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Fig. 1. Forceextension behavior of representative spring and fall threads.
(A) The thread produced in spring extended beyond the yield point and
stiffened again before failing at the plaque (Fb=0.21 N).
(B) The thread produced in fall broke at the plaque during the first tensile
test (solid line, Fb=0.05 N). When retested without the
plaque (broken line), the thread extended beyond the yield point and stiffened
before failing in the proximal region (Fb=0.14 N). Threads
produced in both summer and winter were similar to fall threads, breaking
before reaching the second (yield) phase of the forceextension curve
(data not shown).