Fiber-reinforced Composite Laminates Research Articles

Optimal cure cycle parameters for minimizing residual stresses in fiber-reinforced polymer composite laminates

The curing of a fiber-reinforced composite laminate in an autoclave generally induces residual stresses that may make the cured laminate curved. Here, we find optimal cure cycle parameters for asymmetric cross-ply laminates that (i) provide uniform and nearly complete curing of the laminate (i.e., the degree of curve is the same everywhere and equals at least 0.96) within a specified time period and (ii) minimize residual stresses without adversely affecting the transverse effective elastic modulus of the laminate. We simulate the cure process by using functionalities built in the commercial finite element software ABAQUS, the cure process modeling software COMPRO and the multi-purpose software MATLAB. After having satisfactorily compared the presently computed results for the curing of two laminates with either experimental or numerical findings available in the literature, we use a genetic algorithm and the Latin hypercube sampling method to optimize the cure cycle parameters. It is found that in comparison to the manufacturer’s recommended cure cycle (MRCC), for a cross-ply laminate with the span/thickness equal to 12.5, one optimal cycle reduces residual stresses by 47% and the total cure time from the MRCC time of 5 h to 4 h and another optimal cycle reduces the total cure time to 2 h and residual stresses by 8%. For the same cross-ply laminate with the span to thickness ratio of 125, an optimal cycle reduces the process induced curvature by 13% in comparison to the MRCC but increases the total cure time from 5 to 7.4 h. The approach presented here can be used by manufacturing engineers to obtain cure cycle parameters for fabricating composite laminates of desired quality.

Material orthotropy effects on progressive damage analysis of open-hole composite laminates under tension

The sizes effects on the strengths of open-hole fibre-reinforced composite laminates subjected to tensile loading (OHT) have been investigated widely. However, little attention has been paid to the influence of material orthotropy. This paper presents a progressive damage model for the model failure of notched laminates under tensile loading based on continuum damage mechanics and cohesive elements. The effects of orthotropy on the failure of notched laminates with seven different ply sequences are investigated by our proposed model. The prediction results adopting the Hoffman and Pinho failure criterions to determine matrix damage initiation are compared with the results of experiments. Our proposed models are able to predict the strong influence of orthotropy on strengths of open-hole laminate under tension, and model using Pinho criterion can predict the open-hole tension strength most accurately.

Progressive damage simulation of scaling effects on open-hole composite laminates under compression

The progressive damage simulation and strength prediction of open-hole fibre-reinforced composite laminates subjected to compressive loading is quite difficult due to numerical stability issues. Here, we proposed a progressive damage model for open-hole fibre-reinforced composite laminates subjected to compressive loading based on open-hole fibre-reinforced composite laminates under a tensile load. The proposed model is divided into two parts: the in-plane damage and delamination are modelled by continuum shell elements and cohesive elements, respectively, and the damage mechanics of sublaminate-scaled laminates with ply sequence [45/0/–45/90]ns and ply-level scaled laminates with ply sequence [45m/0m/−45 m/90 m]s are investigated by our proposed model. The complete failure process and mode of notched composite laminate under compressive load are also modelled in our model. The numerical results show good agreement with the experimental results.

Effect of matrix voids, fibre misalignment and thickness variation on multi-objective robust optimization of carbon/glass fibre-reinforced hybrid composites under flexural loading

Abstract The robust and optimal design of carbon/glass fibre-reinforced epoxy hybrid composite laminates under the constraint of a specified minimum flexural strength was investigated in this study. Two conflicting objectives, minimizing material cost and weight, were considered with the design variables being fibre type, fibre orientation angle and fibre volume fraction of the laminas. Three sources of uncertainties, namely, fibre misalignment, lamina thickness variation and the presence of matrix voids were incorporated into the model. This multi-objective robust optimization problem was solved by combining a modified version of the non-dominated sorting genetic algorithm (NSGA-II) with a simple genetic algorithm (GA) as an anti-optimizer. Pareto optimal and robust solutions were found for different levels of minimum flexural strength and the significance of each uncertainty source on the optimal cost and weight of the optimal designs were investigated by conducting analysis of variance (ANOVA) tests. The results indicated that, in general, all three uncertainties affected the cost and weight of the optimal designs with the effect of voids being more critical for void contents of greater than 2%.

Efficient three-node finite shell element for linear and geometrically nonlinear analyses of piezoelectric laminated structures

Fiber-reinforced composite laminates involving piezoelectric layers represent a very attractive material system. It combines the advantages of using rather lightweight and stiff material with the possibility of sensing structural changes and actively influencing its state by means of sensors and actuators. A three-node shell element is proposed as an efficient tool for modeling structures made of such a material system. Thoroughly tested solutions are implemented to resolve locking problems intrinsic for shell elements. The embedded piezoelectric layers are considered to be polarized in the thickness direction. Furthermore, the extension of the formulation to geometrically nonlinear finite element analysis is based on a co-rotational formulation. Numerical examples are given to demonstrate the applicability of developed element in linear and geometrically nonlinear finite element analyses covering both actuator and sensor cases.

Strength property analysis for fiber-reinforced shape memory polymer composite laminate

As a main component of space deployable structure, shape memory polymer composites are exposed to long-term periodic sharp temperature changes. It is necessary to investigate the influence of temperature on strength property of shape memory polymer composites. In this article, a micromechanical strength predication model was developed based on composite bridging model, which was used to define the stiffness matrix and relate the stress increment to the fiber and matrix. Furthermore, the progressive failure strength of shape memory polymer composites was simulated simply based on the properties of the material and the geometric parameters of the laminates. Comparison of the predictions with the experimental measurements was carried out. In general, the overall correlation between the theory and the experiments was reasonable. Furthermore, the model has been applied to predict the transverse strength, axial strength, and in-plane shear strength of different composite laminates (fiber content and ply angle) at different temperatures.

Elastic-damage deformation response of fiber-reinforced polymer composite laminates with lamina interfaces

The single-layer and multi-layer finite element models are developed and examined for adequacy in predicting the elastic-damage response of fiber-reinforced polymer composite laminates. A new experimental-computational approach featuring a two-tier mesh convergence analysis of the finite element models is developed. A 12-ply carbon fiber-reinforced polymer composite laminate beam specimen with anti-symmetric layups is designed and loaded to induce matrix damage under significant deflection without catastrophic fracture. A constitutive model incorporating Hashin’s equations for damage initiation criteria, along with an energy-based damage propagation law is employed in the finite element simulation. The results shows that the multi-layer finite element model predicts well the load–deflection curve of the carbon fiber-reinforced polymer composite laminate, while the single-layer model overestimates the elastic flexural stiffness of the specimen by 47 %. During the flexural deformation, matrix damage initiates in the central and edge regions of the critical laminas under compressive and tensile stresses, respectively. The multi-layer finite element model also predicted the matrix-induced interface delamination along the edges of the critical laminas under tension, as observed experimentally. The model demonstrates the adequacy in representing the role of lamina interface in dictating the elastic-damage response of carbon fiber-reinforced polymer composite laminates manufactured by prepreg layups method.

Failure Analysis of Fibre-Reinforced Composite Laminates

Experimentalinvestigation of failure modes of composite materials requirescorrelating the fundamentals of composite materials, their mechanicalproperties as well as their failure characteristics in the presence of defects. In this paper, three formats of defects of hole (single, double & quadruple) as a discontinuity were incorporated in modal analysisusing mode shape frequency. Unique failure modes of these specimens provided overview regarding mechanical behaviour of composite materials containing defects. Certain correlations were observed between defects and resulting properties.

An Improved Fatigue Failure Model for Multidirectional Fiber-reinforced Composite Laminates under any Stress Ratios of Cyclic Loading

This paper improves an existing model to predicting the fatigue life and material property degradation of arbitrarily oriented composite laminates under different stress ratios. Residual strain energy density is used to model fatigue behavior via a VUMAT subroutine in FEM package. The effects of strength and stiffness reduction are considered to obtain higher predictive accuracy than that derived with the stress-based method. Hashin failure criteria are employed to identify damage onset in the fiber, matrix, and in-plane shear of layers. Based on developed model, a sensitivity analysis is conducted to evaluate geometrical effects on the fatigue life of composite structures.

Strength Enhancement of Basalt Fiber-Reinforced Epoxy Laminates with Biowaste Catalyst Free Carbon Nanospheres

This study aims to analyse the effects of carbon nanospheres (CNSs) on the tensile properties of basalt fibre-reinforced epoxy composite laminate (BFR). The CNSs were obtained from an economical fibrous residue attained from the sago palm tree, which is known as biowaste sago bark. Hand lay-up method was used to fabricate the unidirectional basalt fibre-reinforced epoxy composite laminates. The epoxy resin was mixed with carbon nanosphere particles (i.e., 0.6 wt% - 1 wt %). Tensile tests have been conducted as per ASTM standards. In addition, emphasis on the microstructural investigation using Scanning Electron Microscopy (SEM) is given, in order to study the fracture surfaces of the composite laminates. The results demonstrated significant improvement in tensile strength when carbon nanosphere particles were included in the basalt fibre-reinforced epoxy composite laminate. The best result was obtained at 1.0 wt% CNSs. It displayed an increment of 80.6% in tensile strength, and 120% increment in Young’s modulus, respectively, in comparison to neat basalt fibre-reinforced epoxy composite laminate. The improved accomplishment of CNSs/ basalt fibre-reinforced epoxy composite laminate is due to good distribution of CNSs particles in the epoxy matrix.

Strength Enhancement of Basalt Fiber-Reinforced Epoxy Laminates with Biowaste Catalyst Free Carbon Nanospheres

This study aims to analyse the effects of carbon nanospheres (CNSs) on the tensile properties of basalt fibre-reinforced epoxy composite laminate (BFR). The CNSs were obtained from an economical fibrous residue attained from the sago palm tree, which is known as biowaste sago bark. Hand lay-up method was used to fabricate the unidirectional basalt fibre-reinforced epoxy composite laminates. The epoxy resin was mixed with carbon nanosphere particles (i.e., 0.6 wt% - 1 wt %). Tensile tests have been conducted as per ASTM standards. In addition, emphasis on the microstructural investigation using Scanning Electron Microscopy (SEM) is given, in order to study the fracture surfaces of the composite laminates. The results demonstrated significant improvement in tensile strength when carbon nanosphere particles were included in the basalt fibre-reinforced epoxy composite laminate. The best result was obtained at 1.0 wt% CNSs. It displayed an increment of 80.6% in tensile strength, and 120% increment in Young’s modulus, respectively, in comparison to neat basalt fibre-reinforced epoxy composite laminate. The improved accomplishment of CNSs/ basalt fibre-reinforced epoxy composite laminate is due to good distribution of CNSs particles in the epoxy matrix.

Damage Induced by High-Velocity Impact on Composite Structures Using Finite Element Simulation

In the current study, a finite element model was established to simulate the penetration process of composite laminates under high-velocity impact. A 3D rate-dependent damage constitutive model was developed to simulate the ballistic response of unidirectional fiber-reinforced composite laminate. Numerical models were built based on a damage model where cohesive contact method was involved. The user-developed FORTRAN subroutine (VUMAT) was written and implemented in ABAQUS/Explicit 6.11 version. The ballistic resistance and damage characteristics of composite laminate were discussed, and the damage model was validated. The results of the FEM were observed to agree well with experimental observation. According to the results, the ply angle of the laminate had great influence on the damage distribution; thus, when the ply angle increases, the ballistic resistance and damage areas on both front and rear side of the laminate decrease. Again, the result shows that increasing the thickness of the laminate was advantageous to the ballistic resistance and damage characteristics of the composite laminates. The prediction of the model was proved to have good accuracy and efficiency.

Prediction of the damping properties of fiber-reinforced polymer composite panels with arbitrary geometries

In this work, the modal damping of multilayered, fiber-reinforced polymer composite laminates with an arbitrary geometry have been computed using a mixed finite element-meshless method. The meshless node distribution scheme is used in conjunction with the Lagrangian quadrilateral interpolating functions to ensure the continuity of interelemental displacements. Furthermore, since the distribution of the elements is not confined to the geometry of the problem, any arbitrary geometry can be readily analyzed by using the same node and element distributions. Using the classical plate theory, together with a structural damping model, modal response results have been produced for a number of multilayer fiber-reinforced polymer plate geometries, including triangular and circular as well as rectangular plates with different combinations of free and clamped edges. Comparison of these results with those reported in the literature shows that the proposed method can predict the modal properties of fiber-reinforced polymer laminates with arbitrary geometries and boundary conditions with a good degree of accuracy.

Dynamic response and damage analysis of fiber-reinforced composite laminated plates under low-velocity oblique impact

Fiber-reinforced composite laminates (FRCL) is susceptible to the external impacting. Understanding the crack propagation and structural mechanical properties of the damaged FRCL under low-velocity oblique impact is of great value in practical application. A new analytical dynamic model is developed in this work to research the dynamic response and damage property of FRCL under oblique impacting. The displacement field and strain–displacement relations of the FRCL are established by utilizing higher-order shear plate theory. The matrix damage and fiber rupture in FRCL under oblique impacting are captured by an internal variable-based continuum damage constitutive relation. To accurately predict the oblique impacting force, an analytical dynamic impacting model is proposed basing on a developed contact model, where normal and tangential contact is coupled and solved simultaneously. The whole initial boundary value problem is iteratively solved by synthetically using finite differential method and Newmark-\(\beta \) method. The solving convergence and accuracy of the model is demonstrated and validated. Simulations show that the matrix damage is more easily to appear in FRCL under shear force due to oblique contact when under oblique impacting, and the damage profile is different from normal impacting. The dynamic responses of the FRCL plate under oblique impacting differ also greatly from normal impacting. The current research provides a theoretical basis for FRCL design and its engineering application when under low-velocity impacting.

A nonlinear finite thickness cohesive interface element for modeling delamination in fibre-reinforced composite laminates

Abstract Delamination events are major issues which notably affect the integrity of composite structures. To minimize the experimental efforts, there is an increasing demand for developing reliable numerical tools that can accurately simulate delamination initiation and propagation under mixed-mode loading conditions. The current investigation is concerned with the formulation and the finite element (FE) implementation of a new nonlinear finite thickness cohesive interface model for delamination analysis of fibre-reinforced composite laminates relying on the solid shell concept. The incorporation of geometrically nonlinear effects into the proposed interface formulation is motivated by the recent trend of producing composite structures that can experience large displacements prior to failure, as is the case of postbuckling in stiffened panels. The inelastic material behavior of the interface is modeled using two standard nonlinear decohesion laws: (i) an exponential-based, and (ii) a polynomial-based interface laws. Finally, the performance of the proposed interface element is demonstrated by means of several examples focusing on double cantilever beam (DCB) and rib-stiffened specimens. A excellent level of accuracy is achieved when comparing the numerical predictions and the available experimental data.

A simple test method, NAL-II, to evaluate the strength and elastic modulus of polymer matrix composite laminates

This study proposes and assesses a simple test method (NAL-II) to evaluate compressive properties of carbon fiber-reinforced polymer matrix composite laminates (CFRP). Compressive tests based on ASTM D6641 and NAL-II methods were conducted for direct comparison using three kinds of quasi-isotropic composite laminates (T800H/3633, T800S/3900-2B, and IM600/133). Stress–strain curves including the compressive modulus obtained using the NAL-II method showed good agreement with those obtained using the ASTM D6641. The NAL-II method gave slightly higher (approximately 10%) compressive strengths than the ASTM D6641 method, probably because of suppression of bending (buckling) before failure. The experimentally obtained results suggest that the NAL-II method can be useful for international standard testing of the non-hole compressive strength of CFRP laminates.

Finite element analysis of dynamic progressive failure of plastic composite laminates under low velocity impact

This paper studies dynamic mechanical responses and damage mechanisms of plastic fiber-reinforced polymer matrix composite laminate under low velocity impact. First, the plastic damage model is introduced for intralaminar damage, where Puck’s failure criteria and strain based damage evolution laws for fiber and matrix are used, and the bilinear cohesive model is adopted for delamination. Second, an uncoupled numerical scheme for dealing with the intralaminar plastic deformation and damage evolution by finite element analysis (FEA) is originally proposed based on the strain equivalence hypothesis, in which the effective stresses and strains are first solved using the backward Euler algorithm and then the nominal stresses and damage variables are updated independently. Finally, the proposed algorithm is implemented using ABAQUS-VUMAT by the time stepping algorithm. For two composite specimens under transverse impact, the impact force-time curve, the impact displacement-time curve and the dissipated energy at different impact energies are studied by comparing the results using experiments and FEA. Numerical results show the plastic damage model leads to higher precision than the elastic damage model as the impact energy becomes relatively large.

Evolution of Crack Density in Cross-Ply Laminates - Application of a Coupled Stress and Energy Criterion

The first damage mode to appear in continuous fibre-reinforced composite laminates subjected to in-plane loading is usually transverse cracking, i.e. matrix cracking in the off-axis plies of the laminate. Since the density of transverse cracks has a great influence on the subsequent failure steps like delaminations, it is important to be able to predict it accurately. In this paper, the evolution of crack density with increasing external load is predicted using a combination of the Coupled Criterion of Finite Fracture Mechanics and the Equivalent Constraint Model.

Progressive damage simulation of open-hole composite laminates under compression based on different failure criteria

The strength prediction of open-hole fibre-reinforced composite laminate under compression is very important in the design of composite structures. The modelling of fibre, matrix damage and delamination plays an important role in the understanding of the damage mechanics of laminate under open-hole compression. In this article, a progressive damage model for open-hole compression that is based on continuum shell elements and cohesive elements is established to model in-plane damage and delamination, respectively. The damage mechanics of sublaminate-scaled laminates with ply sequence [45/0/−45/90]ms and ply-level-scaled laminates with ply sequence [45n/0n/−45n/90n]s are investigated by our proposed model. The Tsai-Wu and Hoffman failure criteria are employed for the determination of matrix damage initiation. Compared with the experiments, the numerical results using the Tsai-Wu criterion exhibit better accuracy regarding open-hole compression strength prediction and failure modes simulation.

Damage prediction in notched fiber-reinforced composite laminates

In early loading stage of composite laminates, longitudinal splitting in terms of matrix cracking usually initiates from notch tips and propagates in fiber directions. The extremely high stress concentrations at the notch tips could be drastically alleviated by the splitting. An efficient finite element model is created in this article to perform progressive failure analyses on notched composite laminates. To capture the true stress concentrations at notch tips, surface-based cohesive contacts instead of cohesive elements were introduced to model the splitting. The advantage of the surfaced-based cohesive contact over the traditional cohesive element is that it allows different mesh configurations for different plies. Predicted failure patterns and tensile strengths by the finite element model were compared with tested results from open literature.