In this paper, moisture absorption of carbon/epoxy‐amine 3D woven composite materials is studied by immersion in distilled water at 70°C. If the moisture uptake measured by gravimetry is slow and ...weak over time, various antagonistic phenomena appear. Desorption highlights mass losses due to chemical changes in the material that mask the true water content of the aged samples. The X‐ray photoelectron spectrometry (XPS) reveals a decrease in the carbon and nitrogen proportions and an increase in the oxygen proportions after ageing, allowing to observe surface erosion and oxidation of the matrix. Finally, the rise of silicon is a sign of extraction of the silica‐based particles exuded to the surface. This presence is confirmed by Fourier transform infrared spectroscopy (FTIR).
The hygrothermal ageing of epoxy resins and epoxy matrix composite materials has been studied many times in the literature. Models have been developed to represent the diffusion behaviour of the ...materials. For reversible diffusions, Fick, Dual–Fick and Carter and Kibler models are widely used. Many parameters, correlated or not, have been identified. The objectives of this review by statistical analysis are to confirm or infirm these correlations, to highlight other correlations if they exist, and to establish which are the most important to study. This study focuses on the parameters of the Fick, Dual–Fick and Carter and Kibler models. For this purpose, statistical analyses are performed on data extracted and calculated from individuals described in the literature. Box plot and PCA analyses were chosen. Differences are then noticeable according to the different qualitative parameters chosen in the study. Moreover, correlations, already observed in the literature for quantitative variables, are confirmed. On the other hand, differences appear which may suggest that the models used are inappropriate for certain materials.
This work investigates the hygrothermal cyclic aging of epoxy-based bonded assemblies. The focus is given here to severe long-term environmental conditions. The aging procedure is performed between ...70° C with a relative humidity of 90% and −40° C without humidity, over a cyclic period of 12 h and for a total exposure time of 2 months. The aim of this study is to highlight the consequences of such hygrothermal aging on physico-chemical and mechanical parameters at both the material scale (adhesive) and the structural scale (bonded assemblies). Evolution of water absorption and glass transition temperature with aging cycles are monitored on adhesive bulk specimens by gravimetric analysis and DSC analysis respectively. The evolution of the quasi-static mechanical behavior, strength and elongation at failure, is characterized on adhesive massive specimens and on Single Lap Joint assemblies. Results show a progressive and important degradation of physico-chemical and mechanical properties with the number of cycles, of greater amount than that observed during static aging (loss of SLJ strength by 30% after 56 aging days; loss of the adhesive
T
g
by 45% for around 5% water uptake after aging 21 days). This behavior is related with an embrittling effect at the adhesive scale very specific to water change of state involved in these aging conditions. This combined analysis at different scales ensures a deep understanding of physico-chemical phenomena induced by hygrothermal aging and provides significant information for the further modeling of bonded joints assemblies.
A probe tack test, coupled with in situ imaging, was used to evaluate the influence of an air plasma treatment on glass substrates on the fracture energy of nanostructured epoxy–amine resins. ...Nanostructuration was achieved by the addition of thermoplastic triblock copolymers. The influence of the surface treatment was assessed by splitting the fracture energy (tack energy) into three main contributions (cavitation, viscous flow, and stretch). We showed that before gelation, the interfacial strength depended on the nature of the copolymers and on their interaction with grafted functions (R–COOH and R–CO) by air plasma treatment. The latter also influenced the cohesion of the resins, impacting the copolymers’ phase separation and, as a consequence, conversion rate. The tack test, coupled with rheology and thermal (differential scanning calorimetry) measurements, was relevant to explain how the balance of interactions contributed to the fracture energy up to the gel point.
•Hygrothermal ageing causes various phenomena on the composite material surfaces, which can be problematic for achieving good bonding.•Atmospheric plasma treatment allows, despite slight thermal ...degradation, to chemically activate unaged and aged surfaces by oxygen grafting.•Desorption is found on the aged treated surfaces because of the thermal action of plasma.
In this paper, the effects of hygrothermal ageing and atmospheric plasma surface treatment on a 3D carbon/epoxy-amine woven composite material are studied. The goal is to study the surface evolution of the materials in terms of chemical composition and morphology. Plasma treatment is applied on new and hygrothermally aged samples in order to analyse its contribution to the surface modifications and degradations. It appears that hygrothermal ageing has irreversible absorption behaviour causing hydrolysis, oxidation and particle losses, which modifies the surface chemistry and topology. On the other hand, the atmospheric plasma causes oxidation of the matrix. Indeed, when a repair is necessary, the damaged part could evolve due to moisture absorption related to ageing. As the fibres are exposed, the topology and surface chemistry are modified. Nevertheless, it allows to desorb the humidity adsorbed on the surface and reach an oxidation level similar to unaged treated samples.
•Identification of PT30 resin degradation products by TGA-IR and TGA-MS.•Proposal of a degradation mechanism for PT30 resin in a nitrogen atmosphere.•Identification of the initiation degradation ...reaction based on the results of Density Functional Theory (DFT) calculations which highlight the less energetic network bonds.•Description of each step in the chain scissions of the PT30 resin.•Description of each step in the creation of degradation products.
The non-isothermal thermal degradation of the cured phenolic triazine thermoset resin (PT30) was considered under nitrogen atmosphere. Thermogravimetric analyses (TGA) showed that the degradation mechanism was decomposed in three main steps occurring at 440°C, 550°C, and 720°C. To understand the chemical reactions that happen, TGA experiments were coupled with the analyses of the gaseous products by Fourier transform infrared detection (TGA/FTIR) and by mass spectrometry (TGA/MS). A degradation mechanism is proposed based on these experimental results and on Density Functional Theory (DFT) calculations. It was found that carbon dioxide is the main degradation product generated by the oxygen-carbon chain scissions. In the second step, triazine rings’ rupture led to the formation of cyanide hydrogen and probably cyanic/isocyanic acid. Then, various aromatic compounds are produced from chain scissions and molecules’ recombination. Analyses of these degradation products contributed to proposing assumptions of thermal degradation mechanisms of the PT30 resin.
Adhesives with a variation of properties along the bondline are appealing to the joining industry, yet few developments give easy, versatile implementations and at the same time a control over the ...toughness of the joints. We herein present an original methodology to control the variation of properties in functionally graded epoxy adhesives (FGAs). The FGAs are obtained by putting into contact two plots of compatible adhesives, where the two plots occupy each half of the aluminum substrates. Diffusion of thermoplastic, triblock copolymers in the epoxy-amine adhesive within the joint provokes a gradient of copolymers, inducing in turn a variation of properties along the overlap. We use a driven wedge test (DWT) to assess the variation of properties within the FGAs, by continuously inserting a wedge in the unbonded part of the sample. We discuss on the contribution of the ductility and resilience of the FGAs to the overall energy dissipated, which is found to be superior for FGAs, compared to homogenously filled adhesives. We infer this result to the heterogeneous spatial distribution of the copolymers in the FGAs, due to the diffusion.
Moisture content measurements are performed on scrapped Outlet Guide Vanes (OGV) that have operated in different climates. These measurements are made by three Karl Fischer titration methods. The ...results are separated into two parts. On one side, a comparison of these different techniques highlights their advantages and disadvantages. The methods for studying the samples and the duration of the tests differ. The standard method is not sufficient to extract all the water from the samples. The chemical extraction and grinding methods provide higher water content. On the other side, a mapping of the water content through three scrapped OGV blades is performed with the Karl Fischer titration. Differences are observed according to the service area climate. Concentration gradients are also visible within the part, with more water at the leading edges and less water in the foam. Parts that have flown in hot and humid regions have the lowest water contents by standard Karl Fischer titration. These measurements are compared with the analysis of the damage they have been subjected to. They allow to highlight the composite material degradation, manifested by resin erosion, which is more significant for parts that have operated in wet and humid areas. This erosion involves a lower resin percentage and could explain the lower water contents measured.
The Liquid Resin Infusion (LRI) is a process that has the greatest development and cost reduction potential for the manufacture of large complex parts which made of composite materials. The ...viscosity/temperature pair is the essential criterion for the smooth running of the infusion in order to obtain composite parts of quality. However, humidity is a threatening factor for composite materials. Therefore, aging factors and a predictive model of durability were investigated on a new polymer B and second time on A-150, A-185 polymer systems already certified for use in the aircraft and aerospace industry. Tensile tests were carried out at temperatures T = −40◦C, 25◦C, 70◦C. In this paper, an initial small experimental dataset of 33 samples is used to analyze the strain of polymers systems as a function of aging time, temperature, Young modulus and the breaking stress. In the view of the very small dataset, the strain of polymers systems is predicted by training LevenbergâMarquardt (LM), Bayesian regularization (BR), and Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm with a regularized cost function algorithms. The best results have been obtained with the two regularized artificial neural network from very small data set.
Abstract-This paper present a review of mathematical and physical approaches of homogenization, fractal and multifractal methods for the study of roughness effect in the bonded materials. In ...particular, attention is paid to the effects of roughness on materials joined through an adhesive. Firstly, considering the periodic roughness, the different homogenization methods are presented, including mathematical and physical approaches. Secondly, when the rough surface is no longer considered periodic and taking into account multi-scale of asperities, the article focuses on fractal methods. Lot of research has focused on the effect of roughness irregularities on surface contact, friction or wear, crack propagation using fractal theory. Multifractal analysis was introduced in the 80s and has overcome the limitations of fractal analysis. The multifractal analysis of fractal functions is performed using wavelets instead of boxes like in the classical multifractal formalism.
