Behavior Of Fiber Metal Laminates Research Articles

Tensile behavior of fiber metal laminates with multiple holes at different temperature conditions

In this paper, the tensile properties of fiber metal laminates (FMLs) at 25°C ∼ 180°C temperature conditions and different hole arrangements are researched mainly by means of experiments, theoretical model, and numerical simulation. The stress–strain curves of FMLs are obtained by extensive tensile tests and are analyzed and compared. The fracture morphology of the specimens under different temperature conditions is observed using scanning electron microscopy (SEM). Finally, a progressive damage model on the basis of the subroutine Abaqus-VUMAT is developed to analyze the damage evolution process and failure mode of FMLs. Combined with the numerical simulation results, the damage evolution process, equivalent plastic strain, and interlaminar damage of FMLs under different hole arrangements are investigated and found to be in good agreement. The phenomena such as tough nest fracture, matrix fragmentation, fiber debonding, and fiber pullout at different temperatures are observed and analyzed by SEM. The failure modes of FMLs with multiple holes at different temperatures are discussed in this paper, which provides a solution for the application of FMLs in practical engineering.

Parametric Study of PEKK Based Fiber Metal Laminates Used in Aerospace Applications

Numerical analyses offer a cost-effective and efficient alternative to experimental investigations, and Finite Element (FE) models have become a popular tool to simulate the behavior of Fiber metal laminates (FMLs) under impact loads. This study verified the reliability of the proposed FE models to predict the perforation response of ‎the FMLs investigated under low-velocity impact loadings. The validation of ‎the FE models was assessed through comparison with the corresponding results of the ‎experimental work. The results showed that the proposed simulations are capable of predicting the dynamic response of the laminates investigated with a high degree of success. The parametric studies were conducted on 2/1 titanium FMLs based on 2-ply composite cores and 2/1 aluminum FMLs based on 4-ply composite cores under impact with a variety of loading conditions. The developed FE models were then used to explore the structural behavior of the fiber metal laminates investigated with an extended variation of parameters, i.e., projectile striking angle, impact locations, the geometry of the projectile, and velocity. The results of the FE models are presented in terms of load-displacement traces, energy absorption, and failure modes. The findings of this study contribute to the understanding of the structural behavior of FMLs under impact loads and can inform the design and optimization of FMLs for various engineering applications. The use of FE models provides a cost-effective and efficient means of exploring the structural behavior of FMLs under different impact conditions, which can reduce the need for costly and time-consuming experimental investigations.

Mechanical investigation of inverse FML under mode II loading using acoustic emission and finite element method

Fibre metal laminates (FML) are a specific type of material made of both metal and fibre-reinforced composite layers. In this paper, the authors analyse the behaviour of fibre metal laminates with unusual thermoplastic matrices in composite layers under mode II loading. A three-point bending setup was used along with end notched flexural specimen (ENF) to determine behaviour and of the interface between metal and composite layers under shear stress. Due to nonstandard layup configuration, mixed experimental–numerical method is proposed by authors to determine fracture energy. The finite element method is used to analyse conducted tests. A model with cohesive elements is applied to determine damage in the interface layer. For the purpose of understanding the damage process in particular layers, Acoustic Emission analysis was conducted for each specimen and parameters like amplitude, frequency, duration, root-mean-squared level of noise were obtained. As a result of conducted research critical energy in mode II was obtained GIIC=0.05Nmm as well as critical stress value in local shear direction (initiation criterion) tso=10MPa. The result obtained can be used as part of the material model in assessing the mixed-mode state of the researched material.

Ballistic impact response and failure mechanism of aluminum/ultrahigh molecular weight polyethylene fiber laminates with different adhesive quantity

AbstractThe aim of this study is to investigate the effects of metal‐composite interface (MCI) adhesive quantity on the energy absorption and failure behavior of fiber metal laminates (FMLs) under ballistic impact. The dynamic shear and ballistic impact tests were systematically conducted, and CT scan was employed to quantitatively investigate the damage and failure mechanisms of the FMLs. The results reveal that the dynamic shear strength of MCI initially increases and then remains constant with the increase in the adhesive quantity at a constant strain rate. Moreover, the MCI adhesive quantity has a certain influence on the impact energy absorption of FMLs, and the degree of influence is related to the impact velocity. At an impact velocity of 360 m/s, the difference of energy absorption is maximal, approximately 14.7%. The distribution of total debonding area changes with increase in the adhesive quantity. When the impact velocity is 212 m/s, compared to FMLs with the lowest adhesive quantity, the total debonding area of FMLs with the highest adhesive quantity decreases by 774.57 mm2 (9.20%), otherwise the debonding area near the rear aluminum alloy sheet increases by 595.94 mm2 (58.99%).

Mechanical investigation on interlaminar behaviour of inverse FML using acoustic emission and finite element method

Fibre metal laminates (FML) are a group of materials consisting of layers of both metals and fibre reinforced composites. In this paper, the authors analyse the behaviour of fibre metal laminates with unusual thermoplastic matrices in composite layers under flexural loading. A three-point bending test is used to determine the flexural behaviour and interlaminar shear stress (ILSS). Two configurations of a specimen are taken into account – with fibre parallel to the specimen (A) and with fibre perpendicular to it (B). Numerical simulations using the finite element method are carried out. A model with cohesive elements is applied to model damage and a model with a continuum shell is used to determine ILSS. Both approaches can be successfully used for specimens group A. This proves that obtained previously material data is proper to use in the analysis of more complicated structures. In the case of group B, other causes than only interface damage need to be included. To investigate this, analysis of the acoustic signals is used to describe phenomenon occurring during bending for group A and B specimens. Conclusions based on AE support the hypothesis based on the optical remarks and results from numerical modelling.

Analytical modelling of low-velocity impact response characterization of titanium and glass fibre reinforced polymer hybrid laminate composites

The low-velocity impact behaviour and energy absorption mechanisms of fibre​ metal laminates (FMLs) at different impact energy levels before the first composite failure are derived analytically using a mass–spring arrangement. Four FML layups comprise glass fibre/epoxy layers and titanium alloy Ti-6Al-4V sheets, unveiling the same total metal layer thickness. The impactor mass consequence is also predicted. The results specify that the deformation energy of FML constituents accounts primarily for the FMLs overall energy absorption, 86%–93%, and 87%–93%, with both membrane and bending strain energy, and membrane strain energy only, separately. Here, a higher percentage of energy is absorbed by FML 4/3–0.3, followed by FMLs 3/2–0.3(O), 3/2–0.4, and 2/1–0.6. FMLs are 16 % more impact resistant than equivalent monolithic titanium. Also, the predicted force history of FMLs is in good comparison with experiments at 30 J, with membrane energy only correlating well than with both membrane and bending energy. The estimated maximum force, entire energy absorption of FMLs is realistic with experiments at 30 J, 45 J, and 60 J. The predicted response of aluminium-based FMLs also matches well with experiments at various energy, preserving the presented model strength. Further, the behaviour of FMLs is to be comparable under low- and high-mass impactors. However, FMLs maximum force and energy absorption seem to be correspondingly lower and higher under a high-mass impactor. Higher impact resistance seems to be displayed by titanium- to aluminium-based FMLs. Also, the above FMLs appear to display higher total energy absorption under low- to high-velocity impact.

Tensile mechanical behavior and failure mechanisms of fiber metal laminates under various temperature environments

This paper mainly investigates the tensile behavior of fiber metal laminates (FMLs) under various temperatures ranged from 25 ℃ to 175 ℃ combined experimental measurement, theoretical model and numerical technique. Firstly, based on numerous tensile tests under various temperatures, different tensile load–displacement response and damage modes for FMLs can be obtained and compared. And in virtue of the scanning electron microscopy (SEM), microscopic damage modes are identified through the fracture surface scanning of FMLs subjected to different temperatures. Subsequently, in order to analyze the discreteness of experimental results and evaluate the theoretical tensile strength of FMLs under different temperatures, the two-parameter Weibull statistics model is established for engineering application of FMLs. Finally, the effect of layer direction on damage modes and progressive damage evolution process of FMLs is characterized numerically. These results indicate that the tensile strength of FMLs represents a nonlinear downward trend with the increase of temperature. The complex failure mechanisms under different temperatures can be captured from SEM observation, including fiber/matrix debonding, fiber pull-out, matrix microcrack, delamination damage and so on. The deeper understanding of tensile behavior and failure mechanisms of FMLs under thermal conditions can be provided for the design and utilization of FML structures.

Effect of projectile nose on high‐velocity impact behavior of fiber metal laminates

AbstractFiber metal laminates (FMLs) are a class of hybrid materials consisting of several thin metal layers bonded by layers of composite material. In the present study, the ballistic limit, absorbed energy, specific perforation energy and failure mechanism of FML 2/1 (Al/GFRE/Al) and FML 3/2 (Al/GFRE/Al/GFRE/Al) are numerically and experimentally studied under the high‐velocity impact loading using a single‐stage light gas gun. In addition, the ballistic behavior of FML 2/1 and FML 3/2 is investigated using three different projectile nose geometries. Numerical simulation of the ballistic tests was performed to determine the residual velocity and the FML panel failure mechanism by using AUTODYN. The results indicated that the highest ballistic limit for FML 2/1 and FML 3/2 was obtained for the conical nosed projectile and the ballistic limit of FML 3/2 was 75.63% higher than FML 2/1. Although the FML 3/2 thickness is ~67% higher than FML 2/1, the specific perforation energy of FML 3/2 is improved by 72.51%, 55.26%, and 89.22% compared to FML 2/1 for blunt, hemispherical, and conical nosed projectiles, respectively.

Low-velocity impact perforation response of titanium/composite laminates: analytical and experimental investigation

The low-velocity impact perforation behavior of fiber-metal laminates (FMLs) is evaluated by analytical modeling. Four different FML layups consisting of glass fiber/epoxy layers and titanium alloy Ti–6Al–4V sheets are fabricated, exhibiting the same thickness of total metal layers. The perforation behavior, threshold, and energy absorption mechanisms of FMLs are assessed using a mass-spring system. The results indicate that the elastic–plastic force history of FMLs up to maximum force predicted by both membrane and bending strain energy (M & B) and membrane strain energy only (M only) is found to be in good agreement with experiments, with M only matches closely than both M & B. The principal part of the total energy absorption of FMLs with both M & B and M only accounts for the energy absorption associated with global deformation of titanium and glass/epoxy layers, which is 67–71% and 65–69%, respectively. Here, a higher percentage of energy is absorbed by FML 4/3–0.3, succeeding by FMLs 3/2–0.3(O), 3/2–0.4, and 2/1–0.6. The predicted perforation threshold and overall energy absorption by various damage mechanisms of FMLs are in good comparison with experiments. The perforation response has also been predicted for aluminum-based FMLs, agreeing well with experiments. This insists on the robustness of the offered model. Also, the perforation resistance seems to be higher for titanium-based FMLs than aluminum-based FMLs. The overall energy absorption seems to be higher for titanium-based FMLs under low-velocity impact than high-velocity impact. This is also observed in the case of aluminum-based FMLs.

An experimental investigation on the effect of incorporating graphene nanoplatelets on the low-velocity impact behavior of fiber metal laminates

In this study, experimental investigations are implemented to evaluate the effect of incorporation of graphene nanoplatelets (GNPs) on the low-velocity impact behavior of composites and fiber metal laminates (FMLs). The hand layup technique is employed to fabricate composite specimens and FML panels with 2/1 configuration. Impact response and damage patterns of unmodified and modified specimens subjected to various impact energy levels are compared. The results reveal that the incorporating 0.2 wt% of GNPs strengthens the impact resistance of FMLs so that the modified panels possess higher bending stiffness, peak load, energy absorption and SEA compared to the unreinforced ones. Visual inspections and SEM images exhibit that the inclusion of GNPs enhances the adhesion between resin/fibers as well as composite plies, thereby reducing damage area and increasing penetration threshold of FMLs. In addition, reinforcing composite panels considerably improves the impact behavior in comparison with the unmodified composites.

The residual stress characteristics and mechanical behavior of shot peened fiber metal laminates based on the aluminium-lithium alloy

The effect of shot peen forming on the mechanical behavior of fiber metal laminates (FMLs) based on aluminium-lithium alloy was investigated to reveal the strengthening mechanism and to dispel the suspicion that shot peen forming may result in the performance deterioration of FMLs. The interlaminar, static strength and fatigue properties of shot peened FMLs were investigated. The residual stress characteristics of the shot peened FMLs was also involved with finite element analysis to help understanding the unique mechanical behavior. The results indicated that shot peening caused non-negligible work hardening in external metal layers, which increased the tensile strength of the laminates. But the work hardening did not deteriorate the elongations of FMLs since the failure still dominated by the limitation of fiber failure strain. Moreover, two yield stages were observed in the tensile tests of shot peened FMLs owing to the great difference in stress states between external and internal metal layers. The compressive stress introduced by shot peening effectively improved the FCG properties of FMLs. All metal layers possessed similar crack propagation rates despite that the stress difference was up to 300 MPa, which indicated that the fiber bridging effect still dominated the FCG of FMLs.

Springback Behavior of Fiber Metal Laminates with Carbon Fiber-Reinforced Core in V-Bending Process

Fiber metal laminates (FMLs) are a kind of hybrid composite material that consist of metal sheets and fiber-reinforced composite layers. The use of FMLs has been particularly increasing in the production of aircraft bodies. However, the springback behavior that occurs during the formation of FML parts has a negative impact on the form of the final product. In the present study, FMLs were manufactured by combining aluminum 5754-H22 sheets and carbon fiber-reinforced plastic sheets by using adhesive. A set of experiments were performed to determine the effect of bending angle, face sheet thickness and core thickness on the springback behavior of FMLs. The results showed that the amount of springback in the FML specimen increased as the bending angle increased. It was found that when the thickness of the face sheet increased, the amount of springback in FML specimens was higher in all bending angles. In addition, the amount of springback in FML specimens decreased as core thickness increased.

Influence of impactor shape on low-velocity impact behavior of fiber metal laminates combined numerical and experimental approaches

Abstract Fiber metal laminates (FMLs) are fabricated with composite laminates and metallic alloys. This paper systematically investigates the influence of impactor shape on the low-velocity impact response of FMLs by combining the experimental and numerical methods. A series of impact experiments are conducted to study the low-velocity impact behavior of different FMLs under various impactor shapes and impact energies. The commercially available digital image correlation measuring system is applied to scan the exterior deformations of FMLs after impact. Subsequently, a progressive damage model based on the Hashin and Yeh delamination failure criteria is employed to characterize the damage evolution and failure mechanisms of composite materials through a user defined subroutine (VUMAT) in ABAQUS/Explicit. The study's results demonstrate that the impact behavior of FMLs is strongly dependent on impactor shape, impact energy and metal layer distribution. For the complete penetration case, the smooth perforation resulted from shear effect occurs in FMLs impacted by blunter impactor, while the petaloid cracks caused by tensile tearing damage appears for sharper impactor case in the process of penetration. The predicted results for different impact cases show a good comparison with experimental results in terms of impact loads, total absorbed energies and damage morphologies, which indicate that the numerical simulation could be a helpful tool to evaluate the impact response of FMLs.

The effect of surface modified nanoclay on the interfacial and mechanical properties of basalt fiber metal laminates

Abstract In this study, the effect of different percentages of modified nanoclay (1, 3, and 5 wt%) on the mechanical behavior of fiber metal laminates (FMLs) made up of aluminum and basalt fibers-epoxy composite was investigated. The surface treatment was conducted on aluminum in order to obtain a proper adhesion between aluminum and epoxy. The Charpy test results showed that the absorbed energy values of the samples containing nanoclay were increased compared to the samples without nanoclay. Improving the impact strength of FMLs containing nanoclay was due to the enhancement of the basalt fibers/epoxy interfacial properties and creating some physical entanglement such as mechanical interlocking between the polymer chains and nanoclay. Otherwise, nanoclay addition decreased the interlaminar shear strength of FMLs. The microscopic images of aluminum debonding surfaces revealed that the agglomerated nanoclay particles prevent the epoxy infiltration into porous structures of aluminum layer and consequently, weaken the interlaminar shear strength.

Effect of Shape Memory Alloy Wires on the Buckling Behavior of Fiber Metal Laminates

Buckling behavior of shape memory alloy (SMA) reinforced fiber metal laminates (FML) was experimentally investigated. The SMA reinforced FML specimens with three different pre-strain levels (1, 2 and 3 %) and different number of the embedded wires (2, 4 and 6 wires) were prepared by a specific mold and hydraulic pressure. The effects of the applied pre-strains in the SMA wires, as well as the stacking sequence of the laminate, SMA volume fraction and the location of the wires were studied on the axial and lateral force-displacement diagrams for the specimens during buckling tests. According to the results, 53 % enhancement in the buckling load was obtained for 2 SMA wires reinforced FML specimens in comparison with the specimens without embedded SMA wires. In constant volume fraction of the SMA, pre-straining the wires by 3 % led to 25 % improvement in the buckling load, in comparison with the specimens reinforced with 1 % pre-strained wires. The influence of the FML stacking sequence on the results was also discussed.

Investigation on impact behavior of FMLs under multiple impacts with the same total energy: Experimental characterization and numerical simulation

This paper aims to investigate the low-velocity impact behavior of fiber metal laminates (FMLs) consisting of carbon fiber-reinforced layers and aluminum sheets under multiple impacts with the same total energy. Experimental and numerical methods are implemented to explore the influence of impact energy division, load sequence and metal layer distribution on multiple impact behavior and damage morphologies of FMLs. A series of repeated drop impact tests with different impact energy combinations are implemented on FMLs. Subsequently, an integrated numerical model based on multiple consecutive steps is established to characterize the damage accumulation and failure mechanisms of FMLs, in which a user defined subroutine VUMAT, is developed to consider the stiffness degradation and damage evolution of composite material. The numerical predictions show a good correlation with the corresponding experimental results. The results reveal that multiple impacts with lower energy division and smaller initial impact energy can cause minor damage in FMLs. Generally, the impact load, energy absorption, damage morphologies and the interfacial delamination are closely related to the magnitude, sequence and division of impact energy. In addition, the strain hardening of aluminum sheets after first impact can improve the stiffness of FMLs, and further strengthen the impact resistance significantly.

Effects of applying a combination of surface treatments on the mechanical behavior of basalt fiber metal laminates

The surface treatment of metals has a great role on the adhesion of the metals to the polymers. There are various surface treatment methods for adhesive joint applications. However, the effect of the combination of surface treatment methods on the mechanical behavior of adhesive joints has not been extensively studied. In this study, the effects of applying a combination of surface treatments on the flexural and Charpy impact behavior of fiber metal laminates (FMLs) were investigated. The surface treatments included forest product laboratory etching (FPL), sulfuric acid anodizing (SAA), sandblasting, sandblasting + FPL and sandblasting + SAA. The FMLs were made from Al2024-T3, basalt fibers and epoxy. Scanning electron microscopy (SEM) was used to study the surface morphology of the Al2024-T3 laminates and fracture surface of the samples. Furthermore, the surface roughness of the Al2024-T3 sheets after different surface treatments were evaluated using profilometry. Results showed that the adhesion of Al2024-T3 to polymeric layers was significantly affected by various surface treatments. Results of bending tests indicated that the highest bending strength and strain to failure values were respectively achieved for the SAA and sandblast treated samples. On the other hand, although there was a slight improvement in the bending strength, the application of SAA or FPL etching after sandblasting caused a negative effect on the strain to failure value of the samples. However, impact test findings showed that the combination of FPL or SAA treatments after sandblasting rendered positive effects on the low-velocity impact behavior of the FMLs.

Parametric Sensitivity Analysis of Curing Deformation of Angle-Ply Fiber Metal Laminates

In the process of studying the curing deformation behavior of fiber metal laminates (FMLs) subjected to thermal stress, there are some discrepancies between analytical models and experimental results for the room-temperature stable configuration. The main reason is the uncertainty of the parameters in the analytical calculation. In present paper, a parametric sensitivity analysis of the influence of Young’s modulus, Poisson’s ratio, thermal expansion coefficients, ply thickness, ply angle and temperature difference on the cured stable configuration is carried out to identify the most sensitive properties. Accurate characterization of these sensitive properties and precise control of manufacture process can reduce the discrepancies and obtain a more accurate prediction model. It is believed that the present study can be helpful of guiding the design and manufacture of the FMLs in the engineer application.

The Influences of Fibre Parameters on the Tensile and Flexural Response of Lightweight Thermoplastic Kenaf Fibre Reinforced Metal Composites

ABSTRACT The increasing demand for high performance and lightweight materials has stimulated the development of alternative materials, namely fiber metal laminates (FMLs). FML is a sandwich structure which is formed by bonding the metallic layers with composite as core constituent using an adhesive agent. In this study, the mechanical behavior of FMLs with the core constituents of environmental friendly kenaf bast fiber reinforced polypropylene composites bonded with aluminum skin layers was investigated. The effects of fiber compositions (50, 60, and 70 wt.%), fiber lengths (30, 60, 90 mm), and alkali treatment on the mechanical responses of FML were investigated. The overall results revealed that the increase of fiber composition and fiber length reduces the mechanical strength of FML owing to the agglomeration of natural fibers when the fiber length exceeds the critical limit. However, the chemical treated kenaf bast fiber reinforced FML showed a significant enhancement of the mechanical properties in comparison to the non-treated fiber reinforced FML owing to the improved fiber-matrix adhesion level.

Response and failure of fiber metal laminates subjected to high strain rate tensile loading

The tensile behavior of fiber metal laminates consisting of layers of aluminum 2024-T3 alloy and glass fiber reinforced composites under high strain rate loading is investigated. Fiber metal laminates having four different layups, but all having the same total metal layer thickness, were fabricated using a combined hand lay-up cum vacuum bagging method. The fiber metal laminate specimens were loaded in high strain rate tension using a split Hopkinson tensile bar. The rate-dependent behavior of the glass fiber composite was also obtained as baseline data. The strain on the gage area of the specimen was measured directly using high-speed digital image correlation. Another high-speed camera was used to capture the sequence of damage by viewing the specimen edgewise. The results indicated that the strength of the fiber metal laminates increased at high strain rates primarily due to the rate-dependent behavior of the composite used. The response was also influenced by the distribution of the metallic layers in the fiber metal laminates. The failure in the case where the individual composite layers were separated by metallic layers was more progressive in nature.