Conchúr Mó Brádaigh

Tidal stream energy expansion is limited by the high costs and end-of-life challenges of traditional non-recyclable thermoset composite blades. This study investigates the mechanical performance, bonding and manufacturing feasibility of Elium®, a liquid thermoplastic acrylic resin, for recyclable tidal turbine blades. Unidirectional glass (fibre volume fraction 56%) and carbon fibre (fibre volume fraction 53%) composites were fabricated using vacuum-assisted resin transfer moulding (VARTM) and evaluated across static tensile, compressive, and shear tests. Results show the acrylic-based composites match traditional thermoset performance. Glass achieved 0° tensile, compressive, and shear strengths of 1035.8 MPa, 505.7 MPa, and 43.6 MPa, respectively. Carbon demonstrated high 0° tensile (1681.1 MPa) and shear (59.5 MPa) performance, with 0° compressive strength reaching 629.9 MPa. Replacing general-purpose carbon fibre sizing with a vinyl-ester-targeted coating substantially improved transverse (90°) tensile (+172%), 0° flexural (+52%), and 0° compressive (+15%) properties, while doubling strain-to-failure and increasing ultimate shear strength by 39%. Crucially, Elium® demonstrated superior performance as a structural adhesive via a semi-interpenetrating polymer network (semi-IPN) mechanism. The double-lap shear strength (25.4 MPa) achieved by the Elium® resin-welding process outperformed commercial marine adhesive SAF 30-45 (15.8 MPa) by 60%. When catalysed resin was used it even shifted the failure away from the bond line. These findings establish Elium® as a viable material for high-strength, recyclable thermoplastic tidal turbine blades, which can form the basis of a circular economy in tidal energy turbine manufacture.

During fatigue tests of tidal turbine blades, digital image correlation (DIC) is used to collect vital information about the specimen. DIC provides high-resolution displacement and strain maps of selected blade sections; however, continuous operation is hindered by the need to acquire, transfer, and process large volumes of high-resolution images, precluding real-time use during long tests. We address this problem by optimising sparse sensing locations on the blade surface so that full-field maps can be accurately reconstructed from a small subset of pixel measurements. In contrast to most DIC improvements found in the literature, which focus on accelerating the processing stage, this approach circumvents the need to collect high-resolution data. We evaluate this approach in a case study at FastBlade, a dedicated testing facility for tidal turbine blades. With less than 1% of the original pixels measured, the mean relative error evaluated on the dataset is 0.4% and 16% for displacement and strain maps, respectively, with the larger strain error reflecting the higher spatial complexity of strain fields. The optimised layouts outperform random and grid-like arrangements. The framework enables real-time monitoring and, subject to relevant validation, might be applied to reconstruct high-resolution strain maps directly from strain-gauge readings, potentially extending to in-ocean blade monitoring. Given the high accuracy of deflection reconstructions, using them to derive strain fields is suggested as a direction for further study.

The in-plane deformation kinematics of a pure-Unidirectional Non-Crimp Fabric (pure-UDNCF) is investigated using novel and existing experimental methods to characterise its shear, tensile, and in-plane bending responses under controlled loading. A pure-UDNCF is defined as a fabric in which stabilising tows are absent in the transverse direction relative to the primary tow orientation. The stitching threads in this fabric are made of polyamide, a highly compliant material that allows significant stretch, introducing a low-energy deformation mode that is relatively absent in biaxial engineering fabrics and quasi-UDNCFs (UDNCFs with inextensible stitching and transverse stabilising fibres). To fully characterise its forming behaviour, several novel testing methods are introduced that generate well-defined combinations of fabric shear, in-plane bending and stitch tensile strain. The total normalised axial force measured in the tests is subsequently decoupled into three contributions from shear, tensile strain in the stitch direction, and in-plane bending of the tows. An important finding is that when tested in the picture frame test, in-plane bending generates more resistance to specimen deformation than shearing of the fabric. The testing protocol and resulting data can be used to create appropriate constitutive models for pure-UDNCFs.

Rotor blades are critical components of tidal energy converters, typically manufactured from thermoset fibre-reinforced composite (FRC) materials using vacuum infusion processing. High load demands result in thick-section laminates (10–100 mm), particularly at the blade root, posing manufacturing challenges. While tidal and wind turbine blades appear similar in design, the fundamentally different operational conditions result in distinct structural differences and, therefore, manufacturing requirements, offering opportunities for the tidal sector to innovate. Advances in materials and manufacturing technologies provide potential to rethink current practices for improved design and process efficiency. Additionally, the relative immaturity of tidal technology allows for early integration of circularity principles, minimising waste and optimising resources. This paper serves as a comprehensive resource for the tidal turbine blade sector, reviewing current manufacturing practices and exploring alternative techniques. Combining knowledge from academic literature and industrial reports, it outlines blade design, material selection, and current manufacturing processes. The paper evaluates emerging techniques and potential modifications to established methods. Due to the range of turbine designs in the sector, optimal materials and manufacturing combinations will differ. This study offers manufacturers valuable insights to support informed and strategic choices to improve and advance tidal turbine blade production.

Tidal stream turbines play a pivotal role in harnessing marine energy, yet their reliability remains a critical challenge, impeding the cost-effectiveness of tidal energy. Deviations in blade performance can significantly impact turbine efficiency, potentially leading to unbalanced loads and consequential damage to the turbine and ad- jacent blades. Experience of blade failure, attributed to factors including material fatigue, manufacturing defects, environmental conditions, and operational stresses, under- scores the urgency for comprehensive investigation and development of mitigation strategies. This study addresses these challenges by subjecting a composite tidal blade to a series of incremental static and fatigue tests, culminating in controlled failure experiments conducted at the FastBlade structural fatigue testing facility. The facility’s advanced capabilities include a regenerative digital displacement hy- draulic pump system yielding substantial energy savings; an advanced multi-camera digital image correlation system; and an acoustic emission crack detection system. Using these we systematically explore the factors contributing to blade failure. The failure modes examined in this study include: metal-composite bond failure; crack propagation in thick-section composites; and adhesive failure of the hydrodynamic outer skin. Our findings have significant implications for the structural engineering, composite ma- terial, and tidal energy development communities. Notably, our study offers valuable insights into the mechanisms underlying both blade failure under extreme loads and the accumulation of damage in large, thick composite struc- tures. This research represents an important step towards enhancing the reliability and efficiency of tidal turbine blades, thus advancing the viability of tidal stream energy as a sustainable power source.