Search Results (386)

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. Full article

Glued laminated timber (glulam) is increasingly adopted as a sustainable structural material; however, its performance under bending can be limited by brittle tensile failures and variability caused by natural defects. This study examines the flexural behavior of glulam beams strengthened with externally bonded carbon fiber reinforced polymer (CFRP) sheets. A four-point bending experimental program was carried out on glulam beams with varying CFRP bonded lengths, including unreinforced control beams. The results demonstrate that CFRP reinforcement enhanced load–carrying capacity by up to 48%, increased stiffness, and shifted failure modes from brittle tension–side ruptures to more favorable compression–controlled mechanisms. A nonlinear finite element (FE) model was developed using DIANA software 10.5 to simulate the structural response of both unreinforced and CFRP–strengthened beams. The numerical model accurately reproduced the experimental load–deflection behavior, stress redistribution, and failure trends, with deviations in ultimate load prediction generally within ±16% across all reinforcement configurations. The simulations further revealed the critical influence of CFRP bonded length on stress transfer efficiency and failure mode transition, mimicking experimental observations. By integrating experimental findings with numerical simulations and simplified analytical predictions, the study demonstrates that reinforcement length and bond activation govern the effectiveness of CFRP strengthening. The proposed combined methodology provides a reliable framework for evaluating and designing CFRP strengthened glulam beams. Full article

Carbon-fibre reinforced polymer (CFRP) laminates are susceptible to both static and fatigue-driven delamination. Predicting this type of failure in curved composite structures, often referred to as delamination by unfolding, remains a critical challenge. This work presents the development of a Virtual Crack Closure Technique (VCCT)-based computational method for simulating fatigue-driven delamination propagation under non-constant mixed-mode conditions. The fatigue delamination growth model follows a phenomenological approach based on a Paris–Erdogan-based power-law relationship, where the delamination propagation rate depends on the strain energy release rate. This methodology has been implemented as a user-defined subroutine, UMIXMODEFATIGUE, for Abaqus, integrating the effects of load ratio and mode mixity conditions while leveraging the mode separation provided by VCCT. The proposed approach is validated against an experimental case involving a four-point bending test applied to an L-shaped CFRP curved beam specimen with a unidirectional layup. Unlike the existing standard configuration, the proposed test campaign introduces a non-adhesive Teflon foil insert at the bend, placed within the midplane layers to act as a delamination initiator, representing a manufacturing defect. In addition to the testing machine, digital image correlation (DIC) is used to monitor delamination length. The simulation method developed accurately predicts fatigue delamination propagation under varying mode mixity at the delamination front. By improving delamination modelling in composites, this approach supports timely maintenance and helps prevent fatigue failures. Additionally, it deepens the understanding of how the mode mixity influences the delamination propagation process. Full article

Multifunctional aerostructures that carry mechanical loadings while conducting electrical currents offer a promising approach to reduce the weight of Electrical Power Systems (EPS) of aircraft. However, Carbon Fibre-Reinforced Polymer (CFRP), when used for aerostructures, presents challenges in achieving multi-functionality due to anisotropic mechanical, electrical, and thermal properties. These properties are interdependent on both laminate-level design factors (fibre/resin choice, fibre volume fraction, stacking sequence, and electrode configuration) and system-level EPS constraints (allowable voltage drop, current, and installation geometry). State-of-the-art material design and selection methods lack a coupled mechanical–electro–thermal design and selection approach to overcome these challenges of a complex design space to enable identification of multifunctional CFRP (MF-CFRP) solutions. This paper presents the first methodology for the design and selection of MF-CFRP with combined electrical, structural, and thermal properties. The methodology integrates requirement capture, laminate layup determination, electro-thermal assessment, option ranking, and manufacturing route selection. The methodology couples laminate-level design factors with system-level EPS constraints and includes iterative loops to refine either the CFRP design or the EPS parameters when no solution initially exists. The methodology is demonstrated to enable the design of a CFRP component to conduct the electrical current as part of the 28 V_DC network in an aircraft. This case study demonstrates the value of the methodology to identify knowledge and dataset gaps necessary for MF-CFRP design, alongside enabling the design of MF-CFRP components to enable increased power density of weight-critical EPS. Although the case study focused on a 28 V_DC system, the methodology is generalisable to other aircraft electrical architectures since system-level electrical parameters are used within the methodology as adaptable inputs. Full article

Externally bonded carbon-fiber-reinforced polymer (CFRP) can increase the flexural capacity of steel beams, but the benefit is often limited by the performance of the adhesive interface. This study develops and validates a three-dimensional finite-element model (FEM) with an explicit cohesive-zone representation of the adhesive layer. It reproduced benchmark four-point bending tests in terms of peak load, corresponding mid-span deflection, and the transition from end/intermediate debonding to laminate rupture. A one-factor-at-a-time parametric analysis is carried out to examine the influence of (i) member geometry (beam depth; flange and web thickness), (ii) CFRP configuration (bonded length; laminate thickness), and (iii) bond quality (cohesive normal strength). Within the ranges studied, cohesive strength and bonded length are the primary variables controlling both capacity and failure mode: strengths below about 25 MPa and short plates lead to debonding-governed response. Increasing strength to around 27 MPa and bonded length to 650–700 mm delays debonding, promotes CFRP rupture, and produces the largest incremental gains in peak load, while further increases in length give smaller additional gains. Increasing laminate thickness and steel depth or flange/web thickness always raises peak load, but under baseline bond conditions failure remains debonding and the added material is only partially mobilized. When cohesive strength is increased above the threshold, additional CFRP thickness becomes more effective. A linear regression model is fitted to the FEM dataset to express peak load as a function of bonded length, cohesive strength, laminate thickness, and steel dimensions, and is complemented by a failure-mode map and a cost–capacity chart based on material quantities. Together, these results provide quantitative trends and simple relations that can support preliminary design of CFRP-strengthened steel beams for similar configurations. Full article

Delamination remains a critical failure mode in carbon fiber-reinforced polymer (CFRP) composites, particularly under cyclic loading in aerospace and automotive applications. This study explores whether nanoscale reinforcement with graphene-based materials can enhance delamination resistance and identifies the most effective nanofiller type. Two distinct graphene nanospecies—reduced graphene oxide (rGO) and carboxyl-functionalized graphene nanoplatelets (HDPlas)—were incorporated at 0.5 wt% into CFRP laminates and tested under static and fatigue mode I loading using double cantilever beam (DCB) tests. Both nanofillers enhanced interlaminar fracture toughness compared to the neat composite: rGO improved the energy release rate by 36%, while HDPlas achieved a remarkable 67% enhancement. Fatigue testing showed even stronger effects, with the fatigue threshold energy release rate rising by 24% for rGO and 67% for HDPlas, leading to a fivefold increase in fatigue life for HDPlas-modified laminates. A compliance calibration method enabled continuous monitoring of crack growth over one million cycles. Fractography analysis using scanning electron microscopy revealed that both nanofillers activated crack bifurcation, enhancing energy dissipation. However, the HDPlas system further exhibited extensive nanoparticle pull-out, creating a more tortuous crack path and superior resistance to crack initiation and growth under cyclic loading. Full article

Laser micro-drilling was applied to Fe substrates to enhance the interfacial properties of carbon fiber-reinforced polymer/iron laminates. This architecture is referred to as a resin-interlocked Fe-CFRP hybrid composite. Inspired by human hair follicles’ exceptional adhesion and filling efficiency, novel biomimetic frustum-integrated cylindrical cavities were engineered for Fe surface modification. Experimental results demonstrate that laser-processed surfaces with varied hole geometries (conical, conical frustum, cylindrical, and frustum-integrated cylindrical cavities) exhibit significantly improved interfacial performance compared to untreated Fe controls. Specifically, RI-Fe/CFRP specimens containing frustum-integrated cylindrical cavities achieved the highest shear strength, with a 44.8% increase over non-drilled counterparts. Subsequent molecular dynamics simulations confirmed the critical role of the cavity geometry, demonstrating that the frustum-integrated cylindrical cavity elevates the Fe–Diglycidyl ether of bisphenol-A interfacial energy and van der Waals interactions by 45.44% and 50.66%, respectively, versus the flat surface. The interfacial energy enhancement mechanism via distinct hole configurations was systematically studied. Furthermore, comprehensive micro-hole topology analysis elucidated the reinforcement mechanism in resin-interlocked Fe-CFRP hybrid composites. Results demonstrate that frustum-integrated cylindrical cavities significantly enhance DGEBA-3,3′-diaminodiphenyl sulfone fluidity during interface simulation, promoting mechanical interlocking and optimized resin-filling efficiency. Laser micro-drilling effectively improves Fe-DGEBA interfacial performance. These findings provide critical insights for designing high-performance composites in aerospace and automotive applications. Full article

Modern automotive design has increasingly embraced plastics for bumper construction; however, it can lead to material degradation. To overcome these limitations, the automotive industry is turning to fiber–resin material, namely carbon–epoxy composites. Our research focuses on determining the effects of fiber orientation and angle alignment on the structural stress of the car bumper, examining the hybrid material (carbon–epoxy reinforced by CFRP) in static structural tests, and performing dynamic impact tests at various speeds, applying the Tsai–Wu criterion as a basic failure model. However, Tsai–Wu’s failure in numerical analysis highlights the limitation of not being able to experimentally distinguish between failure modes and their interaction coefficients. To address this issue, we employ ANSYS^® 2024 R1 with a Fortran program, which enables more accurate estimation of failure behavior, resulting in an average error of 13.19%. To identify research gaps, machine learning (ML) plays a vital role in predicting parameter values and assessing data normality using various algorithms. By combining ML and FEA simulations, the result shows strong data performance. Bridging from 2 mm mesh sizing of 50% carbon–epoxy woven/50% CFRP laminate in 6 mm thickness at 0° orientation shows the most distributed shear stresses and deformation, which converged toward stable values. For comprehensive research, total deformation was included in ML analysis as a second target to build a multivariate analysis. Overall, Random Forest (RF) is the best-performing model, indicating superior robustness for modeling shear stress and total deformation. Full article

This work minimizes battery pack enclosure mass (kg) and peak deformation (mm) under a side-pole impact condition and validates the results by finite-element reruns complemented by coupon-level material tests. A 64-run optimal Latin hypercube dataset trained ARD Matérn-5/2 Gaussian-process surrogates, and NSGA-II performed a multi-objective search on a manufacturability grid (${\Delta }_t$ = 0.5 mm). Decision-making processes used knee-region filtering and TOPSIS in the normalized objective space with robustness checks (uncertainty inflation, weight perturbation, and cross-kernel audit). The representative optimum reduced mass from 149.40 kg to 115.20 kg (−22.89%) while keeping peak deformation essentially unchanged (66.17 → 66.25 mm) in independent reruns. To examine material dependence, an orthotropic CFRP cross-check was performed by substituting the upper cover and side walls: the iso-thickness mapping yields 90.40 kg with 68.67 mm (+3.65% vs. aluminum $x^{\star }$), whereas a constrained iso-mass setting ($H_1$ = 7.0 mm, $H_2$ = 7.0 mm) gives 111.70 kg with 80.85 mm (+22.04%). The observed trends are consistent with the laminate’s lower transverse-shear moduli and shear-sensitive load paths; damage evolution and lay-up optimization are outside the present scope. The workflow provides a reproducible route to balance lightweighting and deformation control for battery pack enclosures. Full article

Carbon fiber-reinforced polymer (CFRP) laminates are extensively utilized in aerospace and advanced engineering fields because of their outstanding strength-to-weight ratio and superior fatigue durability. However, despite their high in-plane strength and stiffness, CFRP laminates are inherently susceptible to delamination. This weakness stems from the relatively low interlaminar strength of the resin-rich interfaces between layers compared to the much stronger in-plane fiber reinforcement. During mechanical processes such as drilling and punching, out-of-plane stresses and interlaminar shear forces develop, concentrating at these weak interfaces. This study investigates the delamination behavior of CFRP laminates with 3 to 7 plies under drilling and punching, focusing on the effects of ply count and drilling speed. Experimental tests were conducted using an 8 mm punch and drill bit at 2500, 3000, and 3500 rpm, reflecting typical workshop practices for M8 fastener holes. Scanning electron microscopy (SEM) analyses at different magnifications were used to quantify delamination extent. A three-dimensional finite element model was created in ABAQUS/Explicit, integrating the Hashin failure criterion to predict damage initiation within the plies and cohesive surfaces to simulate interlaminar delamination. The analyses show that with proper support, punching can approach the damage levels of drilling for thin CFRP plates, but drilling remains preferable for thicker laminates due to better integrity and tool longevity. Full article

X-ray micro-computed tomography (Micro-CT) is an advanced technique capable of non-destructive detection of internal defects in materials. Fiber-reinforced polymer (FRP) laminates are prone to forming defects such as pores during the manufacturing process, which significantly affect their mechanical properties. In this study, Micro-CT technology was employed to conduct non-destructive testing on carbon fiber (CFRP), glass fiber (GFRP) and carbon/glass hybrid (C/G) laminates. Combined with the U-Net++ deep learning model, precise segmentation and three-dimensional reconstruction of pores were achieved. A systematic quantitative analysis was carried out on the distribution, size, volume and porosity of pores in six specimens with two layup angles (0/90 and ±45). The research results show that the pores in CFRP are mainly dispersed micro-pores and are relatively evenly distributed; the porosity of GFRP is the highest, and large interlaminar pores are prone to forming. The porosity fluctuates sharply in the thickness direction, revealing that the interlaminar interface is a defect-sensitive area. This provides a reliable quantitative basis and theoretical support for optimization and defect assessment. Full article

In this study, nonlinear Lamb wave-based higher harmonic detection is employed to assess the tensile-induced microdamage in patch-repaired carbon fiber-reinforced polymer (CFRP) structures. With respect to the external repair design optimization model based on proxy technology, the minimum nonlinear coefficients are obtained from the optimal patch design parameters, thereby improving the tensile performance of the repaired structure and capturing the repair effect of the patch. First, the nonlinear Lamb wave propagation behaviors of patch-repaired CFRP laminates are assessed under different tensile displacements, and the accuracy of the finite-element model strategy is confirmed by experimental results. Second, on the basis of the tensile displacement induced under the highest nonlinear response, the effects of the radius, thickness and rotation angle of the patch on the secondary and tertiary nonlinear coefficients of the composite glued repair structure and the tensile damage area of the matrix are discussed. After the effects of individual parameters on the patch repair structure are analyzed, the effect of multiple target parameters on the quadratic relative acoustic nonlinearity coefficient of the patch repair structure is investigated via a Latin hypercube experimental design and the Diffuse Approximation method, and the optimal solutions for the mesh parameters of the patch repair structure are successfully obtained, which provides a reference for the multiparameter optimization of patch repair structures in engineering cases. Full article

The potential for structural health monitoring (SHM) in fibre-reinforced polymers (FRPs) using electrical resistance measurements (ERMs) has gained increasing attention, particularly in carbon fibre-reinforced polymers (CFRPs). Most existing studies are limited to single-axis measurements on coupon-scale specimens, whereas industrial applications demand scalable solutions capable of monitoring large areas, with more complex sensing configurations. Structural health monitoring (SHM) of carbon fibre-reinforced polymers (CFRPs) using electrical resistance measurements offers a low-cost, scalable sensing approach. However, predicting surface resistance between arbitrarily placed electrodes on unidirectional (UD) CFRP laminates remains challenging due to anisotropic conductivity and geometric variability. This study introduces a practical analytical model based on two geometry-dependent parameters, effective width and effective distance, to estimate resistance between any two electrodes arbitrarily placed on UD CFRP laminates with 0° or 90° fibre orientations. Validation through finite element (FE) simulations and experimental testing demonstrates good matching, confirming the model’s accuracy across various configurations. Results show that the dominant electrical current path aligns with the fibre direction due to the material’s anisotropic conductivity, allowing simplification to a single-axis resistance model. The proposed model offers a reliable estimation of surface resistance and provides a valuable tool for electrode array configuration design in CFRP-based SHM. This work contributes to enabling low-cost and scalable electrical sensing solutions for the real-time monitoring of composite structures in aerospace, automotive, and other high-performance applications. Full article

This study investigates seven advanced hybrid composite thermal protection system (TPS) prototypes, featuring an innovative internal air chamber design that reduces heat conduction and enhances overall thermal protection performance. Specimens were manufactured by fused deposition modeling (FDM), an additive manufacturing technique, using a fire-retardant thermoplastic. Selected configurations were reinforced with continuous carbon or glass fibers, coated with ceramic surface layer, or hybridized with carbon fiber reinforced polymer (CFRP) layers or a CFRP laminate disk. To validate performance, a harsh oxy-acetylene torch (OAT) protocol was implemented, deliberately designed to exceed the severity of most reported typical ablative assessments. The exposed surface of each specimen was subjected to direct flame at a 50 mm distance, recording peak temperatures of 1600 ± 50 °C. Two samples of each configuration were tested under 60 and 90 s exposures. Back-face thermal readings at potential payload sites consistently remained below 85 °C, well under the 200 °C maximum standard threshold for TPS applications. Several configurations preserved structural integrity despite the extreme environment. Prototypes 4.1 and 4.2 demonstrate the most favorable performance, maintaining structural integrity and low back-face temperatures despite substantial thickness loss. By contrast, specimen 6.2 exhibited rapid degradation following 60 s of exposure, which served as a rigorous and selective early-stage screening tool for evaluating polymer-based ablative TPS architectures. Full article

Carbon-fiber-reinforced plastic (CFRP) machining by ultrashort-pulse lasers promises high precision but is limited due to the heterogeneous epoxy–carbon fiber structure, which creates heat-affected zones and variable kerf quality. This work investigates synthesized copper hydroxyphosphate as a laser-absorbing additive to improve femtosecond (1030 nm) laser ablation of CFRP. Copper hydroxyphosphate particles were synthesized hydrothermally and incorporated into an epoxy matrix to produce single-ply CFRP laminates. Square patterns (0.5 × 0.5 mm) were ablated with a pulse energy of 0.5–16 μJ. Then, ablated volumes were profiled and materials characterized by SEM and EDS. In neat epoxy the copper additive reduced optimum ablation efficiency and decreased penetration depth, while producing smoother, less porous surfaces. In contrast, CFRP with copper hydroxyphosphate showed increased efficiency and higher penetration depth. SEM and EDS analyses indicate more uniform matrix removal and retention of resin residues on fibers. These results suggest that copper hydroxyphosphate acts as a local energy absorber that trades volumetric removal for improved surface quality in epoxy and enhances uniformity and process stability in CFRP femtosecond laser machining. Full article