Ply Laminates Research Articles

Influence of stacking sequence on flexural properties of hybrid carbon fibre reinforced polymer laminates

This paper presents a numerical investigation of the influence of the stacking sequence and fibre variation of the plies on the flexural properties of carbon fibre-reinforced polymer laminates. The numerical approach utilised a three-point flexural test to evaluate different quasi-isotropic stacking sequences. It also analysed attempts to reinforce failure-prone plies only using a stronger prepreg material to reduce the cost of the laminate. The results were validated by conducting a cantilever bending test and compared with calculations based on classical lamination theory. The beam deflection, normal stress per ply, and the Puck failure criterion inverse reverse factor per ply were used for evaluation and result comparison. The results showed that the quasi-isotropic stacking sequence [0/90/+45/−45]s is the most suitable for beam applications. Replacement of the outer plies of the composite laminate by a stronger ply material made the hybrid laminate performance almost identical to a pure composite laminate consisting of stronger material only.

Susceptibility versus flexural stiffness in the stability of hybrid laminate columns with a rectangular cross section for a 1D model

Hybrid columns of FGM/FML type with inhomogeneous transverse structure perpendicular to their length are discussed. After that, laminated columns with different layups of laminate plies are discussed, with focus put on the effect exerted by many coupling of the stiffness submatrix on the lowest eigenvalue load. All columns were simply supported The study uses three methods for determining the lowest eigenvalues. The first two are analytical beam methods (i.e. 1D modelling approaches) based on the use of the Euler-Bernoulli theory. The proposed 1D methods are a generalisation of the well-known approach of determining the lowest eigenloads of isotropic columns. The first approach is to solve the eigenproblem directly from the differential equation of the deflection line. The second approach assumes that the curvature of the beam depends on the susceptibility of the beam. This is a fundamental assumption in the bending theory of beams and thin plates. The third method is the FEM (3D shell approach) which is used for the verification of the previous calculations. A comparison of the obtained results showed that the proposed 1D (one-dimensional) approach based on the full susceptibility matrix, which is the inverse stiffness matrix was as accurate as the 3D (three-dimensional) FEM shell model. The relative difference does not exceed 3%. Second 1D approach based on the stiffness matrix yields many times unacceptable differences relative to the reference results obtained by the FEM method. This comparison clearly demonstrates that an approach based on the assumption that curvature is directly proportional to susceptibility in flexural composite structures produces accurate results for all types of coupling.The existing literature extensively explores the impacts of stiffness matrix elements on both the linear and non-linear stability of laminate columns. However, there is a notable absence of studies focusing on the influence of susceptibility. This crucial aspect has been overlooked in prior studies. The present paper endeavors to fill this gap by shedding light on the influence of susceptibility, thereby emphasizing its significance in the analysis of laminate column stability.

Prediction of allowable compression load for notched composite laminates combining FEA simulation and machine learning

Determining the allowable compression load (ACL) of notched composite laminates (NCL) requires consideration of buckling, intra- and inter-laminar damage, which is a costly and repetitive task due to the high dimensional and nonlinear relation of ACL to the numerous design variables. In this work, a high-throughput finite element analysis (FEA) and machine learning (ML) combined approach is proposed to predict ACL of laminates. First, the high-throughput FEA model of NCL covering all of the design variables is generated, and the corresponding critical compression loads in terms of buckling, intra- and inter-laminar damage are obtained. Then, ML models are trained, with inputs being the design variables of NCL and outputs being the critical compression loads. ACL and initial failure mode are determined by the minimum compression load of the three failure modes. Moreover, transfer learning is introduced to laminates with new design variables of new ply number, notch shape and laminate type. By fine-tuning the pre-trained ML model using scarce new data, the fine-tuned models are suitable for new laminates. Consequently, ACL and initial failure mode of notched laminates with various design variables are predicted.

Low velocity impact response of Automated Fiber Placement Advanced Placed Ply composites

This study explores the influence of the internal architecture in the low-velocity impact response of Automated Fiber Placement Advanced Placed Ply laminates. AP-PLY laminates with different lay-up are subjected to low velocity impact and compression after impact experiments. Different performance in terms of damage tolerance is obtained as a function of their internal architecture. Triaxial and quasi-isotropic AP-PLY configurations presented a reduced extension of the delamination in comparison to cross-ply panels. As a result, the cross-ply configuration exhibited a drastic loss in residual strength of 49.1% when subjected to 50 J of impact energy. Numerical simulations were employed to provide insight into the deformation and failure mechanisms (e.g., matrix cracking of directly impacted yarns, delamination or tow debonding), and assess the performance of AP-PLY against conventional angle-ply laminates, predicting larger delamination for the latter, showing the potential of the AP-PLY architecture to produce laminates with improved low-velocity impact performance.

Repair Analysis of Overlay Woven Fabric CFRP Laminates

The increase in aerospace composites usage for structural components demands advanced repair analysis. Overlay repairs of carbon fiber-reinforced polymer laminates offer an alternative that is easier to perform and less time-consuming to produce than the widely used tapered scarf repair and stepped lap. Composite specimen manufacturing was based on both twill carbon/epoxy prepreg and wet lay-up. The repair was performed with both prepreg and wet extra plies to the parent prepreg structure. However, the design of overlay joints must be carefully investigated to avoid generating stress concentration regions at free edges. This study examined specific extra ply terminations' impact on peak stresses in the adhesive bond line. Linear finite element analysis was performed to conduct a maximum principal stress study with a focus on three joint design parameters: ply material, overply effect, and stacking sequence. FEA accurately predicted experimentally observed responses and provided further insight into the failure behavior of the structure. Results showed that overlay joints have a strong sensitivity to ply material type, the number of overply, and stacking sequence. The introduction of overplies provided protection and stiffness at joint tips, and an overply material behavior was identified. The location of 0̊ plies in the composite laminates was highlighted as an important factor. The analysis was then extended to three-dimensional FE models for verification. In conclusion, results showed that high-stress concentration in overlay joints can be mitigated with the introduction of overplies and appropriate changes in joint design parameters to reduce stress peaks at joint tips and corners.

On the Double-Double Laminate Buckling Optimum for the 18-Panel ‘Horse-Shoe’ Reference Case

The Double-Double (DD) laminate family allows for simplification in the context of buckling analysis. Stacking-sequence discussions, known from conventional-laminate optimization, made from 0∘, ±45∘, 90∘ plies, omit for DD. The recently presented DD-specific buckling relation is applied in this article to the 18-panel, ‘horse-shoe’ laminate blending reference case. The use case addresses the challenge of identifying a compatible group of laminates for differently loaded, adjacent regions, as it is a common scenario in wing covers and fuselage skins. The study demonstrates how the novel DD-laminate buckling relation simplifies the process of determining a buckling optimum for a group of laminates. The process of determining the optimum blended DD panel is presented. Its determined mass is compared with minimum masses, presented in earlier studies, which focus on stacking optimization and blending for more conventional ply orientations and laminate stacking conventions.

Effect of MWCNTs on mechanical properties of woven angle ply GFRP laminates

Impact of MWCNTs on the mechanical behaviour of woven GFRP angle ply laminates have been studied. GFRP laminates was fabricated with eight layers of fiber orientation (45˚/-45˚) of neat epoxy, 0.5 wt% and 1.0 wt% MWCNTs filled GFRP using vacuum assisted hand layup method. With the aim to perform the mechanical testing like tensile, compression, short beam and three-point bending test, required samples were made from the manufactured laminates in accordance with respective ASTM standards. Addition of 0.5 wt% MWCNTs into GFRP laminates improved the tensile and bending strength. Woven angle ply GFRP modified with 1.0 wt% of MWCNTs enhanced only the ultimate tensile strength. Incorporation of MWCNTs into GFRP has no effect on improvement of compression and interlaminar shear strength.

A Review of Electrospun Nanofiber Interleaves for Interlaminar Toughening of Composite Laminates

Recently, polymeric nanofiber veils have gained lot of interest for various industrial and research applications. Embedding polymeric veils has proven to be one of the most effective ways to prevent delamination caused by the poor out-of-plane properties of composite laminates. The polymeric veils are introduced between plies of a composite laminate, and their targeted effects on delamination initiation and propagation have been widely studied. This paper presents an overview of the application of nanofiber polymeric veils as toughening interleaves in fiber-reinforced composite laminates. It presents a systematic comparative analysis and summary of attainable fracture toughness improvements based on electrospun veil materials. Both Mode I and Mode II tests are covered. Various popular veil materials and their modifications are considered. The toughening mechanisms introduced by polymeric veils are identified, listed, and analyzed. The numerical modeling of failure in Mode I and Mode II delamination is also discussed. This analytical review can be used as guidance for veil material selection, for estimation of the achievable toughening effect, for understanding the toughening mechanism introduced by veils, and for the numerical modeling of delamination.

Drilling process parameter optimization of natural fibre reinforced polymer matrix composites

Machining of polymer matrix composites is a complex phenomenon owing to anisotropic behavior of these materials. Optimization of drilling process parameters were aimed in this work with determination of delamination factor. Polymer matrix composites were fabricated by mixing of matrix and reinforcement under varying ratios of weight and different layers of reinforcement for characterization. Plies were arranged as 8 jute, 6 jute and 2 silk, 4 jute and 4 silk, 2 jute and 6 silk and 8 silk plies respectively. Composite fabrication was followed by drilling of composites with different bit sizes and spindle speeds taking varying bit sizes of 3.20, 4.20, 4.75, 5.56 mm and the spindle speeds of 720, 960, 1200, 1440 rpm respectively. Finally, optimization in Minitab using the TAGUCHI were analyzed and optimized data for minimum delamination determined for different polymer combinations. The hybridized laminates with both jute and silk combinations are observed to have reduced delamination factor here as compared to all jute or all silk ply laminates which can be an important criterion in damage minimization on account of delamination due to drilling. This study presents analysis which can help in improved machining of polymer matrix composites with minimum of wastage and enhance scope of application of these materials in modern technological advancements involving assemblies and thereby requiring drilled holes.

Mathematical and simulation based investigation towards deformation behaviour of bombyx mori moth silk /vinyl ester reinforced laminated composite

ABSTRACT This paper focuses on the composite design with fibres loaded in the longitudinal direction as well as orientated at some certain angles. The study uses Bombyx Mori Moth Silk (BMM Silk) as fibres and vinyl ester as matrix material. The two sorts of composites having cross ply and angle ply laminate were considered for deformation study using the finite element analysis. According to the ASTM D 3039 testing standard, the tensile test was carried out to design and composite study of their occurred deformation. The rule of mixture was employed in order to evaluate the elastic constants of the prepared orthotropic composite laminate along the fibre direction and the evaluation of orthogonal stresses in transverse direction was carried out using the finite element procedure. The maximum orthogonal stress value of cross ply and angle ply was found to be 44.902 and 47.779 MPa, respectively. Also, the deformation occurred for both laminates was found to be of 0.083603 and 0.076428. This concludes that the deformation occurrence is more in case of angle ply and is less in cross ply laminates.

Progressive Failure Analysis of Composite/Aluminum Riveted Joints Subjected to Pull-Through Loading

Out-of-plane mechanical properties of the riveted joints restrict the performance of the wing box assembly of airplane. It is necessary to investigate the pull-through performance of the composite/metal riveted joints in order to guide the riveting design and ensure the safety of the wing box assembly. The progressive failure mechanism of composite/aluminum riveted joint subjected to pull-through loading was investigated by experiments and finite element method. A progressive damage model based on the Hashin-type criteria and zero-thickness cohesive zone method was developed by VUMAT subroutine, which was validated by both open-hole tensile test and three-point bending test. Predicted load-displacement response, failure modes and damage propagation were analysed and compared with the results of the pull-through tests. There are 4 obvious characteristic stages on the load-displacement curve of the pull-through test and that of the finite element model: first load take-up stage, damage stage, second load take-up stage and failure stage. Relative error of stiffness, first load peak and second load peak between finite element method and experiments were 8.1%, − 3.3% and 10.6%, respectively. It was found that the specimen was mainly broken by rivet-penetration fracture and delamination of plies of the composite laminate. And the material within the scope of the rivet head is more dangerous with more serious tensile damages than other regions, especially for 90° plies. This study proposes a numerical method for damage prediction and reveals the progressive failure mechanism of the hybrid material riveted joints subjected to the pull-through loading.

Morphing wing design using integrated and distributed trailing edge morphing

The presented study investigates the design and development of an autonomous morphing wing concept developed in the scope of the SmartX project, which aims to demonstrate in-flight performance optimisation with active morphing. To progress this goal, a novel distributed morphing concept with six translation induced camber morphing trailing edge modules is proposed in this study. The modules are interconnected using elastomeric skin segments to allow seamless variation of local lift distribution along the wingspan. A fluid-structure interaction optimisation tool is developed to produce an optimised laminate design considering the ply orientation, laminate thickness, laminate properties and actuation loads of the module. Analysis of the kinematic model of the integrated actuator system is performed, and a design is achieved, which meets the required continuous load and fulfils both static and dynamic requirements in terms of bandwidth and peak actuator torque with conventional actuators. The morphing design is validated using digital image correlation measurements of the morphing modules. Characterisation of mechanical losses in the actuator mechanism is performed. Out-of-plane deformations in the bottom skin and added stiffness of the elastomer are identified as the impacting factors of the reduced tip deflection.

Influence of shear direction on the buckling of CFRP composite perforated plate

The shear buckling performance of CFRP composite perforated plates taking due account of the influence of the flexural anisotropy is examined in this paper using the finite element analysis procedure. Typical laminated composite lay-up causes many complexities but can easily be dealt with in the numerical simulations. The results from the finite element models are shown to agree favourably with the buckling curves from the independent simulations using finite strip method of analysis. Results in the paper clearly show that care should be taken seriously for the case of composite structural members having opening in their webs. Depending on the nature of the applied shear loading, openings, and varied symmetric angle ply laminates, the buckling behavior and capabilities have also been altered.

Three-dimensional scaled boundary finite element method to study interfacial imperfections in thick laminated composite plates undergoing bi-axial bending

In this work, the scaled boundary finite element method (SBFEM) is employed to model weakly bonded thick laminated composite plates subjected to bi-axial bending. A three-dimensional modelling technique incorporated in the SBFEM framework is used for thick laminated plates, where two-dimensional plate models cease to provide accurate results. Weakly bonded interfaces are modelled using spring layer models with the incorporation of zero-thickness interface elements between the layers. The interface element is subjected to behave in a linearly elastic manner capturing the slippage between the layers. Using SBFEM, it is possible to have fewer discretisation in the through thickness direction of the plate (or individual lamina) without compromising the accuracy of the results. Additionally, the size of interface elements can be kept small without altering the size of the adjoining bulk element. Validation examples covering symmetric, anti-symmetric cross ply and angle ply laminates have been solved using the proposed approach. Results from the proposed method using SBFEM are compared with well-established methods for modelling thick laminated composite under bi-axial bending.

Experimental characterization and numerical modelling of the translaminar fracture of woven-ply hybrid fibers reinforced thermoplastic laminates

The understanding of fracture mechanisms and the assessment of fracture toughness are key factors to the design of high-performance composite structures to be used in aeronautics. Thus, this work addresses the influence of initial notch orientation on the translaminar fracture of woven-ply hybrid fibers reinforced thermoplastic polyether ether ketone (PEEK) laminates. The translaminar fracture of Single-edge-notch bending (SENB) specimens is experimentally characterized depending on two initial notches (0° and 45°). Such geometry results in a complex stress state within the laminates plies as well as simultaneous tension/compression failures. A full-field measurement technique has been implemented to monitor the crack initiation and growth on the specimen surface during mechanical loading. To better understand the role played by the initial notch orientation as well as the plies orientation contribution to fracture behavior, a specific Finite Element mesoscale model was built to account for the deformation mechanisms (namely local plasticity) and the different damage behaviours (fiber breakage in tension and compression, kinking/crushing in compression, delamination) occurring within the plies of quasi-isotropic laminates. Linear elastic fracture mechanics concepts have been applied to quantify the critical translaminar fracture toughness (about 40 kJ/m2 in both cases). Finally, this study provides useful information on the fracture toughness values for engineers willing to design thermoplastic-based composite parts with stress concentrators.

Effect of ply orientation and laminate thickness on carbon fibre reinforced polymers under low‐velocity impact

AbstractComposite materials, which have gained prominence in the aerospace industry due to their high strength‐to‐weight ratio, are vulnerable to delamination damage when struck by low‐speed projectiles due to their low through‐thickness strength. This paper presents the experimental evaluation of a composite plate subjected to low‐velocity impact. The plates under discussion were constructed using a carbon fibre reinforced polymer laminate with a quasi‐isotropic ply structure. Experiments were carried out using a conical‐shaped impactor on carbon/epoxy laminated plates with three different orientations ([0/0] 4 s, [0/90] 2 s, and [45/0–45/90] s) that were put through two distinct impact energies (7 J and 14 J). Impact response is determined using drop‐weight impact tests. The techniques of ultrasonic C‐scan, field emission scanning electron microscopy (FESEM), and surface micrographs were integrated to provide a new and in‐depth understanding of damage evolution and failure mechanisms in composite laminates. Damage resistance appears to decrease as impact energy increases. Furthermore, thicker laminates have lower absorbed energy but, on the other hand, more widespread delamination due to increased bending stiffness. Furthermore, quasi‐isotropic laminates outperform in terms of damage resistance and increased energy absorption rates by 8 % to 15 %. The efficacy and logic of the suggested model were shown by a strong connection between experimental results.

A comparative analysis of thermos-mechanical behavior of CNT-reinforced composite plates: Capturing the effects of thermal shrinkage

In this study, an analytical model based on the classical laminate theory (CLT) is developed for the prediction of the effective thermal expansion coefficients (ETECs) of general angle-ply laminates (symmetrical and asymmetrical). The applications of the derived model are shown by solved examples for the prediction of ETEC of carbon nanotube-reinforced (CNTRC) angle ply laminates for various ply angles. CNTRC laminates with a negative thermal coefficient (NTC) are obtained and considered as a special case. For an extreme case, a laying angle of (35/-35)3T and (55/-55)3T, along with an NTC of −0.79 × 10−5/K is achieved. Meanwhile, the Reddy shear plate model is extended to the framework of Von Kármán nonlinearity. The corresponding dynamic equations are analytically established. With the help of the two-perturbation approach, the deflection time history curves of the forced vibration are obtained. Numerical results show that the thermal-vibration behaviors may be adjusted and controlled by changing the TEC and functionally graded pattern. The presented analytical results not only are theoretically fundamental for understanding the thermal-vibration behavior of FG-CNTRC but also serve as guidelines for NTC design of composited laminated structures.

Vibration Analysis of Composite Laminated Plates Using Analytical and APDL ANSYS Codes

The aim of this work is to investigate analytical (Classical theory) and [ANSYS Parametric Design Language (APDL)] analysis of laminate composite plate. The free vibration analysis with two boundary conditions simply supported (SSSS) & clamped ends (CCCC) are taken into account in this work. The equations of motion that governs the predication of dynamic behavior of cross and angle ply composite are solved theoretically using [Matlab] software. Three degrees of freedom are included in computing the natural frequency and mode shapes of cross and angle ply laminate. The significant effect of various parameters such as number of layers of fibers, aspect ratios, fiber orientation, and modulus ratio on natural frequency is evaluated theoretically and APDL (ANSYS). The numerical analysis is carried out by commercially available ANSYS software. The boundary conditions can significantly affect the natural frequency of the composite laminate plate due to the restraint effect at the edges. In this work a relatively new modeling technique will be adopted. Good agreement is achieved between the analytical and ANSYS results.

Verification of Puck's criterion for CFRP laminates under multiaxial loads at ambient and cryogenic temperatures

Objective of the present study is the verification of Puck's failure criterion for multiaxial mechanical loading situations in the ambient and cryogenic thermal regimes. The assessment is based on the material data and the failure envelope determined in a previous study on uniaxially loaded single-ply specimens study. Here, the pre-existing experimental data base is complemented by experiments on specimens made from angle ply laminates featuring holes, tapered sections and combinations thereof. The specimens were tested at ambient temperature and in a liquid Helium environment at 4.2 K. For determination of the local stress states in the individual plies at the stress concentrations induced by the holes and tapered sections, the experiments were simulated numerically by the finite element method. It is found that Puck's criterion in most cases provides conservative results. Unresolved additional safety margins may develop if a structural failure in an inter-fiber mode requires development of larger delaminations of adjacent plies to form a through crack.

Mesoscale modeling of ultra-thin woven fabric composite subjected to in-plane loading

Ultra-light composites are produced through the spread tow technology. The success of spread tow fabrics lies in their unique woven structure. By interlacing widespread thin flat tapes, instead of regular (and thicker) yarns, more straight fibers and thinner plies are obtained which leads to improvements in the mechanical performance in terms of both stiffness and strength. The available numerical studies on spread tow fabric composites are based on the approximation to equivalent thin ply laminates, where the key observations are dedicated to a delayed or suppressed microcracking. This paper helps to investigate the limitations of considering thin-ply spread tow composites as equivalent laminates, as well as to bring more understanding on how the tow thickness affect the sequence of failure mechanisms. As an aid to these investigations, a parameterized mesoscale model has been developed that preserves the complex geometry of the woven structure and can analyze the tow thickness effect down to 35 µm. By applying shifted periodic boundary conditions through the thickness, the effect of periodic layer shifting is also analyzed without having to discretize and model more than one layer of the composite.