Lay-up Sequence Research Articles

Energy absorption behavior of filament wound CFRP origami tubes pre-folded in Kresling pattern

Pre-folded tubes can exhibit superior energy absorption characteristics under axial crushing compared to conventional straight-walled tubes. However, their construction can be difficult to automate. In this investigation, we present a novel filament winding approach to efficiently manufacture pre-folded carbon fiber reinforced plastic (CFRP) tubes featuring the Kresling fold pattern. We experimentally study the quasi-static axial crushing behavior of three Kresling geometries and compare them to conventional tubes with a circular and square cross-section. The data from experiments is used to develop a finite element model for estimating axial crush indicators. Despite the layup sequence not orienting the fibers in the direction of loading, we obtain superior structural performance in terms of the mean force divided by the initial peak crushing force, which represents the crushing force efficiency of the structure. The tested tubes exhibit further potential to improve their energy absorption performances, while preserving enhanced manufacturability.

Crushing Characteristics Comparison between Aluminum/CFRP and Aluminum/CFRP/Aluminum Hybrid Tubes.

This study experimentally investigated the axial crushing characteristics of the hybrid tubes with the configuration of aluminum/carbon fiber-reinforced polymer (CFRP) (1/1) and aluminum/CFRP/aluminum (2/1). The effects of geometry size and fiber lay-up sequence on the axial crushing energy-absorption performances and failure modes of the two types of hybrid tubes were compared. The results showed that the energy absorption of the specimens with [0°/90°] lay-up sequence was better than that of the ones with [45°/−45°] lay-up sequence for both types of hybrid tubes. The proper length of the tubes should be selected to avoid too small a length-to-diameter ratio so that a stable and controllable progressive crushing failure mode can be achieved. When the crushing failure process was relatively stable, the specific energy absorption and crushing force efficiency of the 2/1 hybrid tubes were not affected by the geometric size. The energy absorption of the hybrid tubes was higher than the sum of the energy absorption of all the corresponding individual tubes, showing a positive hybrid effect.

Maximum Bending Stress Analysis of Jute/Epoxy and Glass/Epoxy Polymer Composites

A surge inthe use of fibre reinforcedcomposites for biodegradable materials, which include both synthetic and natural fibres, to fulfil the strength requirements of composites while also being environmentally friendly has resulted in the use of these materials becoming increasingly popular. Researchers have been working to improve natural fibre qualities to partially replace synthetic fibre, even though not entirely. The research can be accomplished by modelling and simulation techniques, which are becoming more prevalent as technology advances. The approaches have the benefits of being efficient in addressing any material model, boundary conditions, and complicated form structure that may be encountered. This study uses ANSYS APDL, a finite element analysis tool, to carry out flexural test. These factors, as well as the fibre ply orientation, lay-up sequence, and fibre volume percentage, have an impact on the maximum stress of each composite, which are investigated in this study. In the lay-up sequence of [(+θ, -θ)2] s, with fibre ply orientation of 0 ̊ the maximum flexural stress obtains for glass/epoxy (vf=60%), glass epoxy (vf=30%), and jute/epoxy (vf=30%) is 214.64 MPa, 153.77 MPa, and 82.91 MPa and for fibre ply orientation of 90 ̊ the maximum bending stress is 55.41 MPa, 18.39 MPa and 8.37 MPa respectively. Furthermore, the impact of off-axis plies in the 0° fibre ply orientation can be observed in the maximum bending stress of the [θ4,04] s lay-up sequence, which is a function of the number of off-axis plies in the 0° fibre ply orientation. When using the lay-up sequence [904,04]s, the maximum flexural stress for glass/epoxy (vf=60%), glass/epoxy (vf=30%), and jute/epoxy (vf=30%) is 83.39 MPa, 23.04 MPa, and 17.92 MPa, respectively. When bending tests are performed, the 0° fibre ply orientation produces the highest maximum stress, followed by 45° and 90°. When comparing 0° plies composites with off-axis angles to plies composites, the lay-up sequence of 0° plies with off-axis angles exhibits the highest maximum stress.

Finite element analysis of damage mechanisms of composite wind turbine blade by considering fluid/solid interaction. Part II: T-shape adhesive structure

This paper is the second one of two that further studies damage mechanisms of T-shape adhesive structure of composite wind turbine blade. Finite element model by considering fluid/solid interaction is established for the local T-shape adhesive structure. Effects of some important factors on damage mechanisms of blade are discussed including the wind velocity, the strength, thickness and width of adhesive layer. Numerical results by fluid/solid coupling analysis are also compared with those by the blade element momentum (BEM) theory. Results show that: (1) damage in the skin and the adhesive layer increases as the wind velocity adds. (2) appropriate increase of the thickness (e.g., 0.1–0.5 mm) and width of the adhesive layer decreases the structural damage to a large extent. (3) two methods produce some difference for damage predictions of the T-shape adhesive structure under high wind velocity. It is recommended that comprehensive considerations should be given to the layup sequence, the adhesive thickness, size and strength, and the selection of material and processing so as to improve damage tolerance and load-bearing ability of structure.

Accelerating the Layup Sequences Design of Composite Laminates via Theory-Guided Machine Learning Models.

Experimental and numerical investigations are presented for a theory-guided machine learning (ML) model that combines the Hashin failure theory (HFT) and the classical lamination theory (CLT) to optimize and accelerate the design of composite laminates. A finite element simulation with the incorporation of the HFT and CLT were used to generate the training dataset. Instead of directly mapping the relationship between the ply angles of the laminate and its strength and stiffness, a multi-layer interconnected neural network (NN) system was built following the logical sequence of composite theories. With the forward prediction by the NN system and the inverse optimization by genetic algorithm (GA), a benchmark case of designing a composite tube subjected to the combined loads of bending and torsion was studied. The ML models successfully provided the optimal layup sequences and the required fiber modulus according to the preset design targets. Additionally, it shows that the machine learning models, with the guidance of composite theories, realize a faster optimization process and requires less training data than models with direct simple NNs. Such results imply the importance of domain knowledge in helping improve the ML applications in engineering problems.

A detailed study on the damage evolution and failure assessment of single-lap hybrid joints in CFRP laminates under tensile loading

Hybrid joints have potential to improve the joint strength and efficiency compared to the bonded or bolted joint. Several studies have been performed to understand the influence of various design parameters on the hybrid joint strength. However, very few studies have been reported on the complex failure mechanism of the hybrid joint. In this study, a detailed analysis is carried out to understand the failure mechanism of the hybrid joint in Carbon fiber reinforced plastic (CFRP) laminate having [0/+45/90/−45]s layup sequence under tensile loading both experimentally and numerically. Analysis of a simple bonded and bolted joint configurations are also included for comparison purposes. The acoustic emission (AE) technique is utilized for the damage assessment and the 3D digital image correlation (DIC) technique is used to capture the whole field strain around the bolt region. A detailed fractographic study using a digital optical microscope is also carried out to critically ascertain the presence of different damage modes. An in-house instrumented bolt is realized to measure the load transfer through it upon loading. A finite element based progressive damage model (PDM) along with the cohesive element is also developed to predict the damage evolution and failure mechanism for all the joint configurations.

Variable stiffness composite laminated beams - nonlinear free flexural vibration behavior using a sinusoidal based shear flexible structural theory accounting for Poisson’s effect

In the present work, formulation for the nonlinear free vibrational behavior of laminated variable stiffness composite beams with curvilinear fibers is made incorporating sinusoidal function for representing the transverse shear flexibility, geometrical nonlinearity, and accounting for Poisson’s effect through the constitutive equation for analyzing beams with general composite lay-up. Applying Hamilton’s principle combining with a finite element approach based on three-noded C1 beam element, the governing equations are formed through matrices. The solutions for the developed governing equations are evaluated iteratively by introducing eigenvalue analysis and the results are viewed through the frequency–amplitude relationship. A large number of design parameters like curvilinear fiber angles in a layer, number of layers, lay-up sequence, thickness ratio, etc. is assumed to visualize the nonlinear free vibration characteristics of VSCL beams. Also, for the practical situation, the influence of thermal environment and restraint elastically against beam ends rotation, to accommodate other than classical boundary conditions, hybrid beam (consisting of constant and variable stiffness layers) on the non-linear free vibrational behavior is presented.

Characterization of cure residual strain development and associated structural distortion in carbon fiber polymer matrix composites

A comprehensive experimental methodology has been developed to measure the in situ cure residual strain (CRS) generation in carbon fiber reinforced polymer (CFRP) laminates using embedded fiber Bragg grating (FBG) sensors. In order to delineate the effect of anisotropy, heterogeneity, laminate thickness and geometry, in situ CRS is measured in pristine epoxy, uni-directional (UD)-CFRPs, multi-directional (MD)-CFRPs and L-shaped MD-CFRP laminates. In this study, emphasis is laid on quantifying the variation in CRS magnitudes as a function of laminates lay-up sequence and thickness. Calibration of FBG sensors are carried out by following well established procedures. Structural distortion due to CRS is correlated using embedded FBG sensor and measured using the coordinate measurement machine (CMM). The presented results show a uniform CRS development across the thickness in MD-CFRP laminates as compared to L-shaped MD-CFRP laminates.

Effect of glass fiber hybridization on the mechanical properties of unidirectional, alkali‐treated kenaf‐epoxy composites

AbstractDue to environmental issues and high cost of synthetic fibers, natural or cellulosic fibers have emerged as a promising reinforcement for polymer composites. The hybridization of natural fiber with synthetic fiber is a useful technique to improve the mechanical properties instead of using the natural fibers alone. This research aims to evaluate the influence of glass fiber hybridization on the mechanical properties of continuous, unidirectional, alkali (NaOH)‐treated kenaf‐epoxy composites. At first, the effect of treatment of various concentrations (3, 5, 7, and 9% w/v) of NaOH on the structure of single kenaf fiber was characterized using XRD, SEM, FTIR, and tensile testing. At the optimum 5% alkali concentration the tensile strength, modulus, and %elongation of the kenaf fibers were enhanced by 81%, 114%, and 42%, respectively. The effect of hybridization of 5% NaOH treated kenaf along with glass fiber on the improvement in tensile, flexural, and impact properties for hand laid kenaf‐glass‐epoxy hybrid composite laminates was established. The overall matrix to fiber weight ratio of five different layup sequence laminates was maintained constant at 70:30. It can be concluded from the obtained results that the 15% glass and 15% kenaf fiber hybridized composites exhibited the maximum increment in tensile strength and modulus (68.5% and 19.5%, respectively) in comparison to the unhybridized composites. Further, the flexural strength and modulus were also improved by 21% and 67%, respectively, and the impact strength by 153%. The SEM fractography proved that alkali treatment of fibers improved the fiber‐matrix interfacial bonding whereas fiber breakage, fiber pull‐out and debonding were established as the main fracture mechanisms of hybrid composites. The findings of the present investigation on kenaf‐glass hybrid composites corroborate that they are suitable for secondary structural applications in construction and automobile sectors.

On the pacifying influence of an elastomeric foam core on the failure mechanism of sandwich composites with various skin layups

The selection of a crashworthy core for sandwich composite construction has been aimed pursued in various applications. In this article, the response of sandwich beams consisting of elastomeric foam core and laminated fibre-reinforced skins with various layup sequences hereafter referred to as (EFCS) beams is investigated experimentally and numerically. This sandwich configuration provides several advantages for structural applications since the conventionally used rigid foam cores have relatively low crushing strength. The incorporation of the elastomeric foam has been found to enhance the post-failure stability and residual strength/crashworthiness of sandwich composite beams due to the pacifying influence of the core on the failure mechanism, which was further examined by numerical simulations. Both the hyperelasticity of the foam core and the progressive damage of the composite skins were accounted for in the numerical simulation. The efficiency of EFCS beams was established by comparing their performance to their laminated composite counterparts. The results evidence the promising performance of EFCS beams, especially in the context of their residual strength, which could be as high as 70% of their ultimate strength, as well as their enhancing energy absorption capacity. Furthermore, the performances of EFCS beams with angle-ply laminated skins were also examined numerically. The results reflect more advantage of using laminated skins with some specific fibre orientations.

An Efficient Approach into Finite Element Method for Lateral Buckling Analysis of Fiber-Metal Laminates Tapered I-Beams

In this paper, lateral stability analysis of fiber-metal laminated (FML) doubly-symmetric tapered I-beams with symmetrical lay-up for all section walls is perused by presenting a new finite element solution. Vlasov’s thin-walled beam theory is utilized to consider the bending–twisting coupling effect. Based on the classical lamination theory as well as the energy method, the total potential energy is derived for the flexural displacements and the twist angle. Using an auxiliary function, the variational formulation is then constructed only in terms of the twist angle. To precisely determine 4*4 elastic and buckling stiffness matrices, Hermitian cubic polynomial is applied as the shape functions into the resulting variational statement. The most beneficial feature of the present finite element model is to provide a two-node laminated I-beam element with a low number of degrees of freedom. Lateral buckling strength of thin-walled FML profile having varying I-section has been calculated for E-glass/epoxy as composite and aluminum as metal. The obtained results are compared with finite element solutions using ANSYS software and showed excellent agreement with them. Also, the effects of different consequential parameters such as fiber orientation, lay-up sequence, metal volume fraction, web tapering ratio, and transverse load height position on lateral stability resistance of fixed-free FML tapered I-beams subjected to uniformly distributed load are comprehensively investigated.

Effects of layup parameters and interference value on the performance of CFRP–metal interference fit joints

Abstract Based on the thick-wall cylinder theory and composite material mechanics, the stress distribution model of the CFRP shaft tube and metal shaft head has been established, and the relationship between the layup parameters and the value of interference on the maximum assembly force and failure torque in the interference fit joints of the CFRP shaft tube and the metal shaft head is deduced. Combining the three-dimensional finite element analysis model with experimental data, the result shows that the layup angles of the CFRP shaft tube have a greater influence on the joint connection performance than the layup sequence, and the larger the layup angle, the better the joint assembly performance while keeping the value of interference constant. The maximum assembly force and failure torque of the interference fit joints increase linearly while the value of the interference amount increases when the layup parameters are constant.

Procedure to determine deformed shape of laminates made by unsymmetric layup sequences- basis for 4D printing of composites

Un-symmetric laminates, such as those of layup sequence [0m/90n], do not remain flat after curing and cooling to room temperature. The laminate exhibits a curved configuration. While the curvature may be determined using laminate theory, or extended laminate theory, the use of the curvature to determine the deformed shape needs to follow a special procedure in order to obtain the correct result. For the first time, this paper presents this special procedure. In this procedure, the coordinate axes of adjacent material increment need to be updated. The procedure to determine the final shape of un-symmetric laminates serves to enhance the development of composite structures made by using the method of 4D printing of composites.

Three dimensional microscale characterization of off-axis tunnelling cracks in non-crimp fabric based composites

Microscale fatigue damage evolution of off-axis tunnelling cracks was investigated for non-crimp fabric composites used in wind turbine blades. Test specimens fabricated from a multidirectional laminate of the layup sequence [0b/60b/0b/−60b]s (with subscript ’b’ representing backing) with glass fibres and epoxy resin, were subjected to cyclic tension-tension loads. Following the testing, small-sized off-axis samples with sides parallel to the major −60° off-axis fibre bundle were cut from the gauge zone of the tested specimens and were investigated by X-ray computed tomography using a dye penetrant. The height of the tunnelling cracks was found to vary in both the one-bundle +60° and the two-bundle −60°2 plies of the laminate. In the presence of the resin rich pockets above or below crack-tips in the thickness direction, the cracks were observed to penetrate with twisted crack planes aligned perpendicular to the overall loading direction. In the presence of backing, the crack-tips either continued to penetrate between fibres along fibre/matrix interface or deflected at near right angles on the fibre, depending on the orientation of backing fibres. The experimental observations of crack penetration and crack deflection mechanisms were analysed with respect to a crack deflection criterion.

Procedure to determine deformed shape of laminates made by unsymmetric layup sequences – Basis for 4D printing of composites

Un-symmetric laminates, such as those of layup sequence [0m/90n], do not remain flat after curing and cooling to room temperature. The laminate exhibits a curved configuration. While the curvature may be determined using laminate theory, or extended laminate theory, the use of the curvature to determine the deformed shape needs to follow a special procedure in order to obtain the correct result. For the first time, this paper presents this special procedure. In this procedure, the coordinate axes of adjacent material increment need to be updated. The procedure to determine the final shape of un-symmetric laminates serves to enhance the development of composite structures made by using the method of 4D printing of composites.

Formability of roll-formed carbon fibre reinforced metal hybrid components and its experimental validation

Carbon Fibre Reinforced Metal Hybrid (CFRMH) materials that combine a sheet metal substrate with a reinforcing carbon fibre patch represent a promising solution to reduce weight while increasing the structural and crash performance of future automotive vehicles. CFRMHs cannot be formed with conventional stamping processes and at high volumes. This currently reduces their widespread application. Roll forming is increasingly used in the automobile industry for the forming of lightweight and high-strength metal structural components. The major deformation mode in roll forming is simple bending and this reduces interlaminar shear and compressive stresses that lead to fibre failure and delamination issues when stamping CFRMH sheet materials. This work analyses the potential of applying the conventional roll forming process for the manufacture of a simple top hat section shape from CFRMH sheet. For this, first, the material is produced in a hot press and then formed to shape in a laboratory roll forming facility at room temperature. Different layup sequences are tested, and component quality is analysed after roll forming by visual inspection. The results suggest that roll forming presents a promising manufacturing method for the production of automotive components from CFRMH sheets. The roll formed open shells are joined to produce crash box structure and tested in 3-point bending. The results show that depending on the fibre orientation a significant increase in weight specific strength is achieved.

A parametric study on the behavior of FMLs based on UHMWPE composite under high velocity impact loading

Numerical parametric study is performed to investigate ballistic impact performance of a novel fiber metal laminate (FML) based on ultra-high molecular weight polyethylene (UHMWPE) fiber composite and aluminum 2024-T3 layers. A finite element modeling is developed and validated with experimental tests. A user-defined material subroutine based on continuum damage mechanics is used to define damage constitutive model of UHMWPE composite. High velocity impact simulations shows similar modes of failure to that observed in experiments. The effect of various parameters such as metal thickness, composite core thickness, metal volume fraction (MVF), and lay-up sequence on ballistic limit velocity, absorbed energy and specific perforation energy (SPE) of samples has been investigated. The results show that increasing the number of composite layers increases the SPE while increasing the thickness of metal layers decreases the SPE. Although, as the core thickness increases, the growth of SPE decreases. Changes in the lay-up sequence do not have much effect on ballistic velocity and absorbed energy. Whereas, the MVF is an important parameter in the high velocity impact performance of the PERALL specimens. In addition, with equal MVF, stacking sequence change has no significant effect on the ballistic limit velocity. Finally, a simple linear equation is suggested to describe the relationship between MVF and specific perforation energy.

Analysis of the openings of aircraft composite laminated wing beam web under shear load

Abstract In this paper, experiments and finite element methods are used to study the openings of the composite wing spar web of a civil aircraft. First, according to the design principles of composite laminates, determine the layup sequence and layup ratio of the spar, and then lay the beam webs and the beam edge strips integrally; then, calculate the equivalent of the spar by using the classic laminate theory Material properties, the method to calculate the equivalent elastic modulus of composite laminates of different thicknesses is derived; then, the influence of opening shape and opening angle on the strength of composite wing spar web under shear load is analyzed. Finally, the reinforcement design is carried out on the opening position. This research method not only solves specific engineering design problems, but also proposes a set of practical, cost-effective and efficient design methods for composite material opening shapes, which has a certain generality. Its design ideas and methods provide technical support for civil aircraft structural design.

Meso-scale Finite Element (FE) modelling of biaxial carbon fibre non-crimp-fabric (NCF) based composites under uniaxial tension and in-plane shear

Non-crimp-fabrics (NCF) are promising materials in aerospace applications. The complex internal structure of NCF composites could influence the in-plane performances, which needs to be comprehensively studied. The novel three-dimensional (3D) meso-scale repeated unit cell (RUC) models were proposed for biaxial NCF composites based on the Finite Element (FE) method to conduct a systematic parameter study, including layup sequence, out-of-plane tow waviness, resin-rich areas, transverse tow placements and delamination. The meso RUC model could effectively predict the homogenised uniaxial tensile and in-plane shear properties of biaxial NCF composites based on their meso-scale constituent and material properties. A multiscale framework was also developed for biaxial NCF composites. A micromechanical representative volume element (RVE) model provided homogenised mechanical properties for tows, and a macroscopical FE model validated the test results using the homogenised results obtained from meso RUC models. The numerical results were in good agreement with the experiment results. Therefore, the multiscale framework provides an insight into the critical parameters influencing the in-plane properties of NCF composites and an analysis tool for NCF material design.

Influence of imperfection sensitivities on postbuckling of laminated cylindrical panel under axial load: Numerical and experimental investigation

Influence of geometric imperfections on postbuckling of layered (laminated) composite cylindrical panels has been performed under axial compression load using finite element code, ANSYS and validated experimentally. Finite element code was initially validated with available literature for performing the further analyses on the panel. Eigen imperfection irregularities were considered for predicting postbuckling loads of layered composite cylindrical panels with SSSS and SFSF boundary conditions with different r/t ratio and ply sequence and compared the results. Glass-polyester laminated cylindrical panels were fabricated and tested using fixture which accommodates different boundary conditions for investigating the postbuckling phenomenon. Experimental postbuckling analysis was carried out to validate the finite element analysis results and found satisfactory. The influence of imperfections with different r/t, stacking sequences with SSSS and SFSF boundary conditions were carried out and compared. As the r/t ratio of the cylindrical panel increases the postbuckling load decreases for a given boundary conditions and with magnitude of imperfection sensitivities. It has been observed that SFSF boundary conditions with angle play layup sequences taking more axial loads than SSSS boundary conditions with same layup sequence and imperfection sensitivity.