Keynote Lectures

The lecture is about the lessons learnt from a 30 years’ journey of the author as a pioneer, scientist, designer, and lecturer in the field of fibre-polymer composites, applied to structural engineering and architecture. The lecture starts with the appearance of first composite bridges and buildings in the 1990s and then focuses on the development of vehicular bridges, adhesive connections, function integration in building construction, durability and sustainability, and ends with conclusions about opportunities for composites and research needs.

Advanced modeling strategies for composite structures are considered with special attention to the mixed approach that was first completely stated by Reissner in 1984, and therefore often referred to as Reissner Mixed Variational Theorem (RMVT). This variational formulation has the displacements and the transverse stresses as independent field variables, i.e., only those field variables that are required to fulfil the interlaminar continuity across a heterogeneous stack of perfectly bonded plies. For this reason, RMVT can be seen as the "natural variational framework" for constructing structural models for composite structures. The presentation addresses displacement- and stress-driven variants of RMVT and comparisons with the analogous Hellinger-Reissner (HR) principles. Two-dimensional plate/shell models are formulated within the so-called "axiomatic" dimensional reduction procedure, in which trial distributions are introduced for the field variables across the composite stack, and subsequently the dependency on the thickness coordinate is eliminated by carrying out the integrations. The general variable-kinematics approach is here adopted, that was first introduced by Carrera with his Unified Formulation. When dealing with mixed formulations, particular attention must be given to a proper choice of the introduced approximations in order to obtain well-posed problems and avoid non-physical responses. Results are presented for laminated and sandwich structures, obtained by means of semi-analytical as well as numerical solution methods.

Biobased composites have gained considerable attention from industry and academicians in various applications due to their key attributes including high specific-strength-to weight ratios, sustainability and better environmental performance compared to their conventional glass and carbon fibre reinforced composites counterparts. This keynote talk will focus on some of the work performed on natural plant fibre reinforced sustainable lightweight biobased composites for load-bearing engineering applications including marine, automotive, renewable energy and building and construction sectors. Key performance targets (mechanical, thermal, long-term durability and exposure to extreme environmental conditions) relating to key application areas, challenges and ways to achieve them will be presented and discussed. Additionally, microstructures and physicochemical characterisations using advanced characterisations techniques such as micro-CT, SEM and advanced imaging will be presented. The keynote talk will focus on three key aspects: First, the talk will introduce the importance of sustainable natural plant fibre reinforced biobased composites in tackling the current environmental issues caused by use of fossil-based materials in advanced engineering applications. The keynote talk will then concentrate on structure property relationships, influence of exposure to various harsh environmental conditions on the key mechanical, thermal and long-term properties by analysing some results obtained from various experimental works from ongoing and recently completed research projects. Some fabrication techniques and their influence on the various properties will also be discussed. Finally, the potential use of these lightweight sustainable biobased composites in load bearing applications (non-structural, semi-structural and structural) relating to key application areas, major challenges will be further highlighted and discussed by analysing some experimental results and by presenting ways to enhance the key properties by reviewing some current and previously published works. Keywords: Biobased composites; Mechanical property; Morphological characterisation; Long-term durability; X-ray micro-CT; Sustainability; Processing parameters.

Most pultruded composite bars used as internal reinforcement in concrete elements and structures are GFRP rebars (Glass Fiber Reinforced Polymer). The primary driver is economic: when expressed as cost per unit of allowable tensile capacity, GFRP bars are typically around one quarter of the equivalent carbon-FRP option, even after accounting for the lower elastic modulus of GFRP, which may require a larger bar area to control serviceability (crack width and reinforcement strain). In normal-strength concrete, tensile cracking occurs at very small strains (กึ 100จC150 ฆฬฆล, depending on the concrete tensile strength and modulus), making stiffness a governing parameter at SLS. Because of the relatively low modulus of GFRP and the limited ductility of concrete, demolition/deconstruction of GFRP-reinforced concrete tends to impose lower peak stresses on the continuous reinforcement. As a result, pultruded bars may have a higher probability of being recovered intact and potentially reused (after appropriate inspection and qualification), rather than being downgraded to waste. Beyond end-of-life considerations, replacing steel reinforcement with GFRP can reduce the whole-life carbon footprint, primarily by eliminating corrosion-driven deterioration and the associated repair/strengthening cycles. Steel-reinforced concrete durability is often governed by carbonation- or chloride-induced depassivation and corrosion; once alkalinity is reduced and corrosion initiates, repairability and remaining service life can be severely compromised. Corrosion-free reinforcement is therefore particularly attractive for structures in aggressive environments (marine/offshore, saline soils), where it can unlock longer design working life and enable structurally optimized concrete components intended for prolonged exposure to seawater (e.g., coastal protection systems). The talk will quantify these aspects from the literature and will also outline ENEAกฏs ongoing R&D actions aimed at improving the performance, durability, and sustainability of pultruded GFRP rebars, with specific attention to circularity and end-of-life pathways.

Laminated glass components, such as automotive windscreens, architectural glazing, and photovoltaic modules, are routinely subjected to diverse mechanical actions including wind pressure, snow loads, hail impact, and gust-induced loading. Structural analysis of laminated glass is traditionally performed using layer-wise theories, in which each layer is modeled by beam, plate, or shell theories, coupled through compatibility conditions or interlayer force transfer relations. This presentation introduces an extension of classical layer-wise approaches by incorporating peridynamic (PD) nonlocality, enabling a unified and consistent treatment of both intact and damaged laminated glass configurations. Beginning with a single-layer formulation, a first-order shear deformation theory is developed within a peridynamic framework. The approach is then extended to multilayered laminates, resulting in governing equations of motion that allow both cross-sectional responses and interlayer force and moment interactions to exhibit long-range, nonlocal behavior. Local kinematic compatibility between adjacent layers is enforced, which naturally gives rise to nonlocal interaction forces in the peridynamic sense. Numerical examples demonstrate that, for smooth laminated glass beams, the proposed PD layer-wise theory produces results in close agreement with published solutions obtained from classical layer-wise beam formulations. For beams containing pre-existing cracks, the analysis reveals that the crack opening displacement increases with the peridynamic horizon size, highlighting the intrinsic nonlocal character of the PD crack model. In cases where one glass layer is fractured, the maximum interlayer shear force is found to scale inversely with the horizon size, indicating a direct influence of nonlocality on interlayer load transfer mechanisms. The proposed formulation offers a computationally efficient alternative to fully three-dimensional peridynamic models while retaining the ability to capture key physical effects, such as interlaminar load transfer and finite interfacial shear stresses near cracks, regions where classical plane-stress-based approaches often predict singular behavior. Although minor discrepancies arise due to the neglect of transverse normal deformation in compliant interlayers, the overall predictive capability of the model remains robust, making it well suited for practical analysis of laminated glass structures.

Composite repair systems for metallic pipelines presenting a through-wall defect must be qualified in accordance with either ISO 24817 or ASME PCC-2 standards. This qualification method requires a number of hydrostatic tests to obtain the failure pressure, which demands time and high costs. In the oil and gas industry, the failure pressure estimation is often performed using a linear fracture mechanics analysis described in both ISO and ASME standards. These standards require the determination of a constant fracture energy, also called the energy release rate. In the case of monotonically increasing loading histories, in the framework of linear fracture mechanics, brutal interfacial debonding occurs when the fracture energy reaches a critical value. This study is an attempt to show that simpler tests, such as, shaft-loaded, pressurized blister test or DCB joints can be employed as an alternative to hydrostatic tests in the qualification of repair systems. Results show a reasonable similarity between the critical energy values found using such alternatives with the ones obtained with the standard required hydrostatic tests.

It is now well documented in the literature that the inclusion of nanoparticles, such as graphene nanoplatelets (GNP), in matrix materials, such as epoxy, can result in significantly improved fracture toughness in mode I and mixed-mode. One of the mechanisms postulated to increase the effective crack initiation fracture toughness is the crack tip shielding effect due to nanoparticles in the fracture process zone. This effect is deemed to arise due to debonding of nanoparticles from the matrix material in the process zone, which in turn reduces the stress state at the tip of the primary crack via shielding. Thus, debonding of nanoparticles act to redistribute stress in the crack tip region, thereby lowering the near tip stress intensity factor, depending on their orientation relative to the crack. Therefore, higher far-field loads can be achieved before the critical stress intensity is reached at the crack tip. In this paper the novel K-field approach is used in conjunction with molecular dynamics (MD) to model fracture in an amorphous carbon matrix material, with embedded GNPs. Amorphous carbon matrix is deliberately selected to facilitate the computational efficiency of the solution process, because the fracture process zone size for amorphous carbon is relatively small from a MD simulation viewpoint. Moreover, amorphous carbon is gaining popularity as a precursor for high temperature carbon-carbon composites. The effect of GNPs on the shielding of the crack tip, with different orientations (vertical, horizontal, and 45 degrees to the crack plane) and location relative to the crack-tip is thoroughly investigated using detailed virial stress plots, the atomistic J-integral, and compared with linear elastic fracture mechanics (LEFM) predictions. Significant crack-tip shielding by GNPs is predicted from MD simulations, both at crack initiation and also during crack propagation.