Issue 33

A. Winkler et alii, Frattura ed Integrità Strutturale, 33 (2015) 262-288; DOI: 10.3221/IGF-ESIS.33.32 283 The load can now be used to calculate the nominal bending stress,  b = M b /W b . Where Mb is the bending moment, W*L, and W b the bending resistance, bh 2 /6. The nominal bending stress is therefore  b = 6 ⋅ W ⋅ L / bh 2 = 6 ⋅ 25.3 ⋅ 15 / 10 ⋅ 2.54 2  35.3 N/mm 2 , or MPa. The number of repeats can now be extracted using the diagram shown in Fig. 27. The result is approximately 10 5 cycles before the spring fractures. Figure 26 : Spring rate chart for cantilever springs [44]. Figure 27 : Flexural fatigue of Delrin POM [45].