Alberto Diaz

Software application for evaluating interfacial stresses in inelastic symmetrical laminates with free edges

Abstract Authors propose herein a software application called DEILAM, which is able to evaluate the free edge effects in multilayered inelastic structures that essentially bear tensile loads. The inelastic behavior of both layers and interfaces are take into account. The program therefore involves inelastic strain fields in the layers and fields of displacement discontinuities at the interfaces. These inelastic fields, such as thermal strains or interface sliding, are assumed to be known by the user. For evaluating the 3D interfacial stresses, the program uses an approximate model that models the laminate by a superposition of Reissner plates coupled by interfacial stresses. Calculations show that no singularities exist for the model even at the edge and results converge quickly. Calculations are validated by comparing the results with finite element calculations and with Pagano’s local model. Analysing the maximum values of the interfacial stresses for some examples, the authors then show how the software can help predict the place where delamination might appear. Since delamination is a critical failure mode that often takes place at free edges, this program with a delamination criterion involving the maximum interfacial stresses can prove to be an important tool in composite structure design.

Laminated materials with plastic interfaces: modeling and calculation

In this paper, a model of laminated plates called M4-5N and validated in a previous paper is modified in order to take into account interlaminar plasticity by means of displacement discontinuities at the interfaces. These discontinuities are calculated by adapting a 3D plasticity model. In order to compute the model, a Newton–Raphson-like method is employed. In this method, two sub-problems are considered: one is linear and the other is non-linear. In the linear problem the non-linear equations of the model are linearized and the calculations are performed by making use of a finite element software. By iterating the resolution of each sub-problem, one obtains after convergence the solution of the global problem. The model is then applied to the problem of a double lap, adhesively bonded joint subjected to a tensile load. The adhesive layer is modeled by an elastic–plastic interface. The results of the M4-5N model are compared with those of a commercial finite element software. A good agreement between the two computation techniques is obtained and validates the non-linear calculations proposed in this paper. Finally, the numerical tool and a delamination criterion are applied to predict delamination onset in composite laminates.

CRITERION OF DELAMINATION INITIATION IN COMPOSITE LAMINATES

ABSTRACT Abstract: A criterion is proposed to predict delamination initiation in angle-ply laminates. An analytical model permits to calculate interface stresses between two layers in any laminate. The criterion is based on the maximum value of these stresses and takes into account the scale effects (number of layers). The numerical results are validated by a comparison with experimental data of tensile tests.