Performance Of Fiber Metal Laminates Research Articles

Study on static load performance of FMLs based on ultra-thin stainless-steel foils and cross-ply thin CFRP

The ultra-thin stainless steel/CFRP laminates overcome the limitations in application due to the weight drawbacks of conventional thick cold-rolled stainless steel. By laminating these two high-performance materials, it allows enhanced design flexibility and exceptional formability, rendering them highly promising in various industries such as automotive structures, shipbuilding, and electronics. The existing research on steel/CFRP laminates primarily revolves around locally reinforcing CFRP with cold-rolled plates of typical thickness (≥1 mm). Nonetheless, there remains a dearth of investigations examining the mechanical properties of laminates with varying metal thicknesses under the same volume fraction, particularly for ultra-thin stainless steel below 0.1 mm in thickness. In this study, to investigate the influence of micron-scale thickness ultra-thin stainless-steel foils on the performance of fiber metal laminates (FMLs), the laminates were manufactured and characterized using stainless-steel foils with thicknesses of either 0.05 mm or 0.025 mm. The tension and bearing properties of cross-ply thin CFRP (30 g/m2) laminates were examined both with and without the incorporation of ultra-thin stainless-steel foils. The findings confirmed that a substantial improvement in tensile strength of up to 35 % when ultra-thin stainless-steel foils were incorporated, accompanied by a remarkable increase in modulus by 65 %. Furthermore, the addition of stainless-steel foils to CFRP composites shifted their failure mode from brittle failure to progressive damage during three-point bending tests. Notably, utilizing 0.025 mm thick stainless-steel foils not only enhanced the strength and modulus but also mitigated post-yield stiffness loss compared to FMLs incorporating 0.05 mm thick stainless-steel foils for cross-ply thin CFRP laminates. Further researches revealed that ultra-thin stainless-steel foils with a thickness of 0.025 mm exhibited improved compatibility for deformation with cross-ply thin CFRP as evidenced by both tensile and bending damage behavior.

A novel active hydroforming & curing process to manufacture GLARE laminates: Numerical and experimental investigations

Fiber Metal Laminates (FMLs) are preferable thin-walled structures in several fields for their exceptional mechanical properties. However, how to manufacture thin-walled FMLs structures with complex shapes and guarantee the high mechanical properties is still a challenge. To address these, this paper proposes an innovative hybrid forming method, referred to as active warm hydroforming and curing, to enhance the formability and performance of FMLs in GLARE form by combining the forming and curing process into a single step. The hybrid method was verified on a box-shaped part as a proof-of-concept to assess the feasibility and parameter influence. Online curing was utilized to enhance efficiency and quality. The outcomes revealed that the new method increases the ultimate tensile stress by 12.1 % and reduces curing deformation from 3.1 mm to 1.3 mm compared to the vacuum bagging method. Furthermore, the critical parameters in forming of thin-walled structures, including blank holder force (BHF), pressure rate (PR), maximum pressure (MP), and forming temperature (FT), were identified using experimental, mathematical, and numerical approaches. Four defects in the formed thin-walled structures were observed and successfully eliminated through the control of these parameters. The method and results presented in this paper also provide direct guidance for optimizing the process parameters of FMLs warm hydroforming.

Enhanced interlaminar mechanical behavior of advanced fiber metal laminates via nano Al2O3‐IPN formation and surface pre‐treatments

AbstractThe inferior delamination resistance and out‐of‐plane performance of fiber metal laminates (FMLs) are of serious concerns. This work employs two modification methods, namely metal surface's chemical pre‐treatment and nano Al2O3 embedded interpenetrating polymer network (IPN) formation for improving the delamination resistance of aluminum and glass fiber‐reinforced polymer (GFRP) composite‐based FMLs. The synergetic effect of the two modification techniques resulted in high degrees of improvement in delamination resistance that were ~28% for critical strain energy release rate during mode‐I interlaminar fracture toughness (ILFT), that is (GIC) and ~37% for GIIC. Simultaneously, the flexural strength, tensile strength, and interlaminar shear strength improved by ~23%, ~17%, and ~24%, respectively. Scanning electron microscopy, atomic force microscopy, and surface energy measurement studies showed that the chemical pre‐treatment significantly influenced the surface morphology, surface roughness, and surface energy responses of aluminum, respectively. Fractographic study validated the effect of modification methods on the failure behavior under various testing modes.

Experimental investigation on mechanical behavior of fiber–metal laminates reinforced by hybrid carbon nanotubes and nanosilica under quasi-static pressure load

In this study, the effect of carbon nanotubes (CNT) and silica nanoparticles on quasi-static behavior of fiber–metal laminates (FML) has been experimentally scrutinized. FML consists of two layers of aluminum alloy plates and four composite layers including CNT/nanosilica-reinforced epoxy resin and glass fibers. The effect of weight percentage of carbon nanotube and nanosilica incorporated and their weight ratio in resin epoxy on the performance of FMLs against quasi-static compressive load has been considered. Furthermore, the design of experiments method and response surface methodology have been put into practice to develop an accurate mathematical relationship between the input parameters and the response variable. After designing and performing the experiments based on analysis of variance, a mathematical model corresponding to the real process is obtained. Moreover, the presented model has been validated by statistical methods. The results of this study indicate that the energy absorption capacity of these materials significantly increase through adding CNT to the FML, the highest failure force of 11.64 kN was obtained for FLMs comprising 0.6 wt.% of CNT and 3 wt.% of SiO2. An improvement of 27.88% and 45.86% in the absorbed energy and failure force was achieved, respectively, by adding 3 wt.% of SiO2 and 0.6 wt.% of CNT to FLM compared to pristine FLM.

Enhanced bonding strength of AZ31B/carbon-fiber-reinforced plastic laminates by anodization treatment in a saturated Na2SiO3 solution

Surface treatment of the metal substrate plays a critical role in improving the bonding performance of fiber metal laminates. In this work, we use a saturated Na2SiO3 solution to fabricate an anodized film on an AZ31B substrate by an anodizing process and achieve enhanced bonding strength between the AZ31B substrate and carbon-fiber-reinforced plastic (CFRP) composites. The results indicate that the primary breakdown voltage of anodization is reduced to approximately 35 V in the saturated Na2SiO3 solution. The film presents a porous/linear texture composite structure after anodizing for 2 min, and the porous structure is composed of micro- and nano-pores. The bonding strength of the AZ31B substrate anodized for 2 min/CFRP laminate reaches 15.96 MPa, which is 106% higher than that of the uncoated sample. The enhanced bonding strength is mostly attributed to the mechanical interlocking effect caused by the micro- and nano-pore composite structure. With anodizing time prolonged to 30 min, the surface roughness of the substrate obviously increases, but larger pores and gaps form in the film, resulting in a lower film strength and thus a lower bonding strength.

Experimental investigation, statistical modeling and multi-objective optimization of creep age forming of fiber metal laminates

The experimental assessment of the creep age forming performance of fiber metal laminates was considered in this study. To this end, different fiber metal laminates with the stacking sequence of [Al/02/Al] were manufactured using aluminum alloy 6061 sheets as skins along with E-glass fiber-reinforced polypropylene and E-glass fiber-reinforced polyamide 6 as two different cores. Next, a comprehensive investigation was conducted on the impacts of two main parameters in the creep forming process, i.e. the effect of time and temperature on the spring-back properties of deformed fiber metal laminates. Initially, using the design of experiments and based on the response surface methodology, an imposed spring-back of the creep age formed fiber metal laminates was modeled and the governing linear regression equations were derived and verified. Then, to find the best combination yielding the minimum spring-back, the process inputs (time and temperature) were optimized. The results proved that with an increase in either time or temperature, the spring-backs of the two types of creep age formed fiber metal laminates decreased due to the decrease in elastic strains and the increase of creep strains. Also, to achieve a creep age formed fiber metal laminate with minimum spring-back according to multi-objective optimization in both fiber metal laminates, the most proper values of time and temperature should be taken as 6 h and approximately 160°C, respectively.

Effect of through thickness metal layer distribution on the low velocity impact response of fiber metal laminates

The effect of distribution of aluminum layer through the thickness of fiber metal laminates (FMLs) on their low velocity impact response was studied. The FMLs were prepared using aluminum 2024-T3 layers (0.3, 0.4, 0.6 mm thickness) and glass fiber reinforced epoxy (two layers of 0° and 90° each) through hand layup followed by vacuum bagging. The four different layups considered had metallic layers placed at different locations through the thickness while maintaining the total metal layer thickness constant. The FMLs were subjected to low-velocity impact using a drop weight testing machine. The performance of FMLs was evaluated using different parameters such as maximum force, energy absorbed, damage degree, dent depth and maximum deflection. Among the four FMLs, it was observed that the FML 2/1–0.6 in which the composite layers were stacked together had lower levels of cracking and deformation and recorded the highest force for the same impact energy level, whereas the FML 4/3–0.3 in which two adjacent composite layers having different fiber orientations were separated by metallic layer recorded the lowest force and maximum cracking and deformation. The lateral spread of delamination and interlayer opening was comparatively greater for 2/1–0.6 when compared to 4/3–0.3, indicating that distributing the aluminum layers in the FML can decrease the lateral spread of damage within the FML.

Vibroacoustic performance of fiber metal laminates with delamination

ABSTRACTIn the present work, the numerical assessment of vibroacoustic (VA) performance of fiber metal laminates (FML) with mid-plane center delamination is presented. A fluid structure interaction study has been done using finite element method (FEM). Experimental validation is performed on an aluminium (AL) panel for verifying the correctness of finite element (FE) idealization procedure to simulate the fluid-structure interaction. Delamination is introduced in the FE model of FML panel and VA analysis is subsequently carried out. Sound transmission loss (STL) is computed on the panel with center delamination and without delamination. The overall sound pressure level (OASPL) shows that the presence of delamination (40% in total area) in FML has not changed the total energy of the transmitted sound when compared to aluminium and composites. However, in the narrow frequency bands (150–200 Hz, 200–250 Hz), the sound transmission nature has been significantly affected due to local delamination modes participating in the fluid-structure interaction process.

A comparison of the effect of riveting and cold expansion on the strain distribution and fatigue performance of fiber metal laminates

Fatigue tests carried out on three configurations (unexpanded, cold expanded and riveted) of fiber metal laminate material clearly demonstrated the beneficial effect of riveting compared to cold expansion in zero load transfer joints, for an approximately equivalent level of interference. Digital image correlation was used to measure the in-plane surface strain on cold expanded and riveted coupons during fatigue loading, and for the first time, digital image correlation was combined with pressure sensitive films to measure the strains resulting from the application of the rivet, including those under the rivet head. A comparison of the resultant strain field showed that the application of a rivet significantly reduces the stress concentration at the central hole and is effective in extending fatigue life. Some rivet heads were removed by milling, and the results from subsequent fatigue tests were used together with closed-form calculations to explain the findings of this study. It was concluded that the beneficial effect of riveting was less as a result of interference hole filling on the part of the rivet shank, but more a combination of the effect of interference and compression through the joint thickness.