Damage Mechanics and Predictive Modelling of Failure in Laminated Fiber-Reinforced Composites and Adhesive Layers : A Continuum Approach

Abstract

Laminated polymer matrix composites and high-quality adhesive films are widely used across aerospace, automotive, civil engineering, and electronics industries due to their excellent in-plane mechanical properties and relatively low density. Despite these benefits, delamination and bondline failure remain persistent challenges, especially in complex loading conditions. The objective of this thesis is to improve the numerical modelling of delamination initiation and fracture process zones (FPZ) in laminated structures. The focus points are i) fibre-reinforced polymer (FRP) laminates, and ii) adhesive films with layered configuration of fibrous carrier and matrix constituents. The study leverages Continuum Damage Mechanics (CDM) and Cohesive Zone Model (CZM) to improve predictive accuracy in simulating composite failure mechanisms, specially matrix cracking, addressing limitations of the approaches in the current scientific literature.

The thesis is based on five case studies: (1) the analyzing of chemical aging effects on ply and laminate strength in cross-ply glass fiber-reinforced polymers (GFRP), (2) the studying of damage at high-strain rates and out-of-plane compression, (3) the evaluating of failure prediction in carbon fiber-reinforced laminates subjected to impact and, (4) and (5) implementing a multi-layer CDM framework for adhesive FM 300-2 to account for size-thickness effects under Mode-I and Mode-II fracture. Each study reports the performance of a continuum mechanics model capable of capturing the interplay between localization of cracks and multi-directional stresses. The thesis explores the 3D Hashin strength criterion’s performance in predicting failure initiation at multi-directional FRP laminates under normal transverse loads. This model achieves high accuracy in capturing tensile transverse crack initiation in laminates, though challenges remained in addressing shear stresses when laminate’s strength degraded due to chemical aging. The predictions of matrix failure modes at the ply level in laminates subjected to through-thickness impact loads under low and high-strain rates demonstrate reliable performance when validated against experimental fracture surface observations. For adhesive films, a new multi-layer CDM model incorporating Bažant’s crack band theory and the corresponding toughness energies accurately simulates Mode-I and Mode-II fractures. The comparison to experimental work is performed with Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) tests.

The main novelty of the thesis is a multi-layer CDM model that provides a ro- bust alternative to CZM, capturing the evolution of intra- and inter-laminar damage across the thickness of laminated fibre-reinforced material systems. By precisely reproducing experimental force-displacement responses, FPZ characteristics, and mixed-mode fractures, the developed model represents a viable, validated framework for complex delamination scenarios.