Issue 35

A. Tzamtzis et alii, Frattura ed Integrità Strutturale, 35 (2016) 396-404; DOI: 10.3221/IGF-ESIS.35.45 398 Figure 1 : Incremental crack growth in HAZ. By calculating in Eq. (5) for mode I loading the stress amplitude σ A at the position of fracture r c for an isotropic linear elastic material and by and using the Coffin-Manson relationship [21-22] to derive Δε p,, the crack growth equation can be derived:         1 1 1 ' 2 2 3 1 2 2 1 2 4 2 1 1 1 c c c f c c c cr n d r dN v n                                 (6) Eq. (7) can be written in the following simplified form:   m k m d A B dN    (7) where parameter m is related to the Coffin-Manson parameter m as m=1/c+1 and c A r  (8) 2 3 2 2 c k c    (9)       1 ' 2 2 4 2 1 1 1 c f cr n B v n                          (10) Parameters n΄, K cr , c, ε f ΄, Ε can be determined experimentally. Crack growth rate in Eq. (7) is dependent on parameter B, which includes material properties and therefore provides a physical background in the crack growth analysis. The only fitting parameter I Eq. (7) is length r c , which is also an undefined parameter in the SED theory. actual crack length Material with HAZ cyclic local properties r c