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- Interlaminar Adhesive Strength of Nano-Reinforced Glass/Epoxy LaminatesPublication . Silva, H.; Ferreira, J. A. M.; Costa, J. D. M.; Capela, C.Interlaminar fracture is significantly influenced by the adhesive strength of fiber/matrix interfaces. Critical strain energy release rate (GC) is the most common parameter used to quantify the interfacial strength. However, subcritical debonding can occur at lower mechanical loads than those required for interlaminar fracture toughness (IFT). This study was performed using nanoclay-reinforced epoxy/glass fiber laminates in order to analyze the influence of the addition of nanoclay and hydro aging on IFT and subcritical crack growth. Hydro aging was done immersinga batch of specimens in distilled water at 25°C for 30 days. Mode I IFT was significantly improved by the incorporation of nanoclays into the resin, the improvement reaching 31% for 3% of nanoclays content. The results of subcritical debonding were plotted in terms of da/dt versus G curves, for dry materials and long term hydro aged composites. Hydro aged composites exhibit not only a reduction of GI c, of about 14% for 3% of nanoclays, but also a higher subcritical crack propagation rate. The addition of nanoparticles reduces subcritical crack propagation rate.
- Influence of Superposition Length on Transverse Impact Response of Single-Strap Adhesive JointsPublication . Reis, P. N. B.; Ferreira, J. A. M.; Pereira, A. M.; Antunes, F. J. V.Adhesive joints are usually designed to carry in-plane loads, but in many cases they are also prone to transverse loading. On the other hand, the impact response of adhesive joints has received limited attention compared to quasi-static loading. Therefore, the present paper aims to study the influence of superposition length on transverse impact response of single-strap adhesive joints. For this purpose, low-velocity impact tests were performed using a drop weight-testing machine with a hemispherical impactor falling at the center of a bi-clamped specimen. The specimens were manufactured using Docol 1000 high-elastic limit steel, with 1.5 mm of thickness, and an Araldite® 420 A/B adhesive (Huntsman Advanced Materials, Everberg, Belgium). The collapse thresholds obtained were 61.6 J, 75.1 J, and 77.5 J, respectively, for adhesive joints with gap length of ℓo = 0, 10, and 20 mm. An adhesive fracture occurred for the three geometries and the cracks initiated at the corner of the joint where the deflection is higher. Joints with higher ℓo have higher impact energies, despite the lower bonding area, as consequence of the lower local deformation. A numerical study was developed and the zero gap (ℓo = 0) gives maximum peel stress.