Laminate Parameters Research Articles

Flexural properties and evaluation of Al‐CFRP self‐pierce riveted laminates under three‐point bending loads

AbstractThis study aims to investigate the bending performance and evaluation of aluminum‐carbon fiber reinforced plastic (Al‐CFRP) riveted laminates under varying parameters via self‐pierce riveting and three‐point bending tests. Through the self‐pierce riveting process test, a riveted joint meeting standard requirement was obtained. Based on this joint combination form, Al‐CFRP self‐pierce riveted laminates were prepared. The bending performance test showed the riveted laminate with a span of 80 mm had the greatest bending resistance at a thickness of 2 mm, and the overall strain of the Al‐CFRP self‐pierce riveted laminates was observed by digital image correlation (DIC) technology. Subsequently, validated numerical simulation modeling was conducted by correlating with the test results. On this numerical simulation model basis, further parametric studies and bending performance evaluations (including number of rivets, CFRP lay‐up angle, and laminates width) of the Al‐CFRP self‐pierce riveted laminates were systematically carried out. It was found that the peak load F and bending strength R improved by 1.32% and 26.66%, respectively, while the mass M reduced by 8.99%, for the design variables of var1 of 20 mm, var2 of 6, and var3 of [0/90°]2s.Highlight An Al‐CFRP riveted laminate structure is proposed to improve the bending properties of riveted laminates by changing the rivet parameters and laminate parameters. The bending properties of riveted laminates with different spans were investigated under three‐point bending loading conditions. The DIC technique observed the changes in the strain field of riveted laminates during bending. The effects of different structural parameters on the bending performance of Al‐CFRP riveted laminates were investigated by numerical simulation. An evaluation method combining the gray correlation degree and the combination assignment method is proposed to obtain the optimum riveted laminate structure under bending load conditions.

Influence of Laminate Parameter and Draping Variations on Locally Reinforced Composite Parts

Fibre-reinforced plastics (FRP) are a modern high-tech material and offer enormous lightweight potential. However, the material properties of composite materials lead to new challenges in the design and manufacturing process. Methods considering the anisotropic material behaviour during the design phase have been developed recently, leading to an optimised nominal laminate layout that often consists of a base laminate with local reinforcement patches. Yet, the laminate parameters suffer from variations during the manufacturing process. Additionally, deviations from the nominal fibre angles occur when draping the laminate of curved parts and interact with the occurring parameter variations. So far, the mentioned variations are insufficiently considered in combination with draping and reinforcement patches in the design of FRP parts. In order to overcome this shortcoming, a novel simulation approach for the draping of reinforcement patches is presented, which allows a more accurate prediction of fibre angles after adding random variations and draping deviations. The novelty of this approach lies in the consideration of variations in the draping simulation and their influence on the resulting draping deviations. It also enables further investigations, such as the influence on the draping deviations if the draping starting point is not the centre of the patch. The influence of different parameter variations on the component quality is then investigated by performing structural analyses of the part using the results from the draping simulation.

Mechanism and Influence Research on the Bending and Torsion Damping of Composite Hollow Tube

The internal damping has a significant influence on the dynamic performance of carbon fiber-reinforced plastic (CFRP) drive shaft. In this paper, the traditional damping strain energy model of composite structures was modified using the reverse off-axis transformation. The damping ratio of CFRP hollow tube pieces is then tested using the vibration method, and the accuracy and efficiency of the modified damping numerical model are verified. Meanwhile, the modified model was proposed to study the damping characteristics and contribution rate of the CFRP hollow tube. The results show the influence law of the laminate parameters on the bending and torsion damping of the CFRP hollow tube. How the strain energy dissipation affects the damping of the CFRP hollow tube is discussed, and the mechanism relationship between the laminate parameters and damping is explored. This study provides theoretical guidance for the design of the bending and torsion damping of CFRP hollow tube.

Probabilistic aeroelastic analysis of high-fidelity composite aircraft wing with manufacturing variability

Safety margins of aerospace structures can be improved through altering the laminate parameters of composite materials to increase flutter and divergence velocities. Existing work demonstrates the impact of material uncertainties on low-fidelity structural models that are not sufficient to represent realistic aircraft designs. A gap exists in quantifying laminate parameter uncertainties on aeroelasticity for high-fidelity three-dimensional composite structures in realistic tailored designs. This paper puts forward an efficient methodology for uncertainty quantification on the aeroelastic characteristics of three-dimensional composite structures using FE-based parametric composite models and advanced Kriging surrogate models. The methodology is tested on both low and high fidelity case studies to represent the composite wing structure. Similarities between the case studies are observed in the coefficient of variance of all hard flutter modes being within 0.15-1.4% of each other. The difference was found for divergence and soft flutter velocities where the coefficient of variance could be over ten times higher in the high fidelity case. Global sensitivity results revealed similar physical behavior cases can be produced from both studies at early design stages.

Effect of laminate parameters on nonlinear dynamic characteristic of the composite rotor-bearing system with pedestal looseness

The nonlinear dynamics of the composite shaft rotor-bearing system are greatly affected by the orientation angle layer and its proportion of the ply, i.e., the ratio of the orientation angle layer in the laminate. This paper presents a nonlinear dynamic analysis of a composite rotor-bearing system with pedestal looseness that considers the nonlinear oil film force and the pedestal looseness. Nonlinear phenomena including periodic, quasi-periodic, and chaotic motions are analyzed. The analysis results indicate that the stiffness and damping coefficients of a composite shaft tube can be influenced strongly by the laminate parameters, which can in turn affect the instability speed of the rotor system. To enhance the oil film instability speed of the composite rotor system, it is essential to maximize the ratio of the small orientation angle layer or the ±45° layer. Additionally, increasing the ratio of the small orientation angle layers in the shaft tube leads to a higher rotational speed for loosening instability. The research results obtained in this paper have important theoretical value for the design of composite rotor-bearing systems.

Enhanced Delamination Tolerance Levels by Hybridizing Carbon Laminates with Glass Plies: Parametric Study

Laminated composites are extensively used in the aerospace industry and one of the key issues is delamination tolerance in these configurations during the operational phase. This paper demonstrates that hybridization is an effective strategy to achieve higher delamination tolerance sizes. For the above purpose, this paper presents a method to hybridize two different practical laminated carbon composite panels with glass fibers and also a parametric study to evaluate the influence of various hybrid laminate parameters on the delamination tolerance. Geometrical non-linear finite element analysis is carried out on three-dimensional models of delaminated non-hybrid and hybrid composite laminates. The mode I Strain Energy Release Rate (SERR) is estimated using Modified Virtual Crack Closure Integral (MVCCI). The SERR components are compared for the hybrid and the non-hybrid laminates. It is demonstrated that an appropriate hybridization with glass plies in between a few top and bottom carbon layers enhances delamination tolerance levels without significantly affecting the stiffness of the laminate.

Increasing the Compressive Strength of Helicoidal Laminates after Low-Velocity Impact upon Mixing with 0° Orientation Plies and Its Analysis.

The helicoidal laminate is a kind of nature inspired fiber reinforced polymer, and the ply orientation affects their mechanical properties for engineering structural applications. A variety of helicoidal laminates with uniform and non-linear pitch angles mixed with additional 0° plies are fabricated to investigate the impact resistance through low-velocity impact and after-impact compression tests. Additionally, helicoidal laminates with constant pitch angles, quasi-isotropic laminate, and cross-ply laminates are also fabricated for a comparative study. The impact characteristics and the compressive strength are analyzed in view of the impact model, shear stress distribution, and fracture toughness. The results suggest that 10° or 20° are the better basic pitch angles before mixing 0° orientation plies. The 0° orientation plies may affect the contact stiffness, bending stiffness, damage extent, and compressive modulus. The compressive strength reaches the highest in tests on two samples with different percentages of 0° orientation plies and ply setups. Bending stiffness also dominates the impact response. The analysis on the laminate parameters provides ideas to improve the residual strength of helicoidal laminate.

Analytical bending stiffness model of composite shaft with breathing fatigue crack

In this paper, an improved stiffness model of the breathing crack of the composite shaft tube was established based on the Layer-wise theory, which considered the influence of orientation angle and stacking sequence of the cracked layers. Then, the model was compared with the horizontal neutral axis model, Mayes' model and analytical model. The results showed that the improved model can more effectively reflect the influence of the laminate parameters on the stiffness. Based on the model, the bending stiffness characteristics of the cracked composite shaft were studied, and the effects of laminate parameters on the stiffness were obtained.

Influence of polymer matrix on the induction heating behavior of CFRPC laminates

Within this study, the influence on the induction heating rate of different matrix polymer systems in combination with different reinforcing fabrics made of carbon fibers (CF) was experimentally investigated for a frequency of 480 kHz. Additionally, an electrical model representing CF-CF junctions in non-crimped fabrics, as well as roving-roving junctions in woven fabrics, was developed. The dielectric properties of the polymer matrix have no significant influence on the induction heating behavior of CFRPC compared to other laminate parameters. Compared to the heat dissipated due to the contact resistance m, the heat dissipated at one cross-junction due to dielectric losses is up to twelve decades lower. The dominant heating mechanism for induction heating of CFRPC laminates crucially depends on the magnitude of contact resistivity at the cross-junction. Below a contact resistivity of 10−5 Ω*m2 the losses due to Joule heating and beyond 10−5 Ω*m2 the losses due to contact resistances dominate.

Analytical modeling and investigation of constrained layer damping in hybrid laminates based on a unified plate formulation

Hybrid laminates, such as fiber metal laminates, are increasingly used in engineering applications due to their outstanding damage tolerance and weight-specific performance. Prone to vibrations, fiber metal laminates have recently been complemented by viscoelastic elastomer layers in order to achieve a desired level of damping following the principles of constrained layer damping. This paper presents an analytical modeling approach based on a unified plate formulation for the rapid and precise analysis of such hybrid laminates regarding their deformation and dynamic behavior. In order to account for the transverse shear deformation in the damping layers, the Reissner’s Mixed Variational Theorem is employed. The viscoelastic, thus frequency-dependent, material behavior is taken into account and the resulting damping quantities analyzed. Damped and undamped natural frequencies are computed using an iterative algorithm and the results are compared to the plate’s response to forced vibration. The approach is numerically validated using refined finite element models. Additionally, laminate parameters are varied in order to investigate their influence on the damping capabilities of these hybrid laminates.

Variation Analysis of Design Parameters of Fibre-Reinforced Plastic Parts

AbstractLightweight Design as an engineering domain is becoming more and more important in terms of sustainable mobility. Therefore, a large number of researchers is developing methods for utilisation of modern, but as well more complex materials with high lightweight potential. One subgroup of these materials are fibre-reinforced plastics (FRP). A lot of work is done supporting the design engineer in exploiting the structural and mechanical behaviour as good as possible. Whereas variations of laminate parameters, resulting from production, are poorly studied. Their impact especially on defined measures under load is of high importance, e.g. having a look on clearances in automotive industry. Because of the high complexity of FRP-parts, resulting from many laminate parameters, tolerancing is not an intuitive process. This is reflected in the fact that there is no defined procedure for tolerancing of FRP- parts. To support the design engineer the authors perform sensitivity analysis for simple loadcases to identify layers with a high importance on a defined measure. The results then are generalised to provide general guidelines to the design engineer.

Influence of layer thickness variations on the structural behaviour of optimised fibre reinforced plastic parts

Fibre reinforced plastics (FRP) are considered as a modern high-tech material. The enormous lightweight potential, especially of carbon fibre reinforced plastics, accelerates its spreading in many industrial applications. However, as good as the lightweight potential of FRP is, as difficult is the optimal use in products because of its anisotropic material properties. Recently, methods considering the anisotropic material behavior during the product development process have been developed. These result in optimized nominal laminate layouts with defined laminate parameters like fibre orientation, ply thickness and ply stack-up order. Yet, during the manufacturing process, variations of these parameters, compared to the nominal design, occur. The variations result in asymmetric laminates, which causes couplings in the stiffness matrix and consequently undesired deformations. The effects of varying laminate design parameters have so far mainly been investigated with focus on manufacturing activities. However, to support the design engineer in considering the influence of varying laminate parameters on product behavior, this paper studies the effects on the structural behavior of optimized FRP-parts. The main novelty and contribution of the paper can be found in providing a new approach for the consideration of uncertainties in the ply thickness on FRP parts with optimized fibre layout. For this purpose, sensitivity analyses are performed with the aim of investigating the importance of the parameters on the structural behavior. With this knowledge, the product developer is able to distinguish between critical and non-critical laminate parameters and consider their variations in the product development process as early as possible.

Stress-biased laminated composites for smooth folds in origami structures

Origami folding principles are attractive for morphing structures due to their potential for realizing drastic changes in shape. Laminated composites enable adaptive lightweight solutions for the implementation of rigid origami structures. This paper presents a strategy for the creation of smooth folds in finite-thickness laminated composites; the approach is applicable to smart folding structures with reconfigurable creases. An analytical laminated-plate model, based on strain energy minimization, is presented to calculate fold angle as a function of laminate parameters. Folds, realized as localized curvature at a crease, are modeled using piecewise displacement polynomials. Folded composites, created using prestressed elastomers with zero in-plane Poisson's ratio, are fabricated for demonstration and model validation. The calculated out-of-plane deflection of the curved creases is in agreement with measurements. A parametric study is conducted to characterize the sensitivity of fold angle and sharpness to variations in laminate modulus and thickness, crease width, and prestrain orientation. Narrow creases require higher prestress for a given fold angle than wider creases. Fold sharpness can be maximized by minimizing crease width and thickness. Anisotropy in the prestressed elastomer is a tradeoff between achieving zero in-plane Poisson’s ratio for unidirectional prestress and maximizing the range of crease orientations for foldability.

Stability analysis of internally damped rotating composite shafts using a finite element formulation

This paper deals with the stability analysis of internally damped rotating composite shafts. An Euler–Bernoulli shaft finite element formulation based on Equivalent Single Layer Theory (ESLT), including the hysteretic internal damping of composite material and transverse shear effects, is introduced and then used to evaluate the influence of various parameters: stacking sequences, fiber orientations and bearing properties on natural frequencies, critical speeds, and instability thresholds. The obtained results are compared with those available in the literature using different theories. The agreement in the obtained results show that the developed Euler–Bernoulli finite element based on ESLT including hysteretic internal damping and shear transverse effects can be effectively used for the stability analysis of internally damped rotating composite shafts. Furthermore, the results revealed that rotor stability is sensitive to the laminate parameters and to the properties of the bearings.

Crashworthy response of fibre metal laminate top hat structures

The axial crushing response of fibre metal laminates (FML), in particular GLARE top-hat structures, has been investigated using experimental and numerical techniques, which are reported in this paper. Crushing performance (crush force, energy absorption) was evaluated for formed GLARE top-hat structures as an analogue for an energy absorbing aircraft sub-floor structure. A numerical simulation methodology was established which could accurately predict the crushing performance of GLARE top hat structures using commercial explicit finite element (FE) analysis tool LS-DYNA. Material characterisation at coupon level was conducted to measure the appropriate material properties required for the model to achieve good predictability. The successful demonstration of GLARE energy absorbing structures widens options to enhance crashworthiness; numerous applications of such GLARE structures could be envisaged, including reinforcement of aircraft sub-floors.The crushing modes of GLARE top-hat structures were found to be complex, exhibiting mixed-mode failure which was a combination of the individual constituent failure modes. The metallic layers plastically deformed by folding and tearing while the composite layer failed with a wide range of failure patterns i.e. splaying, delamination and cracking. The top hat structures, most importantly, crushed in a stable progressive manner making them suitable for energy absorbing (EA) applications. The GLARE top hat structure’s crushing response is superior to its bare metal equivalent.Given the complexity of the FML crushing process, there is tremendous scope for optimisation of the laminate parameters to maximise energy absorption. The good agreement obtained between the numerical and experimental results highlights the benefits of using simulation to predict the overall crashworthiness of FMLs.

Optimal control and design of composite laminated piezoelectric plates

The present paper is concerned with the optimal control and/or design of symmetric and antisymmetric composite laminate with two piezoelectric layers bonded to the opposite surfaces of the laminate, and placed symmetrically with respect to the middle plane. For the optimal control problem, Liapunov-Bellman theory is used to minimize the dynamic response of the laminate. The dynamic response of the laminate comprises a weight sum of the control objective (the total vibrational energy) and a penalty functional including the control force. Simultaneously with the active control, thicknesses and the orientation angles of layers are taken as design variables to achieve optimum design. The formulation is based on various plate theories for various boundary conditions. Explicit solutions for the control function and controlled deflections are obtained in forms of double series. Numerical results are given to demonstrate the effectiveness of the proposed control and design mechanism, and to investigate the effects of various laminate parameters on the control and design process.

Optimization Methodology for Composite Stiffened Panel Based on Genetic Algorithm

A novel optimization methodology for stiffened panel is proposed in this paper. The purpose of the optimization methodology is to improve the first buckling load of the panel which is obtained by finite element method. The stacking sequence of the stiffeners is taken as design variables. In order to ensure the manufacturability of design, the design guidelines of stacking sequence are taken into account. A DOE based on Halton Sequence makes the initial points of genetic algorithm spread more evenly in the design space of laminate parameters and consequently accelerates the search to convergence. The numerical example verifies the efficiency of this method.

Using Depth-of-Penetration Tests to Design Transparent Armor

The depth-of-penetration (DOP) test has been modified for application to transparent armor materials. Armor materials to be tested are bonded to a polycarbonate substrate and penetration into the substrate measured. The tests can be used both for comparing armor materials and for evaluating laminate parameters. Materials tested were all armor-grade transparencies: borosilicate glass, soda-lime glass, glass ceramic, and spinel. For blunt projectiles, armor material performance is inversely correlated with density. For hard, sharp projectiles, material strength is most important, with spinel providing the best performance. The efficiency of spinel-glass laminates was only weakly dependent on the spinel thickness. Linear scaling can reconcile data obtained with different size projectiles. Relatively thick bond layers do not adversely affect the efficiency of laminates. DOP tests can be used to evaluate effects of damage from single cracks and multiple hits, and results also provide an estimate of optimal armor design against the threat used in the DOP experiments.

Material microstructure optimization for linear elastodynamic energy wave management

We describe a systematic approach to design material microstructures to achieve desired energy propagation in a two-phase composite plate. To generate a well-posed topology optimization problem we use the relaxation approach which requires homogenization theory to relate the macroscopic material properties to the microstructure, here a sequentially ranked laminate. We introduce an algorithm whereby the laminate layer volume fractions and orientations are optimized at each material point. To resolve numerical instabilities associated with the dynamic simulation and constrained optimization problem, we filter the laminate parameters. This also has the effect of generating smoothly varying microstructures which are easier to manufacture. To demonstrate our algorithm we design microstructure layouts for tailored energy propagation, i.e. energy focus, energy redirection, energy dispersion and energy spread.

Dynamic Analysis of a Rotating Composite Shaft

This paper is concerned with the dynamic analysis of a rotating composite shaft. The numerical finite element technique is utilized to compute the eigen pairs of laminated composite shafts. A finite element model has been developed to formulate the stiffness matrices using lamination theory. These matrices take into account the effects of axial, flexural and rotating on the eigen-nature of rotating composite shaft. The Campbell diagram is utilized to compute the critical speed of rotating composite shaft and instability regions to achieve accuracy and for controlling the dynamic behavior of the system in resonance state. The influence of laminate parameters: stacking sequences, fiber orientation, boundary conditions and fiber volume fractions effect on natural frequencies and instability thresholds of the shaft are studied. The results are compared to those obtained by using the finite element method and experimental measurements using frequency response function method (FRF) by applying the autogenously excitation from self excitation due to driving motor. In the experimental part, the response of composite shaft with various types of boundary conditions and five lamina orientations were recorded and analyzed by utilizing fast Fourier transform dual channel analyzer in conjunction with the computer. The comparison between the numerical and experimental results proves that the suggested finite element models of the composite shaft provide an efficient accurate tool for the dynamic analysis of rotating composite shaft.