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Service lifetimes of polymers and polymer composites are impacted by environmental ageing. The validation of new composites and their environmental durability involves costly testing programs, thus calling for more affordable and safe alternatives, and modelling is seen as such an alternative. The state-of-the-art models are systematized in this work. The review offers a comprehensive overview of the modular and multiscale modelling approaches. These approaches provide means to predict the environmental ageing and degradation of polymers and polymer composites. Furthermore, the systematization of methods and models presented herein leads to a deeper and reliable understanding of the physical and chemical principles of environmental ageing. As a result, it provides better confidence in the modelling methods for predicting the environmental durability of polymeric materials and fibre-reinforced composites.

Recently, significant events took place that added immensely to the sociotechnical pressure for developing sustainable composite recycling solutions, namely (1) a ban on composite landfilling in Germany in 2009, (2) the first major wave of composite wind turbines reaching their End-of-Life (EoL) and being decommissioned in 2019–2020, (3) the acceleration of aircraft decommissioning due to the COVID-19 pandemic, and (4) the increase of composites in mass production cars, thanks to the development of high volume technologies based on thermoplastic composites. Such sociotechnical pressure will only grow in the upcoming decade of 2020s as other countries are to follow Germany by limiting and banning landfill options, and by the ever-growing number of expired composites EoL waste. The recycling of fiber reinforced composite materials will therefore play an important role in the future, in particular for the wind energy, but also for aerospace, automotive, construction and marine sectors to reduce environmental impacts and to meet the demand. The scope of this manuscript is a clear and condensed yet full state-of-the-art overview of the available recycling technologies for fiber reinforced composites of both low and high Technology Readiness Levels (TRL). TRL is a framework that has been used in many variations across industries to provide a measurement of technology maturity from idea generation (basic principles) to commercialization. In other words, this work should be treated as a technology review providing guidelines for the sustainable development of the industry that will benefit the society. The authors propose that one of the key aspects for the development of sustainable recycling technology is to identify the optimal recycling methods for different types of fiber reinforced composites. Why is that the case can be answered with a simple price comparison of E-glass fibers (~2 $/kg) versus a typical carbon fiber on the market (~20 $/kg)—which of the two is more valuable to recover? However, the answer is more complicated than that—the glass fiber constitutes about 90% of the modern reinforcement market, and it is clear that different technologies are needed. Therefore, this work aims to provide clear guidelines for economically and environmentally sustainable End-of-Life (EoL) solutions and development of the fiber reinforced composite material recycling. © 2021 by the authors. Licensee MDPI, Basel, Switzerland, published under the CC BY 4.0 license., Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.

In this paper we explore the opportunities and challenges of deploying a Wireless Sensor Network to monitor the structural health of civil infrastructure using Vibro-Acoustic Modulation. The fundamentals of the method are explained and the challenges for a sensor network in a practical implementation are investigated. Ideas and requirements for the sensor nodes are analyzed and presented.

Exposure to marine environment causes a degradation of the interlaminar shear performance of composites. This effect has been reported in several studies, but the mechanisms that lead to failure in composites subjected to cyclic loading under water exposure are still not fully understood. In this work a novel test method, the I-beam short beam shear, was used to determine shear properties and accelerate fluid saturation in glass fiber epoxy specimens. The interlaminar shear performance of the material was studied experimentally. From the analysis of the cyclic parameters recorded during the test and from optical micrographs it was possible to observe a change in failure mode between dry samples and conditioned samples. The failure of dry samples was a creep dominated effect, which led to inter-ply cracks, while the failure of conditioned samples was a damage growth dominated effect, which led to intra-ply failure. Optical micrographs showed that fiber/matrix debonding occurs in conditioned samples prior to mechanical loading, which are potential damage onset spots.

Finite elements simulations of fluid diffusion for composite structures are becoming more common in marine and offshore applications. Input parameters for such simulations are the orthotropic diffusion constants for the materials. Diffusivity in fiber direction is faster than diffusivity in transverse direction; it is therefore important to determine all these constants to predict long-term fluid diffusion in composite structures. Current standards for the determination of the diffusion constants prescribe a sample geometry that enforces 1-D diffusion, but thin samples are not easy to fabricate, especially from thick laminates. Edges with metallic coatings are also prescribed, which can influence the calculation of the moisture saturation content and may detach during the experiments. Furthermore, axial symmetrical structures are often used offshore, requiring 3-D diffusion analysis in cylindrical coordinates. The aim of this paper is to provide a 3-D theory and methods for obtaining diffusion constants for plates, rods and pipes.

Multidirectional composite laminates are often used in marine and offshore applications. Upon cyclic loading, cracks appear early in the off-axis plies and generate delaminations, which accelerate fluid diffusion. In this work, a theoretical model was developed for the prediction of fluid diffusion in laminates having cracks and delaminations. The model is based on the definition of a representative volume element subjected to Fickian diffusion. The geometry and dimensions of the representative volume element are determined by the crack density and the length of delaminations. Experiments were performed on both statically loaded samples having transverse cracks and fatigue loaded samples having transverse cracks and delaminations. The presence of delaminations increased the apparent diffusivity of the laminate by 5.4 times. The experimental results showed good agreement with the theory.

Composite structural components are often subjected to service loads that cause cracks in off-axis layers, without compromising the load bearing capability of the structure. In marine or humid environments fluid ingress in the material can be accelerated by the presence of such cracks, leading to further strength degradation. Several studies have been dealing with the effect of cracks on fluid diffusion in composites, sometimes with contradictory results. In this work the difference between cracks on the external and internal plies of the laminate has been addressed both experimentally and analytically, showing that the first ones have a strong influence on diffusivity, while the second have a negligible effect.

Fatigue is a process (succession of mechanisms) which under the action of time-varying strains or deformations modifies the local properties of a material. These can lead to the formation of cracks and eventual rupture of the structure. Fatigue is in particular characterized by an extent of variation in stress which may be well below the yield strength of the material. The main stages of fatigue failure of an assembly are the initiation of cracks (if defects are not already present in the material), the propagation of cracks and the final rupture. The parameters often used to predict the fatigue behavior and thus the number of cycles at break of a structure is: The amplitude of the stress (loading or imposed strain), its average value, the surface state and the medium In which the structure will be used. Even if the study of fatigue is based on theoretical considerations (in particular the mechanics of the rupture), it is essentially an experimental field. The characterization of a material, a part, an assembly, a structure, requires numerous tests and measurements. The work deals with multiaxial fatigue power of specimens which are notched and all made of 40CrMoV13.9. Circumferentially V-notched specimens and semicircular notched were tested under combined tension and torsion loading, both, in phase or out of phase. Geometry of symmetric axis of V notched issues has been characterized of a notch radius constant from (1 mm) and V-notch opening angle of 90°. The semicircular specimens were characterized by a constant notch tip radius. For both situations the net diameter sectional area was 12 mm. The results from multi-axial tests are discussed together with those obtained being all under loading pure torsion and tension by the issues notched having the same geometry. Altogether more than 120 new fatigue data are summarized in the present work. All presented fatigue data are first in terms of nominal amplitudes stress and then reanalyzed in terms of the mean value of the strain energy density evaluated over a finite size semicircular sector surrounding the tip of the notch.