GLARE Laminates Research Articles

Experimental study of mechanical behavior for GLAREs and alloy steel samples against Charpy impact test

The effect of fiber orientation on impact properties of GLARE laminates is investigated. Nine groups of specimens based on ISO179-1 are prepared by conventional hand-layup method followed by light compression molding procedure and tested. Lowest and highest energy absorption these specimens are obtained. The energy absorption of specimen with 45–135/45–135 fiber orientation is more than 28.04% higher than with 0–90/0–90 fiber orientation. In order to get information about the statistical significance of fibers angle changes on Charpy impact energy absorption, Taguchi’s experimental design plan and analysis of variance (ANOVA) are performed on experimental data. Effect of fibers angle changes in the first and second layers on impact energy absorption are 64.74% and 35.26% respectively. Effect of fibers angle changes in the first and second layers on the area of layers separation by impact are 66.66% and 34.33%, respectively. To compare the energy absorption of steel samples with GLARE specimens, the particular energy absorption is used. The particular energy absorption (J/N) is the energy absorption divided by the weight of specimens. Preparing surface for appropriated treatment and improved fibers alignment, it is possible to make FML, which has the least layer separation and the most absorption of impact energy. This specimen is comparable to metal samples in terms of strength, while it has very low weight. Ratio of energy absorbance to weight in GLARE with 45–135/45–135 fibers orientation is more than 10.35% higher than ST37 steel and 0.82% higher than ST52 steel, respectively.

Propagation of damage in bolt jointed and hybrid jointed GLARE structures subjected to the quasi-static loading

GLARE laminate is a high-performance material used extensively in industry. This study investigates the progression of damage in bolt jointed and hybrid (bolt/bonded) jointed GLARE structures through a series of tests, including double cantilever beam experiments, end notched flexure experiments and tensile tests. Numerical simulations of tensile tests on bolt and bonded jointed GLARE structures are performed using finite element software ABAQUS. The experimental and numerical results provide evidence that delamination is the dominant failure mode as a result of the weak interlaminar strength between the metal and the glass fiber reinforced polymer (GFRP) layers and the secondary bending moment. Bearing damage occurs mainly around the bolt hole, and the matrix with 90°directional fibers is damaged more easily than the layer with 0°directional fibers. A suggestion is proposed to design the optimal hybrid jointed GLARE structures by adjusting the stiffness of the liquid shim.

Experiment investigations of effect of laminate thickness on flexural properties of GLARE and GFRP laminates

The study focuses on the fabrication of Glass Fiber Reinforced Aluminum (GLARE) laminates and evaluation of their flexural properties. Aluminum 2024 (T3) sheets were used for the fabrication of GLARE laminates along with E-glass fiber in the form of chopped strand mat and epoxy resin. Different thickness of aluminum sheets ranging from 0.2 mm to 3.5 mm was used to fabricate the GLARE laminates. Hand layup technique is used to bond together aluminum sheets and epoxy/E-glass fiber laminates under different configurations. The test specimens were prepared as per ASTM standards, and standard three-point bending test was carried out to evaluate different bending characteristics. An increase of 60% in load-bearing capacity was observed when aluminum sheet thickness was an increase from 0.2 mm to 0.35 mm. Similar The results were compared with similar glass fiber reinforced plastic (GFRP) laminates to analyze improvements, whereas, the maximum deflection of the laminate decreased. There were not many improvements in case of bending strength and bending modulus when aluminum sheet thickness was varied. Fracture surface analysis indicated three modes of failure namely, interfacial delamination, delamination bonding, and fiber breakage. When compared with glass fiber reinforced plastics of similar configuration, a substantial increase in bending strength was observed.

Interlaminar fracture toughness of GLARE laminates based on asymmetric double cantilever beam (ADCB)

Interlaminar fracture toughness of GLARE laminates (Glass reinforced aluminum laminates) with different fiber orientation, such as cross-plies/0° and unidirectional-plies/0°, were investigated by the combination of experiments and finite element analyses. The Beam Theory and Fracture mechanics theory were used to calculate the proportion of Mode I and Mode II and further to predict the interlaminar fracture toughness of GLARE laminates. Also, the effect of loading rates (1 mm/min, 5 mm/min and 10 mm/min) on the interlaminar fracture properties was studied. Finite element analyses were carried out based on cohesive zone model (CZM) to numerically simulate delamination propagation by using the above experimental GIC. The results showed that the interlaminar fracture toughness in cross-plies/0° laminates(0.248 kJ/m2) was higher than that in unidirectional-plies/0° laminates(0.093 kJ/m2), and the interlaminar fracture toughness was increased with the growth of the loading rates. The numerical results agreed well with the experiments at crack initiation and furthermore supported the absence of mode mixity. The deviation between theoretical calculations and experimental results gradually increased with the crack propagation. Meanwhile, they were conformed to the linear function for unidirectional-plies/0° and cross-plies/0° laminates, respectively. Besides, the experimental data are highly consistent with both theoretical calculation and numerical simulation results.

Interlaminar failure behavior of GLARE laminates under double beam five-point-bending load

GLARE laminates were prepared in this work to characterize their interlaminar shear failure behavior by Double Beam Shear (DBS) method. The effect of span-to-thickness ratio (L/h ratio) and lay-up configuration on the interlaminar failure feature of the laminates was investigated respectively. The results indicated that the failure mode in DBS method was single interlaminar shear delamination due to the existence of pure shear stress points. Furthermore, the apparent interlaminar shear strength (ILSS) values measured by DBS method were higher than those of Short-beam Shear (SBS) method, which were closer to the true value. However, the two methods did not show exclusiveness.

Finite element investigation on mode I crack tip characteristics in residually stressed glare

PurposeBehavior of mode I crack tip in fiber metal laminate (FML) differs from that in homogeneous or plain specimen made of metal used in the laminate due to the load transfer effect in the laminate caused by property mismatch between dissimilar material layers. The purpose of this paper is to present a finite element investigation on the characteristics of crack tip in monotonically loaded and residually stressed FML.Design/methodology/approachCrack tip characteristics are assessed by: the sizes of various zones that form at the tip; and crack tip energy release rates. The same are found by modeling two types of Glare laminates under monotonic tension with different crack orientations in SSY regime – Type I and Type II. Residual stresses are externally introduced in the models. Delaminations are modeled by cohesive elements. Crack tip zone sizes are measured from finite element solutions. Values of J integrals are computed over cyclic paths near the crack tips. Identically cracked and loaded plain aluminum alloy specimens are also modeled for comparison.FindingsThe sizes of crack tip zones in Glare laminates are found to be different than those in plain specimens. Process zone is observed to form at crack tip in Type I laminate whereas it does not develop in Type II laminate, the reverse being true in plain specimens. Values of J integrals near crack tips are also found to deviate from those in plain specimens, higher in Type I laminate due to crack tip stress amplification and lower in Type II laminate due to stress reduction. Crack orientation decides the amplification or shielding effect in the laminate.Research limitations/implicationsThere is scope for validating the numerical results reported in the paper by theoretical models.Practical implicationsThe method to quantify crack tip shielding and amplification is presented that shall be useful in checking the structural integrity/safety of the laminate during actual service conditions.Originality/valueShielding and amplification effects are explicitly described and illustrated in the paper. Suitability of using J integrals over paths crossing non-homogeneous and property mismatched material layers is tested. Use of cohesive zone method that is readily applicable in finite element procedures and is relatively simple, fast and reasonably accurate is also demonstrated.

Detection and Evaluation of Pre-Preg Gaps and Overlaps in Glare Laminates

Gaps and overlaps between pre-preg plies represent common flaws in composite materials that can be introduced easily in an automated fibre placement manufacturing process and are potentially detrimental for the mechanical performances of the final laminates. Whereas gaps and overlaps have been addressed for full composite material, the topic has not been extended to a hybrid composite material such as Glare, a member of the family of Fibre Metal Laminates (FMLs). In this paper/research, the manufacturing, the detection, and the optical evaluation of intraply gaps and overlaps in Glare laminates are investigated. As part of an initial assessment study on the effect of gaps and overlaps on Glare, only the most critical lay-up has been considered. The experimental investigation started with the manufacturing of specimens having gaps and overlaps with different widths, followed by a non-destructive ultrasonic-inspection. An optical evaluation of the gaps and overlaps was performed by means of microscope image analysis of the cross sections of the specimens. The results from the non-destructive evaluations show the effectiveness of the ultrasonic detection of gaps and overlaps both in position, shape, width, and severity. The optical inspections confirm the accuracy of the non-destructive evaluation also adding useful insights about the geometrical features due to the presence of gaps and overlaps in the final Glare laminates. All the results justify the need for a further investigation on the effect of gaps and overlaps on the mechanical properties.

Bending failure mechanism and flexural properties of GLARE laminates with different stacking sequences

Failure mechanisms of GLARE laminates with different structure were investigated by the combination of experiment and numerical simulation methods to predict the damage behaviors of GLARE in practical applications. In this study, bending properties were obtained under varied experiment parameters. Results indicated that the value of span-to-thickness ratio (L/h ratio), which could change the failure mode of laminates, had the most significant impact on bending properties. Effective bending failure occurred when L/h ratio ranged from 14 to 24. Moreover, the bending properties of GLARE laminates with different structures such as 3/2 (3 aluminum sheets and 2 glass/epoxy plies), 4/3, 5/4 and 6/5 were measured and compared. The data revealed that bending modulus decreased with structural expansion. However, the bending strength of unidirectional laminates increased with structural expansion, while the bending strength of cross-ply laminates decreased. SEM observation showed that the failure of GLARE laminates consisted of elastic stage, plastic stage, local fracture of fiber layer and delamination stage.

Effect of drilling parameters on hole quality and delamination of hybrid GLARE laminate

The hole-drilling technique of hybrid GLARE laminate described herein utilizes conventional high-speed steel cobalt and carbide tools with two cutting parameters such as feed rate and cutting speed. The selection of the optimal cutting parameters is important when drilling multi-layered material because each constituent material in the GLARE laminate requires a different set of cutting parameters. The parametric influences on thrust force, torque, surface qualities and delamination extent were experimentally evaluated. In addition, the mechanical model for predicting the critical thrust force at the onset of delamination was established based on classical bending theory and the mechanics of GLARE laminate. The analytical findings were consistent with the delamination extent quantitatively measured by ultrasonic inspection. The carbide produces better hole quality and size tolerance compared to the HSS-Co. Furthermore, feed rate is considered to significantly impact the indentation over the uncut thickness of the material, resulting in a greater influence on delamination onset at the metal-prepreg interface. The faster penetration of the cutting tool through the work-piece due to the increase of the feed rate increases the hole deflections and vibrations in the cutting tool causing higher circularity errors. Compared to the feed rate, the cutting speed effect is relatively insignificant.

Finite Element Analysis of an Aircraft Wing Leading Edge Made of GLARE Material for Structural Integrity

The present paper characterizes the structure of 3D model of an aircraft wing leading edge of a passenger aircraft considering GLARE laminates as one of the candidate materials through finite element analysis. The investigation is carried out on different types of GLARE configurations and the results of finite element analysis are well compared analytically with benchmark tests to demonstrate the performance of the modeling technique adopted. The GLARE laminate materials are found suitable for their application in the wing leading edge with some reservation on GLARE 3/2 and GLARE 4/3 for Al alloy 2024-T3 thickness, between 0.2 and 0.4 mm. The finite element approach is able to predict the mechanical behavior of structural elements fast enough so that the results can be incorporated into normal design iteration processes.

A Theoretical Model for Estimation of Yield Strength of Fiber Metal Laminate

The paper presents a theoretical model for estimation of yield strength of fiber metal laminate. Principles of elasticity and formulation of residual stress are employed to determine the stress state in metal layer of the laminate that is found to be higher than the stress applied over the laminate resulting in reduced yield strength of the laminate in comparison with that of the metal layer. The model is tested over 4A-3/2 Glare laminate comprising three thin aerospace 2014-T6 aluminum alloy layers alternately bonded adhesively with two prepregs, each prepreg built up of three uni-directional glass fiber layers laid in longitudinal and transverse directions. Laminates with prepregs of E-Glass and S-Glass fibers are investigated separately under uni-axial tension. Yield strengths of both the Glare variants are found to be less than that of aluminum alloy with use of S-Glass fiber resulting in higher laminate yield strength than with the use of E-Glass fiber. Results from finite element analysis and tensile tests conducted over the laminates substantiate the theoretical model.

Numerical Analysis of Bird Impact on Glass-Reinforced Leading Edge of an Aircraft Wing

The paper describes the methodology of modeling and simulation of bird impact mechanism of GLARE laminate structures. The bird is modeled using Lagrangian concept. Explicit finite element techniques have been developed to simulate the impact mechanics. The study involves deeper understanding of impact dynamics and contact mechanics. The bird impact analysis has been carried out on typical configuration of GLARE 3/2, 4/3, 5/4, 6/5, 7/6 and 8/7. The results of stress propagation and material deformation at high strain rate have been obtained. Results from the numerical analysis are compared with experimental results, and the material is found to be capable of absorbing the impact energy. The results also show that the bird material model chosen to simulate for carrying out impact mechanics analysis is found to be capable of capturing most of the complex behavior exhibited by functional structural material GLARE.

Buckling and postbuckling behaviour of Glare laminates containing splices and doublers. Part 2: Numerical modelling

A 3D finite element model using cohesive elements and continuum (bulk) material damage models was developed to examine the progressive damage and failure behaviour of Glare® Fibre Metal Laminate (FML) specimens subjected to in-plane compressive loading. The specimens contained internal ‘splice’ and ‘doubler’ features and were either pristine or contained simulated manufacturing defects in the form of artificial delaminations. The initiation and growth of delaminations at the inter-laminar interfaces, damage in the glass fibre reinforced polymer (GFRP) plies, ductile damage in the resin pockets (FM94 epoxy) and the onset of plasticity in the metal layers were examined. Geometric imperfections and load eccentricity were incorporated in an explicit dynamic nonlinear analysis implemented in the software Abaqus/Explicit. A series of buckling tests on specimens with and without artificial delaminations were conducted for validation, which are described in detail in a companion paper. Tests were monitored using Digital Image Correlation (DIC) for visualisation of full-field displacements and strains whilst Acoustic Emission (AE) monitoring enabled detection and localisation of the onset and progression of damage. Results for ‘Glare 4B’ specimens incorporating longitudinal and transverse delaminations into both splice and doubler geometries are presented. These results revealed that in order for the finite element analyses to be validated, all the damage and plasticity mechanisms described above need to be accounted for, as well as load eccentricity and geometry imperfections.

Buckling and postbuckling behaviour of Glare laminates containing splices and doublers. Part 1: Instrumented tests

The progressive damage and fracture behaviour of Glare® fibre-metal laminates (FMLs) was investigated experimentally for the buckling and postbuckling regimes of laminates containing internal ‘splice’ and ‘doubler’ joints. Specimens were either ‘pristine’ or contained artificial delaminations in the form of strips of release film to represent manufacturing defects. Each was tested under in-plane compression. Tests were monitored using Digital Image Correlation (DIC) for visualisation of three-dimensional full-field displacements whilst acoustic emission (AE) monitoring – combined with the novel Delta-T location algorithm – was used for the first time to detect and locate damage events in these FML structures. Results were validated using Scanning Electron Microscopy (SEM) to determine the damage mechanisms present. Large numbers of AE events were recorded at the splice and doubler locations during initial loading and throughout the postbuckling regime, suggesting that the novel AE location algorithm used is suitable for the monitoring of delaminations and matrix cracks in internal features in Glare® laminates. Moreover, AE events located away from internal features correlated well with buckling and postbuckling deformation as identified by the full-field DIC data. Finally, good correlation was observed between the onset of buckling and a rapid increase in cumulative AE energy, demonstrating that as well as locating damage, AE monitoring is able to indicate quite clearly when the buckling load has been reached.

An experimental study on the low velocity impact resistance of fibre metal laminates under successive impacts with reduced energies

The response of Glare 3 and Glare 5 to repeated impacts and dropped tools was experimentally investigated using drop weight equipment. Two repetition sequences were tested. The first sequence consisted of successive impacts with the same impact energy, but lower than the first impact. In the second sequence the rebound energy of one impact was taken as the impact energy for the subsequent impact. This sequence represents the drop weight impact.The damage was evaluated using visual inspection and ultrasonic C-scan. Three categories of impact damage were observed: visible deformation without internal or external damage, visible internal damage (C-scan) without external damage, and visible internal and external damages.The “threshold energy” defined as the magnitude of maximum impact energy in successive impacts that caused no further damage after the first impact. For the successive impacts with energy between the threshold energy and the first impact, repeated impacts were observed to cause damage propagation. Successive impacts with impact energy less than the threshold did not reveal any effect on the structural integrity.The dropped tool sequence revealed that the rebound energies do not have a considerable effect; the force–time and force–displacement curves for Glare laminates did not change with successive rebound impacts. Therefore, it can be concluded that damage propagation due to rebound energies is negligible.

Microstructural investigation of drilling induced damage in fibre metal laminates constituents

Fibre metal laminates (FMLs) are used in the upper fuselage of the Airbus A380 aircraft. Machining FMLs might cause various forms of damage around the hole either in the composite layers or the metallic sheets, all of which are known as drilling-induced damage which deteriorates the surface quality of the metal/composite. The current study investigates the effects of cutting parameters on the drilling-induced damage during drilling of GLARE FMLs at a microstructural level. This study extends the previous investigation of our study on dry drilling of GLARE laminates by incorporating two modern cooling technologies namely cryogenic liquid nitrogen (LN2) and minimum quantity lubrication (MQL) to investigate their impact on drilling-induced damage in FMLs. The results showed that both cutting parameters had an impact on the drilling induced damage in the borehole, while using MQL and cryogenic coolants showed the ability to eliminate waste formation on the machined borehole surface.

Experimental Investigation of Static & Dynamic Loading Conditions for Glare Material

Now a day’s weight plays a very important role in aircraft industries. The reason behind this is efficient & effective working of aircraft. It also needs the high strength to weight ratio. This requirement is fulfilled by the composites. In this research, GLARE is a hybrid composite consisting of thin aluminum, glass fiber & epoxy layer. GLARE materials have been using over 36 years for wide range of advance aerospace structural applications. GLARE laminates offer a distinctive amalgamation of properties such as outstanding fatigue resistance, high specific static properties, exceptional impact resistance, good flame resistance, corrosion resistance and ease of manufacture and repair. But the delaminating occurs in the sheets of aluminum and similarly aluminum wire mesh is used. Solicitation of GLARE materials for the skin or the outer parts here presented the need of GLARE materials in supportive structural members; the present work focuses on the fabrication various structural cross sections of glare material. For fabrication purpose, selected method is hand lay-up. Static & dynamic analysis of these glare material cross sections was carried out; it follows a comparative study with the aluminum cross sections gives that the glare has a better performance.

Evaluation of Workpiece Temperature during Drilling of GLARE Fiber Metal Laminates Using Infrared Techniques: Effect of Cutting Parameters, Fiber Orientation and Spray Mist Application.

The rise in cutting temperatures during the machining process can influence the final quality of the machined part. The impact of cutting temperatures is more critical when machining composite-metal stacks and fiber metal laminates due to the stacking nature of those hybrids which subjects the composite to heat from direct contact with metallic part of the stack and the evacuated hot chips. In this paper, the workpiece surface temperature of two grades of fiber metal laminates commercially know as GLARE is investigated. An experimental study was carried out using thermocouples and infrared thermography to determine the emissivity of the upper, lower and side surfaces of GLARE laminates. In addition, infrared thermography was used to determine the maximum temperature of the bottom surface of machined holes during drilling GLARE under dry and minimum quantity lubrication (MQL) cooling conditions under different cutting parameters. The results showed that during the machining process, the workpiece surface temperature increased with the increase in feed rate and fiber orientation influenced the developed temperature in the laminate.

Interlaminar failure behavior of GLARE laminates under short-beam three-point-bending load

Abstract In this paper, interlaminar failure behavior of GLARE-3/2-0.3 laminates under short-beam three-point-bending load were investigated with various span length-to-specimen thickness ratios (L/h). Failure modes and damage characteristics at different loading stages were observed by Scanning Electron Microscopy (SEM) to assess the failure behavior. It was found that failure modes changed accordingly with varying L/h ratios. A valid shear dominant failure mode was obtained at the L/h ratio of 8. Moreover, there were significant differences in failure modes and damage characteristics among three GLARE variants. The results also showed that lay-up configuration of glass/epoxy layer strongly affected load-deflection response, especially the failure load, and corresponding failure mode.

Comparison of J–R curves and JC values of C(T) and M(T) specimens of bidirectional GLARE 3 5/4 0.3 fiber-metal laminates

The experimental evaluation and comparison of J–R curves from compact tension C(T) and middle-crack tension M(T) specimens of commercial GLARE 3 5/4 0.3 fiber-metal laminates was done. Fracture tests were performed on 50mm wide C(T) specimens with crack to width ratio a/W=0.5, and 230mm wide M(T) specimens having two different crack to width ratios, 2a/W=0.25 and 0.35. For C(T) specimens J–R curves were evaluated based on the ASTM E1820 standard methodology, whereas for M(T) specimens the ASTM E561 standard methodology was applied. In both cases crack length was measured through unloading compliance. The results indicate that unloading compliance is applicable to bidirectional GLARE laminates in both geometries, estimating the stable crack growth during the tests with reasonable accuracy. The results also showed good agreement between J–R curves from both geometries, as well as similar J values at the beginning of stable crack growth. The experimental J–R curves were slightly higher for M(T) specimens, which were many times larger than C(T) ones.