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•Tension-tension fatigue behaviour of a woven hemp/epoxy (±45)7 composite is studied.•Three conditionings (Ambient, Wet and Wet/dry) are performed.•Damage mechanisms are analysed by ...acoustic emission and micro-CT.•Wet conditioning leads to the highest fatigue resistance and the greatest damage quantity.•Wet/dry specimens behave like pre-damaged Ambient ones.
For the last 20 years, plant fibres have emerged as an alternative to glass fibres in composites. However, a crucial issue with plant fibre composites is their durability, i.e. their long-term hygrothermal and fatigue performances. This study deals with the influence of different conditionings (Ambient, Wet and Wet/dry) on the fatigue behaviour of (±45)7 hemp/epoxy composites. The induced damage mechanisms are investigated by acoustic emission and micro-CT. Results show that the Wet samples exhibit the lowest fatigue sensitivity despite their greatest damage quantity, whereas the Wet/dry specimens behave like pre-damaged Ambient ones. Micro-CT scans show that the same type of damage appears in all cases: cracks are made of a coalescence of partial debondings at hemp yarn/matrix interfaces, which can lead to macro-cracks crossing the sample thickness. Moreover it is demonstrated that, during fatigue tests, the evolution of cumulative AE energy and hysteresis loop energy, and the evolution of damage quantity measured by micro-CT and final hysteresis energy, are very similar whatever the conditioning.
Inter-individual transmission of cancer cells represents a unique form of microparasites increasingly reported in marine bivalves. In this study, we sought to understand the ecology of the ...propagation of
Bivalve Transmissible Neoplasia 2 (MtrBTN2), a transmissible cancer affecting four
mussel species worldwide. We investigated the prevalence of MtrBTN2 in the mosaic hybrid zone of
and
along the French Atlantic coast, sampling contrasting natural and anthropogenic habitats. We observed a similar prevalence in both species, probably due to the spatial proximity of the two species in this region. Our results showed that ports had higher prevalence of MtrBTN2, with a possible hotspot observed at a shuttle landing dock. No cancer was found in natural beds except for two sites close to the hotspot, suggesting spillover. Ports may provide favourable conditions for the transmission of MtrBTN2, such as high mussel density, stressful conditions, sheltered and confined shores or buffered temperatures. Ships may also spread the disease through biofouling. Our results suggest ports may serve as epidemiological hubs, with maritime routes providing artificial gateways for MtrBTN2 propagation. This highlights the importance of preventing biofouling on docks and ship hulls to limit the spread of marine pathogens hosted by fouling species.
Despite the academic interest in using plant fibres as reinforcement in polymer composites to replace glass fibres, the industrial exploitation of resulting composites in semi- or structural ...applications is still limited. This is mainly due to the poor adhesion at the plant fibre/polymer matrix interface dictated by their surface chemistry and strong hydrophilic behaviour. In the present work, an assessment of the interfacial adhesion at the yarn scale has been carried out. Fragmentation tests have been performed on flax/epoxy and flax/vinylester single yarn composites. High-resolution microtomography has allowed a 3-D reconstruction of the breaking area of the flax yarn. The flax/epoxy system has shown the lowest values of critical fragment length and interfacial debonding length, and the highest values of IFSS. For both epoxy and vinylester samples, it was found that the breakage of flax has been mainly concentrated in the peripheral zone of the yarn.
In an attempt to improve mechanical properties of basalt fibre/epoxy composites, the present work provides a comparison between the effects of a commercial coupling agent, a thermal de-sizing ...treatment and a plasma polymerization process on the fibre/matrix interfacial strength. The different basalt fibres were characterized in terms of surface morphology, by FE-SEM observations, and chemical composition, performing FT-IR analysis. The interfacial adhesion has been investigated by single fibre fragmentation test on single filament composite samples. The plasma polymerization process was able to produce a homogeneous tetravinylsilane (pp-TVS) coating on the surface of basalt fibres, which resulted in a significant increase in the fibre/matrix adhesion. The surface roughness of the untreated and treated basalt fibres has been measured by AFM and a relationship between the surface roughness and the fibre/matrix adhesion quality was found. High-resolution microtomography (µ-CT) has been used to support the analysis of the damage modes during fragmentation tests.
The effect of the matrix/fibre interface strength on the in-plane and out-of-plane impact performances of glass woven fabric/polypropylene laminates, prepared by means of film stacking technique, was ...investigated. The interface strength between polymer and fibres was varied by means of a coupling agent added to two different polypropylene grades in order to evaluate its contribution to the impact resistance of the laminates. The static characterization showed that the flexural strength of compatibilized laminates was higher with respect to that of composites based on neat matrices. On the contrary, composites with low interface strength between fibres and polymer showed a strong improvement in impact resistance, in both Charpy and falling dart impact tests. This was related to the possibility of fibres to slip into the matrix and dissipate energy through friction, and to the improved capability to bear load before fibre failure, allowed by the limited propagation of cracks through the laminate. The damage after impact was assessed by means of micro-computed tomography, which elucidated the role of the weak matrix/fibre interface in improving the impact resistance.
This paper aims to evaluate the influence of water ageing on nanoindentation response of the in situ components of hemp/epoxy composites. Specific samples have been tested, made of single hemp yarn ...composites with two different epoxy resins. Analysis of indentation points depending on their location in the yarn microstructure has been performed. Measurements showed the influence of neighbouring fibres on the reduced modulus in the confined resin. Water induces a decrease in nanoindentation properties, and maximum decrease in reduced modulus takes place in the interfacial zone, which shows the significant degradation of the fibre/matrix interface caused by water ageing. Evolutions in the indentation properties induced by water are similar for both partially bio-based and fully synthetic epoxy resin composites. All these results bring insights into the influence of water ageing of each constituent of hemp fibre reinforced composites and give interesting data for developing eco-composite materials.
In the present work, the adhesion between an impregnated hemp yarn and the epoxy matrix was investigated. The micromechanical tests usually used to characterise the fibre/matrix interface were ...adapted to the yarn/matrix interface. Single yarn composite specimens with yarn axis at 0° were manufactured and submitted to fragmentation tests to determine the experimental interfacial shear strength (IFSS). Specific single yarn composite specimens with yarn axis at 90° from the loading direction were also tested to track by digital image correlation the strain fields in the yarn, in the resin and at the yarn/matrix interface. A finite element analysis was developed and optimised to simulate the fragmentation process and provides a conservative value of IFSS.
•Laser induced shockwave to certify bonded assembly.•No NDT currently available to assess bonded CFRP structures integrity.•Detection capabilities of the S-LASAT to assess bond integrity of ...contaminated lab samples.•Behaviour of both healthy and contaminated bonded CFRP under laser shock.•Demonstration of the S-LASAT detection capabilities on real aircraft parts.
This study aims to assess the capability of the LAser Shock Adhesion Test to detect weak bonds in assemblies made of carbon fibre reinforced polymer laminates as well as understand the behaviour of different bonded composite structure under a shock load. A specific setup based on symmetrical laser shocks has been used. After each test, ultrasounds are used to determine if the bond has been damaged or not. At first, samples with two contaminants - de-icing fluid and finger prints - were studied. Then, the bond quality of two partially contaminated aircraft parts were investigated. These original results demonstrate the efficiency of the symmetrical laser shocks method as a Non-Destructive Test for bonded carbon fibre reinforced polymer assemblies.
This study addresses the effect of basalt fibre hybridization on the damage tolerance of carbon/epoxy laminates subjected to laser shock wave tests. Interply hybrid specimens with two different ...stacking sequences (sandwich-like and intercalated) were tested at different laser intensities and residual post-shock properties of the different configurations have been characterized by quasi-static three point bending tests monitored by acoustic emission. Results indicate that the best compromise in terms of both quasi-static properties (2% reduction in flexural strength compared to all carbon laminates) and damage tolerance appears to be the sandwich-like structure with basalt fibre skins. In particular, this configuration exhibited the highest damage tolerance among the hybrids, with a percent decrease in flexural strength of about 5% compared to 15% in the case of all carbon laminates. Damage induced by laser shock testing in carbon-basalt woven fabric/epoxy composites is mainly inter-ply delamination. This study also highlights the tougher behaviour of basalt plies in response to a sudden application of load compared to carbon layers with a favourable hybridization effect.
We investigate if a mean equivalent flow model can be defined to describe hydraulic head variations in a crystalline aquifer characterized by multiscale heterogeneity. We analyzed in particular the ...hydraulic response of a crystalline aquifer to pumping tests covering a large range of spatial and temporal scales. Pumping tests appear to be well designed to test the medium hydraulic properties and to track scaling effects, since the perturbation induced by pumping grows with time and samples increasingly large volumes. We tested well‐test interpretation frameworks underpinned by equivalent media models that basically contain scaling information. Interpretations of drawdown time series, recorded in piezometers located at distances ranging from 2 to 400 m from the pumping well and of durations ranging from 5 to 90 days, show that the temporal evolutions of drawdown are well modeled by fractional flow models Barker, 1988; Acuna and Yortsos, 1995. Estimates of flow dimensions are consistent across the whole site and lie in the range 1.4–1.7. To investigate the nature of diffusion, we defined a methodology based on the evolution of the characteristic time or amplitude of hydraulic head variations with the distance from the pumping well. For most of the piezometers, those aligned along the main fault, it is possible to define a scaling law for all piezometers with a unique set of parameters. The derived exponents imply that hydraulic head diffusion is anomalously slow, a characteristic that is taken into account only in the model of Acuna and Yortsos 1995, based on diffusion in fractals.
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