequences are studied numerically and experimentally. Both the intra- and inter-laminar failure patterns are shown to be well captured by the computational framework.

Cost Cut with High Impact Value of Sandwich Structure with Inexpensive ABS Core between High Strength CFRP Laminate Plies

Sandwich structural composites (CFRP/ABS/CFRP) of inexpensive acrylonitrile butadiene styrene (ABS) cores (2.0 mm thickness) between carbon fiber reinforced epoxy (CFRP) laminate plies (2.5 mm thickness) were suggested and prepared, since the materials cost of ABS resin was about 8% that of CFRP. Although Young’s modulus of CFRP/ABS/ CFRP is slightly smaller than that of CFRP, Charpy impact value (auc) of the CFRP/ABS/CFRP approximately corresponded to that of CFRP composite. Furthermore, applying homogeneous low voltage electron beam irradiation (HLEBI) to both side surfaces improved the auc of CFRP/ABS/CFRP. Since the irradiated depth estimated is about 119 ± 23 μm, the irradiation effects mostly acted within the CFRP sheet. The Charpy impact value (auc) of CFRP/ABS/CFRP at mid-fracture probability (Pf ) after irradiation at 0.30 MGy (kJg_1) was approximately 25 % higher than that before treatment. It was approximately equal to that for irradiated CFRP and was also about 20% higher than that of the CFRP before treatment. Although the use of ABS resin as the core reduced other mechanical properties of tensile and bending, the materials cost of CFRP/ABS/CFRP was approximately 25 % that of CFRP. Thus, the sandwich structural composites of CFRP/ABS/CFRP could be utilized for daily articles.

Tensile behavior of hybrid epoxy composite laminate containing carbon and basalt fibers

AbstractThis paper investigated the effect of the incorporation of basalt fibers on the tensile properties of carbon fiber-reinforced epoxy laminates manufactured by vacuum-assisted resin transfer molding. The purpose of this research was to design a carbon-basalt/epoxy hybrid composite material that is of low cost in production, is lightweight, and has good strength and stiffness. The tensile strength and stiffness of the hybrid laminates demonstrated a steady, linear decrease with an increase in basalt fiber content, but the fracture strain gradually increased together with the increase in the basalt layer content. In this study, the incorporation of basalt fibers into the carbon fiber-reinforced polymer (CFRP) showed lower tensile strength than CFRP but has higher tensile strain. Furthermore, we found that the arrangement and enhancement of basalt fiber into the CFRP significantly influence the mechanical properties of interply hybrid composites.

Development of a Finite Element Model for Progressive Damage Analysis of Composite Laminates Subjected to Low Velocity Impact

Fiber reinforced polymer laminates are susceptible to transverse low velocity impact which can cause significant damages, such as matrix cracks, delamination and fiber breakage. A 3-Dimensional (3-D) finite element model (FEM) is presented for the progressive damage analysis of fiber reinforced laminates subjected to low velocity impact. The constitutive equations of material used in the FEM are based on the continuum damage mechanics (CDM). The modified HASHIN failure criterions are used in the material model to detect the initiation of all the failure modes of laminates. A simplified material stiffness degradation scheme is used to characterize the material degradation due to damages. The failure criterions and material degradation scheme have been incorporated in the software ABAQUS/Explicit through the user defined material subroutine VUMAT. The available experiments of thin carbon fiber reinforced epoxy laminates subjected to low velocity impact were used to validate the developed FEM. The good agreement of the impact contact force history and damage area between the analysis results and the experimental data shows the validation of the developed FEM.

Fusion Bonding of Carbon Fiber Reinforced Epoxy Laminates

Technique of including an amorphous thermoplastic film as the outermost layer of thermoset composites have been developed to join the thermoset composites using fusion bonding methods. Based on a WLF temperature dependence and a time dependence of t1/4, isothermal and non-isothermal models were developed to relate the recovery of bonding strength to welding temperature and time. The isothermal model failed to take into account the time taken for the bonding interface to reach the glass transition temperature and final desired bonding temperature and lacked predictive power for experiments with short bonding times and low shear strength recovery. The non-isothermal model provided an excellent fit to the experimental date, showing a significant improvement over the isothermal model.

Effect of moisture absorption on the mechanical behavior of carbon fiber/epoxy matrix composites

A carbon fiber/epoxy unidirectional laminated composite was exposed to a humid environment and the effect of moisture absorption on the mechanical properties and failure modes was investigated. The composites were exposed to three humidity conditions, namely, 25, 55, and 95 % at a constant temperature of 25 °C. The carbon fiber–epoxy laminated composites for two different carbon fiber surface treatments were used. The results showed that the mechanical properties differ considerably for each fiber surface treatment. The application of a coupling agent enhanced the fiber-matrix adhesion and reduced dependence of the properties on humidity. The damage mechanism observed at micromechanical level was correlated to acoustic emission signals from both laminated composites. The untreated carbon fiber failure mode was attributed to fiber-matrix interfacial failure and for the silane-treated carbon fiber reinforced epoxy laminate attributed to matrix yielding followed by fiber failure with no signs of fiber-matrix interface failure for moisture contents up to 1.89 %.

Characterization and optimization of orbital drilling of woven carbon fiber reinforced epoxy laminates

The emerging process of orbital drilling (OD) can greatly reduce or eliminate the defects associated with the drilling of composites; e.g., delamination, and thermal damage. The effects of the OD process parameters on the hole quality attributes were established in the form of machinability maps; an aspect that has not been reported before. The results showed significant enhancement in the hole quality compared to conventional drilling, due to the reduced axial force and cutting temperature, resulting from the redistribution of the load exerted by cutting edges and the cooling effect of the unstable rotational air flow in the tool-workpiece annular gap.

Improvements in mechanical properties of a carbon fiber epoxy composite using nanotube science and technology

Abstract Carbon fiber reinforced epoxy composite laminates, with strategically incorporated fluorine functionalized carbon nanotubes (f-CNTs) at 0.2, 0.3 and 0.5 weight percent (wt.%), are studied for improvements in tensile strength and stiffness and durability under both tension–tension ( R = +0.1) and tension–compression ( R = −0.1) cyclic loadings, and then compared to the neat (0.0 wt.% CNTs) composite laminate material. To develop the nanocomposite laminates, a spraying technology was used to deposit nanotubes on both sides of each four-harness satin weave carbon fiber fabric piece for the 12 ply laminate lay up. For these experimental studies the carbon fiber reinforced epoxy laminates were fabricated using a heated vacuum assisted resin transfer molding (H-VARTM®) method followed by a 2 soak curing cycle. The f-CNTs toughened the epoxy resin-fiber interfaces to mitigate the evolution of fiber/fabric-matrix interfacial cracking and delamination under both static and cyclic loadings. As a consequence, significant improvements in the mechanical properties of tensile strength, stiffness and resistance to failure due to cyclic loadings resulted for this carbon fiber reinforced epoxy composite laminate.