UD Composite Research Articles

Developing Superperforming Composites by Harnessing Fiber Orientation and Processing Technology.

The current research on the development and performance evaluation of unique composites focuses on an unexplored combination of fibers of PBO (polybenzoxazole Zylon) as reinforcement and PEEK (polyetheretherketone) as a matrix. Their fibers were braided in equal ratios and then compression-molded to develop composites by manipulating all long fibers in one direction (unidirectional, a UD composite) and for the other one half in one direction and the remaining half in the perpendicular direction (bidirectional, a BD composite). The performance was evaluated by hardness (micro- and scratch) studies followed by tensile and impact strength. Furthermore, the lap shear strength of the adhesive joints developed with these fibers in various orientations was also analyzed. The performance properties were compared with those of neat PEEK. It was observed that an exceptional increase compared to neat PEEK in impact strength of 10,000% and tensile strength of 662% was achieved in the case of the UD composite. Scanning electron microscopy (SEM) and microcomputed X-ray tomography were used on failed specimens to analyze the reasons for failure.

Optimising Recycling Processes for Polyimine-Based Vitrimer Carbon Fibre-Reinforced Composites: A Comparative Study on Reinforcement Recovery and Material Properties.

We investigated the recycling process of carbon fibre-reinforced polyimine vitrimer composites and compared composites made from virgin and recycled fibres. The vitrimer matrix consisted of a two-component polyimine-type vitrimer system, and as reinforcing materials, we used nonwoven felt and unidirectional carbon fibre. Various diethylenetriamine (DETA) and xylene solvent ratios were examined to find the optimal dissolution conditions. The 20:80 DETA-xylene ratio provided efficient dissolution, and the elevated temperature (80 °C) significantly accelerated the process. Scaling up to larger composite structures was demonstrated. Scanning electron microscopy (SEM) confirmed effective matrix removal, with minimal residue on carbon fibre surfaces and good adhesion in recycled composites. The recycled nonwoven composite exhibited a decreased glass transition temperature due to the residual solvents in the matrix, while the UD composite showed a slight increase. Dynamic mechanical analysis on the recycled composite showed an increased storage modulus for nonwoven composites at room temperature and greater resistance to deformation at elevated temperatures for the UD composites. Interlaminar shear tests indicated slightly reduced adhesion strength in the reprocessed composites. Overall, this study demonstrates the feasibility of recycling vitrimer composites, emphasising the need for further optimisation to ensure environmental and economic sustainability while mitigating residual solvent and matrix effects.

A damage model for matrix cracks in composite laminates under fatigue loading based on continuum damage mechanics

A damage model for transverse matrix cracks in composite laminates under fatigue loading was presented in this paper. The model was prosed based on the theory of continuum damage mechanics (CDM) at macro level and could capture the ‘edge effect’ of matrix cracks in composite laminate under fatigue loading. To obtain the constitutive equation of UD lamina containing transverse matrix cracks, a polynomial Gibbs free energy function was derived, and a macro damage parameter was introduced to characterize the influence of matrix cracks on multidirectional stiffness properties of UD composite. To predict the initiation and evolution of matrix cracks, a previously deduced initial crack initiation life function and a Paris-like equation in terms of damage driving force were employed, respectively. Prediction results of two cross-ply laminates under fatigue loading with different stress levels were compared to the experimental results and prediction results obtained from previously proposed model. The comparison results indicate the presented model is more effective and reliable in predicting the initiation and evolution of matrix cracks and the corresponding stiffness degradation in composite laminates under fatigue loading.

A non-local finite element model to assess the compressive strength of composite structures

Compression failure is a mechanism of non-local ruin that depends on the composite structure (layer thickness, load gradient), which makes it a peculiarity. The mechanism has been described and modeled with particular numerical tools in the literature. Only a few researchers modeled the mechanism at a mesoscopic scale, which is limited to UD composites. A homogenized non-local finite element model is proposed in this article. This is similar to Mindlin's II gradient theory to assess the compressive strength of the carbon/epoxy long fiber composite at the mesoscopic/structural scale. The framework of this non-local modeling is more general than that of Drapier et al. (1999) to assess microbuckling phenomenon in UD and woven composites. The developed non-local numerical model has been implemented in User Element (UEL) subroutine for analysis in ABAQUS®, which permits the simulation of the behavior of 2D and 3D cases. A 2D continuous (C1) type super-parametric non-local element (NL U32) is developed for both linear and non-linear (geometry and material) case. Various tests results are presented to validate the non-local FE model for 2D case by comparing the results of the homogenized non-local element with ABAQUS® iso-parametric elements. The classical (elastic and plastic) and non-local material properties (elastic) of the non-local model are identified by comparison to the responses of a Representative Volume Element (RVE) of full heterogeneous microstructures. A comparison of the compressive behavior of UD composite with the results in the bibliography shows the capabilities of this numerical tool.

Finite element analysis of Epoxy/E-Glass composite material based mono leaf spring for light weight vehicle

A great deal of work is put into decreasing the fuel consumption of automotive vehicles, which may be accomplished by reducing the bulk of the vehicles. One component that may be explored is the leaf spring, which is extensively utilized in many sorts of cars, including electric ones. For the leaf spring, four distinct materials are considered: standard steel, Epoxy/E-Glass UD composite, Epoxy/E-Glass Wet composite, and Epoxy/S-Glass UD composite. The FEA study executed with the help of the ANSYS finite element code. Firstly, the 3-D model of the leaf spring with different thickness varying from 15mm to 65mm is designed using SolidWorks software which is then imported to the ANSYS software for the static analysis. Along with this, the finite element analysis under full load on 3-D composite multi leaf spring model is executed using ANSYS 2020 R1 by taking three different materials and then the result for the different static behaviour of the leaf spring are compared for all the materials assigned. In this paper we describe design and analysis of composite leaf spring. The leaf spring model used for this purpose is a rear leaf spring used in MAHINDRA “MODEL-COMMANDER 650 DI”. When compared to traditional steel, the mass of hybrid composite material is 62% lower. Hybrid composite materials have 36% lower equivalent (Von-Mises) stress than steel. Utlimately, the hybrid composite material may be employed as a leaf spring, decreasing the total weight of automobiles.

Non-linear mean-field modelling of UD composite laminates accounting for average asymmetric plasticity of the matrix, debonding and progressive failure

As an effective and accurate method for modelling composite materials, mean-field homogenization is still not well studied in modelling non-linear and damage behaviours of UD composites. Investigated micro FE-simulations show that the matrix of UD composites exhibits different average plastic behaviour, named as average asymmetric matrix plasticity (AAMP), when the composite behaves different under shear, longitudinal and transverse loadings. In this study, a non-linear mean-field debonding model (NMFDM) combining a mean-field model and a fibre–matrix interface debonding model, is developed to simulate UD composites under consideration of AAMP, fibre–matrix interface damage and progressive failure. AAMP is considered by using so-called stress mode factor, which is expressed in terms of basic invariants of the matrix deviatoric stress tensor and is used as an indicator for detection of differences in the loading mode. The material behaviour of UD composites with imperfect interface is assumed identical as for perfect interface and stiffness reduced fibres. Progressive failure criteria are established with consideration of fibre breakage and matrix crack for different fibre orientations. As a representative example for the NMFDM, a C30/E201 UD composite is studied. To verify the model, experiments are conducted on polymers, carbon fibres and UD CFRPs. Finally, the model is applied to simulate a perforated CFRP laminate, which shows excellent prediction ability on deformation, debonding and progressive failure.

Numerical study of the influence of gaps between tiles and backing type on overall high-velocity impact performance of a ceramic-faced protective structure

The intelligent design of lightweight, protective systems requires the use of numerical simulations widely to weed unsuccessful tests and minimise the number of expensive experiments. At the same time, it is necessary to have verified numerical models of all materials that are used in a protective structure to obtain adequate numerical simulation results. In this research, the impact performance of the ceramic-faced mosaic panel against the impactor with a complicated structure was studied using numerical simulations in thу commercially available package LS-DYNA. Backing types being considered were Aluminium AA 5083 and Dyneema® HB80 UD composite. A new mesoscale model of 99.5% alumina based on the bonded particle method was calibrated and verified through the comparison with the known experimental data. Further, designs with different configurations of mosaic ceramic layers having hex tiles were studied and compared. The results indicated that even small lateral gaps between ceramic tiles decreased the overall panel performance regardless of both the impact site and a backing type. At the same time, the presence of gaps reduces damages of the ceramic layer and can change the impactor trajectory that can be used in multi-layered structures with distant layers. Thus, it is necessary to find a balance between survivability and mass efficiency for each protective structure.

Monitoring temperature effects on flax cell-wall mechanical properties within a composite material using AFM

PeakForce Quantitative Nano-Mechanical property mapping (PF-QNM) was applied to explore the nano-mechanical properties of the cell wall of two kinds of flax fibre preparation: isolated and within a poly-(butylene succinate) (PBS) or maleic anhydride grafted poly-(propylene) (PP-MAPP) matrix in unidirectional flax (UD) composites. Isolated flax fibres were subjected to a thermal cycle of 8 min from ambient temperature to 250 °C. At the same time, flax fibres in a matrix were subjected to an identical cycle from 140 °C to 250 °C, depending on the nature of the matrix. At the macroscopic scale, tensile tests on both types of sample preparation showed the same trends in temperature effects on the mechanical properties. At the cell wall scale, although no gradient in the cell-wall indentation modulus was revealed by PF-QNM for isolated fibres, a very slight global loss was observed above 210 °C, in accordance with the literature. This decrease was more pronounced for flax fibres within a matrix due the confinement effect of the polymer matrix which isolates fibres from the external environment during thermal treatment. The evolution of the mechanical behaviour of the cell walls leads to embrittlement of the UD composite, underlining the importance of time-temperature couple monitoring during the processing of plant fibre composites.

Extension of Puck's inter fibre fracture (IFF) criteria for UD composites

Puck's action plane failure criteria have already proven their capability in the first and second world-wide failure exercises (WWFE-I and WWFE-II). However, Puck and his co-workers have only recommended inclination parameters for GFRP/Epoxy and CFRP/Epoxy. These UD composites generally have high transverse compressive-to-tensile strength ratios YC/YT, and are regarded by them as intrinsically brittle materials. Therefore, Puck's inter fibre fracture (IFF) criteria might not be directly applied to other types of UD composites with low YC/YT ratios. In particular, Puck's original IFF criteria will result in unrealistic predictions if YC/YT is extremely low. In the present study, Puck's original IFF criteria are extended to all types of UD composite materials to solve the problem. Composites are divided into three categories, namely semi-brittle materials, brittle materials, and intrinsically brittle materials. Depending on the material category, three different algorithms are proposed for determination of the two parameters in Puck's IFF criteria, namely the resistance of the action plane against transverse tensile stressing, R⊥At, as well as the inclination parameter of contour lines of the fracture body, p⊥⊥. The present criteria are theoretically evaluated for composites with low YC/YT ratios, while the predictions of the present criteria are compared with the test results of composites with high YC/YT ratios such as thermoset GFRP and CFRP. Theoretical and experimental assessment demonstrates the reasonableness of the extension of Puck's IFF criteria.

Virtual characterization and macroscopic material modeling of a carbon fiber-reinforced PA6 UD composite

Despite the increasing use of continuously fiber-reinforced composites with thermoplastic matrices in load-bearing structural applications, published research on their deformation behavior in general and their long-term behavior in particular is very limited. As a result, adequate material models to describe their time- and direction-dependent behavior on a macroscopic scale are lagging. The present study uses micromechanical representative volume element models and numerical homogenization techniques to analyze the material behavior of a carbon fiber-reinforced PA6 material as a function of load direction and time. The matrix is modeled as viscoelastic–viscoplastic. Based on the results of the representative volume element model, a homogenized macroscopic modeling approach is proposed. It is shown that the time dependency of the unidirectional composite is highly anisotropic. Plastic deformation occurs in the matrix, but may be neglected in the homogenized composite at laminate-relevant strain levels. The proposed homogenized orthotropic, nonlinear viscoelastic material model adequately captures the behavior of the heterogeneous unidirectional composite.

Ballistic experiments on the mechanism of protective layer against domino effect caused by projectiles

The mechanism of protective layer against the domino effect caused by high velocity and low mass projectiles was investigated using ballistic experiments, under various values of thickness, surface density, fabric structure, and impact velocity. The results showed that unit absorption energy generally decreased and then increased with thickness and surface density. The critical value of thickness existed, the highest absorption was demonstrated in UD composite, and the back convex reached the maximum when impact velocity reached the ballistic limitation. Stretching fracture of fiber was the major way of energy absorption. Finally, four layers were designed for the protective layer.

A Note on mori-tanaka's method

Explicit expressions of Mori-Tanaka's tensor for a transversely isotropic fiber reinforced UD composite are presented. Closed-form formulae for the effective elastic properties of the composite are obtained. In a 3D sense, the resulting compliance tensor of the composite is symmetric. Nevertheless, the 2D compliance tensor based on a deteriorated Mori-Tanaka's tensor is not symmetric. Nor is the compliance tensor defined upon a deteriorated 2D Eshelby's tensor. The in-plane effective elastic properties given by those three approaches are different. A detailed comparison between the predicted results obtained from those approaches with experimental data available for a number of UD composites is made.

Modified water diffusion kinetics in an unidirectional glass/fibre composite due to the interphase area: Experimental, analytical and numerical approach

This paper deals with the study of water diffusion in unidirectional composite associating experimental data, analytical and numerical models. A fibre/matrix interphase with a gradient of molecular mobility is characterized by microthermal analysis. The fibre dispersion observed by optical microscopy shows an important heterogeneity and many contacts between fibres. This particular fibre distribution as well as the interphase thickness have been considered to model our composite microstructure accurately. Diffusion kinetic parameters from water absorption measurements on both the resin and the UD composite were then used in the finite element analysis of the composite. The comparison between experimental data, analytical and numerical models show the influence of fibre distribution and interphase properties on water diffusion kinetic. An average water diffusion coefficient is then identified for the interphase.

Structural elastic and creep models of a UD composite in longitudinal shear

The transient creep of a UD composite with a quadratic arrangement of elastic fibers of quadratic cross section is investigated. The deformational properties of the composite are determined from the known properties of its constituents. A structural model of the UD composite is developed, whose minimal elementary cell contains four elements. The stress-strain state of the elements is assumed homogeneous. Two types of basic and resolving governing equations of transient creep are deduced, which are based on static or kinematic assumptions. In each of the cases, a formula for the longitudinal elastic shear modulus of the composite is found. The stationary solutions of creep equations allow one to obtain formulas of the steady-state creep of the composite in a form similar to Norton’s law. Numerical calculations are also performed, and a comparison of the results with data given in the literature bears witness to the efficiency of the models developed and the solutions obtained.

Examination of heat resistant tensile properties and molding conditions of green composites composed of kenaf fibers and PLA resin

Disposing of conventional fiber-reinforced polymers (FRPs) poses an environmentally challenging problem. Disposal of FRPs by combustion discharges carbon dioxide in the air because the resin of FRPs is made of fossil fuel. When they are disposed of in the ground, FRPs remain semi-permanently without decomposing. In response to these problems, green composites are now being developed and are extensively studied as a material that produces a lower environmental burden. In this paper, green composites using kenaf fiber yarn bundles and PLA (poly(lactic acid)) are fabricated and their tensile properties are evaluated in the experiment. The tensile Young's modulus of all of the laminations is larger than that of PLA alone and the tensile strength of some laminations is larger than that of PLA alone. In particular, the value of UD composite of 0° shows double the tensile strength of PLA alone. Furthermore, the molding conditions for fabricating with a hot press are investigated and the heat resistant tensile properties of green composites are also reported.

Delamination properties of translaminar-reinforced composites

In the paper the delamination crack propagation is investigated in 3D woven carbon and glass fiber composites. Composites were produced in 3TEX company and had volume fraction of transverse fibers equal 2–5% of total volume of fibers. The reinforcement acts as crack bridging, greatly improving material resistance to delamination. In this paper investigation of this material has been performed using double cantilever beam technique and models elaborated for large scale bridging in UD composites. The following alterations and novelties are introduced: 1) The appropriate form and shape of specimens with glued additional metallic tabs was elaborated allowing to avoid the premature break of specimen arms; 2) Original loading device was designed to transfer high load directly to crack faces, and additional measurement of crack opening was proposed (as in the case of UD composite) to find the bridging law; 3) The convenient analytical formula for G I c calculation was proposed and used; 4) Instead of traditional R curve which is geometry dependent it was proposed to characterize the delamination resistance as function of crack opening displacement. The quantitative delamination characteristics for materials investigated are presented.

Structure and Thermo-Elastic Properties of SMC

A calculation process was developed to determine the whole set (in-plane as well as in the cross direction) of thermo-elastic properties of SMC materials on the basis of known properties of components. A typical feature of SMC structure (that the ma jority of reinforcing fibres remain collected in bundles acting as a sieve during the wetting process) is discussed. SMC-composite is held for a transverse isotropic material and is modeled by a symmetric three-layer composite with the centre layer consisting of plane isotropically reinforced fibre composite and the border layers represented by the isotropic particulate composite. The classical laminate theory is used to find the effective deforma tion characteristics of SMC. The properties of the centre layer are expressed in terms of a UD composite. The Kerner-Hashin theory has been proven satisfactory for prediction of particle composite properties in the case when the particle form doesn't differ too much from the spherical one (e.g., the case of a CaCO3 filler). The application of the Lewis-Nielsen theory allows a good agreement between theoretical and experimental values when platelet particle form must be considered (the case of a kaolin filler). An application of a low-profile additive reduces the stiffness of the resin and enhances its thermal expansion. This effect was found especially significant at higher temperatures and could not be described by means of a mechanical model only.