Carbon Fiber Laminate Research Articles

Comparison of Immersion and Portable Ultrasonic Housing to Quantify the Adhesive Bond Thickness and Sizing of Foreign Objects.

High-performance materials, such as carbon fiber laminates, are costly to manufacture and are often used in demanding environments requiring the use of high-resolution non-destructive testing (NDT) methods to confirm the integrity of the parts. One NDT method that has shown promise for qualifying carbon fiber laminates is the use of immersion ultrasound with spherically focused probes. However, many parts may not be submersible in an immersion tank due to size or material constraints. These parts must be scanned with contact transducers with inferior resolutions or with expensive and messy systems such as bubblers. This research presents the use of a novel housing system that allows for the use of focused immersion transducers in an out-of-tank portable ultrasonic scanning application. This work presents a comparison between scans taken using a custom high-resolution immersion system and scans taken using the presented housing. There are a wide variety of potential inspection applications for this novel system, and the present work focused on two specific applications: the quantification of the spatially varying adhesive thickness in bonded carbon fiber laminates and the quantification of foreign object inclusions in carbon fiber laminates. The results presented show that scans using the portable housing are comparable in quality to scans performed using an immersion system. Specifically, both inspection approaches had an average error of 0.04 mm when quantifying the adhesive thickness of a bonded composite, and for the foreign object detection, the error in quantifying the dimensions of the embedded foreign object was 0.1 mm and 0.2 mm for the immersion system and the portable inspection system, respectively. The demonstration was performed in a laboratory setting, but a discussion is provided for the necessary improvements needed to extend the system for use in field applications.

Experimental and numerical investigation of the damage propagation in regularly arrayed short fiber reinforced composite laminates under low‐velocity impact

AbstractThe outstanding mechanical performance and flowability of unidirectionally arrayed chopped strands (UACSs) give them an advantage in the manufacture of engineering structures with complex geometry. For the application of practical structures, the impact responses and damage evolution of material under low‐velocity impact must be investigated in advance. In this study, UACS laminates and continuous carbon fiber laminates with a stacking sequence of [0/90]4s and a thickness of 2 mm were fabricated for low‐velocity impact tests at 7, 11, 15, and 20 J. The impact responses and postimpact intralaminar damage area were analyzed according to the experimental results, including impact load responses and ultrasound C‐scan inspections. Moreover, to predict the damage evolution of the internal structure, the 3D finite element models were constructed in ABAQUS using a progressive damage model (PDM) through a user‐material subroutine VUMAT. Compared with continuous carbon fiber laminates, the dissipated energy of UACS laminates increases by approximately 10.64% and 57.37% for the 15 and 20 J, respectively. However, the intralaminar damage area of UACS laminates decreased by 29.96% and 28.16% at 15 and 20 J, respectively, since the discontinuous slits in UACS laminates can guide damage paths and suppress damage propagation.Highlights The regularly arrayed short fiber reinforced composite was studied. Revealed the low‐velocity impact responses and predicted the damage evolution. UACS and CFRP laminates have comparable impact performance. Illustrated the slits design can suppress the damage to a relatively small area.

Fatigue Characteristics Analysis of Carbon Fiber Laminates with Multiple Initial Cracks

In the entire wind turbine system, the blade acts as the central load-bearing element, with its stability and reliability being essential for the safe and effective operation of the wind power unit. Carbon fiber, known for its high strength-to-weight ratio, high modulus, and lightweight characteristics, is extensively utilized in blade manufacturing due to its superior attributes. Despite these advantages, carbon fiber composites are frequently subjected to cyclic loading, which often results in fatigue issues. The presence of internal manufacturing defects further intensifies these fatigue challenges. Considering this, the current study focuses on carbon fiber composites with multiple pre-existing cracks, conducting both static and fatigue experiments by varying the crack length, the angle between cracks, and the distance among them to understand their influence on the fatigue life under various conditions. Furthermore, this study leverages the advantages of Paris theory combined with the Extended Finite Element Method (XFEM) to simulate cracks of arbitrary shapes, introducing a fatigue simulation method for carbon fiber composite laminates with multiple cracks to analyze their fatigue characteristics. Concurrently, the Particle Swarm Optimization (PSO) algorithm is employed to determine the optimal weight configuration, and the Backpropagation neural network (BP) is used to train and adjust the weights and thresholds to minimize network errors. Building on this foundation, a surrogate model for predicting the fatigue life of carbon fiber composite laminates with multiple cracks under conditions of physical parameter uncertainty has been constructed, achieving modeling and assessment of fatigue reliability. This research offers theoretical insights and methodological guidance for the utilization of carbon fiber-reinforced composites in wind turbine blade applications.

Experimental investigation of reinforced concrete deep beams with openings and strengthened using carbon fiber laminates

Experimental investigation of reinforced concrete deep beams with openings and strengthened using carbon fiber laminates

The effect of nickel‐titanium alloy particles on the vibration response and the mechanical properties of carbon fiber laminates

The effect of nickel‐titanium alloy particles on the vibration response and the mechanical properties of carbon fiber laminates

Geometric tunability of interlaminar resistance

The inherent weakness and variability in the interlaminar properties of composites and associated delamination pose significant challenges, compromising the performance of composite structures. This study investigates a strategy to tailor the apparent interlaminar resistance by altering the geometry of the interface to control crack propagation. We have developed analytical models, which propose a formulation that links the geometry, i.e. the interface width change rate and shape factor of the crack growth plane, with the reaction force–displacement curve. The results obtained, a family of power law relations followed during interlaminar crack growth, indicate that the analytical formulation is valid for all geometries tested, including those with significant width change rates; however, it may not always be easy to use or interpret. An approximated solution, constrained to slowly varying geometries, is also proposed. The limits of using this model are presented and discussed. The final validation of the models is performed using numerical and experimental approaches, considering the delamination of carbon fiber laminates. This work offers new insights into the design of composites and the fracture process in general, featuring unique shapes and improved crack resistance. It also addresses practical issues, e.g., related to composite repairs, which can enhance the performance and longevity of composite structures. Specifically, the proposed formulations can be easily adopted to obtain optimized patch geometries.

Bridging the Gap: Correlating Ultrasonically Quantified BVID with the Compressive Strength of CFRP Composites

ABSTRACT Carbon fiber laminates are susceptible to impact damage due to the lack of fibers in the direction of impact. Often such damage can be difficult to find with visual assessment, prompting the need for detection via nondestructive testing techniques. This study quantifies the ultrasonically characterized impact damage diameters in 22 layered CFRP samples from 16 J, 18 J, 20 J, 22 J, and 24 J impact energies. These energies result in damage often defined as barely visible impact damage. This study utilizes x-ray computed tomography as a baseline to verify the results of the ultrasonic testing. Compression after impact test measurements are used in this study to find the ultimate compressive residual strength of the impacted carbon fiber laminates and to investigate the negative correlation between impact energy and residual mechanical properties of the damaged carbon fiber laminates. Many studies focus on the characterization of impact damage from various impact energies and setups via ultrasonic testing or, separately, the effect of the impact setups on the residual strength of the composite. This study strengthens the bridge between the barely visible impact damage quantified via ultrasonic testing and the residual compressive strength of the affected composite. Overall, this paper offers further insights into the relationship between internal damage size obtained using ultrasonic testing and correlates the characterized internal damage geometry to the resultant compressive strength reduction, providing a path for future studies in predictive modeling of the residual strength after impact.

Empirical model for the effect of air humidity during manufacturing on the glass transition temperature of carbon fiber reinforced hot curing epoxy – a case study

Carbon fiber-epoxy laminates are used in aerospace manufacturing, e.g. as substrates for solar cells of satellites. Commonly, fibers or fibermats are impregnated with epoxy resin and placed in the required orientation. During subsequent curing, the resin molecules are crosslinked. Cured parts are characterized by their glass transition temperature (Tg). It has been observed that Tg of epoxy matrix resin vary with recorded absolute air humidity during wet fiber placement manufacturing. Based on the production data of a series production of 203 carbon fiber laminates for space application, an empirical linear relationship between the absolute air humidity at the beginning of each production day and the observed glass transition temperature of the fully cured laminate is formulated and validated. The empirical equation describes a linear decrease of achievable glass transition temperature with increasing absolute air humidity. The quantitative nature of the results encourages straightforward practical application to determine the maximum achievable Tg for given production conditions.

Repairing of recycled hybrid carbon fiber laminates

Repairing of recycled hybrid carbon fiber laminates

Data-driven simulation-assisted-Physics learned AI (DPAI) for heat diffusion in large grain polycrystalline materials

In this paper, we propose Data-driven simulation-assisted Physics-learned Artificial Intelligence (DPAI), a deep-learning algorithm to simulate heat diffusion in large-grain polycrystalline materials. The DPAI model captures the spatio-temporal representation of heat diffusion in the material from input sequences from the training dataset. The training dataset consists of various temperature plots of polycrystalline materials taken from Finite Element (FE) simulations having varying numbers of grains oriented in random directions with a single-point heat source at the center. The arbitrary plane of the 3D microstructure of these materials is represented using 2D Voronoi tessellations. Voronoi configurations are used to model the geometry of the 2D Computer-Aided Design (CAD) model. Each cell of the Voronoi tessellation represents one grain of the microstructure. This CAD model is used as an input to the FE for solving heat diffusion equations. To model the near-realistic material anisotropy and accurately measure temperature differences at cell boundaries, a smaller mesh size is required in FE modeling, which takes considerable solver time. Therefore, the proposed Deep learning model significantly reduces the computational time while maintaining accuracy as compared to conventional numerical techniques. After training, the effectiveness of the trained DPAI model is examined by modeling larger domain problems involving a greater number of grains and varying material properties. The simulation result is qualitatively compared with the experiment. A scaled-up version of the microstructure is represented using Unidirectional Carbon Fiber laminate. The laminate is heated with a point heat source and the temperature plots are captured using Infrared Camera.

The development of bend clamp of carbon-based fiber offshore gas lift pipelines: A primary experimental approach

The work reports the proposed development of the laminated carbon fiber-reinforced polymer composites (CFRP), at a uniaxial angle as a primary bend clamp material assembly of the offshore gas lift pipelines. Generally, the clamps are utilized to repair the defect of the metallic pipelines due to their practical and mechanical strength. The existing bend clamp model poses challenges especially when applied to the J-tube bending side due to mechanical buckling and corrosion. This study evaluates the effect of laminated CFRP subjected to uniform uniaxial and in-plane compression on API 5 L X52. Several tests, including tensile, bend, and impact tests, are chosen to assess the effect of multiple and thick carbon layers to improve the clamp's mechanical properties. Scanning electronic microscope (SEM) intends to reveal the surface characterization of carbon fiber clamp. The result shows that laminated carbon fiber increases the durability and mechanical properties of the bend clamp for two weeks. The tensile test result shows that the uniaxial orientation has the highest tensile strength of about 2000N and is affected by the strong interfacial bond between the fiber and metal layers. The high impact energy of 2242 ± 0.001 J of the same orientation shows the stability of the clamp under unprecedented dynamic load and enhances the safety. The SEM result at uniaxial shows the resistance towards fracture has increased and was initiated from the air pocket in the composite.

The tensile properties of adhesively bonded single lap joints with short kevlar fiber

In this paper, short Kevlar fiber was added to epoxy resin adhesive to form a short fiber toughened adhesive, and its effect on the static strength and elongation at break of Carbon fiber laminate adhesively bonded single lap joints was investigated. 1 wt%, 2 wt%, 3 wt% and 4 wt% short Kevlar fibers were added to make short fiber toughened adhesive joints to investigate the effects of different contents of short Kevlar fibers on the connecting properties of the test pieces of Carbon fiber laminate single lap adhesively bonded joints; In addition, microscopic toughening mechanism of short Kevlar fiber in adhesives revealed by combining DIC technique and SEM technique. The test results showed that the addition of appropriate amount of short Kevlar fiber could slow down the crack extension compared with the without toughening specimens, but the toughening effect was weakened by excessive content. 2 wt% short Kevlar fiber toughened specimens achieved the best toughening effect, with 30.52 % increase in peak load and 25.78 % increase in elongation in tensile test. The combination of DIC and SEM further showed that short Kevlar fiber toughened joints absorb crack strain energy through fiber-bridging thus increasing adhesive properties.

Machine learning approach to evaluating impact behavior in fabric-laminated composite materials

Fabric-layered composites play a crucial role in safety and surveillance applications, making it imperative to accurately predict their impact behavior. This research focuses on creating a machine-learning model to predict the impact behavior of fabric-stacked composites, specifically carbon and Kevlar fabrics. Low-velocity impact tests were performed with varying parameters, and the impact energy and laminate thickness information were used to train machine-learning models to predict impact properties such as impact force, displacement, and absorbed energy. It was observed that the impact force increased by 118.5 % in carbon-laminated fibers and 175.8 % in Kevlar-laminated fibers, while the hybrid layer showed a 101.4 % increase upon impact from 16J. Displacement can affect the stability of the layered structure; thus, a similar stacking sequence is less stable than the hybrid laminated structure. In terms of absorbed energy, as the laminated layers increase, carbon fiber laminate absorbs 4.8 times more energy, and Kevlar fiber and hybrid laminated structures absorb 3 times more energy at higher impact energy. Furthermore, four machine learning models were used to investigate the impact behavior of identical and mixed-layered laminated composites. The impact force and displacement were predicted with higher accuracy using the polynomial regression model, achieving 80 % and 89 % accuracy, respectively. The support vector machine predicted the absorbed energy with approximately 96 % accuracy. In continuing, the experimental results closely matched the predictions made by the other machine learning models utilized in this study. Additionally, the importance of distinctive features and their influence on the performance of the machine learning-based model were interpreted using transposed features of importance and dependency plots. Various failure modes in fabric laminated composites were also identified, providing insights to enhance the performance of stacked fiber materials.

Mechanical and failure analysis of “outer single lap” adhesive joints of carbon fiber reinforced plastics under hygrothermal conditions

Carbon fiber reinforced plastics (CFRP)laminates are widely used in aircrafts. The laminates are often assembled into components by adhesive joints, which will be affected by elevated temperature and humidity during use, resulting in performance degradation. In this study, a compression test of “Outer Single Lap” adhesive joints of CFRP on the rear fuselage of a certain type of navigable aircraft was carried out to investigate the influence of hygrothermal conditions on their performance. The experimental environment includes the elevated temperature and wet condition (ETW) (71 °C, 85%RH) and Room temperature drying (RTD) (23 %, 30%RH). The test results show that RTD specimens have different stages, and the initial stage has good plasticity and no damage. However, when the load reached 50 %, the initial opening pattern damage occurred, which eventually led to the failure of the 20° opening. Compared with RTD samples, the compression properties of ETW samples decreased by 47.7 %, and the opening damage disappeared. Fracture features and stain analysis were performed. The findings suggest the fracture characteristic can change from a brittle fracture to a ductile fracture in different testing conditions, and the influence of the humid and thermal environment on the resin structural adhesive layer itself, the compression state of the carbon fiber laminates, the interface between the carbon fiber laminates and the resin structural adhesive layer should be fully considered in the design.

Experimental research of the effect of manufacturing holes and defects on the mechanical characteristics of laminated polymer composite

The paper presents a developed methodology for experimental research of the mechanical characteristics of a laminated polymer composite, taking into account manufacturing holes and defects. The results of experimental determination of mechanical characteristics are presented, the influence of the filler material, the type of fabric fiber weave, holes and manufacturing defects on the mechanical characteristics of laminated carbon fiber reinforced plastic are analyzed. The test specimens were made from carbon fiber 200T, 200P, ACM C300X and binder “Inject SL(B)”. Static tests of specimens for uniaxial tension, compression and three-point bending were performed.

Discontinuous interleaving strategies for toughening, damage sensing and repair in multifunctional carbon fibre/epoxy composites

Thermoplastic interleaving is a well-established approach to toughen carbon fibre thermoset laminates, studied over the past five decades. Recently, it has been revisited to create functional smart composites with damage sensing and repair capabilities with a renewed focus on the sustainability and longevity of components. However, the introduction of thermoplastic films within the interlaminar region often lowers fibre volume fraction and performance at elevated temperature, while the addition of impermeable continuous films during manufacture may also limit compatible fabrication methods. Moreover, the incorporation of dielectric thermoplastic films inevitably reduces through-thickness electrical conductivity and prevents accurate damage sensing of delamination in carbon fibre laminates. In this study, strategies of using discontinuous interleaving to improve both fracture toughness and thermomechanical properties of carbon fibre epoxy laminates, with the ability to monitor delamination damage and restore mechanical properties after a short healing step have been explored. Both the interleaving design and the physical properties of the thermoplastic were assessed, which has not been addressed previously. Interleaving high molecular weight thermoplastic with decreasing interleaf width and distance between interleaf zones results in increased fracture toughness (+347 %), by creating a superior toughened interlaminar zone, forcing a migration of delamination into the intralaminar region. A repair efficiency of 77 % was achieved when using a lower molecular weight of thermoplastic; however, the lack of thermoplastic over the entire fracture surface area affects the repairing performance universally. Damage sensing and thermomechanical properties were significantly improved compared to continuous interleaving, demonstrating that discontinuous thermoplastic interleaving strategies offer a favourable combination of toughening, thermal performance and accurate damage sensing for multifunctional high-performance composites.

Effects of translaminar edge crack and fiber angle on fracture toughness and crack propagation behaviors of laminated carbon fiber composites

Abstract In this study, the translaminar fracture toughness of carbon fiber laminated composites with different layer sequences was investigated experimentally and numerically for different crack directions. In the numerical study, first of all, the critical stress intensity factor was determined by using the M-integral method. Three-dimensional model and M-integral analysis were achieved in the ANSYS finite element package program. The non-local stress fracture criterion was used to in order to find failure curves of the materials. Then, in order to find the crack propagation directions numerically, the solid model was transferred to the LS-DYNA program and progressive failure analysis was performed. Fracture toughness decreased by 9.92 % with the change of crack angle from 15° to 90°. As the fiber angle changed from 0° to 45°, it decreased by 9.17 %. The biggest error between the experimental and numerical study results was found at α = 45°, with a rate of 12.3 %.

Automated Foreign Object Detection for Carbon Fiber Laminates Using High-Resolution Ultrasound Testing.

Carbon fiber laminates have become popular in the manufacturing industry for their many desirable properties, like good vibration damping, high strength-to-weight ratio, toughness, high dimensional stability, and low coefficient of thermal expansion. During the manufacturing process, undesirable foreign objects, such as peel-ply strips, gloving material, and Kapton film, can be introduced into the part which can lead to a localized weakness. These manufacturing defects can function as stress concentration points and oftentimes cause a premature catastrophic failure. In this study, a method using high-resolution pulse-echo ultrasound testing is employed for the detection and quantification of the dimensions of foreign object debris (FOD) embedded within carbon fiber laminates. This research presents a method to create high-resolution C-scans using an out of immersion tank portable housing ultrasound scanning system, with similar capabilities to that of a full immersion system. From the full-waveform dataset, we extract the FOD depth and planar dimensions with an automatic edge detection technique. Results from several carbon fiber laminates are investigated with embedded foreign objects that are often considered undetectable. Results are presented for FOD identification for two different shapes: circles with diameters ranging from 7.62 mm to 12.7 mm, and 3-4-5 triangles with hypotenuses ranging from 7.6 mm to 12.7 mm. CT imaging is used to confirm proper FOD placement and that the FOD was not damaged or altered during manufacturing. Of importance for the ultrasound inspection results, in every single case studied, the FOD is detected, the layer depth is properly identified, and the typical error is less than 1.5 mm for the primary dimension.

Numerical fatigue assessment of a cross-ply carbon fiber laminate using a probabilistic framework

A probabilistic framework is developed utilizing a two-scale modeling approach to efficiently consider the material variability that is typical for composite materials. The modeling integrates a macro-scale model with effective elastic properties extracted from micro-mechanical simulations. Using a weakest link modeling approach for fatigue assessment the combined effects of defects on fatigue strength in a Carbon Fiber Reinforced Polymer (CFRP) material can be investigated. A full fatigue test program is presented and is used to calibrate the probabilistic fatigue model. By including material variability in the numerical model, the calibrated probabilistic model improves the fatigue life prediction.

The effects of ply clustering positions and orientations on multi‐directional composite laminates' low velocity impact resistance

AbstractIn this paper, nine different carbon fiber laminates containing clusters are designed using the ant colony ACO algorithm, which have similar equivalent bending stiffnesses and B‐matrices, with the differences being the fiber orientation of the clusters and the position of the clusters in the laminates. The dynamic mechanical characterization of laminates for low velocity impact (LVI) at three different energies was carried out by means of a falling weight impact experiment. The experimental results show that the main form of failure of the laminate is delamination failure at low energy impacts, and shear fracture becomes more and more obvious with the elevation of the impact energy, which was observed in detail by the stereo microscope and electron microscope. The damage area of the laminate and the force and displacement curves after 30 J energy impact were compared by x‐ray scanning to derive the effects of the angle of the ply cluster fibers and the different positions of the ply clusters in the laminate on the impact resistance of the laminate. In conclusion, when designing the laminate, consideration should be given to designing 45° clusters on the impacted side and 90° clusters in the middle layer of the laminate to obtain the best impact resistance.Highlights Designed 9 types of laminates with different laminate structures based on ACO algorithm. Different laminates have similar equivalent bending stiffnesses and the B matrix as close to 0 as possible. LVI tests at three energies were performed on 9 types of laminates. The effects of different orientations of the clusters and the position of the clusters in the laminate on the impact resistance of the laminate were investigated.