Developments in the wind industry reveal intricate engineering challenges, one of them being the erosion on the leading edge of the wind turbine blades. In this review work, the main issues for the wind industry in the experimentation with respect to erosion are examined. After a historical and general overview of erosion, this review focuses on the rain erosion on the leading edge of the wind turbine blades giving prominence to (1) the rain simulations, (2) experimental erosion facilities, and (3) variables to characterise erosion. These three factors have to be improved to establish a research field enabling the prediction of erosion behaviour and providing useful information about how the rainfall affects the leading edge of the wind turbine blades. Moreover, these improvements in the experimentation of the erosion would be a first step to understand and predict the erosion damage of the wind turbine blades. Finally, this review work also will help to cope with experimental investigations and results in the rain erosion on the leading edge with a deeper critical thinking for future researchers.

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Controlling the pressure at which liquids intrude (wet) and extrude (dry) a nanopore is of paramount importance for a broad range of applications, such as energy conversion, catalysis, chromatography, separation, ionic channels, and many more. To tune these characteristics, one typically acts on the chemical nature of the system or pore size. In this work, we propose an alternative route for controlling both intrusion and extrusion pressures via proper arrangement of the grains of the nanoporous material. To prove the concept, dynamic intrusion−extrusion cycles for powdered and monolithic ZIF-8 metal−organic framework were conducted by means of water porosimetry and in operando neutron scattering. We report a drastic increase in intrusion−extrusion dynamic hysteresis when going from a fine powder to a dense monolith configuration, transforming an intermediate performance of the ZIF-8 + water system (poor molecular spring) into a desirable shockabsorber with more than 1 order of magnitude enhancement of dissipated energy per cycle. The obtained results are supported by MD simulations and pave the way for an alternative methodology of tuning intrusion−extrusion pressure using a macroscopic arrangement of nanoporous material.

The mechanical behaviour of zinc dialkyldithiophosphate (ZDDP) tribofilms on diamond-like carbon (DLC) coatings has been studied by combining the nano-indentation experimental data and finite-element modelling. Different constitutive models, whose analysis was performed using a global algorithm that consists of forward and inverse algorithms, were chosen to establish which of them more accurately predicts the actual mechanical behaviour of the ZDDP tribofilms. A non-homogeneous, dual structure, which was also verified by the local stiffness using the AFM force-modulation mode, was found. Based on the proposed algorithm, the mechanical properties of the ZDDP tribofilms were found, e.g. the elastic modulus E=26 GPa and the yield stress Y=1.55 GPa for the harder component and approximately E=1.65 GPa and Y=0.144 GPa for the softer component.

Thermoplastic polyurethane elastomers (TPUs) are a kind of elastomer that can be processed as thermoplastics. These elastomers exhibit a highly nonlinear behavior characterized by hyper-elastic deformability. Furthermore, the mechanical behavior of these elastomers is time-dependent, that is, they exhibit a viscoelastic behavior. We describe the material response of a TPU under moderate strains (ɛ < 1) by using an overlay visco-hyperelastic model assuming separation of time dependence from nonlinear stress–strain behavior. To achieve this goal, cyclic loading–unloading experimental tests are carried out for two homogeneous deformation states, uniaxial tension and pure shear, and the strain–stress data are then analyzed to fit a hyperelastic model. Conversely, a viscoelastic model is obtained from relaxation tests. Finally, the visco-hyperelastic model is implemented in a finite element calculation tool (ABAQUS), and the numerical results show a reasonable correlation with experimental data. As a result, a overlay visco-hyperelastic model depending on maximum strain is proposed.

Rain erosion on the leading edge of wind turbine blades is an intricate engineering challenge for the wind industry. Based on an energetic approach, this work proposes a methodology to characterise the erosion capacity of the raindrop impacts onto the leading edge blades. This methodology can be used with meteorological data from public institutions or from direct measurements at the wind turbine locations. The erosion characterisation is analysed using accumulative and per impact erosive variables, that is, total kinetic energy and kinetic energy per impact. To consider the frequency of impacts, two erosive variables are proposed, namely, total kinetic power and kinetic power per impact. These variables are calculated using the data from the Royal Netherlands Meteorological Institute (Koninklijk Nederlands Meteorologisch Instituut, KNMI) of the last 25 years jointly with the operation specifications of an actual wind turbine model (Suzlon S111). The main contribution to the erosive variables was found to be the wind speed because it controls the rotational velocity of the wind turbine. Also, the intensity of the rainfall and the frequency of meteorological data logging, that is, the temporal resolution of data, play a significant role.

The evolution of the mechanical behaviour of zinc dialkyldithiophosphate (ZDDP) tribofilms on diamond-like carbon (DLC) coatings during sliding contact has been studied by combining nano-indentation experimental data and finite element modelling. The nano-indentation data from the ZDDP tribofilms were obtained for two different sliding distances of the tribological tests after 15,000 and 216,000 cycles, which correspond to 25 minutes and 6 hours respectively. A non-homogeneous structure was found for the ZDDP tribofilms after both sliding distances, which were also verified by the local stiffness using the AFM forcemodulation mode. A dual structure is observed for the ZDDP tribofilms after 15,000 cycles, while three distinct components with different mechanical behaviours were found after 216,000 cycles. It was also found that the mechanical behaviour of the harder component of the ZDDP tribofilms remains almost unchanged for both sliding times, while the softer component tends to stiffen slightly over the sliding time. In addition, using the proposed algorithm with finite element simulations, the mechanical properties of the different components have been obtained, e.g. the elastic modulus E=25.5 GPa and the yield stress Y=1.585 GPa of the harder component for both sliding times. The softer component exhibits E=1.65 GPa and Y=0.144 GPa after 15,000 cycles and E=3.5 GPa and Y=0.17 GPa after 216,000 cycles. Finally, an intermediate component with E=11.7 GPa and Y=0.94 GPa has been only found at 216,000 cycles.