Carbon Fiber Composite Laminates Research Articles

High-velocity impact damage and compression after impact behavior of carbon fiber composite laminates: Experimental study

In this paper, the impact resistance of carbon fiber/resin composite laminates with a thickness of 2.5 mm at different impact velocities, angles and positions was investigated experimentally. In the process of high-velocity impact, fiber shear failure and tension failure are the main failure modes. When the impact velocity is 300 m/s, the fiber tension failure and matrix compression failure under oblique impact are more than that under normal impact, and the energy absorption of laminates is also lager than that under normal impact. The ballistic limits, energy absorption and delamination area of the center and edge impact of laminate are similar. In addition, the CAI tests are conducted to study the influence of different positions on the residual compressive strength of laminates after high-velocity impact, and the fracture loads and failure modes of two impact positions are quite different. The failure modes of the center impact laminate are main buckling failure, and the failure modes of the edge impact laminate are compression failure near the bullet hole side of the fixture and buckling failure near the center of the laminate. The research results can provide a reference for the residual strength of laminates after impact at different locations in practical situations.

Fatigue strength of self-piercing riveted joints of carbon fiber reinforced composite and Al5052 alloy plates

Self-piercing riveting (SPR) is an alternative to the conventional spot-welding method when joining sheets of dissimilar materials. In this study, the static and fatigue strengths of the SPR joints of carbon fiber composite laminate and an Al5052 aluminum alloy plate under various loading conditions were evaluated. Fatigue test results show that the load amplitudes, corresponding to the fatigue endurance limit, based on a lifetime of one million cycles, were 680 N, 323 N, and 305 N for loading angles of 0°, 45° and 90°, respectively, with corresponding fatigue ratios of the joints of 33%, 23% and 24%. The fatigue strengths at the loading angles of 45°, and 90° in terms of the equivalent stress intensity factor were found to be much higher than those at a loading angle of 0°. This is partially due to the difference in the fatigue failure modes. Regarding the fatigue strength designs of SPR joints consisting of composite laminate and aluminum alloy plates under various loads, it can be suggested that the tensile-shear strengths dominate the SPR fatigue strengths of the joints because they are highly vulnerable to tensile-shear loading.

Scalable High Tensile Modulus Composite Laminates Using Continuous Carbon Nanotube Yarns for Aerospace Applications.

An approach is established for fabricating high-strength and high-stiffness composite laminates with continuous carbon nanotube (CNT) yarns for scaled-up mechanical tests and potential aerospace structure applications. Continuous CNT yarns with up to 80% degree of nanotube alignment and a unique self-assembled graphitic CNT packing result in their specific tensile strengths of 1.77 ± 0.07 N/tex and an apparent specific modulus of 92.6 ± 3.2 N/tex. Unidirectional CNT yarn reinforced composite laminates with a CNT concentration of greater than 80 wt % and minimal microscale voids are fabricated using filament winding and aerospace-grade resin matrices. A specific tensile strength of up to 1.71 GPa/(g cm-3) and specific modulus of 256 GPa/(g cm-3) are realized; the specific modulus exceeds current state-of-the-art unidirectional carbon fiber composite laminates. The specific modulus of the laminates is 2.76 times greater than the specific modulus of the constituent CNT yarns, a phenomenon not observed in carbon fiber reinforced composites. The results demonstrate an effective approach for fabricating high-strength CNT yarns into composites for applications that require specific tensile modulus properties that are significantly beyond state-of-the-art carbon fiber composites and potentially open an unexplored performance region in the Ashby chart for composite material applications.

Low-velocity impact and compression-after-impact behaviors of twill woven carbon fiber/glass fiber hybrid composite laminates with flame retardant epoxy resin

Composite structures suffer from significant residual strength reduction as a result of invisible damage caused by impacts, which can cause severe harm without any prior warning. Fibers play a crucial role in improving the impact resistance of composite materials by providing strength, toughness, and energy absorption. This work explores the dynamic response and residual compressive strength of composite laminates reinforced with twill woven carbon fiber, glass fiber, and carbon fiber /glass fiber hybrid, subjected to low-velocity impact (LVI) and compression-after-impact (CAI) testing. First, the performance of woven carbon fiber composite laminates infused with flame retardant epoxy resin and general epoxy resin was studied. The results indicated a lower load-bearing capacity and elongation of the former. To enhance the impact resistance of the laminates, we explored the effects of incorporating glass fibers into the woven carbon fiber composite laminates. Our findings demonstrated that the introduction of glass fibers alteres the impact damage mode of the laminates and effectively improved their impact resistance and CAI strength. Further, several techniques were adopted to characterize the corresponding damage morphologies and failure mechanisms of the woven carbon fiber composite laminates, which provides valuable insights for their structural design and performance improvement.

A scientific view on composite inlays in running shoes: The influence of epoxy crosslink density on bending and fatigue properties

This study highlights the need for a deeper understanding of the structure-property relationships of carbon fiber reinforced thermosets applications, whenever considered as a functional part for running footwear. This is done, investigating the static and dynamic flexural properties of three different epoxy resins in prepreg-based carbon fiber composite laminates, varying the glass transition temperature (Tg). In this way, the inherent morphology of the resin was correlated with the fatigue properties of the laminate, which is crucial for the design of composite stiffening inlays for running shoes. First, it was shown that the crosslink density and aromatic content of the resin, which correlates with Tg, drastically affect the compressive strength of the matrix and are therefore crucial for the static and dynamic flexural properties of CFRP. Increasing the Tg from 147 °C to 269 °C leads to stiffening of the resin and thus increased resistance to fiber buckling, resulting in improved bending stiffness, flexural strength, bending angle, overall fatigue strength and thus durability of CFRP plates for running shoes. Moreover, the percentage of fibers in the loading direction can be considered as the main factor affecting the flexural properties of the laminate. Here, a quasi-isotropic stacking order leads to an increased bending angle but to a decrease in bending stiffness, flexural strength and fatigue strength compared to a unidirectionally reinforced composite due to a high load bearing capacity of the 0° fibers. This knowledge creates a basis to bridging the gap between composite material and biomechanical sports science for future work.

Study on the Stability of a Repair Process for Carbon Fiber Laminates

Carbon fiber-reinforced resin matrix composites are often used in the surface structure of helicopters. In the process of flight, the structure often suffers from different degrees of damage due to the influence of the harsh environment. To explore the superiority of the repair method and obtain a good repair process, the intact and damaged carbon fiber composite laminates were prepared in this paper. The damaged specimens were repaired by single-sided double-layer patch bonding. The allowable value of tensile strength of carbon fiber laminates was tested, and the mechanical properties of carbon fiber composite laminates after repair were studied. Combined with the failure mode of the specimen after failure, the results show that the mechanical properties of the repaired specimen can be restored to about 81.9 % of the non-destructive specimen. The single-sided double-layer patch can effectively improve the mechanical properties of the middle loading area. The repair process has high reliability and good stability, which provides a new method for the repair of the composite laminate structure.

Compression-After-Impact analysis of carbon/epoxy and glass/epoxy hybrid composite laminate with different ply orientation sequences

This article is a continuation study of the LVI and CAI response of the plain carbon fiber composite laminates and explores the experimental & numerical study of the post-impact damage propagation in carbon/epoxy and glass/epoxy hybrid laminate under compression. LVI (Low-Velocity Impact) tests are first carried out at three different energy levels, and the same specimens are put under a displacement-controlled compression test. The damage initiation and propagation in both impact tests and compression tests are studied using X-ray computed tomography. The results matched well with the results obtained from the finite element model, simulated using ABAQUS/explicit. The effect of the changing impact energy and the influence of the stacking orientation on post-impact damage propagation is studied. The strain maps during the compression tests are studied through Digital Image Correlation (DIC) technique based on which the stress–strain histories are plotted by using well-calibrated strain values. Upon completing the study, it is observed that the CAI (Compression-After-Impact) strength depends on the factors like properties of the constituent material, ply orientations and stacking sequence of the laminate. It is observed that even when the damage is barely visible on the surface of the specimen, compressive strength has been reduced drastically. The observed mode of damage propagation in CAI testing is buckling of the sub-laminates in the vicinity of the damage zone formed by the impact event. The size of the impact damage zone depends on the impact energy, which actually governs the CAI strength.

Optimum Design of Ply-up of T800 Carbon Fiber Composite Laminates with Holes

Based on the HyperWorks software, this paper takes the layup sequence of carbon fiber composite laminates as the design variables, the main strain of the laminates and the continuous angle layup not exceeding four layers as constraints, and the maximum bearing capacity as the design goal. The optimized design of the laminate and the corresponding experimental verification were carried out. The experimental results are in good agreement with the simulation analysis results, indicating that the optimization design method proposed in this paper is reasonable.

Impactor Diameter and Ply Number Effects on the Impact Behavior of Carbon Fiber Composite Laminates

As it is known, impact damage is a major mechanical phenomena for composite materials especially used in the aerospace structures. The factors affecting the impact behaviour of the composites depend on the impactor systems as well as the target material. In this study ply number and impactor geometry effects of carbon fiber reinforced epoxy composites were investigated by impact tests. In this context, drop weight impact tests were carried out at 6J, 12J and 24J energy levels by using hemispherical impactors with 10 mm and 20 mm diameters. Laminated composites were manufactured in 6, 10 and 14 plies with vacuum infusion method. The effects of laminate thickness, impactor diameter and impact energy effects on the force, velocity, absorbed energy and damage surfaces were investigated. It is observed that impactor geometries and velocities caused the different damage mechanisms in composites and impactors played an important role in determining the penetration and perforation behaviours of composites.

An experimental and numerical study of industrially representative wrinkles in carbon fibre composite laminates

Wrinkles (out-of-plane waviness) are a common carbon fibre composite manufacturing defect that causes significant reductions in the components’ mechanical properties. The substantial cost implications of empirical testing has led to industrial demands for reliable and representative wrinkle models. This paper presents a novel modelling method for laminates with wrinkle geometries measured from non-destructive testing and/or sample cross-sections. The resulting finite element modelling pre-processor offers a self-contained system of mesh generation, local material orientation calculation, material assignment, boundary condition selection and solver specification. The approach was validated by comparison with pre-existing analytical models and experimental data. Through the resulting rapid model generation, the influence of various physical wrinkle parameters were assessed at an unprecedented rate and sensitivity. For example, this highlighted the dominant dependence of wrinkle angle on the laminate’s compressive strength. Additionally, increases in wrinkle extent and reductions in amplitude decay rate were shown to be detrimental to mechanical properties.The model was then validated against an experimental study on industrially relevant carbon-epoxy laminate samples to understand the effect out-of-plane waviness on compressive properties. The model results showed good agreement to the experimental values (<15% error) and at least a 32% reduction in compressive strength.

Experimental and numerical study on the ballistic impact resistance of the CFRP sandwich panel with the X-frame cores

Fiber reinforced composite sandwich structures have wide applications in reducing the weight of high-speed aircrafts due to their processibility and high specific performance. It is of great significance for the safety to study the failure mechanism of composite sandwich structures under the ballistic impact and improve the structural impact resistance. However, the previous researches mainly focus on the performance of the hybrid sandwich structures with foam cores or metal grid cores. The main novelty of this study is to investigate the ballistic impact resistance of a composite composite sandwich panel with the fiber reinforced X-frame cores by using the projectile impact tests and numerical simulations. The impact resistance of this integrally molded fiber reinforced cores is less reported and is expected to be superior than that of the common aluminum, polymer and foam cores. For comparison, the carbon fiber composite cross-ply laminates with the identical areal density and the foam reinforced sandwich panels with the X-frame are tested. The experimental results indicate that the ballistic limit of the X-frame sandwich panel is similar to that of its equivalent laminate under the normal projectile penetration. Filling foams increase the structural ballistic limit velocity and energy absorbing amount by 18.2% and 33.9%, respectively. The widest range of fiber breakage and delamination on the sandwich panel observed appear at impact velocities approaching the ballistic limit, while the local damage is found under the high-speed perforation. The numerical results indicate that the projectile kinetic energy dissipated by the X-frame core accounts for over 50% of the total under the normal impact and the core has the better specific energy absorption capacity than the skins. The impact oblique angle and impact position are found to have a significant effect on the impact resistance of the X-frame sandwich panel through the numerical calculations.

Damage Characterization of Carbon Fiber Composite Pressure Vessels Based on Modal Acoustic Emission.

This study characterized the damage characteristics of carbon fiber composite pressure vessels by the modal acoustic emission (MAE) method. The study showed how to use the extracted damage modal features and established MAE parameters to determine the damage mode of composite pressure vessels. First, the A0 and S0 Lamb modes of the AE signal were split through mode separation, and the time window was selected to establish the MAE characteristic parameters. Subsequently, based on the MAE parameters and the damage mode characteristics established from single damage experiments, a damage mode discrimination method was established. A bending test of carbon fiber composite laminates proved that the modal separation method and the MAE parameters establishment are reasonable and effective. The results from the hydraulic test of the graded loading performed on 20 MPa carbon fiber composite pressure vessels showed the accuracy of the damage mode discrimination method, and the damage state of the pressure vessel could be analyzed using the fiber fracture damage threshold according to the MAE parameters.

Degradation mechanism for mechanical property of carbon fiber reinforced epoxy composite under simulated seawater absorption coupled with flexural load

Property evolution of carbon fiber reinforced epoxy composite used in marine environment was investigated in this paper. The moisture absorption and flexural properties of carbon fiber composite laminate were studied under the combined pretreatment condition of simulated seawater and three-point flexural load. An in-situ observation system was used during mechanical test to analyze damage initialization and development on dry and wet composites. Theoretical analysis considering hydro-mechanical coupling was conducted, based on experimental data, moisture simulation and stress analysis. Stress distribution under flexural load was discussed using finite element method, and its effects on moisture diffusion and failure process were analyzed based on the theoretical and experimental results. It demonstrates that moisture absorption of composites is inhibited as flexural load is applied during moisture absorption. It is attributed to compressive stress concentration of composite on the loading region. The retention of flexural property shows slight increase under moisture coupled with flexural load, which is resulted from decreased moisture content. Failure process of composite during three-point flexural test after immersion is different from that of dry composite, especially for the position and number of crack formation and propagation. Weakened interlaminar interface and more large cracks are found after immersion coupled with flexural load, which are explained based on water degradation and initial damage at stress concentration region. It denotes that more attentions should be paid on failure process of wet composite structure in marine field.

Analysis of vibration attenuation characteristics of large thickness carbon fiber composite laminates

The vibration attenuation and damping characteristics of carbon fiber reinforced composite laminates with different thicknesses were investigated by hammering experiments under free boundary constraints in different directions. The dynamic signal testing and analysis system is applied to collect and analyze the vibration signals of the composite specimens, and combine the self-spectrum analysis and logarithmic decay method to identify the fundamental frequencies of different specimens and calculate the damping ratios of different directions of the specimens. The results showed that the overall stiffness of the specimen increased with the increase of the specimen thickness, and when the thickness of the sample increases from 24mm to 32mm, the fundamental frequency increases by 35.1%, the vibration showed the same vibration attenuation and energy dissipation characteristics in the 0° and 90° directions of the specimen, compared with the specimen in the 45° direction, which was less likely to be excited and had poorer vibration attenuation ability, while the upper and lower surfaces of the same specimen showed slightly different attenuation characteristics to the vibration, the maximum difference of damping capacity between top and bottom surfaces of CFRP plates is about 70%.

A Comparative Study to Evaluate the Essential Work of Fracture to Measure the Fracture Toughness of Quasi-Brittle Material.

In the present work, three different woven composite laminates were fabricated using the hand lay-up method. The woven reinforcement fibres were carbon fibres (CFRP), glass fibres (GFRP-W) and (GFRP-R) in combination with epoxy resin. Then, the central notch specimen tensile test (CNT) was used to measure the fracture toughness and the corresponding surface release energy (). Then, the data were compared with the essential work of fracture (we) values based on the stored energy of the body to obtain a new standard fracture toughness test for composite laminates using relatively simple techniques. In addition to an extended finite element model, XFEM was implemented over a central notch specimen geometry to obtain a satisfactory validation of the essential work of fracture concepts. Therefore, the average values of () were measured with CNT specimens 25.15 kJ/m2, 32.5 kJ/m2 and 20.22 kJ/m2 for CFRP, GFRP-W and GFRP-R, respectively. The data are very close as the percentage error for the surface release energy measured by the two methods was 0.83, 4.6 and 5.16 for carbon, glass and random fibre composite laminates, respectively. The data for the fracture toughness of XFEM are also very close. The percentage error is 4.6, 5.25 and 2.95 for carbon, glass and random fibre composite laminates, respectively. Therefore, the fundamental work of the fracture concept is highly recommended as a fracture toughness test for composite laminates or quasi-brittle Material.

Research on Tensile Properties of Carbon Fiber Composite Laminates

In order to study the thread tensile performance of carbon fiber composite laminates, the connection between the test piece, connecting bolts, bushings, and the composite matrix, was leveraged for loading, and combined with an ultra-sound scanning imaging system, experiments were carried out on the dynamic response to record the failure behavior of the laminate structure of equal thickness. The effects of different pull-off loading strengths on the dynamic failure process, deformation profile, midpoint deformation, failure mode, and energy dissipation ratio of the thread were studied. The results show that (1) with the increase in pull-off strength, the response speed of mid-point deformation increases, the thread deformation mode changes from overall deformation to partial deformation, and the localized effect increases, accompanied by severe matrix and fiber fracture failure; (2) the thread energy dissipation ratio ascends with increasing pull-off strength and exhibits three distinct stages, i.e., elastic deformation, central fracture, and complete failure, which are directly related to the structural failure mode; (3) the failure load increases with the increment of the thickness of the laminate, and the maximum failure surface of the specimen will move from the upper layer of the laminate to the lower layer along the thickness direction; (4) the deformation velocity of the midpoint augments with the increase in the tensile rate, which can be included as a factor to assess the tensile properties of carbon fiber composites.

Effect of CNTs deposition on carbon fiber followed by amination on the interfacial properties of epoxy composites

To enhance the interfacial properties of carbon fiber/epoxy composites, a layer of carbon nanotubes (CNTs) about 25–30 nm thickness was deposited on carbon fiber surface at low temperature by chemical vapor deposition (CVD), and then the CNTs were aminated to increase the surface wettability. Microbond test was conducted to characterize the interfacial shear strength (IFSS) of carbon fiber reinforced epoxy resin composites and the interlaminar shear strength (ILSS) and modeⅠfracture toughness (GIC) of carbon fiber composite laminates were also measured to characterize the interlaminar properties. The results showed that this surface treatment method significantly increased the fiber surface energy, effectively improving the interfacial bonding of the composites. The IFSS, ILSS and GIC of composites reinforced by the final treated carbon fiber were 39.42%, 32.21% and 95.33% higher than that of composites reinforced by the raw carbon fiber. The fracture surfaces also indicated a great interphase appeared in the composites, which was formed by the mechanical interlocking of CNTs and the chemical reaction between surface functional groups and resin.

Failure mechanism of carbon/ultra-high molecular weight polyethylene twill fiber reinforced hybrid laminates under ballistic impact

Carbon fiber reinforced plastic (CFRP) have been widely used in recent years for their high specific strength and stiffness. However, due to the high brittleness and low elongation, its application in protection engineering was limited. The introduction of other ductile fibers can ameliorate this shortcoming. In this paper, laminated construction and failure mechanism of twill carbon fiber and ultra-high molecular weight polyethylene (UHMWPE) fiber hybrid composite laminates under ballistic impact were comprehensively studied. Three different interface properties were characterized by peeling test. The simulation results were in good agreement with the ballistic impact experimental results. The sample of 4C4P with carbon fiber in the front and UHMWPE fiber in the back shows the best impact energy absorption performance,with the specific energy absorption increased by 92.22%. Based on the computed tomography (CT) scanning, delamination damage cloud images of the composite laminates were presented for the first time. The improvement of interlayer fracture toughness can enhance the impact resistance of laminates, which mainly depending on the stacking sequence and interface properties. It provided a new idea for the study of impact damage of laminated structures.

Experiment and analysis of mechanical properties of carbon fiber composite laminates under impact compression

Abstract Composite materials are more and more widely used in aircraft structural design, and impact damage is the most serious defect/damage form of aviation composite structures in service. Therefore, it is of great significance to study the impact resistance of composites with different materials and structural forms for aircraft structural design. In this article, the damage of reinforced fiber/resin composite laminates with unidirectional carbon fiber prepreg (UIN23100), carbon fiber woven fabric (W-3021FF), and carbon fiber-aramid fiber blended fabric (W-38211) under the same impact energy were studied. The impact damage area was scanned and analyzed by ultrasonic C-scan, and the impact resistance of the three laminates were obtained. Finally, the compression bearing capacity of carbon fiber laminates after impact was tested, and the compression failure mode of each material has been analyzed. The results show that the impact resistance of carbon fiber unidirectional prepreg was stronger than that of carbon fiber woven fabric; the compression bearing capacity of carbon fiber laminate after impact was higher than that of carbon fiber unidirectional prepreg; the post impact bearing capacity of W-38211 was higher than that of W-3021FF.

Experimental and numerical studies on low‐velocity impact damage of composite laminates toughened by nickel‐coated carbon fiber veil

AbstractThe low‐velocity impact response of carbon fiber composite laminates toughened by nickel‐coated carbon fiber (NiCF) veil interleaves was investigated experimentally and numerically. The experimental results indicated that the impact resistance of laminates with a layer of NiCF veil of 34 g/m2inserted in the midplane was improved, especially in terms of increased peak impact force and residual compressive strength (by 16.15%), and reduced damage area (by 30.92%). The enhancement mechanisms were attributed to the breakage, pull‐out, and crack bridging of the NiCF veil, as well as the peeling of nickel coating, which enhanced the carbon fiber/resin interfacial adhesion. A numerical model based on continuum damage mechanics and cohesive zone model was developed and its validity was verified. The simulation results confirmed that NiCF veils reduced energy absorption by enhancing the interlaminar properties of laminates, thereby reducing impact damage. Moreover, laminates with higher areal density and more layers of NiCF veils had higher impact force and smaller damage area, and thus had better impact resistance.