Metal-composite Interface Research Articles

Enhancing the properties of metal-composite interface by a nano-TiO2 coating

The application of metal-polymer structures has been restricted by challenges in achieving effective bonding between the two materials. To address this, nano-TiO2 coatings were introduced to improve the interfacial bonding between the treated 6061 Al alloy and carbon fiber-reinforced thermoplastic composite (CFRTP) during the laser joining process. The results highlighted that the joints created with nano-TiO2 coatings achieved significantly higher tensile shear force and strength, reaching 1.43 and 1.37 times the values of those without particles, respectively. This improvement can be attributed to the following factors: firstly, the incorporation of coatings led to an increase in the absorption of hydroxy groups, thereby improving the wettability of the Al alloy, which in turn promoted the formation of hydrogen bonds at the interface. Secondly, the increased surface roughness favored the chemical interaction between the Al alloy and CFRTP, ascribed to the enlarged contact area. Moreover, this change influenced the thermal contact conductance (TCC), thereby changing the temperature at the interface and joining areas of the two materials. Finally, a notable transformation in the failure mode was observed, transitioning from adhesive failure to cohesive failure when compared to joints without nano-TiO2 coatings. This underscored the reinforcing role played by nano-TiO2 particles, providing an innovative solution for enhancing the interface bonding between dissimilar materials.

Ultrasonic Joining of Additively Manufactured Metal-Composite Hybrid Joints: A Comparison between Vertical and Horizontal Vibration Modes

Ultrasonic Joining (U-Joining) is a novel friction-based joining technique that produces through-the-thickness reinforced hybrid joints between surface-structured metals and thermoplastics. The process feasibility has been successfully demonstrated to join metals and unreinforced or fiber-reinforced polymer parts by applying horizontal vibration. However, intense tool wear was observed for the explored combinations of materials, which could diminish the mechanical performance of the produced joints and hinder the process application. These investigations left an unexplored field regarding the application of different vibration modes, which could represent good solutions to minimize the intense tool wear reported. Therefore, the present study aims to explore the application of vertical vibration and to identify possible advantages and disadvantages of this variation. The case-study combination of additively manufactured 316L stainless steel and 20%-short-carbon-fiber reinforced poly-ether-ether-ketone was selected for this purpose. Initially, a set of optimized joining parameters was obtained for the vertical variation following a one-factor-at-a-time approach. In a previous study, the joining parameters were already optimized for the horizontal mode, and the results were used for comparison purposes. Single-lap shear joints were produced using both optimized modes, and the process monitoring indicated that joints produced using vertical vibration reached a lower joining energy input for a given joining time. The produced joints were tested, and joints produced with the horizontal variation achieved higher ultimate lap shear forces than the ones achieved by the vertical ones: 3.6 ± 0.3 kN and 1.6 ± 0.3 kN, respectively. Microstructural investigations at the fractured surfaces showed that this difference is due to insufficient frictional heat generation at the metal-composite interface when vertical vibration is applied. Therefore, the temperatures reached during the joining cycle are not enough to melt the polymer completely at the interface, preventing a complete surface wetting of the metal and reducing the micromechanical interlocking and adhesion bond between the parts, thereby diminishing the mechanical performance of the produced joints.

First principles study of V/Pd interface interactions and their hydrogen absorption properties

Hydrogen permeation through vanadium/palladium (V/Pd) metal composite membranes is an effective and practical method of separating hydrogen from gas mixtures. In order to gain an insight into the relation between the interfacial structure and hydrogen adsorption/diffusion properties of the catalytic Pd layer bonded to the metal membrane, and then improve the ability of the alloy membrane to purify hydrogen, the first principle based on the density functional theory is used to study the hydrogen adsorption/diffusion behavior at the V/Pd metal composite membrane interface. The results show that because the charge density at the V/Pd interface increases with the V/Pd bonding increasing, the dissolution energy of hydrogen atom (H) increases with it approaching to the interface, and it has the highest dissolution energy near the V/Pd interface (0.567 eV). Hydrogen migration energy barrier calculations show that compared with the maximum energy barrier for horizontal diffusion of H along the V/Pd interface (0.64 eV), the H vertical V/Pd interface energy barrier (0.56 eV) is small, thus H tends to migrate vertically V/Pd interface and diffuse from the Pd layer to the V substrate side. As the hydrogen solvation energy of the Pd layer at the V/Pd interface (0.238 eV) is higher than that on the V membrane side (–0.165 eV), H will gather on the V film side of the interface, which is easy to cause hydrogen to be embrittled. Calculations of Pd/Fe doping of the V matrix show that comparing with the undoped energy barrier (0.56 eV), Pd/Fe doping can significantly reduce the maximum energy barrier (0.45 eV/0.54 eV) in the diffusion path of the interface, which is favorable for hydrogen permeation and diffusion. And the doped interface can inhibit the interdiffusion of V layer and catalytic Pd layer to a certain extent, which improves the structural stability of the composite film.

Comparison of the debonding force of metal, glass and polyethylene Fiber reinforced composite retainers: Mechanical and finite element analyses

The studies evaluating the efficiency of fiber reinforce composite (FRC) retainers are few and contradictory. This study aimed to compare the debonding force of metal, glass FRC (GFRC) and polyethylene FRC (PFRC) retainers, assess the interactions between the materials and forces, and pattern of load distribution by finite element analysis (FEA). Forty-eight sound lower incisors were collected and randomly assigned to 3 groups (n=8; each sample included 2 teeth). Next, 15mm of the three retainers (multi-stranded metal wire, GFRC, and PFRC) were bonded to the lingual surface of the teeth and debonding force was measured by a universal testing machine. For FEA, 3D models were designed. The data related to geometrical models and material properties were transferred to ANSYS software. A 187-Newton load was applied to the incisal edge of the two centrals. Then different parameters were assessed. The three groups were compared by one-way Anova and Tukey's test. Type one error was considered to be 0.05. The debonding force decreased in the order: Metal (143.71N)≥GFRC (108.29N)>PFRC (45.08N). The difference between metal retainer and GFRC was not significant. In contrast, PFRC group showed significantly lower debonding force compared to other groups (P<0.05). FEA showed stress peak value in metal-composite interface. Maximum total deformation was noted in central, followed by lateral and canine. Glass-FRC can serve as an alternative to metal retainers as the difference in debonding force is not significant. However, the difficulty of repairing or replacing the Glass-FRC should be taken into account given the large number of failure in the interproximal dental area.

Laser-Generated Guided Waves for Damage Detection in Metal-Lined Composite-Overwrapped Pressure Vessels.

This paper characterizes laser-generated guided waves in a metal-lined composite-overwrapped pressure vessel (COPV) to assess typical damage, including interfacial debonding and low-velocity impact damage. First, an eigenfrequency approach that avoids additional coding is utilized to theoretically analyze the dispersion characteristics of a COPV. The theoretical results show that interfacial debonding significantly alters dispersion curves, and the wavenumber of the L(0, 1) mode is sensitive to impact damage. Experimental verifications were conducted based on the full wavefield acquired using a scanning laser-ultrasonic system with a repetition rate of 1 kHz. By comparing the experimental dispersion curves with the theoretical ones, it was found that the metal-composite interface was not bonded. In addition, a local wavenumber estimation method was established to detect the impact damage by obtaining the spatial distribution of the wavenumber of the L(0, 1) mode.

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%).

Evaluation of Surface Treatment for Enhancing Adhesion at the Metal-Composite Interface in Fibre Metal-Laminates.

The paper presents the issues of metal surface treatment in fibre metal laminates (FML) to obtain high adhesion at the metal–composite interface. Aluminium 2024-T3 and titanium Grade 2 were analysed. The metal surface modifications were carried out by mechanical (sandblasting, Scotch-Brite abrasion), chemical (P2 etching, phosphate-fluoride process), electrochemical (chromic and sulphuric acid anodizing), and plasma treatment, as well as the application of sol-gel coatings. In terms of surface geometry, the analysis included roughness and 3D surface topography examination. The morphology was examined using scanning electron and atomic force microscopy. The surface free energy and its components (polar and dispersive) were determined using the Owens–Wendt method. The novelty of this study is the determination of the effect of different surface treatments on the surface free energy, topography, and morphology in terms of the possible appropriate adhesion in fibre metal laminates. Chromic acid anodizing is still the most effective in enhancing the expected adhesion. A suitable technique may be the use of P2 etching of aluminium. It results in low roughness, numerous micro-irregularities, and the presence of porosity. The obtained test results show that the application of sol-gel coating increases the surface free energy and may increase the adhesion.

Dynamic response of single curved fiber-metal hybrid lamina composites subject to low-velocity impact

Fiber-metal hybrid lamina composites (FM-HLCs) are a new kind of fiber-metal composites, which aims at addressing the metal-composite interface failure in conventional fiber-metal laminates. In the current study, the low-velocity impact tests were conducted to examine the dynamic response of single curved FM-HLCs. The influence of weave pattern of fiber-metal hybrid lamina, impact velocity and radius of curvature on the dynamic response is considered in the experiment. The deformation/failure modes, force-time histories and energy absorption were obtained. The high-speed cameras were used to capture the deformation/failure processes of FM-HLCs and the instantaneous images for digital image correlation analysis. The results indicate that the “fiber-metal hybrid lamina” strategy can efficiently help maintain the integrity of FM-HLCs outside the impact region. The increase of fiber content can efficiently decrease the deformation/failure region and permanent deflection of FM-HLCs, thus, enhancing its impact resistance. When the fiber content along circumferential and longitudinal directions is not consistent or the radius of curvature decreases, there forms an elliptical deformation region of FM-HLCs. The current work is expected to be of significance for the follow-up research and the potential applications of FM-HLCs. In addition, it is also a good reference for investigating the dynamic response of orthotropic panels/shells under low-velocity impact.

Deformation and failure of a novel fiber-metal hybrid lamina composite under quasi-static and impact loading

A novel composite comprising two laminae, each integrating fiber and metal within a single layer, is established, with the objective of addressing the common problem of structural degradation via debonding between composite and metals in conventional Fiber-Metal Laminates (FMLs). Each lamina consists of an aluminium sheet with rectangular perforations punched out in a grid-like pattern; basalt roving is then “woven” into the sheet by running parallel strips of roving in one direction through the perforations, alternating above and below of metal segments. This results in interlocking of the roving and metal constituents, and the lamina can be considered an assembly of many small metal-composite interface (MCI) units, where the roving and metal are in mutual contact. Two such laminae are stacked together, and epoxy is infused into them to create a bi-layer composite. Specimens are then subjected to quasi-static and projectile impact tests, to examine the deformation and failure induced. Examination of post-test samples show failure and debonding within only a limited number of MCI units in a lamina, because of the intimate integration and interlocking between the fiber and metal components. Moreover, no debonding between the two adjacent laminae is observed. This indicates that the novel architecture of the composite, endows it with excellent resistance against crack propagation, not only within MCI units, but also within the basalt-reinforced epoxy component. It is envisaged that with appropriate optimization, the mechanical properties of these new fiber-metal composites can be further enhanced and implemented in applications where conventional FMLs encounter limitations.

Modeling anisotropic fracture in a metal-fiber reinforced composite system

Hybrid structures consisting of metal and composites can be applied to specific requirements of different applications. The computational modeling of composites is quite complex compared to homogeneous and isotropic materials like metals because of the heterogeneity introduced due to the presence of different phases such as matrix, fiber and matrix-fiber interface, and anisotropy due to the fiber alignment. The crack propagation in a composite material depends on a combination of various damage modes, namely, fiber pull-out, matrix cracking, delamination. The strength and stiffness of the composite depend on the mechanical and fracture properties of the individual phases, and the fiber inclination. The metal-composite interface is modeled using the cohesive zone approach. A nonlocal diffused approach is proposed to model the anisotropic failure in composites reinforced with unidirectional and woven fibers and the interaction of the crack with the interface. Parametric studies are conducted to understand the role of fiber orientation and interface fracture properties of the system. The proposed model is illustrated through numerical examples to understand various failure mechanisms in a metal-composite system.

Effect of metal type on the energy absorption of fiber metal laminates under low-velocity impact

The energy dissipation mechanisms during impact including damage evolution and plastic deformation of FMLs with different metal layers named aluminum and magnesium was experimentally and numerically studied. A 3D failure criterion for composite damage evolution was developed. The impact energy of the FMLs was mostly dissipated by metal layers, where the plastic dissipation energy of each aluminum layer in aluminum-based FMLs was distinctly higher than that of magnesium layer in magnesium-based FMLs. Replacing aluminum in FMLs with magnesium leads to faster perforation and passive energy dissipation, but will also reduce delamination damage at metal-composite interface due to smaller plastic deformation.

Interaction of anisotropic crack phase field with interface cohesive zone model for fiber reinforced composites

A new phase field model considering the interfacial damage for different configurations of a fiber reinforced composite is proposed and formulated. Crack and non local interface are considered to be diffused. A coupled traction separation law based on a potential function is adopted to represent the behavior of the interface. Anisotropy is introduced into the elastic equilibrium by considering the distinct contributions of fiber and matrix in different modes. The present model captures the predominant failure phenomena in a composite such as matrix failure, delamination by considering the role of fiber orientation, interface fracture properties and configuration of lamina. The proposed formulation is extended to a fiber reinforced composite lamina consisting of two fiber families oriented in different directions. Parametric studies are conducted to understand the effect of anisotropy parameter, length scales, fracture properties of fiber, matrix and interface on crack propagation and mechanical response of the whole system. Numerical examples are performed to validate the proposed model, understand the anisotropic crack growth for unidirectional and woven fiber reinforced composites, study the interaction of anisotropic crack with composite-composite interface and metal-composite interface.

Lattice material infiltration for hybrid metal-composite joints: Manufacturing and static strenght

An innovative technological solution for the manufacturing of high strength and high toughness metal-composite interface is here investigated, in which a 3DP printed cellular structure at the metal side is infiltrated by Advanced Sheet Molding Compound composite, in order to understand the effect of main geometric and processing parameters. Some hybrid metal-composite joints were produced, in which the effect of fiber orientation and cell dimension were considered as representative of the main processing issues. The outcome of the infiltration process was first checked on the hybrid joints, then samples were extracted for mechanical characterization of the bond, in comparison with cellular structure free joints.

Surface Treatment to Promote Joining of Glass Fiber Reinforced Plastic and AZ31 Magnesium Alloy for Fiber Metal Laminates via Hot Metal Pressing

When fabricating fiber metal laminates, the joining between the metal sheet and the composite is affected by the chemical and mechanical properties at the interface. To this end, this study investigated the influence of different induced-surface characteristics of AZ31B magnesium alloy sheets when joint with glass fiber reinforced polyamide 6. The treatments, carried out to modify the AZ31B surfaces, were annealing, sandblasting, and their combination. The mechanical and chemical interlocking at the metal-composite interface was assessed in terms of macroscopic and microscopic defects as well as lap shear strength. The obtained results indicated that the joint effectiveness was mainly affected by the annealing treatment, which induced both a chemical and morphological modification of the surface. The formed oxide layer at the interface, combined with surface topography modification, were capable to increase the lap shear strength up to 87%.

Effect of Different Coupling Agents on Interfacial Properties of Fibre-Reinforced Aluminum Laminates.

Metal composite interface properties significantly affect the integrity, bonding properties, and interface structure of Fibre Metal Laminates (FMLs). Interfacial bonding strength’s effect on Carbon Fibre-Reinforced Aluminium Laminate (CARALL) mechanical behaviours was investigated via three-point bending and low-velocity impact tests. AA6061 sheets were subjected to surface pretreatments under three conditions (anodizing and A-187 and A-1387 surface modifications) to obtain different interfacial bonding strengths. The bonding interfaces of CARALL were analysed using scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Interfacial bonding strength between aluminium alloy and epoxy resin was determined by the tension-shear test. CARALL’s energy absorption capacity and failure mode were analysed after low-velocity impact and three-point bending under different aluminium alloy volume contents and surface pretreatments. Upon modification of metal surfaces, the interfacial bonding strength increased, and the highest was obtained by silane coupling agent A-1387. Improved strength maintained FML’s integrity under quasi-static and dynamic loadings. A-1387 improved the bonding ability of aluminium alloy and Carbon Fibre-Reinforced Plastics (CFRP). The composite interface strongly resisted crack propagation because of its functional group characteristics. When the volume content of aluminium alloy was less and greater than that of CFRP, the energy absorption capacity of CARALL weakened and strengthened, respectively, with increasing interfacial bonding strength.

The fracture properties of fiber metal laminates based on a 3D printed glass fiber composite

Fiber Metal Laminates (FML) are structures that contain a sequential arrangement of metal and composite materials, which are of great interest to the aerospace sector due to the superior mechanical performance. The traditional manufacturing process for FML involves considerable investment in manufacturing resources depending on the design complexity of the desired components. To mitigate such limitations, 3D printing enables direct digital manufacturing to create FML with customized configurations. In this work, a preliminary mechanical characterization of additively-manufacturing-enabled FML has been investigated. A series of continuous glass fiber-reinforced composites were printed with a Markforged system and placed between layers of aluminum alloy to manufacture hybrid laminate structures. The laminates were subjected to tensile, interfacial fracture toughness, and both low-velocity and high-velocity impact tests. The results showed that the FMLs appear to have a good degree of adhesion at the metal-composite interface, although a limited intralaminar performance was recorded. It was also observed that the low and high-velocity impact performance of the FMLs was improved by 9–13% relative to that of the constituent elements. The impact performance of the FML appeared to be related to the fiber fracture, out of plane perforation and interfacial delamination within the laminates. The present study can provide an initial research foundation for considering 3D printing in the production of hybrid laminates for static and dynamic applications.

Machinability and surface integrity of adhesively bonded Ti/CFRP/Ti hybrid composite laminates under dry and cryogenic conditions

The current work compares the machinability of conventional drilling of hybrid titanium/carbon fiber reinforced plastics/titanium ( Ti/CFRP/Ti ) stack laminates in a single shot under dry and cryogenic conditions. Damage at metal-composite interface (MCI), thrust force, torque, burr height, surface roughness, average hole size, circularity error, and perpendicularity error are considered as experimental outcomes to investigate the influence of cryogenic cooling on the machinability of Ti/CFRP/Ti stacks. The experimental outcomes indicate that the hole quality significantly improved under cryogenic condition compared to dry drilling for the range of drilling parameters chosen. However, cryogenic cutting yields an increased thrust force due to increase in the hardness of Ti sheet at low temperatures. Scanning acoustic microscopy (SAM) was capable of capturing damage at MCI. Scanning electron microscope (SEM) and micro-computed tomography (μ-CT) are also used to assess the drilling induced damages on hole wall surface under both (dry and cryogenic) conditions.

Interlaminar Shear Strength and Failure Analysis of Aluminium-Carbon Laminates with a Glass Fiber Interlayer after Moisture Absorption.

This article presents selected aspects of an interlaminar shear strength and failure analysis of hybrid fiber metal laminates (FMLs) consisting of alternating layers of a 2024-T3 aluminium alloy and carbon fiber reinforced polymer. Particular attention is paid to the properties of the hybrid FMLs with an additional interlayer of glass composite at the metal-composite interface. The influence of hygrothermal conditioning, the interlaminar shear strength (short beam shear test), and the failure mode were investigated and discussed. It was found that fiber metal laminates can be classified as a material with significantly less adsorption than in the case of conventional composites. Introducing an additional layer of glass composite at the metal-composite interface and hygrothermal conditioning influence the decrease in the interlaminar shear strength. The major forms of damage to the laminates are delaminations in the layer of the carbon composite, at the metal-composite interface, and delaminations between the layers of glass and carbon composites.

Fabrication of Fibre Metal Laminates with Multiscale Toughening Mechanisms

Although Fibre Metal Laminates (FMLs) show many advantages compared to other composite materials, their layered structure, a result of bonding dissimilar materials, makes FMLs prone to delamination. Conventional solutions to toughen the metal-composite interface have already reached their limit. For further improvement to the metal-composite interfacial bonding properties, a multiscale approach involving micro/nanotoughening mechanisms needs to be implemented. However, the fabrication of FMLs with controlled toughening at different length scales is complicated. This paper introduces a new methodology to manufacture FMLs having micro-and nanosized features using a 3D interconnected silver nanowire interleave at the metal-composite interface. The effects of processing parameters on the extent and effectiveness of the multiscale toughening mechanisms are presented.

Investigation of hole quality in drilled Ti/CFRP/Ti laminates using CO2 laser

The machinability of titanium (Ti) and carbon fiber reinforced plastic (CFRP) (Ti/CFRP/Ti) laminates using CO2 laser is presented in this work. The effect of line energy and laser frequency on output responses such as heat affected zone (HAZ), taper angle (TA), metal composite interface (MCI) damage, surface roughness, dross height, and circularity were investigated. Line energy - the most influential parameter - demonstrated a threshold behavior; no drilling was observed below a certain line energy. Scanning acoustic microscopy (SAM), scanning electron microscopy (SEM), micro-computed tomography (μ-CT), and other imaging techniques were used to establish a correlation between laser parameters and CO2 laser machined damage in Ti/CFRP/Ti laminates. The results show that using a higher frequency and lower line energy can significantly improve the hole quality. However, dross free holes with minimum taper can be obtained using higher line energy.