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The hardness of materials, H, is dependent on grain diameter, d, in a similar way as the flow stress in the Hall‐Petch relation: H = Ho + KHd−1/2, where, Ho and KH are constants. The microhardness of 2S‐Al (99.5% Al), pure Cu, Al‐MD 105 (Al‐1% Al2O3), and Duralumin (Al‐3.94% Cu) is found to vary with grain size according to the Hall‐Petch equation with reasonable accuracy. The grain boundary hardening KH of Al‐MD 105 is found to be the highest although this material recrystallizes to larger grain sizes than those for the other materials; this is attributed to the resistance of boundaries to deformation arising mainly from the presence of hard, second phase alumina particles. However, the contribution of solution, precipitation, and dispersion hardening may be added to grain boundary hardening according to Hansen and Lilholt.

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Polyamidoamine hyperbranched polymer (Hyp)/clay nanocomposites were synthesized by using both of montmorillonite and laponite clays. Poly amidoamine hyperbranched polymer (Hyp) was prepared by one-pot polymerization via couple monomer methodology. Afterward, the amino ends of Hyp were modified with methyl methacrylate (MMA), styrene (St) and butyl methacrylate (n-BuMA) polymers which were previously prepared via ATRP (atom transfer radical polymerization) to form the corresponding new hyperbranched polymers Hyp 1 , Hyp 2 and Hyp 3 . Those formed polymers were inserted into the modified clay, such as montmorillonite and laponite to form their nanocomposites. The formed polymer/clay nanocomposites were characterized via XRD, TEM, and thermal analyses. The formed hyperbranched polymers generally showed intercalation behavior more than the exfoliation one mostly because of the bulkiness of the hyperbranched skeleton.

Background: Scalp and forehead defects represent one of the most complex defects for reconstruction. The nature of these sites being hair bearing, together with the complicated nature of the injuries, for example, electrical burns and motor vehicle accidents, and of course the aesthetic concern being in the face, all add to the complexity of reconstruction. Methods: This is a case series representing the experience of the authors in using the “crane principle” in the reconstruction of various defects in the forehead and the scalp presented to emergency department, Cairo University Hospital, for the period between January 2018 and January 2019. Results: Twenty patients, 15 men and 5 women, presented with various soft tissue defects of the forehead and the scalp. The injuries of eighteen patients were due to motor vehicle accidents, and 2 patients had postelectrical burns. Age range was from 20 to 65 years, with a mean follow-up of 8 months. The number of total complications was 5. Three patients had wound dehiscence, and 2 patients had ulceration in the grafts placed at the flap donor site. Conclusion: Crane principle represents an adequate reconstruction tool for forehead and scalp defects especially when the access to free flap and more complex reconstruction techniques is not available.