This paper presents a novel carbon fiber reinforced polymer (CFRP) crash box design, incorporating numerical analysis and manufacturing aspects. Within the design and analysis phases, a novel numerical methodology is employed to mitigate computational costs in estimating specific energy absorption (SEA). The proposed approach involves a reduction in ply interfaces and modification of pertinent material properties to optimize energy dissipation, achieving more than 50% reduction in simulation time. This methodology is applied to the design of a composite crash box made of unidirectional (UD) carbon/epoxy prepregs, resulting in a new geometry: sun-like shape featuring four sinusoidal arms connected to a central circular core. Subsequent manufacturing and testing reveal a SEA value of 79.46 J/g for designed geometry, surpassing metallic counterparts by a factor of 3 to 4. Furthermore, this study conducts a comparative analysis of energy absorption performance between unidirectional and woven fabric prepregs for the same geometry. Utilizing carbon/epoxy woven fabric (WF) prepregs further enhances the SEA to 89.26 J/g. Finally, the application of edge tapering to the crash box structure is shown to eliminate initial peak loads, thereby preventing excessive deceleration.

One of the key challenges in using CFRP (Carbon Fiber Reinforced Polymer) structures is their susceptibility to low-energy impact damage, often indicated as barely visible impact damage (BVID). Such defects are difficult to detect and can compromise structural integrity. This study investigates the use of immobilized non-Newtonian fluids (NNF) as protective layers for CFRP composites subjected to low-energy impacts. Experimental tests were carried out with an Instron 9440 drop-weight impact tower (impact energy range 5–40 J) and high-speed imaging, comparing NNF coatings with rubber-based, caoutchouc-based, and spray-based protective layers. Non-destructive evaluation using computed tomography confirmed that NNF coatings dissipate impact energy through shear-thickening behavior, reducing delamination while preserving clear visual indicators of the impact site. Furthermore, the study assessed post-impact fatigue bending performance, revealing that the inclusion of NNF—either as an outer layer or as part of a sandwich structure—significantly enhanced the residual fatigue strength of the composites. Moreover, NNFs inherently preserve visible traces of penetration, thereby improving the detectability of impact locations through both unaided visual inspection and advanced imaging modalities such as computed tomography. In addition to external coatings, NNF was applied as a core in sandwich structures, demonstrating improved impact resistance compared to monolithic CFRP laminates and conventional CFRP–foam sandwiches. The protective performance was found to depend on fluid thickness and threshold shear rates required for viscosity transition, indicating that thicker layers do not always provide superior protection.

Abstract It is well known that the amount of damage caused by lightning strikes to protected composite airframe structures depends on the paint characteristics, often applied on the surface of composite structures to protect from environmental effects and to personalise a product. In this work, physically based models of the mechanical loads induced by lightning strikes are employed in the generation of the mechanical overpressure fields due to a simulated lightning strike, while accounting for the paint thickness. These fields are then implemented into a three-dimensional finite element framework and combined with a damage model to predict the effect of paint thickness on the mechanical damage in composite structures subjected to this type of events. These models accurately predict the increase of damage extent with the increase of paint thickness, which is corroborated by experimental observations from industry and by the experimentally observed trends reported in literature.

This paper focuses on the challenging problem of detecting the surface delamination damage during the drilling of carbon fiber reinforced polymer (CFRP). Considering the issues such as the low efficiency of traditional manual inspection, the limitations of non-destructive testing technologies, and the deficiencies of machine vision inspection algorithms, the point cloud processing technology is innovatively introduced. By analyzing the delamination damage mechanism and evaluation criteria, a drilling experiment is designed, and the point cloud data are collected. Voxel grid filtering and statistical filtering are applied to preprocess the point cloud. The moving least squares (MLS) method is adopted to smooth the point cloud. Based on the region growing algorithm and combined with the dual constraints of curvature and normal vector, the precise segmentation of the point cloud is realized. The experimental results demonstrate that the algorithm proposed in this paper achieves an accuracy rate of 91% for the detection of the surface delamination area with a repeatability accuracy of 1 mm 2 , and an accuracy rate of 93% for the depth detection with a repeatability accuracy of 40 μm. This provides a novel solution for the detection of surface delamination damage during the drilling of CFRP.

Virtual-to-real mapping: an AE missing signal generation and assisted localization method for defects in CFRP plates.

Delamination-induced buckling and brittle failure of carbon fibre reinforced polymer (CFRP) laminates in wind turbine blades

Reclaiming carbon fibers from waste carbon fiber-reinforced polymer composites via oxidative pyrolysis

Agitation-enhanced mild solvolysis using hybrid solvents for accelerating recycling of carbon fiber-reinforced polymer

Carbon fibre reinforced polymer (CFRP) sheets have a high strength to weight ratio and corrosion resistance, and consequently they have attracted much attention for flexurally strengthening deteriorated reinforced concrete (RC) beams. The study experimentally evaluated the flexural performance of RC beams strengthened with two types of CFRP materials carbon fibre fabric (CFF) and silicone coated carbon fibre laminates (SCCFL), under static cyclic loading (load-controlled). Three series of beam specimens were static cyclically loaded until significant damage including unstrengthened control beams and beams strengthened with single and double layers of CFF and SCCFL. As key parameters ultimate load capacity, the load deflection behaviour, the energy dissipation, crack propagation and stiffness degradation were evaluated. Results indicated that strengthening of the beam with CFRP increased the nominal flexural strength, and its fatigue resistance. The two materials used for strengthening exhibited different performance behaviour, among which the SCCFL strengthened beams exhibited higher load capacity and energy dissipation, less crack width and retained stiffness under static cyclic loading (load-controlled). SCCFL is proved to be more effective in retrofitting RC structure to dynamic or fatigue loadings.

Abstract Carbon Fiber Reinforced Polymer (CFRP) composites are widely used in reinforced concrete beams (RCBs) due to their high strength-to-weight ratio, corrosion resistance, and ease of application. However, accurately predicting the failure mode characteristics in these beams remains a significant challenge. This study presents a comprehensive framework for analyzing and predicting the failure modes of CFRP-strengthened RCBs using Deep Residual Neural Networks (DRNNs), finite element modeling (FEM), and Density-Based Sensitivity Analysis (DBSA). The proposed framework integrates experimental data and FEM simulations, leveraging DRNNs to model complex, nonlinear relationships between input parameters and failure mechanisms. DRNNs' architecture—comprising convolutional layers, residual building units, and batch normalization—facilitates accurate prediction of debonding loads, displacements, and failure modes. Residual shortcuts (i.e., connections), unlike other neural network architectures, allowed to bypass a few layers in the deep network architecture, circumventing the regular training with high accuracy problems. The DRNNs were instrumental in reducing reliance on large-scale physical experiments by generating synthetic data points required for DBSA convergence, making this framework practical for real-world applications. The study highlights the efficiency of DRNNs in reducing experimental requirements, achieving a high prediction accuracy of 90% and an AUC of 0.87. Validation of FEM with experimental results confirmed the framework's reliability in replicating real-world structural behavior. DBSA identified CFRP thickness and concrete density as critical factors influencing debonding load and displacement, while dry fiber density predominantly affects failure modes. Also, elastic properties of CFRP and concrete are essential for influencing debonding patterns.

Strengthening of reinforced concrete (RC) beams by externally bonded Carbon Fiber Reinforced Polymer (CFRP) is found to be a very effective method to increase their flexural strength capacity. However, the strengthening cost of the CFRP technique is very high and clients tend to avoid such expensive retrofitting methods. An alternative strengthening material, such as Glass Fiber Reinforced Polymer (GFRP), is a much less expensive material compared to CFRP. The GFRP strengthening method can achieve comparable strength gain and is an effective solution for strengthening RC beams. However, due to the lower strength and stiffness, a larger thickness of GFRP is required to obtain the target tensile strength. This increase in fiber thickness results in the commonly observed debonding failure of the GFRP-plated RC beams. Therefore, this study investigates the end anchoring technique by testing five beams under three-point bending. The first beam served as a controlled beam, while the second and the third beams were strengthened with one and three layers of GFRP to investigate the effect of the number of GFRP layers on debonding behavior. Anchored bolts were used to prevent debonding in the fourth specimen. The innovative W-shape inclined jacket technique was used for the last specimen. The test results revealed that the GFRP could effectively increase the beam's flexural strength. Nevertheless, when a larger number of GFRP layers was used, the debonding of GFRP occurred at an early loading stage. With the anchored bolted technique, the flexural strength of the RC beam was found to increase twice compared to the controlled specimen before failure due to the pulling off of the anchored bolts. Widespread shear cracks were observed near the failure stage. For the W-shape inclined jacket strengthening technique, the flexural strength was increased to a similar order as the anchored bolted technique, but the failure mode was due to slippage of the GFRP against the W-shape inclined jacket. Due to the use of a W-shape inclined jacket, the shear strength of the beam increased significantly. Therefore, the crack patterns near the final stage were controlled by flexure. The test results revealed that both techniques are effective methods to enhance the flexural strength of the GFRP-strengthened beam by achieving a similar magnitude of strength gain but failing in different failure mechanisms.

This study presents an experimental and analytical investigation into the impact behavior of electrospun polyacrylonitrile (PAN) nanofiber interleaved carbon fiber-reinforced polymer (CFRP) composites. Experimental testing was conducted using a single-stage gas gun, with photogrammetry employed to capture the high-speed impact dynamics. An energy-based analytical model was developed to identify dominant energy absorption mechanisms during impact. Results indicate that the nano-interleaved CFRP (Nano) exhibited superior ballistic performance compared to the baseline composite (Control). The ballistic limit increased from 70 m/s for Control to 80 m/s for Nano, a 14% improvement along with a 24% increase in energy absorption per unit areal density. Damage analysis revealed distinct failure patterns between the two. The analytical model accurately predicted energy absorption contributions: tensile failure of primary fibers (37%), secondary fiber deformation (33%), delamination (14%), and matrix cracking (15%) in Control; versus secondary fiber deformation (33%), delamination (26%), matrix cracking (25%), and minimal tensile failure (15%) in Nano. The strong correlation between experimental and analytical results confirms that PAN nanofiber interleaving significantly enhances the ballistic properties of CFRP, offering promising potential for future advancements in impact-resistant composite materials.

ABSTRACT This study investigates the potential of utilizing waste low‐density polyethylene (LDPE) as a protective coating against UV exposure for carbon fiber reinforced polymer (CFRP). The LDPE and epoxy‐coated CFRP samples were subjected to accelerated UV‐aging of up to 2000 h. This work simulates the open environment conditions where degradation products remain trapped in the polymer matrix and accelerate photo‐oxidation, thereby revealing the true extent of UV‐induced damage. Thermogravimetric analysis (TGA) analyses revealed progressive thermal degradation, with epoxy showing a delayed onset of decomposition and LDPE exhibiting decomposition onset after 500 h of UV‐aging. LDPE‐coated CFRP composites exhibited a steady decline in mechanical properties but retained more than 50% of their initial tensile strength up to 1000 h of UV‐aging. Morphological analysis of aged samples revealed increasing surface fragmentation and embrittlement in LDPE‐coated samples after 1000 h of UV‐aging. The carbonyl index calculated from Fourier Transform Infrared (FTIR) spectra reached ~0.6 after 1000 h of UV‐aging, suggesting the onset of extensive photo‐oxidative degradation. The results highlight that waste LDPE can serve as a low‐cost, moderate‐performance alternative coating for CFRP in non‐critical construction applications, offering a sustainable route for plastic waste reuse.

This work presents a structured screening of seven alternative carbon fiber reinforced polymer (CFRP) systems for use in Type IV hydrogen pressure vessels. The objective was to reduce carbon fiber usage while maintaining mechanical integrity and industrial viability. The investigated configurations included matrix-modified epoxies, chemically functionalized fibers, and a high-strength fiber variant. All laminates were manufactured using wet filament winding and assessed through standardized mechanical and thermal testing. To capture industrial relevance beyond material performance, a criteria-based evaluation framework was applied, incorporating processability, cost, scalability, sustainability, and regulatory compatibility. The results show that most variants achieved structural performance comparable to the reference system. A combined nanofiller–silane matrix delivered the highest strength values but exhibited reduced process stability, while a silane-modified matrix provided a more balanced performance profile with favorable practical scores. A radar-based comparison across five evaluation axes highlights trade-offs between mechanical performance and implementation feasibility. The study demonstrates that multi-dimensional screening approaches are essential for identifying viable composite systems at an early development stage. The proposed evaluation framework is transferable in its methodological structure and decision logic, while absolute numerical scores remain application- and dataset-dependent.

This paper explores the application of vacuum technology as a blue ocean strategy within the emerging electric vertical take-off and landing (eVTOL) industry. The research begins by outlining the broad applications of vacuum science in traditional industrial sectors. It then focuses on the prospects and challenges of eVTOL aircraft, identified as a high-potential future market. The core analysis demonstrates how vacuum pumps are critical in key eVTOL manufacturing and testing processes, including the curing of carbon fiber reinforced polymer (CFRP) composites for lightweighting, simulation testing of battery thermal management systems (BTMS), and optimization of hydrogen fuel cell systems under low-pressure conditions. By applying the Blue Ocean Strategy framework—including the ERRC (Eliminate, Reduce, Raise, Create) Grid and the Six Paths Framework—the study argues that the eVTOL sector represents an uncontested market space for vacuum technology. The conclusion emphasizes that vacuum science, by enabling lightweight material production and system validation, is poised to be a key enabler for urban air mobility, especially within China's policy-supported low-altitude economy landscape. (Approximately 150 words)

This study presents an approach to improve the performance of Carbon Fibre Reinforced Polymers (CFRPs) through the integration of Multi-Walled Carbon Nanotube (MWCNT)-doped copolyamide veils, focusing on the effects of aging and manufacturing techniques. Copolyamide veils containing 7.0 and 10.0 wt.% MWCNTs were introduced into the laminate structure using a novel pre-pressing step applied to unidirectional carbon fabric prior to the infusion process. This approach, which has not been previously reported, enables simultaneous enhancement of electrical conductivity and selected mechanical properties of CFRPs. The improvements are attributed to the exceptional adhesion achieved at the Carbon Fibre (CF)-copolyamide veil interface and the formation of effective conductive pathways across CF layers, in addition to the uniform distribution of MWCNTs within the veils. Furthermore, the results demonstrate that hygrothermal aging has a pronounced influence on the mechanical integrity of the modified CFRPs, leading to a reduction in mechanical performance associated with degradation of both the epoxy matrix and the copolyamide veils.

ABSTRACT In the research of infrared non-destructive testing (IR NDT) technology, the effectiveness of prefabricated defects is a crucial factor. This paper proposes a new method based on the vacuum-assisted thermal curing process (VATCP) for prefabricating delamination defects of carbon fibre reinforced polymer (CFRP) composites. This method simulates delamination by inserting a thin film with air-like thermal resistance between carbon fiber plies. Long-pulse excitation infrared non-destructive testing experiments and defect characterisation were conducted on the equivalent specimens to verify the rationality of the specimen design. This study proposes polyurethane (PU) as a new simulation material. Combined with the experimental and simulation methods, a systematic comparative analysis was conducted on the thermal response differences between several materials and real air delamination defects. Using multi-dimensional evaluation criteria, the reliability of polyurethane and polytetrafluoroethylene in simulating delamination defects was assessed. Results across these multiple analytical dimensions indicate that the thermal response characteristics of PU-simulated defects in CFRP most closely resemble those of air. Finally, the detection capability was quantitatively evaluated using long-pulse thermography combined with post-processing algorithms.

Carbon fiber reinforced polymer (CFRP) is prone to delamination damage during drilling, which seriously affects the processing quality. This study focuses on the use of variable parameter drilling technology. Firstly, an anisotropic constitutive model and a Hashin failure model for CFRP were constructed. Then, based on ABAQUS and VUMAT user subroutines, the influence laws of cutting parameters (spindle speed and feed rate) on delamination damage were explored. For the two methods of conventional fixed parameter drilling and variable parameter drilling (dynamic adjustment of feed rate when the drill reaches the exit plane), comparative simulation experiments were conducted. Subsequently, the genetic algorithm was introduced to optimize the spindle speed and feed rate under the variable parameter mode, and the results were verified through hole-making experiments. The results show that: under a constant spindle speed, the delamination damage factor increases monotonically with the increase in feed rate; under a constant feed rate, the delamination damage factor decreases first and then increases with the increase in spindle speed, presenting a nonlinear change characteristic. Among them, the variable parameter strategy of “first high feed, then low feed” can significantly reduce the delamination damage; the obtained optimal parameters can effectively balance the drilling quality and processing efficiency. This research provides theoretical and experimental support for optimizing CFRP hole-making parameters, addressing delamination control challenges in traditional drilling, and facilitating CFRP applications in aerospace and intelligent manufacturing.

The mechanical behavior of carbon-fiber-reinforced polymer (CFRP) laminates manufactured using plasma-assisted solvolysis recycled fibers was evaluated experimentally through a comprehensive mechanical testing campaign. The plasma-assisted solvolysis parameters were selected based on an earlier sensitivity analysis. Prepregs made from both virgin and recycled carbon fibers were fabricated via a hand lay-up process and manually stacked to produce unidirectional laminates. Longitudinal tension tests, longitudinal compression tests, and interlaminar shear strength (ILSS) tests were performed to assess the fundamental mechanical response of the recycled laminates and quantify the retention of mechanical properties relative to the virgin-reference material. Prior to mechanical testing, all laminates underwent ultrasonic C-scan inspection to assess manufacturing quality. While both laminate types exhibited generally satisfactory quality, the recycled-fiber laminates showed a higher density of defects. The recycled laminates preserved around 80% of their original tensile strength and maintained an essentially unchanged elastic modulus. Compressive strength was more susceptible to imperfections introduced during remanufacturing, with the recycled laminates exhibiting roughly a 14% decrease compared with the virgin material. On the contrary, the compressive modulus was largely retained. The most substantial reduction occurred in ILSS, which dropped by 58%. Overall, the results demonstrate that plasma-assisted solvolysis enables the recovery of carbon fibers suitable for remanufacturing CFRP laminates, while the observed reduction in mechanical properties of recycled CFRPs is mainly attributed to defects in manufacturing quality rather than to intrinsic degradation of the recycled carbon fibers.

Vibration-Based Structural Health Monitoring (SHM) systems offer significant potential for damage detection due to their non-destructive nature and real-time capabilities, while reducing maintenance costs for aerospace and automotive applications. This study investigates the effect of damage on the modal parameters of a Carbon Fiber Reinforced Polymer (CFRP) fixed-free beam, with the goal of identifying damage location and severity. The lamina material properties of the CFRP were evaluated using composite lamination theory (CLT). By altering the location and depth of the damage, numerical analyses were conducted on the CFRP beam, and discrepancies between the intact and damaged models were examined. Modal frequency shifts were quantified using Relative Natural Frequency Change (RNFC), and RNFC-based mapping surfaces dependent on damage location and severity were generated for first four transverse vibrational modes of the beam. The model was validated through experiments on the intact and damaged CFRP specimens. The beam was excited with an impact hammer near the fixed-end, and responses were collected by piezoelectric sensors placed along the beam and laser vibrometer focused on the free end of the beam. The modal parameters were extracted using Ho-Kalman’s subspace method and experimental RNFC results of damaged samples were calculated. Then Nearest Neighbor search algorithm was successfully employed to estimate the damage location and severity by comparing experimental results to generated RNFC-based mapping surfaces.