Towards understanding residual strength and damage evolution in damaged composite laminates

Fibre reinforced polymer composites have found increasing use in aircraft structures. This means that fleet managers need damage assessment tools for such materials, in order to decide on appropriate sustainment strategies. Developing such tools is hindered by the difficulty of generalising from lab tests to predict the behaviour of full-scale...

Compression after impact fatigue damage growth in CFRP – what does no-growth really mean?

Impacts on carbon fiber reinforced composites (CFRP) can produce a complex internal damage comprising multiple delaminations, which is hard to detect from visual inspection. This situation is known as barely visible impact damage (BVID). Considering that every airplane faces several impacts during its operational life, and that the majority of...

Probability of Delamination Detection for CFRP DCB Specimens Using Rayleigh Distributed Optical Fiber Sensors

Distributed Optical Fiber Sensors (DOFS) show several inherent benefits with respect to conventional strain-sensing technologies and represent a key technology for Structural Health Monitoring (SHM). Despite the solid motivation behind DOFS-based SHM systems, their implementation for real-time structural assessment is still unsatisfactory...

Enhancement of mode I fracture toughness of adhesively bonded secondary joints using different layup patterning of CFRP

Delamination growth in fibre reinforced polymer composites is generally evaluated with experiments that have been standardized for quasi-static load conditions. These tests characterize unidirectional delamination growth in mode I (DCB), mode II (ELS or ENF) of mixed mode conditions (MMB). However, little attention is paid in literature to the...

Do standard delamination tests relate to planar delamination growth?

Delamination growth in fibre reinforced polymer composites is generally evaluated with experiments that have been standardized for quasi-static load conditions. These tests characterize unidirectional delamination growth in mode I (DCB), mode II (ELS or ENF) of mixed mode conditions (MMB). However, little attention is paid in literature to the...

Progressive Damage Accumulation Process of CFRP Cross-Ply Laminates during the Early Fatigue Life

The present work aims at investigating the progressive damage accumulation process of CFRP laminates in an interactive scheme, with a special focus on the early fatigue life where mainly matrix-dominant damage accumulates and stiffness degrades significantly. An in-situ damage monitoring system, containing edge observation, digital image...

Application of shearography and the percussion method for the structural inspection of wall paintings: A case study of St. Christopher in Maria Church, Nisse

Structural delamination in mural paintings is a complex phenomenon and is considered among the most frequent types of damage. In conservation practice, the most common technique to identify structural detachments is the percussion method. Full-field optical techniques based on interferometry, such as shearography, can provide a more...

Effects of Humidity and the Presence of Moisture at the Bond-line on the Interfacial Separation of Laminated Glass for Flat Glass Re-use

The built environment is under scrutiny to address environmental design challenges by considering a whole-life holistic approach that seeks reductions in operational emissions whilst simultaneously pursuing reductions in embodied emissions. Reduced embodied emissions can be found through the responsible sourcing of resources and re-use of...

Simulation of cusp formation in composite materials using the thick level set method

On the microlevel, cusps are formed during delamination crack growth under mode II loading conditions. In this work, the Thick Level Set (TLS) approach is used to simulate the cusp formation process. A plasticity model for polymers is implemented in the TLS method and a new loading scheme is devised to deal with permanent strain. A numerical...

Higher order adaptively integrated cohesive element

Cohesive Element (CE) is a well-established finite element for fracture, widely used for the modelling of delamination in composites. However, the computational time of CE-based method is prohibitive. This is because the steep and non-smooth stress gradient in the cohesive zone requires a very fine mesh. In this context, a new type of CE is...

A geometrically nonlinear floating node method for damage modelling of composites

Tremendous efforts have been put into the study of structural integrity and the understanding of failure mechanisms in composites. Geometric non-linearity, receiving few attention in coupon-level simulations, can play an important role in the design and analysis of larger structures. This paper aims at extending the recently-developed...

Fatigue crack propagation in composite laminates by a novel approach based on the S-N diagrams

This paper focuses on a novel numerical formulation based on cohesive elements and S-N diagram to simulate fatigue-driven delamination in composite laminates. The constitutive model adopts a two-parameters heuristic equation, which coefficients are evaluated using an idealization of the S-N diagram rather than the more commonly used Paris law....

Modeling fatigue-driving delamination using a thick level set interface model

This paper presents a new discontinuous damage model for simulating fatigue-driven delamination in composites. Fatigue models commonly describe crack growth using the Paris law which provides the link between the energy released due to delamination and the crack growth rate. A core issue in implementing the Paris law is to accurately compute the...