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Nomex honeycomb cores have been widely used in composite sandwich panels. To accomplish meso-scale finite element modeling of these cores, cell wall mechanical properties are required, for which limited data are available. In this work, tensile testing was performed on Nomex paper, phenolic resin, and Nomex paper coated with phenolic resin. Flatwise tension and compression tests were also performed on two types of Nomex honeycomb cores. Test results were calibrated in finite element modeling to account for strain gage local stiffening effects and thickness normalization. Identified cell wall material properties were implemented in a honeycomb core finite element model and further calibrated by matching simulation results to manufacturer test data. The cells' double-wall thickness was also adjusted. These calibrations and adjustments led to an exact simulation match with test data. Numerically matching cell wall material properties depends on modeling sophistication and is subject to core test result variability and core construction differences among manufacturers. [ABSTRACT FROM AUTHOR]

The gap is one of the most common defects during the AFP process, which has a nonnegligible impact on the mechanical properties of laminates. This paper proposes a novel three-dimension reconstructive gap model based on the in-process serial layer scanned point clouds, which can characterizes the gap features inside the laminate and pre-determine the mechanical performance before the subsequent procedures. The measured point cloud will be transformed into eligible and processible formats and then be used to generate a finite element grid using the element-based material property assignment method. The local material properties and fiber orientation are defined by previously assigned classes and grid geometries respectively. The effect of gap size on the in-plane tensile strength and damage evolution of laminates is investigated and both the experimental and simulation results find that the ultimate strength and stiffness show a significant decrease with the increase of gap size. [ABSTRACT FROM AUTHOR]

During operational conditions, extreme environments combined with unexpected high loading rates can induce severe damages or, inclusively, premature fails. Therefore, this paper intends to study the effect of different hostile solutions on the longitudinal impact strength in order to establish design criterions. For this purpose, samples of GFRP composites were immersed into alkaline and acid solutions as well as distilled water. Variables like exposure time, temperature and concentration of the solution were analysed in detail. The effect of pre-damages was also studied for different pre-loads, where the severity of the damages introduced was quantified by acoustic emission. It was possible to conclude that, independently of the solution, the exposure time and temperature were determinant to decrease the tensile impact strength. Finally, the magnitude of the initial damage has a significant influence on the impact resistance. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental investigations of the tensile properties of different types of CFRP plates. Coupon specimens of low, normal and ultra-high modulus CFRP plates were prepared and tested under tensile loading. Four different strain rates were used, including one low strain rate and three high strain rates. Two methods of capturing strain were used: image correlation photogrammetry and foil strain gauges. The results showed a significant increase in the tensile strength, ultimate strain and elastic modulus for coupons under high strain rates. The CFRP coupons were prepared and tested in accordance with the ASTM3039-08 standards. Finite element analysis was performed and the results agreed very well with the experimental results. [ABSTRACT FROM AUTHOR]

The effect of ply thickness on the onset of intralaminar and interlaminar damage is extremely important for the structural response of laminated composite structures. This subject has gained particular interest in recent years due to the introduction in the market of spread-tow, ultra-thin carbon-fibre reinforcements with different configurations. In the present paper, an experimental test campaign was carried out to study the structural response of aerospace-grade plain weave spread-tow fabrics (STFs) of different areal weights. The results showed that, in spite of an apparent superior longitudinal tensile strength of the thick STF, the multidirectional thin-STF laminate exhibited an improved tensile unnotched strength over the thick-STF laminate, attributed to its damage suppression capability. However, damage suppression was also responsible for similar tensile notched strengths. In compression, the thin-STF laminate performed substantially better than the thick-STF laminate in both unnotched and notched configurations. Finally, a similar bearing response was obtained in both STF laminates, in spite of a slightly higher resistance of the thin-STF laminate to the propagation of subcritical damage mechanisms. [ABSTRACT FROM AUTHOR]

This paper aims at investigating the effect of alkali treatment and water ageing on several short Alfa fibre reinforced polypropylene composites. For this purpose, different composites with untreated and treated fibres were elaborated by extrusion and injection moulding processes and subjected to water ageing. The obtained results showed that the alkali treatment enhances significantly the Young’s modulus and tensile strength of the Alfa fibre reinforced polypropylene composites and reduces their loss during water ageing. The acoustic emission analysis showed that the use of alkali treatment plays a major role in the improvement of the fibre-matrix interface of both unaged and aged composites. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an experimental and analytical study into the strengthening and toughening of sandwich composite joints by z-pinning. Cleats connecting the vertical stiffener and horizontal base panel to T-shaped sandwich joints were reinforced in the through-thickness direction with pins. Tensile (stiffener pull-off) tests revealed that pinning increased the ultimate fracture load and fracture energy by resisting crack growth along the cleat–skin and skin–core interfaces, which were the weakest points in the unpinned joint. The peak fracture load and fracture energy increased with the volume content of z-pins. The strengthening and toughening effect of the pins was analysed using multiple pin pull-out tests performed on the sandwich composite material. It is shown that elastic deformation, debonding and pull-out of the pins from the face skins to the sandwich composite is the primary toughening mechanism of the pinned T-joints. The pin pull-out process, which is the cause for the high strengthening and toughening of the T-joints, is analysed using bridging traction modelling. [Copyright &y& Elsevier]