A Review on the Mechanical Modeling of Composite Manufacturing Processes

© 2016, The Author(s). The increased usage of fiber reinforced polymer composites in load bearing applications requires a detailed understanding of the process induced residual stresses and their effect on the shape distortions. This is utmost necessary in order to have more reliable composite manufacturing since the residual stresses alter the internal stress level of the composite part during the service life and the residual shape distortions may lead to not meeting the desired geometrical tolerances. The occurrence of residual stresses during the manufacturing process inherently contains diverse interactions between the involved physical phenomena mainly related to material flow, heat transfer and polymerization or crystallization. Development of numerical process models is required for virtual design and optimization of the composite manufacturing process which avoids the expensive trial-and-error based approaches. The process models as well as applications focusing on the prediction of residual stresses and shape distortions taking place in composite manufacturing are discussed in this study. The applications on both thermoset and thermoplastic based composites are reviewed in detail

Buckling optimisation of sandwich cylindrical panels

In this paper, the buckling load optimisation is performed on sandwich cylindrical panels. A finite element program is developed in MATLAB to solve the governing differential equations of the global buckling of the structure. In order to find the optimal solution, the genetic algorithm Toolbox in MATLAB is implemented. Verifications are made for both the buckling finite element code and also the results from the genetic algorithm by comparisons to the results available in literature. Sandwich cylindrical panels are optimised for the buckling strength with isotropic or orthotropic cores with different boundary conditions. Results are presented in terms of stacking sequence of fibers in the face sheets and core to face sheet thickness ratio

Distortions and Residual Stresses of GLARE Induced by Manufacturing

GLARE is used in fuselage panels for its improved fatigue and residual strength. In this thesis, predictive models are developed for residual stresses and distortions of GLARE induced by manufacturing. Material behaviour of the epoxy adhesive and the glass-epoxy prepreg is characterised for thermal and curing circumstances. The derived temperature dependent viscoelastic properties can also be used in other applications in which time and/or temperature changes are of concern. The results of this research are important for three main reasons: first, the material thermo-viscoelastic response is derived for the first time and the thermal properties differ from the ones already used in literature for the design of panels made of GLARE. Second, two new models are developed, applicable to any orthotropic material including Fibre Metal Laminates, for cure and thermo-viscoelastic analyses. Third, the predicted residual stresses can improve the design where properties like fatigue and residual strength need to be considered. With the developed models, other effects like cutting, bonding doublers and stringers can be simulated to obtain the results for a completely featured fuselage panel made of GLARE.Aerospace Structures and MaterialsAerospace Engineerin

A geometrically nonlinear structural model for aerostructural optimization of ultra-high aspect ratio composite wings

This paper presents the development of a coupled-adjoint aerostructural optimizati on tool for strut-braced Ultra High Aspect Ratio (UHAR) wings made of composite materials . The formulation of the structure model is based on thin to moderately thick composi te wings with special considerations applicable to the large deformations of the flexible UHAR wings with small strains. Transverse shear deformations and moderate twist angles are considered, making the model novel for the preliminary design of such structures. The finite element model has been validated based on available data in the literature. The coupled aerostructural analysis and the coupled-adjoint sensitivity analysis have been verified based on the cantilever wing design of A320 like aircraft. Then, the tool has been applied to optimize a strut-braced with a high aspect ratio.</p

A large displacement orthotropic viscoelastic model for manufacturing-induced distortions in Fibre Metal Laminates

Distortions and residual stresses are predicted in Fibre Metal Laminates (FMLs) under large deformations. A new modelling procedure is presented for small and large deformation analysis of thermo-viscoelastic problems of orthotropic materials. The material model is implemented in a finite element package which can be used for cure and/or temperature dependent response of composites undergoing large rotations but with small strains.Temperature-dependent and viscoelastic responses are characterised for GLARE, as the mostly used type of FMLs. The geometrically nonlinear thermo-viscoelastic model is used to predict the manufacturing-induced warpage of panels. The curing stresses are calculated from a previously developed model accounting for chemical shrinkage and stiffness evolution of the prepreg layers during cure. The shape deviation of some non-symmetric GLARE panels are predicted and compared to the real measurement of fabricated laminates. The accuracy of the model is verified which can be used in further studies to improve the precision of manufacturing and assembly and also to have better prediction of the fatigue life and residual strength.Structural Integrity & CompositesAerospace Structures & Material

Novel thermomechanical characterization for shrinkage evolution of unidirectional semi-crystalline thermoplastic prepregs (PPS/CF) in melt, rubbery and glassy states

Shrinkages, distortions and high residual stresses in the thermoplastic composite parts are induced due to high processing temperature, anisotropy, and fiber–matrix shrinkage mismatch. In this paper the shrinkages have been investigated experimentally and modeled by thermo-mechanical constitutive equations for PolyPhenylene Sulfide (PPS) and the unidirectional Carbon Fiber (PPS/CF) composite prepreg. The thermal shrinkage and the crystallization shrinkage were retrieved from Thermal Mechanical Analysis and compared to a Pressure specific volume Temperature diagram. To describe the crystallization shrinkage in the cooling process accurately, the crystallization kinetics of PPS was evaluated using Differential Scanning Calorimetry. The temperature-dependent elastic modulus was measured by a shear rheometer to formulate a new constitutive model. The mathematical model for shrinkage was validated by a press consolidated [0]12 laminate and unbalanced laminates in four lay-ups. The thermo-mechanical model results presented here provide significant rules for the thermomechanical and shrinkage predictions for the industrial applications of thermoplastic composite.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aerospace Manufacturing Technologie

Prediction models for distortions and residual stresses in thermoset polymer laminates: An overview

This paper reviews predictive models developed for the development of residual stresses and shape distortions during the manufacturing of thermoset polymeric/composite materials. Different sources that produce residual stresses and shape changes in the laminated panels are described and reviewed. An overview is presented on the characterisation and predictions of the phenomena resulting in residual stresses. The focus will be on the models accounting for the parameters during the cure cycle of the thermoset composite materials published in the literature from 2005 until 2018. The material types covered here range from thermoset adhesives, full composites, and fibre metal laminates. Furthermore, selected works are reviewed on the reduction of the shape changes and residual stresses of composites and fibre metal laminates consisting of thermoset polymers.Structural Integrity & CompositesAerospace Manufacturing Technologie

Effect of prepreg gaps and overlaps on mechanical properties of fibre metal laminates

During the automated manufacturing of fibre reinforced laminates, defects can be produced. Gaps and overlaps between adjacent prepreg layers can be produced in composites during the tape-layup process. However, the topic is not yet studied for hybrid materials, in which metal sheets and thin prepreg layers lead to different effects due to the defects than in full composites. Here, the effect of gaps and overlaps on the mechanical properties of the Fibre metal laminates (FML) is evaluated. Specimens are manufactured with a specified width of gaps/overlaps and the mechanical performance of the panels is evaluated by some selected mechanical tests. Gaps show to have a considerable effect on the mechanical performance of FML. Compression strength of samples with overlaps was rather increased. Discussions are presented on the influence on each mechanical property according to the severity of the defect (gaps/overlap) and the failure mode(s) under consideration.Structural Integrity & Composite