| Περίληψη: | The significance of composite laminated structures is increasing in several industrial sectors. The expansion of their use in the manufacturing of structural components makes the development of tools for the analysis of their behaviour a critical part of the design process. The present thesis presents an efficient numerical methodology, suitable for the analysis of the mechanical behaviour of laminated anisotropic structures, subjected to quasi-static, low and high velocity impact loading.
In the frame of the developed methodology, a laminated structure is considered to be a set of discrete, interacting layers, based on the principles of the stacked shell modelling approach. The simulation of sublaminates is performed using two different approaches: the first utilizes shell elements, while the other method employs solid-like-shell elements, commonly known as thick shells. The sublaminates that constitute the numerical model of the composite structure are held together using penalty-based contact laws. At the same time, a damage model for prediction of intralaminar and interlaminar failure is incorporated in the finite element model of the laminate. The development of the methodology combines different theories and modelling techniques to enhance the efficiency of the model while retaining the necessary level of accuracy.
The developed methodology is validated using different cases that cover a wide range of geometries and loading conditions, in order to investigate its applicability and performance. Initially, the prediction of the elastic response under quasi-static loading is investigated. Three well known cases that incorporate different geometries of various thicknesses are chosen for the verification. Emphasis is given on the predictions of maximum displacements and through-thickness stress distributions. Subsequently, a Mode-I experimental campaign is performed. This series of experimental tests is used for the extraction of valuable information that serve as reference for the validation of the developed methodology in the case of interlaminar damage initiation and propagation. The effect of important modelling parameters on the prediction of the response of laminated structures is thoroughly examined.
The application of the methodology is extended in the case of low velocity impact on fibre reinforced laminated structures. The numerical investigation of this experiment showcases the predictive capabilities of the approaches presented in the present thesis, through comparison of numerically derived results to the respective experimental output. Emphasis is given on maximum load and delamination predictions, as well as to the investigation of the methodology’s efficiency in comparison to respective numerical models of the literature.
The final step of the validation process concerns the use of the developed methodology for the simulation of a demanding high-velocity impact experimental procedure, namely bird strike on composite laminated panels. Essential features of bird strike modelling are examined, and parameters that affect the simulation of an artificial bird are discussed. Validation of the methodology is achieved through comparison of numerical results to results of high-speed cameras, used during the experimental procedure for recording of the impact event.
The developed methodology is shown to provide a robust analysis numerical tool that presents sufficient accuracy, without sacrificing the required numerical efficiency. The application of the methodology to cases that cover a wide range of geometries, slenderness values and loading conditions for the validation of its behaviour, demonstrates the intrinsic capabilities of the developed models for the prediction of the elastic and damage response of laminated composite structures.
|
|---|
