Curing Deformation Research Articles

An improved approach to compensating for cure‐induced deformation to manufacture composite aircraft skin accurately

AbstractThe purpose of this paper is to compensate for the cure‐induced deformation to manufacture composite aircraft skin with variable curvature accurately. Firstly, a finite element analysis (FEA) method appropriate for curing simulation was described. Then, the discrete curvature‐based displacement adjustment (DC‐DA) method for mold surface compensation was proposed. The DC‐DA method utilizes the discrete curvature of the section points to obtain a smooth compensated curve. Finally, a skin part was selected to prove its effectiveness. The experimental results showed that after the mold's surface was modified by the DC‐DA method with the FEA‐predicting deformation as input, the forming shape could meet the requirement of the part accuracy in one cycle. The DC‐DA method was also compared with the displacement adjustment (DA) method and proved to be more efficient for the compensation of composite skin with variable curvature.Highlights The FEA is appropriate for the calculation of the skin's curing deformation. The DC‐DA method is efficient for compensating for the skin's deformation. The shape of the case part could meet the requirement of accuracy in one cycle.

Analysis of curing deformation for resin matrix composite T-shaped stiffened panel

In this work, a multi-field coupled finite element simulation method involving thermochemistry and mechanics was devised to predict the curing deformation (C-DE) of a T-shaped stiffened panel (T-SSPL), a typical aircraft structural component, during the autoclave forming process. A more comprehensive and detailed analysis of the factors affecting the C-DE of T-SSPL is also carried out. The methodology uses the Fortran language to write different user subroutines and establish corresponding mathematical models to simulate the different mechanical states of components, and ultimately simulate the entire molding process of the product in the autoclave. And investigates the effects of process parameters, including heating rate, cooling rate, curing pressure, and structural parameters, including the number of bars and height of stringer on the C-DE of T-SSPL, and obtains the following conclusions: the heating rate and curing pressure are positively correlated with the C-DE, and the cooling rate has little influence on the C-DE, and C-DE hardly changes with the change of cooling rate; C-DE increases with the ribs count; however, it decreases and then increases with the stringer height, and these conclusions provides a theoretical basis for the manufacturing of T-SSPL.

Experimental and numerical analysis of new thermoplastic composite mandrels

In the field of aerospace, the application of carbon fiber composite parts is increasing year by year. As an important factor in the manufacturing of composite parts, tools play a crucial role in the manufacturing accuracy of composite parts, and composite tools have higher accuracy to better meet the manufacturing requirements. In this study, the properties of the novel thermoplastic composite mandrel of the new polymethyl methacrylate matrix are further investigated and a model is proposed to simulate the curing and spring back process of the composite part with the proposed composite mandrel. In detail, the glass transition temperature test and dynamic frequency test were carried out for the thermoplastic composite mandrel. The material constitutive equation of the thermoplastic composite mandrel was constructed based on the experimental data, and the accuracy of the constitutive equation of thermoplastic matrix material was verified by tensile experiments of matrix materials under constant strain conditions. Finally, the simulation result is compared with the fabricated part, and the effectiveness of the proposed method has been verified. This proved that the developed constitutive model of thermoplastic composite mandrel can effectively predict the curing deformation of composite parts with complex structures.

Effect of layup sequence on cure deformation and accurate prediction of composite pressure vessels

The application of composite winding pressure vessels is becoming more and more widespread, and the magnitude of deformation during curing can have a significant impact on service performance, but there are fewer studies on the accurate prediction of the numerical and experimental validation of the deformation during the curing process of pressure vessels. To accurately predict the effect of different angles of layup on the curing deformation of high-pressure hydrogen storage vessels made of T700S-12 K/4251A4B2 carbon fiber/epoxy composites in cylindrical and dome sections. In this paper, WCM-ABAQUS segmented pressure vessel accurate modeling method is proposed for the first time, using the method of converting the chemical shrinkage coefficient of epoxy resin into thermal expansion coefficient equivalently, the finite element prediction of the deformation of the pressure vessel during the curing process in different layup sequences was carried out, and the deformation values of the pressure vessel in different layup sequences were analyzed comparatively. Finally, the winding curing experiments were carried out on pressure vessels with different layup sequences, and the curing deformation values of the experimental tests on pressure vessels with different layup sequences were compared with the finite element simulation values, respectively, and the minimum error value 13.07%. It provides a reliable basis for accurately predicting the deformation value of the pressure vessel curing process, and also provides a reference for subsequent experiments to reduce the curing deformation value.

A novel active hydroforming & curing process to manufacture GLARE laminates: Numerical and experimental investigations

Fiber Metal Laminates (FMLs) are preferable thin-walled structures in several fields for their exceptional mechanical properties. However, how to manufacture thin-walled FMLs structures with complex shapes and guarantee the high mechanical properties is still a challenge. To address these, this paper proposes an innovative hybrid forming method, referred to as active warm hydroforming and curing, to enhance the formability and performance of FMLs in GLARE form by combining the forming and curing process into a single step. The hybrid method was verified on a box-shaped part as a proof-of-concept to assess the feasibility and parameter influence. Online curing was utilized to enhance efficiency and quality. The outcomes revealed that the new method increases the ultimate tensile stress by 12.1 % and reduces curing deformation from 3.1 mm to 1.3 mm compared to the vacuum bagging method. Furthermore, the critical parameters in forming of thin-walled structures, including blank holder force (BHF), pressure rate (PR), maximum pressure (MP), and forming temperature (FT), were identified using experimental, mathematical, and numerical approaches. Four defects in the formed thin-walled structures were observed and successfully eliminated through the control of these parameters. The method and results presented in this paper also provide direct guidance for optimizing the process parameters of FMLs warm hydroforming.

Effect of mold on curing deformation of resin transfer molding‐made textile composites

AbstractIn the process of preparing textile composites by resin transfer molding (RTM) method, both the upper and lower surface of the mold will interact with the composite parts due to the mismatch of thermal expansion coefficient between the mold and the part, resulting in warpage deformation. To address this key technical problem, this article first studied the effect of mold on the warpage deformation of composite material under different fiber volume fractions. Then a mold–part interaction modeling method for RTM process with nonthermoelastic deformation is proposed. By introducing shear layers between the upper and lower surfaces of the mold and the composite part, a finite element simulation model for predicting the curing deformation of the component is established and experimentally verified. The results show that the effect of mold–part interaction on the warpage deformation of the composite decreases with increasing fiber volume fraction. Meanwhile, the proposed modeling method can avoid complete material characterization, and the comparison between experimental and simulation results proves that the model can accurately simulate the curing deformation of composite components under the same process conditions. Finally, the analysis reveals that the interaction caused by thermal mismatch between the composites and the mold is less related to the intermediate layup, but mainly related to the fiber orientation of the layup layer in contact with the mold.Highlights The warpage deformation law of the mold on the composites with different fiber volume fractions is investigated. A mold–part interaction modeling method for a resin transfer molding process with nonthermoelastic deformation is proposed, where the mold stretching effect is represented by the cumulative effect of the interaction between the two layers on the upper and lower surfaces of the part.

Experimental and numerical investigation of stringer’s 90° plies optimization of composite material stiffened panels

In this paper, the optimal design of I- and T-shaped stringer’s 90° plies is investigated to improve the performance of composite stiffened panel’s strength and curing deformation. A theoretical method is deduced to build the constitutive equations of curing and buckling, which indicates that the stringer’s 90° plies play an important role in the curing deformation of the structure. The finite element method (FEM) is adopted to simulate the curing and instability path of the structure, and the simulation model’s accuracy is verified by strain assurance criterion. In addition, the experimental analysis is performed by a series of I- and T-shaped specimens with different stringer’s 90° plies. The good agreement between the results of theoretical method, FEM, and experiment confirms the reliability and feasibility of the analytical methods proposed in this paper. Furthermore, the optimal stringer’s 90° plies ratio is explored. The curves fitted in this investigation reveal that in the stages of (I) and (II), the percentage of stringer’s 90° plies θ has significant effect on curing deformation, while bearing capacity has little change. The reasonable range of θ is 5%∼20%, in which the bearing capacity and curing deformation reach the optimal solution. Therefore, the structures that are not sensitive to curing deformation are recommend to remove the stringer’s 90° plies, which is benefit to reduce weight, optimize structural design and improve process quality. The results provide a reference to design I-, T-, L- and C- shaped composite panel.

Study on Curing Deformation of Composite Thin Shells Prepared by M-CRTM with Adjustable Injection Gap.

A composite thin shell with a high fiber volume fraction prepared by resin transfer molding (RTM) may have void defects, which create deformations in the final curing and lead to the final product being unable to meet the actual assembly requirements. Taking a helmet shell as an example, a multi-directional compression RTM (M-CRTM) method with an adjustable injection gap is proposed according to the shape of the thin shell. This method can increase the injection gap to reduce the fiber volume fraction during the injection process, making it easier for the resin to penetrate the reinforcement and for air bubbles to exit the mold. X-ray CT detection shows that the porosity of the helmet shell prepared by the newly developed technology is 36.6% lower than that of the RTM-molded sample. The void's distribution is more uniform, and its size is decreased, as is the number of voids, especially large voids. The results show that the maximum curing deformation of the M-CRTM-molded helmet shell is reduced by 13.7% compared to the RTM molded sample. This paper then further studies the deformation types of the shell and analyzes the causes of such results, which plays an important role in promoting the application of composite thin shells.

Prediction of the Temperature of Large Framed Mold and Curing Deformation of Composite Components in the Autoclave Process

The temperature uniformity and thermal deformation of the tool in the autoclave forming process have an important influence on the forming quality of the composite components. In this paper, the prediction methods of the temperature distribution of the tool and the curing deformation of composite components in the autoclave forming process were developed. Using Ansys CFX fluid analysis technology, the temperature field of a large framed tool in the autoclave process was simulated, and the distribution of the surface temperature of the large framed tool was obtained. The calculated temperature field was then applied in the cure-induced deformation simulation of composite components. The thermo-chemical-mechanical coupling analysis was conducted to simulate the curing deformation of the composite components, and the numerical results were verified by practical engineering application.

Influence of variable‐stiffness layup configuration on curing deformation of curved‐surface structures

AbstractAccurate prediction the curing‐induced deformation is the key to the fabrication of high‐quality composite structures. Aiming at controlling shape distortion of curved‐surface parts during curing process, a layup optimization strategy is proposed based on a variable stiffness (VS) placement method, which uses geodesic curves as fiber‐tow paths. Taking an offset parabolic antenna reflector (PAR) for example, chemical shrinkage and thermal deformation of curved‐surface composites during the curing process and after demolding are modeled. By combining Fourier heat conduction theory, curing kinetics, and generalized Maxwell viscoelastic model, the interactions between chemical cross‐link reaction, heat transfer, and mechanical deformation are taken into account. By comparing the deformation characteristics of VS and traditional constant stiffness structures, the proposed simulation strategy of curing process for composites can predict the factors that influence the curing deformation of VS structures are analyzed. The results show that the maximum of VS PAR decreases by 11.02%, and the average magnitude decreases by 32.35%.

Study of Critical Material Parameters for Curing Deformation of Aerospace Wing Composites before Numerical Simulation

Because of the advantages of lightweight and high-strength integrated molding of composite materials at low cost, thus, large-scale carbon fiber composite structures are widely used in aerospace applications. However, the curing deformation of large-scale composite structures will produce a certain shape deviation, which cannot meet the needs of the installation. If forced assembly will form large installation stress, which will seriously jeopardize the mechanical properties and lifetime of the composite parts. Therefore, it is being studied to control the curing deformation of largescale composite structures, which is important to ensure the quality of the structure, reduce the cost and improve the service life of the structure. The traditional composite parts development model requires large-scale sample testing, uncontrollable manufacturing quality, low efficiency, and other problems. In particular, the curing and molding process involves the intersection of several disciplines such as thermal, chemical and mechanics, so it is increasingly important to study the curing deformation of large-scale composite structures to improve R&D efficiency, control quality, and reduce cost.

An Analytical Model for Cure-Induced Deformation of Composite Laminates.

Curing deformation prediction plays an important role in guiding the tools, curing process design, etc. Analytical methods can provide a rapid prediction and in-depth understanding of the curing deformation mechanism. In this paper, an analytical model is presented to study the cure-induced deformation of composite laminates. Based on the classical laminate theory, the thermal stress and deformation of composites during the curing process are calculated by considering the evolution of the mechanical properties of resin. Additionally, the coupling stiffness of the laminate is taken into consideration in the analytical model. An interface layer between the tool and the part is developed to simulate the variation of the tool–part interaction with the degree of resin cure. The maximum curing deformations and deformation profiles of different lay-up composite parts predicted by the proposed model are compared with the results of the finite element method and previous literature reports. Then, a comprehensive parametric study is carried out to investigate the influence of curing cycle, geometry, tool thermal expansion, and resin characteristics on the curing deformation of composite parts. The results reveal that geometry has a significant influence on the curing deformation of composite parts, but for dimensionally determined parts, curing deformation is mainly attributable to their own anisotropy in macro and micro aspects, as well as the stretching effect of the tool on the part. The percentage contribution of different factors to curing deformation composites with different lay-ups and geometries is also discussed.

Multi-Objective Optimization of Curing Profile for Autoclave Processed Composites: Simultaneous Control of Curing Time and Process-Induced Defects.

The contribution of this work is introducing a multi-objective optimization method based on finite element (FE) numerical simulation to simultaneously control the curing time and cure-induced defects of C-shaped composites during a curing cycle. Thermochemical and thermomechanical coupled analysis is performed and validated experimentally to understand the evolution details of temperature, degree of cure and curing deformation. Aiming to achieve the simultaneous control of manufacturing cost and composite quality, the curing profile is optimized by employing the critical factors including the total curing time, the maximum degree of cure difference, and the curing deformation. The optimization result shows that the designed curing profile can effectively reduce the curing time and guarantee the curing quality. The total curing time of the optimization is reduced by 19%. The verification experiment is also conducted to prove the accuracy and effectiveness of the proposed optimization method.

Simulation Prediction and Forming Quality Control of Hemming Structure with Dissimilar Materials Oriented to Process Chain

Multi-material mixed-use has become an important way to realize autobody lightweight. However, due to the difference of material properties, the structure is prone to material mismatch when using thin and dissimilar materials. In this paper, a deformation compensation method oriented to the process chain is proposed to eliminate the quality defects. Based on the simulation and prediction of the process chain, the final deformation is advanced to the spreading preparation stage to realize the geometric pre-compensation of the structure. Firstly, in the spreading and hemming stage, the prediction of hemming with adhesive was realized by establishing SPH (Smoothed particle method)-FEM (Finite element method) coupling model. Then, a coupled thermal-chemical-structural model is established to predict the curing deformation. Finally, the deformed dimension is fed back to the spreading stage to achieve the deformation compensation. The results show that the multi-field coupling model can achieve accurate prediction, and the structural deformation is reduced to more than 95%. This provides a basis for material matching and optimization of the whole process chain.

Numerical simulations and optimization of foam filled free-curved surface composite part

The purpose of this study is to predict the curing deformation of a foam-filled free-curved surface composite part and reduce the occurrence of curing deformation through process optimization. This research introduces a finite element simulation method and an optimization method for forming parameters for a foam-filled free-curved surface composite part. Meanwhile, sample manufacturing experiments and a comparative analysis between the simulation and actual objects were conducted. The results showed that finite element simulation analysis could effectively predict the curing deformation of the composite part. After the optimization simulation analysis of the molding process parameters, it was found that the curing deformation of the foam-filled free-curved surface composite part could be as small as 2.30 mm.

Review of curing deformation control methods for carbon fiber reinforced resin composites

AbstractUnder the influence of extrinsic curing conditions and intrinsic properties of carbon fiber reinforced resin composites, the formation of curing deformation is inevitable, which makes the shape of the manufactured components differ from the designed structure, and even exceeds the assembly tolerance, resulting in the scrap of parts. Therefore, it is very urgent and important to optimize the curing deformation of carbon fiber reinforced resin composites. In this paper, the mechanism of stress and curing deformation is reviewed firstly, and then the factors affecting the curing deformation are summarized. In particular, from the point of view of materials in curing process, three curing deformation control strategies, including (i) reinforcement structure optimization, (ii) resin modification and process optimization, (iii) die surface compensation and tool‐part contact optimization, were proposed. And with the development of curing deformation simulation technology, the (iv) inverse design strategy before curing and (v) hot sizing method from the view of after cured were further put forward, respectively. By analyzing the link between processing details and curing deformation, it is found that the dominant factor affecting deformation may change under different conditions, so the interaction between factors needs to be further discussed. Subsequently, the effect of these distortion control methods on curing deformation was analyzed and evaluated, and the shortcomings were pointed out. Finally, the challenges existed in curing deformation research were identified, in order to contribute to the development of curing deformation research.

An alternative method to reduce process-induced deformation of CFRP by introducing prestresses

Process-induced deformation is an important limiting factor to the application of high performance composite structures. An alternative method to reduce process-induced deformation is proposed by introducing prestress to a single layer or part of the layers instead of all the applicable layers. In this method, the necessary prestress level that applied to the single layer was in the reasonable range. Two kinds of unsymmetric laminates are manufactured at varying prestress levels. The experimental results described that the curing deformation is changed rapidly with the growing prestress level and flipped after a certain prestress level. Moreover, there is a good linear relationship between prestress level and final curing deformation, which gives a convenient way to calculate the prestress level that can fully counteract the curing deformation. The numerical model to predict the curing deformation was built. A good agreement between the numerical and the experimental results shows the effectiveness of the numerical model. To predict the prestress level that can fully counteract the curing deformation, an analytical model is also proposed. Theoretically, the prestress method can fully counteract the curing deformation of the specimens, while the experimental results show that the prestressing layer reduces more than 80% of the curing deformation.

The effect of curing deformation on the vibration behavior of laminated composite beams

In this paper, the effect of curing deformation on the vibration behavior of a laminated composite beam is studied. The analysis model of the vibration of the laminated composite beam with arbitrary boundary conditions considering the curing deformation is established based on the first-order shear deformation theory. Curing deformation is considered as one kind of geometric imperfections and introduced into the analysis model. The geometric imperfection model in the form of parabolic functions is developed to describe the curing deformation in which curing temperature, ply stacking sequence, and tool-part interaction are taken into account. The Rayleigh-Ritz method is used to obtain the natural frequencies of the laminated composite beam considering curing deformation. The results reveal that the initial curing deformation has a great influence on the vibration behavior of laminated composite beam. Due to the existence of curing deformation, the first order natural frequencies of laminated composite beam with clamped–clamped (C–C) boundary condition have increased. The influences of the ply stacking sequence, the curing temperature, boundary conditions and the tool-part interaction on the free vibration behavior of the laminated beam are discussed.

Research on energy conservation and emission reduction technology of free-form surface thermosetting forming composites

Thermosetting composites will produce spring-back deformation after curing, and the mold is the key factor affecting the curing of components. In this paper, the solidification and spring-back deformation process of free-form surface composite parts are simulated by finite element simulation. By comparing the deformation of components under invar steel mold, 304 stainless steel mold and composite mold, the influence of thermal expansion coefficient, mold structure and molding process on the curing deformation of composite materials was analyzed, and the optimal molding scheme of free-form surface composite parts was obtained.

Simulation analysis of deformation spring-back of free-form surface composite with cellular foam filling

Due to the complex thermo-chemical-mechanical coupling during the curing and forming process of composite materials, spring-back is commonly observed after forming, which makes the shape of parts after curing and forming deviate from the design shape, resulting in difficult or even impossible assembly. In order to reduce the influence of the spring-back deformation on the forming, the finite element analysis software was used to analyze the curing deformation of the free-form composite part with foam filling, and the numerical simulation and analysis of the curing deformation of the complex curved parts were realized. The simulation analysis involves warping deformation under different angles and radii, which breaks through the unitary shape of previous research objects. In addition, the effect of foam on skin is also considered in the simulation process, and it is found that the shrinkage of the foam will affect the spring-back deformation of parts. Through finite element software, the spring-back simulation of multi-surface composite material after curing was carried out, and the results were compared with those obtained by digital measurement, the comparative analysis shows the effectiveness of the curing deformation prediction model in this paper.