The increasing developments in wind turbine technology, coupled with an unpredictable operating environment, present significant challenges regarding erosion issues on the leading edge of the blade tips. This review examines the potential degradation posed by the different environmental variables, with specific emphasis on both rain droplet and hailstone impact on the blade leading edge. Drawing on both the insights from experimental results and recent field data from the literature, the mechanisms of leading edge erosion are discussed. Meteorological tools that may enable rain and hailstone erosion prediction are addressed, as well as potential experimental and numerical approaches that may provide insight into the nature of impact and erosion on the blade surface.

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On erosion issues associated with the leading edge of wind turbine blades

Crack initiation in brittle materials is not covered by classical fracture mechanics that deals only with the growth of pre-existing cracks. In order to overcome this deficiency, the Finite Fracture Mechanics concept assumes the instantaneous formation of cracks of finite size at initiation. Within this framework, a coupled criterion was proposed at the beginning of the 2000’s requiring two necessary conditions to be fulfilled simultaneously. The first one compares the tensile stress to the tensile strength, while the other uses an energy balance and the material toughness. The present analysis is restricted to the 2D case, and, through a wide list of references, it is shown that this criterion gives predictions in agreement with experiments in various cases of stress concentration, which can be classified in two categories: the singularities, i.e. indefinitely growing stresses at a point, and the non-singular stress raisers. It is applied to different materials and structures: notched specimens, laminates, adhesive joints or embedded inclusions. Of course, a lot of work remains to do in these domains but also in domains that are almost not explored such as fatigue loadings and dynamic loadings as well as a sound 3D extension. Some ideas in these directions are issued before concluding that FFM and the coupled criterion have filled a gap in fracture mechanics.

A review of Finite Fracture Mechanics: crack initiation at singular and non-singular stress raisers

About the fatigue crack propagation threshold of metals as a design criterion – A review

Introduction to the damage tolerance behaviour of railway rails – a review

Following their discovery in the early 1960s, there has been a continuous quest for ways to take advantage of the extraordinary properties of shape memory alloys (SMAs). These intermetallic alloys can be extremely compliant while retaining the strength of metals and can convert thermal energy to mechanical work. The unique properties of SMAs result from a reversible diffussionless solid-to-solid phase transformation from austenite to martensite. The integration of SMAs into composite structures has resulted in many benefits, which include actuation, vibration control, damping, sensing, and self-healing. However, despite substantial research in this area, a comparable adoption of SMA composites by industry has not yet been realized. This discrepancy between academic research and commercial interest is largely associated with the material complexity that includes strong thermomechanical coupling, large inelastic deformations, and variable thermoelastic properties. Nonetheless, as SMAs are becoming increasingly accepted in engineering applications, a similar trend for SMA composites is expected in aerospace, automotive, and energy conversion and storage-related applications. In an effort to aid in this endeavor, a comprehensive overview of advances with regard to SMA composites and devices utilizing them is pursued in this paper. Emphasis is placed on identifying the characteristic responses and properties of these material systems as well as on comparing the various modeling methodologies for describing their response. Furthermore, the paper concludes with a discussion of future research efforts that may have the greatest impact on promoting the development of SMA composites and their implementation in multifunctional structures.

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Review and perspectives: shape memory alloy composite systems

The effects of the hole size and the specimen width on the fracture behavior of several woven fabric composite plates are experimentally investigated in tension. It is shown in this paper that the characteristic length (do) in the Point Stress Criterion (PSC) depends on the hole size and the specimen width. A modified PSC for predicting the notched strength is proposed. An excellent agreement is found between the experimental results and the analytical predictions using the modified PSC. When the unstable fracture occurred, the equivalent critical crack length (ac) corresponding to the damage zone size is about twice the characteristic length. The characteristic length decreases with an increase in the notched strength. The critical energy release rate (Gc) corresponding to the unstable fracture criterion is independent of the hole size for the same specimen width. Gc increases with an increase in the specimen width. These results can be explained by the correlation between the Gc and the notch sensitivit...

Notched Strength and Fracture Criterion in Fabric Composite Plates Containing a Circular Hole

It is necessary to evaluate the fatigue behavior of rail steel under mixed mode loadings to assure the safety of railway vehicles. For this purpose, the stress analysis to investigate static failure and fatigue behavior under mixed mode loadings is performed. The stress analysis results show that the K I / K II tends to increase as the transverse crack below the surface propagates. For the mixed mode, the fatigue crack growth behavior was evaluated using various comparative stress intensity factor ranges Δ K V . Fatigue crack growth rate under the condition of mixed mode is slower than that under mode I, and this difference decreases with the increase of the stress ratio R .

Jung-Kyu Kim

Papers

Notched Strength and Fracture Criterion in Fabric Composite Plates Containing a Circular Hole

Fatigue crack growth behavior of rail steel under mode I and mixed mode loadings

Effect of shape memory alloy on impact damage behavior and residual properties of glass/epoxy laminates under low temperature

The variation in fatigue crack growth due to the thickness effect

Probabilistic analysis for the fatigue life of carbon/epoxy laminates