Fig. 4.

Breaking-strain map for nanotubes of different symmetry (χ) at various load durations (t) and thermal conditions (T). The yield mechanism is determined by what borderline is crossed first as the tension is applied from ε = 0 upward. Brittle-bond breaking is marked by the failure intervals (dark blue segments) for specific tube samples and by extrapolated dependence on the chiral angle χ (blue-domain border); it has no perceptible dependence on T or t. Plastic yield through thermally activated bond rotation depends on temperature and test duration, as shown by the strain required to form a defect within the given test time (t = 1 s, 1 h, 1 yr); it was computed for specific tubes (red triangles) and extrapolated to arbitrary tube symmetry (red-level rims) by using Eqs. 2 and 3. Additional thin red lines show the yield strain at very low (T = 1 K) and higher (T = 600 K) for t = 1 s. At very high T (>2,000 K), the yield is no longer limited by activation but is rather controlled by the thermodynamic benefit of SW defects, achieved at ε ≈ 5 [sin (2χ + 30°)]⁻¹% (13).