Natural materials are renowned for their strength and toughness1,2,3,4,5. Spider dragline silk has a breakage energy per unit weight two orders of magnitude greater than high tensile steel1,6, and is representative of many other strong natural fibres3,7,8. The abalone shell, a composite of calcium carbonate plates sandwiched between organic material, is 3,000 times more fracture resistant than a single crystal of the pure mineral4,5. The organic component, comprising just a few per cent of the composite by weight9, is thought to hold the key to nacre's fracture toughness10,11. Ceramics laminated with organic material are more fracture resistant than non-laminated ceramics11,12, but synthetic materials made of interlocking ceramic tablets bound by a few weight per cent of ordinary adhesives do not have a toughness comparable to nacre13. We believe that the key to nacre's fracture resistance resides in the polymer adhesive, and here we reveal the properties of this adhesive by using the atomic force microscope14 to stretch the organic molecules exposed on the surface of freshly cleaved nacre. The adhesive fibres elongate in a stepwise manner as folded domains or loops are pulled open. The elongation events occur for forces of a few hundred piconewtons, which are smaller than the forces of over a nanonewton required to break the polymer backbone in the threads. We suggest that this ‘modular’ elongation mechanism might prove to be quite general for conveying toughness to natural fibres and adhesives, and we predict that it might be found also in dragline silk.

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Molecular mechanistic origin of the toughness of natural adhesives, fibres and composites

Recent developments in explosive welding

Impact loading of plates and shells by free-flying projectiles: A review

A comprehensive review of solid particle erosion modeling for oil and gas wells and pipelines applications

Load and health monitoring in glass fibre reinforced composites with an electrically conductive nanocomposite epoxy matrix

Explosively driven impact welding is a true example of multidisciplinary research as the phenomena associated with it fall under the various branches of engineering science. A great deal of the work in, and collaboration between various specialised fields have been expended on the subject. However, a comprehensive quantitative theory capable of giving an accurate description and prediction of the parameters and of the characteristic features of explosively welded components does not exist. Most of the investigators considered the welding process as a solid state welding process, but some believed that the process is a fusion welding process. Interfacial waves are the most discussed aspect of explosive welding. The presence of jet in the collision region, and the transient fluid-like behaviour under high pressure have led many investigators to seek an explanation and a characterisation of these waves in terms of a flow mechanics of one kind or another. In this study, part of the welding process was numerically analysed. A finite difference engineering package was used to model the oblique impact of a thin flyer plate on a relatively thick base. The results were validated by data from carefully controlled experiments using a pneumatic gun. Straight and wavy interfaces and jetting phenomena were modelled, and the magnitude of the waves and the velocity of jet predicted. The numerical analysis predicted a hump ahead of the collision point. Wave formation appears to be the result of variations in the velocity distribution at the collision point and periodic disturbances of the materials. Higher values of plastic strain were predicted in wavy interfaces. Bonding was found to be a solid state welding process. Phase changes which occur may be due to high temperatures (but less than the melting temperature) at the collision point.

S.T.S. Al-Hassani

Papers

Numerical and experimental studies of the mechanism of the wavy interface formations in explosive/impact welding

Electrical resistance measurement technique for detecting failure in cfrp materials at high strain rates

Explosive welding of metal plates

Simulation of explosive welding using the Williamsburg equation of state to model low detonation velocity explosives

Strain Rate Effects on GRP, KRP and CFRP Composite Laminates