Ivica Smojver

On the effect of fibre directions in laminated composite torispherical shells

A linear and geometrically non‐linear computation of a laminated composite torispherical shell subjected to internal pressure was performed by using the layered finite element whose formulation is based on degeneration principle. Geometric non‐linearity in terms of large deformations with total Lagrangian formulation was taken into account. The effect of the lamination schemes on geometric non‐linear behaviour and stress resultant distributions was analysed. The fibre directions have not a great influence on the shape of the load‐displacement curves. In contrast to the hoop stress resultant distribution, the moment distribution is significantly influenced by the lamination schemes. The influence of the lamination schemes on bending moments is greater in non‐linear than in linear computations. Likewise, the effect of the fibre orientation is greater on the hoop than on the meridional moment distribution. In unsymmetric laminated shells the values of the hoop moments exceed those of the meridional moments w...

Bird impact at aircraft structure – Damage analysis using Coupled Euler Lagrangian Approach

Numerical bird strike damage prediction procedure has been applied on the very detailed large airplane secondary structure consisting of sandwich, composite and metallic structural items. The impacted inboard flap finite element model is modelled using 3D, shell and continuum shell elements, coupled with appropriate kinematic constraints. The bird has been modelled using Coupled Euler Lagrangian approach, in order to avoid the numerical difficulties connected with mesh distortion. Various failure modes, such as Carbon Fibre Reinforced Plastics (CFRP) face layer rupture, failure of composite matrix, damage initiation / evolution in the sandwich structure Nomex core and elastoplastic failure of a metallic structure have been investigated. Besides, general contact has been applied as to efficiently capture the contact between Eulerian bird material and the structure, as well as large deformations of the different structural components. Compared to the classic Lagrangian modelling of the bird, the analysis has proven to be more stable, and the results, such as damage areas, physically more realistic. The impact has been applied in the area that is the most probably subjected to the impact damage during exploitation.

On damage modelling of laminated composite shells subjected to low velocity impact

Publisher Summary The numerical procedure presented in this chapter is an extension of the research performed in the field of damage analysis of impact loaded composite plates. A novel numerical approach has been applied in the barely visible impact damage analysis of layered fiber composite shells. In the assessment of damage, only delaminations and matrix cracks have been taken into account by means of numerical procedures that discretise shell continua with eight nodded 3D elements. Transient dynamic analysis with contact algorithms has been applied in the calculation of the kinematics of impact. Mechanical properties of the composite lamina are calculated using the micromechanical Mori-Tanaka approach with gradual degradation of properties after damage initiation. The exploitation of layered composite shell structures has revealed some serious drawbacks if subjected to impact loading. This includes the appearance of damage, predominantly in the form of matrix cracks and delaminations, and this can be observed at micro-, macro or meso levels. The application of solid finite elements coupled with usage of appropriate coordinate systems, different from rectangular ones applied in the plate analysis, enabled the implementation of similar numerical procedures in the analysis of shell structures. The work is currently aimed at the implementation of different shell geometries and improved models for characterisation of damaged material.