Interphase analysis of hierarchical composites via transmission electron microscopy

<p>Observation and analysis of the interphase are essential for a detailed understanding of the global composite properties when nanofillers are incorporated as interfacial agents. Techniques such as atomic force microscopy and nano-indentation provide valuable information on interfacial properties associated with the viscoelastic behavior of each phase. However, when the morphology of this region is observed in detail, instrumental errors may regularly appear, decreasing the accuracy of measurements. In this work, the use of transmission electron microscopy (TEM) was explored to image the glass fiber-reinforced polymer GFRP interphase containing interfacial nanocellulose. TEM lamellas were prepared via a focused ion beam to observe the phases disposed within the composite arrangement. Energy dispersive X-ray spectroscopy was also performed to determine the elemental composition in each sample phase. Interphase sizes between 25 and 50 nm thick were found, highlighting the ability of this characterization route to give accurate interfacial measurements. This kind of measurement will open new routes for getting rich information on hierarchically structured composites containing a nanostructure as an interfacial agent.</p

Low-cost, environmentally friendly route for producing CFRP laminates with microfibrillated cellulose interphase

In this paper, a cost-effective and eco-friendly method to improve mechanical performance in continuous carbon fiber-reinforced polymer (CFRP) matrix composites is presented. Unsized fiber fabric preforms are coated with self-assembling sugarcane bagasse microfibrillated cellulose, and undergo vacuum-assisted liquid epoxy resin infusion to produce solid laminates after curing at ambient temperature. Quasi-static tensile, flexural and short beam testing at room temperature indicated that the stiffness, ultimate strength and toughness at ultimate load of the brand-new two-level hierarchical composite are substantially higher than in baseline, unsized fiber-reinforced epoxy laminate. Atomic force microscopy for height and phase imaging, along with scanning electron microscopy for the fracture surface survey, revealed a 400 nm-thick fiber/matrix interphase wherein microfibrillated cellulose exerts strengthening and toughening roles in the hybrid laminate. Market expansion of this class of continuous fiber-reinforced-polymer matrix composites exhibiting remarkable mechanical performance/cost ratios is thus conceivable

Load Ratio Estimation Through Striation Height and Spacing Analysis of an Aerospace Al Alloy 7475-T7351

It is well known that striation spacing may be related to the crack growth rate, da/dN, through Paris equation, as well as the maximum and minimum loads under service loading conditions. These loads define the load ratio, R, and are considered impossible to be evaluated from the inter-spacing striations analysis. In this way, this study discusses the methodology proposed by Furukawa to evaluate the maximum and minimum loads based on the experimental fact that the relative height of a striation, H, and the striation spacing, s, are strongly influenced by the load ratio, R. Fatigue tests in C(T) specimens were conducted on SAE 7475-T7351 Al alloy plates at room temperature and the results showed a straightforward correlation between the parameters H, s, and R. Measurements of striation height, H, were performed using scanning electron microscopy and field emission gun (FEG) after sectioning the specimen at a large inclined angle to amplify the height of the striations. The results showed that for increasing R the values of H/s tend to increase. Striation height, striation spacing, and load ratio correlations were obtained, which allows one to estimate service loadings from fatigue fracture surface survey