For the first time, an experimental investigation is presented quantifying out-of-plane wrinkle formation and in-plane deformations occurring in prepreg slit tape specimens during automated fiber placement (AFP). The AFP process is conducted on 6.35 mm wide individual prepreg tows that are placed along a straight path and steered along circular paths with radii of curvature, ρ = 2540 mm, 1270 mm and 305 mm. Full-field shape, displacement and strain measurements are obtained using StereoDIC in three successive stages; (i) immediately after lay-up of the tow, (ii) one hour after lay-up and (iii) after reheating of the as-placed tow by traversing the AFP head close to the tow path and exposing the specimen to the same levels of heating as employed during the initial lay-up (without compaction pressure). Measurements obtained in stage (i) showed that (a) all tows exhibited local wrinkling at locations where the underlying substrate had defects (e.g., gaps, overlaps), (b) excluding the substrate defect locations, tows steered with ρ = 2540 mm showed no evidence of additional out-of-plane wrinkling after placement, (c) tows steered with ρ = 1270 mm exhibited several small amplitude wrinkles initiated at locations outside the substrate overlap regions and (d) tows steered with ρ = 305 mm incurred significant additional localized wrinkling along the inner radius of the tow with an increase in both the amplitude and frequency of the wrinkles. In addition, higher variability in the wrinkle wavelength is observed for ρ = 305 mm. Measurements obtained in stages (ii) and (iii) showed an increase in wrinkle amplitude, indicating that wrinkle amplitude is a function of both time and temperature for an as-placed tow.

Experimental investigation of prepreg slit tape wrinkling during automated fiber placement process using StereoDIC

This work presents a refined beam model based on the Carrera Unified Formulation for the free-vibration analyses of variable stiffness composite laminate characterized by layers with curvilinear fibers. These models introduce a refined kinematic description over the cross-section to obtain a 3D displacement field. Taylor and Lagrange polynomials have been used to describe the cross-sectional variables that is, equivalent single layer and layer-wise approaches have been considered. Variable stiffness composite materials have been introduced considering a continuous variation of the lamination angle thanks to an ad hoc integration scheme. Extensive validation of the models has been performed including convergence analyses and comparisons with commercial codes. The results obtained using the present models have been compared with those from open literature considering composites with different values of thickness, lamination, and boundary conditions. The results show that the use of refined models is mandatory for the analysis of such structures where complex laminations may create strong mechanical couplings.

Analysis of variable angle tow composites structures using variable kinematic models

Free vibration analysis of variable angle-tow composite wing structures

Energy absorption and vibration of smart auxetic FG porous curved conical panels resting on the frictional viscoelastic torsional substrate

The free vibration characteristics of the variable stiffness composite laminated plates containing embedded cutout of desired shapes is investigated. The circular, elliptical and quadrilateral perforation geometries are taken into account. In order to provide a strongly flexible calculation tool, an isogeometric analysis formulation based on the non-uniform rational B-splines (NURBS) along with the Nitsche technique is developed based on the first order shear deformation plate theory. The effects of change in the mechanical properties of tow steered laminates throughout the geometry due to fibers following prescribed curvilinear paths are taken into account in the integration procedures. The accuracy and reliability of the calculations is shown through some representative comparisons. The effects of change in the cutout geometry, location and orientation in conjunction with the curvilinear fiber placement are studied.

Xiaodong Chen

Papers

Buckling analysis of variable angle tow composite plates with a through-the-width or an embedded rectangular delamination

Application of rayleigh-Ritz formulation to thermomechanical buckling of variable angle tow composite plates with general in-plane boundary constraint

Dynamic instability of variable angle tow composite plateswith delamination

Prebuckling and buckling analysis of moderately thick variable angle tow composite plates considering the extension-shear coupling

Nonlinear thermal flutter analysis of variable angle tow composite curved panels in supersonic airflow