Cross-ply Laminates Research Articles

Effect of hygrothermal aging on compression behavior of CFRP material with different layups

This study investigates the mechanical degradation mechanism and statistical analysis of residual compressive strength of three lay-up laminates under more than one-year seawater environment. Fick and Langmuir model were used to describe the moisture absorption process with a maximum moisture equilibrium content of 3.78% and various characterization methods were used to reveal the microstructural evolution of CFRP during aging. Experimental results demonstrate that the multiple fiber directions in the MD specimens provide additional moisture absorption channels, leading to a stronger wicking effect and a higher equilibrium moisture content. The layups can significantly affect the compression failure mode after long-term aging. The compressive strength of the cross-ply and multidirectional laminates decreased by 50% while that of unidirectional laminates decreased by 28%, and surface cracking is easily observed in the aged specimens. An empirical prediction model based on the Langmuir model and experimental data was proposed and verified by the data from the literature, with at least a 10% improvement in prediction accuracy. Meanwhile the three-parameter Weibull distribution was used to describe the residual compressive strength after hygrothermal aging and tested by Kolmogorov-Smirnov test. It is expected to provide insight for the application of CFRP in seawater environment.

Clarifying the mechanisms of edge glow generation in CFRP laminates exposed to simulated lightning currents

This study examines edge glow mechanisms of CFRP laminates exposed to simulated lightning current by performing direct electrical conduction tests. An impulse electric current, in accordance with SAE ARP 5412B, was applied to the laminates. Numerical simulations based on finite element analysis (FEA) were performed to clarify the voltage and temperature distributions of the CFRP laminates. The analytical results were validated using the experimentally obtained I–V characteristics and temperature responses. Resultingly, edge glow was observed in quasi-isotropic but not in unidirectional and cross-ply laminates. The edge glow was suppressed more in silicone oil than in air. When the edge glow did not occur, the numerical simulation results, I–V characteristics, and temperature response, exhibited good agreement with the experimentally obtained results. Contrary to Joule heating, potential differences of several hundred volts between each layer, which cause dielectric breakdown in the testing atmosphere, are the criterion for edge glow formation.

Dynamic response of piezoelectrically actuated bistable cross-ply laminates under oscillating impulse voltages

Multistable composite laminates are ideal candidates for morphing applications due to their ability to switch between multiple stable states with proper actuation mechanisms. Surface-bonded macro fiber composite (MFC) actuators to trigger snap-through between one stable shape to another by applying external voltages have attracted considerable attention recently. In this work, dynamic snap-through of bistable unsymmetric cross-ply laminate using MFC actuators under oscillating impulse voltages has been investigated. Both unimorph and bimorph laminate-MFC configurations are considered for the analysis. The stable equilibrium configurations of the MFC-actuated bistable laminate, considering the effects of MFC bondage, are discussed using the proposed finite element (FE) framework. Under the action of oscillating impulse voltages, the single-well and cross-well oscillations of the active bistable plate are analyzed in detail through time responses and phase portraits. The FE results show the advantage of actuating MFC layers through the oscillating impulse voltages as it leads to a reduction in the maximum snap-through voltage requirements.

Effects of Hygrothermal Aging on the Flexural Properties of Cross-Ply and Angle-Ply CFRP Composite Laminates

Effects of Hygrothermal Aging on the Flexural Properties of Cross-Ply and Angle-Ply CFRP Composite Laminates

Quantification of hygrothermal aging-induced interfacial debonding of carbon fiber/epoxy composites at nano-to-micrometer length scales

This work investigated the phenomenon of interfacial debonding due to hygrothermal aging (HA), which was quantified using Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM). Several micrographs of carbon fiber/epoxy cross-ply laminate coupons were analyzed, including unaged (HA/0) samples, as well as those aged for 1000 h (HA/1000) and 2000 h (HA/2000). To quantify the extent of debonding, an image thresholding tool was employed. For HA/0, HA/1000, and HA/2000 coupons, the average interfacial debonding arc length of inner plies was longer than that of the respective outer plies by 14%, 17%, and 21%, respectively. Residual stress variation across inner plies is more pronounced compared to outer plies due to the latter's freedom of expansion. The debonding that occurred without external loading was due to the combined effects of matrix and interface plasticization, chemical reaction, viscoelastic changes, and swelling. The AFM 3-D surface topography revealed that HA/0, HA/1000, and HA/2000 specimens had progressively lower peak-valley distances of 135 nm, 113 nm, and 82 nm, respectively, due to matrix swelling.

Hydrogen permeability of thin-ply composites after mechanical loading

Hydrogen is a sustainable alternative to conventional fuels, and it may be obtained with near zero carbon footprint. However, hydrogen storage remains a key challenge, and the use of composite tanks has gained significant interest over the last few years. In addition, thin-ply composites promote fibre damage by delaying matrix microcracking and free edge delamination. In this work, the H2 permeation/diffusion performance of virgin and mechanically loaded thin cross-ply laminates is studied. In addition, Scanning Electron Microscopy (SEM) is used to identify defects and micro-damage in the laminates and explain the experimental values. The study shows that the hydrogen (H2) barrier performances of thin-ply composites are lower than conventional metallic systems. Obtained permeability values, however, resulted well below the allowable limits for most combinations of temperature and pressure and remain unaffected despite the application of high tensile strains showing that permeation is not accelerated.

Damage and failure mechanisms of CFRP due to manufacturing induced wrinkling defects

Out-of-plane wrinkling is a typical defect in the manufacturing process of carbon fiber reinforced plastics (CFRP). The cross-ply composite laminates containing various wrinkles were designed and prepared based on a hybrid generation method of gaps and transverse strips. An analytical model based on the sine function was proposed to characterize the shape of wrinkles, and the severity of the defect was characterized by the wrinkle angle. With the aim to investigate the compression and out-of-plane shear failure performance of CFRP with wrinkles, experimental and numerical studies were conducted. Results show that the existence of wrinkled zone can significantly reduce the compressive strength of laminates and exacerbate delamination during compression failure, a maximum of 26.9% and 2.8% drop in the compressive and interlaminar shear strength was reported in the most severe experimental conditions. Meanwhile, it is indicated that wrinkles have little effect on interlaminar shear strength, but it can change the location and severity of the delamination failure. In addition, the failure mechanism of several models with different levels of wrinkling defects was studied through numerical analysis techniques. It is confirmed that the numerical model can effectively predict the failure intensity and failure modes. These findings are of great significance for the accurate evaluation of the mechanical properties of composites containing wrinkling defects.

Numerical modeling thermo-hygro-mechanical coupling of cross-ply laminate composites using a nonlocal discrete approach

Laminate composites are widely used in various industrial applications and are frequently subject to extreme temperature and moisture environment. This paper presents numerical modeling thermo-hygro-mechanical coupling of cross-ply laminate composites using a nonlocal discrete approach formulated based on the local continuum mechanics theory. In the developed model, the material domain is modeled as an assembly of regularly packed material particles whose interaction with neighboring material particles via bonds is nonlocal. Bond parameters are derived based on equivalency of energy and diffusing material transfer rate between the discrete descriptions and their continuum counterparts. The orthotropy of material properties is modeled using rotation of discretization lattice rather than the coordinate transformation that used in the local continuum mechanics theory. The interface and its effect on the material response are investigated by assigning different parameters to bond straddling different material phases. Numerical verification using single and four-ply laminate composites shows excellent accuracy of the developed model.

Numerical and experimental analysis of ultra-thin plies in carbon/epoxy cross-ply laminates subjected to bending after tensile cyclic loading

As a result of a fatigue testing campaign in cross-ply laminates with different thicknesses in the 90° ply block (conventional and ultra-thin), different cracking patterns were observed. While laminates with conventional 90° ply thickness show a damage pattern with transverse cracks in the 90° ply block and delaminations along the 0°/90° interface, laminates with ultra-thin plies show paths of debonds inside the ultra-thin 90° ply block both transverse and longitudinal to the loading direction. In order to see the influence that these different fatigue damage patterns could have on the mechanical behaviour of the laminates, static bending tests have been carried out after cyclic loading, and apparent flexural stiffness loss (concerning the pristine state) was measured. Numerical simulations of the bending test, including the cyclic damage pattern (and detailed non-linear frictionless contact conditions) were also carried out for a deeper understanding of the experimental evidence. Although the morphology of the fatigue damages encountered is different for the two studied 90° ply block thicknesses, their flexural behaviours are quite similar, in terms of apparent flexural stiffness loss, for both cross-ply laminates, independently of its 90° ply block thickness.

Three-dimensional modeling of frontal polymerization for rapid, efficient, and uniform thermoset composites manufacturing

Due to the incapability of one-dimensional (1D) and two-dimensional (2D) models in simulating the frontal polymerization (FP) process in laminated composites with multiple fiber angles (e.g., cross-ply, angle-ply), modeling a three-dimensional (3D) domain, which is more representative of practical applications, provides critical guidance in the control and optimization of the FP process. In this paper, subroutines are developed to achieve the 3D modeling of FP in unidirectional and cross-ply carbon fiber laminates with finite element analysis, which are validated against the experimental data. The 3D model is employed to study the effect of triggering direction in relevance to the fiber direction on the FP process, which cannot be studied using traditional 1D/2D models. Our findings suggest that triggering in the fiber direction leads to a higher front velocity, in comparison to cases where front was triggered in the direction perpendicular to the fiber. Moreover, the average front velocity in cross-ply laminates is on average 20–25% lower than that in unidirectional laminates. When triggered using two opposite fronts in the in-plane direction, the maximum temperature of the thermal spike in the cross-ply laminate, when two fronts merge, is about 100 °C lower than that in the unidirectional laminate. In cross-ply laminates, a sloped pattern forms across the thickness direction as the front propagates in the in-plane direction, as opposed to the traditionally observed uniform propagation pattern in unidirectional cases. Furthermore, the effect of thermal conductivity is studied using two additional composite laminates with glass (1.14 W/m·K) and Kevlar fibers (0.04 W/m·K). It is shown that the frontal velocity, degree of cure, and the thermal spike temperature decrease as the thermal conductivity reduces.

Finite element analysis of cross-ply and quasi-isotropic laminate plates with a center hole for variable thickness under transverse loading using shear deformation theories

Finite element analysis of cross-ply and quasi-isotropic laminate plates with a center hole for variable thickness under transverse loading using shear deformation theories

Stability and mode shape analysis of doubly- and cross-helicoidal laminated sandwich plates inspired from dactyl’s club

The present work intends to use higher-order zigzag theory to analyze double- and cross-helicoidal laminated sandwich plates under buckling conditions. Geometry and boundary effects on buckling and mode shapes are examined. The behavior of helicoidal sandwich plates is compared with the cross-ply and quasi-isotropic lamination schemes. In the case of plates with free edges, the bio-inspired laminated sandwich plates outperform the more traditional cross-ply and quasi-isotropic laminated schemes. Numerous more findings are provided as well, all of which may be used as a standard by which to measure the success of comparable future research efforts.

Bending analysis of glass fiber reinforced epoxy composites/copper-clad laminates for multi-layer printed circuit boards

Printed circuit board (PCB) is the most important part of any electronic device which is made of copper-clad laminate and glass fiber-reinforced composites. Since the ply orientation of fiber-reinforced composites and lamina thickness have a significant influence on the mechanical properties of the whole composite laminate it is necessary to investigate the effects of ply orientation and lamina thickness on the bending properties of PCB so that they can be manufactured to meet the service requirements. In this work, the bending properties of PCB were investigated for seven different ply orientations of glass fiber-reinforced composite laminas and for eight different thickness combinations (for a constant laminate thickness) of glass fiber-reinforced composite lamina and copper-clad laminate. A commercially available finite element analysis software (Abaqus) was used to simulate a three-point bending test of PCBs and the simulation results were validated using experimental results. It is found that the bending stiffness is maximum for the cross-ply laminate. The introduction of angle ply improves the maximum von-Mises stress of the PCB with an insignificant cost of bending stiffness (less than 5% reduction). It is found that the bending stiffness and the maximum von-Mises stress of the PCB can be regulated through the variation of thickness of the constituent lamina. The laminate stiffness can be increased by increasing the thickness of stiffer laminas or by placing the stiffer laminas towards the surface of the laminate. The outcome of this research would provide a comprehensive understanding of the bending characteristics of the multi-layered PCBs which can be directly utilized by the PCB manufacturers. However, the effects of ply orientation and lamina thickness variation on the behavior of the PCBs subject to temperature variation, impact loading, vibration, and other conditions that might affect the service life of the PCBs should be investigated.

First-Ply Failure Analysis of Helicoidal/Bouligand Bio-Inspired Laminated Composite Plates

Among the first, the present paper focuses on studying the first-ply failure load for bio-inspired helicoidal laminated composite plates. Five different layup schemes, namely, helicoidal recursive, helicoidal semicircular, helicoidal exponential, Fibonacci helicoidal, and linear helicoidal, were studied. The performance of the five helicoidal layups was compared with the commonly used cross-ply and quasi-isotropic lamination schemes. Maximum stress, maximum strain, Tsai–Hill, Tsai-Wu, and Hoffman failure theories were employed in the framework of the recently proposed finite-element-based higher-order zigzag theory to determine the first-ply failure load. It was observed that the maximum strain theory predicted the lowest value of the first-ply failure load, whereas Tsai–Wu predicted the highest one. For some cases, Tsai–Hill and Tsai–Wu theories were not able to predict the first-ply failure load. For plates having free edges, the bio-inspired plates exhibited the first-ply failure load compared to the conventional layup sequences.

Stochastic dynamic analysis of composite plates in thermal environments using nonlinear autoregressive model with exogenous input in polynomial chaos expansion surrogate

The application of composite materials has increased manifolds in aerospace and high-speed vehicle industries, where structures experience dynamic loads along with temperature variation. To ensure safety of these structures, the stochastic dynamic analysis in varying thermal environments is essential. The generalized polynomial chaos (gPC) expansion method is a well-known metamodel used to quantify uncertainties in engineering systems instead of using the direct Monte Carlo simulation. Though the gPC expansion method is used extensively for engineering systems, its classical version has some limitations while implementing in dynamical systems. The accuracy of the gPC expansion method reduces in delayed time domain and can be improved to some extent by increasing the order of polynomial, which though is computationally intensive. Furthermore, the classical gPC expansion method is suitable for low-dimensional problems having independent random parameters. To overcome these limitations in the classical gPC expansion method, a system identifier, i.e., nonlinear autoregressive model with exogenous input (NARX) is coupled with it to avoid response degeneration in delayed time domain. The temperature-dependent material properties of composite lamina can be random and correlated, however the classical gPC expansion method is unable to accommodate the correlated random parameters. To address these challenges, the NARX-gPC expansion method is modified to conduct stochastic dynamic analysis of composite plates using correlated random material properties of the composite lamina in varying thermal environments. The study indicates that the correlation has a significant effect on the stochastic dynamic response at low and high temperatures for cross-ply laminates in comparison with angle-ply laminates, which is not captured through uncorrelated random material properties. The prediction efficiency of the developed surrogate by using the adaptive NARX-gPC expansion method is established even though it is trained using data in a shorter time domain, thereby computational performance is enhanced. Additionally, this surrogate is implemented effectively for higher order randomness in the input parameters.

First-Ply Failure Analysis of Bioinspired Double and Cross-Helicoidal Laminated Sandwich Plates

Inspired from the helicoidal schemes available from biological creatures, the present paper aims to predict the first-ply load for laminated composite and sandwich plates inspired from biological creatures. The laminated composite and sandwich plates are assumed to be made up of double- and cross-helicoidal lamination schemes. The first-ply failure load is determined using the recently proposed higher-order zigzag theory. Five different failure criteria (namely, maximum stress, maximum strain, Tsai–Hill, Tsai–Wu, and Hoffman’s theory) are used to predict the first-ply failure load. The performance of the helicoidal plate is compared with the cross-ply and quasi-isotropic lamination schemes. The influences of the end conditions, the ratio of the thickness of the core to the face layers, and the thickness-to-side ratio on the first-ply failure load are carried out. It has been observed that for helicoidal plates, a higher value of the first-ply failure load is observed as compared to quasi-isotropic and cross-ply laminates, especially for plates having free edges. The maximum strain theory should not be used for predicting the failure load for helicoidal laminated plates because it undermines the strength of the plate.

A Lay-up-Oriented CFRP-Substrate Metamaterial Absorber with High Insensitivity to Polarization

Metamaterial absorbers with carbon fiber reinforced polymer (CFRP) substrates, which are called meta-CFRPs, have recently gained recognition for their excellent mechanical and electromagnetic performance. Different from traditional metamaterial absorbers with an isotropic substrate, meta-CFRPs with a highly anisotropic CFRP substrate are facing challenges in acquiring polarization-insensitive absorption. Here, a lay-up-oriented structure design method is proposed to solve this problem. Considering the lay-up configuration of CFRP laminates, metallic patterns are designed under corresponding polarization angles and then united together to form an integral structure. A meta-CFRP with a typical CFRP lay-up configuration([0°/45°/90°/−45°]3s ) is designed and tested. The experimental results exhibit over 99% microwave absorptivity at 2.44 GHz for all polarization angles. The maximum shift among the resonance peaks of the curves at all polarization angles is only 0.021 GHz. Further studies show that when there are cross-ply laminates in the first few layers of the CFRP substrate, the lay-up-oriented design method can be effectively simplified by ignoring the subsequent lay-up orientations after the first cross-ply layers. Our method can not only provide an effective way for acquiring polarization-insensitive microwave response on meta-CFRPs but also be expected to be promoted to metamaterial absorbers with other anisotropic materials.

Increasing the Compressive Strength of Helicoidal Laminates after Low-Velocity Impact upon Mixing with 0° Orientation Plies and Its Analysis.

The helicoidal laminate is a kind of nature inspired fiber reinforced polymer, and the ply orientation affects their mechanical properties for engineering structural applications. A variety of helicoidal laminates with uniform and non-linear pitch angles mixed with additional 0° plies are fabricated to investigate the impact resistance through low-velocity impact and after-impact compression tests. Additionally, helicoidal laminates with constant pitch angles, quasi-isotropic laminate, and cross-ply laminates are also fabricated for a comparative study. The impact characteristics and the compressive strength are analyzed in view of the impact model, shear stress distribution, and fracture toughness. The results suggest that 10° or 20° are the better basic pitch angles before mixing 0° orientation plies. The 0° orientation plies may affect the contact stiffness, bending stiffness, damage extent, and compressive modulus. The compressive strength reaches the highest in tests on two samples with different percentages of 0° orientation plies and ply setups. Bending stiffness also dominates the impact response. The analysis on the laminate parameters provides ideas to improve the residual strength of helicoidal laminate.

Effect of Strain Rate on Tensile Properties of Carbon Fiber-Reinforced Epoxy Laminates with Different Stacking Sequences and Ply Orientations.

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.

Experimental investigation on Compression-After-Impact (CAI) response of aerospace grade thermoset composites under low-temperature conditions assisted with acoustic emission monitoring

Low-velocity impact (LVI) can provoke catastrophic failure depending on the impact energy, lay-up configuration, and the operating temperature in fiber-reinforced composite structures via damage accumulation during the service. Additionally, extreme operating temperature is an important factor affecting the damage initiation and growth mechanism and understanding the compression-after-impact (CAI) response is a promising way to predict the damage-growth dynamics. For this purpose, this study investigates the LVI response and CAI strength of composite laminates under the −55 °C temperature considering the low-temperature (LT) service conditions of aerospace applications. The experiments are performed on cross-ply ([0/90°]4s) and angle-ply ([±45°]4s) lay-up composites for impact energy levels of 1.4 J and 10 J. After LVI tests, the occurred damages are examined by infrared thermography (IRT). Furthermore, the effect of the impact damage on the failure mechanism under compression loading is elaborated using acoustic emission (AE) inspection. The CAI test results reveal that the LT increases the compressive residual strength. However, this change is directly related to the load and lay-up configuration. The alternation in the damage growth mechanism of angle-ply laminates under LT operating temperature is more significant compared to the cross-ply laminates.