Strength Of Fiber Metal Laminates Research Articles

The assessment of the compressive strength of fibre metal laminates after low-velocity impact

The aim of the work was to assess the compressive strength of Fibre Metal Laminates after impact. The main objective of the evaluation of the compression after impact assessment of FMLs was the deep analysis of damage growth range, size and mechanisms during load from various initial damage states and final post-impact strength. The glass fibre/titanium and carbon fibre/titanium Fibre Metal Laminates were tested and analysed. Laminates previously subjected to impact energies ranging from 5 to 35 J were tested. Based on the research, three load bearing states of fibre-metal laminates were identified and characterized on the basis of an analysis of force reduction characteristics. In addition, it was found that the strength reduction of FMLs in relation to impact energy does not decrease significantly. One of the most crucial grounds for the above is the protective role of the elastic–plastic metal layers against rapid local buckling of the strength-carrying composite component.

Low velocity impact response of fiber metal laminates with nano-patterned metal surfaces

A nano-scale electrochemical sculpture (NES) method has been developed to enhance the bonding strength of fiber metal laminates (denoted as FMLs-NES). The influence of NES surface treatments on the low velocity impact response and static mechanical behavior of FMLs was systematically investigated and compared with traditional surface treatments such as mechanical polishing and NaTESi anodizing (denoted respectively as FMLs-PS and FMLs-NaTESi). The examination of the damage area and energy absorption under different impact energy levels revealed that the FMLs-NES specimen exhibited the smallest damage area and energy absorption while maintaining the structural integrity after impact. Finite element simulations were conducted to inform the impact damage progression and failure mechanisms, the results indicate that the interfacial failure mainly occurred between the middle titanium sheet and the bottom 90° fiber layer and propagated from the long edge to the center of FMLs. The experimentally validated finite element model can also be employed to optimize the stacking sequence of FMLs and to predict the residual strength after impact, where the FMLs-NES showed the highest residual strength.

An experimental investigation on infusion time and strength of fiber metal laminates made by vacuum infusion process

The vacuum infusion process can be used to fabricate fiber metal laminates with reduced manufacturing time and cost. In this method, the holes in the aluminum layers are created due to the better flow of the resin and to ensure that the fibers are completely impregnated. Created holes can cause problems in using these fiber metal laminates. For example, structural strength is reduced and some parts of the composite layers are exposed to environmental conditions. A proper solution to these problems has been proposed and investigated in this article. If a non-perforated aluminum layer is used as the first layer to be in contact with the mold, this layer becomes the outer layer of the structure made of fiber metal laminates. This non-symmetric fiber metal laminate will still be resistant to moisture and other environmental conditions due to the presence of an intact aluminum layer on the outermost layer, such as conventional fiber metal laminates. This aluminum layer also increases the strength of fiber metal laminates in comparison with fiber metal laminates that its all aluminum layers are perforated. In this paper, the effect of holes diameter of aluminum layers on the resin flow rate (consequently the duration of the fabrication) and the mechanical strength of the structure were investigated. The results showed that holes in the upper and middle layers of aluminum can significantly increase the speed of fabrication, but the presence of the holes causes a slight decrease in the final strength of the sample.

Development and Experimental Characterization of Fibre Metal Laminates to Predict the Fatigue Life

During the last two decades, the concept of Fibre Metal Laminates (FMLs) has been evolved to find solution to the requirement of improving mechanical properties and reducing structural weight of elemental components of aircraft structures. In this work FML is prepared using Al 2024 by placing alternately with glass/carbon/aramid Fibres. From experimental results of FML shows greater advantage in mechanical properties then aluminium monolithic layer and this composite fibre laminates individual. The FMLs tested in this work were made of 3 layers of 2024 T3 aluminium alloy 0.28 mm thickness and fibre mats. The 5-3/2 laminates of size 300x300 mm with 3 mm thick were prepared using Vacuum Assisted Resin Transfer Moulding (VARTM) in cold compaction and test specimen were cut by using abrasive water jet machining as per ASTM Standards. The adhesion between fibre and metal layer will play a major role in strength of FML. By keeping this in consideration FMLs were prepared without blow holes and capable of withstanding delamination while preparing specimens through water jet and during various tests employed. The fracture surfaces of destructed specimens are studied with help Scanning Electron Microscope (SEM) image. Similarly, the numerical simulation of all the tests were done using Ansys APDL 10.0 Software. It is observed that aramid FML have substantially stronger in longitudinal directions. Hence, more priority given in this paper to investigate tensile strength and fatigue life of aramid FML.

The Influences of Fibre Parameters on the Tensile and Flexural Response of Lightweight Thermoplastic Kenaf Fibre Reinforced Metal Composites

ABSTRACT The increasing demand for high performance and lightweight materials has stimulated the development of alternative materials, namely fiber metal laminates (FMLs). FML is a sandwich structure which is formed by bonding the metallic layers with composite as core constituent using an adhesive agent. In this study, the mechanical behavior of FMLs with the core constituents of environmental friendly kenaf bast fiber reinforced polypropylene composites bonded with aluminum skin layers was investigated. The effects of fiber compositions (50, 60, and 70 wt.%), fiber lengths (30, 60, 90 mm), and alkali treatment on the mechanical responses of FML were investigated. The overall results revealed that the increase of fiber composition and fiber length reduces the mechanical strength of FML owing to the agglomeration of natural fibers when the fiber length exceeds the critical limit. However, the chemical treated kenaf bast fiber reinforced FML showed a significant enhancement of the mechanical properties in comparison to the non-treated fiber reinforced FML owing to the improved fiber-matrix adhesion level.

A generalized solution to the crack bridging problem of fiber metal laminates

The slow crack growth and high residual strength of fiber metal laminates (FMLs) results from bridging, the transfer of loads from cracked metal layers to intact fiber layers that “bridge” the cracks over delaminations between the laminae. Understanding and improving the structural performance of FMLs therefore depends on characterizing the bridging phenomenon. Previously, mathematical models of bridging load transfer have been developed and verified for simplified circumstances:thin laminates with identical thicknesses and material composition through the laminate, identical crack lengths and delamination sizes, and simple tension loads. These models use a compatibility requirement at the delamination boundary to derive the bridging stress. This paper presents a generalized approach to solving the bridging problem that solves simultaneously for compatibility at every delamination boundary in the laminate, allowing the bridging load distribution to be derived for a laminate of arbitrary layup (different thicknesses and materials) with arbitrary damage (independent crack lengths and delamination sizes and shapes) and subject to arbitrary loading (any combination of applied tension and bending moment). The approach is evaluated by comparing its results to bridging stress distributions derived from finite element analysis. Good agreement was obtained for varied laminate and damage configurations, but some discrepancy exists in the presence of bending.

Experimental Investigation of Low-Velocity Repeated Impacts on Glass Fiber Metal Composites

The aim of this study was to experimentally investigate the effect of repeated low-velocity impacts on tensile strength of fiber metal laminates (FMLs) using instrumented drop weight impact tester. FMLs were fabricated layer by layer intercalating three layers of aluminum 6061 and two layers of glass fiber-reinforced epoxy. The FMLs were subjected to repeated low-velocity impacts (<10 m/s) at the same location on the FML. The degradation of mechanical property due to impact(s) was studied using Zwick UTM at distances of 0, 20, 40, and 60 mm from the impact point. Results indicate that ultimate tensile strength, failure strain, and ductility of all specimens initially decrease, and then remain constant with increase in number of impacts. A closer examination of impacted FML by scanning electron microscope indicates that thinning and shear fracture in aluminum layers, as well as delamination, and fiber failure in composites plies were present.

Estimating the failure strength of fiber metal laminates by using a hybrid degradation model

Different analytical formulations are reported in recent works to model the failure strength and the progressive failure of different fiber metal laminates (FMLs). Although the basis for all these formulations is classical lamination theory (CLT), the models differ with each other while modeling the stiffness degradation. A common analytical formulation that is independent of configuration of the laminate will be very helpful for the designers in this field. Present work is aimed to develop such a model with the help of a hybrid degradation scheme, which uses constant degradation factors based on the condition of the adjacent lamina. This hybrid degradation scheme has helped to model the occurrence of multiple failures inside a lamina during failure progression. The formulation is tested with three types of FMLs and the results show that the formulation is very much helpful in predicting the failure strength and progressive failure.

Experimental Characterization of the Bearing Strength of Fiber Metal Laminates

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.

Evaluation of residual strength of notched fiber metal laminates

Fiber metal laminates (FML) are a family of hybrid materials consisting of alternating layers of thin metal sheets and fiber-reinforced epoxy prepregs. In contrast to aluminum alloys, the presence of notches in FML causes significant strength reductions. The objective of this study was to evaluate the residual strength of fiber-reinforced metal laminates with a circular open hole. Mechanical testing was performed to determine the unnotched tensile properties and notched strength of bi-directionally reinforced fiber metal laminates. The influence of specimen dimension and notch size on residual strength and notch sensitivity of fiber metal laminates was investigated. A modified point stress criterion was introduced to predict the residual strength of fiber metal laminates with open hole. An excellent agreement between experimental results and model prediction was obtained. The residual strength predicted from this modified model also correlated very well with the experimental data in the literature for various other types of fiber metal laminates. A computer simulation based on finite element method was performed to study stress concentration and stress concentration around notch. Failure modes, damage initiation and progression of notched fiber metal laminates are also characterized and discussed.

The Bearing Strength of Fiber Metal Laminates

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.

충격손상을 받은 섬유 금속 적층판의 잔류 강도 연구

Residual strength of fiber metal laminates after impact was studied. 3/4 lay up FML was fabricated using 4 ply prepreg, 2 ply aluminum sheets, and I ply steel sheet. Quasi isotropic ([0/45/90/-45]s) and orthotropic ([0/90/0/90]s) FRP were also fabricated to compare with FML Impact test were conducted by using instrumented drop weight impact machine (Dynatup, Model 8250). Penetration load and absorbed energy of FML were superior to those of FRPs. Tensile tesls were conducted to evaluate the residual strength after<br/> impact. Strength degradation of FML was less than that of FRP. This means that the damage tolerance of FML is excellent than that of FRP'. Residual strength of each specimen was predicted by using Whitney and Nuismer(WN) Model. Impact damage area is assumed as a circular notch in WN model. Damage width is defined as the average of back face and top face damage width of each specimen. Average stress and point stress criterions were used to calculate the characteristic length. It is supposing that a characteristic length is a constant. The distribution of characteristic length shows that the assumption is reasonable. Prediction was well matched with experiment under both stress criter ions.

Static Properties of Fibre Metal Laminates

In this article a brief overview of the static properties of Fibre Metal Laminates is given. Starting with the stress-strain relation, an effective calculation tool for uniaxial stress-strain curves is given. The method is valid for all Glare types. The Norris failure model is described in combination with a Metal Volume Fraction approach leading to a useful tool to predict allowable blunt notch strength. The Volume Fraction approach is also useful in the case of the shear yield strength of Fibre Metal Laminates. With the use of the Iosipescu test shear yield properties are measured.

A study of tension test specimens of laminated hybrid composites

This paper is a continuation of the research work reported on earlier in Part I: a study of tension test specimens for laminated hybrid composites. Effects of specimen size and alignment of the tensile testing machine were investigated. It is demonstrated that the variation of strength with size is significant, and alignment of the testing machine is critical. In summary, the use of a straight-sided specimen for tension testing of fibre-metal laminates is recommended. However, if one can maintain good control of alignment from the tensile testing machine, use of a dogbone-type test specimen is also applicable. The effect of specimen size on the strength of fibre-metal laminates is also examined in this study. The strength of fibre-metal laminates exhibits no size (width) effect over the range 6.4 to 38.1 mm, holding the strain rate constant.