Numerical analysis of parametric effects on consolidation of angle‐bended composite laminates

In the previous study, the finite element formulation has been developed by our group based on two‐dimensional resin flow and fiber compaction model. Good agreement between simulations and experimental results was found under the one‐dimensional flow condition. In this article, the two‐dimensional model was used to simulate the consolidation of angle‐bended laminates with the convex tool in autoclave process. The effects of material properties on the consolidation were studied. It was found that the fiber bed shear modulus significantly affects the compaction behavior in the corner section of angle‐bended laminate, the fiber bed compaction property decide the laminate deformation, and the resin viscosity and fiber bed permeability affect the rate of laminate compaction and consolidation time. The angle‐bended T700/BMI QY8911‐Ilaminates were manufactured in autoclave process. The experimental data validate the numerical simulation method for the consolidation of the angle‐bended laminates. These results are greatly helpful for the optimization of processing parameters, improvement of composite parts quality, and reduction of the fabrication cost. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Pressure window analysis for thin laminated composites in autoclave process

The curing temperature, pressure, and curing time have significant influence on finished thermosetting composite products. The external pressure and the time of pressure application are two major factors affecting the laminate thickness, fiber volume fraction, and void content. Based on the resin flow/fiber compaction model and corresponding program developed by our group, the genetic algorithm is accepted to design the pressure window for the consolidation of thin laminate. The objective of the optimization is to find the time of pressure application that achieves the desired average fiber volume fraction under given pressure. The pressure windows are analyzed for S‐2 glass fiber/5228 and T700S/5228 laminates with unidirectional and bidirectional lay‐up. It is found that no special viscosity region can be defined as pressure window for many factors affecting the consolidation process. The fiber and lay‐up type largely affect the time of pressure application. For laminates with the same fiber and lay‐up type, the fiber distribution is not much influenced by pressure cycle. The uneven degree of fiber distribution is larger for the fiber bed having higher deformation properties. With the genetic algorithm optimization system, the time of pressure application can be gotten quickly. It is helpful for the improvement of composite parts quality, reduction of the fabrication cost. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

A model for resin flow during composite processing part 2: Numerical analysis for unidirectional graphite/epoxy laminates

In this paper numerical results are presented for resin flow during processing of unidirectional graphite/epoxy laminates. Resin pressure and velocity profiles, as well as resin loss, specific permeability, and resulting thickness changes, were computed to examine the effects of one and two-dimensional flow, initial laminate thickness, and various cure cycles. Input data to the model are also discussed in detail. Analysis of the input data on the stress-strain behavior of graphite fiber beds showed that the bed consolidation behavior can be divided into three regions. “Free-bleeding” (O psig and negligible bleeder resistance to flow at the boundaries) during two-dimensional resin flow leads to rapid decay in resin pressure. Comparison of the predicted results for the resin mass loss and the average final thickness per ply with experimentally determined values shows good agreement.     

Properties of carbon fiber composite laminates fabricated by coresin film infusion process for different prepreg materials

A new cocured process called coresin film infusion (co‐RFI) process, which combines RFI process and prepreg/autoclave process, was introduced and four kinds of commercial carbon fiber prepreg material systems and a kind of resin film were applied to fabricate co‐RFI laminates. The compatibility between the resin film and the prepreg matrix and the application of co‐RFI process were investigated based on the resin flowability, glass transition temperature of cured resin, processing quality of laminate, and variation in resin modulus on cocured interphase region measured by nanoindentation. Furthermore, mode I (G_IC), mode II (G_IIC) delamination fracture toughness, and flexural strength and modulus were measured to evaluate the mechanical properties of cocured laminates with different prepreg materials. The experimental results show that thickness and fiber volume fraction of co‐RFI laminates with the four kinds of prepreg materials are similar to those of prepreg laminates and RFI laminate with acceptable differences. In addition, there are no obvious defects in co‐RFI laminates. Moreover, the reduced modulus of resin at cocured interface and glass transition temperature values of the mixed resin reflect good compatibility between prepreg matrix resin and RFI resin. The G_IC, G_IIC values, and flexural performances of cocured laminates lie between and even exceed those of prepreg laminates and RFI laminates, indicating no weakening effect in the cocured interface. Therefore, the co‐RFI process is believed to effectively fabricate composite with low cost and it can be applied using various prepreg systems. POLYM. COMPOS., 34:2008–2018, 2013. © 2013 Society of Plastics Engineers     

Transmission of ultraviolet light through reinforcement fabrics and its effect on ultraviolet curing of composite laminates

The ultraviolet transmission of various reinforcement textiles was quantified experimentally for the case of incidence of light normal on the fabric plane, and correlated with the curing behavior of laminates incorporating these fabrics. For glass fiber fabrics wetted with polyester resin, light is transmitted through the voids between the fiber bundles and through the fiber bundles. Multiscale modeling of the fabric geometry allows the local transmission to be estimated and the average total transmission to be quantified. The results of curing experiments suggest that the degree of through‐cure achieved after a given cure time is correlated to the fabric transmission. Both are determined by the laminate thickness, the fabric architecture and the fiber volume fraction, i.e., the fiber packing density. While the transmission is reduced by the presence of the reinforcement fabrics, the total resin volume is reduced when compared with that of a resin only sample of the same thickness. A lower radiation dose is sufficient for curing, which partially compensates for the effect of reduced transmission. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Press-forming of continuous-fiber-reinforced thermoplastic composites

Process-induced effects on thermoplastic-based composites were investigated for laminates processed under high production rate conditions. Press-formed carbon-fiber-reinforced poly(ether ether ketone) (PEEK) was used as a model system. The morphology and laminate quality were investigated on unidirectional laminates processed at cooling rates from 0.3 to 120°C/s and annealing of 177°C and 300°C. The laminate quality was examined for degree of consolidation, compaction, and fiber-matrix uniformity. Combined calorimetric and density measurements, as well as micrographic techniques, were used for examination of the laminates. The fracture toughness for the laminate was measured as a function of the position over the thickness of a 40-ply thick unidirectional laminate. This study clearly demonstrates the importance of uniform pressure distribution over the laminate to achieve a void free and homogeneous laminate.     

Structural degradation and mechanical fracture of hybrid fabric reinforced composites

This investigation involves the study of accelerated environmental aging in two polymer composite laminates reinforced by hybrid fabrics based on carbon, Kevlar and glass fibers. Composite laminate configurations are defined as a laminate reinforced with E‐glass fiber and Kevlar 49 fiber hybrid fabric (GK) and another laminate reinforced with E‐glass fiber and AS4 carbon fiber hybrid fabric (GC). Both laminates were impregnated with epoxy vinyl ester thermosetting resin (Derakane 470‐300) consisting of four layers. Morphological studies (photo‐oxidation process and structural degradation) of environmental aging were conducted, in addition to comparative studies of the mechanical properties and fracture characteristics under the action of uniaxial tensile and three‐point bending tests in specimens in the original and aged conditions. With respect to uniaxial tensile tests for both laminates, good mechanical performance and little final damage (small loss of properties) was caused by the aging effect. However, for the three‐point bending tests, for both laminates, the influence of aging was slightly higher for all parameters studied. The low structural deterioration in the laminates is attributed to the high performance with the heat of the matrix (Derakane 470‐300) and the characteristics of the hybrid fabric, exhibiting fiber/matrix interface quality. POLYM. ENG. SCI., 56:657–668, 2016. © 2016 Society of Plastics Engineers     

The comparison of low‐velocity impact resistance of aluminum/carbon and glass fiber metal laminates

This article presents the low‐velocity impact response of fiber metal laminates, based on aluminum with a polymer composite, reinforced with carbon and glass fibers. The influence of fiber orientations as well as analysis of load‐time history, damage area and damage depth in relation to different energy levels is presented and discussed. The obtained results made it possible to determine characteristic points, which may be responsible for particular stages of the laminate structure degradation process: local microcracks and delaminations, leading to a decrease in the stiffness of the laminate, as well as further damage represented by laminate cracks and its perforation. The damage mechanism of fiber metal laminates is rather complex. In case of carbon fiber laminates, a higher tendency to perforation was observed in comparison to laminates containing glass fibers. Delaminations in composite interlayers and at the metal/composite interface constitute a significant damage form of fiber metal laminates resulting from dynamic loads. Fiber metal laminates with glass fibers absorb energy mainly through plastic deformation as well as through delamination initiation and propagation, whereas laminates containing carbon fibers absorb energy for penetration and perforation of the laminate. POLYM. COMPOS. 37:1056–1063, 2016. © 2014 Society of Plastics Engineers     

An asymmetric FRP laminate with a circular precrack to determine impact‐induced damage

An asymmetric laminate is employed to study impact‐induced damage of subpenetration experiments. The configuration of the asymmetric laminate is chosen to have its stiffness characteristics almost identical to those of a symmetric laminate. The impact is made with a mild steel striker to have impact energy close to 12 J and impact velocity close to 50 m/s. A circular precrack is also introduced to facilitate failure on the midplane of a laminate. Due to material discontinuity at the midplane the damage area extension (DAE) of the precrack is found to be 1.83 cm² on asymmetric laminates against 0.73 cm² on symmetric laminates. Impact experiments are also conducted on bonded GFRP specimen with Epibond 1590 A/B adhesive using asymmetric laminates. DAE of adhesive interface is found to be substantially smaller than DAE of interlaminar failure. DAE of adhesive interface is further reduced when the adhesive is modified with 7.5% XNBR. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Interlaminar stresses in tapered laminates

Tapered laminates of unidirectional layers of glass/epoxy and graphite/epoxy are investigated. These laminates have a thickness variation along their length. This was accomplished by having layers dropped off near the midlength of the laminate. Stress and strain variations were obtained using three-dimensional finite element models. Calculated values using the finite element method compare well with experimental results for the point of first delamination. This agreement allows the determination of a suitable finite element mesh for subsequent models of other tapered laminates with fiber orientations other than unidirectional.     

Three‐dimensional anisotropic moisture absorption in quartz‐reinforced bismaleimide laminates

The three‐dimensional anisotropic moisture absorption behavior of quartz‐fiber‐reinforced bismaleimide (BMI) laminates is investigated by collecting 21 months of experimental gravimetric data. Laminates of six, twelve, and forty plies and various planar aspect ratios are used to determine the three‐dimensional anisotropic diffusion behavior when exposed to full immersion in distilled water at 25°C. The long‐term moisture absorption behavior deviates from the widely used Fickian model, but can be accurately captured by the three‐dimensional, anisotropic hindered diffusion model (3D HDM). Excellent agreement is achieved between experimental gravimetric data and the 3D HDM for all laminate thicknesses. Recovered model parameters are shown to slightly vary with laminate thickness due to the small changes in the cured‐ply thickness. However, model parameters identified for a given laminate thickness are observed to accurately predict the absorption behavior of samples with different planar dimensions. Equilibrium moisture content of 1.72, 1.69, and 1.84% and corresponding diffusion hindrance coefficients of 0.807, 0.844, and 0.671 are recovered for six, twelve, and forty‐ply laminates, respectively, thus confirming strong non‐Fickian behavior. Moisture absorption parameters may be determined successfully at 16.5 months of immersion, before reaching approximately 85% of the equilibrium moisture content at 21 months. Subsequent gravimetric measurements up to 21 months are consistent with the predicted long‐term behavior. POLYM. ENG. SCI., 54:137–146, 2014. © 2013 Society of Plastics Engineers     

Open hole flexural and izod impact strength of unidirectional flax yarn reinforced polypropylene composites as a function of laminate lay‐up

An open hole flexural strength and impact energy of flax yarn‐reinforced polypropylene (PP) composites were studied in this work. Highest flexural strength and strength retention were observed for axial (0₆) and cross‐ply (0/90/0)_s laminates, respectively, while also examining the influence of laminate lay‐up and open hole size on flexural strength. It was found that maleic anhydride‐grafted polypropylene (MAPP)‐treated composite laminates achieved marginal improvement on flexural strength for all kinds of laminate lay‐up. Off‐axial laminates (±45₆) showed a good strength retention for open hole laminates after MAPP treatment. The fractography study confirmed microbuckling and matrix crack propagation over the compressive and tensile side of the laminate, respectively. Furthermore, severe surface damage was detected over the tensile side of 8‐mm hole size laminates. Impact test of the flax/PP laminates showed slight improvement by MAPP treatment. High‐ and low‐impact energy was experienced for axial and off‐axial laminates. The damaged impact sample shows evidence of fiber pull‐out for untreated flax yarn reinforced laminates. POLYM. COMPOS., 34:1912–1920, 2013. © 2013 Society of Plastics Engineers     

界面渗透率对厚复合材料层板流动-压实过程影响的数值分析

基于有效应力原理与达西渗流定律,建立了厚复合材料层板流动-压实过程的多场耦合有限元数值模型,通过与厚单向板试验结果的对比,验证了模型的正确性。建立了含界面层的厚正交层合板流动-压实计算模型,分析了垂直于层间界面方向的界面渗透率对正交层合板流动-压实过程的影响。通过与同等厚度单向板的分析结果对比表明,当不同方向铺层层间界面渗透率高时,厚正交层合板的流动-压实过程几乎与相同厚度单向板的流动-压实过程相同。但当层间界面的渗透率低时,会阻碍内部树脂的流动,导致正交层合板内部纤维体积含量提升慢,且越靠近内部,界面渗透率的影响越明显,最终在界面处纤维含量出现明显的跳跃分布。     

Defect reduction strategies for the manufacture of contoured laminates using vacuum BAG‐only prepregs

Complex structures manufactured using low‐pressure vacuum bag‐only (VBO) prepreg processing are more susceptible to defects than flat laminates because of complex compaction conditions present at sharp corners. Consequently, effective defect mitigation strategies are required to produce structural parts. In this study, we investigated the relationships between laminate properties, processing conditions, mold designs, and part quality in order to develop science‐based guidelines for the manufacture of complex parts. Generic laminates consisting of a central corner and two flanges were fabricated in a multipart study that considered variation in corner angle and local curvature radius, the applied pressure during layup and cure, and the prepreg material and laminate thickness. The manufactured parts were analyzed in terms of microstructural fiber bed and resin distribution, thickness variation, and void content. The results indicated that defects observed in corner laminates were influenced by both mold design and processing conditions and those optimal combinations of these factors can mitigate the defects and improve quality. POLYM. COMPOS., 38:2016–2025, 2017. © 2015 Society of Plastics Engineers     

Modeling the effective properties and thermomechanical behavior of SMA‐SMP multifunctional composite laminates

The research work presents the modeling of effective properties and thermo‐mechanical behavior of shape memory fiber (SMF) and shape memory polymer (SMP) composite laminates using micromechanical approaches based on the method of mixtures (MOM) and method of cells (MOC). The fiber is made of a nickel‐titanium (Ni‐Ti) shape memory alloy (SMA), while the matrix consists of a shape memory thermoset epoxy polymer (SMP). The use of an SMP matrix provides large strain compatibility with the SMA fiber, while being active at high temperatures without losing its elastic properties. Additionally, the SMP matrix is also able to produce similar pseudoelastic and shape memory effects, which are noticed in SMAs. In the analysis, a two step homogenization scheme is followed. In the first step the effective properties of each layer are determined via a micromechanics approach with iso‐strain conditions. In the second step the effective properties of the SMF‐SMP composite are computed making a thin plate theory assumption, which takes into account the transverse shear deformations. The possible elastic couplings for SMF‐SMP laminates are discussed, and the laminate force and moment resultants are computed for various laminate configurations. The analysis takes into account the effects of phase transformations and the resulting change in the fiber–matrix modulus. The results have been compared by considering different fiber volume fractions, temperatures, fiber orientations, and lamina stacking sequences. The results show that adaptive SMA‐SMP composites laminates can be developed that provide shape controllability via tunable laminate stiffnesses leading to optimal response. Furthermore, the work presents the necessary framework for a reliable and efficient analysis of SMA‐SMP laminates for practical applications. The theory can be directly used in established plate and shell formulations of finite element analysis. Finally, the variations in force and moment resultants with respect to fiber orientations and stacking sequences are presented, which are useful to study the bending and buckling characteristics of active composites for shape control of adaptive structures. The work concludes that efficient adaptive laminate development for high performance composite applications, exhibiting large shape adaptivity, high stresses, and increased stiffness, are feasible as compared to SMA composites without active matrix. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Effects of quasi‐3D stacking architecture on interlaminar shear strength and void content of FRP

To improve the interlaminar shear strength (ILSS) of composite laminate, three different quasi‐3D stacking architecture (q‐3DSA) laminates were fabricated by using automated fiber placement process and a traditional 2D stacking architecture (2DSA) laminate was fabricated as the control sample. The distribution of voids, the density, and the ILSS of four types of laminates were tested. The results indicated that the void content of the different q‐3DSA laminates was approximately 0.71%–3.07% greater than that of the 2DSA laminate, but the ILSS of q‐3DSA laminates was 5.49%–12.54% better than that of the 2DSA laminate. The microstructure images showed that the cracks spread along the interface between the adjacent layers in the 2DSA laminate, while the cracks cross two or more layers in the q‐3DSA laminates. This behavior indicated that the q‐3DSA improved the ILSS by dispersing the interlaminar load through the bended and interlaced tows in the laminate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41076.     

Effect of surface preparation on electroless Ni‐P plating on carbon fiber‐Reinforced Cyanate Ester Resin Laminate

The effect of surface preparation on electroless Ni‐P plating on carbon fiber reinforced cyanate ester resin laminate has been investigated. Three different surface chemical etching ways were performed, namely: (i) hexanediamine etching, (ii) hexanediamine followed by aniline etching, and (iii) aniline etching. The results indicated that Ni‐P coating on hexanediamine etching or hexanediamine followed by aniline etching pretreated carbon fiber reinforced cyanate ester resin laminates usually tended to be cracked, veined, and low adhesion, while aniline etched laminates showed a homogenous roughing surface which is suitable for subsequently uniform, cellular, and good adhesion Ni‐P plating. POLYM. COMPOS., 37:1161–1166, 2016. © 2014 Society of Plastics Engineers     

Initial Failure Maps for Fibrous CMC Laminates

A simple micromechanics-based procedure is used to evaluate initial failure maps for brittle composite laminates under combined in-plane loads and temperature changes. The maps are derived from local stresses in the fiber, matrix and at their interfaces, and from selected magnitudes of the respective strengths. In a particular loading plane or space, the maps indicate the damage-free load range of the laminate, and the source of likely initial failure by fiber or matrix cracking, or by fiber debonding. An application to Al₂O₃/MoSi₂ laminates with unidirectional and (0/±45)_slayups is presented. In this system, the thermal stresses are very small in the 1200°–20°C range; hence laminate failure is dominated by mechanical loads. Propensity to fiber debonding appears to limit the load magnitudes that can be safely applied to the angle-ply laminate.     

Consolidation and cure simulations for laminated composites

Fiber reinforced polymer composites have been increasingly used in various structural components. One of the important processes for fabricating high performance laminated composites is autoclave assisted prepreg lay-up. Since the quality of laminated composites is largely affected by the cure cycle, selection of the cure cycle for each particular application is important and must be optimized. Thus, some fundamental model of the consolidation and cure processes is necessary to properly select the suitable parameters for each application. This study used the viscoelastic solid model for the consolidation of the laminate. In addition, variations of permeability and thermal properties caused by the change of the fiber volume content during the consolidation process were also included. Simulated thickness variations of epoxy continuous carbon fiber prepreg (AS4/3501-6 from Hercules) laminate under consolidation were compared to the experimental results to test the model. Based on the model analysis, one can predict the pressure, velocity, and laminate thickness during the consolidation process, which can be used to properly select the cure cycle for applications of laminated composites.