Higher-order Single-layer Theory Research Articles

An efficient approach for multilayered beams and wide plates with imperfect interfaces and delaminations

In multilayered systems with interfacial imperfections, such as imperfect bonding of the layers or delaminations, or where the plies are separated by thin interlayers allowing relative motion, the displacement field is highly discontinuous in the thickness, with a characteristic zig-zag pattern and interfacial jumps. Stresses also have large variations, especially for highly deformable interlayers or fully debonded layers. These effects cannot be captured using classical, first- or higher-order single-layer theories. A mechanical model is formulated for the solution of multilayered beams/wide plates with an arbitrary number of imperfect interfaces/delaminations loaded dynamically. The formulation is in the framework of the discrete-layer approach and the interfaces are described through affine traction laws which relate interfacial tractions and relative displacements. Homogenization and variational techniques define novel equilibrium equations depending on only four generalized displacement functions. Comparison with 2D elasticity solutions shows that complex discontinuous fields in thick, highly-anisotropic plates with an arbitrary number of sliding-interfaces are accurately predicted. The approach extends the range of problems which can be solved analytically compared to discrete-layer models where the unknowns depend on the number of layers/interfaces. The affine traction laws describe arbitrary branches of piecewise linear functions approximating nonlinear traction laws to represent different interfacial mechanisms.

Three-dimensional nonlinear analyses of scarf repair in composite laminates and sandwich panels

A special-purpose analysis tool based on the finite element method is presented for parametric design studies of composite laminates and sandwich panels with scarf repairs. This design tool provides the complete three-dimensional stress and strain fields in scarf-repaired panels without any requirements on the nature of the lamination and the type of loading. The adherends are modeled using a plate element based on a higher-order single-layer theory, and the adhesive is modeled using a solid element. The higher-order nature of the plate theory makes it suitable for analyzing thick laminates and sandwich panels comprised of numerous plies. The model takes into account geometric nonlinearity in the adherends and assumes a bilinear stress-strain relationship for the adhesive. The responses of composite laminates with single- and double-sided repairs and sandwich panels with both full and partial repairs of the top face sheets are investigated.

Residual strength of sandwich panels with hail damage

Hail strikes, possibly exceeding an energy level of 50 J, may cause damage to thin-gauged composite airplane structures in the form of an indentation or puncture of the top facesheet. If not repaired properly, they may trigger extensive damage to airplane structures and disruptions to airline operations, therefore posing a major maintenance and repair concern for the airlines. It is important that both the original equipment manufacturer and the airlines be able to classify the hail strike damage in order to establish appropriate repair procedures. This study presents a methodology to assist engineers in the classification of the repair type for hail strike damage through the determination of allowable damage size. The methodology involves an accurate prediction of stress and strain fields and residual strength prediction. The stress analysis is performed by utilizing a plate element based on a higher-order single-layer theory. The damage zone model, previously used for notched panels, has been employed to predict the residual strength of sandwich panels with indented facesheets subjected to tensile load. The failure load is established when crack propagation in the facesheet becomes unstable.