Ply Stacking Sequence Research Articles

Composite sandwich impact response: experimental and numerical analysis

The use of composite materials allows to have a great flexibility in terms of mechanical and physical characteristics. One of the most used composite structure in naval field, is the sandwich, which is composed by a stacking sequence of different plies. The designer, in preliminary phase, must handle a great quantity of degree of freedom (types of materials, orientation of the fibres, position along the stack, thickness, etc.) in order to reach the best compromise between mechanical behaviour, environmental impacts and production costs. Finite Element analysis represents a useful tool in order to optimize all these parameters and to estimate the outcome of experimental tests at design stage. The main goal of this work is to develop and to validate a FE model for the simulation of a particular family of composites, widely used in naval field and, in particular, in High Speed Crafts and powerboats. The first part of the paper concerns the experimental tests on two different types of sandwich specimens. Two families of tests were conducted: four-point bending tests and impact drop tests. The second part of the paper focuses on the validation of a FE model for both experimental setups.

Mode I delamination fatigue resistance of unidirectional and quasi-isotropic composite laminates reinforced with rectangular z-pins

This paper presents an experimental study on the mode I delamination properties of circular and rectangular z-pins in hot-cured carbon fiber/epoxy laminates. Specimens with two different ply stacking sequences (unidirectional and quasi-isotropic) are used to investigate the effect of different pin geometries on the interlaminar fracture toughness and fatigue resistance. Due to a change in the debonding behavior during the cooling stage after the curing process in an autoclave, the use of rectangular z-pins results in an increased mode I fracture toughness compared to circular pins in both unidirectional and quasi-isotropic hot-cured laminates. Furthermore, Paris curves obtained from delamination fatigue resistance tests reveal that rectangular z-pins are more effective at increasing delamination resistance than circular z-pins in quasi-isotropic laminates. In unidirectional laminates, a change in the cross-section geometry of the pins only slightly affects the mode I fatigue resistance of z-pinned composite laminates.

Numerical Investigation on Aeroelastic Behavior of Composite Material Plate Excited by Pulsed Air Jet

Nowadays, carbon fiber composite material is becoming more and more popular in aero engine industry due to its high specific strength and stiffness. Laminate carbon fiber composite material is widely used to manufacture the high load wide chord fan blade, containment casing, etc. The aeroelastic behavior of composite product is critical for the optimization of the product design and manufacturing. In order to explore its aeroelastic property, this paper discusses the coupled simulation of aerodynamic excitation applied on laminate composite material plate. Mechanical behavior of composite material plate is different from that of isotropic material plate such as metal plate, because it is anisotropy and has relative high mechanical damping due to resin between plies. These plates to be studied are designed using 4 different layup configurations which follow the design methods for composite fan blade. The numerical simulation of force response analysis mainly uses single frequency mechanical force input to simulate the electromagnetic shakers or other actuators, which could transmit mechanical force to the test parts. Meanwhile, pulsed air excitation is another way to “shake” the test parts. This excitation method induces aero damping into the test part and simulates the unsteady flow in aero engine, which could cause aeroelastic problems, such as flutter, forced response and non-synchronous vibration (NSV). In this study, numerical simulation using coupled method is conducted to explore the characteristics of laminate composite plates and the property of aerodynamic excitation force generated by pulsed air jet device. Modal analysis of composite plate shows that different ply stacking sequences have a significant impact on the plate vibration characteristics. Air pulse frequency and amplitude in flow field analysis are calibrated by hot wire anemometer results. As the air pulse frequency and amplitude are varied, incident angle of flow and layup configurations of plate can be analyzed in details by the simulations. Through the comparisons of all these factors, air pulse excitation property and the aeroelastic behavior of composite material plate are estimated. It would provide a possible way to guide the next-step experimental work with the pulsed air rig. The new composite fan blade design can be evaluated through the process.

Three-dimensional solutions for free vibration of variable stiffness laminated sandwich plates with curvilinear fibers

This paper is concerned with the free vibration of variable stiffness laminated sandwich plates with curvilinear fibers. The three-dimensional elasticity theory and the p-version of the finite element method are adopted for the analysis. The skin is composed of one or more plies with curvilinear fibers. The fiber path orientation angle in a ply is assumed to vary linearly with the x coordinate. The plies may be stacked symmetrically or anti-symmetrically with respect to the middle surface of the plate. Each layer is modeled as one brick p-element. The principle of virtual displacements is used to derive the element stiffness and mass matrices. The generalized displacements at vertices, edges, and faces shared by elements are matched to ensure inter-element compatibility. Since no solutions are available for the free vibration of such variable stiffness laminated sandwich plates, the validity, convergence, and accuracy of the present three-dimensional method are established by comparing with existing three-dimensional frequencies for constant stiffness laminated sandwich plates with rectilinear fibers. The study reveals that inter-layer modal bending stresses are discontinuous; modal transverse shearing stresses are constant in the core; the sign of modal transverse shearing stresses can change through the thickness of the skin; and the shape of modal cross-sectional warping is influenced by the mode number and stacking sequence of plies. Three-dimensional frequencies are presented for different fiber orientation angles, boundary conditions, aspect ratios, thickness ratios, core/skin thickness ratios, and stacking sequences of plies. The accurate results presented here will serve as a benchmark for future investigations.

Experimental investigation on impact performance of glass–polypropylene hybrid composites: Effect of water aging

The effect of water aging on the impact performance of glass (G)–polypropylene (P)-reinforced epoxy composites was investigated. Specimens were fabricated using the hand layup process with constant overall fiber volume fraction. Specimens were immersed in distilled water and seawater at room temperature, until reaching their water content saturation point. The dry and water-immersed specimens were subjected to edge-wise and flat-wise impact tests. Fractured surfaces were examined using scanning electron microscopy, SEM. The results showed that the impact performance of G-reinforced epoxy composite has been enhanced through hybridizing it with P-fiber but water uptake has been increased. Water uptake reduces the impact strength of all tested specimens. Composites exposed to seawater absorb less water than those exposed to distilled water. The water absorption percentage and impact performance can be effectively controlled by changing the hybrid configuration, plies stacking sequence and P/G fiber ratio.

Experimental study of the influence of thickness and ply-stacking sequence on the compression after impact strength of carbon fibre reinforced epoxy laminates

Composite structures are particularly vulnerable to impact which drastically reduces their residual strength [1–3]. In this work, the influence of laminate thickness, ply-stacking sequence and scaling technique on the impact damage tolerance of CFRP laminates is investigated by means of compression after impact (CAI) tests. Drop-weight impact tests were carried out to determine impact response of the different composite laminates. CAI tests were performed in a non-standard CAI device in order to obtain the compression residual strength. In addition, open-hole compression (OHC) tests were performed for comparative purposes. Ultrasonic C-scanning and cross-sections of CAI samples were examined to assess failure mechanisms of the different configurations.It was observed that damage tolerance decreases as impact energy increases. In addition, thicker laminates show higher CAI strength due to higher bending stiffness. Furthermore, angle-ply laminates depict better performance in terms of damage tolerance. Finally, the results obtained demonstrate that introducing ply blocking had a negative effect on the damage resistance but, conversely, an improvement of the CAI strength.

Evaluation of mechanical properties of jute/glass/carbon fibers reinforced hybrid composites

A study on the tensile and flexural properties of jute-glass-carbon fibers reinforced epoxy hybrid composites in inter-ply configuration is presented in this paper. Test specimens were manufactured by hand lay-up process and their tensile and flexural properties were obtained. The effects of the hybridization, different fibers content and plies stacking sequence on the mechanical properties of the tested hybrid composites were investigated. Two-parameter Weibull distribution function was used to statistically analyze the experimental results. The failure probability graphs for the tested composites were drawn. These graphs are important tools for helping the designers to understand and choose the suitable material for the required design and development. Results showed that the hybridization process can potentially improve the tensile and flexural properties of jute reinforced composite. The flexural strength decreases when partial laminas from a carbon/epoxy laminate are replaced by glass/epoxy or jute/epoxy laminas. Also, it is realized that incorporating high strength fibers to the outer layers of the composite leads to higher flexural resistance, whilst the order of the layers doesn’t affect the tensile properties.

Pull-out performance of rectangular z-pins in hot-cured carbon fiber reinforced laminates

This paper presents an experimental study on the pull-out performance of circular and rectangular z-pins in hot-cured carbon fiber/epoxy laminates. Pull-out specimens with two different ply stacking sequences (unidirectional and quasi-isotropic) were reinforced with z-pins, arranged in a 4 × 4 pattern and a volume content of 2.0%. Rectangular z-pins were found to provide much higher bridging forces in both unidirectional and quasi-isotropic laminates. Since this enhancement cannot be solely attributed to the larger surface area provided by the rectangular z-pins, optical microscopy was used to investigate the interface between the z-pins and the surrounding laminate. Results showed that a change in the debonding behavior after the post-curing cool-down period leads to higher achievable shear stresses within the pin/laminate interface, and thereby, to superior bridging loads during pin pull-out.

Crashworthiness characteristics of carbon–jute–glass reinforced epoxy composite circular tubes

This article provides an experimental investigation into the crashworthiness of carbon–jute–glass reinforced epoxy circular composite tubes. The test specimens were fabricated of 6 layers with different stacking sequence using wet‐wrapping process and tested under uniaxial quasi‐static compression loading up to complete crushing. The effects of hybrid reinforcement, stacking sequence, and relative reinforcement amounts on the energy absorption capabilities and failure modes were studied. Also, the crush load–displacement response, initial crushing failure load, total energy absorption, specific energy absorption, average crushing load, and crushing force efficiency were determined and discussed. The scanning electron microscope study was considered to analyze the failure modes of the crushed specimens. Results indicate that specimens' failure modes and energy absorption capabilities were highly dominated by the reinforcement combinations and plies stacking sequence. Also, hybrid carbon–jute–glass reinforced epoxy composite tubes have the potential to be used as energy absorbers as compared to jute‐reinforced epoxy composite tubes. The JGC composite tube has a higher load carrying capacity and energy absorption capability compared to other hybrid composite tubes, so it seems to be the best appropriate choice for energy absorbing devices. POLYM. COMPOS., 39:E2245–E2261, 2018. © 2017 Society of Plastics Engineers

Nondestructive Evaluation of Porosity Content in the Curved Corner Section of Composite Laminates Using Focused Ultrasonic Waves

The feasibility of utilizing focused ultrasonic waves for the nondestructive evaluation of porosity content in curved corner sections of carbon fiber reinforced plastic (CFRP) laminate structures is investigated numerically as well as experimentally. For this purpose, two-dimensional (2D) finite element simulations are carried out to clarify the wave propagation behavior and the reflection characteristics when the nonfocused or focused ultrasonic wave impinges on the corner section of unidirectional and quasi-isotropic CFRP laminates from the inner side via water. The corresponding reflection measurements are carried out for the CFRP corner specimens in the pulse-echo mode using nonfocusing, point-focusing, and line-focusing transducers. The numerical simulations and the experiments show that the use of focused ultrasonic waves is effective in obtaining clearly distinguishable surface and bottom echoes from the curved corner section of CFRP laminates. The influence of the porosity content on the reflection waveforms obtained with different types of transducers is demonstrated experimentally. The experimental results indicate that the porosity content of the CFRP corner section can be evaluated based on the amplitude ratio of the surface and bottom echoes obtained with focusing transducers, if the calibration relation is appropriately established for different ply stacking sequences.

Damage resistance of carbon fibre reinforced epoxy laminates subjected to low velocity impact: Effects of laminate thickness and ply-stacking sequence

A major concern affecting the efficient use of composite laminates is the effect of low velocity impact damage on the structural integrity [1–3]. The aim of this study is to characterize and assess the effect of laminate thickness, ply-stacking sequence and scaling technique on the damage resistance of CFRP laminates subjected to low velocity impact. Drop-weight impact tests are carried out to determine impact response. Ultrasonic C-scanning and cross-sectional micrographs are examined to assess failure mechanisms of the different configurations.It is observed that damage resistance decreases as impact energy increases. In addition, thicker laminates show lower absorbed energy but, conversely, a more extensive delamination due to higher bending stiffness. Thinner laminates show higher failure depth. Furthermore, quasi-isotropic laminates show better performance in terms of damage resistance. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the damage resistance and on the delamination area.

Three-dimensional vibration analysis of sandwich and multilayered plates with general ply stacking sequences by a spectral-sampling surface method

This paper investigates the three-dimensional (3-D) vibration characteristics of sandwich and multilayered plates with general ply stacking sequences and arbitrary restraints based on a spectral-sampling surface method. The theoretical formulation is undertaken by the 3-D theory of elasticity such that it is able to study the dynamic behavior of sandwich and multilayered plates very well, even in the presence of soft layers. Under the current framework, a set of sampling surfaces along the thickness direction of each plate layer are primarily selected and the displacements of these surfaces are chosen as basic plate variables. Consequently, vibration solutions for sandwich and multilayered plates with different thicknesses, material properties and ply stacking sequences can be derived up to desired accuracy by selecting sufficient number of sampling surfaces. In addition, the penalty technique and Lagrange multiplier method are adopted to relax the enforcement of the boundary conditions. As a result, the proposed formulation can be applied efficiently to the 3-D vibration analysis of sandwich and multilayered plates with general restraints. The final solutions are determined by a modified variational principle, in which each of the basic plate variables is approximated by the spectral method. Results show that the present method is capable of calculating highly accurate numerical results for thick sandwich and multilayered plates with general ply stacking sequences and arbitrary boundary conditions.

Flexural Fatigue Performance of Glass Fiber/Epoxy Step-Wise Functionally and Non-Functionally Graded Composites of Different Structures

Abstract Flexural fatigue performance of newly developed step-wise functionally graded (FG) composites has been investigated experimentally. Two unidirectional glass fiber (UGF)/epoxy FG composites with overall fiber volume fraction of 39.9 ± 0.3% and thickness of 6.0 ± 0.1 mm were fabricated using hand lay-up technique. The fabrication proposed technique depends on the variation of the composite structure achieved by three different templates. A non-functionally graded (NFG) composite laminate with the same overall fiber volume fraction and thickness was also fabricated using a fourth template for comparison. Each of the FG and NFG composites is made of six plies. Each ply has a thickness of 1.0 mm. This occurs by controlling the amount of matrix in each ply (constant matrix amount for all plies). Fatigue tests were performed at zero mean stress. A 20% reduction of the initial flexural stiffness was taken as a failure criterion. The S–N curves for the fabricated FG and NFG composites have been constructed as design curves. For FG composites, the effects of the spatial gradient of fiber content and plies stacking sequence on both S–N relationships and the specimens’ surface temperature rise were studied. Two-parameter Weibull distribution function was used to statistically analyze the fatigue life results.

Influence of ply stacking pattern on the structural properties of quasi-isotropic carbon-epoxy laminates in fire

An experimental investigation is presented into the effect of the ply stacking pattern to quasi-isotropic carbon-epoxy laminates on their structural properties in fire. Small-scale simulated fire tests are performed on laminates with different stacking sequences of the 0, 90, +45 and −45 plies loaded in tension or compression. Testing revealed that the internal temperature and fire-induced delamination cracking of the laminates depends on the ply stacking pattern. The tension softening rate and stress rupture time of laminates also depends on the ply stacking pattern, particularly at low applied tensile stresses. However, the fire response of laminates under compression loading appears less sensitive to the ply stacking sequence, due in part to their much shorter failure times. The research reveals that the structural survivability of carbon-epoxy laminates when exposed to fire can be influenced by the ply stacking sequence, with composites with 0 mid-plane plies having superior performance.

Influence of the stacking sequence on the mechanical proprieties of glass fiber reinforced polymer

The reinforced composite materials are in a very impressive development in the last decades. In this paper the influence of the plystacking sequence of glass fiber reinforced polymer on mechanical properties is investigated. Composite material structures consist of layers from glass mat and fabrics with different disposal sequence. The mechanical properties of the manufactured composite materials have been determined by tensile and bending tests. The obtained results are used to design the optimal materials architecture.

Investigation of mechanical behavior of woven/knitted hybrid composites

The objective of this research is to develop the woven/knitted hybrid composites for improved in plane as well as out of plane mechanical properties. Two different type of structures and two different materials were used in this study. Firstly, the woven and knitted fabrics were developed with glass and Kevlar yarn. Secondly, the laminated composite samples were fabricated with different stacking sequence of fabric plies. The epoxy resin was used as matrix. The cured samples were characterized for impact, tensile and dynamic mechanical properties. The behavior of composite materials was then analyzed with percentages of different fiber and fabric types. The samples with higher percentages of knitted reinforcement gave better impact strength but failed to provide better tensile properties. Moreover, the samples with higher percentages of woven structure and glass materials gives better modulus values.

환경조건간 합동을 이용한 복합재료 허용치 생성 기법

The properties of composite materials, when compared to those of metallic materials, are highly variable due to many factors including the batch-to-batch variability of raw materials, the prepreg manufacturing process, material handling, part-fabrication techniques, ply-stacking sequences, environmental conditions, and test procedures. It is therefore necessary to apply reliable statistical-analysis techniques to obtain the design allowables of composite materials. A new composite-material qualification process has been developed by the Advanced General Aviation Transport Experiments (AGATE) consortium to yield the lamina-design allowables of composite materials according to standardized coupon-level tests and statistical techniques; moreover, the generated allowables database can be shared among multiple users without a repeating of the full qualification procedure by each user. In 2005, NASA established the National Center for Advanced Materials Performance (NCAMP) with the purpose of refining and enhancing the AGATE process to a self-sustaining level to serve the entire aerospace industry. In this paper, the statistical techniques and procedures for the generation of the allowables of aerospace composite materials will be discussed with a focus on the pooling-across-environments method.

The natural armors of fish: A comparison of the lamination pattern and structure of scales

Fish scales exhibit a unique balance of flexibility, strength and toughness, which is essential to provide protection without encumbering locomotion. Although the mechanical behavior and structure of this natural armor are of recent interest, a comparison of these qualities from scales of different fish species has not been reported. In this investigation the armor of fish with different locomotion, size and protection needs were analyzed. Scales from the Arapaima gigas, the tarpon (Megalops atlanticus) and the carp (Cyprinus carpio) were compared in terms of the stacking sequence of individual plies and their microstructure. The scales were also compared with respect to anatomical position to distinguish site-specific functional differences. Results show that the lamination sequence of plies for the carp and tarpon exhibit a Bouligand structure with relative rotation of 75° between consecutive plies. The arapaima scales exhibit a cross-ply structure, with 90° rotation between adjacent plies. In addition, results indicate that the volume fraction of reinforcement, the number of plies and the variations in thickness with anatomical position are unique amongst the three fish. These characteristics should be considered in evaluations focused on the mechanical behavior.

Blending design of composite panels with lamination parameters

ABSTRACTIn this paper, a new optimisation method incorporating lamination parameters and a guide-based blending model is proposed. Lamination parameters for a guide laminate and ply number of each panel are employed as design variables for optimisation with a parallel real-coded genetic algorithm incorporating structure behaviour and manufacturing constraints. During the optimisation process, with a form of least squares fitting adopted, another genetic algorithm is used to obtain the guide stacking sequence of the guide laminate from the guide lamination parameters, and then the laminate configurations of each panel are obtained from the guide stacking sequence and number of plies for each panel. The proposed framework is demonstrated via design of an 18-panel horseshoe configuration, where each panel is optimised individually with a buckling constraint. Numerical results indicate that the present algorithm is capable of obtaining fully blended designs.

Composite stacking sequence optimization for aeroelastically tailored forward-swept wings

A method for stacking sequence optimization and aeroelastic tailoring of forward-swept composite wings is presented. It exploits bend-twist coupling to mitigate aeroelastic divergence. The method proposed here is intended for estimating potential weight savings during the preliminary aircraft design stages. A structural beam model of the composite wingbox is derived from anisotropic shell theory and the governing aeroelastic equations are presented for a spanwise discretized forward swept wing. Optimization of the system to reduce wing mass is undertaken for sweep angles of −35° to 0° and Mach numbers from 0.7 to 0.9. A subset of lamination parameters (LPs) and the number of laminate plies in each pre-defined direction (restricted to {0°,±45°, 90°}) serve as design variables. A bi-level hybrid optimization approach is employed, making use of a genetic algorithm (GA) and a subsequent gradient-based optimizer. Constraints are implemented to match lift requirements and prevent aeroelastic divergence, excessive deformations, airfoil stalling and structural failure. A permutation GA is then used to match specific composite ply stacking sequences to the optimum design variables with a limited number of manufacturing constraints considered for demonstration purposes. The optimization results in positive bend-twist coupling and a reduced structural mass. Results are compared to an uncoupled reference wing with quasi-isotropic layups and with panel thickness alone the design variables. For a typical geometry and a forward sweep of −25° at Mach 0.7, a wingbox mass reduction of 13 % was achieved.