Cross-ply Laminates Research Articles

Experimental results for fatigue damage growth in laminated fiber reinforced cross-ply laminates

In this paper, experimental results for fatigue damage growth behavior of a single-edge notched cross-ply laminate obtained using Digital Image Correlation (DIC), thermography, and supplemented by prior X-ray computed microtomography (mCT) data, are presented. These experimental results are used to develop a novel multi-scale fatigue life estimation model, whose details are reported elsewhere [1].

Detection of matrix cracks in composite laminates using embedded fiber-optic distributed strain sensing

We used an optical frequency-domain reflectometry fiber Bragg grating (FBG) distributed strain measurement system to detect matrix cracks in carbon fiber-reinforced plastics. Load/unload tests were performed on cross-ply laminates under ambient-, high-, and low-temperature conditions using embedded 100mm gauge FBG sensors. We measured the strain distributed along the gauge and examined the crack initiation using optical microscopy and soft X-ray inspection. A peak appeared in the distributed strain corresponding to the occurrence of cracks. The strain distribution during crack initiation was calculated in each temperature range via finite element analysis and compared with the measurement results. We determined that the number and location of cracks can be determined by extracting the peaks from the distributed strain. However, the peaks in the distributed strain do not correspond to the occurrence of cracks that are close to each other, warranting a measurement method with a higher strain resolution.

Effect of Nanostructure and Crosslinks on Impact Resistance of Carbon Nanotube Films Under Micro-Ballistic Impact.

Carbon nanotube (CNT) films show great promise as an advanced bulletproof materials due to their excellent energy dissipation ability under impact loadings. However, it is challenging to determine the optimized architecture structure of CNTs to enhance the impact resistance of CNT films. In this study, the impact behavior of CNT films with various architecture structures werestudied by micro-ballistic impact experiments and coarse-grained molecular dynamics (CGMD) simulations. The micro-ballistic impact experimental results showed that the cross-ply laminated (CPL) structure enhances significantly the specific energy absorption (SEA) of CNT films compared to that with disordered structure due to the synergistic interactions between covalent bonds in CNT chains. On this basis, four CPL-CNT (CCNT) films with the same areal density (ρ2D) but different single-layer areal density ( ) and one disordered CNT (DCNT) film with the same ρ2D as the CCNT films wereconstructed in CGMD models. The simulation results showed that the SEAs of all the four CCNT films are higher than DCNT film, which is consistent with experiments. In addition, the SEAs of CCNT films increase with decreasing . However, too small can lead to local plugging failure of the CNT film and therefore decrease SEA of the CNT film. Moreover, adding crosslinks could further increase the SEAs of both the DCNT and the CCNT films due to the strengthened interactions of adjacent CNTs. The crosslinked CCNT films with appropriate ρ2D is still much higher than the crosslinked DCNT films. Furthermore, it wasfurther found that when the strength of the crosslinks aligns with that of the CNT beads, the CNT film achieves preeminent impact resistance. This study provides a pathway for enhancing the impact resistance of CNT films by optimizing the microstructure and introducing crosslinks betweenCNTs.

Analysis of initiation and growth of new transverse cracks in high crack density regions in cross-ply laminates

In cross-ply laminates under loading, multiple intralaminar (transverse) cracking in the 90-layers causes laminate stiffness reduction which can be predicted by analytical models studying average of the stress perturbation between transverse cracks. The commonly used analytical models such as shear-lag type or variational-type models assume that stress in damaged 90-layers does not depend on the laminate thickness coordinate. But with increase in crack density, the stress perturbations created by transverse cracks start to interact, generating high stress gradients in through-the-thickness direction in the 90-layers. Location of a new crack and features of its propagation in a high stress gradient region between two cracks in a cross-ply laminate are analyzed in this paper. FEM is used to calculate stress distribution between two cracks. The location of the next crack and its initial orientation is found using principal stresses and orientation of principal axes. Most often these cracks are initiated at ply interface in the middle between already existing cracks. Their propagation across the layer thickness is analyzed using energy release rate based criterion. It is shown that at very high crack density the crack propagation across the layer thickness is unstable in the beginning, but it is stopped when approaching the middle of the layer where the crack opening becomes zero. Presence of local delaminations at the tips of existing cracks changes the energy release rate for propagation of new transverse cracks.

In situ analysis of three-dimensional microcrack propagation in cross-ply laminates using synchrotron radiation X-ray computed tomography

This study utilized synchrotron radiation X-ray computed tomography to investigate the initiation and propagation of microcracks in cross-ply carbon fiber-reinforced polymer (CFRP) laminates under mechanical loading. Initially, static tensile loads were applied to detect microcracks within a ply thickness of 160 μm. The crack propagation was subsequently characterized, extending across adjacent carbon fibers and along the interfaces of individual fibers into the material's interior. The experiment was repeated with cyclic loading, where the laminates were imaged periodically. Analysis of the images revealed the presence of microcracks and provided insights into their progression from the point of initiation. Notably, microcracks exhibited the initiation toward the interior of the material rather than across the neighboring carbon fibers, whereas their propagation is more significant across the adjacent carbon fibers particularly under the static loading. Under cyclic loading, however, the crack propagation toward the interior of the material was more pronounced, implying different propagation behavior than when under static loading. These findings were also validated through the distribution of energy release rate and stress triaxiality along the crack tip calculated by finite element analysis.

Free vibration analysis of bio-inspired helicoidal laminated composite square and annular plates having circular openings using isogeometric analysis

Present work aims to carry out free vibration analysis of bio-inspired helicoidal laminated composite square and annular-shaped plates with circular openings. Refined plate theory, created within the context of isogeometric analysis (IGA) is used during the present study. The theory is coded in MATLAB to study the behavior of the plates and the results are validated with the frequencies obtained using ABAQUS. Recursive, semi-circular, exponential, and Fibonacci helicoidal schemes are used during the present study for studying the free vibration behavior and the frequency is compared with the conventional cross-ply and quasi-isotropic laminates. Influence of position of opening, dimensions of opening, number of plies, and end condition, on the free vibration behavior of square and annular shaped bio-inspired helicoidal plates is carried out. The plates with CCCC and CCCF ends having openings at the quarter length are found to have higher frequency by 3.518 % and 0.3897 % compared to the values of the frequency of the plate with opening at the centre with the same perimeter. Opposite trend is observed for plate with PPPP, CFCF, and CFFF end conditions, where the plate with opening at centre exhibits higher value of the frequency by 2.427 %, 0.821 %, and 1.232 %, respectively. When the opening is near to the corners, the decrease in frequency by 3.913 %, 1.576 %, 1.193 %, and 1.437 % is observed for CCCC, CCFF, CCCF, and CFCF end conditions while increase by 1.490 % and 2.717 % is observed for the CFFF and PPPP end conditions. The mode shape of the plate is found to be greatly influenced by the position and dimension of the hole and end conditions of the plate.

A two-layered cross-ply laminate model for a single-ply satin woven fabric composite under thermal loads

The dominant fiber direction of a single-ply satin woven fabric is different depending on whether it is the upper or lower side. This affects the thermal distortion of laminates and principal curvature directions. Therefore, we propose a two-layered cross-ply laminate model for a single-ply satin woven fabric composite to consider the dominant fiber directions. To verify our model, we derive analytical solutions of antisymmetric angle-ply laminates under thermal loads for the conventional and proposed models. By comparing the analytical solutions with experimental results of unidirectional and satin woven fabric composites, we confirm that the proposed model accurately predicts the principal curvature direction.

Numerical investigation on effects of blast loading on anti-fragment performance of hollow cylindrical UHMWPE cross-ply laminate

Ultra-high-molecular-weight polyethylene (UHMWPE) fiber composites are widely applied for bullet and explosion proofing. This study numerically investigated the dynamic response of a hollow cylindrical UHMWPE cross-ply laminate subjected to combined blast and fragment loading produced by an improvised explosive device (IED). A strain-rate-dependent, anisotropic, elastoplastic constitutive model with progressive failure was adopted for the laminates via a user subroutine and comprehensively verified against the experimental results from the literature. Three sets of simulations of fragment-only loading, blast-only loading and the combined loading were performed on different configurations of IEDs and laminates. It was found that the effects of the blast loading were much weaker than those of the fragment loading and caused very small deformation of the laminate’s middle, including somewhat pre-tension along the circumferential direction but almost no fiber fracture. Both with and without blast loading, the dense penetrations of the multiple fragments dominated the response of laminates, including perforated holes that were interconnected with each other and global ply splitting. As a result, the blast effects barely affected the anti-fragment performance of the laminates.

A simplified approach for predicting last ply failure load of VO-notched laminated composite components

In this study, the last ply failure (LPF) load of composite laminates with VO-notches under pure mode I and mixed mode I/II was investigated experimentally, analytically, and numerically. The efficiency of the virtual isotropic material concept (VIMC) in combination with a new combined failure criterion was also evaluated. The J-integral and average strain energy density failure criteria were combined with VIMC. Using analytical expressions for the J-integral and the average strain energy density (ASED), the prediction of the fracture load of notched components was simplified and expedited. The experimental fracture loads of notched specimens were determined for quasi-isotropic and cross-ply laminates under mode I and mixed mode I/II. The fracture loads were predicted using analytical expressions for the J-integral and ASED, combined with VIMC. The VIMC-ASED and VIMC-J-integral failure criteria demonstrated good accuracy in predicting the LPF, with the highest accuracy for mode I, slightly reduced accuracy for mixed mode I/II. VIMC, in combination with energy-based failure criteria, effectively predicts the fracture load. The use of analytical expressions further simplified and expedited the prediction process without losing accuracy, making it a practical approach for engineering applications. Additionally, this approach significantly reduces the time and cost associated with extensive experimental testing.

Off-axis mechanical behavior and dynamic characteristics of UHMWPE composite laminates

An understanding of the off-axis mechanical behavior and failure mechanisms of ultra-high molecular weight polyethylene (UHMWPE) cross-ply laminates subjected to quasi-static and dynamic loadings is developed, with focus on the influence of off-axis angle and strain rate. For off-axis tension, UHMWPE laminates exhibit polymer shear response characteristics. An orientation-hardening phenomenon is captured, as fiber rotation leads to local increment of load capacity along the loading orientation. The failure strength presents an evidentially descending trend with off-axis angle from 0° to 45°. A non-monotonic variation of strength with strain rate is further observed: increasing with strain rate up to 500 s−1 but decreasing above, which is attributed to failure mode switching from plastic failure to brittle failure. The Tsai-Wu failure criterion, on homogenized cross-ply laminae, is experimentally modified with rate dependence. Further investigation on detailed information of the unidirectional properties should be conducted with the backing-out scheme to establish unidirectional failure criterion.

Nonlinear effect on stable state and snap-through bistability of square composite laminate

Bistable structures with the elastic instability caused by buckling are confirmed to perform significantly in micro-electromechanical systems, metamaterials, energy harvester, vibration isolation and morphing structures. The target of this paper is to explore the dynamic responses of cross-ply bistable composite laminate, focusing on the nonlinear effect of the single- and double-well vibration. Both theoretical and finite element (FE) methods are employed to simulate the nonlinear vibration and dynamic snap-through of bistable composite laminate under the foundation excitation at the center. In the theoretical model, the governing equations are established via Lagrange's equation based on the first-order shear deformation theory, von Karman nonlinear strain-displacement relation and Rayleigh-Ritz method. The fourth-order Runge-Kutta method is adopted to solve the governing equations, and the numerical results are validated by FE model. Subsequently, the details of the dynamic responses are analyzed to identify the nonlinear effects in the form of bifurcation diagram, phase portrait, time history, Poincare maps and amplitude spectrum. The dynamic responses are examined for a series of excitation parameters in both time and frequency domain. Through fixed frequency and frequency sweep tests, the nonlinear phenomenon of the single- and double-well vibrations are analyzed including superharmonic resonance, stiffness softening, hysteresis phenomenon, various periodic and chaotic vibration. The diverse responses to external inputs contribute significantly to efficiently predicting mechanical behaviors in real-world conditions, thereby offering indispensable theoretical support for structural design applications.

Combined computational-experimental investigation of residual stresses and pre-cracking in mode I behaviour of thick adhesively bonded GFRP composite joints

This paper presents a novel Finite Element (FE) simulation approach to examine the mode I fracture of thick adhesive joints used particularly in the trailing edge of the wind turbine blades. The approach involved FE models of the DCB specimens focusing on aspects overlooked in the existing literature. There has been limited investigation on residual stresses caused by thermal mismatch between composites and adhesives. Similarly, the impact of generating notches/pre-cracks in the adhesive layer during the preparation of Double Cantilever Beam (DCB) specimens on residual stresses has received minimal attention. Additionally, the Cohesive Zone Model, commonly used for simulating elastoplastic adhesives, may be inadequate due to its inability to account for the plastic deformation of the adhesive. In the present work, the pre-cracks were virtually generated in DCB FE models so that their effect on the stresses within the joint could be examined, making it a novel contribution to the field. The components were assigned with appropriate thermal expansion coefficients, and a simulation of the cool-down process was conducted to determine the thermal residual stresses. Furthermore, the Drucker-Prager plasticity criteria were used to capture the elastoplastic behaviour of adhesives in the FE simulations. Concurrently, the T-stresses were assessed through numerical investigations. For validation, experiments were conducted on DCB specimens made of two cross-ply composite laminates bonded with a ∼ 10 mm thick layer of an epoxy-based adhesive. A good agreement between computational and experimental results was observed, confirming the effectiveness and reliability of the proposed approach.

Equivalent tensile elastic modulus measurement of cross-ply composite plates using S1 mode of Lamb wave

Abstract This paper proposes a simple and effective Lamb wave-based measurement method for the elastic moduli of cross-ply composite plates with large thickness, considered equivalent to a single-layer orthotropic plate with nine independent elastic constants. Due to the low-frequency signals required for measuring large thickness plates and the large wavelength of the low-frequency signals, the size of composite plates is highly required. Therefore, it is considered to use the first order symmetric (S1) mode wave to increase the signal frequency and reduce the wavelength. The effects of elastic constants on the phase velocities of the S1 mode are investigated. The phase velocity of the S1 mode depends only on the equivalent tensile elastic modulus and in-plane Poisson’s ratio in the low-dispersive frequency-thickness product regime. Moreover, the in-plane Poisson’s ratio of cross-ply laminates changes sufficiently small to neglect its effect on the phase velocities of the S1 mode. Therefore, the tensile elastic moduli of the cross-ply laminated plates can be estimated using the S1 mode, and the mapping relations between the phase velocities of S1 mode and the elastic moduli are established. The proposed approach has been numerically and experimentally tested on cross-ply glass fiber reinforced laminates with large thickness, and validated by theoretical values and conventional tensile tests.

An efficient neural network approach for laminated composite plates using refined zigzag theory

This paper presents an innovative methodology employing the One-dimensional Convolutional Gated Recurrent Unit neural network (1D-CGRU) algorithm for the analysis of laminated composites using the Refined Zigzag theory (RZT). The RZT methodology is utilized to assess laminated plate structures and generate essential data, forming the basis for training the 1D-CGRU model. The synergistic application of RZT and 1D-CGRU demonstrates exceptional global–local accuracy in predicting the mechanical behavior of laminated composite plates. For efficient data generation, RZT not only provides high precision, but also exhibits computational efficiency, making it suitable for finite element simulations with a C0-continuous kinematic approximation. Additionally, the 1D-CGRU model integrates the strengths of a One-dimensional Convolutional Neural Network (1D-CNN) for spatial feature extraction and dimensionality reduction, coupled with a Gated Recurrent Unit (GRU) network for discerning temporal relationships and mapping them to the target domain. Furthermore, quantitative accuracy measurements, including Mean Squared Error (MSE), Root Mean Squared Error (RMSE), and Mean Absolute Error (MAE), are used to validate the superior performance of the 1D-CGRU model compared to other surrogate models. For angle-ply and cross-ply composite laminates, the 1D-CGRU model achieves remarkable accuracy (98.15% and 99.45%, respectively) with low RMSE values. These results highlight the potential of the proposed framework to enhance predictive analysis for laminated composite structures, offering valuable insights for engineering applications and design optimizations.

Dynamic Effect of Ply Angle and Fiber Orientation on Composite Plates

Composite materials have revolutionized industries such as aerospace and automotive with their impressive strength-to-weight ratios and customizable properties. Ply angle and fiber orientation are critical factors that significantly impact the dynamic behavior of composite structures, influencing stiffness, strength, and vibrational characteristics. This research delves into the dynamic characteristics of composite plates, explicitly examining how ply angle and fiber orientation affect vibrational behavior. Through finite element analysis (FEA), composite plates with varying ply angles and fiber orientations were modeled to understand their influence on natural frequencies, mode shapes, and dynamic responses under various loading conditions. The study reveals that cross-ply [0/0/0/0] exhibits the highest stiffness and superior stress handling, while the cross-ply balanced laminate [90/0/0/90] demonstrates better vibrational characteristics. The findings highlight the intricate relationships between design parameters and structural vibrational behavior, offering opportunities for optimizing composite structures. Additionally, harmonic analysis showed that a cut-out increases the natural frequency. The results underscore the importance of optimizing composite plate configurations to enhance vibrational characteristics and align natural frequencies with operational requirements, thereby mitigating resonance-related issues.

Microscopic damage behavior in CFRP cross-ply laminates at cryogenic temperature

For the practical use of cryogenic propellant tanks made of CFRP laminates, experimental elucidation of the laminates’ microstructural damage propagation behavior at cryogenic temperatures is important. This paper presents a newly developed tensile test rig that enables in-situ observation of microscopic damage using an optical microscope at cryogenic temperatures using a Gifford–McMahon refrigerator. In-situ observations of microscopic damage under uniaxial tensile loading were done at room temperature (290 K, 17 °C) and at 30 K (−243 °C) on cross-ply thin-ply CFRP specimens of three kinds with different 90° layer thicknesses. The results demonstrated that the crack propagation behavior is independent of temperature, that the matrix crack density is higher, and that the onset of matrix crack initiation strain is lower at 30 K than at 290 K. Furthermore, the thermal strain within 90° layer at 30 K and at 290 K was estimated using finite element analyses (FEA). The FEA results suggest that the decrease in onset strain of matrix crack initiation at 30 K is mainly attributed to the increase in the thermal strains within the 90° layer.

Effect of the level of anisotropy on the macroscopic failure of notched thin-ply laminates

This work presents a detailed experimental study conducted for a range of different lay-ups using thin-ply carbon fiber reinforced polymer (CFRP) laminates. The selection of the laminates was performed relying on their level of anisotropy. The laminates vary from a quasi-isotropic (QI) laminate, which is weakly anisotropic, to a cross-ply (CP) laminate, which is strongly anisotropic. The laminates were tested in on-axis and off-axis open hole tension (OHT). The main objective was to observe the effect of the level of anisotropy of the laminate on the macroscopic failure and observed failure patterns. It is shown that, contrary to most existing observations so far, depending on the lay-up and consequently its level of anisotropy, open-hole, quasi-homogeneous thin-ply laminates do not necessarily exhibit a fiber dominated failure mode, but could develop sub-critical damage mechanisms in a large extent prior to ultimate failure, reminiscent of what is observed for standard-ply CFRP laminates.

The Effect of Stacking Sequence and Ply Orientation with Central Hole on Tensile Behavior of Glass Fiber-polyester Composite

An experimental investigation was carried out to study the effect of circular cross-holes on the failure behavior of unidirectional glass fiber reinforced with unsaturated polyester resin composites, varying cross-ply laminates that were subjected to axial tensile load. This paper deals with the effects of the circular notch and the number of plies on nominal tensile and net tensile strengths. Tensile strengths were investigated for composites with cross-ply([0/90]. [90°/0°/90°] and [0°/90°/0°].90°), orientation and varying the laminate layers with a central hole, and effects of volume fraction and number of ply on mechanical properties for un-notched (smooth) and notched specimens were also studied. The results showed that increasing the number of plies has a marginal effect on tensile strength values. The fraction of volume has significant effects and for increasing the number of plies about 9% decreases in nominal tensile strength and about 11% decrease in the net tensile strength was observed. The same results were obtained with finite element analysis.

Prediction of viscoelastic effective creep compliances in cracked cross-ply composite laminates

Viscoelastic effective creep compliances were predicted for symmetric composite laminates with constant matrix crack density. Following previous analytical models, the governing equations were solved in the Laplace domain, and the resulting displacement field was inverse Laplace transformed to obtain the displacement field, damage variables, and strain response to a given stress in the time domain. For the displacement field, both a series solution and a non-series solution were obtained. The non-series solution was then used to calculate the strain response of a cross-ply laminate subjected to constant stress under constant matrix crack density via the numerical inverse Laplace transform. To validate the model, the creep strains predicted using the model were compared with a finite element analysis solution, experimental results, and a synergistic damage mechanics solution.

On the isogeometric analysis of vibration and buckling of bioinspired composite plates using inverse hyperbolic shear deformation theory

Inspired by the remarkable energy absorption and damage tolerance capabilities observed in mantis shrimp crustaceans, this study delves into the intricate realm of biological composites with helicoidal structures. However, the effect of the relative orientation of fibers within the helicoidal structure matrix on the buckling and vibration characteristics still warrants comprehensive investigation for the better design of the bioinspired structures. For the first time, a Non-Uniform Rational B-Splines (NURBS)-based isogeometric analysis (IGA) framework termed NURBio is proposed to investigate the vibration and buckling characteristics of bioinspired laminated composite structures. The framework employs NURBS basis functions for exact complex geometric representation and field approximation and offers superior computational accuracy and efficiency as compared to conventional finite element method (FEM). The present analysis is underpinned by an inverse hyperbolic shear deformation theory (IHSDT) capable of accurately capturing the interlaminar stress distribution. This research investigates the performance of various bioinspired layup configurations encompassing recursive, exponential, semicircular, and Fibonacci helicoidal designs and compares them with those of unidirectional, and cross-ply laminates. A series of numerical examples on the buckling and vibration response of bioinspired composite plates are presented to demonstrate the versatility and efficacy of the proposed isogeometric framework. The influence of different layups, loading and boundary conditions, and geometric properties on the response of different bioinspired plate structures are meticulously examined. The study offers valuable insights into the design and optimization of high-performance bioinspired structures.