Abstract

The present work includes a summary of the doctoral thesis entitled "Complexity of the structural response of fibre reinforced polymer matrix composites". This PhD thesis focused on analyzing the nonlinear mechanical response of a set of stacking sequences, with main interest in angle-ply laminates, to detail the stress-strain behaviour under a range of loading states: uniaxial tension/compression, loading-unloading-reloading tensile tests, three-point bending and plane stress states. The aim is to delve into the mechanisms of coupling and damage and their influence on the mechanical behaviour, in some cases highly nonlinear, aiming to achieve that the material withstands large strains with the consequent delay of the final failure and the increase in energy absorption capacity. Thanks to the characterization through standard testing, it is possible to calibrate material models based on progressive damage, providing two different numerical approaches which are tested against the different experimentally generated states of plane stress. In addition, it is worth mentioning the biaxial tests on cruciform specimens under different loading ratios, which provide experimental data closer to the actual response of composite structures in service. These tests, due to their greater complexity and lack of standardization, are analyzed in detail by applying numerical simulations and analytical models that ensure the validity of the results, highlighting the possible instabilities generated in the presence of compressive loads.

Abstract

A numerical and experimental study is performed on biaxial tests with cruciform specimens in which at least one direction is under compression. Continuous carbon fibre reinforced polymer matrix laminates are studied in angle-ply sequences. The high complexity of the biaxial test is analysed, highlighting the non-linear behavior of the material with pseudo-ductile response. In addition, the presence of compression loads lead to tests in which it is necessary to avoid instabilities in order to obtain adequate results. The numerical simulations based on the Finite Element Method allow to study of the initiation and evolution of the damage in the laminate. The combination of numerical techniques with experimental results, obtained by means of the test instrumentation with strain gauges and Digital Image Correlation, allows to perform a complete characterization of the behaviour of the material in order to achieve less conservative designs of composite structures.