ABSTRACT--In the development of new materials, researchers have recently turned to nature for inspiration and assistance. A special emphasis has been placed on understanding the development of biological materials from the traditional correlation of structure to property, as well as correlating structure to functionality. The natural evolution of structure in biological materials is guided by the interaction between these materials and their environment. What is most notable about natural materials is the way in which the structure is able to adapt at a wide range of length scales. Much of the interaction that biological materials experience occurs through mechanical contact. Therefore, to develop biologically inspired materials it is necessary to quantify the mechanical behavior of and mechanical influences on biological structures with the intention of defining the natural structureproperty-functionality relationship for these materials. In particular, the role mechanics has assumed in understanding biological materials, and the biologically inspired materials developed from this knowledge, will be clarified. The following will serve to elucidate on this role: the helical structure of fibrous tissue, the multi-scale structure of wood, and the biologically inspired optimal structure of functionally graded materials.

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Experimental work using multiple strain gauges has investigated the take-up of load by a wire at either side of a break and how this is affected by fatigue cycling. In addition the effect of a wire break on other wires at the same cross-section has been investigated. The results indicate that a significant amount of slippage can occur for up to 20 000 cycles after a wire has broken, causing the load transfer length to change from two strand lay lengths to around three. The transfer length was found to be much lower for Lang's lay rope than ordinary lay and this was attributed to the greater interlayer forces in Lang's lay ropes. With respect to the effect of wire breaks on other wires at the same cross-section it was found that the primary increase is in the strains in wires in the same strand, although wire strains in adjacent strands also increase to some extent. Wires on the opposite side of the rope construction were found to show a decrease in surface strain after the break which may be attributed to local bending effects.

This paper investigates wire strain variations in tension-tension fatigue for two six-strand rope constructions under normal and overloaded conditions. It has been found that for ropes in tension there is a considerable variation in wire strains both on different wires at the same cross-section and to a marginally lesser extent along the length of the same wire. It has also been found that a Lang's lay rope has a wider variation of strains than the identical ordinary lay rope. Load cycling has been found to reduce the distribution slightly for an initial period, around 8 per cent of the rope's life (for the load range used), after which the variations in wire strains do not change significantly for the rest of the life of the rope. Tests involving initial overload have shown a considerable reduction in wire strain variation. By way of an example for an ordinary lay rope an initial overload caused the wire strain standard deviation to decrease from 22 per cent of mean to 11 per cent of mean and was accompanied by an increase in rope endurance by a factor of 2.4. A statistical model has been used to illustrate the influence of strain range distribution on the fatigue endurance of a rope using a Gaussian probability distribution. It is suggested that wire strain distribution (measured by standard deviation as a percentage of mean) provides a good indicator of rope manufacturing quality.

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