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The reduction of weight elements is considered as a major objective of several manufacturing companies. This objective will help in growing application sections of the used fiber composites for important structural elements. Modern fiber metal laminate (FML) having lightweight properties is established to be used instead of other substances in different applications including those related to the aerospace industrial sector. Fiber metal laminate is being deemed as an alternative significant substance that is being extensively explored due to its operation, unlike other current materials. There are different profitable FML such as GLARE (glass-reinforced aluminum laminate), established on elevated intensity ARALL glass fibers (aramid-reinforced aluminum laminate), built on fibers of aramid, in addition to CARALL (carbon-reinforced aluminum laminate), centered on fibers of carbon. This paper analyzes important information that contributes to the mechanical characteristics of FMLs under tensile, flexure, impact, etc. conditions. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FMLs) are a special type of composite structure consisting of metal sheets bonded to composite laminas. The current study investigated the effect of the replacement of cross-ply (0/90°) glass fiber reinforced epoxy laminas with woven glass fiber reinforced polyester laminas in GLARE laminates on the tensile, bending and interlaminar fracture toughness of the laminate. Test results showed that the existence of woven glass fiber laminas increased the tensile strength with a decrease in corresponding strain, the flexure strength decreased significantly due to the existence of polyester instead of epoxy resin, and the mode I interlaminar fracture toughness increased. ABAQUS® software was used to simulate the tests, and ductile damage was employed to detect the failure of aluminum layers, the Hashin failure criteria to model the failure of composite layers in the laminate, and the cohesive surface interaction to capture delamination between layers. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FMLs) are new hybrid materials which are widely used in aircraft industry due to their higher mechanical properties compared to monolithic metal and epoxy based composites. In this work, mechanical behavior of the FML is investigated by experiment and simulation. The FML used in this study is made of two layers of aluminum 2024 and a layer of glass-fiber reinforced epoxy (GFRE). The experiments showed nonlinear elastic behavior for GFRE layer. This behavior is due to damage evolution and material degradation. Therefore, a simple nonlinear damage is presented to improve the results of the proposed material model. Mechanical properties of the layers are measured by uniaxial tensile test. Numerical simulations are performed by implementing the material model into the user subroutine of MSC MARC FE code. The results of the proposed model showed a reasonable agreement with the experiments. The agreement confirms the nonlinear damage behavior of the FMLs observed in the experiments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An experimental investigation focusing on the hygrothermal aging-structural degradation-mechanical property relationship of GLARE 4A laminates was conducted. Water immersion conditioning at 80 °C for up to 4 months was carried out on GLARE 4A laminates. It was found that although the outer aluminum layers effectively protected the glass/epoxy composite layers from hygrothermal attack, the composite layers absorbed moisture through the edges. Consequently, significant decrease in both, the tensile strength and fatigue life of the GLARE 4A laminates, was observed although no structural defects were apparently identifiable in the microstructures of the conditioned laminates. Detailed experimental investigation was conducted to study the mechanism of mechanical property decay due to hygrothermal aging. It is proposed that the strength of the S2-glass fibers was not fully realized due to the weakening of the fiber/matrix interface and the deterioration of the sizing, which consequently led to the reduction in the tensile strength and fatigue life of the GLARE 4A laminates. The stiffness degradation characteristics of GLARE 4A laminates under cyclic loading were also investigated. [ABSTRACT FROM AUTHOR]

Glass laminate aluminium reinforced epoxy (GLARE) is an advanced aircraft material because of its excellent fatigue crack resistance, high impact strength, high strength-to-weight ratio and high stiffness-to-weight ratio. While drilling on composite/metal stacks has been investigated, the drilling of GLARE, which consists of several alternate thin layers of aluminium and composites, has not been addressed separately in the open literature. The focus of present experimental work is to understand the cutting mechanism and relative effect of cutting parameters and tool geometry on the delamination and burr formation during drilling of GLARE. Thrust force, torque and acoustic emission (AE) signals were acquired for analyzing the cutting mechanism, burr and delamination formation. Also, several measurements of burrs, delamination and hole size were taken in order to understand the hole quality. It has been observed that, 2-fluted drill is the best out of four different geometries used, giving zero delamination and acceptable burr formation followed by the 4-faceted drills. The conventional 3-fluted and 8-faceted drills that are otherwise superior for drilling of fiber reinforced plastics (FRP) composites, performed poorly in drilling of the GLARE laminates. Analyzing the processing parameters, feed again has a dominant role in controlling delamination and burr formation than speed. [ABSTRACT FROM AUTHOR]

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.

Experiments enforcing a pin bearing loading configuration were performed on a fully orthotropic GLARE 4 variant. The protocol employed in such experiments stemmed from a similar methodology performed on quasi-isotropic GLARE variants though now incorporating a local measurement scheme using biaxial strain gauges rather than uniaxial ones. The aim of this local measurement was both the extraction of novel bearing yield strength values and the detection of buckling within the aluminum layers. The encouragement of delamination and buckling was key since they not only form an integral portion of the proposed yielding through delamination buckling (YDB) mechanism but in addition, the pin bearing configuration - which ipso facto, encourages the former(s) - has been identified in the literature as the most conservative and accurate means for analyzing joint behavior and collapse. Analytical calculations previously performed support the empirical findings and provide direct evidence for the hegemony of aluminum yield strength in joint collapse. The proposed and employed protocol has been shown to be effective across a comprehensive range of GLARE variants and may be extended analogously to other standardized testing methodologies. [ABSTRACT FROM AUTHOR]

A novel experimental methodology extended from ASTM D953 was developed and implemented to conduct pin bearing experiments on GLARE3-5/4-0.3 and GLARE3-4/3-0.3 variants with the aim to examine a bearing load configuration from a local perspective as well as a global one. This was accomplished by introducing previously unconsidered testing fixtures and additional instrumentation, including bonded strain gages, as a means of measuring the local strain field generated by a bearing load. Load-displacement curves were produced as per the standard but were subject to numerous plateaus and significant statistical scatter, attributed to pin seating and global displacement measurement. Conventionally defined bearing yield strengths were calculated but lacked physical meaning, prompting the production of novel bearing strength vs. measured strain profiles. These new profiles, derived from the additionally acquired data, were void of the plateau anomalies and depicted a well defined trend, indicative of a more complete characterization of material response. Examination of these profiles resulted in a new, more intuitive definition of bearing yield strength that incorporated influence from the entire curve rather than idealizing it bilinearly. The phenomenological basis of the new definition suggests an analogous extension to additional methodologies such as standard tensile or compressive tests. [ABSTRACT FROM AUTHOR]

Finite element (FE) analyses are carried out on bolt bearing testing scenarios based on data found in the literature. Both layer-by-layer and smeared property FE models are created to calculate the compressive characteristic dimension (CCD) for three GLARE variants. A novel re-definition of conventional CCD is proposed which is governed by the yield strength of aluminum. The new definition also incorporates the two-phase nature of GLARE, as well as the delamination/ buckling phenomenon for pin/bolt bearing, in a bearing failure mode. A previously unconsidered, orthotropic plate buckling analysis is also conducted in a conservative, worst case scenario sense on the laterally unsupported prepreg layers. Results of the buckling analysis suggest that the prepreg contribution to bearing strength, in a bearing failure mode, is at best negligible and joint collapse is governed by the yielding and delamination of the aluminum layers. Calculation of a CCD, based on the new yield strength definition, produced consistent values amongst all GLARE variants considered in the layer-by-layer analysis suggesting that the CCD is a property of the material alone. [ABSTRACT FROM AUTHOR]

The bearing strength, in particular the edge distance sensitivity, of several fiber metal laminates of the GLARE family is experimentally evaluated. The behavior of the fiber layer is investigated in detail to obtain a better understanding of its failure mode. Parallel with these experiments, the bearing behavior is studied using a finite element (FE) model. The plasticity in the metal layers, failure of the fiber layers, and friction between pin and laminate, are all implemented in the model. A comparison between experimental and FE results shows a good resemblance in strength and in internal damage pattern for the GLARE laminates. The FE model is used to define the optimal fiber orientation of standard GLARE laminates when loaded in bearing. [ABSTRACT FROM AUTHOR]

Process-induced residual stresses in fiber-metal laminates depend on the stress-free temperature T sf , which refers to the moment during the manufacturing process where a resilient mechanical connection between metal and fiber-reinforced epoxy layers is established. T sf is often determined reversely by evaluating distortions of FML specimens with asymmetric layup. The present paper focusses on an in situ strain-measurement-based procedure, which allows for the direct determination of the stress-free temperature during manufacturing. The paper reports on a combined application of strain-gage and fiber-Bragg sensors, during manufacturing of a GLARE laminate in an oven environment. The experiment setup allowed for the simultaneous measuring of strains in both constituents along the entire fabrication process. The in situ technique gives insight into mechanical interactions of the GLARE constituents during processing. As will be shown, T sf can be identified from the monitored strains and therefrom, the material's residual stress state is quantified. [ABSTRACT FROM AUTHOR]