Fiber Reinforced Aluminum Laminates Research Articles

Mechanical properties of carbon fibre reinforced aluminium laminates using two different layering pattern for aero engine application

ABSTRACTThe properties of carbon reinforced fibre with aluminium alloy 2024-T3 sheets of different sequence were studied. The aim of the research is to analyse and compare the mechanical properties of two different layering sequences of the composite. The composites uses hand lay-up method in its fabrication in a mould. Tensile, compressive and flexural strength were investigated in the study using an Instron 3382 Universal Testing Machine according to their ASTM standard. There is about 11%, 7% and 53% increase on tensile strength, tensile modulus, and elongation at break for carbon fibre reinforced aluminium laminates with aluminium alloy at front and rear face. This was also true for flexural strength of the two composites; where a greater value was obtained for the aluminium alloy at front and rear face of the composite with the same compressive strength and lower difference on compressive modulus. Therefore, the study show that the two composites have good mechanical properties that can withstand a load in fire designated zone of an aircraft engine.

Effect of Resin Rich Veil Cloth Layers on the Uniaxial Tensile Behavior of Carbon Fiber Reinforced Fiber Metal Laminates

The influence of stacking sequence and resin rich (polyester veil cloth) layers, which were used to improve the adhesion between carbon fiber/epoxy (CFRP) and aluminum layers (AL), on the uniaxial tensile response of carbon fiber reinforced aluminum laminates (CARALL) was investigated in this research study. The metal volume fraction was varied to prepare two types of CARALL laminates having a 3/2 configuration with the help of a vacuum press without using any adhesive film. Numerical simulations were performed by utilizing commercially available finite element (FE) code, LS-Dyna to predict the tensile response of these laminates with initialization of predicted thermal residual stresses that developed during curing of laminates. Delamination failure was considered in the numerical simulation by utilizing the well-known B-K mixed-mode damage propagation model. It was found that addition of epoxy resin rich (polyester veil cloth) layers used for enhancement of interfacial bond adhesion and to ensure no separation between AL-CFRP layers increased the tensile strength of CARALL laminates.

Influence of metal layer distribution on the projectiles impact response of glass fiber reinforced aluminum laminates

The effect of the distribution of aluminum layer through the thickness of fiber metal laminates (FMLs) on their projectiles impact response is studied using high speed 3D digital image correlation technique (DIC). The FMLs consisting of aluminum alloy 2024-T3 sheets of thicknesses 0.3 mm, 0.4 mm, and 0.6 mm and glass fiber reinforced epoxy layers (two layers with each of 0° and 90°) were prepared by the hand layup process followed by vacuum bagging. The metallic layers are placed at different locations through the thickness of four different layups while keeping the total metal layer thickness constant. The hemispherical and conical nose projectiles of the same mass are impacted normal to the FMLs plate using nitrogen gas gun. The performance of the FMLs is evaluated using different parameters such as the deformation history, residual deformation and also the surface and internal damages. FML 4/3–0.3 in which the two adjacent composite layers with different fiber orientations separating by an aluminum layer exhibited the highest deformation with hemispherical projectile impact for the same impact energy level. The deformation was found to be lower and nearly same for the other three FMLs. This observation is also noticed in the case of drop weight impact (low velocity impact). The FML 2/1–0.6 in which the composite layers were stacked together exhibited a comparatively higher lateral spread of delamination and interlayer opening with hemispherical projectile impact when compared to FML 4/3–0.3, indicating that the lateral spread of damage within the FML can be decreased by distributing the aluminum layers in the FML. This is also observed in the case of drop weight impact.

Drawing potential of fiber metal laminates in hydromechanical forming: A numerical and experimental study

It is known that fiber metal laminates as one of hybrid materials with thin metal sheets and fiber/resin layers have limited formability in conventional forming methods. This paper presents an experimental and numerical study for drawability of glass fiber-reinforced aluminum laminates under hydromechanical drawing technique. Fiber metal laminates comprised of a layer of woven glass fiber-reinforced prepreg, sandwiched between two layers of aluminum alloy. In order to produce fiber metal laminates, the laminates were subjected to a sufficient squeezing pressure under a controlled heating time and temperature by using a hydraulic hot press. A hydromechanical tooling equipped with blank-holder force and fluid pressure control system was used to form the initial circular fiber metal laminate blank. Finally, the effect of parameters such as pre-bulging pressure, final chamber pressure, and drawing ratio on process variables was evaluated. Also, the characteristic curve of hydromechanical drawing of fiber metal laminate i.e. chamber pressure in terms of drawing ratio was achieved by means of experimental tests and numerical simulations. The results showed that the maximum drawing ratio of defect-free fiber metal laminates, namely without any tearing, wrinkling, and delamination was obtained at pre-bulging and chamber pressure of 35 and 80 bar, respectively.

The Influence of the Thickness and Areal Density on the Mechanical Properties of Carbon Fibre Reinforced Aluminium Laminates (CARAL)

A novel composite material consisting of a laminate of several thin aluminium sheets bonded with layers of carbon fibre mat/epoxy resin. Carbon fibre reinforced aluminium laminates (CARAL) offer specific advantageous properties such as better strength, fatigue, impact, corrosion resistance, fire resistance and weight savings. CARAL is a kind of fibre metal laminate system. In the present work, CARAL was prepared and experimental tests were conducted to evaluate the influence of the thickness and areal density on the mechanical properties of CARAL. Mechanical properties such as, the tensile strength and flexural strength of the laminates were increased with the increase in thickness and areal density. CARAL with four aluminium layers and three carbon fibre mat layers have superior strength than the laminates with lesser number of layers due to thickness of laminates and areal density.

Effect of metal layer placement on the damage and energy absorption mechanisms in aluminium/glass fibre laminates

This study focuses on the effect of metal layer distribution in glass fibre reinforced aluminium laminates (GLARE) subjected to low velocity impact. Four GLARE variants specimens were considered in which the metal layers of different thicknesses were placed at various positions in the layup while keeping the same total metal layer thickness. Experiments and Finite element (FE) analysis were performed to understand the behaviour of the GLARE specimens. A user written material subroutine VUMAT which incorporates Hashin failure criteria along with Puck's action plane concept were used to predict the response of the composite layers. The damage was evolved for each failure mode using the exponential damage evolution law. Interface delamination between the layers was initiated by cohesive surface behaviour which includes the friction effect between the plies. It was found that placement of thinner metal layer on top of the laminate and its distribution inside the layup lowers the impact resistance of GLARE. Moreover, the patterns of delamination are also affected by the placement of metal layer within the laminates. It was further shown that the propagation direction of delamination is governed by the fibre direction of lower ply of the interface.

An experimental investigation into the high velocity penetration resistance of CFRP and CFRP/aluminium laminates

Carbon fibre-reinforced composite materials are of high potential as protective casing in the aerospace area, acting as an effective solution to lighten components against the collision. The high velocity penetration resistance abilities of unidirectional CFRP laminates and two carbon fibre reinforced aluminium laminates CRALL2/1 and CRALL3/2 (fabricated from T700S CFRP layers combined with aluminium alloy 2024-T3 layers) were evaluated by the ballistic tests with a flat, hemispherical or conical nosed projectile. Revealed from ballistic tests that fracture modes, ballistic limits and specific energy absorptions of CRALLs and CFRP were sensitive to nose shapes. Higher ballistic limits and specific energy absorption ability were performed by CRALLs than monolithic CFRP impacted by all shapes due to the strain rate hardening effect and failure conversion effect. In particular situation of flat nose projectiles penetrating, the specific energy absorption of the CRALL3/2 was 8% higher than that of monolithic aluminium alloy 2024-T3 at same thickness. The CRALLs may then be designed as effective lightweight structures to protect frames against collision in the aerospace area and outperform the traditional single CFRP laminates.

Impact Response and Damage Characteristics of Carbon Fibre Reinforced Aluminium Laminates (CARAL) under Low Velocity Impact Tests

This paper investigates impact response of a novel fibre metal laminate (FML) system based on a carbon fibre reinforced Aluminium Laminates (CARAL). These composites are fabricated using hand lay-up technique and the detailed preparation methodology was presented. Epoxy resin along with TETA hardener was used as the excellent adhesion agent throughout the layer. Three types of layers were prepared from CARAL and machined as per ASTM Standard. Low velocity impact response and damage characteristics of CARAL specimens were studied. Damage characteristics were evaluated using drop weight impact tester. Impact properties of CARAL were increased with the increase in number of layers of CARAL laminates. Finally cross- sectional morphology analysis was done using scanning electron microscope (SEM) and the internal structure of the broken specimen was discussed.

Effect of various surface preparation techniques on the delamination properties of vacuum infused Carbon fiber reinforced aluminum laminates (CARALL): Experimentation and numerical simulation

Carbon fiber reinforced aluminum laminates (CARALL) are one of the aluminum based Fiber metal laminates (FMLs) which, due to their high strength to weight ratio and good impact resistance are greatly replacing aluminum alloys in aircraft structures. In this research work, interlaminate shear strength of Vacuum assisted resin transfer molding (VARTM) manufactured CARALL has been investigated. Numerical simulation model incorporated with real time material data has been developed to predict the delamination behavior of CARALL laminates. Standard CARALL specimens with different surface morphologies were prepared by electric discharge machining, mechanical, chemical and electrochemical surface treatments. T-peel tests were carried out according to standard ASTM D1876-08 to find out inter laminate shear strength. FMLs made out of mechanically, chemically and electrochemically cleaned metal sheets depicted high interlaminate shear strength. SEM micrographs of failed surfaces verify the high adhesive strength of epoxy. Developed numerical simulation model accurately predicts the delamination behavior of CARALL as observed during experimentation.

Application of energy dissipation approach for notched behavior in fiber metal laminates

Characterization of the complicated failure behavior in fiber metal laminate (FML) depends on well understanding of the contributions from metal and composite layers. It seems to be very cumbersome to deal with this by conventionally collecting the stress, strain and damage patterns through experiments or numerical simulations, especially when complicated load (e.g., off-axis load) or a more hybrid degree is adopted. Since all mechanical responses in nature are governed by energy principles, in the present study an energy dissipation approach was introduced in FML. Analyses were carried out with employing the available history outputs in Abaqus, where four kinds of energy variables in terms of internal or total strain energy (Eint), elastic or recoverable strain energy (Eelast), energy dissipated by plastic deformation (Eplast) and damage (Edam) were requested for both the constituents and the laminates. Two issues were clarified by this energy approach: off-axis dependence of mechanical response and damage behavior in notched glass fiber reinforced aluminum laminate (Glare), and the reinforced effect of titanium on notched Glare (a more hybrid case). Results have shown the potentiality of energy approach in straightforwardly and effectively characterizing the failure behavior of FMLs.

Optimization of Corrosive Properties of Carbon Fiber Reinforced Aluminum Laminates due to Integration of an Elastomer Interlayer

Fiber-Metal-Laminates (FML) show superior dynamic mechanical properties combined with low densities. The mechanical performance of for example commercially available fiber-metal-laminate, glass laminate aluminum reinforced epoxy, can be improved by the substitution of glass fibers with carbon fibers. However, carbon fiber reinforced aluminum laminate introduces a mismatch of coefficients of thermal expansion and the possibility of galvanic corrosion. The fiber-metal-laminate is altered by the integration of an elastomer interlayer which is desired to solve both problems. The high electrical resistance is supposed to inhibit the corrosion. This study focuses on the effect of galvanic corrosion caused by neutral salt spray tests on fiber-metal-laminates, the influence of an elastomer interlayer and the quantification of the residual mechanical properties. The galvanic corrosion affects the interfaces of the laminates, therefore in this study edge shear tests and flexural tests were carried out to quantify the residual properties and thereby the corrosive damage. The elastomer interlayer was found to inhibit galvanic corrosion in the salt spray chamber, whereas the fiber-metal-laminate without interlayer showed corrosive damage. Furthermore, the mechanical properties of the fiber-metal-laminate with elastomer interlayer remained constant after the corrosion tests, whilst the fiber-metal-laminate’s properties decreased with corrosive loads.

Open‐hole tensile behaviour and failure prediction of carbon fibre reinforced aluminium laminates

In this article, the open‐hole tensile behaviour of carbon fibre reinforced aluminium laminates (CARALL) were investigated experimentally and numerically. Two specimens with different fibre orientations ([0°/90°/0°] and [45°/0°/−45°]), consisting of T700 carbon fibre/epoxy prepreg and 2024‐T3 aluminium with a 3/2 configuration, were manufactured by the autoclave process. Damage initiation and progression were considered in modelling the CFRP layers and interface bonding layers. Isotropic hardening behaviour was defined for aluminium layers. A major contribution of this study was to reveal the failure mechanisms and failure sequences of notched CARALL with different fibre orientations by numerical method. Damage evolution processes of the two specimens were compared. Effects of hole sizes and laminate configurations (stacking sequences & stacking structures) on both the specimens were further evaluated based on simulation. Point stress failure criterion and Wu's modified point stress failure criterion were applied in comparison with the numerical method as well. POLYM. COMPOS., 39:4123–4138, 2018. © 2017 Society of Plastics Engineers

In-plane flexural behaviour and failure prediction of carbon fibre-reinforced aluminium laminates

This paper investigated the in-plane bending behaviour of carbon fibre-reinforced aluminium laminates (CARALL). The flexural progressive damage and failure mechanisms were analysed numerically and experimentally. Four types of CARALL specimens with a 3/2 configuration were prepared via hot-pressing using different aluminium alloy materials (2024-T3, 7075-T6 aluminium alloy) and fibre orientations ([0°/90°/0°]3, [45°/0°/−45°]3). The three-point bending tests were conducted under static loading. It was found that the primary damage modes were aluminium layer yielding in the mid-span and delamination between the aluminium and carbon fibre-reinforced polymer (CFRP) layers. A user-defined FORTRAN subroutine VUMAT based on ABAQUS was used to simulate the failure of the CFRP, a cohesive zone model was used to predict the inter-laminar failure, and a von Mises plastic model was used to define the isotropic hardening behaviour of the aluminium layers. The predicted results agreed well with the experimental ones. Two convenient calculation methods based on the elasticity mechanics and material mechanics were derived. And the non-linear behaviour of aluminium was considered in the elasticity mechanics method. The theoretical results matched closely with the experimental findings during the linear elastic deformation process.

Novel fibre metal laminate sandwich composite structure with sisal woven core

Fibre metal laminates (FMLs) have been widely used to manufacture airframe components. This work describes novel sisal fibre reinforced aluminium laminates (SiRALs) that have been prepared by cold pressing techniques and tested under tensile, flexural and impact loading. The pristine sisal fabric and the sisal fibre reinforced composites (SFRCs) were also tested to understand the difference in mechanical performance of the sisal fibre metal laminates. The SiRALs achieved not only the highest modulus and strength, but also the highest specific properties. The mean specific tensile strength and modulus of the SIRALs reached increases of 132% and 267%, respectively, when compared to the sisal fibre reinforced composites (SFRCs). Moreover, the mean specific flexural strength and modulus of the SiRALs were significantly higher than SFRCs, revealing increases of 430% and 973%, respectively. A delamination fracture mode was noted for SiRALs under bending testing. The SiRALs can be considered promising and sustainable composite materials for structural and multifunctional applications.

Local Reinforcement in Notched Fiber Metal Laminates by Bonding Titanium Patch

In order to reduce the stress concentration in notched fiber metal laminate (FML) and improve its damage tolerance, the local reinforcement concept was employed in present paper. Two different reinforced structures were proposed by bonding titanium patch on single side or double sides of the standard glass fiber reinforced aluminum laminate (GLARE). Tensile tests were conducted on these reinforced GLARE, and their mechanical properties were compared for evaluating the reinforced effect of titanium patch, as well as the damage behavior which dominated the mechanical response was analysed later to capture the failure mechanism of the reinforced GLARE. The reinforced effect of titanium patch on mechanical response of GLARE laminate was usually characterized by the improvements of modulus and yield strength, as well as the significant increase of ultimate strain and strength. Cohesive failure and adhesive failure were detected in the adhesive between titanium patch and GLARE laminate, where the adhesive failure corresponded to the weak reinforced case. In addition, the variation of delamination in GLARE laminate was also closely related to the reinforced effect on mechanical response. It is expected that the present investigation can provide technical support for damage tolerance design of fiber metal laminates.

Compression after impact characteristics of carbon fiber reinforced aluminum laminates

The influence of layer structure and resin rich (polyester veil cloth) layers which were used for enhancement of interfacial bond adhesion on the compression after impact response of carbon fiber reinforced aluminum laminates (CARALL) was investigated in this research study. The addition of resin rich layers at interfaces of CFRP and aluminum layers shows significant reduction in delaminated area (40–50%) due to crack bridging effect. The residual compressive strength of CARALL laminates was increased by 30–35% as a result of reduction in delamination area. Excessive damage was found in CARALL-B FMLs during impact events as compared to CARALL-A FMLs. Thus, the Compressive residual strength of these laminates was lower as compared to standard CARALL-A laminates having aluminum layers placed exterior to CFRP layers. Numerical simulations were performed by utilizing commercially available finite element (FE) code, LS-DYNA to predict the CAI response of these laminates. Compressive residual strength vs. delamination area results showed good correlation between experimental and FEA results for CARALL-A and CARALL-B FMLs at lower energy levels (14–21J) but diverged at high impact energy level (31J). Numerical simulation was found to successfully capture the location and initiation of compressive buckling in specimens.

Mechanical Analysis of Polybenzoxazine Matrix in Fiber Metal Laminates

In this work we investigated the application of a novel high performance polymer, polybenzoxazine, as a polymeric matrix in Fiber Metal Laminates (FML). This polymer, when applied on the development of FMLs, generated higher mechanical properties in comparison to fiber metal laminates obtained with epoxy. To investigate the mechanical performance of the polybenzoxazine matrix in FMLs, a mechanical behavior comparison was carried out among epoxy matrix laminates - glass fiber reinforced aluminum laminate (GLARE) and carbon fiber reinforced aluminum laminate (CARALL) - and FML constructed with aluminum and carbon fiber reinforced polybenzoxazine. The mechanical properties were characterized by drop weight impact and flexural methods, and the polybenzoxazine curing behavior through differential scanning calorimetry (DSC). Polybenzoxazine FML generated increasing of: 18% of maximum load, 11% of maximum elongation under flexure and 7.5% of impact energy absorption compared to other fiber metal laminates.

Effect of Layer Structure on Dynamic Response and Failure Characteristics of Carbon Fiber Reinforced Aluminum Laminates (CARALL)

The effect of placing carbon fiber reinforced composite layers exterior or interior to the aluminum layers on the low-velocity impact performance of CARALL FMLs was investigated in this research study. In this study, CARALL laminates having 3/2 configuration, with aluminum in the outer layer for the first case (CARALL A) and one with carbon fiber composite (CFC) layer in the outer layer (CARALL B) were prepared using a vacuum press without using any adhesive film. In addition, CARALL-A FML was modified with a thin veil cloth layer between CFC and aluminum layers (CARALL-C). Force–displacement histories, damage morphologies and energy absorption capabilities of these laminates in relation to different energy levels are presented and discussed. The influence of resin rich layers (veil cloth) at the interfaces of aluminum and carbon fiber/epoxy layers on the impact behavior and damage size is also investigated. CARALL-A FMLs absorb the energy mainly through plastic deformation and delamination initiation and propagation whereas CARALL-B absorbs the impact energy through penetration and perforation of the laminate. The introduction of resin rich layers (veil cloth) affects the overall dynamic response with higher contact forces, smaller ultimate central deflections, reduced delamination damage area, and provides hindrance to the growth of cracks in the non-impacted aluminum layer and thereby increasing the impact resistance of CARALL-C FMLs.

Experimental and numerical investigation of flexural behavior of carbon fiber reinforced aluminum laminates

Fiber metal laminates (FML) combine the strength of carbon fiber composite layer with ductility of the aluminum layer for desirable mechanical characteristics. For these composites, progressive failure behavior can be complex and require attention. In this study, two carbon fiber reinforced aluminum laminates (CARRAL) with a 3/2 configuration, with aluminum in the outer layer for the first case and one with carbon fiber composite layer in the outer layer were prepared using a vacuum press without any adhesive layer between the layers—a significant departure from similar aerospace materials. Epoxy from the prepreg provides adequate adhesion during consolidation in these lower cost FMLs with a pressure level of 0.35 MPa. Three-point flexural behaviors of these two material systems were evaluated under static loading and failure modes were recorded. Primary failure modes observed were crack in lower aluminum layer, carbon fiber (CFRP) layer fracture and delamination between upper aluminum and CFRP layer. A major contribution of this study was to predict the flexural response of these FMLs using LS-DYNA finite element code. Modeling the progressive damage behavior of FML by considering stress based material failure and shear stress based delamination failure between adjacent layers were key aspects of finite element modeling. Predicted mechanical behavior matches well with experimental results and the progressive nature of damage are recovered in the model.

Modeling Low Velocity Impact Response of Carbon Fiber Reinforced Aluminum Laminates (CARALL)

Fiber metal laminates (FMLs) have shown great potential in lightweight aerospace applications. Carbon fiber reinforced aluminum laminates (CARALL) is a lightweight system that has received less attention than aramid reinforced aluminum laminates. These FMLs have adhesively bonded layered plies. We have developed CARALL without the use of adhesives. The epoxy resin from the carbon fiber epoxy is used to adhesively bond the aluminum layers. In this study, CARALL laminates having a 3/2 configuration, with Aluminum 5052-H32 as the outer layer were prepared using a vacuum press without using any adhesive film. Primary failure modes observed were cracks in non-impacted aluminum layer, carbon fiber (CFRP) layer fracture and delamination between aluminum and CFRP layers. Finite element modeling was used to predict low velocity impact response of these FMLs by considering Chang–Chang damage criteria for CFRP layers and nonlinear elasto-plasticity along with progressive damage mechanics for aluminum layers. Delamination was modeled by using traction separation law and damage criterion proposed by Benzeggagh–Kenane was used for interface damage evolution. The damage size of CARALL FMLs was characterized using C-scan equipment and compared with the finite element predictions. Numerical simulation was used to predict load–displacement histories, delamination area, absorbed energy, damage morphologies on impacted and non-impacted sides and tensile failures of CFRP layers for impact event at three different energy levels. Predicted impact behavior results match well with experimental results. The threshold impact energy, energy at which perforation failure was induced in all metallic and fiber reinforced layers for these CARRAL laminates was found to be around 31 J.