Study of Stress-Strain Behavior of the Laminated Plate Damaged by Delamination

Abstract

The process of manufacturing of the structures of polymeric composite materials is accompanied by various technological defects. Delamination defects have the greatest impact on the bearing capacity of the composite structures. The method for assessment of the stress-strain behavior of a panel structure made of polymeric composite materials, which is damaged by delamination, has been developed. This method allows determining the degree of stress concentration in the area of step change in thickness and identifying the most dangerous point where the structural failure may start. In contrast to the classical theory of laminated plates, the proposed model gives an opportunity to simplify three-dimensional problem by setting the displacement field on the interfaces of layers and their linear interpolation over the plate thickness, taking into account the transverse shear deformation. Stress-strain behavior of the plate with delamination was determined according to the computational model of the plate with a cut for the case when the layers in the defect area cannot take up the applied load. According to the results obtained, distribution of stresses over the plate thickness changes significantly in the area of step transition to the delamination and near it. At the distance, it approaches the stress distribution in a plate of the uniform thickness. It allowed confirming the previous conclusions that maximum rise in stresses may occur in the weakened layer near the delamination, initiating the failure of the structure. Reliability of the developed mathematical model is confirmed by comparison with the results of experimental studies. The resulting maximum error does not exceed 7% and demonstrates good convergence of results. With the use of the developed method, it is possible to solve the important practical tasks of studying the loss of performance of the panel structures made of polymeric composite materials with delaminations and determining the optimal methods for repair of such defects.

Stress–Strain Behaviour of Reparable Composite Panel with Step-Variable Thickness

“…It is important for the determination of the stress-strain behaviour near the areas of distortion of the stress state, i.e., the area near the patch attachment and stepped variation of thickness of the structure being repaired [36]. The results of the work provide generalization of the previously obtained results for a flat panel [39] on composite shells of double curvature. Taking these factors into account allows us to proceed to consideration of a broader class of problems.…”

“…We assume that most often the notch or patch have a rectangular shape, as it is the simplest shape widely used in practice [33,39]. Figure 1 shows the boundary at which the shell thickness variates stepwise by an amount corresponding to thickness of the patch or depth of the notch, by a dashed line (Figure 2).…”

“…The complex shape of bending of the panel with step-variable thickness is the reason for the choice of the energy technique to solve the problem [39]. Total deformation energy of the elastic system is written as:…”

“…To verify the results of theoretical calculations according to the proposed mathematical model, the deformed state of the notched panel under action of the uniformly distributed transverse load was experimentally investigated. In order to simplify the sample preparation, experiments were carried out on flat panels [39]. Because of non-uniformity of the deformation field caused by stepped variation of the thickness of samples under study, method of strain measurement was not effective [46].…”

“…Conditions for the consistency of expansions for displacements and minimization of the resulting residuals, as well as boundary conditions, are formulated. The similar approach to simplification of a three-dimensional problem is described in [39]. The method for assessment of the stress-strain behaviour of the damaged panel composite structure is developed.…”