Search Results (18)

Deployable reflector antennas demand high geometric precision; the Ruze equation directly links surface error to RF gain. Arc-shaped CFRP ribs are vulnerable to thermal deformation, as their curvature converts in-plane expansion into out-of-plane displacement, which symmetric laminates cannot suppress. Classical laminate theory (CLT) underestimates the coefficient of thermal expansion (CTE) of cross-ply laminates by factors of 1.75–2.38 for the laminate configurations investigated in this study, causing up to 79.4% of displacement prediction errors in symmetric designs. Here, we present an asymmetric laminate that overcomes both limitations. The upper skin (nine plies) and lower/web skins (seven plies) from the same prepreg batch create a CTE mismatch (Δα = 6.30 × 10⁻⁷ K⁻¹), activating coupling stiffness to generate a thermal moment opposing curvature-driven displacement. Because both skins share identical batch history, CTE prediction errors cancel through common-mode rejection. Compared with the symmetric design, the asymmetric design achieved a 50.4% reduction in thermal deformation (from 210 µm to 104 µm) and improved FEA accuracy from 79.4% error to 4.8% error under experimental schemes. The method uses only conventional 0/90° prepreg and standard autoclave processing, with the upper-surface ply count as the sole design variable for a given section’s geometry, establishing retained coupling stiffness as a practical route to dimensional stability in curved space structures. Full article

Compression testing of high-performance carbon fiber composites remains challenging due to premature failure modes in unidirectional laminates, which can underestimate true material strength. This study investigates the compressive behavior of T800-grade carbon fiber-reinforced polymer (CFRP) cross-ply ([90/0]_2s) and unidirectional ([0]₈) laminates using finite element simulation and experimental testing following the SACMA SRM-1R-94 standard, combined with macroscopic and microscopic failure analysis. The results show that cross-ply laminates consistently exhibit valid mid-gauge failure with lower data dispersion (coefficient of variation: 3.44%), whereas unidirectional laminates are prone to invalid root failures (crushing or shear). The compressive strength derived from cross-ply laminates using the back-out factor (2040 MPa) is 13% higher than that from direct unidirectional testing (1802 MPa), attributed to the in situ effect where adjacent 90-degree plies suppress fiber microbuckling. The cross-ply approach provides a more reliable and practical method for characterizing the true in situ compressive strength of high-performance CFRP composites. Full article

Carbon fiber-reinforced plastics (CFRP) are widely used in deployable space structures due to their strength-to-weight ratio, yet their inherent brittleness and limited damage tolerance constrain their performance under large deformation. This study reports a new concept, the Kevlar composite deployable lenticular tube (CDLT), for improved toughness and reliable stowability. The buckling response of Kevlar CDLT under axial compression and torsion was characterized, and its stowability was verified through experiments and finite element analysis (FEA). Axial compression studies show that the load–displacement curve transitions from linear elastic to nonlinear deformation at the critical buckling load; meanwhile, local stress magnification occurs in the central arc region. Damage analysis further reveals that buckling instantaneously induces localized wrinkling and matrix failure. Torsional analysis shows that the CDLT exhibits an initially linear torque–twist response, governed by shear stiffness. However, once the critical torque is exceeded, torque decreases sharply due to localized collapse and overall buckling. Moreover, the outermost layers bear the highest stresses, whereas the inner layers remain comparatively uniform and less stressed. Furthermore, the influence of different layup sequences, ply numbers, and total thickness on the load-bearing capacities of CDLT was investigated, ultimately determining the optimal layup scheme. Finally, the stowability analysis demonstrates that the Kevlar CDLT, configured as a six-ply laminate with a total thickness of 0.72 mm, achieves an optimal balance between stiffness and flexibility. In this comparison, both the Kevlar and CFRP CDLTs employ identical lenticular cross-sectional geometries, fully consistent boundary conditions, the same overall laminate thickness (0.72 mm), and an identical stacking sequence of [45°/−45°/90°/90°/45°/−45°], with the material properties being the only variable. Under these strictly controlled conditions, the coiling torque of the Kevlar CDLT is reduced by at least 48% relative to that of the CFRP CDLT. This study preliminarily verifies the load-bearing capacity and stowability of novel Kevlar CDLTs, providing valuable guidance for the design of deployable space structures. Full article

Thermoplastic carbon fiber-reinforced polymer (CFRP) composites possess the intrinsic capability to heal delamination and matrix cracks via thermal re-melting. However, under impact loading, they are prone to severe fiber fracture, which significantly compromises their repairability. To address this, this study introduced polytetrafluoroethylene (PTFE) films as pre-set interlaminar defects within continuous carbon fiber-reinforced polyamide 6 (CF/PA6) thermoplastic cross-ply laminates. Low-velocity impact tests were conducted at varying energy levels to comparatively investigate the impact response and damage mechanisms of the CFRPs with and without embedded defects. Experimental results indicate that the embedded interlaminar defects triggered a transition in the failure mode of the CFRP from brittle fracture to progressive damage behavior. Compared to the baseline laminates, the specimens with embedded defects maintained higher flexural stiffness under low-energy impact. Furthermore, they effectively reduced the extent of fiber breakage by dissipating impact kinetic energy through extensive delamination, interlaminar frictional sliding, and plastic micro-deformation. These findings verify the feasibility of achieving macroscopic pseudo-ductility through interlaminar microstructural tailoring. This research provides an experimental basis and methodological support for the pseudo-ductile design of thermoplastic composites. Full article

Composite pressure vessels have attracted significant attention in recent years owing to their lightweight characteristics and superior mechanical performance. However, analyzing composite layers remains challenging due to complex filament-winding (FW) pattern structures and the associated high computational costs. This study introduces a homogenization method to achieve cross-scale modeling of carbon fiber-reinforced plastic (CFRP) layers, accounting for both lay-up sequence and in-plane FW diamond-shaped form. The stacking sequence in an FW Type IV composite pressure vessel is numerically investigated through ply modeling and cross-scale homogenization. The composite tank structure, featuring a polyamide PA66 liner, is designed for a working pressure of 70 MPa and comprises 12 helical winding layers and 17 hoop winding layers. An FW cross-undulation representative volume element (RVE) is developed based on actual in-plane mesostructures, suggesting an equivalent laminate RVE effective elastic modulus. Furthermore, six different lay-up sequences are numerically compared using ply models and fully and partially homogenized models. The structural displacements in both radial and axial directions are validated across all modeling approaches. The partial homogenization method successfully captures the detailed fiber-direction stress distribution in the innermost two hoop or helical layers. By applying the Hashin tensile failure criterion, the burst pressure of the composite tank is evaluated, revealing 7.56% deviation between the partial homogenization model and the ply model. Fatigue life analysis of the Type IV composite pressure vessel is conducted using ABAQUS^® coupled with FE-SAFE, incorporating an S-N curve for polyamide PA66. The results indicate that the fatigue cycles of the liner exhibit only 0.28% variation across different stacking sequences, demonstrating that homogenization has a negligible impact on liner lifecycle predictions. The proposed cross-scale modeling framework offers an effective approach for multiscale simulation of FW composite pressure vessels, balancing computational efficiency with accuracy. Full article

Spherical shells exhibit superior strength-to-geometry efficiency, making them ideal for industrial applications such as fluid storage tanks, architectural domes, naval vehicles, nuclear containment systems, and aeronautical and aerospace components. Given their critical role, careful attention to the design parameters and engineering constraints is essential. The present paper investigates the buckling responses of bio-inspired helicoidal laminated composite spherical shells under normal and torsional loading, including the effects of a Winkler elastic medium. The pre-buckling equilibrium equations are derived using linear three-dimensional (3D) elasticity theory and the principle of virtual work, solved via the classical finite element method (FEM). The buckling load is computed using a nonlinear Green strain formulation and a generalized geometric stiffness approach. The shell material employed in this study is a T300/5208 graphite/epoxy carbon fiber-reinforced polymer (CFRP) composite. Multiple helicoidal stacking sequences—linear, Fibonacci, recursive, exponential, and semicircular—are analyzed and benchmarked against traditional unidirectional, cross-ply, and quasi-isotropic layups. Parametric studies assess the effects of the normal/torsional loads, lamination schemes, ply counts, polar angles, shell thickness, elastic support, and boundary constraints on the buckling performance. The results indicate that quasi-isotropic (QI) laminate configurations exhibit superior buckling resistance compared to all the other layup arrangements, whereas unidirectional (UD) and cross-ply (CP) laminates show the least structural efficiency under normal- and torsional-loading conditions, respectively. Furthermore, this study underscores the efficacy of bio-inspired helicoidal stacking sequences in improving the mechanical performance of thin-walled composite spherical shells, exhibiting significant advantages over conventional laminate configurations. These benefits make helicoidal architectures particularly well-suited for weight-critical, high-performance applications in aerospace, marine, and biomedical engineering, where structural efficiency, damage tolerance, and reliability are paramount. Full article

A numerical simulation investigating the frequency dependence of fatigue damage progression in carbon fiber-reinforced plastics (CFRPs) is conducted in this study. The initiation and propagation of transverse cracks under varying fatigue test frequencies are successfully simulated, consistent with experiments, using an enhanced degradable Hashin failure model that was originally developed by the authors in 2022. The results obtained from the numerical simulation in the present study, which employs adjusted numerical values for the purpose of damage acceleration, indicate that the number of cycles required for the formation of three transverse cracks was 174 cycles at 0.1 Hz, 209 cycles at 1 Hz, and 165 cycles at 10 Hz. Based on these results, it is demonstrated that under high-frequency cyclic loading, internal heat generation caused by dissipated energy from mechanical deformation, attributed to the viscoelastic and/or plastic behavior of the material, exceeds thermal dissipation to the environment, leading to an increase in specimen temperature. Consequently, damage progression accelerates under high-frequency fatigue. In contrast, under low-frequency fatigue, viscoelastic dissipation becomes more pronounced, reducing the number of cycles required to reach a similar damage state. The rate of damage accumulation initially increases with test frequency but subsequently decreases. This observation underscores the importance of incorporating these findings into discussions on the fatigue damage of real structural components. Full article

Ultrasonic attenuation measurements were conducted on cross-ply and quasi-isotropic lay-ups of eight types of carbon-fiber reinforced composites (CFRPs) using through-transmission methods with diffraction correction. Attenuation values were substantially higher than those of unidirectional composites and other structural materials. Wave modes, fiber distributions, matrix resins, and consolidation methods affected total attenuation. Transverse mode, quasi-isotropic lay-up, and polyimide and thermoplastic resins generally produced higher attenuation. No clear trends from the fiber distribution were revealed, indicating that it is not feasible presently to predict the attenuation of various lay-ups from the unidirectional values. That is, direct attenuation tests for different laminate lay-ups are needed. This work expanded the existing attenuation database by properly determining the attenuation coefficients of two additional layup types of CFRP laminates. Results showed the merit of ultrasonic attenuation measurements for quality control and structural health monitoring applications. A crucial benefit of the through-transmission methods is that they enable the prediction of Lamb wave attenuation in combination with software like Disperse (ver. 2.0.20a, Imperial College, London, UK, 2013). Full article

In practical application situations, a carbon fiber-reinforced polymer (CFRP) is often subjected to complex dynamic loadings. The effect of the strain rate on mechanical properties is very important for the CFRP design and product development. In this work, static and dynamic tensile properties of CFRP with different stacking sequences and ply orientations were investigated. The results showed that the tensile strengths of CFRP laminates were sensitive to the strain rate, while Young’s modulus was independent of the strain rate. Moreover, the strain rate effect was related to the stacking sequences and ply orientations. The experimental results showed that the strain rate effects of the cross-ply laminates and quasi-isotropic-ply laminates were lower than that of the unidirectional-ply laminates. Finally, the failure modes of CFRP laminates were investigated. Failure morphology demonstrated that the differences in strain rate effects among cross-ply laminates, quasi-isotropic-ply laminates, and unidirectional-ply laminates were caused by the mismatch between the fiber and the matrix when the strain rate increased. Full article

Carbon-fiber-reinforced epoxy-matrix composite (CFRP) laminates with thin plies have strong damage-resistance properties compared with standard prepregs. The static and fatigue tensile fracture behavior of cross-ply CFRP laminates with thin plies should be further studied to establish the applicability of thin-ply prepregs for industrial structures. In this study, the static and fatigue tensile properties of cross-ply, high-strength polyacrylonitrile (PAN)-based carbon-fiber (T800SC)-reinforced epoxy-matrix composites with thin plies were investigated. The fiber orientations of the CFRP specimens were set to cross-ply with [0/90]_10S (subscript S means symmetry), [(0)₅/(90)₅]_2S, and [(0)₁₀/(90)₁₀]_S. The static and fatigue tensile characteristics of the cross-ply CFRPs with thick plies with [0/90]_2S and [(0)₂/(90)₂]_S were also investigated for comparison. Under static loading, the tensile strength and failure strain of the thinnest 90°-ply-CFRP specimens were more than 5% higher than those of the other 90°-ply-thickness specimens. However, the tensile moduli and Poisson’s ratios were comparable between the cross-ply CFRPs with thin and thick plies. Under fatigue loading, the fatigue responses of the thinnest 90°-ply-CFRP specimens were 3% higher than those of the other 90°-ply-thickness specimens during lower-fatigue-cycle testing (<10⁵ cycles). However, during higher-fatigue-cycle testing (>10⁵ cycles), the fatigue responses decreased, with a decrease in the 90°-ply thickness, and the fatigue characteristics of the thinnest 90°-ply-CFRP specimen were 7% lower than those of the other cross-ply thin- and thick-ply-CFRP specimens. Full article

The transverse cracking behavior of a carbon-fiber-reinforced plastic (CFRP) cross-ply laminate is investigated using a fatigue test and an entropy-based failure criterion in this study. The results of fatigue experiments show that the crack accumulation behavior depends on the cyclic number level and frequency, in which two obvious transverse cracks are observed after 10⁴ cyclic loads and 37 transverse cracks occur after 10⁵ cycles. The final numbers of transverse cracks decrease from 29 to 11 when the load frequency increases from 5 Hz to 10 Hz. An entropy-based failure criterion is proposed to predict the long-term lifetime of laminates under cyclic loadings. The transverse strength of 90° ply is approximated by the Weibull distribution for a realistic simulation. Progressive damage and transverse cracking behavior in CFRP ply can be reproduced due to entropy generation and strength degradation. The effects of stress level and load frequency on the transverse cracking behavior are investigated. It is discovered that, at the edge, the stress σ₂₂ + σ₃₃ that is a dominant factor for matrix tensile failure mode is greater than the interior at the first cycle load, and as stress levels rise, a transverse initial crack forms sooner. However, the initial transverse crack initiation is delayed as load frequencies increase. In addition, transverse crack density increases quickly after initial crack formation and then increases slowly with the number of load cycles. The proposed method’s results agree well with those of the existing experimental method qualitatively. In addition, the proposed entropy-based failure criterion can account for the effect of load frequency on transverse crack growth rate, which cannot be addressed by the well-known Paris law. Full article

This paper reports analyses of a 5-degrees-of-freedom (5-DOF) carbon fiber-reinforced polymer (CFRP) robot manipulator, which has been developed for farm applications. The manipulator was made of aluminum alloy (AA) and steel materials. However, to check the effectiveness of CFRP materials on the static and free-vibration performance of the manipulator, the AA parts were replaced with CFRP. For this purpose, the effects of various cross-sections and layups on three design criteria—deflection, load-carrying capacity, and natural frequency—were investigated. Two types of thin-walled laminated sections, specifically the I section and rectangular tubular sections, were used for the composite parts. These parts were made from three hollow square section (“SSS” section) beams and three I section (“III” section) beams. These multi-cell beams were modeled using the finite element (FE) method. Three configurations were selected for analysis based on the manipulator’s most common operating conditions. The results indicated that the use of CFRP increased the manipulator’s natural frequencies, increased the load-carrying capacity, and decreased the manipulator’s tip deflection when compared with its AA counterpart. An analysis showed that using CFRP in the manipulator’s structure could improve static and vibrational performances. It was observed that the “SSS” section beams were 1.17 times stiffer, could carry a 1.20 times higher load, and were 1.40 times heavier than the “III” section beams. Also, decreasing the fiber direction in angle-ply layups from 90° to 0° and adding 0° plies, while keeping the total number of layers constant, decreased the manipulator’s tip deflection and increased its natural frequencies. Full article

The effect of matrix cracking on the delamination morphology inside carbon fiber reinforced plastics (CFRP) laminates during low-velocity impact (LVI) is an open question. In this paper, the relationship between matrix cracking and delamination is studied by using cross-ply laminates. Several methods, including micrograph, C-scan, and visual inspection, were adopted to characterize the damage after LVI experiments. Based on the experimental results, finite element (FE) models were established to analyze the damage mechanisms. The matrix cracking was predicted by the extended finite element method (XFEM) and the Puck criteria, while the delamination was modeled by cohesive elements. It was revealed that the matrix crack in the bottom ply not only promoted the outward propagation of delamination but also contributed to the narrow delamination beneath the impact location. Multiple matrix cracks occurred in the middle ply. The ones close to the plate center initiated the delamination and prevented large-scale delamination beneath the impact location. For the cracks that were far away, no significant effect on delamination was found. In conclusion, the stress redistribution caused by the crack opening determines the delamination. Full article

The study of propagating, evanescent and complex wavenumbers of guided waves (GWs) in high-performance composites using a stable and robust semi-analytical finite element (SAFE) method is presented. To facilitate understanding of the wavenumber trajectories, an incremental material change study is performed moving gradually from isotropic aluminum alloy to carbon fiber reinforced polymer (CFRP) composites. The SAFE results for an isotropic aluminum alloy plate are compared with the exact analytical solutions, which shows that N = 20 SAFE elements across the thickness provides <0.5% error in the highest evanescent wavenumber for the given frequency-wavenumber range. The material change study reveals that reducing the transverse and shear moduli moves the wavenumber solution towards one similar to composite material. The comparison of the propagating, evanescent and complex wavenumber trajectories between composites and aluminum alloy show that antisymmetric imaginary Lamb wave modes always exist in composites although they may not exist in isotropic aluminum alloy at some frequencies. The wavenumber trajectories for a unidirectional CFRP plate show that the range of real wavenumber is much smaller than in the isotropic aluminum alloy. For laminated CFRP composite plates (e.g., unidirectional, off-axis, transverse, cross-ply and quasi-isotropic laminates), the quasi Lamb wave and shear horizontal (SH) wave trajectories are also identified and discussed. The imaginary SH wave trajectories in laminated composites are distorted due to the presence of ±45 plies. The convergence study of the SAFE method in various CFRP laminates indicates that sufficient accuracy can always be achieved by increasing the number of SAFE elements. Future work will address the stress-continuity between composite layers. Full article

In this article, the interlaminar shear behavior of a [±45°]_4s laminated carbon fiber reinforced plastic (CFRP) specimen is investigated, by utilizing microscale strain mapping in a wide field of view. A three-point bending device is developed under a laser scanning microscope, and the full-field strain distributions, including normal, shear and principal strains on the cross section of CFRP, in a three-point bending test, are measured using a developed sampling Moiré technique. The microscale shear strain concentrations at interfaces between each two adjacent layers were successfully detected and found to be positive-negative alternately distributed before damage occurrence. The 45° layers slipped to the right relative to the −45° layers, visualized from the revised Moiré phases, and shear strain distributions of the angle-ply CFRP under different loads. The absolute values of the shear strain at interfaces gradually rose with the increase of the bending load, and the sudden decrease of the shear strain peak value implied the occurrence of interlaminar damage. The evolution of the shear strain concentrations is useful in the quantitative evaluation of the potential interlaminar shear failure. Full article