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

Abstract

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.

Optimisation study of tapered scarf and stepped-lap joints in composite repair patches

“…Although tapered scarf joint failure predictions based on 2D models can be consistent with 3D applications, the application of 2D design methodology can result in overly conservative design guidelines and lead to excessive material removal [8,9], particularly when investigating compressive loading cases. Analysis methods used by engineers to assess joint design can be analytical [10][11][12] or based on a finite element (FE) modelling approach [13][14][15]. Several certification frameworks for composite repairs have also been proposed [16][17][18].…”

Strength improvement of adhesively-bonded scarf repairs in aluminium structures with external reinforcements

“…The optimisation of stresses is a higher strength for the same bond area than strap repairs [9], which renders scarf repairs more suited to critical applications. The substantial or full strength recovery achieved by this method, provided that the repair is correctly designed, usually makes scarf repairs as permanent [10,11]. Thus, in high responsibility structures requiring a full or significant strength recovery, or when a flush surface is imposed by aerodynamic or stealth reasons, an adhesively-bonded scarf repair is often used.…”

“…However, it should be noted that small scarf angles, necessary to obtain higher efficiencies, may not be applicable since they require a larger repair area [8]. The scarf repair technique has become particularly important in the last decades, due to the increasing use of sandwich panels in aircraft structures [10].…”

Numerical evaluation of three-dimensional scarf repairs in carbon-epoxy structures

“…The outcome of the optimization of stresses is a higher strength for the same bond area than strap repairs [24], which renders scarf repairs more suited to critical applications [25]. The substantial or full strength recovery achieved by this method, provided that the repair is correctly designed, usually makes scarf repairs as permanent [26][27][28][29]. Conversely to strap techniques, scarf repairs are also flush with the damaged structure, which is an important advantage since aerodynamic disturbance is prevented and stealth characteristics (if relevant) are not compromised.…”

“…In specific cases, a flush surface may be imposed to avoid interference between components. The scarf repair technique has become particularly important in the last decades, due to the increasing use of sandwich panels in aircraft structures [28,30].…”