a while (from A to C) and successively, it was pulled again at C. When stopping the machine, the meniscus is changing its curvatures very slowly due to its high viscosity and hence, the load drop occurs steeply. Using the curvatures at the stable period (B), the surface tension was estimated to be about 65±3 mN/m. This is nearly equal to that of water (73mN/m). This is plausibly due to the fact that the sticky liquid just after collected may contain a fairly large fraction of water. Microstructure As soon as urea liquid is dropped on the threads, swelling began at their both ends and moved to the central part. In the case where the concentrations of urea and NaCl are high, the interior substance becomes milky and flows out from the outer ring of the thread like a balloon. For the short thread, only the outer ring remains occasionally, the core material being solved out. This may indicate that the outer layer is stronger to swelling agents such as rain and fog than the core material. The observation of the short SC thread stained in a reagent of Coomassie Brilliant Blue shows that the thread consists of 3 layers, those are, the outer layer, the middle layer and the core. The middle layer from which the outer layer is striped off at the recoil test can be seen in a fortunate case. This observation may show that the middle layer consists of numerous micro-fibrils parallel to the thread axis, which may be important for supporting the strength of dragline. These features are illustrated schematically in Fig.5. Tensile behavior Load(P)-draw ratio(λ) curves of dry and wet draglines with ambient SCRs are shown in Fig.6 (a) and (b). The value of P is calculated by (1-SCR) F where F is the actually recorded load, the cross sectional area being 1/(1-SCR) times larger than that of SCR=0. λ is defined as L/Lc where L is the length under deformation and Lc=(1-SCR)L0 is the original length before deformation as defined above. P-λcurves in a dry state have a steep knee point denoting yield. The knee point tends to decrease with an increase in SCR. The P-λcurves after yielding are upwardly concave like rubber. But in a wet state, they are upwardly concave (J-shaped) without any distinct knee point. This may be similar to that of rubber. Viscid droplets attached to capture threads were dissolved out into water. After the capture threads were soaked in water during 1 minute and more than 1 hours, they were sufficiently dried in air and were provided for tensile tests. If the capture thread was soaked in water during more than 1 hour, viscid droplets were completely removed from them and only the core threads remain. The dry core threads without any droplets were pulled. The P-λcurves for dry(②,③) and wet(①)capture threads are shown in Fig.7. The P-λcurves of wet capture threads has nearly the same shape as that of capture threads with viscid droplets. As the soaking time increases and the viscid droplets are much removed, the yield load increases. The P-λcurves of dry capture threads without any viscid droplet are very similar to those of dry draglines. This may be supposed by the fact that the amino acid compositions for both threads are nearly the same. These behaviors may be explained well on the basis of a 3 elements model consisting of yield, rubber and spring elements as shown in Fig.8. The yield element does not move due to friction until the stress is lower than the yield stress Y. The rubber element shows rubber elasticity where the relationship between stress andλ is expressed by Langevin function. The spring element represents an elastic spring. If the applied stress exceeds Y, the behavior is governed by the rubber element. The yield stress Y is a function of SCR. In the case of wet thread, Y is chosen 0. CONCLUSION For the deformation behavior, it was shown that (1) the P-λcurve for capture thread without any viscid droplet was not different from that of dragline and (2) the capture thread with viscid liquid behaved like the dragline wetted and swollen by water sufficiently. The author wishes to acknowledge Mr. T.Kitayama, Technical expert of Kanazawa Univ., and Mrs. M.Yasutomi and A.Furukawa, Master course student of Kanazawa Univ. for their technical assistance. References 3
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