Ply Drop-off Research Articles

Ply curving termination for enhancing tensile strength of composite ply drop-off: static evaluation and failure mechanism

Composite structures are optimized in shape by terminating specific plies gradually. However, stress concentration at the ply drop-off can cause interlaminar delamination from the ply edge. In this study, Ply Curving Termination (PCT), which is introduced by locally curving fibers at 0° ply edges, is used to enhance tensile strength of the ply drop-off. To clarify the dependence of the PCT strength on the curved fiber angle (PCT angle), static tensile tests using ply drop-off specimens are conducted, followed by detailed damage observations using X-ray CT. The results indicates that the strength significantly increases with PCT but the fracture behavior differs depending on the PCT angle. Interestingly, specimens with large PCT angles fail from the position where the fibers curve, away from the ply edge. This PCT-specific failure mechanism is then elucidated using finite element analysis and the virtual crack closure technique, indicating that shear lag caused by the stiffness change due to fiber curving is important. Finally, using the revealed PCT failure mechanism, PCT angles that are the most effective in enhancing tensile strength is discussed.

Crashworthiness optimization of variable stiffness B-pillar with thermoplastic composites

This study focuses on enhancing of crashworthiness and lightweight of the automotive B-pillar structure by using continuous carbon fiber reinforced thermoplastic composites (CFRTP) and optimized layer design. Firstly, the B-pillar is divided into four regions with variable stiffness. Quasi-static three-point bending test and numerical simulation are performed to calculate the stiffness of the structure. Then, the four regions of the B-pillar with different CFRTP layers are structurally designed to realize variable stiffness. Considering manufacturing requirements, a draping simulation is employed to predict potential layer defects. The results demonstrate that B-pillar structural performance is enhanced after the reorientation of CFRTP prepreg. Afterward, the crashworthiness of the CFRTP B-pillar considering the ply drop-off is evaluated and compared with the traditional Q235 steel counterparts. The results indicate that the CFRTP B-pillar exhibits superior crashworthiness but a substantial reduction in mass by 53.1%. Finally, the multi-island genetic algorithm (MIGA) is employed to achieve the optimal layer design scheme for lay-up optimization of the CFRTP B-pillar, and the crashworthiness of the CFRTP B-pillar with variable stiffness is further improved. The current work highlights a structural design strategy for CFRTP components for vehicles, which is crucial for the updating of automobile engineering.

Improving fatigue characteristics of ply drop-off in composite laminate with ply curving termination

Ply drop-off is a weak point of a tapered composite laminate, where stress concentration occurs and delamination initiates. By suppressing delamination from the ply drop-off, more optimized structural design and further weight reduction are possible. Ply Curving Termination (PCT), which locally changes the fiber direction at the edge of the dropped ply, is one of the promising delamination suppression mechanisms. To improve the technical maturity of PCT, this study conducted tensile fatigue tests using asymmetric taper configuration. Damage initiation, delamination propagation, and final failure were evaluated in detail by changing the PCT fiber angle and loading level, confirming that large PCT angles are effective in improving the fatigue properties of tapered laminates and that controlling the location of initial damage is necessary to maximize the effectiveness of PCT. Based on the findings, an effective design guideline for tapered laminates with PCT was presented.

Numerical shape, thickness and stacking sequence optimisation and experimental study of hybrid composite plates under in-plane shear loading

Shape, thickness and stacking sequence optimisation of a damage tolerant hybrid (GFRP-CFRP) composite laminate is performed using the commercial Optistruct solver. The results of the optimisation study are compared to both a benchmark non-damage tolerant CFRP laminate (without protective surface GFRP plies known as type 1 laminate) and a damage tolerant traditionally optimised hybrid CFRP-GFRP laminate (having X shape CFRP plies known as type 2 laminate), designed and tested in a previous study. The optimised laminate is manufactured using three different manufacturing techniques. The experimental buckling and post-buckling performance of the manufactured laminates are investigated. The optimised hybrid laminate is approximately 8% heavier than the type 1 but 17% lighter than type 2, but with the benefit of protective surface GFRP plies in favour of a damage tolerant design as shown in a previous study. Both numerical and experimental buckling and post-buckling performance studies show that the optimised laminates demonstrate higher pre-buckling stiffness compared to the type 1 design. However, the experimental buckling and failure/collapse loads, unlike the numerically predicted loads, are 24.31% and 26.70% lower, respectively. This is due to the significant number of ply drop-offs in the hybrid laminate design, and hence geometric imperfections and stress concentration effects at these locations leading to early buckling and failure in the post-buckling region.

A novel parallel method for layup optimization of composite structures with ply drop-offs

This paper presents a novel parallel optimization method for obtaining blended layups of composite laminates which closely match target lamination parameters. Firstly, a guide-based adaptive genetic algorithm (GAGA) which stochastically searches the layups is developed. Then the parallel optimization method DLBB-GAGA is developed by combining GAGA and a dummy layerwise branch and bound method (DLBB) which performs a logic-based search in a parallel computation, during which optimization information is shared between the two methods. The combination of these two different methods gives the parallel DLBB-GAGA method the advantages of both, enhancing the searching ability for the blended layup optimization. The superiority of the parallel DLBB-GAGA method is demonstrated through comparisons between the three methods, and it is concluded that the method is particularly effective for practical design where more layup design constraints are considered.

An integrated approach for rapidly and precisely predicting the spring-in of U-shaped composite parts with ply drop-offs

This paper aims to predict the spring-in of U-shaped composite parts with ply drop-offs rapidly and precisely. To this end, an integrated approach was proposed by combining an analytical model for the zones of equal thickness with a proxy model for the effects of ply drop-offs. Firstly, a parametric finite element analysis (FEA) of ply drop-offs was used to collect initial data for the proxy model. Based on these data, the response surface method (RSM) and analysis of variance (ANOVA) were used to determine the input parameters of the proxy model. Then, considering the computational efficiency and accuracy, the radial basis function (RBF) model was selected for ply drop-offs among three data-driven methods to couple with the analytical model for the equal-thickness zones. As the prediction results of the proposed approach were compared with the experimental results, acceptable accuracy was achieved, and computation time was greatly reduced compared to FEA. Consequently, the integrated approach can quickly and accurately predict the spring-in of U-shaped composite parts with ply drop-offs.

Free vibration analysis and prediction modeling of delaminated tapered FRP composite plates

Delamination (the separation between plies) is a common failure in Fiber Reinforced Polymer (FRP) laminated composites. The presence of delamination reduces the structural stiffness and changes in dynamic responses. The change in dynamic parameters can be successfully used for assessing structural health monitoring (SHM) for composite structures. SHM requires large amount of numerical/experimental data. This study focuses on the influence of the delamination parameters (size and in-plane location) on vibration behavior of a laminated tapered fiber reinforced polymer (FRP) composite plate with ply drop-off. Furthermore, developing a surrogate model as a fast-executing model to predict the shift in the natural frequency to reduce the computational effort for solving forward problems. The layerwise theory (LWT) has been used, and the delamination is modeled by “constrained mode” were solved using the finite element method (FEM). The numerical model was validated with an experimental modal analysis of tapered plates without delamination to make the model more robust. The effect of delamination was studied using surface plots produced using response surface methodology (RSM). The results show that the delamination size and location significantly affect the natural frequency shift. The RSM and ANN models were considered as surrogate models, and it was evaluated using an experimental modal analysis. The results shows that the single-output ANN model can predict the shift in the natural frequency with a minimum Root Mean Square Error (RMSE).

The effect of ply drop-off on tensile strength of thermoplastic carbon fiber composite: a numerical and experimental study

PurposeIn laminate composite structure design, it is common to deal with the need of varying thickness to reach project requirement or improve performance. This change of thickness can be achieved by terminating or adding plies at different locations over the laminate. Unfortunately, the inherent weakness of this construction is the presence of material and geometric discontinuities at the ply drop region that induce premature interlaminar failure at interfaces between dropped and continuous plies.Design/methodology/approachIn this work, tensile strength tests were performed on tapered laminates with internal ply drop-off using digital image correlation (DIC) technique. The laminate based on a new thermoplastic ELIUM® 150 reinforced by a plain weave carbon fabric was manufactured via VARTM. Stress, strain, displacement and tensile strength were analyzed. A 3D finite element analysis (FEA) and design of experiments (DOEs) were carried out for the analysis of effect of position and angle orientation of dropped plies near the thinner section of the tapered laminate. Tsai Wu's criterion was implemented to predict initiation of first ply failure.FindingsNumerical and experimental results showed that position and angle orientation of ply drop-off near the thinner thickness influence tensile strength of tapered laminate. Tensile static strength increases 12% when drop-off near the midplane is oriented at ±45° instead of 0°. Results showed a trend of improvement in the tensile strength when drop-off is positioned over midplane of the laminate composite. Results obtained through the DOEs were able to adjust the metamodel according to a linear model with great efficiency. They show the significant relevance of the manufacturing variables and the interaction between the factors.Originality/valueThe present work aims to evaluate the effect of ply drop-off on the strength of carbon fiber thermoplastic composite laminates with internal drop-off under tensile load and propose a design guideline about angle orientation and position of dropped plies closer to the thinner section of the laminate.

Simultaneous Design of Stacking Sequence and Drop-off Placement for Ply Drop-off Laminated Composite Plate

This study proposes a simoultaneous design optimization for a ply drop-off laminated composite to maximize strength at the regin pocket in terms of both the stacking sequence and the ply drop-off placement under several empicical stacking constraints. Genetic algorithms including the gene repair strategy and adaptive mutation is adopted for efficient searching. The strength is evaluated based on the stress index based on FEM analysis using the three-layer model. Through numerical examples, the validity of the proposed simultaneous design method is demonstrated.

Parametric study on influence of ply drop-offs on buckling behaviour in composites

Parametric study on influence of ply drop-offs on buckling behaviour in composites

Optimum design of composite structures with ply drop-offs using response surface methodology

PurposeMany studies only take into account the ply stacking sequence as the design variable to determine the optimal ply drop-off location; however, it is necessary to optimize other parameters that have a direct influence on the ply drop-off site such as which plies should be dropped and in which longitudinal direction. That way, the purpose of this study is to find the most significant design variables relative to the drop-off location considering the transversal and longitudinal positions, seeking to achieve the optimal combination of ply drop-off locations that provides excellent performance for the laminate plate.Design/methodology/approachThis study aims to determine the optimal drop-off location in a laminate plate using the finite element method and an approach statistical with design of experiments (DOE).FindingsThe optimization strategy using DOE revealed to be satisfactory for analyzing laminate structures with ply drop-offs, demonstrating that not all design factors influence the response variability. The failure criterion response variable revealed a poor fit, with an adjusted coefficient of determination lower than 60%, thus demonstrating that the response did not vary with the ply drop-off location. Already the strain and natural frequency response variables presented high significance. Finally, the optimization strategy revealed that the optimal drop-off location that minimizes the strain and maximizes the natural frequency is the ply drop-off located of the end plate.Originality/valueIt was also noted that many researchers prefer evolutionary algorithms for optimizing composite structures with ply drop-offs, being scarce to the literature studies involving optimization strategies using response surface methodology. In addition, many studies only take into account the ply stacking sequence as the design variable to determine the optimal ply drop-off location; however, in this study, the authors investigated other important parameters that have direct influence on the ply drop-off site such as which plies should be dropped and in which longitudinal direction.

Buckling optimization of blended composite structures using lamination parameters

In this paper, a new lamination parameter based method is proposed for the layup optimization of built-up composite laminates with ply drop-offs. The optimization process is divided into two stages. In the first stage, the multilevel optimization feature of the exact strip software VICONOPT MLO is extended to use the lamination parameters and laminate thicknesses of each component panel as design variables to minimize the weight of the whole structure subject to buckling and lamination parameter constraints. For the second stage, instead of using the common heuristic optimization methods, a novel dummy layerwise branch and bound (DLBB) method is proposed to search the manufacturable stacking sequences to find those needed to achieve a blended structure based on the use of 0°, 90°, +45° and −45° plies and having lamination parameters equivalent to those determined in the first stage. The DLBB method carries out a logical search to circumvent the stochastic search feature of heuristic methods for the determination of stacking sequences. This two-stage method is an extension of a previous highly efficient two-stage method for a single laminate (Liu et al., 2019) [1]. The effectiveness of the presented method is demonstrated through the optimization of a benchmark wing box.

Static deflection and thermal stress analysis of non-uniformly heated tapered composite laminate plates with ply drop-off

The effective design of tapered laminated composite structures subject to non-uniform temperature fields requires a thorough understanding of their static behaviour. In this study, a finite element analysis of tapered laminated composite plates with ply drop-off has been carried out to study the static deflection and normal stress patterns developed under non-uniform heating. The study revealed that the nature of the taper configuration, the nature of the applied temperature field and the structural boundary conditions influence the static deflection behaviour and the normal stresses developed in the tapered composite plates. It is found that the static deflection pattern of a tapered plate subject to a particular temperature profile is not sensitive to the nature of the taper configuration. It is also observed that the static deflection pattern of a tapered plate is significantly influenced by the nature of temperature field. Normal stress variation of tapered plates subject to various temperature fields reflects the nature of the temperature profile. Maximum normal stress occurs at locations where the highest temperature exists for that particular temperature field. The stresses are also influenced by the nature of the taper - Taper D plates experience low stresses while Taper B and Taper C plates experience similar values. It was also found that large variations in stresses are observed at resin pockets.

Structural optimization of tapered composite sandwich plates partially treated with magnetorheological elastomers

This study investigates the optimal locations of magnetorheological elastomer (MRE) segments in partially treated tapered composite MRE sandwich plates to maximize the natural frequencies and the loss factors. Various partially treated tapered composite MRE sandwich plate configurations are developed by dropping-off the plies longitudinally in top and bottom orthotropic (composite) layers with uniform core layer thickness. The core layer is made of natural rubber and MRE. The classical laminated plate theory is used to derive the governing differential equations of motion of the various partially treated MRE tapered composite sandwich plate configurations. The equations of motion are solved by using finite element formulation. Various cases of optimization problems are formulated and solved using genetic algorithm (GA) in order to obtain optimal locations to yield maximum natural frequencies and loss factors corresponding to the first five modes. The proposed methodology is validated by comparing the results evaluated in identifying optimal locations of MR fluid pockets filled in between uniform composite face layers, available in literature. It is observed that according to the user/designer requirements on achieving the optimal functions and their maximum value, the optimal locations of MRE pockets vary. It has also been demonstrated that the end conditions of the sandwich plate could play an important role in identifying the optimal locations of the MRE pockets. Further, it is observed that the optimal locations of MRE pockets are influenced by the ply drop off and resin locations. Hence it is concluded that the efficient design layout of a partially treated tapered composite MRE sandwich plate configurations would provide the guidelines for the designer to control the vibration effectively.

Buckling Behavior of Non-Uniformly Heated Tapered Laminated Composite Plates with Ply Drop-Off

The thermal buckling characteristics of non-uniformly heated tapered laminated composites plates with ply drop-off have been investigated numerically. Detailed parametric studies have been carried out for the effects of taper configuration, temperature variation, aspect ratio and structural boundary conditions on critical buckling temperatures and buckling mode shapes. It is found that the nature of taper as well as the applied temperature field have considerable effects on the critical buckling temperatures of laminated composite tapered plates. Square plates buckle at the highest temperature when subjected to the decreasing temperature profile. Additionally, it is noted that Taper B and Taper C plates show the best behavior under buckling for most structural boundary conditions. Moreover, the change in buckling mode shapes with respect to temperature profile and taper configuration is significant for rectangular plates in comparison with square plates.

Strength Evaluation of Ply Drop-off Tapered Composites

Strength Evaluation of Ply Drop-off Tapered Composites

Optimum Design of Ply Drop-off Placement for Laminated CompositeOptimum Design of Ply Drop-off Placement for Laminated Composite

Optimum Design of Ply Drop-off Placement for Laminated CompositeOptimum Design of Ply Drop-off Placement for Laminated Composite

Structural design and global sensitivity analysis of the composite B-pillar with ply drop-off

Vehicle lightweight and safety design becomes an increasingly critical issue nowadays. In order to improve the crashworthiness of side impact and roof crush with the consideration of the manufacturing process, a new composite B-pillar structure with ply drop-off is proposed in this paper. It improves the crashworthiness by changing the section thickness of structure and reduces the weight of B-pillar. The ply drop-off regions on the outer part and inner part of B-pillar are divided into three sub-laminates respectively, named as thick panel, taper panel and thin panel. The thickness of the panel are determined by the number of lay-up. Based on traditional sensitivity analysis, this paper derives some new equations and clearly evaluates and quantifies the importance of uncertainty design parameters. Finally, the comprehensive performance of the lightweight and crashworthiness for the composite B-pillar with ply drop-off is improved through structural optimization.

Experimental study of compression after impact of asymmetrically tapered composite laminate

This paper presents an experimental study of CAI (compression after impact) of tapered composite laminate. Two types of layup with thickness changing from 4mm to 6mm are considered. A new CAI testing rig, suitable for the specimens and a brief description of impact damage are presented first. Then, the behavior of impacted specimens under compressive loading is discussed along with the effects of ply drop-off parameters (taper angle, ply drop-off disposition and configuration) and impact point location on the failure mechanism. Finally, the residual strength in CAI of tapered laminates is compared with equivalent flat laminates. The results show that compressive behavior of the specimens is mostly governed by a coupling between compression and bending, generated by the discontinuity of the neutral axis in the tapered region. Despite this difference of behavior with flat laminates, the presence of ply drop-off has little effect on the residual strength in CAI.

Structural optimization of rotating tapered laminated thick composite plates with ply drop-offs

In this study, structural optimization of rotating tapered thick laminated composite plates with ply drop-offs has been investigated numerically. The governing differential equations of motion of the tapered composite plate have been presented including the energy associated with the inertia force, coriolis force, displacement dependent centrifugal force and initial stress resultants due to steady state rotation. Four noded quadrilateral finite element has been formulated based on the first order shear deformation theory. Finite element analysis results are validated with experimental results for natural frequencies of the tapered plate with various configurations. Various cases of optimization problems are formulated with different objective functions in terms of maximization of natural frequencies and damping factors (individually and combined) and solved using genetic algorithm in order to obtain optimal ply sequence and ply orientation. It is shown that the optimization problem with maximization of fundamental modal damping factor without rotating condition yields the optimal layout as 90° for all the layers in the plate. It is also observed that maximization of the fundamental modal damping factor yields identical optimal orientation for uniform and all the configurations of a tapered composite plate.